CATALYTIC STEAM CRACKING OF HYDROCARBONS AND CATALYSTS THEREFOR
United States Patent 3725495
Steam cracking of saturated hydrocarbons to form unsaturated hydrocarbons, such as ethylene, propylene, butylenes, butadiene, and aromatics, is carried out in the presence of a catalyst comprising a major proportion of oxides of zirconium or hafnium associated with active alumina together with oxides of chromium, manganese or iron and promoted with compounds of alkali metals and alkaline earth metals. High conversion efficiences are achieved at high space velocities and without carbon deposition.
US Patent References:
Dehydrogenation of hydrocarbons
Linn - January 1946 - 2392750
Insulator
Kirshenbaum - July 1956 - 2754354
Manufacture of para-xylene
Bloch et al. - July 1959 - 2894046
Process for preparing aromatic hydrocarbons
Schmetterling et al. - June 1960 - 2941016
Preparation of a chromia-alumina hydrocarbon conversion catalyst
Gremillion - April 1965 - 3179602
Dehydrogenation of hydrocarbons
Linn - January 1946 - 2392750
Insulator
Kirshenbaum - July 1956 - 2754354
Manufacture of para-xylene
Bloch et al. - July 1959 - 2894046
Process for preparing aromatic hydrocarbons
Schmetterling et al. - June 1960 - 2941016
Preparation of a chromia-alumina hydrocarbon conversion catalyst
Gremillion - April 1965 - 3179602
Inventors:
Wrisberg, Johannes (Gammel Holte, DK)
Andersen, Kjeld Jorn (Tulstrup, DK)
Mogensen, Erik (Ramlose, DK)
Andersen, Kjeld Jorn (Tulstrup, DK)
Mogensen, Erik (Ramlose, DK)
Application Number:
05/099271
Publication Date:
04/03/1973
Filing Date:
12/17/1970
View Patent Images:
Export Citation:
Assignee:
Haldor, Frederik Axel Toksoe (Frydenlundsvej Vedbaek, DK)
Fluor Corporation (Los Angeles, CA)
Fluor Corporation (Los Angeles, CA)
Primary Class:
Other Classes:
585/615, 208/124, 208/122, 585/418, 585/613, 585/950, 585/421, 208/123, 585/652
International Classes:
B01J23/16; B01J23/76; C07C4/06; C07C4/00; C10G11/04; C07C3/34
Field of Search:
260/683,680,673,673.5,683.3 208/135,136,137,122,123,124
US Patent References:
| 3624176 | CATALYTIC PROCESS FOR PRODUCING GAS MIXTURES HAVING HIGH ETHYLENE CONTENTS | November 1971 | Lhonore et al. |
Primary Examiner:
Gantz, Delbert E.
Assistant Examiner:
Spresser C. E.
Claims:
What is claimed is
1. A process for the manufacture of unsaturated hydrocarbons by a gaseous catalytic reaction wherein a feedstock substantially comprising saturated hydrocarbons is contacted at a temperature below 1,000°C and a pressure in the range 0.1-50 atm.abs. in the presence of added steam with a catalyst comprising 50-80 wt.% of at least one oxide of zirconium and/or hafnium, together with 5-30 wt.% active alumina, as well as 5-40 wt.% of at least one oxide of chromium, manganese and/or iron and 0.1-10 wt.% of at least one compound of an alkali metal or an alkaline earth metal.
2. A process according to claim 1, wherein the reaction is carried out at a temperature in the range 200°-900°C.
3. A process according to claim 2, wherein the reaction is carried out at a pressure of 1-15 atm.abs. measured at the reactor outlet.
4. A process according to claim 1, wherein the reaction is carried out at a temperature in the range 500°-850°C.
5. A process according to claim 1, wherein the feedstock consists entirely of a saturated hydrocarbon or a mixture of saturated hydrocarbons.
6. A process according to claim 1, wherein the feedstock comprises a major proportion of saturated hydrocarbons and a minor proportion of unsaturated hydrocarbons.
7. A process according to claim 1, wherein the reaction is carried out in the presence of sulfur.
8. A process according to claim 7, wherein the sulfur is added to the feedstock in the form of free sulfur, hydrogen sulfide, carbon disulfide or an organic sulfur compound.
9. A process according to claim 7, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.1-1.0.
10. A process according to claim 1, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.01-10.
11. A process according to claim 10, wherein the ratio of steam to hydrocarbon feedstock is 0.1-1.0.
12. A process for the manufacture of unsaturated hydrocarbons by a gaseous catalytic reaction wherein a feedstock substantially comprising saturated hydrocarbons is contacted at a temperature in the range 500°-850°C and a pressure in the range 1-15 atm.abs. measured at the reactor outlet in the presence of added steam with a catalyst comprising 50-80 wt.% zirconium and/or hafnium oxide, together with 5-30 wt.% active alumina, as well as 5-40 wt.% of at least one oxide of chromium manganese and/or iron and 0.3-7.0 wt.% of at least one compound of an alkali metal and/or alkaline earth metal.
13. A process according to claim 12, wherein the feedstock consists entirely of a saturated hydrocarbon or a mixture of saturated hydrocarbons.
14. A process according to claim 12, wherein the feedstock comprises a major proportion of saturated hydrocarbons and a minor proportion of unsaturated hydrocarbons.
15. A process according to claim 12, wherein the reaction is carried out in the presence of sulfur.
16. A process according to claim 15, wherein the sulfur is added to the feedstock in the form of free sulfur, hydrogen sulfide, carbon disulfide or an organic sulfur compound.
17. A process according to claim 15, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.1-1.0.
18. A process according to claim 12, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.01-10.
19. A process according to claim 18, wherein the ratio of steam to hydrocarbon feedstock is 0.1-1.0.
1. A process for the manufacture of unsaturated hydrocarbons by a gaseous catalytic reaction wherein a feedstock substantially comprising saturated hydrocarbons is contacted at a temperature below 1,000°C and a pressure in the range 0.1-50 atm.abs. in the presence of added steam with a catalyst comprising 50-80 wt.% of at least one oxide of zirconium and/or hafnium, together with 5-30 wt.% active alumina, as well as 5-40 wt.% of at least one oxide of chromium, manganese and/or iron and 0.1-10 wt.% of at least one compound of an alkali metal or an alkaline earth metal.
2. A process according to claim 1, wherein the reaction is carried out at a temperature in the range 200°-900°C.
3. A process according to claim 2, wherein the reaction is carried out at a pressure of 1-15 atm.abs. measured at the reactor outlet.
4. A process according to claim 1, wherein the reaction is carried out at a temperature in the range 500°-850°C.
5. A process according to claim 1, wherein the feedstock consists entirely of a saturated hydrocarbon or a mixture of saturated hydrocarbons.
6. A process according to claim 1, wherein the feedstock comprises a major proportion of saturated hydrocarbons and a minor proportion of unsaturated hydrocarbons.
7. A process according to claim 1, wherein the reaction is carried out in the presence of sulfur.
8. A process according to claim 7, wherein the sulfur is added to the feedstock in the form of free sulfur, hydrogen sulfide, carbon disulfide or an organic sulfur compound.
9. A process according to claim 7, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.1-1.0.
10. A process according to claim 1, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.01-10.
11. A process according to claim 10, wherein the ratio of steam to hydrocarbon feedstock is 0.1-1.0.
12. A process for the manufacture of unsaturated hydrocarbons by a gaseous catalytic reaction wherein a feedstock substantially comprising saturated hydrocarbons is contacted at a temperature in the range 500°-850°C and a pressure in the range 1-15 atm.abs. measured at the reactor outlet in the presence of added steam with a catalyst comprising 50-80 wt.% zirconium and/or hafnium oxide, together with 5-30 wt.% active alumina, as well as 5-40 wt.% of at least one oxide of chromium manganese and/or iron and 0.3-7.0 wt.% of at least one compound of an alkali metal and/or alkaline earth metal.
13. A process according to claim 12, wherein the feedstock consists entirely of a saturated hydrocarbon or a mixture of saturated hydrocarbons.
14. A process according to claim 12, wherein the feedstock comprises a major proportion of saturated hydrocarbons and a minor proportion of unsaturated hydrocarbons.
15. A process according to claim 12, wherein the reaction is carried out in the presence of sulfur.
16. A process according to claim 15, wherein the sulfur is added to the feedstock in the form of free sulfur, hydrogen sulfide, carbon disulfide or an organic sulfur compound.
17. A process according to claim 15, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.1-1.0.
18. A process according to claim 12, wherein sufficient steam is added to give a weight ratio of steam to hydrocarbon feedstock in the reactor of 0.01-10.
19. A process according to claim 18, wherein the ratio of steam to hydrocarbon feedstock is 0.1-1.0.
Description:
The present invention relates to the catalytic steam cracking of hydrocarbons and catalysts for this purpose and particularly, but not exclusively to the manufacture of unsaturated hydrocarbons from saturated hydrocarbons.
Ethylene and propylene are commonly manufactured by thermal cracking of higher hydrocarbons, such as light naphtha, in the presence of steam. This process of steam cracking is normally carried out with a temperature above 800°C in the cracking zone. Using a light naphtha as feed, a typical steam cracker produces methane and hydrogen 18 percent, ethylene 32 percent, ethane 5 percent, propylene 18 percent, butadiene 5 percent, butylene 4 percent, and gasoline/fuel oil 18 percent (percent by weight of feed).
The high temperature and large heat-flux in the cracking zone makes great demands of the materials of construction of the reactor. Furthermore, the required correlation between space velocity, temperature distribution, pressure drop in the system, and linear velocity is relatively costly, requiring considerable pilot-plant evaluation work.
It is also known to manufacture unsaturated hydrocarbons by catalytic cracking of higher saturated hydrocarbons at temperatures of 500°-700°C, using silica-alumina catalysts. However, these processes are troubled by carbon deposits on the catalyst which require frequent removal during operation.
Other catalyst compositions for steam cracking of hydrocarbons have been proposed. These compositions include combinations of zirconium oxide and one or more of a number of other oxides among which are oxides of the rare earth metals, antimony oxide, and inactive oxides rich in magnesium oxide. Further oxides which might optionally be included in the catalyst composition in small amounts are iron oxide, aluminum oxide, copper oxide, calcium oxide, barium oxide, silicium oxide, and titanium oxide. These catalysts are claimed to operate without carbon deposition at rather low space velocities.
It is an object of the present invention to provide a catalytic process for the manufacture of unsaturated hydrocarbons, such as ethylene, propylene, butylenes, butadiene, and aromatics, from saturated hydrocarbons which gives improved yield and thermal efficiencies while being capable of operating at high space velocity without significant carbon deposition on the catalyst.
According to the present invention we provide a process for the manufacture of unsaturated hydrocarbons by a gaseous catalytic reaction wherein a feedstock substantially comprising saturated hydrocarbons is contacted at a temperature below 1,000°C and a pressure of 0.1-50 atm.abs. in the presence of added steam with a catalyst comprising a major proportion of at least one oxide of zirconium or hafnium together with at least 5 percent of active aluminum oxide as well as at least 5 percent of at least one oxide of manganese, chromium or iron, and a small amount not exceeding 10 percent of at least one compound of an alkali metal or alkaline earth metal.
Further according to the present invention we provide a catalyst for the manufacture of unsaturated hydrocarbons from saturated hydrocarbons in the presence of steam comprising a major proportion of at least one oxide of zirconium or hafnium, together with at least 5 percent of active aluminum oxide, as well as at least 5 percent of one oxide of manganese, chromium, or iron, and a small amount not exceeding 10 percent of at least one compound of an alkali metal or alkaline earth metal.
In a preferred embodiment of the invention, the process is carried out at a temperature in the range 200°-900°C, preferably in the range 500°-850°C. It is also preferred to use pressures in the range 1-15 atm.abs. measured at the reactor outlet.
The major component of the catalyst used in the process according to the present invention is zirconium or hafnium oxide or both. This component should be present in an amount of at least 50 wt.% up to 80%. It should be noted that a catalyst substantially consisting of, for example, zirconium oxide is not very practicable because such a catalyst does not possess adequate mechanical strength unless it is subjected to a heat treatment at high temperatures such as temperatures above 1,000°C. It has been found that the presence of active aluminum oxide in the catalyst composition facilitates its preparation so that a satisfactory strength can be obtained from a heat treatment at a temperature below 1,000°C. The reactive aluminum oxide is added during the preparation of the catalyst either as such or as a compound which on heating transforms into an active aluminum oxide such as for example precipitated aluminum hydroxide. The amount of active aluminum oxide is not very critical and an amount of at least 5 wt.% is satisfactory. The catalyst may contain up to 30 wt.% of active alumina, 10 wt.% being the preferred level.
In addition, the catalyst used in the process according to the present invention contains at least 5 wt.% up to about 40 wt.% of one or more of the oxides of manganese, chromium, or iron together with an alkali metal compound or an alkaline earth metal compound or both in a total amount of 0.1 to 10 wt.% calculated in the oxide. If an alkaline earth compound is present it is preferred to have a compound of an alkali metal present also. The use of a potassium compound in an amount of 0.3 to 7 wt.% calculated as the oxide is especially preferred.
When a catalyst composition in accordance with the present invention is used the hydrocarbon feedstock can be fed to the catalyst at a high space velocity while still a break-through of unconverted hydrocarbon feed is avoided. A complete conversion of the hydrocarbon feed has been obtained at a space velocity as high as 8.6 liq.vol./vol.catalyst/h.
The feedstock may consist of a single saturated hydrocarbon, or a mixture of saturated hydrocarbons and may contain a minor proportion of unsaturated hydrocarbons if this is required to obtain desired products. Suitable saturated hydrocarbons include methane, ethane, propane, butane as well as liquid hydrocarbons such as light naphtha and even crude oil. Our process and catalyst readily tolerate the presence of sulphur which is even desirable since it can passivate the free metal surfaces in the reactor. The sulphur may be originally present in the feedstock or it may be added in the form of the free element or as compounds such as organic sulphur compounds, hydrogen sulphide, or carbon disulphide.
Steam should be added to give a weight ratio of steam to hydrocarbon feedstock of 0.01-10 in the reactor. The ratio should be preferably the lowest which avoids significant carbon deposition on the catalyst, say 0.1-1.0.
Our process can be operated at lower temperatures than those used hitherto, and the lower energy requirements give higher thermal efficiencies. The demands made on the equipment are accordingly reduced, resulting in lower capital costs and also in reduced vulnerability of materials during operation. The design/operating requirements are less stringent, giving much greater flexibility and safety. Furthermore, conversion efficiencies are improved, giving higher production rate and higher yields of the desired unsaturated hydrocarbons.
In order that the invention should be better understood, it will now be described in further detail with reference in particular to the following examples:
PREPARATION OF CATALYSTS
A. catalyst comprising Al 2 O 3 --ZrO 2 --Cr 2 O 3 --K 2 O
A suspension was prepared of 600 g ZrO 2 in 6 l water at 65°C and 370 g Cr(NO 3 ) 3 . 9 H 2 O and 1,840 g Al(NO 3 ) 3 . 9 H 2 O then dissolved therein. To this was added 1,518 g NH 4 HCO 3 in 1 l water at 65°C, the resulting precipitation taking 25 minutes. The mixture was then stirred for one hour before filtering, and the collected precipitate washed with 6 l water. This precipitate was then dried for 16 hours at 120°C followed by 1 hour at 400°C.
The dried precipitate was mixed with 37 g graphite and 28 g cellulose fiber and ground for 6 hours in a ball mill, after which the mixture was tabletted. The tablets were then calcined for 2 hours at 850°C.
117 g of these tablets were impregnated using a solution of 240 g KNO 3 dissolved in 500 ml water, and then calcined for a further 2 hours at 400°C.
The resulting catalyst A had the following composition (percentages by weight):
25% Al 2 O 3 -- 61% ZrO 2 -- 7% Cr 2 O 3 -- 7% K 2 O
B. catalyst comprising Al 2 O 3 -- ZrO 2 -- MnO -- K 2 O
A suspension of 56 kg ZrO 2 in 1,000 l of deionized water at 65°C was prepared and 108 kg Mn(NO 3 ) 2 . 4 H 2 O and 100 kg Al(NO 3 ) 3 , 9 H 2 O dissolved therein. 145 kg NH 4 HCO 3 was added to this over 1 hour and thereafter stirred for 12 hours. After adding a further 200 l of water the mixture was filtered in a pressure filter. The filtrate was dried for 12 hours at 200°C whilst thoroughly blown by air, after which it was crushed and dried for a further two hours at 300°C. The resulting dried product was mixed with 4 wt.% graphite and 3 wt.% cellulose fiber and tabletted in the form of hollow cylinders 7 mm high with an i.d. of 6 mm and an o.d. of 13 mm, the tablets then being calcined for two hours at 800°C. The cylindrical tablets were impregnated using a solution of 50 wt.% KNO 3 in water, then heated for one hour at 80°C and finally for 1 hour at 500°C.
The resulting catalyst B had the following composition (by weight) 13% Al 2 O 3 -- 52% ZrO 2 -- 27% MnO -- 8% K 2 O.
Further catalysts were prepared by similar methods but substituting one or more constituents giving catalysts of the following compositions:
C 13% al 2 O 3 -- 53% ZrO 2 -- 27% MnO -- 7% Cs 2 O
D 14% al 2 O 3 -- 56% ZrO 2 -- 24% Fe 2 O 3 -- 6% K 2 O
E 14% al 2 O 3 -- 52% TiO 2 -- 28% MnO -- 6% K 2 O
(comparative Catalyst)
F 14% al 2 O 3 -- 51% ZrO 2 -- 28% MnO -- 3% BaO -- 4% K 2 O
These catalysts were evaluated in a small tube reactor (Reactor One) holding 125 ml catalyst. To this was fed a mixture of 2 parts naphtha and 1 parts water to give an eventual steam-naphtha weight ratio of 0.5. The naphtha had a weight composition of 24.1 percent iso-pentane, 53.6 percent n-pentane, 13.5 percent iso-hexane, 5.6 percent n-hexane, and 3.2 percent aromatics. The naphtha-water feed was first passed through a preheater and then through the reactor, the space velocity being 4.2 liq. vol./vol. catalyst/h. The feed passed downwards through the reactor, the temperature at the top of the catalyst bed being 590°C and the temperature at the center and at the bottom of the bed being 750°C. The reactor effluent was quenched by water injection in the reactor outlet and the composition of the effluent product gas determined on a gas-chromatograph. The results of these investigations are shown in the accompanying table I.
Catalysts A, B, C, and D, which are in accordance with the present invention, all gave an almost complete conversion of the hydrocarbon feed with about 1 percent or less unconverted hydrocarbon feed in the product. Catalyst E, which is not in accordance with the present invention, gave a complete conversion right from the start, however, there was a gradual increase in unconverted hydrocarbon feed in the product, and after 120 hours' operation 20 percent of the hydrocarbon feed passed the catalyst almost unchanged. In the experiment with catalyst F, which is in accordance with the present invention, the conversion was incomplete from the start, however, after a few hours' operation the conversion became complete and during the remaining part of the experiment the amount of unconverted hydrocarbon feed in the product was insignificant.
Because of unrealistic linear velocities of feed and product in a small tube reactor, the results are not representative as far as regards the yields of unsaturated hydrocarbons. Therefore, in order to obtain a more realistic evaluation of a catalyst in accordance with the present invention, catalyst B was tested in a pilot plant reactor (Reactor Two) having a height of 6 m and an internal diameter of 0.09 m. A series of oil-fired burners were provided to heat the reactor. To this reactor was fed a feed of 200 kg/h of naphtha of the same composition as before, together with 120 kg/h steam (i.e., a steam-naphtha ratio of 0.6). The inlet pressure was 7 kg/cm 2 , the outlet pressure 0.3 kg/cm 2 , inlet temperature 500°C and outlet temperature 825°C. The heat flux at the inner reactor wall was 80,000 Kcal/m 2 /h.
The results of investigations using 36 l of catalyst B in this reactor are shown in table II. Although a very high space velocity of 8.6 liq.vol./vol.catalyst/h was used in this experiment only insignificant amounts of unconverted hydrocarbon feed appeared in the product, the liquid product consisting mainly of aromatics.
TABLE I
(REACTOR ONE)
Experiment No. 1 2 3 4 5 6 Catalyst A B C D E F Duration of experiment,hrs. 138 240 66 200 120 325 Inlet pressure, atm.abs. 1.2 1.2 2.6 1.2 1.2 1.2 Space velocity, liq.vol./ vol.cat./h 4.2 4.2 4.2 4.2 4.2 4.2 Yield at start: C 2 H 4 , wt.% of feed 12.4 13.7 11.5 11.4 10.2 14.0 C 3 H 6 , wt.% of feed 13.8 9.3 12.8 10.0 9.5 10.9 Liquid Product + vol.% of feed 1.3 0 0 0 0 5.0 Yield at end: C 2 H 4 , wt.% of feed 12.4 14.4 10.7 10.3 10.2 -- C 3 H 6 , wt.% of feed 9.8 10.7 9.5 8.3 9.5 -- Liquid product + vol.% of feed 0.3 0.6 0.8 0 20 0.1 + Mainly unconverted hydrocarbon feed
TABLE II
(REACTOR TWO)
Experiment No. 7 Catalyst B Duration of experiment, hrs. 100 Inlet pressure, atm.abs. 8 Outlet pressure, atm.abs. 1.3 Space velocity, liq.vol./vol.cat./h 8.6 Yield: C 2 H 4 , wt.% of feed 31.5 C 2 H 6 , wt.% of feed 4.5 C 3 H 6 , wt.% of feed 20.0 C 4 H 8 , wt.% of feed 8.0 C 4 H 6 , wt.% of feed 7.0 Liquid product + , wt.% of feed 8.0 + Mainly aromatics
Ethylene and propylene are commonly manufactured by thermal cracking of higher hydrocarbons, such as light naphtha, in the presence of steam. This process of steam cracking is normally carried out with a temperature above 800°C in the cracking zone. Using a light naphtha as feed, a typical steam cracker produces methane and hydrogen 18 percent, ethylene 32 percent, ethane 5 percent, propylene 18 percent, butadiene 5 percent, butylene 4 percent, and gasoline/fuel oil 18 percent (percent by weight of feed).
The high temperature and large heat-flux in the cracking zone makes great demands of the materials of construction of the reactor. Furthermore, the required correlation between space velocity, temperature distribution, pressure drop in the system, and linear velocity is relatively costly, requiring considerable pilot-plant evaluation work.
It is also known to manufacture unsaturated hydrocarbons by catalytic cracking of higher saturated hydrocarbons at temperatures of 500°-700°C, using silica-alumina catalysts. However, these processes are troubled by carbon deposits on the catalyst which require frequent removal during operation.
Other catalyst compositions for steam cracking of hydrocarbons have been proposed. These compositions include combinations of zirconium oxide and one or more of a number of other oxides among which are oxides of the rare earth metals, antimony oxide, and inactive oxides rich in magnesium oxide. Further oxides which might optionally be included in the catalyst composition in small amounts are iron oxide, aluminum oxide, copper oxide, calcium oxide, barium oxide, silicium oxide, and titanium oxide. These catalysts are claimed to operate without carbon deposition at rather low space velocities.
It is an object of the present invention to provide a catalytic process for the manufacture of unsaturated hydrocarbons, such as ethylene, propylene, butylenes, butadiene, and aromatics, from saturated hydrocarbons which gives improved yield and thermal efficiencies while being capable of operating at high space velocity without significant carbon deposition on the catalyst.
According to the present invention we provide a process for the manufacture of unsaturated hydrocarbons by a gaseous catalytic reaction wherein a feedstock substantially comprising saturated hydrocarbons is contacted at a temperature below 1,000°C and a pressure of 0.1-50 atm.abs. in the presence of added steam with a catalyst comprising a major proportion of at least one oxide of zirconium or hafnium together with at least 5 percent of active aluminum oxide as well as at least 5 percent of at least one oxide of manganese, chromium or iron, and a small amount not exceeding 10 percent of at least one compound of an alkali metal or alkaline earth metal.
Further according to the present invention we provide a catalyst for the manufacture of unsaturated hydrocarbons from saturated hydrocarbons in the presence of steam comprising a major proportion of at least one oxide of zirconium or hafnium, together with at least 5 percent of active aluminum oxide, as well as at least 5 percent of one oxide of manganese, chromium, or iron, and a small amount not exceeding 10 percent of at least one compound of an alkali metal or alkaline earth metal.
In a preferred embodiment of the invention, the process is carried out at a temperature in the range 200°-900°C, preferably in the range 500°-850°C. It is also preferred to use pressures in the range 1-15 atm.abs. measured at the reactor outlet.
The major component of the catalyst used in the process according to the present invention is zirconium or hafnium oxide or both. This component should be present in an amount of at least 50 wt.% up to 80%. It should be noted that a catalyst substantially consisting of, for example, zirconium oxide is not very practicable because such a catalyst does not possess adequate mechanical strength unless it is subjected to a heat treatment at high temperatures such as temperatures above 1,000°C. It has been found that the presence of active aluminum oxide in the catalyst composition facilitates its preparation so that a satisfactory strength can be obtained from a heat treatment at a temperature below 1,000°C. The reactive aluminum oxide is added during the preparation of the catalyst either as such or as a compound which on heating transforms into an active aluminum oxide such as for example precipitated aluminum hydroxide. The amount of active aluminum oxide is not very critical and an amount of at least 5 wt.% is satisfactory. The catalyst may contain up to 30 wt.% of active alumina, 10 wt.% being the preferred level.
In addition, the catalyst used in the process according to the present invention contains at least 5 wt.% up to about 40 wt.% of one or more of the oxides of manganese, chromium, or iron together with an alkali metal compound or an alkaline earth metal compound or both in a total amount of 0.1 to 10 wt.% calculated in the oxide. If an alkaline earth compound is present it is preferred to have a compound of an alkali metal present also. The use of a potassium compound in an amount of 0.3 to 7 wt.% calculated as the oxide is especially preferred.
When a catalyst composition in accordance with the present invention is used the hydrocarbon feedstock can be fed to the catalyst at a high space velocity while still a break-through of unconverted hydrocarbon feed is avoided. A complete conversion of the hydrocarbon feed has been obtained at a space velocity as high as 8.6 liq.vol./vol.catalyst/h.
The feedstock may consist of a single saturated hydrocarbon, or a mixture of saturated hydrocarbons and may contain a minor proportion of unsaturated hydrocarbons if this is required to obtain desired products. Suitable saturated hydrocarbons include methane, ethane, propane, butane as well as liquid hydrocarbons such as light naphtha and even crude oil. Our process and catalyst readily tolerate the presence of sulphur which is even desirable since it can passivate the free metal surfaces in the reactor. The sulphur may be originally present in the feedstock or it may be added in the form of the free element or as compounds such as organic sulphur compounds, hydrogen sulphide, or carbon disulphide.
Steam should be added to give a weight ratio of steam to hydrocarbon feedstock of 0.01-10 in the reactor. The ratio should be preferably the lowest which avoids significant carbon deposition on the catalyst, say 0.1-1.0.
Our process can be operated at lower temperatures than those used hitherto, and the lower energy requirements give higher thermal efficiencies. The demands made on the equipment are accordingly reduced, resulting in lower capital costs and also in reduced vulnerability of materials during operation. The design/operating requirements are less stringent, giving much greater flexibility and safety. Furthermore, conversion efficiencies are improved, giving higher production rate and higher yields of the desired unsaturated hydrocarbons.
In order that the invention should be better understood, it will now be described in further detail with reference in particular to the following examples:
PREPARATION OF CATALYSTS
A. catalyst comprising Al 2 O 3 --ZrO 2 --Cr 2 O 3 --K 2 O
A suspension was prepared of 600 g ZrO 2 in 6 l water at 65°C and 370 g Cr(NO 3 ) 3 . 9 H 2 O and 1,840 g Al(NO 3 ) 3 . 9 H 2 O then dissolved therein. To this was added 1,518 g NH 4 HCO 3 in 1 l water at 65°C, the resulting precipitation taking 25 minutes. The mixture was then stirred for one hour before filtering, and the collected precipitate washed with 6 l water. This precipitate was then dried for 16 hours at 120°C followed by 1 hour at 400°C.
The dried precipitate was mixed with 37 g graphite and 28 g cellulose fiber and ground for 6 hours in a ball mill, after which the mixture was tabletted. The tablets were then calcined for 2 hours at 850°C.
117 g of these tablets were impregnated using a solution of 240 g KNO 3 dissolved in 500 ml water, and then calcined for a further 2 hours at 400°C.
The resulting catalyst A had the following composition (percentages by weight):
25% Al 2 O 3 -- 61% ZrO 2 -- 7% Cr 2 O 3 -- 7% K 2 O
B. catalyst comprising Al 2 O 3 -- ZrO 2 -- MnO -- K 2 O
A suspension of 56 kg ZrO 2 in 1,000 l of deionized water at 65°C was prepared and 108 kg Mn(NO 3 ) 2 . 4 H 2 O and 100 kg Al(NO 3 ) 3 , 9 H 2 O dissolved therein. 145 kg NH 4 HCO 3 was added to this over 1 hour and thereafter stirred for 12 hours. After adding a further 200 l of water the mixture was filtered in a pressure filter. The filtrate was dried for 12 hours at 200°C whilst thoroughly blown by air, after which it was crushed and dried for a further two hours at 300°C. The resulting dried product was mixed with 4 wt.% graphite and 3 wt.% cellulose fiber and tabletted in the form of hollow cylinders 7 mm high with an i.d. of 6 mm and an o.d. of 13 mm, the tablets then being calcined for two hours at 800°C. The cylindrical tablets were impregnated using a solution of 50 wt.% KNO 3 in water, then heated for one hour at 80°C and finally for 1 hour at 500°C.
The resulting catalyst B had the following composition (by weight) 13% Al 2 O 3 -- 52% ZrO 2 -- 27% MnO -- 8% K 2 O.
Further catalysts were prepared by similar methods but substituting one or more constituents giving catalysts of the following compositions:
C 13% al 2 O 3 -- 53% ZrO 2 -- 27% MnO -- 7% Cs 2 O
D 14% al 2 O 3 -- 56% ZrO 2 -- 24% Fe 2 O 3 -- 6% K 2 O
E 14% al 2 O 3 -- 52% TiO 2 -- 28% MnO -- 6% K 2 O
(comparative Catalyst)
F 14% al 2 O 3 -- 51% ZrO 2 -- 28% MnO -- 3% BaO -- 4% K 2 O
These catalysts were evaluated in a small tube reactor (Reactor One) holding 125 ml catalyst. To this was fed a mixture of 2 parts naphtha and 1 parts water to give an eventual steam-naphtha weight ratio of 0.5. The naphtha had a weight composition of 24.1 percent iso-pentane, 53.6 percent n-pentane, 13.5 percent iso-hexane, 5.6 percent n-hexane, and 3.2 percent aromatics. The naphtha-water feed was first passed through a preheater and then through the reactor, the space velocity being 4.2 liq. vol./vol. catalyst/h. The feed passed downwards through the reactor, the temperature at the top of the catalyst bed being 590°C and the temperature at the center and at the bottom of the bed being 750°C. The reactor effluent was quenched by water injection in the reactor outlet and the composition of the effluent product gas determined on a gas-chromatograph. The results of these investigations are shown in the accompanying table I.
Catalysts A, B, C, and D, which are in accordance with the present invention, all gave an almost complete conversion of the hydrocarbon feed with about 1 percent or less unconverted hydrocarbon feed in the product. Catalyst E, which is not in accordance with the present invention, gave a complete conversion right from the start, however, there was a gradual increase in unconverted hydrocarbon feed in the product, and after 120 hours' operation 20 percent of the hydrocarbon feed passed the catalyst almost unchanged. In the experiment with catalyst F, which is in accordance with the present invention, the conversion was incomplete from the start, however, after a few hours' operation the conversion became complete and during the remaining part of the experiment the amount of unconverted hydrocarbon feed in the product was insignificant.
Because of unrealistic linear velocities of feed and product in a small tube reactor, the results are not representative as far as regards the yields of unsaturated hydrocarbons. Therefore, in order to obtain a more realistic evaluation of a catalyst in accordance with the present invention, catalyst B was tested in a pilot plant reactor (Reactor Two) having a height of 6 m and an internal diameter of 0.09 m. A series of oil-fired burners were provided to heat the reactor. To this reactor was fed a feed of 200 kg/h of naphtha of the same composition as before, together with 120 kg/h steam (i.e., a steam-naphtha ratio of 0.6). The inlet pressure was 7 kg/cm 2 , the outlet pressure 0.3 kg/cm 2 , inlet temperature 500°C and outlet temperature 825°C. The heat flux at the inner reactor wall was 80,000 Kcal/m 2 /h.
The results of investigations using 36 l of catalyst B in this reactor are shown in table II. Although a very high space velocity of 8.6 liq.vol./vol.catalyst/h was used in this experiment only insignificant amounts of unconverted hydrocarbon feed appeared in the product, the liquid product consisting mainly of aromatics.
TABLE I
(REACTOR ONE)
Experiment No. 1 2 3 4 5 6 Catalyst A B C D E F Duration of experiment,hrs. 138 240 66 200 120 325 Inlet pressure, atm.abs. 1.2 1.2 2.6 1.2 1.2 1.2 Space velocity, liq.vol./ vol.cat./h 4.2 4.2 4.2 4.2 4.2 4.2 Yield at start: C 2 H 4 , wt.% of feed 12.4 13.7 11.5 11.4 10.2 14.0 C 3 H 6 , wt.% of feed 13.8 9.3 12.8 10.0 9.5 10.9 Liquid Product + vol.% of feed 1.3 0 0 0 0 5.0 Yield at end: C 2 H 4 , wt.% of feed 12.4 14.4 10.7 10.3 10.2 -- C 3 H 6 , wt.% of feed 9.8 10.7 9.5 8.3 9.5 -- Liquid product + vol.% of feed 0.3 0.6 0.8 0 20 0.1 + Mainly unconverted hydrocarbon feed
TABLE II
(REACTOR TWO)
Experiment No. 7 Catalyst B Duration of experiment, hrs. 100 Inlet pressure, atm.abs. 8 Outlet pressure, atm.abs. 1.3 Space velocity, liq.vol./vol.cat./h 8.6 Yield: C 2 H 4 , wt.% of feed 31.5 C 2 H 6 , wt.% of feed 4.5 C 3 H 6 , wt.% of feed 20.0 C 4 H 8 , wt.% of feed 8.0 C 4 H 6 , wt.% of feed 7.0 Liquid product + , wt.% of feed 8.0 + Mainly aromatics