Title:
GASOLINE UPGRADING
United States Patent 3658690
Abstract:
A combination processing arrangement of reforming, isomerization, aromatics recovery and intervening fractionation is described which will improve upon the yield of gasoline product having a lead free octane rating above 90 by particularly upgrading C6 hydrocarbons.
US Patent References:
Upgrading gasoline
Sutherland - September 1959 - 2905619
Neohexane production
Wade et al. - January 1965 - 3165461
Dehydrocyclization process for producing a high octane gasoline and aromatics
Engel et al. - October 1966 - 3280022
Conversion of hydrocarbon distillates to motor fuel mixtures rich in aromatic and isoparaffins
Gerhold et al. - September 1961 - 3001927
Up-grading hydrocarbons
Skraba - February 1964 - 3121676
Upgrading gasoline
Sutherland - September 1959 - 2905619
Neohexane production
Wade et al. - January 1965 - 3165461
Dehydrocyclization process for producing a high octane gasoline and aromatics
Engel et al. - October 1966 - 3280022
Conversion of hydrocarbon distillates to motor fuel mixtures rich in aromatic and isoparaffins
Gerhold et al. - September 1961 - 3001927
Up-grading hydrocarbons
Skraba - February 1964 - 3121676
Application Number:
05/019377
Publication Date:
04/25/1972
Filing Date:
03/13/1970
View Patent Images:
Export Citation:
Assignee:
Mobil Oil Corporation (New York, NY)
Primary Class:
Other Classes:
208/93, 208/92, 208/79, 208/63
International Classes:
C10L1/06; C10L1/00; C10G39/00
Field of Search:
208/62-66,80,92,93
US Patent References:
| 2965561 | Process for upgrading desulfurized naphthas | December 1960 | Carr et al. |
Primary Examiner:
Levine, Herbert
Claims:
I claim
1. A combination process for upgrading gasoline boiling range material obtained as straight run naphtha, coker gasoline, gasoline product of hydrocracking and catalytic cracking and mixtures thereof which comprises:
2. The method of claim 1 wherein said gasoline boiling range material is desulfurized before effecting separation thereof.
3. The method of claim 1 wherein desulfurization of the fractions is accomplished after the separation of step (a).
4. The method of claim 1 wherein C7 hydrocarbons removed in step (e) are converted to useful product materials by thermal and catalytic cracking.
1. A combination process for upgrading gasoline boiling range material obtained as straight run naphtha, coker gasoline, gasoline product of hydrocracking and catalytic cracking and mixtures thereof which comprises:
2. The method of claim 1 wherein said gasoline boiling range material is desulfurized before effecting separation thereof.
3. The method of claim 1 wherein desulfurization of the fractions is accomplished after the separation of step (a).
4. The method of claim 1 wherein C7 hydrocarbons removed in step (e) are converted to useful product materials by thermal and catalytic cracking.
Description:
BACKGROUND OF THE INVENTION
The need for providing lead-free gasoline products to accommodate gasoline combustion engines employing regular and high test leaded gasoline has been prompted by the need to reduce air pollution problems confronting areas of high automobile density. Thus it is predictable that major air pollution reductions can be realized particularly in areas of high automobile density by eliminating lead additive to regular and high octane gasoline. Recent press releases have emphasized the need for such controls and in fact plans are in progress to grant the Secretary of Health, Education and Welfare, authority to set standards of composition of fuel which includes the removal of lead from gasoline. Thus the present invention is concerned with a processing arrangement or sequence one might now employ in present refinery arrangements with a minimum of additional investment to upgrade low octane gasoline material unsuitable for use in present gasoline combustion engines to an acceptable unleaded higher octane product suitable for use in the combination engine as we know it now and changes recommended with respect thereto in the immediate future. In some instances it has been recommended that the compression ratio of today's engines by reduced so that they will be more compatable for operating on gasoline products having an octane rating clear in the range of 90 to 100 octane. Some prior art patents of interest in upgrading gasoline are U.S. Pat. Nos. 2,905,619, 3,165,461 and 1,900,323.
SUMMARY OF THE INVENTION
The present invention is directed to a processing arrangement for upgrading gasoline boiling range material of unsatisfactory octane rating to a higher octane gasoline product suitable for use in gasoline combustion engines without lead additives. In a particular aspect the present invention is directed to the combination of processing steps comprising hydrogenation, reforming, aromatic extraction and C 6 hydrocarbon isomerization as they relate to one another in the combination for upgrading low octane constituents of the gasoline charge to acceptable higher octane product. One important aspect of the processing combination of this invention relates to upgrading low octane C 6 hydrocarbon components.
BRIEF DESCRIPTION OF THE DRAWING
The drawing diagrammatically presents one arrangement of processing steps for upgrading gasoline material boiling from about C 5 hydrocarbons up to about 380° F. by a processing combination which includes reforming, isomerization, aromatic recovery and intervening separation steps designed to concentrate desired octane constituents from undesired gasoline component of low octane rating which are convertable to higher octane blending components.
DESCRIPTION OF A SPECIFIC EMBODIMENT
THe present invention is concerned with a processing arrangement which may be utilized in present day refinery operations to upgrade low octane gasoline material and particularly C 6 components thereof to a much higher octane product suitable for blending with reformed gasoline product of a desired higher octane rating. More particularly the processing arrangement identified by this invention upgrades particularly C 6 and higher boiling hydrocarbons in the gasoline boiling range by the operating arrangement of reforming, isomerization, aromatic recovery with intervening stabilization and fractionation designed to particularly upgrade, with much greater emphasis, the low octane C 6 hydrocarbon components. In the specific processing scheme shown by the drawing, a relatively low octane gasoline boiling charge such as defined below and having an initial boiling point of about C 4 hydrocarbons and an end boiling point of about 380° F. is introduced to the process by line 2 for passage to hydrogenation pretreater 4 such as desulfurization. In pretreater 4 the gasoline charge is subjected to hydrogenation conditions which will be effective for removing sulfur and nitrogen components found in the gasoline charge. The amount of sulfur and nitrogen components in the charge will vary considerably depending upon the source of the gasoline charge. That is, the gasoline charge may be either a straight run naphtha, coker gasoline, gasoline product of hydrocracking or catalytic cracking, and/or mixtures thereof. The hydrogenated charge is thereafter stabilized as by fractionation to remove undesired low boiling constituents. The stabilized charge is passed by line 6 to a depentanizer tower 8. The depentanizer tower 8 is maintained under operating conditions particularly selective to separate C 5 and lower boiling hydrocarbons from a higher boiling hydrocarbon fraction comprising C 6 and higher boiling hydrocarbons. The C 5 and lower boiling hydrocarbons are removed from the upper portion of tower 8 by line 10. The C 6 and higher boiling hydrocarbons having, for example, the composition of C 6 and higher boiling gasoline hydrocarbons are withdrawn from the bottom of depentanizer tower 8 by line 12. It is to be understood that the separation effected in depentanizer tower 8 is designed to carry substantially all of the C 6 and higher boiling hydrocarbons into the bottom phase and thus it is expected that some C 5 hydrocarbons will be carried along therewith. However, the bottom fraction in line 12 is primarily C 6 and higher boiling hydrocarbons comprising the higher boiling components of the gasoline fraction boiling up to about 380° F. Desulfurization of the gasoline boiling charge may be effected after passing through the depentanizer rather than before. The thus obtained depentanized charge is passed by line 12 to a platinum reforming operation in zone 14 wherein the reforming severity conditions are selected to provide reformate product varying considerably in octane rating. Depending on conditions employed and reformate cut point, it may have a relatively high octane rating as high as about 104 or 106 octane numbers clear or it may be considerably lower and as low as 90 octane clear basis. The reforming operation effected in zone 14 relies upon a platinum-type reforming catalyst provided with suitable catalyst promoters to achieve the results desired. Although not specifically shown it is to be understood that a typical reforming operation known in the prior art and comprising three or more reactors with separation equipment so that the effluent obtained from reforming will pass through one or more separation zones to stabilize the reformate product and effect the recovery of normally gaseous components rich in hydrogen from a higher boiling reformate product containing C 5 and higher boiling hydrocarbons. The separated normal gaseous components not shown in the drawing and comprising a hydrogen rich recycle gas may be recycled to the reformer or used in another suitable portion of the processing sequence herein discussed. The reformate product obtained from reforming zone 14 and comprising primarily C 5 and higher boiling hydrocarbons is then passed by line 16 to a depentanizer tower 18. Depentanizer tower 18 is maintained under conditions designed to permit separation and recovery of primarily C 6 and higher boiling hydrocarbons having the characteristics identified in Table 1. This C 6 and higher boiling reformate fraction is withdrawn from the bottom portion of the tower by line 20 with primarily C 5 hydrocarbon components and any lower boiling material being withdrawn from the upper portion of the tower by line 22.
TABLE 1
PtR Yields and Reformate PONA (paraffins, olefins, naphthenes and aromatics) Composition for 350 psig Reforming of C 6 -380° F. TBP (total boiling point) MCS (Mid-Continent Sour) Naphtha After Adjustment for a 1.5% vol Loss in C 5 + Reformate Yield
Recycle Gas Water Level -- Optimum
Octane C 5 +, R+3 104.0 C 5 +, R+0 99.7 C 6 +, R+3 105.1 C 6 +, R+0 101.7 Yields Vol Wt Mol C5+ 73.6 78.7 86.7 C 5 S 7.9 6.6 10.2 C 4 S 8.6 6.6 12.8 DG 14.6 150.6 H 2 1.8 102.3 C 1 2.4 17.1 C 2 4.0 15.0 C 3 6.3 16.2 IC 4 3.5 2.6 5.1 NC 4 5.1 4.0 7.7 IC 5 4.9 4.1 6.4 NC 5 2.9 2.5 3.8 C 6 + 65.7 72.2 76.4 Total 82.21 100.0 250.0 H 2 S Cf/Bbl 906. C 5 + Reformate Properties Sp. Gr. 0.8021 Mol. Wt. 102.0 RVP (reed vapor pressure) 3.79 Recycle Gas Composition H 2 71.1 C 1 11.3 C 2 8.1 C 3 5.8 IC 4 1.1 NC 4 1.3 IC 5 0.5 NC 5 0.3 IC 6 0.2 NC 6 0.1 C 6 0.1 C 7 +0.3 Mol. Wt. 10.8 Sp. Gr. 0.3716 C 6 + Yields Vol Wt Mol Paraffins 18.5 16.7 19.9 Olefins 1.0 0.9 1.3 Naphthenes 0.5 0.5 0.7 Aromatics 45.7 54.0 54.6 C 6 P 9.3 8.2 10.7 C 7 P 6.9 6.4 7.1 C 8 P 2.2 2.1 2.1 C 9 + P -0.0 -0.0 -0.0 Benzene 3.0 3.5 5.1 Toluene 13.2 15.3 18.7 C 8 Aromatics 14.6 16.9 17.9 C 9 + Aromatics 14.9 18.2 12.9
The C 5 and lower boiling hydrocarbons recovered from depentanizers 8 and 18 are combined and passed to a debutanizer tower 24 wherein C 4 and lower boiling hydrocarbons are separated from C 5 hydrocarbons. The C 4 and lower boiling hydrocarbons are withdrawn from debutanizer tower 24 by line 26. The C 5 hydrocarbon rich stream comprising about 50.4% n-C 5 hydrocarbons are passed by line 28 to deisopentanizer tower 30. In deisopentanizer tower 30, a separation is made between normal pentane and isopentane so that a 95 percent rich isopentane stream may be withdrawn from the upper portion of the tower by line 32. Normal pentane is recovered from the bottom of tower 30 and passed by line 34 to an isomerization zone 36. Isomerization zone 36 is relied upon to convert normal pentane to isopentane and the product obtained therefrom is passed to deisopentanizer tower 30 by way of line 38 and 28. The isomerization of pentanes is well known in the art and known catalyst compositions and operating conditions may be employed to effect such an isomerization. It is intended that any of the well known and reliable isomerization processes be employed and particularly one which will economically convert normal pentane to isopentane. The product obtained from isomerizing step 36 is passed to tower 30 by line 38 for effecting separation of normal from isopentane. The recovered isopentane in line 32 may then be employed as blending stock in gasoline product or used for other purposes known in the art.
The reforming effluent recovered from the bottom of depentanizer tower 18 and having the composition identified in Table 1 above is thereafter passed by line 20 to dehexanizer tower 40 wherein the operating conditions are maintained to effect a separation between a hydrocarbon fraction boiling in the range of from about C 6 hydrocarbons up to a cut point in the range of from about 150° F. to 225° F. from a reformate fraction boiling above the cut point selected and comprising the high octane gasoline reformate product of reforming zone 14.
It is known that the product of platinum reforming contains some very low octane components comprising C 6 and C 7 hydrocarbons which can be readily separated by distillation. These low octane materials are primarily C 6 and C 7 paraffins which have not been converted during reforming as by dehydrogenation, aromatization, isomerization and hydrocracking. Thus reformate splitting in dehexanizer tower 40 permits one to adjust the octane rating and yield of the product obtained as illustrated by the Table below.
Reformer Charge -- C 6 -- 380° F. MCS
Reformer pressure -- 350 psig
Start-of-cycle Conditions
Reformer Severity, C 5 +R+ 3 cc TEL 104 106 108 C 6 + Reformate Estimated Yield, % vol of PtR Charge 66.9 62.1 57.3 Estimated Octane Number, R+0 99.3 102.0 104.2 158° F. + Reformate Estimated Yield, % vol of PtR Charge 57.3 55.0 53.3 Estimated Octane Number, R+0 102 106 109.5 200° F. + Reformate Estimated Yield, % vol of PtR Charge 48.7 48.3 48.3 Estimated Octane Number, R+0 105 108 110
the light hydrocarbon fractions resulting from reformate splitting, as suggested above, may be upgraded by processes such as hexane isomerization, shape selective processing and alkylation after conversion to suitable olefins, or disposed of as fuel. The octane number of these light fractions are represented below.
Reformer Charge -- C 6 --380° F. MCS
Reformer Pressure -- 350 psig.
Start-of-cycle Conditions
Reformer Severity, C 5 + R+ 3 cc TEL 104 106 108 C 6 -158° F. Fraction Estimated Yield, % vol of PtR Charge 9.6 7.1 4.0 Estimated Octane Number, R+0 68.3 69.1 71.8 C 6 -200° F. Fraction Estimated Yield, % vol of PtR Charge 18.2 13.8 9.0 Estimated Octane Number, R+0 75.3 79.2 86.7
the relatively high octane reformate product obtained, as above suggested, is recovered from the bottom of dehexanizer 40 by line 42 for passage to gasoline pool. The lower boiling constituents separated in dehexanizer 40 and boiling as above identified depending upon the cut point selected require a further upgrading before use, for example, in an unleaded gasoline product. This overhead fraction removed from dehexanizer 40 by line 44 may comprise some C 7 hydrocarbons.
In the processing arrangement of this invention the hydrocarbon fraction in line 44 is first treated to remove aromatics therefrom and C 7 hydrocarbons. Since it is known that aromatics in an isomerization charge have an undesirable influence upon the isomerization reaction, the aromatics are removed such as by liquid phase extraction, molecular sieve adsorption techniques or any other available means for accomplishing the same. The aromatics thus recovered are removed by line 48 for use as desired. In some instances they may be combined with the gasoline product or used in the chemical industry. The aromatics may be separately recovered through line 50.
The aromatic freed hydrocarbon fraction comprising C 6 + hydrocarbons and possibly some C 7 hydrocarbons is thereafter passed to tower 47 provided to effect separation of C 7 hydrocarbons which are withdrawn from the bottom of the tower. The remaining C 6 hydrocarbon stream is then passed by line 52 to hydrogenation step 54 wherein the conditions employed are such as to hydrogenate any aromatics remaining in the charge after the treatment just discussed. The hydrogenated product freed of aromatics and difficulty isomerizable C 7 hydrocarbons is then passed by line 56 to isomerization zone 58. In the isomerization zone 58 the conditions of operation such as low temperatures are selected which will be effective in producing 2,2-dimethylbutane. The products of isomerization obtained in zone 58 are then passed by line 60 to a separator tower 62 wherein separation is made, for example, to recover 2,2-dimethylbutane along with some 2,3-dimethylbutane from the upper portion of the tower by line 64. Higher boiling material is withdrawn from the bottom portion of the tower by line 66 for passage, all or in part, to platinum reforming or recycle by line 68 to isomerization step 58. Care must be taken to avoid build-up of naphthenes as by recycle in the charge to the isomerization zone 58 and thus conversion of this material as by platinum reforming, thermal and catalytic cracking and olefinic product thereof by alkylation is contemplated.
It is clear from the above discussion that the novel process arrangement of the present invention selectively separates and upgrades low octane components into acceptable higher octane products. Thus by separating out low octane C 5 and C 6 components and separately upgrading them to acceptable octane product under essentially more optimum conversion conditions, substantially improved yield results are also obtained and these improved results permit increased yield of regular as well as premium grade gasoline product.
The combination of reforming and isomerization discussed herein is relied upon to upgrade the gasoline charge comprising C 6 and higher boiling hydrocarbons. The reforming operation, either a regenerative type such as powerforming or a semiregenerative type is effected in a plurality of reactors suitably connected as known in the prior art at a temperature in the range of from about 700° F. up to about 1,050° F. to effect the known reforming reactions of dehydrogenation, cyclization, aromatization, isomerization and some limited cracking of the charge. The reforming operation may be effected at a pressure in the range of from about 100 psig up to about 1,000 psig, it being preferred to employ as low a pressure as possible to achieve the results desired. Generally the pressure will not be significantly above 500 psig and more usually the pressure will be below about 350 or 400 psig. A liquid hourly space velocity selected from within the range of 0.5 up to about 10 may be employed in the presence of hydrogen in a mol ratio with hydrocarbon in the range of 0.5 up to about 20. The reforming catalysts employed are usually Group VIII metals of the platinum type dispersed on a suitable carrier material such as alumina in the eta, gamma or mixed eta-gamma form. The platinum hydrogenation-dehydrogenation component may be used alone or in combination with other metal promoters known in the art. The amount of platinum used varies in the range of from about 0.01 percent up to as high as about 2 or 3 percent, it being preferred to use less than about 1 percent in most cases. The reforming catalyst may contain a halogen promoter and is usually of a particle form size suitable for use in a fixed bed reforming operation.
The isomerization of either C 5 or C 6 hydrocarbons may be effected with solid type isomerization catalyst rather than the more corrosive liquid isomerization catalysts. A solid type of reforming catalyst may comprise platinum disposed on alumina and promoted with an acidic agent such as halogen or boron. Low temperatures are particularly desirable in the isomerization reactions. The production of neohexane by aluminum chloride isomerization at temperatures above and below about 200° F. is known. Furthermore isomerizing with the solid type of isomerization catalyst at temperatures in the range of from about 200° F. up to about 800° F. may be employed with low temperatures in the range of 200° F. to about 350° F. preferred. Of course the various isomerization catalysts are not necessarily equivalent and operating conditions employed will be tailored to the specific catalyst employed. The isomerizing pressure may be selected from within the range of 50 psig up to about 1,000 psig but is preferably selected from within the range of 100 to about 500 psig. Regardless of the particular isomerization process employed, the operating conditions will be selected so that a selective operation is pursued which minimizes cracking and other undesired side reactions. Therefore, in the interest of optimizing the selectivity of the present operation, normal pentanes are separately isomerized from the normal hexanes. The isomerization of pentanes and hexanes is discussed in the literature and the method of the present invention intends to rely upon this information to its maximum advantage.
The removal of aromatics from the C 6 hydrocarbons isolated by the method of the present invention is particularly important since such aromatics in the charge to isomerization are known to be most undesirable. Furthermore, C 7 hydrocarbons are isomerized only with extreme difficulty and their removal from the C 6 hydrocarbon charge to be isomerized is also most desirable. The removal of aromatics such as benzene and toluene may be accomplished by extraction, molecular sieve adsorption or any other known available method. Thereafter C 7 hydrocarbons may be removed from normal C 6 hydrocarbons by fractionation carefully controlled.
Having thus provided a general description of the present invention and presented a specific example in support thereof, it is to be understood that no undue restrictions are to be imposed by reason thereof except as defined by the following claims.
The need for providing lead-free gasoline products to accommodate gasoline combustion engines employing regular and high test leaded gasoline has been prompted by the need to reduce air pollution problems confronting areas of high automobile density. Thus it is predictable that major air pollution reductions can be realized particularly in areas of high automobile density by eliminating lead additive to regular and high octane gasoline. Recent press releases have emphasized the need for such controls and in fact plans are in progress to grant the Secretary of Health, Education and Welfare, authority to set standards of composition of fuel which includes the removal of lead from gasoline. Thus the present invention is concerned with a processing arrangement or sequence one might now employ in present refinery arrangements with a minimum of additional investment to upgrade low octane gasoline material unsuitable for use in present gasoline combustion engines to an acceptable unleaded higher octane product suitable for use in the combination engine as we know it now and changes recommended with respect thereto in the immediate future. In some instances it has been recommended that the compression ratio of today's engines by reduced so that they will be more compatable for operating on gasoline products having an octane rating clear in the range of 90 to 100 octane. Some prior art patents of interest in upgrading gasoline are U.S. Pat. Nos. 2,905,619, 3,165,461 and 1,900,323.
SUMMARY OF THE INVENTION
The present invention is directed to a processing arrangement for upgrading gasoline boiling range material of unsatisfactory octane rating to a higher octane gasoline product suitable for use in gasoline combustion engines without lead additives. In a particular aspect the present invention is directed to the combination of processing steps comprising hydrogenation, reforming, aromatic extraction and C 6 hydrocarbon isomerization as they relate to one another in the combination for upgrading low octane constituents of the gasoline charge to acceptable higher octane product. One important aspect of the processing combination of this invention relates to upgrading low octane C 6 hydrocarbon components.
BRIEF DESCRIPTION OF THE DRAWING
The drawing diagrammatically presents one arrangement of processing steps for upgrading gasoline material boiling from about C 5 hydrocarbons up to about 380° F. by a processing combination which includes reforming, isomerization, aromatic recovery and intervening separation steps designed to concentrate desired octane constituents from undesired gasoline component of low octane rating which are convertable to higher octane blending components.
DESCRIPTION OF A SPECIFIC EMBODIMENT
THe present invention is concerned with a processing arrangement which may be utilized in present day refinery operations to upgrade low octane gasoline material and particularly C 6 components thereof to a much higher octane product suitable for blending with reformed gasoline product of a desired higher octane rating. More particularly the processing arrangement identified by this invention upgrades particularly C 6 and higher boiling hydrocarbons in the gasoline boiling range by the operating arrangement of reforming, isomerization, aromatic recovery with intervening stabilization and fractionation designed to particularly upgrade, with much greater emphasis, the low octane C 6 hydrocarbon components. In the specific processing scheme shown by the drawing, a relatively low octane gasoline boiling charge such as defined below and having an initial boiling point of about C 4 hydrocarbons and an end boiling point of about 380° F. is introduced to the process by line 2 for passage to hydrogenation pretreater 4 such as desulfurization. In pretreater 4 the gasoline charge is subjected to hydrogenation conditions which will be effective for removing sulfur and nitrogen components found in the gasoline charge. The amount of sulfur and nitrogen components in the charge will vary considerably depending upon the source of the gasoline charge. That is, the gasoline charge may be either a straight run naphtha, coker gasoline, gasoline product of hydrocracking or catalytic cracking, and/or mixtures thereof. The hydrogenated charge is thereafter stabilized as by fractionation to remove undesired low boiling constituents. The stabilized charge is passed by line 6 to a depentanizer tower 8. The depentanizer tower 8 is maintained under operating conditions particularly selective to separate C 5 and lower boiling hydrocarbons from a higher boiling hydrocarbon fraction comprising C 6 and higher boiling hydrocarbons. The C 5 and lower boiling hydrocarbons are removed from the upper portion of tower 8 by line 10. The C 6 and higher boiling hydrocarbons having, for example, the composition of C 6 and higher boiling gasoline hydrocarbons are withdrawn from the bottom of depentanizer tower 8 by line 12. It is to be understood that the separation effected in depentanizer tower 8 is designed to carry substantially all of the C 6 and higher boiling hydrocarbons into the bottom phase and thus it is expected that some C 5 hydrocarbons will be carried along therewith. However, the bottom fraction in line 12 is primarily C 6 and higher boiling hydrocarbons comprising the higher boiling components of the gasoline fraction boiling up to about 380° F. Desulfurization of the gasoline boiling charge may be effected after passing through the depentanizer rather than before. The thus obtained depentanized charge is passed by line 12 to a platinum reforming operation in zone 14 wherein the reforming severity conditions are selected to provide reformate product varying considerably in octane rating. Depending on conditions employed and reformate cut point, it may have a relatively high octane rating as high as about 104 or 106 octane numbers clear or it may be considerably lower and as low as 90 octane clear basis. The reforming operation effected in zone 14 relies upon a platinum-type reforming catalyst provided with suitable catalyst promoters to achieve the results desired. Although not specifically shown it is to be understood that a typical reforming operation known in the prior art and comprising three or more reactors with separation equipment so that the effluent obtained from reforming will pass through one or more separation zones to stabilize the reformate product and effect the recovery of normally gaseous components rich in hydrogen from a higher boiling reformate product containing C 5 and higher boiling hydrocarbons. The separated normal gaseous components not shown in the drawing and comprising a hydrogen rich recycle gas may be recycled to the reformer or used in another suitable portion of the processing sequence herein discussed. The reformate product obtained from reforming zone 14 and comprising primarily C 5 and higher boiling hydrocarbons is then passed by line 16 to a depentanizer tower 18. Depentanizer tower 18 is maintained under conditions designed to permit separation and recovery of primarily C 6 and higher boiling hydrocarbons having the characteristics identified in Table 1. This C 6 and higher boiling reformate fraction is withdrawn from the bottom portion of the tower by line 20 with primarily C 5 hydrocarbon components and any lower boiling material being withdrawn from the upper portion of the tower by line 22.
TABLE 1
PtR Yields and Reformate PONA (paraffins, olefins, naphthenes and aromatics) Composition for 350 psig Reforming of C 6 -380° F. TBP (total boiling point) MCS (Mid-Continent Sour) Naphtha After Adjustment for a 1.5% vol Loss in C 5 + Reformate Yield
Recycle Gas Water Level -- Optimum
Octane C 5 +, R+3 104.0 C 5 +, R+0 99.7 C 6 +, R+3 105.1 C 6 +, R+0 101.7 Yields Vol Wt Mol C5+ 73.6 78.7 86.7 C 5 S 7.9 6.6 10.2 C 4 S 8.6 6.6 12.8 DG 14.6 150.6 H 2 1.8 102.3 C 1 2.4 17.1 C 2 4.0 15.0 C 3 6.3 16.2 IC 4 3.5 2.6 5.1 NC 4 5.1 4.0 7.7 IC 5 4.9 4.1 6.4 NC 5 2.9 2.5 3.8 C 6 + 65.7 72.2 76.4 Total 82.21 100.0 250.0 H 2 S Cf/Bbl 906. C 5 + Reformate Properties Sp. Gr. 0.8021 Mol. Wt. 102.0 RVP (reed vapor pressure) 3.79 Recycle Gas Composition H 2 71.1 C 1 11.3 C 2 8.1 C 3 5.8 IC 4 1.1 NC 4 1.3 IC 5 0.5 NC 5 0.3 IC 6 0.2 NC 6 0.1 C 6 0.1 C 7 +0.3 Mol. Wt. 10.8 Sp. Gr. 0.3716 C 6 + Yields Vol Wt Mol Paraffins 18.5 16.7 19.9 Olefins 1.0 0.9 1.3 Naphthenes 0.5 0.5 0.7 Aromatics 45.7 54.0 54.6 C 6 P 9.3 8.2 10.7 C 7 P 6.9 6.4 7.1 C 8 P 2.2 2.1 2.1 C 9 + P -0.0 -0.0 -0.0 Benzene 3.0 3.5 5.1 Toluene 13.2 15.3 18.7 C 8 Aromatics 14.6 16.9 17.9 C 9 + Aromatics 14.9 18.2 12.9
The C 5 and lower boiling hydrocarbons recovered from depentanizers 8 and 18 are combined and passed to a debutanizer tower 24 wherein C 4 and lower boiling hydrocarbons are separated from C 5 hydrocarbons. The C 4 and lower boiling hydrocarbons are withdrawn from debutanizer tower 24 by line 26. The C 5 hydrocarbon rich stream comprising about 50.4% n-C 5 hydrocarbons are passed by line 28 to deisopentanizer tower 30. In deisopentanizer tower 30, a separation is made between normal pentane and isopentane so that a 95 percent rich isopentane stream may be withdrawn from the upper portion of the tower by line 32. Normal pentane is recovered from the bottom of tower 30 and passed by line 34 to an isomerization zone 36. Isomerization zone 36 is relied upon to convert normal pentane to isopentane and the product obtained therefrom is passed to deisopentanizer tower 30 by way of line 38 and 28. The isomerization of pentanes is well known in the art and known catalyst compositions and operating conditions may be employed to effect such an isomerization. It is intended that any of the well known and reliable isomerization processes be employed and particularly one which will economically convert normal pentane to isopentane. The product obtained from isomerizing step 36 is passed to tower 30 by line 38 for effecting separation of normal from isopentane. The recovered isopentane in line 32 may then be employed as blending stock in gasoline product or used for other purposes known in the art.
The reforming effluent recovered from the bottom of depentanizer tower 18 and having the composition identified in Table 1 above is thereafter passed by line 20 to dehexanizer tower 40 wherein the operating conditions are maintained to effect a separation between a hydrocarbon fraction boiling in the range of from about C 6 hydrocarbons up to a cut point in the range of from about 150° F. to 225° F. from a reformate fraction boiling above the cut point selected and comprising the high octane gasoline reformate product of reforming zone 14.
It is known that the product of platinum reforming contains some very low octane components comprising C 6 and C 7 hydrocarbons which can be readily separated by distillation. These low octane materials are primarily C 6 and C 7 paraffins which have not been converted during reforming as by dehydrogenation, aromatization, isomerization and hydrocracking. Thus reformate splitting in dehexanizer tower 40 permits one to adjust the octane rating and yield of the product obtained as illustrated by the Table below.
Reformer Charge -- C 6 -- 380° F. MCS
Reformer pressure -- 350 psig
Start-of-cycle Conditions
Reformer Severity, C 5 +R+ 3 cc TEL 104 106 108 C 6 + Reformate Estimated Yield, % vol of PtR Charge 66.9 62.1 57.3 Estimated Octane Number, R+0 99.3 102.0 104.2 158° F. + Reformate Estimated Yield, % vol of PtR Charge 57.3 55.0 53.3 Estimated Octane Number, R+0 102 106 109.5 200° F. + Reformate Estimated Yield, % vol of PtR Charge 48.7 48.3 48.3 Estimated Octane Number, R+0 105 108 110
the light hydrocarbon fractions resulting from reformate splitting, as suggested above, may be upgraded by processes such as hexane isomerization, shape selective processing and alkylation after conversion to suitable olefins, or disposed of as fuel. The octane number of these light fractions are represented below.
Reformer Charge -- C 6 --380° F. MCS
Reformer Pressure -- 350 psig.
Start-of-cycle Conditions
Reformer Severity, C 5 + R+ 3 cc TEL 104 106 108 C 6 -158° F. Fraction Estimated Yield, % vol of PtR Charge 9.6 7.1 4.0 Estimated Octane Number, R+0 68.3 69.1 71.8 C 6 -200° F. Fraction Estimated Yield, % vol of PtR Charge 18.2 13.8 9.0 Estimated Octane Number, R+0 75.3 79.2 86.7
the relatively high octane reformate product obtained, as above suggested, is recovered from the bottom of dehexanizer 40 by line 42 for passage to gasoline pool. The lower boiling constituents separated in dehexanizer 40 and boiling as above identified depending upon the cut point selected require a further upgrading before use, for example, in an unleaded gasoline product. This overhead fraction removed from dehexanizer 40 by line 44 may comprise some C 7 hydrocarbons.
In the processing arrangement of this invention the hydrocarbon fraction in line 44 is first treated to remove aromatics therefrom and C 7 hydrocarbons. Since it is known that aromatics in an isomerization charge have an undesirable influence upon the isomerization reaction, the aromatics are removed such as by liquid phase extraction, molecular sieve adsorption techniques or any other available means for accomplishing the same. The aromatics thus recovered are removed by line 48 for use as desired. In some instances they may be combined with the gasoline product or used in the chemical industry. The aromatics may be separately recovered through line 50.
The aromatic freed hydrocarbon fraction comprising C 6 + hydrocarbons and possibly some C 7 hydrocarbons is thereafter passed to tower 47 provided to effect separation of C 7 hydrocarbons which are withdrawn from the bottom of the tower. The remaining C 6 hydrocarbon stream is then passed by line 52 to hydrogenation step 54 wherein the conditions employed are such as to hydrogenate any aromatics remaining in the charge after the treatment just discussed. The hydrogenated product freed of aromatics and difficulty isomerizable C 7 hydrocarbons is then passed by line 56 to isomerization zone 58. In the isomerization zone 58 the conditions of operation such as low temperatures are selected which will be effective in producing 2,2-dimethylbutane. The products of isomerization obtained in zone 58 are then passed by line 60 to a separator tower 62 wherein separation is made, for example, to recover 2,2-dimethylbutane along with some 2,3-dimethylbutane from the upper portion of the tower by line 64. Higher boiling material is withdrawn from the bottom portion of the tower by line 66 for passage, all or in part, to platinum reforming or recycle by line 68 to isomerization step 58. Care must be taken to avoid build-up of naphthenes as by recycle in the charge to the isomerization zone 58 and thus conversion of this material as by platinum reforming, thermal and catalytic cracking and olefinic product thereof by alkylation is contemplated.
It is clear from the above discussion that the novel process arrangement of the present invention selectively separates and upgrades low octane components into acceptable higher octane products. Thus by separating out low octane C 5 and C 6 components and separately upgrading them to acceptable octane product under essentially more optimum conversion conditions, substantially improved yield results are also obtained and these improved results permit increased yield of regular as well as premium grade gasoline product.
The combination of reforming and isomerization discussed herein is relied upon to upgrade the gasoline charge comprising C 6 and higher boiling hydrocarbons. The reforming operation, either a regenerative type such as powerforming or a semiregenerative type is effected in a plurality of reactors suitably connected as known in the prior art at a temperature in the range of from about 700° F. up to about 1,050° F. to effect the known reforming reactions of dehydrogenation, cyclization, aromatization, isomerization and some limited cracking of the charge. The reforming operation may be effected at a pressure in the range of from about 100 psig up to about 1,000 psig, it being preferred to employ as low a pressure as possible to achieve the results desired. Generally the pressure will not be significantly above 500 psig and more usually the pressure will be below about 350 or 400 psig. A liquid hourly space velocity selected from within the range of 0.5 up to about 10 may be employed in the presence of hydrogen in a mol ratio with hydrocarbon in the range of 0.5 up to about 20. The reforming catalysts employed are usually Group VIII metals of the platinum type dispersed on a suitable carrier material such as alumina in the eta, gamma or mixed eta-gamma form. The platinum hydrogenation-dehydrogenation component may be used alone or in combination with other metal promoters known in the art. The amount of platinum used varies in the range of from about 0.01 percent up to as high as about 2 or 3 percent, it being preferred to use less than about 1 percent in most cases. The reforming catalyst may contain a halogen promoter and is usually of a particle form size suitable for use in a fixed bed reforming operation.
The isomerization of either C 5 or C 6 hydrocarbons may be effected with solid type isomerization catalyst rather than the more corrosive liquid isomerization catalysts. A solid type of reforming catalyst may comprise platinum disposed on alumina and promoted with an acidic agent such as halogen or boron. Low temperatures are particularly desirable in the isomerization reactions. The production of neohexane by aluminum chloride isomerization at temperatures above and below about 200° F. is known. Furthermore isomerizing with the solid type of isomerization catalyst at temperatures in the range of from about 200° F. up to about 800° F. may be employed with low temperatures in the range of 200° F. to about 350° F. preferred. Of course the various isomerization catalysts are not necessarily equivalent and operating conditions employed will be tailored to the specific catalyst employed. The isomerizing pressure may be selected from within the range of 50 psig up to about 1,000 psig but is preferably selected from within the range of 100 to about 500 psig. Regardless of the particular isomerization process employed, the operating conditions will be selected so that a selective operation is pursued which minimizes cracking and other undesired side reactions. Therefore, in the interest of optimizing the selectivity of the present operation, normal pentanes are separately isomerized from the normal hexanes. The isomerization of pentanes and hexanes is discussed in the literature and the method of the present invention intends to rely upon this information to its maximum advantage.
The removal of aromatics from the C 6 hydrocarbons isolated by the method of the present invention is particularly important since such aromatics in the charge to isomerization are known to be most undesirable. Furthermore, C 7 hydrocarbons are isomerized only with extreme difficulty and their removal from the C 6 hydrocarbon charge to be isomerized is also most desirable. The removal of aromatics such as benzene and toluene may be accomplished by extraction, molecular sieve adsorption or any other known available method. Thereafter C 7 hydrocarbons may be removed from normal C 6 hydrocarbons by fractionation carefully controlled.
Having thus provided a general description of the present invention and presented a specific example in support thereof, it is to be understood that no undue restrictions are to be imposed by reason thereof except as defined by the following claims.