Title:
PROCESS FOR HYDROLYTIC DEGRADATION OF CELLULOSIC MATERIALS TO SUGARS
United States Patent 3640768
Abstract:
Cellulosic materials are chemically degraded in a percolator vessel by introducing a liquid agent from below into the cellulosic materials placed above the filter area of the vessel while the vessel is at about atmospheric pressure and introducing steam at a higher pressure than atmospheric from below the cellulosic material to raise the temperature in the vessel to at least 100° C., the displaced air being permitted to escape and then introducing steam at a pressure of about 1 atmosphere above atmospheric pressure from the top of the vessel to expel the liquid which is in excess of the absorptive power of the cellulosic material through the bottom of the vessel and then introducing further steam from the bottom of the vessel to bring up the temperature to the reaction temperature and recovering the reaction product. The invention also embraces a vessel for practising the above process which is provided with a filter subdivided in at least two sections, one over the other, and provided with multilevel horizontal rows of perforations having a minimum diameter of 2-5 mm., increasing towards the periphery of the filter, and having a cross section of 0.2 to 4 percent of the cylindrical cross section of the percolator vessel, measured at the narrowest point of the conical holes, the rows of perforations preferably having a downwardly decreasing distance from each other.
US Patent References:
Purification of cellulose material
Bassett - August 1933 - 1923292
Apparatus for the saccharification of cellulose
Scholler - July 1937 - 2086963
Method and apparatus for hydrolyzing cellulosic materials
Wallace et al. - March 1956 - 2739086
Hydrolysis of hemicellulose and alphacellulose to produce sugar
Hignett et al. - August 1957 - 2801939
Selective hydrolysis of lignocellulose materials
Hess et al. - October 1965 - 3212932
Purification of cellulose material
Bassett - August 1933 - 1923292
Apparatus for the saccharification of cellulose
Scholler - July 1937 - 2086963
Method and apparatus for hydrolyzing cellulosic materials
Wallace et al. - March 1956 - 2739086
Hydrolysis of hemicellulose and alphacellulose to produce sugar
Hignett et al. - August 1957 - 2801939
Selective hydrolysis of lignocellulose materials
Hess et al. - October 1965 - 3212932
Application Number:
04/767669
Publication Date:
02/08/1972
Filing Date:
10/15/1968
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
122/1R, 530/500, 162/34, 162/14, 162/16
International Classes:
C13K1/02; C13K13/00; D21C3/22; D21C7/00; C13K1/00; D21C3/00; C13K1/02; C13K9/00; C13K1/04
Field of Search:
127/1,37 162/14,16,34,81 260/124
Other References:
Harris et al., I, "Hydrolysis of Wood," Ind. E. Ch. 37: 12-23 (1945). .
Harris et al., II, "Madison Wood Sugar Process," Ind. E. Ch. 38: 890-95 (1946)..
Primary Examiner:
Wolk, Morris O.
Assistant Examiner:
Conlin D. G.
Claims:
I claim
1. A process for the chemical degradation of a cellulosic material by percolating a liquid agent therethrough comprising
2. The process of claim 1 wherein the liquid agent is discharged from the lower of said two filter areas.
3. The process of claim 1 wherein the acid is nitric acid.
4. The process of claim 1 wherein the degradation of the cellulosic materials is carried out in two stages, in the first stage the hemicellulose being subjected to an acid hydrolysis whereupon the sugars thus formed are removed by washing followed by addition of an alkaline reaction liquor through said upper filter area and of steam through said lower filter area and proceeding as defined in (c), (d) and (e) of claim 1 so as to dissolve the lignin and finally removing the solution product by washing.
5. The process of claim 1 wherein the degradation of the cellulosic material is carried out b a saccharification in two stages, in the first stage the hemicellulose being subjected to a preliminary hydrolysis, the ion concentration in the acid in said first stage corresponding to the ion concentration in about 1 percent sulfuric acid whereupon the sugars formed in said first stage are recovered followed by treating the remaining cellulosic material in a second stage at a higher reaction temperature and acid concentration than the reaction temperature and acid concentration employed in the preliminary hydrolysis, said higher acid concentration having an ion concentration corresponding to about 3 to 5 percent sulfuric acid.
6. The process of claim 5 wherein the cellulosic material consists of wood shavings, wherein the product extracted in the preliminary hydrolysis is principally xylose, and wherein the product extracted in the hydrolysis of the cellulose is primarily dextrose.
7. The process of claim 5, wherein in a further stage the residue left after the hydrolysis of the cellulose is subjected to additional steam treatment at an elevated pressure to remove the lignin upon expulsion of the steam.
8. The process of claim 5 wherein during the hydrolysis in the second stage fresh liquid agent is added followed by washing of the product at increasingly lower temperatures and acid concentrations.
9. The process of claim 5 wherein the reaction temperature during the preliminary hydrolysis in the first stage is 130°-140° C. at a reaction time of about 40 minutes and wherein in the second stage the hydrolysis of the cellulose is effected initially at a temperature of 160° to 170° C. during a reaction time of about 40 minutes and thereafter at a temperature of 170° to 190° C. during a time of 30 minutes.
10. The process of claim 5 wherein the sugars formed are recovered by washing in multiple successive steps, the recovery in each step being effected when the sugar concentration has reached the point of at least 70 percent and at most 90 percent of the maximum concentration obtainable in said preliminary hydrolysis and the several washing steps being effected at increasingly lower temperature and lower acid concentration.
11. The process of claim 10 wherein the washing out of the sugars formed in the reaction is effected with a plurality of liquid charges of decreasing sugar concentration obtained from previous runs followed as a final step by a washing with water.
1. A process for the chemical degradation of a cellulosic material by percolating a liquid agent therethrough comprising
2. The process of claim 1 wherein the liquid agent is discharged from the lower of said two filter areas.
3. The process of claim 1 wherein the acid is nitric acid.
4. The process of claim 1 wherein the degradation of the cellulosic materials is carried out in two stages, in the first stage the hemicellulose being subjected to an acid hydrolysis whereupon the sugars thus formed are removed by washing followed by addition of an alkaline reaction liquor through said upper filter area and of steam through said lower filter area and proceeding as defined in (c), (d) and (e) of claim 1 so as to dissolve the lignin and finally removing the solution product by washing.
5. The process of claim 1 wherein the degradation of the cellulosic material is carried out b a saccharification in two stages, in the first stage the hemicellulose being subjected to a preliminary hydrolysis, the ion concentration in the acid in said first stage corresponding to the ion concentration in about 1 percent sulfuric acid whereupon the sugars formed in said first stage are recovered followed by treating the remaining cellulosic material in a second stage at a higher reaction temperature and acid concentration than the reaction temperature and acid concentration employed in the preliminary hydrolysis, said higher acid concentration having an ion concentration corresponding to about 3 to 5 percent sulfuric acid.
6. The process of claim 5 wherein the cellulosic material consists of wood shavings, wherein the product extracted in the preliminary hydrolysis is principally xylose, and wherein the product extracted in the hydrolysis of the cellulose is primarily dextrose.
7. The process of claim 5, wherein in a further stage the residue left after the hydrolysis of the cellulose is subjected to additional steam treatment at an elevated pressure to remove the lignin upon expulsion of the steam.
8. The process of claim 5 wherein during the hydrolysis in the second stage fresh liquid agent is added followed by washing of the product at increasingly lower temperatures and acid concentrations.
9. The process of claim 5 wherein the reaction temperature during the preliminary hydrolysis in the first stage is 130°-140° C. at a reaction time of about 40 minutes and wherein in the second stage the hydrolysis of the cellulose is effected initially at a temperature of 160° to 170° C. during a reaction time of about 40 minutes and thereafter at a temperature of 170° to 190° C. during a time of 30 minutes.
10. The process of claim 5 wherein the sugars formed are recovered by washing in multiple successive steps, the recovery in each step being effected when the sugar concentration has reached the point of at least 70 percent and at most 90 percent of the maximum concentration obtainable in said preliminary hydrolysis and the several washing steps being effected at increasingly lower temperature and lower acid concentration.
11. The process of claim 10 wherein the washing out of the sugars formed in the reaction is effected with a plurality of liquid charges of decreasing sugar concentration obtained from previous runs followed as a final step by a washing with water.
Description:
BACKGROUND OF THE INVENTION
The invention relates to a process and an apparatus for the chemical degradation of cellulosic materials in a percolator.
The conventional processes of this type are designed in a manner that the cellulosic material is first subjected to heat by means of steam in order to dispel the air from the percolator. It has also been proposed to evacuate the percolator prior to heating in order to remove at least the major part of the air. The reaction liquid is then added subsequently to the initial heating step. The liquid is usually preheated to a temperature above 100° C. Very substantial amounts of liquid are necessary to effect the impregnation of the material up to saturation because of the absorptive power of cellulosic materials.
The difficulty with these processes of the prior art is that certain portions of the material are left which are not completely saturated with liquid. The well-known Scholler percolation process as disclosed for instance in German Pat. 640775 therefore uses a multiplicity of liquid charges of equal acid concentration in succession. The probability of an insufficient impregnation with liquid in this case is usually eliminated after a few successive charges.
However, there are problems with the rather high amount of liquid that is necessary and the concentration obtained in the final product.
SUMMARY OF THE INVENTION
The present invention therefore has the object of obtaining a uniform impregnation of the entire material in the percolator with a comparatively small amount of steam.
Another object of the invention is a process of this type wherein a comparatively high concentration of different desired final products, in particular sugar solutions, is obtainable.
Another object is to provide a process of this type wherein not only low amounts of steam may be used but where there are also limitations on the necessary amounts of reaction liquid without having an unfavorable effect on the concentration of the final reaction product.
These objects are accomplished by a process for the chemical degradation of cellulosic materials by percolating a liquid agent therethrough comprising
a. supporting the material in a closed percolator vessel at a level intermediate the top and bottom end of the vessel above the filter area of the vessel;
b. introducing the liquid agent from below into the cellulosic material in an amount sufficient to substantially cover the said material, the agent being introduced at an elevated temperature below its boiling point, and maintaining the pressure in the said vessel substantially at atmospheric pressure;
c. simultaneously introducing steam at a pressure higher than the pressure in said vessel from below into the cellulosic material in an amount to raise the temperature in the vessel to at least 100° C. while permitting the displaced air and uncondensable gases to escape through the top of the vessel;
d. thereafter introducing steam at about 1 atmosphere above atmospheric pressure from the top of said vessel, thereby expelling the amount of liquid exceeding the absorptive power of said cellulosic material through said filter area from said vessel;
e. thereafter introducing further steam from below the cellulosic material in an amount sufficient to bring the temperature up to the reaction temperature and maintaining this temperature until the reaction is complete, followed by recovery of the reaction product.
The invention also embraces a percolator vessel for the process described which has a filter subdivided in two sections, one over the other, and provided with multilevel horizontal rows of perforations having a minimum diameter of 2-5 mm., increasing towards the periphery of the filter, and having a total cross section of 0.2 to 4 percent of the cylindrical cross section of the percolator vessel, measured at the narrowest point of the conical holes, the rows of perforations preferably having a downwardly decreasing distance from each other.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows a percolator vessel as used in the process of the invention in a schematic manner.
DESCRIPTION OF PREFERRED EMBODIMENTS
As has been stated, the invention involves as a first step the introduction of the reaction liquid and steam at a temperature of at least 100° whereby a reaction liquid steam mixture rises upwardly in the percolator. As a result, the open space between the cellulosic particles is completely taken up and in addition the reaction liquid will penetrate into the individual particles and the displaced air in each case will rise towards the top. After complete covering of the charge with liquid, one may permit the charge to stand for a few minutes to accomplish complete saturation. The amount of liquid which is in excess of the saturation of the cellulosic material and which is in the interstices between the cellulosic particles is then drained downwardly through the filter. It is only after this step that the remaining material which is now just saturated with liquid is heated by the admission of steam through the filter and is thus brought up to the reaction temperature.
This kind of procedure results in a substantial saving in the amount of steam and, on the other hand, because of the lower amounts of liquid required, permits a higher concentration of the sugars to be obtained in the same reaction time.
There results also a substantially lower flow resistance for the steam which rises from the bottom to the top and thus a lower pressure and temperature differential from bottom to top.
If the purpose of the process is the saccharification of the cellulosic material, the reaction liquid will be a suitable mineral acid solution of which the ion concentration in the first stage where the saccharification of the hemicellulose is effected may amount to about that of a 1 percent concentrated sulfuric acid, while in the second stage where the cellulose is subjected to saccharification after the sugars formed from the hemicellulose have been washed out at a reduced temperature and reduced acid concentration, acid may be used of which the ion concentration is equivalent to that of a 3-5 percent sulfuric acid.
Preferably, a preliminary hydrolysis of the hemicellulose of the pentosane-containing starting material is effected followed by an alkali conversion of the cellulose. The process of the invention contemplates that in this case a reaction liquid is used for at least part of the conversion of the hemicellulose consisting of dilute mineral acid solution having a hydrogen ion concentration corresponding to about 1 percent sulfuric acid. The reaction temperature should be below 140° C. This will be followed by a washing out of the sugars formed from the hemicellulose at reduced temperature and acid concentration by means of a plurality of liquid charges of reduced sugar concentration. These charges may be obtained from previous percolation runs. The last wash is effected with water. After that, a new reaction liquid is added which contains solvents for the lignin such as sodium hydroxide, sodium sulfide and sodium carbonate in a concentration to provide for the necessary reagent in the cellulosic material after expulsion of the excess liquid. A reaction temperature in this stage is used of at least 140° C. The soluble alkali lignin is then again washed out by means of a plurality of liquid charges of decreasing temperature and decreasing concentration of alkali lignin and other unspent reagent. These liquid charges are again obtained from previous percolation runs. Finally, there follows a wash with water. The necessary temperature is accomplished by means of steam which is introduced in each case between two charges. As a result, pure cellulose will remain in the percolator.
Preferably, nitric acid of a hydrogen ion concentration as indicated is used, at least in case of the hemicellulose saccharification, that is during the preliminary hydrolysis, but possibly also during the hydrolysis of the cellulose.
The fresh reaction liquid which is necessary for the conversion of the cellulose may contain alkali lignin obtained from a previous percolation run in addition to fresh solvents for the lignin.
Preferably, the fresh reaction liquid consists at least partially of one or several discharges resulting from previous lignin solution percolations to which the necessary additional fresh chemical may be added. After starting the reaction with the cellulosic material which is saturated with acid, the subsequent reaction time necessary to accomplish the saccharification of the hemicellulose or cellulose is of course accompanied also by decomposition of the formed sugar under the conditions of the reaction. As a result, a certain flattening out of the possible maximum sugar concentration occurs after a certain reaction time. The sugar concentration at a continuation of the reaction would decrease.
It is therefore an additional feature of the invention that the reaction time is selected so that the formed sugar has at least 70 percent, and at most 90 percent, of its possible maximum concentration. When this point is reached the sugar is then washed out at a reduced temperature and acid concentration. New reaction liquid is subsequently added, particularly in cases of the saccharification of the cellulose followed again by washing out at reduced temperature and acid concentration.
The elution or washing out of the formed sugar can be effected by a plurality of liquid charges as indicated.
The temperature is preferably 130°-140° C. for the conversion of the hemicellulose with a reaction time of about 40 minutes. In the first stage of the conversion of the cellulose, the temperature is 160°-170° C. with a reaction time of 40 minutes, and in the second stage of the conversion of the cellulose the reaction temperature is between 170° and 190° C., preferably 180° C. with reaction time of 30 minutes.
A suitable apparatus for operating the described process is a percolator which in its lower conical section has a vertically subdivided filter. The filter comprises a plurality of filter trays held in flanges of the conical wall portions of the percolator. The filter trays have perforations with a diameter which increases from the center to the periphery. The minimum diameter is between 2 and 5 millimeters, preferably between 3 and 4 millimeters. The perforations are distributed at about equal distances throughout the entire filter surface. The total cross section of all perforations is between about 0.2 and 4 percent, preferably between 0.5 and 1.5 percent, of the inner percolator cross section measured at the narrowest point of the conical holes.
The two sections of the filter are sealed against each other and are provided with a number of inlets which are arranged uniformly at the periphery of the conical portion and are controlled by common control valves. Usually, the filter is divided into two separate sections. It is, however, also possible to use more than two sections.
A further feature of the invention is the arrangement of the perforations in a manner that the perforations in the different superposed levels have a distance from the preceding level which decreases downward and at the lowermost levels is about one-half to one-third of the maximum level existing in the top levels.
The perforations of the several perforation trays or levels are preferably set off against each other so that the distance of the individual perforations be as uniform as possible.
The upper outer wall of the conical filter portion is preferably without perforations in order to prevent undesirable peripheral circulation of the steam and liquid.
In order to obtain desirable flow conditions, the lower filter portion has about 50-67 percent more perforations than the upper filter portions.
EXAMPLE 1
Thirty-three t. of beech shavings containing about 26 t. dry wood substance were placed in a percolator having a contents of 100 m. 3 and a diameter of 3.2 m. in its upper cylindrical portion 1, while the lower conical portion 2 had an inclination of 60° and a total height of 2.7 m. The percolator also was provided with a top dome 3 in which there were disposed rapid-action closures 3', a liquid valve 4 and a steam inlet valve 5, as well as a steam outlet valve 6 and a distributor 4' for both the liquid and the steam. The beech shavings were then subjected to a preliminary hydrolysis to xylose and to a main hydrolysis to dextrose followed by a processing of the lignin residue. The percolator consisted of copper-plated sheet steel and was adjusted to withstand an operation pressure of 13 atmospheres above atmospheric pressure.
In the lower conus portion, a vertically subdivided filter consisting of copper sheets 7, 7' was installed which was supported by flanges 8. The upper filter portion 7 had a height of about 700 mm. measured in the wall portion of the conical section of the percolator and was sealed against the lower filter portion 7' which had a height of about 1,400 mm. (measured again in the conical wall portion) by a sealing ring 9. The upper filter section had perforations of conical form arranged in horizontal rows 10. The perforation had a diameter at the center of about 3 mm. and at the periphery of about 5 mm. with a horizontal distance from each other of 50 mm. The rows of perforations in the top levels were spaced by 50 mm. which was reduced at the lower edge of the upper filter section to about 40 mm. The perforations of the individual rows were offset against each other.
The lower filter section likewise had perforations 10' arranged in horizontal rows and having the same diameters and same horizontal distances. At the upper edge of the lower filter section the distance of the perforation rows was about 40 mm. which was reduced gradually up to the lower edge to about 20 mm. The perforations of the individual rows again were offset against each other.
In this manner, there were obtained about 50 percent more perforations in the lower filter section than in the upper filter section.
It is also possible to use percolators which are steel plated with a nickel-chromium, noncorroding steel ("V 4 A") which are similar to the conventional cellulose boilers. The filter in the conical portion in this case likewise is formed from V 4 A sheet steel. This type of filter is particularly useful for obtaining pure cellulose after carrying out the preliminary hydrolysis.
The different stages of the process carried out in the above-described apparatus will now be discussed:
I. first Stage--Preliminary Hydrolysis of Hemicellulose
In order to effect the complete covering of the wood charge consisting of beech wood shavings, about 63 m. 3 of sulfuric acid of a concentration of about 1 percent were used. The initial heating of the charge was effected by means of steam admitted through the valve 11 and the lower filter section 7'. The heating was carried out to a temperature of about 100° C. and a brief circulation of the steam was effected by opening the upper outlet valve 6. Dilute sulfuric acid was then admitted at a temperature of about 90° C. during a period of about 12 minutes through the upper filter section 7 of the filter by means of opening the valve 12 and closing the valve 12'. Simultaneously, steam was introduced through the lower filter section 7' while throughout this operation a small amount of steam was permitted to escape through the upper outlet valve 6. Thus, a mixing temperature of at least 100° C. was obtained right above the liquid-filled percolator zone.
After covering the charge with liquid the upper steam outlet valve 6 was closed and steam was admitted through the upper inlet valve 5 into the upper section of the percolator until a pressure of about 1 atmosphere above atmospheric was reached, which was then maintained at a constant value by adjusting further admission of steam. The excess liquid of about 25 m. 3 was drained through both filter sections by opening the valve 12' and by means of the control valve 13, while a pressure difference was maintained between the percolator top section and the space behind the filter (impulse control device 14) between zero at the beginning of the discharge and increasing gradually to 0.5 atmospheres at the end of the discharge, which altogether lasted for about 15 minutes. The charge which now was saturated with dilute sulfuric acid was then heated, after closing the control valve 13 and opening the valves 11 and 15, to a temperature of 135° C. by admitting steam through the two filter sections. The temperature corresponded to a saturated steam pressure in the percolator upper part which resulted from maintaining a pressure difference of at least 0.8 atmospheres between the lower and the upper portion by means of the impulse control device 14.
After reaching this pressure in about 15 minutes, steam was passed through the entire vessel for a few minutes by a slight opening of the upper outlet valve 6 in order to obtain a completely uniform heating of the charge. The outlet 6 was subsequently closed and the desired pressure in the upper section of the percolator was maintained for the reaction time of about 40 minutes by specific additions of steam through the filter (valve 11 and possibly valve 15). This means that preferably the steam was introduced only through the lower filter section (valve 11) whenever a comparatively small amount of steam was necessary in order to maintain the reaction temperature.
Thereafter, a liquid charge of about 32 m. 3 containing a xylose concentration of about 8 percent and having a temperature of about 90° C. was pumped into the percolator from above through the valve 4. This resulted in a substantial cooling and development of steam in the cake and provided for a mixing temperature of about 120° C. corresponding to a pressure of 1 atmosphere above atmospheric pressure.
Thereafter, steam was introduced from the top and the pressure was increased from 1 atmosphere above atmospheric to 2 atmospheres and this pressure was maintained by introducing further controlled amounts of steam. The liquid thereby was forced into the cake and caused condensation of the steam which was at a higher temperature and which was still left in the pores of the material. This resulted in an increased extraction effect.
The liquid was then drained through the valve 13 by adjusting the pressure difference between the upper percolator part and the space behind the filter sections to a value of initially zero, and then increasing during the reaction time of about 15 minutes to a value of 0.5 atmospheres.
A new liquid charge was thereafter admitted in an amount of 32 m. 3 having a xylose concentration of about 6 percent and a temperature of about 90° through the valve 4. This resulted in a further reduction of the mixing temperature to about 110° C. The further process was similar to the above-described operation and also appears from the following schedule: ------------------------------------------------------------ --------------- TABLE I
Xylose Xylose Liquid concen- concen- Charge tration Amount Discharge tration Amount m. 3 No. wt.-% m. 3 No. wt.-% ____________________________________________________________ ______________ 1 8 32 1 9.3 33 2 6 32 2 8.5 34 3 4 32 3 6.5 34 4 3 25 4 5 26 5 -- 25 5 4 27 6 -- 20 6 2.5 21 ____________________________________________________________ ______________
The first discharge and part of the second discharge constituted the so-called extraction amounting to 5.9 t. extract having a xylose contents of 4.7 t. in an about 9 percent solution. This corresponded to a yield of 18 percent of the beech wood dry substance. This extract could then be processed further to the desired final products.
The remaining discharges were saved for making the extraction charges 1 to 4 for the next run. They were stored in storage vessels. The fifth and sixth charge preferably consisted of deionized water.
Ii. second Stage--Hydrolysis of Cellulose
After completion of the preliminary hydrolysis, which at the end proceeded with a temperature of only slightly above 100° C., a new charge was added in an amount of 40 m. 3 at a temperature of about 90° and consisting of about 4 percent sulfuric acid. This charge was added from below through the upper section of the filter while at the same time steam was introduced through the lower filter section in order to obtain a mixing temperature of at least 100° C.
After permitting the mixture to stand for a few minutes, the steam percolator pressure in the upper section was increased to 1 atmosphere above atmospheric by a heavy addition of steam from the top. This pressure was then maintained by admitting controlled additional amounts of steam. The excess liquid was again drained through the liquid outlet valve after adjusting the pressure difference to a value of zero at the beginning of the discharge and increasing to about 0.5, this pressure difference existing between the percolator upper portion and the space behind the filter. The discharge lasted about 15 minutes. A reaction temperature was then established of about 165° C. by introducing steam through the entire filter surface at a pressure difference of at least 0.8 atmospheres between the lower and the upper section of the percolator. This reaction temperature corresponded to the saturation steam pressure in the percolator upper part. The time for heating to the desired temperature amounted to about 20 minutes.
The stated reaction temperature was then maintained for about 40 minutes by admitting controlled amounts of steam through the lower filter section (this was the reaction time for the first phase of the sugar formation in the main hydrolysis). The washing of the sugar took place thereafter at a reduced temperature and acid concentration in a similar manner as in the preceding description and observing the following schedule: ------------------------------------------------------------ --------------- TABLE II
Dextrose Dextrose Liquid concen- concen- Charge tration Amount Discharge tration Amount No. wt.-% m. 3 No. wt.-% m. 3 ____________________________________________________________ ______________ 1 5.8 32 1 7.3 37 2 4.5 32 2 6.1 32 3 3.0 32 3 4.5 32 4 1.6 25 4 3.2 25 5 -- 20 5 2.1 20 ____________________________________________________________ ______________
The first discharge and part of the second discharge totaling about 4.6 t. of extract, of which 3.85 t. were dextrose, and which were present in a solution of 58 t. were then eliminated and used for the further processing to desired end products. The other discharges as in the previous case were employed to prepare the charges 1 to 4 for the next run and for this purpose were placed in storage tanks.
Iii. third Stage--Hydrolysis of Remaining Cellulose
About 30 m. 3 of 4 percent sulfuric acid were then pumped at a temperature of 90° through the upper filter section into the percolator. Simultaneously, steam was added through the lower filter section as in the preceding case.
By increasing the pressure in the upper portion of the percolator to about 1 atmosphere above atmospheric, the excess liquid was drained in the same manner as previously. There then followed the heating of the charge through the entire filter to a reaction temperature of about 180°, that is, to a corresponding saturated steam pressure in the upper section of the percolator. This temperature was maintained for about 25 minutes by introducing controlled amounts of steam through the lower filter section. This was then followed by again washing out the formed sugar as in the previous example, but following the scheme shown in Table III. ------------------------------------------------------------ --------------- TABLE III
Dextrose Dextrose Liquid concen- concen- Charge tration Amount Discharge tration No. wt.-% m. 3 No. wt.-% Amount m. 3 ____________________________________________________________ ______________ 1 5.4 26 1 6.1 36 2 4.0 25 2 5.3 25 3 3.6 20 3 4.6 20 4 1.65 20 4 3.4 20 5 -- 20 5 1.8 20 ____________________________________________________________ ______________
The first discharge with an extract of 3.2 t. in the form of a solution of about 38 t. and containing 2.4 t. dextrose was then eliminated and, together with the extracts from the preceding extraction, was subject to the further processing to obtain the desired end products. Altogether there were obtained in this process 7.8 t. extract in the form of a solution of 96 t. which contained 6.25 t. dextrose. This corresponded to a mean concentration of about 6.5 weight percent dextrose or 8.1 percent dry substance constituting a degree of purity of about 80 percent.
Iv. fourth Stage--Lignin Recovery
At the end of this entire extraction process, there were left in the percolator a lignin residue comprising about 9 to 9.5 t. dry substance and containing still about 18 to 19 t. water. The evacuation of this residue was effected through an evacuation gate 16 at the bottom end of the conical portion of the percolator after the temperature of the percolator was brought up by admitting steam from below (valves 17, 11 and 15 which were opened consecutively) to 150°-175° C. corresponding to a steam pressure between 5 and 8 atmospheres above atmospheric. The lignin cake thus was broken up by expansion of the water under pressure and was removed mixed with steam in about 1 minute. The lignin-steam mixture was then separated in a cyclone in which the lignin residue was received at the bottom end and the steam permitted to escape at the top. After closing of the evacuation gate the percolator was then ready for another run.
EXAMPLE 2
It may be of interest in a particular case only to go through the preliminary hydrolysis and subsequently to obtain the lignin from the more or less still intact cellulose of the starting material such as beechwood. The preliminary hydrolysis in this example therefore was the same as in example 1 except that a shorter reaction was used in order not to damage the cellulose and also employing nitric acid instead of sulfuric acid in order to be able to work with a percolator that was plated with chromium nickel steel plates of the "V 4 A" type. The xylose rate thereby was reduced from 18 percent to between 10 and 16 percent of the initial beechwood dry substance.
The concentration of the xylose solution is therefore somewhat lower and in case of somewhat reduced amounts of liquid amounted to about 8.0 percent. After the preliminary hydrolysis there was obtained a contents in the percolator amounting to about 20 t. of hot dry substance which were then processed to pure cellulose as presently described.
Cellulose Recovery
A charge was formed by dissolving fresh free agents or the melt obtained from burning the waste liquor. This material was dissolved in a suitable fraction of waste liquor. The conversion could then be effected by the so-called sulfate process. In that case the melt dissolved in a fraction of the waste liquor was reacted with alkali for instance of the type Ca(OH) 2 . There resulted an amount of fresh free agent dissolved in spent liquor of about 5.2 t. consisting of about 3.5 t. NaOH, 0.85 t. Na 2 S and 0.85 t. Na 2 CO 3 . This presupposed that the excess from the last run which resulted after the percolator filling was included in a composition. The charge then contained: 5.2 t. of fresh free reagent plus 4.6 t. waste liquor-dry substance plus 30 t. water.
The liquid excess then contained 1 t. chemicals +1 t. waste liquor-dry substance +15 t. water. This excess was drained through the lower portion of the percolator after admission of the charge through the upper portion of the filter and simultaneous admission of steam through the lower portion followed by a short time of standing in order to effect the equalization of the concentration. In the percolator there then remained 20 t. of hot dry substance saturated with a solution containing 4.2 t. chemicals, 3.6 t. waste liquor and 55 t. water.
These contents of the percolator which was saturated with liquid were now heated to a temperature of 145° by admitting steam through the filter and establishing a pressure difference of at least 0.8 between the lower and the upper part of the percolator and then subsequently maintaining the temperature for about 30 minutes by admitting controlled additional amounts of steam.
This step was followed by the washing out of the formed alkali-lignin by means of a plurality of liquid charges which had been obtained from the waste liquor of the previous runs. The first or the first two discharges however were eliminated. These discharges contained the highest concentration. The last two charges of liquid were again water in order to obtain a well-washed cellulose. The temperature in the percolator could be kept at a decreasing level for consecutive extraction steps similar to the previously described operation. The temperature prior to the last charge should still be at least 110° C. The following table illustrates the details of the proceeding. ------------------------------------------------------------ --------------- TABLE IV
Waste Waste Liquid Liquid-Dry Liquid-Dry Charge Substance Amt. Discharge Substance Amt. No. Wt.-% m. 3 No. Wt.-% m. 3 ____________________________________________________________ ______________ 1 10 30 1 17.6 47 2 7.4 30 2 12.7 31 3 3.6 30 3 8.8 31 4 1.6 25 4 7.1 25 5 -- 25 5 3.8 25 6 -- 25 6 2.0 25 ____________________________________________________________ ______________
The first discharge containing 10 t. of waste liquor-dry substance was then split as follows: 3.2 t. waste liquor-dry substance and 15 t. water were used together with the excess from the reaction which contained 1 t. fresh reagents, 1 t. waste liquor-dry substance and 15 t. water for the purpose of dissolving 3.2 t. fresh reagents containing about 0.4 t. filler materials. Instead of fresh reagents, it is, of course, also possible to use the melt from the firing of the liquor which then must be subjected to an alkaline treatment. The total solution was used as a charge for the next run.
The remainder of the first run amounting to:
from the first charge 6.8 t. waste liquor-dry substance in 32 t. water from the second charge 3.7 t. waste liquor-dry substance in 25.5 t. water amt. altogether to: 10.5 t. waste liquor-dry substance in 57.5 t. water
was eliminated and used for the burning of the waste liquor for the purpose of steam generation and recovery of free agents.
The remainder of the second discharge and the following discharge were used for making up in sequence the charges 1 to 4 for the next percolation run.
It is noted that it would also be possible to distribute the chemicals added to 2 or 3 charges in which case the second and even the third charge may already be simultaneously extraction charges.
Prior to these reaction-extraction steps, the mixture may be heated in a similar manner as in the preceding examples to between 140° and 150° C. and be maintained at this temperature for 15 to 30 minutes. The further extraction charges could be carried out at stepwise lower temperatures. There resulted in the percolator a cellulose (12 to 13 t. of dry substances) having a high content of α cellulose which could then be evacuated with water to a cellulose storage tank and could later be submitted to further processing.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.
The invention relates to a process and an apparatus for the chemical degradation of cellulosic materials in a percolator.
The conventional processes of this type are designed in a manner that the cellulosic material is first subjected to heat by means of steam in order to dispel the air from the percolator. It has also been proposed to evacuate the percolator prior to heating in order to remove at least the major part of the air. The reaction liquid is then added subsequently to the initial heating step. The liquid is usually preheated to a temperature above 100° C. Very substantial amounts of liquid are necessary to effect the impregnation of the material up to saturation because of the absorptive power of cellulosic materials.
The difficulty with these processes of the prior art is that certain portions of the material are left which are not completely saturated with liquid. The well-known Scholler percolation process as disclosed for instance in German Pat. 640775 therefore uses a multiplicity of liquid charges of equal acid concentration in succession. The probability of an insufficient impregnation with liquid in this case is usually eliminated after a few successive charges.
However, there are problems with the rather high amount of liquid that is necessary and the concentration obtained in the final product.
SUMMARY OF THE INVENTION
The present invention therefore has the object of obtaining a uniform impregnation of the entire material in the percolator with a comparatively small amount of steam.
Another object of the invention is a process of this type wherein a comparatively high concentration of different desired final products, in particular sugar solutions, is obtainable.
Another object is to provide a process of this type wherein not only low amounts of steam may be used but where there are also limitations on the necessary amounts of reaction liquid without having an unfavorable effect on the concentration of the final reaction product.
These objects are accomplished by a process for the chemical degradation of cellulosic materials by percolating a liquid agent therethrough comprising
a. supporting the material in a closed percolator vessel at a level intermediate the top and bottom end of the vessel above the filter area of the vessel;
b. introducing the liquid agent from below into the cellulosic material in an amount sufficient to substantially cover the said material, the agent being introduced at an elevated temperature below its boiling point, and maintaining the pressure in the said vessel substantially at atmospheric pressure;
c. simultaneously introducing steam at a pressure higher than the pressure in said vessel from below into the cellulosic material in an amount to raise the temperature in the vessel to at least 100° C. while permitting the displaced air and uncondensable gases to escape through the top of the vessel;
d. thereafter introducing steam at about 1 atmosphere above atmospheric pressure from the top of said vessel, thereby expelling the amount of liquid exceeding the absorptive power of said cellulosic material through said filter area from said vessel;
e. thereafter introducing further steam from below the cellulosic material in an amount sufficient to bring the temperature up to the reaction temperature and maintaining this temperature until the reaction is complete, followed by recovery of the reaction product.
The invention also embraces a percolator vessel for the process described which has a filter subdivided in two sections, one over the other, and provided with multilevel horizontal rows of perforations having a minimum diameter of 2-5 mm., increasing towards the periphery of the filter, and having a total cross section of 0.2 to 4 percent of the cylindrical cross section of the percolator vessel, measured at the narrowest point of the conical holes, the rows of perforations preferably having a downwardly decreasing distance from each other.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows a percolator vessel as used in the process of the invention in a schematic manner.
DESCRIPTION OF PREFERRED EMBODIMENTS
As has been stated, the invention involves as a first step the introduction of the reaction liquid and steam at a temperature of at least 100° whereby a reaction liquid steam mixture rises upwardly in the percolator. As a result, the open space between the cellulosic particles is completely taken up and in addition the reaction liquid will penetrate into the individual particles and the displaced air in each case will rise towards the top. After complete covering of the charge with liquid, one may permit the charge to stand for a few minutes to accomplish complete saturation. The amount of liquid which is in excess of the saturation of the cellulosic material and which is in the interstices between the cellulosic particles is then drained downwardly through the filter. It is only after this step that the remaining material which is now just saturated with liquid is heated by the admission of steam through the filter and is thus brought up to the reaction temperature.
This kind of procedure results in a substantial saving in the amount of steam and, on the other hand, because of the lower amounts of liquid required, permits a higher concentration of the sugars to be obtained in the same reaction time.
There results also a substantially lower flow resistance for the steam which rises from the bottom to the top and thus a lower pressure and temperature differential from bottom to top.
If the purpose of the process is the saccharification of the cellulosic material, the reaction liquid will be a suitable mineral acid solution of which the ion concentration in the first stage where the saccharification of the hemicellulose is effected may amount to about that of a 1 percent concentrated sulfuric acid, while in the second stage where the cellulose is subjected to saccharification after the sugars formed from the hemicellulose have been washed out at a reduced temperature and reduced acid concentration, acid may be used of which the ion concentration is equivalent to that of a 3-5 percent sulfuric acid.
Preferably, a preliminary hydrolysis of the hemicellulose of the pentosane-containing starting material is effected followed by an alkali conversion of the cellulose. The process of the invention contemplates that in this case a reaction liquid is used for at least part of the conversion of the hemicellulose consisting of dilute mineral acid solution having a hydrogen ion concentration corresponding to about 1 percent sulfuric acid. The reaction temperature should be below 140° C. This will be followed by a washing out of the sugars formed from the hemicellulose at reduced temperature and acid concentration by means of a plurality of liquid charges of reduced sugar concentration. These charges may be obtained from previous percolation runs. The last wash is effected with water. After that, a new reaction liquid is added which contains solvents for the lignin such as sodium hydroxide, sodium sulfide and sodium carbonate in a concentration to provide for the necessary reagent in the cellulosic material after expulsion of the excess liquid. A reaction temperature in this stage is used of at least 140° C. The soluble alkali lignin is then again washed out by means of a plurality of liquid charges of decreasing temperature and decreasing concentration of alkali lignin and other unspent reagent. These liquid charges are again obtained from previous percolation runs. Finally, there follows a wash with water. The necessary temperature is accomplished by means of steam which is introduced in each case between two charges. As a result, pure cellulose will remain in the percolator.
Preferably, nitric acid of a hydrogen ion concentration as indicated is used, at least in case of the hemicellulose saccharification, that is during the preliminary hydrolysis, but possibly also during the hydrolysis of the cellulose.
The fresh reaction liquid which is necessary for the conversion of the cellulose may contain alkali lignin obtained from a previous percolation run in addition to fresh solvents for the lignin.
Preferably, the fresh reaction liquid consists at least partially of one or several discharges resulting from previous lignin solution percolations to which the necessary additional fresh chemical may be added. After starting the reaction with the cellulosic material which is saturated with acid, the subsequent reaction time necessary to accomplish the saccharification of the hemicellulose or cellulose is of course accompanied also by decomposition of the formed sugar under the conditions of the reaction. As a result, a certain flattening out of the possible maximum sugar concentration occurs after a certain reaction time. The sugar concentration at a continuation of the reaction would decrease.
It is therefore an additional feature of the invention that the reaction time is selected so that the formed sugar has at least 70 percent, and at most 90 percent, of its possible maximum concentration. When this point is reached the sugar is then washed out at a reduced temperature and acid concentration. New reaction liquid is subsequently added, particularly in cases of the saccharification of the cellulose followed again by washing out at reduced temperature and acid concentration.
The elution or washing out of the formed sugar can be effected by a plurality of liquid charges as indicated.
The temperature is preferably 130°-140° C. for the conversion of the hemicellulose with a reaction time of about 40 minutes. In the first stage of the conversion of the cellulose, the temperature is 160°-170° C. with a reaction time of 40 minutes, and in the second stage of the conversion of the cellulose the reaction temperature is between 170° and 190° C., preferably 180° C. with reaction time of 30 minutes.
A suitable apparatus for operating the described process is a percolator which in its lower conical section has a vertically subdivided filter. The filter comprises a plurality of filter trays held in flanges of the conical wall portions of the percolator. The filter trays have perforations with a diameter which increases from the center to the periphery. The minimum diameter is between 2 and 5 millimeters, preferably between 3 and 4 millimeters. The perforations are distributed at about equal distances throughout the entire filter surface. The total cross section of all perforations is between about 0.2 and 4 percent, preferably between 0.5 and 1.5 percent, of the inner percolator cross section measured at the narrowest point of the conical holes.
The two sections of the filter are sealed against each other and are provided with a number of inlets which are arranged uniformly at the periphery of the conical portion and are controlled by common control valves. Usually, the filter is divided into two separate sections. It is, however, also possible to use more than two sections.
A further feature of the invention is the arrangement of the perforations in a manner that the perforations in the different superposed levels have a distance from the preceding level which decreases downward and at the lowermost levels is about one-half to one-third of the maximum level existing in the top levels.
The perforations of the several perforation trays or levels are preferably set off against each other so that the distance of the individual perforations be as uniform as possible.
The upper outer wall of the conical filter portion is preferably without perforations in order to prevent undesirable peripheral circulation of the steam and liquid.
In order to obtain desirable flow conditions, the lower filter portion has about 50-67 percent more perforations than the upper filter portions.
EXAMPLE 1
Thirty-three t. of beech shavings containing about 26 t. dry wood substance were placed in a percolator having a contents of 100 m. 3 and a diameter of 3.2 m. in its upper cylindrical portion 1, while the lower conical portion 2 had an inclination of 60° and a total height of 2.7 m. The percolator also was provided with a top dome 3 in which there were disposed rapid-action closures 3', a liquid valve 4 and a steam inlet valve 5, as well as a steam outlet valve 6 and a distributor 4' for both the liquid and the steam. The beech shavings were then subjected to a preliminary hydrolysis to xylose and to a main hydrolysis to dextrose followed by a processing of the lignin residue. The percolator consisted of copper-plated sheet steel and was adjusted to withstand an operation pressure of 13 atmospheres above atmospheric pressure.
In the lower conus portion, a vertically subdivided filter consisting of copper sheets 7, 7' was installed which was supported by flanges 8. The upper filter portion 7 had a height of about 700 mm. measured in the wall portion of the conical section of the percolator and was sealed against the lower filter portion 7' which had a height of about 1,400 mm. (measured again in the conical wall portion) by a sealing ring 9. The upper filter section had perforations of conical form arranged in horizontal rows 10. The perforation had a diameter at the center of about 3 mm. and at the periphery of about 5 mm. with a horizontal distance from each other of 50 mm. The rows of perforations in the top levels were spaced by 50 mm. which was reduced at the lower edge of the upper filter section to about 40 mm. The perforations of the individual rows were offset against each other.
The lower filter section likewise had perforations 10' arranged in horizontal rows and having the same diameters and same horizontal distances. At the upper edge of the lower filter section the distance of the perforation rows was about 40 mm. which was reduced gradually up to the lower edge to about 20 mm. The perforations of the individual rows again were offset against each other.
In this manner, there were obtained about 50 percent more perforations in the lower filter section than in the upper filter section.
It is also possible to use percolators which are steel plated with a nickel-chromium, noncorroding steel ("V 4 A") which are similar to the conventional cellulose boilers. The filter in the conical portion in this case likewise is formed from V 4 A sheet steel. This type of filter is particularly useful for obtaining pure cellulose after carrying out the preliminary hydrolysis.
The different stages of the process carried out in the above-described apparatus will now be discussed:
I. first Stage--Preliminary Hydrolysis of Hemicellulose
In order to effect the complete covering of the wood charge consisting of beech wood shavings, about 63 m. 3 of sulfuric acid of a concentration of about 1 percent were used. The initial heating of the charge was effected by means of steam admitted through the valve 11 and the lower filter section 7'. The heating was carried out to a temperature of about 100° C. and a brief circulation of the steam was effected by opening the upper outlet valve 6. Dilute sulfuric acid was then admitted at a temperature of about 90° C. during a period of about 12 minutes through the upper filter section 7 of the filter by means of opening the valve 12 and closing the valve 12'. Simultaneously, steam was introduced through the lower filter section 7' while throughout this operation a small amount of steam was permitted to escape through the upper outlet valve 6. Thus, a mixing temperature of at least 100° C. was obtained right above the liquid-filled percolator zone.
After covering the charge with liquid the upper steam outlet valve 6 was closed and steam was admitted through the upper inlet valve 5 into the upper section of the percolator until a pressure of about 1 atmosphere above atmospheric was reached, which was then maintained at a constant value by adjusting further admission of steam. The excess liquid of about 25 m. 3 was drained through both filter sections by opening the valve 12' and by means of the control valve 13, while a pressure difference was maintained between the percolator top section and the space behind the filter (impulse control device 14) between zero at the beginning of the discharge and increasing gradually to 0.5 atmospheres at the end of the discharge, which altogether lasted for about 15 minutes. The charge which now was saturated with dilute sulfuric acid was then heated, after closing the control valve 13 and opening the valves 11 and 15, to a temperature of 135° C. by admitting steam through the two filter sections. The temperature corresponded to a saturated steam pressure in the percolator upper part which resulted from maintaining a pressure difference of at least 0.8 atmospheres between the lower and the upper portion by means of the impulse control device 14.
After reaching this pressure in about 15 minutes, steam was passed through the entire vessel for a few minutes by a slight opening of the upper outlet valve 6 in order to obtain a completely uniform heating of the charge. The outlet 6 was subsequently closed and the desired pressure in the upper section of the percolator was maintained for the reaction time of about 40 minutes by specific additions of steam through the filter (valve 11 and possibly valve 15). This means that preferably the steam was introduced only through the lower filter section (valve 11) whenever a comparatively small amount of steam was necessary in order to maintain the reaction temperature.
Thereafter, a liquid charge of about 32 m. 3 containing a xylose concentration of about 8 percent and having a temperature of about 90° C. was pumped into the percolator from above through the valve 4. This resulted in a substantial cooling and development of steam in the cake and provided for a mixing temperature of about 120° C. corresponding to a pressure of 1 atmosphere above atmospheric pressure.
Thereafter, steam was introduced from the top and the pressure was increased from 1 atmosphere above atmospheric to 2 atmospheres and this pressure was maintained by introducing further controlled amounts of steam. The liquid thereby was forced into the cake and caused condensation of the steam which was at a higher temperature and which was still left in the pores of the material. This resulted in an increased extraction effect.
The liquid was then drained through the valve 13 by adjusting the pressure difference between the upper percolator part and the space behind the filter sections to a value of initially zero, and then increasing during the reaction time of about 15 minutes to a value of 0.5 atmospheres.
A new liquid charge was thereafter admitted in an amount of 32 m. 3 having a xylose concentration of about 6 percent and a temperature of about 90° through the valve 4. This resulted in a further reduction of the mixing temperature to about 110° C. The further process was similar to the above-described operation and also appears from the following schedule: ------------------------------------------------------------ --------------- TABLE I
Xylose Xylose Liquid concen- concen- Charge tration Amount Discharge tration Amount m. 3 No. wt.-% m. 3 No. wt.-% ____________________________________________________________ ______________ 1 8 32 1 9.3 33 2 6 32 2 8.5 34 3 4 32 3 6.5 34 4 3 25 4 5 26 5 -- 25 5 4 27 6 -- 20 6 2.5 21 ____________________________________________________________ ______________
The first discharge and part of the second discharge constituted the so-called extraction amounting to 5.9 t. extract having a xylose contents of 4.7 t. in an about 9 percent solution. This corresponded to a yield of 18 percent of the beech wood dry substance. This extract could then be processed further to the desired final products.
The remaining discharges were saved for making the extraction charges 1 to 4 for the next run. They were stored in storage vessels. The fifth and sixth charge preferably consisted of deionized water.
Ii. second Stage--Hydrolysis of Cellulose
After completion of the preliminary hydrolysis, which at the end proceeded with a temperature of only slightly above 100° C., a new charge was added in an amount of 40 m. 3 at a temperature of about 90° and consisting of about 4 percent sulfuric acid. This charge was added from below through the upper section of the filter while at the same time steam was introduced through the lower filter section in order to obtain a mixing temperature of at least 100° C.
After permitting the mixture to stand for a few minutes, the steam percolator pressure in the upper section was increased to 1 atmosphere above atmospheric by a heavy addition of steam from the top. This pressure was then maintained by admitting controlled additional amounts of steam. The excess liquid was again drained through the liquid outlet valve after adjusting the pressure difference to a value of zero at the beginning of the discharge and increasing to about 0.5, this pressure difference existing between the percolator upper portion and the space behind the filter. The discharge lasted about 15 minutes. A reaction temperature was then established of about 165° C. by introducing steam through the entire filter surface at a pressure difference of at least 0.8 atmospheres between the lower and the upper section of the percolator. This reaction temperature corresponded to the saturation steam pressure in the percolator upper part. The time for heating to the desired temperature amounted to about 20 minutes.
The stated reaction temperature was then maintained for about 40 minutes by admitting controlled amounts of steam through the lower filter section (this was the reaction time for the first phase of the sugar formation in the main hydrolysis). The washing of the sugar took place thereafter at a reduced temperature and acid concentration in a similar manner as in the preceding description and observing the following schedule: ------------------------------------------------------------ --------------- TABLE II
Dextrose Dextrose Liquid concen- concen- Charge tration Amount Discharge tration Amount No. wt.-% m. 3 No. wt.-% m. 3 ____________________________________________________________ ______________ 1 5.8 32 1 7.3 37 2 4.5 32 2 6.1 32 3 3.0 32 3 4.5 32 4 1.6 25 4 3.2 25 5 -- 20 5 2.1 20 ____________________________________________________________ ______________
The first discharge and part of the second discharge totaling about 4.6 t. of extract, of which 3.85 t. were dextrose, and which were present in a solution of 58 t. were then eliminated and used for the further processing to desired end products. The other discharges as in the previous case were employed to prepare the charges 1 to 4 for the next run and for this purpose were placed in storage tanks.
Iii. third Stage--Hydrolysis of Remaining Cellulose
About 30 m. 3 of 4 percent sulfuric acid were then pumped at a temperature of 90° through the upper filter section into the percolator. Simultaneously, steam was added through the lower filter section as in the preceding case.
By increasing the pressure in the upper portion of the percolator to about 1 atmosphere above atmospheric, the excess liquid was drained in the same manner as previously. There then followed the heating of the charge through the entire filter to a reaction temperature of about 180°, that is, to a corresponding saturated steam pressure in the upper section of the percolator. This temperature was maintained for about 25 minutes by introducing controlled amounts of steam through the lower filter section. This was then followed by again washing out the formed sugar as in the previous example, but following the scheme shown in Table III. ------------------------------------------------------------ --------------- TABLE III
Dextrose Dextrose Liquid concen- concen- Charge tration Amount Discharge tration No. wt.-% m. 3 No. wt.-% Amount m. 3 ____________________________________________________________ ______________ 1 5.4 26 1 6.1 36 2 4.0 25 2 5.3 25 3 3.6 20 3 4.6 20 4 1.65 20 4 3.4 20 5 -- 20 5 1.8 20 ____________________________________________________________ ______________
The first discharge with an extract of 3.2 t. in the form of a solution of about 38 t. and containing 2.4 t. dextrose was then eliminated and, together with the extracts from the preceding extraction, was subject to the further processing to obtain the desired end products. Altogether there were obtained in this process 7.8 t. extract in the form of a solution of 96 t. which contained 6.25 t. dextrose. This corresponded to a mean concentration of about 6.5 weight percent dextrose or 8.1 percent dry substance constituting a degree of purity of about 80 percent.
Iv. fourth Stage--Lignin Recovery
At the end of this entire extraction process, there were left in the percolator a lignin residue comprising about 9 to 9.5 t. dry substance and containing still about 18 to 19 t. water. The evacuation of this residue was effected through an evacuation gate 16 at the bottom end of the conical portion of the percolator after the temperature of the percolator was brought up by admitting steam from below (valves 17, 11 and 15 which were opened consecutively) to 150°-175° C. corresponding to a steam pressure between 5 and 8 atmospheres above atmospheric. The lignin cake thus was broken up by expansion of the water under pressure and was removed mixed with steam in about 1 minute. The lignin-steam mixture was then separated in a cyclone in which the lignin residue was received at the bottom end and the steam permitted to escape at the top. After closing of the evacuation gate the percolator was then ready for another run.
EXAMPLE 2
It may be of interest in a particular case only to go through the preliminary hydrolysis and subsequently to obtain the lignin from the more or less still intact cellulose of the starting material such as beechwood. The preliminary hydrolysis in this example therefore was the same as in example 1 except that a shorter reaction was used in order not to damage the cellulose and also employing nitric acid instead of sulfuric acid in order to be able to work with a percolator that was plated with chromium nickel steel plates of the "V 4 A" type. The xylose rate thereby was reduced from 18 percent to between 10 and 16 percent of the initial beechwood dry substance.
The concentration of the xylose solution is therefore somewhat lower and in case of somewhat reduced amounts of liquid amounted to about 8.0 percent. After the preliminary hydrolysis there was obtained a contents in the percolator amounting to about 20 t. of hot dry substance which were then processed to pure cellulose as presently described.
Cellulose Recovery
A charge was formed by dissolving fresh free agents or the melt obtained from burning the waste liquor. This material was dissolved in a suitable fraction of waste liquor. The conversion could then be effected by the so-called sulfate process. In that case the melt dissolved in a fraction of the waste liquor was reacted with alkali for instance of the type Ca(OH) 2 . There resulted an amount of fresh free agent dissolved in spent liquor of about 5.2 t. consisting of about 3.5 t. NaOH, 0.85 t. Na 2 S and 0.85 t. Na 2 CO 3 . This presupposed that the excess from the last run which resulted after the percolator filling was included in a composition. The charge then contained: 5.2 t. of fresh free reagent plus 4.6 t. waste liquor-dry substance plus 30 t. water.
The liquid excess then contained 1 t. chemicals +1 t. waste liquor-dry substance +15 t. water. This excess was drained through the lower portion of the percolator after admission of the charge through the upper portion of the filter and simultaneous admission of steam through the lower portion followed by a short time of standing in order to effect the equalization of the concentration. In the percolator there then remained 20 t. of hot dry substance saturated with a solution containing 4.2 t. chemicals, 3.6 t. waste liquor and 55 t. water.
These contents of the percolator which was saturated with liquid were now heated to a temperature of 145° by admitting steam through the filter and establishing a pressure difference of at least 0.8 between the lower and the upper part of the percolator and then subsequently maintaining the temperature for about 30 minutes by admitting controlled additional amounts of steam.
This step was followed by the washing out of the formed alkali-lignin by means of a plurality of liquid charges which had been obtained from the waste liquor of the previous runs. The first or the first two discharges however were eliminated. These discharges contained the highest concentration. The last two charges of liquid were again water in order to obtain a well-washed cellulose. The temperature in the percolator could be kept at a decreasing level for consecutive extraction steps similar to the previously described operation. The temperature prior to the last charge should still be at least 110° C. The following table illustrates the details of the proceeding. ------------------------------------------------------------ --------------- TABLE IV
Waste Waste Liquid Liquid-Dry Liquid-Dry Charge Substance Amt. Discharge Substance Amt. No. Wt.-% m. 3 No. Wt.-% m. 3 ____________________________________________________________ ______________ 1 10 30 1 17.6 47 2 7.4 30 2 12.7 31 3 3.6 30 3 8.8 31 4 1.6 25 4 7.1 25 5 -- 25 5 3.8 25 6 -- 25 6 2.0 25 ____________________________________________________________ ______________
The first discharge containing 10 t. of waste liquor-dry substance was then split as follows: 3.2 t. waste liquor-dry substance and 15 t. water were used together with the excess from the reaction which contained 1 t. fresh reagents, 1 t. waste liquor-dry substance and 15 t. water for the purpose of dissolving 3.2 t. fresh reagents containing about 0.4 t. filler materials. Instead of fresh reagents, it is, of course, also possible to use the melt from the firing of the liquor which then must be subjected to an alkaline treatment. The total solution was used as a charge for the next run.
The remainder of the first run amounting to:
from the first charge 6.8 t. waste liquor-dry substance in 32 t. water from the second charge 3.7 t. waste liquor-dry substance in 25.5 t. water amt. altogether to: 10.5 t. waste liquor-dry substance in 57.5 t. water
was eliminated and used for the burning of the waste liquor for the purpose of steam generation and recovery of free agents.
The remainder of the second discharge and the following discharge were used for making up in sequence the charges 1 to 4 for the next percolation run.
It is noted that it would also be possible to distribute the chemicals added to 2 or 3 charges in which case the second and even the third charge may already be simultaneously extraction charges.
Prior to these reaction-extraction steps, the mixture may be heated in a similar manner as in the preceding examples to between 140° and 150° C. and be maintained at this temperature for 15 to 30 minutes. The further extraction charges could be carried out at stepwise lower temperatures. There resulted in the percolator a cellulose (12 to 13 t. of dry substances) having a high content of α cellulose which could then be evacuated with water to a cellulose storage tank and could later be submitted to further processing.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.