CA2561986A1

CA2561986A1 - Simultaneous dehydrogenation of ethylbenzene and ethane in the presence of co2 or steam

Info

Publication number: CA2561986A1
Application number: CA002561986A
Authority: CA
Inventors: Ronald Scott Smith
Original assignee: Nova Chemicals Corp
Current assignee: Nova Chemicals Corp
Priority date: 2006-10-02
Filing date: 2006-10-02
Publication date: 2008-04-02

Abstract

The addition of CO2 to a process for the simultaneous dehydrogenation of ethylbenzene and ethane improves the yield of styrene and ethylene by acting as a mild oxidant and by removing hydrogen via the reverse water-gas shift reaction. The ethylene in the product stream may be recycled to an alkylation unit to produce more ethylbenzene. The addition of steam to a process for the simultaneous dehydrogenation of ethylbenzene and ethane improves the yield of styrene and ethylene by acting as a diluent.

Description

FIELD OF THE INVENTION

The present invention relates to the dehydrogenation (cracking) of a dilute mixed stream of one or more C2_4 alkylbenzenes and one or more C2_4 paraffins in the presence of either CO2 or H20. The resulting product stream yields a dilute stream of corresponding olefins and alkenylbenzenes and paraffins and alkyl benzenes. The paraffins and alkylbenzenes may be recycled and the olefins could be used for example to alkylate benzene. The reaction equilibrium in the presence of CO2 is shifted towards the alkenylbenzenes. The process is particularly useful in the formation of styrene.

BACKGROUND OF THE INVENTION

There are a number of patents relating to the dehydrogenation of dilute streams of paraffins or aromatic paraffins.

United States patent 2,604,495 issued July 22, 1952 to Erkko, assigned to Hercules Powder Co. Ltd. teaches dehydrogenation of paraffins such as ethane in the presence of carbon dioxide to produce the corresponding olefin (ethylene) and carbon monoxide in an appropriate ratio for the formation of the n+1 saturated carboxylic acid (propionic acid also known as propanoic acid).

United States patent 3,406,219 issued Oct. 15, 1968 to Danford, assigned to Marathon Oil Co. teaches the oxidative dehydrogenation of ethylbenzene using CO2 in molar ratios of greater than 3, preferably from 5 to 25. The disclosure appears to recognize the water gas reaction.
However, in the examples the conversion of ethylbenzene is in the order of

2% which is not commercially viable.

M:\Trevor\TTSpec\2006105Ca n. doc United States patent 5,981, 818 issued November 9,1999 to Purvis et al., assigned to Stone and Webster Engineering Corp., teaches cracking a hydrocarbon stream and recovering a mixed stream of ethylene and ethane (e.g. dilute ethylene). The patent discloses alkylating benzene with the resulting dilute stream to produce ethyl benzene. However, the patent does not appear to disclose dehydrogenation of the resulting ethylbenzene nor does it suggest dehydrogenation in the presence of H20 or CO2 as required by the present invention.

European Patent Application 0 225 143 in the name of Brophy et al., assigned to The British Petroleum Company, published 10.06,87 teaches the partial oxidation of a gaseous paraffinic feed stream together with hydrogen and an oxygen containing gas to produce a product stream which is subsequently hydrogenated in the presence of carbon monoxide and hydrogen to remove acetylenes. The patent does not teach or suggest the dehydrogenation of ethylbenzene.

United States patent 6,037,511 issued March 14, 2000 to Park et al, assigned to Korea Research Institute of Chemical Technology (KR) discloses dehydrogenation of ethylbenzene in the presence of an iron catalyst on a specific zeolite in the presence of CO2. The patent does not suggest the feed stream could also contain ethane part of which may be concurrently dehydrogenated to ethylene.

United States patent 6,958,427 issued Oct. 25, 2005 to Park et al., assigned to Korea Research Institute of Chemical Technology (KR) discloses dehydrogenation of ethylbenzene in the presence of a catalyst on a specific zeolite in the presence of CO2. The patent does not suggest

3 M: \Trevor\TTSpec\2006105Can. doc the feed stream could also contain ethane part of which may be concurrently dehydrogenated to ethylene.

United States patent 6,031,143 issued February 29, 2000 to Buonomo, et al., assigned to Snamprogetti S.p.A. discloses concurrently dehydrogenating a mixed stream of ethylbenzene and ethane in the presence of a catalyst. However, the patent does not teach the feed stream contains CO2 or H20 as required by the present invention.

The present invention seeks to provide a simple efficient method for dehydrogenating a mixed feed stream comprising ethylbenzene and ethane and a member selected from the group consisting of CO2 and H20 in the presence of a catalyst to generate a mixed product stream comprising styrene ethylbenzene, ethylene, ethane, hydrogen, water, and optionally carbon monoxide, and carbon dioxide. The resulting stream can be easily separated into heavy components such as styrene and ethylbenzene which can be further separated, a mixed stream of ethane, and ethylene which may be recycled in other processes such as alkylation of benzene or polymerization, a hydrogen stream, water, and possibly a stream of CO2 and CO.

SUMMARY OF THE INVENTION

The present invention provides a process for producing a product stream comprising a mixture of C2_4 alkyl benzene and corresponding C2_4 alkyenylbenzene, a mixed stream of C2_4 paraffin and corresponding olefin, H2, and H20, and optionally CO and CO2 comprising feeding a mixture comprising from 15 to 60 weight % of a C2_4 alkylbenzene and from 85 to 40 weight % a C2_4 paraffin, and one member selected from the group

4 M:\Trevor\TTSpec\2006105Can.doc consisting of CO2 and H20 in a molar ratio to hydrocarbon from 2:1 to 20:1 to a dehydrogenation unit at a temperature from 500 C to 700 C and an absolute pressure from 68.94kPa to 344.7 kPa in the presence of a dehydrogenation catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph showing the equilibrium conversion of ethylbenzene to styrene in the presence of various diluent streams.

Figure 2 is a graph plotting the theoretical conversions for the concurrent conversion of ethane and ethylbenzene in the same reactor in the presence of steam and CO2 as well as data from example 1 (enlarged points) of U.S. patent 7,002,052 where no steam or CO2 are present.

DETAILED DESCRIPTION

The present invention relates to a novel process to dehydrogenate C2_4 alkyl aromatics, particularly ethylbenzene to produce styrene. The traditional process is to pass a stream of relatively pure ethylbenzene vaporized in a preheater over a catalyst and recover a stream of styrene and hydrogen. The process is energy intensive to drive the equilibrium towards the styrene product.

In accordance with the present invention the feed stream is not as pure as in the prior art. Typically the feed comprises from 15 to 60, preferably from 40 to 60 weight % of a C2_4 alkylbenzene and from 85 to 40, preferably from 60 to 40 weight % a C2_4 paraffin, and one member selected from the group consisting of CO2 and H20 in a molar ratio to hydrocarbon from 2:1 to 20:1, preferably from 5:1 to 15:1. One suitable

5 M:\Trevor\TTSpec\2006105Can. doc C2_4 alkyl benzene is ethylbenzene and C2_4 paraffins may be selected from the group consisting of ethane and propane, preferably ethane.
The reaction is typically conducted in the presence of a supported catalyst. The support may be selected from the group consisting of activated carbon, alumina, Ti02, W03, silica, SiO2/ZrO, and zeolites, preferably activated carbon, y-alumina and zeolites. Generally the support will have a surface area of greater than 250, preferably greater than 300, most preferably greater than 350 m2/g and a cumulative pore volume greater than 0.2, preferably greater than 0.6, most preferably greater than 1 cc/g of support. Useful zeolite supports include ZSM-5, ZSM-8, ZSM-1 1, LZ-105, LZ-222, LZ-223, LZ-241, LZ-269, L2-242, AMS-1 B, AZ-1, BOR-C, FZ-1, NU-4, NU-5, T5-1, TSZ, TSZ-III, TZ01, TZ, USC-4, USI-108, ZBH, ZB-11, ZBM-30, ZKQ-1 B, ZMQ-TB. The zeolite may be used in neutral or basic form (e.g. exchanged with an alkali or alkali earth compound such as Na). The cumulative pore volume and pore size may be determined using nitrogen adsorption and the BET method.

The catalyst may be selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sn, Sb, Pt, elements, preferably Fe, or oxides thereof and alkali or alkali earth elements or oxides thereof and mixtures thereof. Some catalyst and catalyst combinations include V205, Fe2O3iCaO, Fe304, Fe/Ca. Fe/Mn, Fe/Cr, FeN, V/SbO,, V/Mn, V/Cr, Na20, preferably Fe/Cr, FeN, V/SbOX, and Na20. Preferred supports are gamma alumina and ZSM-5. The catalyst may be added to the support using any convenient technique, preferably spray drying to provide a metal loading

6 M: \Trevo r\TTS pec\2006105 C a n. doc (calculate d as oxide) from about 0.01 to about 0.1 g per gram of support (e.g. 1% to 10 % by weight based on the weight of the support).

The conditions in the dehydrogenation reactor are typically at a temperature from 500 C to 700 C, preferably from 550 C to 650 C and an absolute pressure from 68.94kPa to 344.7 kPa, preferably 68.94 kPa to 172.4 kPa.

The feedstock is fed to the reactor to provide a WHSV (weight hourly space velocity) from 8 to 20 hr -1. The reaction may be conducted in a fluidized bed in a continuous manner optionally with a side arm to charge new or regenerated catalyst.

The reaction should have a selectivity for styrene greater than 40, preferably greater than 80%, a styrene yield greater than 70%, preferably greater than 85 % and a conversion of ethylbenzene greater than 40%, preferably greater than 60%.

In one embodiment of the broadest aspect of the present invention the feed stream to the dehydrogenation unit comprises CO2 (without water). In this aspect of the invention the CO2 acts as a soft oxidization agent (e.g. less aggressive than for example air) and therefore there is a reduced risk of a run away reaction. More importantly using CO2 as a component in the feed stream to the dehydrogenation unit (in the absence of water (e.g. steam)) shifts the equilibrium towards the formation of styrene by partially consuming produced hydrogen via the reverse water-gas shift reaction. Further, CO2 has a higher heat capacity than steam so the reaction is more energy efficient. Additionally in this aspect of the invention the product stream contains CO and CO2. These components,

7 M:\Trevor\TTSpec\2006105Can.doc along with additional steam, may be fed to a water-gas shift reactor (H20 +CO <=> H2 +C02) to produce a stream enriched in CO2 that may be recycled back to the dehydrogenation unit, H2, and H20. Both the forward and reverse water-gas shift reactions may be carried out in the presence of conventional catalysts, well known to those skilled in the art. At the temperatures for the conversion of ethylbenzene to styrene (i.e. greater than 5000 C) one would use a high temperature water shift catalyst including those based on iron (i.e. Fe203/Fe3O4) and chrome (i.e. Cr0 /Cr203) and potentially Fischer - Tropsch synthesis catalysts.

In a different embodiment of the broadest aspect of the present invention the feed stream to the dehydrogenation unit comprises H20 (without C02). In this aspect of the invention the product stream from the dehydrogenation reactor contains H2, and H20 (in addition to the styrene, ethane and ethylene).

In a further aspect of the present invention the feed stream for the dehydrogenation reactor is obtained from an alkylation reactor to which is fed a mixed stream of ethylene and ethane. The ethylbenzene, ethane, and possibly small amounts of ethylene leaving the alkylation reactor may be fed directly to the dehydrogenation reactor. Additionally, unconverted ethylbenzene may be recycled to the dehydrogenation reactor and unreacted ethane may be recycled either to the alkylation reactor or to the dehydrogenation rector or both (e.g. the stream could be split and recycled to both reactors). Preferably the alkylation reactor has a conversion such that not less than 70%, preferably not less than 75 % most preferably not

8 M: \Trevo r\TTSpec\2006105Ca n . doc less than 80 % of the ethylene fed to the reactor is converted to ethylbenzene.

It is preferred if the present invention is practiced with a chemical cracking and alkylation unit. The cracker could use a heavier feed to produce a mixed stream of ethane, ethylene, and benzene. The stream could be used as feed for the alkylation unit without the need for separating ethane resulting in a reduced back end cost by minimizing the need for expensive cryogenic separation. The product from the alkylation unit could be fed to the dehydrogenation unit again without the need for extensive product separation. Additionally, the resulting hydrogen stream could be used in a number of other applications such as fertilizer manufacture.

The present invention will be illustrated by the following non limiting examples.

EXAMPLES
The calculations in the examples are based on software that accurately models the ethyl benzene equilibrium in the current conventional reaction (using steam) ethylbenzene reactors used by NOVA
Chemicals Inc.

Example 1 In a reactor where CO2 is fed together with ethylbenzene the first stage product is styrene and water and CO. However, the water and CO
is in an equilibrium with hydrogen and CO2 (the water gas equilibrium -within the dehydrogenation reactor). The equilibrium constant for the reactions can be calculated using the equation

9 M: \Trevor\TTS pec\2006105Ca n. d oc Ln(Ke) = AGe / RT where Ke is the equilibrium constant, AGe is the Gibbs free energy of the reaction, R is the ideal gas constant and T is the absolute temperature. The Gibbs free energy can be obtained from literature sources or determined experimentally. A plot was made of the individual equilibrium conversion at various temperatures for the dehydrogenation of ethylbenzene in the presence of steam or CO2 at a 6:1 molar ratio of C02: ethylbenzene and a 6:1 molar ratio of steam to ethylbenzene). In addition, the conversion for a conventional ethylbenzene conversion in the presence of steam alone under commercial conditions is indicated. The data is shown in figure 1. The overlap of the calculated equilibrium for steam and the current process demonstrates the accuracy of the calculations.

The figure shows at 863 K (about 590 C) the conversion of the ethylbenzene to styrene in the presence of CO2 is about 33% higher than that for a conventional commercial process. Another way of looking at this is the process in the presence of CO2 could be run about 63 C(100 F) cooler and the same conversion would be obtained.

Example 2 Using the same software and comparable equations as in figure 1 a further series of theoretical equilibrium calculations were carried out using the theoretical Gibbs Free energy for the concurrent reactions:
C6H5CH2CH3 <--> C6H5CHCH2 + H2;

CH3CH3 <::> CH2CH2 + H2 ; and CO2 +H2 <* CO + H2O.

M:\Trevor\TTSpec\2006105Can.doc The calculations were done assuming a temperature of 873 K
(600 C), a pressure of 1 atmosphere absolute and a molar ratio of ethylbenzene to ethane of 1:4. The calculations were carried out molar ratios of diluent to feed. The results are shown in figure 2. Figure 2 also contains example data from example 1 (enlarged points) of U.S. patent 7,002,052 where no steam or CO2 are present.

The figure shows that the presence of CO2 on the concurrent dehydrogenation of ethylene and ethylbenzene in the same reactor significantly improves the conversion of both the ethylbenzene to styrene and the ethane to ethylene.

M:\Trevor\TTSpec\2006105Can.doc

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing a product stream comprising a mixture of C2-4 alkyl benzene and corresponding C2-4 alkyenylbenzene, a mixed stream of C2-4 paraffin and corresponding olefin, H2, and H2O, and optionally CO, and CO2 comprising feeding a mixture comprising from 15 to 60 weight % of a C2-4 alkylbenzene, from 85 to 40 weight % a C2-4 paraffin, and one member selected from the group consisting of CO2 and H2O in a molar ratio to hydrocarbon from 2:1 to 20:1 to a dehydrogenation unit at a temperature from 500°C to 700°C and an absolute pressure from 68.94kPa to 344.7 kPa in the presence of a dehydrogenation catalyst and optionally a water gas shift catalyst.

2. The process according to claim 1, wherein the dehydrogenation catalyst is selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sn, Sb, Pt, elements or oxides thereof and alkali or alkali earth elements or oxides thereof and mixtures thereof.

3. The process according to claim 2, wherein the dehydrogenation catalyst is supported on a support selected from the group consisting of activated carbon, alumina, TiO2, WO3, silica, SiO2/ZrO, and zeolites.

4. The process according to claim 3 wherein the support for the dehydrogenation catalyst is selected from the group consisting of activated carbon, .gamma.-alumina and zeolites.

5. The process according to claim 4, wherein the molar ratio of H2O or CO2 to hydrocarbon is from 5:1 to 15:1.

6. The process according to claim 5, wherein the C2-4 alkylbenzene is ethyl benzene and the C2-4 paraffin is ethane.

7. The process according to claim 6, wherein the product stream from the dehydrogenation reaction is separated into a styrene stream, an ethylbenzene stream, a mixed stream of ethane and ethylene and a stream of H2, H2O, and optionally CO2 and CO.

8. The process according to claim 7, wherein the reaction is conducted at a temperature from 550°C to 650° C.

9. The process according to claim 8, wherein the reaction is conducted at pressures from 68.94 kPa to 172.4 kPa.

10. The process according to claim 9, wherein at least a portion of the ethylbenzene and ethane in the feedstock are product stream from an alkylation reactor which is fed with benzene and a mixed stream of ethylene and ethane having a conversion such that not less than 75 % of the ethylene in the feed is converted into ethylbenzene.

11. The process according to claim 10, wherein the mixed stream of ethane and ethylene is fed to an alkylation reactor without separation.

12. The process according to claim 11 wherein the feed to the dehydrogenation unit contains CO2.

13. The process according to claim 12, wherein the H2, H2O, CO and optionally CO2 from the dehydrogenation reaction is fed to a water gas shift reactor containing an iron or chrome based catalyst or a mixture thereof, together with additional water to produce a product stream comprising H2, H2O, and CO2.

14. The process according to claim 13, wherein the product stream from the water gas shift reactor is separated to produce a stream of water, a stream of CO2, and a stream of H2.

15. The process according to claim 14, wherein the stream of CO2 is recycled to the dehydrogenation reactor.

16. The process according to claim 10, wherein the mixed stream of ethane and ethylene is separated and the ethane stream is fed to the dehydrogenation reactor and the ethylene stream is fed to the alkylation reactor.

17. The process according to claim 16 wherein the feed to the dehydrogenation unit contains CO2.

18. The process according to claim 17, wherein the stream of H2, H2O, CO and optionally CO2 is fed to a water gas shift reactor together with additional water to produce a product stream comprising H2, H2O, and CO2.

19. The process according to claim 18, wherein the product stream from the water gas shift reactor is separated to produce a stream of water, a stream of CO2, and a stream of H2.

20. The process according to claim 19, wherein the stream of CO2 is recycled to the dehydrogenation reactor.