CA1270240A

CA1270240A - Process for up-grading steam-cracking products

Info

Publication number: CA1270240A
Application number: CA000519081A
Authority: CA
Inventors: Raymond Le Van Mao
Original assignee: INSTITUT DE L'AMIANTE (L')
Current assignee: INSTITUT DE L'AMIANTE (L')
Priority date: 1986-09-25
Filing date: 1986-09-25
Publication date: 1990-06-12
Anticipated expiration: 2007-06-12
Also published as: DE3777305D1; EP0262049A2; JPS6397233A; EP0262049B1; EP0262049A3

Abstract

ABSTRACT OF THE DISCLOSURE

There is provided with the present invention a new process for up-grading products resulting from the steam-cracking of hydrocarbons which comprises bringing the steam-cracking reaction products in contact with a catalyst comprising a mixture of from 2.5 to 7.5%
wt of Cr2O3, 5 to 17.5% wt of A12O3 and 75 to 85% wt of a Zn-ZSM-5 zeolite or a Zn-ZSM-5 zeolite/asbestos and recovering the desired products.

Description

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BACKGROUND OF TIIE INVENTION
Steam-cracking is one of the most widely used basic petrochemical processes. It is used by industries to produce light olefins such as ethylene, propylene, butenes and butadiene and it is also relied upon for the production of aromatics such as benzene, toluene and xylenes.
Basically, steam-cracking comprises a step in which the hydrocarbon mixture to be transformed is mixed with steam and submitted to elevated temperatures in a tubular reactor. The different resulting products, gaseous and liquid hydrocarbons are then collected and separated. Thus, product distribution depends on the nature of the initial hydrocarbon mixture as well as experimental conditions.
Among the products obtained, C2-C4 light olefins, as well as benzene, toluene, ethylbenzene and xylenes have the highest commercial values and since enormous quantities are processes throughout the world, even small yield improvements lead to substantial profit increases.
In recent years, ZSM-5 zeolite catalysts have drawn considerable attention because of their abil.ity to increase selectivity in a variety of industrial processes such as xylene isomerization, toluene dis-proportionation, aromatic alkylation and methanol conversion.
, It has been shown that the zeolite's selec-tivity properties are the result of its tridimensional channel network and of the different pore sizes of its structure.
One of the most interesting areas where ZSM-5 zeolites have shown substantial catalytic activity is in the process in which methanol is converted into hydro-carbons. Thus, by using appropriate reaction conditions, very high yields in C5-C11 gasoline hydrocarbons can be obtained. However, this reaction presents the drawback of producing small quantities of durene, an undesirable reaction product.
Furthermore, modiEications of the catalyst can also lead to highly efficient production of light ole-:Eins resulting :Erom methanol conversion.
Thus, it can be seen that modified zeolite catalysts have the possibilities to present very inter-esting properties for enhancing yields in petrochemical reactions.
Therefore, since steam-cracking is one of the most widespread petrochemical processes, it would be highly desirable to provide means for increasing pro~
duction of the most valuable reaction products.
SUMMARY OF T~E INVENTION
. The present invention relates to a process for ~`7~

up-grading products resulting from the steam-cracking of hydrocarbons which comprises bringing the steam-cracking reaction products in contact with a multifunctional Zn-ZSM-s zeolite/cr2o3/Al2o3 catalyst comprising of a mixture of from 2.5 to 7.5% wt of Cr2O3, 5 to 17.5% wt of Al2O3 and 75 to 85% wt of a Zn-ZSM-5 zeolite or a Zn-ZSM-5 zeolite/asbestos. Such a process allows for significant yield increases in C2-C~ olefins. Further-more, the commonly obtained pyrolysis oil is up-graded to a high grade gasoline, rich in mono-aromatics and free from undesirable durenes and long aliphatic chains.
DETAILED DESCRIPTION OF THE INVENTION
The main feature of the present invention resides in the presence of a catalytic reactor at the outlet of -the steam-crac]~ing reactor. This catalytic reactor contains a multifunctional catalyst which com-prises a zeolite cf the ~SM-5 type coupled with metallic oxides.
These oxides can either be coupled to the zeolite by being directly deposited on the zeolite or mechanically mixed with the zeolite.
The metallic oxides can be selected from oxides such as Cr2O3, Al2O3, or from any metallic oxide having a hydrogenating/dehydrogenating function.
In the case of the Cr2O3/Al2O3 proportions of Cr2O3 ranging between 2.5 and 7.5% wt, proportions of

2~0 A12O3 ranging between 5 and 17.5% wt and proportions of the zeolite catalyst ranging between 75 and 85% wt can be used.
Although the catalytic reactor used in the present invention was a fixed-bed reactor, it will be understood that any suitable design commonly used for catalytic reactions could have been chosen.
In the drawings: Figure 1 represents a sche-matic drawing of the bench scale setting for the cata-lytic up-grading of products resulting from the steam-cracking of hydrocarbons.
Figure 2 represents a comparison between the amounts of C2-C~ olefins obtained by steam-cracking alone and by steam-crackincJ along with various zeolite catalysts.
Figure 3 represents a comparison between the amounts of ethylene obtained by steam-cracking alone and by steam-cracking along with various zeolite catalysts.
Referring now to Figure 1, the starting hydro-carbon material 2 is first mixed with a stripping gas 4.It is to be noted, however, that the use of a stripping gas is optional. In the context of the actual experi-ments, a stripping gas was used only for convenience.
The resulting mixture is then forwarded to a vaporizer-mixer 6, in which steam is injected by means of an infusion pump 8. The gaseous mixture thus obtained enters a steam-cracking tubular reactor 10 heated at a temperature ranging between 760 and 860C.
In a further step, products coming out of the steam-cracking tubular reactor 10 are sent into a catalytic reactor 12 heated at a temperature ranging between 450 and 550C. The resulting products are then cooled by a series of condensers 14 (wa-ter~cooling condensers and ice bath). Immediately following the cooling step, the liquid and gaseous phases are separated. The liquids are first collected in a liquid-collector cylinder 16 while the gases flow through the liquid-collector cylin-der to be collected for on line analysis in a dynamic sampler cylinder 18 located at a higher position than the liquid collector cylinder.
The present invention will be more readily understood by reEerring to the Eollowing examples which are given to illustrate rather than limit the scope of the invention.
E~AMPLE 1 Propane is the starting hydrocarbon material on which the steam-cracking process was performed. It was introduced into the system at a flow rate of 45 ml/min. or 4.95 g/hour. It was first mixed with helium acting as a stripping gas. After having been flown through the vaporizer-mixer, in which steam was injected at a rate of 1.7 g/hour, the gaseous mixture was then sent into the steam-cracking reactor whose internal temperature had been set to 780C at atmospheric pres-sure. The residence time of the starting material in the steam-cracking reactor was approximately 1 second.
The resulting product was then separated into its liquid and the gaseous phases. The liquid fraction was analyzed by GC using a capillary column (length:
50 m, PONA~ type, fused silica coated with a cross-linked polymer). The gases were analyzed on line by gas chromatography. A column having a length of 3.5 m packed with Chromosorb9 P coated with 20% by weight of Squalane~ was used for the analysis. The GC used was a dual FID Hewlett-Packard Model 5790 equipped with a 3392A Model integrator. Results are shown in Table 1.
EX~MPLE 2 The same procedure as in Exc~mple 1 was re-peated the only modification being the internal temper-ature of the steam-cracking reactor which was set at 800C. Results are shown in Table 1.
EXAMPI.E 3 The same procedure as in Example 1 was re-peated the only modification being the internal temper-ature of the steam-cracking reactor which was set at 835C. Results are shown in Table 5.

As in Example 1 propane was chosen as the t;~

starting hydrocarbon material. It was mixed with helium and flown through the vaporizer-mixer. The gaseous mixture was then forwarded through the steam-cracking reactor whose internal temperature had been set to 780C. The resulting products were then sent to the catalytic reactor which had been previously embedded with 4 g of a Zn-Mn-2SM-5 zeolite which was prepared according to the procedure described in Can. Pat. Appl.
S.N. 471,463. The temperature of the catalytic reactor had been previously set at 500C, with a pressure of 1 atmosphere and a W.~I.S.V. (weight hourly space velocity) of 1 h 1, The final products were analyzed using the techniques discussed in Example 1. Results are shown in Table 2.
EX~MPLE 5 The same procedure as in Example 4 was re-peated, the only modification being the internal temper-ature of the steam-cracking reactor which was set at 800C. Results are shown in Table 2.

The same procedure as in Example 4 was re-peated, except for the following modifications the catalytic reactor was embedded with 4 g of a Zn-Mn-ZSM-5 zeolite/asbestos catalyst prepared according t~ the procedure described in Can. Pat. Appl. S.N. 471,463.
Results are shown in Table 3.

, - ~7~

The same procedure as in Example 6 was re-peated, the only modification being the internal temper-ature of the steam-cracking reactor which was set at 800C. Results are shown in Table 3.
E~AMPLE 8 The same procedure as in Example 4 was re-peated, except for the following modification: the catalytic reactor was embedded with a Zn-ZSM-5 zeolite/
asbestos/Cr2O3/A12O3 catalyst. The Zn-ZS~-5 zeolite/
asbestos catalyst was prepared according to the method described in Can. Pat. Appl. S.N. 471,463. Then, 4.5 g of the Zn-ZSM-5 zeolite/asbestos catalyst obtained were wet with a solution prepared from 0.3 g of Cr2O3 and 0~4 g of sodium aluminate dissolved in 5 ml of distilled water. The resulting multifunctional catalyst was dried at 120C for 12 hours and actuated at 500C for another 12 hour period. Finally, the catalyst was reduced in hydrogen at 350C for at least 1 hour. Results are shown in Table 4.

The same procedure as in Example 8 was re-peatedt the only modification being the internal temper-ature of the steam-cracking reactor which was set at ~00C. Results were shown in Table 4.
When studying the results obtained from the various examples, it is to be noted that in the steam-cracking process alone (Table 1) significant increases in highly valuable compounds such as ethylene, benzene and toluene are observed when the internal temperature of the reactor is increased from 780 to 800C. The amount of less valuable products such as methane is higher at 800C but this increase is compensated by a decrease in C2-C4 paraffins.
As for the aromatic content, there is a dramatic decrease in less valuable C5-Cll aliphatics, resulting in the obtention of more interesting products such as benzene, xylenes and toluene. In examples 4 to 7, æn-Mn-ZSM-5 zeolite and Zn-Mn-ZSM-5 zeolite/asbestos, two known catalysts were used to form the catalytic bed.
As it can be seen in Tables 2 and 3, and in Figures 2 and 3, inferior results were obtained when compared to steam-cracking alone as far as the olefin content is concerned, regardless of the temperature at which the reactions were performed.
As for the aromatic content, better results were obtained, but these results are at the best suf-ficient and no more, to compensate the quality loss on the side of the olefin production, especially, as far as ethylene is concerned, since ethylene is the most valu-able steam-cracking product.
Thus, in the light of these results, one could ~;~7~

~ 10 ~

tend to be led away from using zeolite catalysts as means to improve steam~cracking processes.
In Examples 8 and 9, the results obtained by using a multifunctional catalyst point out better results in both olefin and aromatic productions. Thus, it has been discovered as it can be seen in Figures 2 and 3, that the use of metal oxides co~catalyst coupled with a zeolite type catalyst unexpectedly increases the amounts of valuable steam~cracking products. In fact, the total amount of C2-C4 olefins and especially ethyl-ene obtalned by using the multifunctional catalyst after a steam-cracking reaction of 780 (55.8~ wt) is even superior to the amount obtained when performing the steam-cracking reaction alone at 800 (47.1 wt).
Moreover as described in Example 3,a run without catalyst was performed at 835C. This tempera~
ture was fairly close to temperatures used in industrial steam-cracking facilities usin~ propane as a starting hydrocarbon material. When the product distribution oE
such a run is compared to the run performed in presence of the Zn~ZSM~5 zeolite/asbestos/Cr2O3/~12O3 catalyst and with the steam~cracking reactor temperature set at 800C, as described in Example 9, it can be seen, as it is shown in Table 5, that in the presence of the multi-functional catalyst and with a much lower steam~cracking temperature, higher yields in ethylene and propylene were obtained. The propylene yield was nearly doubled (due mainly to a lower steam-cracking temperature) and the ethylene yield was increased by S wt percentage points while methane formation was significantly lower.
Furthermore, the liquid yield was much lower for the run performed at a lower steam-cracking tempera-ture in the presence of the multifunctional catalyst.
However, the BTX aromatics (benzene, toluene, ethyl-benzene and xylenes) content in the licluid hydrocarbon ln products was much higher and there was no formation of undesirable hydrocarbons.
Thus, by performing the steam-cracking of propane at a lower temperature and by using a multi-functional catalyst, the total "ethylene -~ propylene"
yield can be increased by 10 wt percentage points and the ethylene/propylene wt ratio can be decreased to a very large extent (see Table 5).
~ rom an industrial viewpoint, this would represent a real advantage since the present market trends are Eor a lower demand in ethylene and an in-creasing demand in propylene.
It will be appreciated that even though yields increase in valuable products ranging from 5 to 10% wt do not seem to be of significant importance, because of the enormous amounts of hydrocarbon material refined every day throughout the world, even a 0.5~ wt yield

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increase represents millions of dollars of profits for petrochemical industries. Therefore, it is submitted that every invention increasing production yields in the petrochemical conversion processes has tremendous com-mercial values for these industries.
It will also be understood that although the process of the present invention has been developed for up-grading steam produets, it can also be applied to every situation where starting materials such as pyroly-sis oil, pyrolysis gasoline, mixtures of light olefins, light paraffins or mixture thereof are flown directly into the catalytic reactor without requiring any passage through a steam-cracking reactor.
In such cases, the multifunctional properties of the catalyst are expressed through several actions such as acid-catalyzed reactions (cracking, oligomer-ization, isomerization, transmutation) and redox re-actions on intermediates leading to the final products or on the products themselves.
Therefore, in the framework of the present invention, the reactor containing the multifunetional catalyst can be located either after the steam-cracking reactor or after the liquid/gases separation operation ~thus intercepting the liquid or gaseous products) and still obtain similar end results.

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Claims

WHAT IS CLAIMED IS:

1. A process for up-grading products re-sulting from the steam-cracking of hydrocarbons which comprises bringing the steam-cracking reaction products in contact with a catalyst comprising of mixture of from 2.5 to 7.5% wt of Cr2O3, 5 to 17.5% wt of A12O3 and 75 to 85% wt of a Zn-ZSM-5 zeolite or a Zn-ZSM-5 zeolite/asbestos and recovering the desired products.

2. The process of Claim 1, wherein Cr2O3 and A12O3 are directly deposited on the Zn-ZSM-5 zeolite or the Zn-ZSM-5 zeolite/asbestos.

3. The process of Claim 1, wherein Cr2O3 and A12O3 are mechanically mixed with the Zn-ZSM-5 zeolite or the Zn-ZSM-5 zeolite/asbestos.

4. The process of Claim 1, wherein the cata-lyst is packed in a tubular reactor.

5. The process of Claim 4, wherein the cata-lytic tubular reactor temperature is maintained between 400° and 600°C.

6. A catalyst suitable for up-grading products resulting from the steam-cracking of hydrocarbons, said catalyst comprising 2.5 to 7.5% wt of Cr2O3, 5 to 17.5%
wt of A12O3 and 75 to 85% wt of a Zn-ZSM-5 zeolite or a Zn-ZSM-5 zeolite/asbestos.

7. The catalyst of Claim 6, wherein Cr2O3 and A12O3 are mechanically mixed with the Zn-ZSM-5 zeolite or the Zn-ZSM-5 zeolite/asbestos.

8. The catalyst of Claim 6, wherein Cr2O3 and A12O3 are directly deposited on the Zn-ZSM-5 zeolite or the Zn-ZSM-5 zeolite/asbestos.

9. A process for up-grading products re-sulting from the steam-cracking of hydrocarbons which comprises:
a) setting the steam-cracking reactor at a temperature lower by 30°C to 50°C than that normally used, b) bringing the steam-cracking reaction products in contact with a catalyst comprising of a mixture of from 2.5 to 7.5% wt of Cr2O3, 5 to 17.5% wt of A12O3 and 75 to 85% wt of a Zn-ZSM-5 zeolite or a Zn-ZSM-5 zeolite/asbestos and recovering the desired products.

10. A catalyst consisting of 2.5 to 7.5% wt of Cr2O3, 5 to 17.5% wt of A12O3 and 75 to 75% wt of an Zn-ZSM-5 zeolite or Zn-ZSM-5 zeolite/asbestos.

11. The catalyst of claim 10 wherein Cr2O3 and A12O3 are mechanically mixed with the Zn-ZSM-5 zeolite or the Zn-ZSM-5 zeolite/asbestos.

12. The catalyst of claim 10 wherein Cr2O3 A12O3 are directly deposited on the Zn-ZSM-5 zeolite or the Zn-ZSM-5 zeolite/asbestos.