WO1996002612A1

WO1996002612A1 - Shape selective hydrogenation of aromatics

Info

Publication number: WO1996002612A1
Application number: PCT/US1994/008100
Authority: WO
Inventors: Ralph Moritz Dessau
Original assignee: Mobil Oil Corporation
Priority date: 1992-12-18
Filing date: 1994-07-19
Publication date: 1996-02-01

Abstract

Non-acidic tin-, lead-, or indium-modified Pt/ZSM-5 catalysts are effective catalysts for the shape selective preferential hydrogenation of certain aromatic hydrocarbons in admixture with others. These catalysts can be used to reduce the aromatic content of gasoline and distillates.

Description

SHAPE SELECTIVE HYDROGENATION OF AROMATICS

This invention relates to a process for selectively hydrogenating certain aromatic components in a mixture of aro atics contained in a gasoline or distillate pool of a petroleum refinery. It also provides a method for increasing the octane rating of the gasoline by-product from a hydrofinishing process.

The demand for gasoline as a motor fuel is one of the major factors which dictates the design and mode of operation of a modern petroleum refinery. The gasoline product from a refinery is derived from several sources within the refinery including, for example, gasoline from the catalytic cracking unit, straight run gasoline, reformate and gasoline obtained as a low boiling by-product from various refinery operations, especially catalytic processes such as catalytic dewaxing. The octane number of the gasoline from these different sources varies according to the nature of the processing and the octane rating of the final gasoline pool will depend upon the octane ratings of the individual components in the pool as well as the proportions of these components. The increasing use of unleaded gasoline coupled with increasing engine efficiencies in road vehicles has led to a demand for increased gasoline pool octane which, in turn, makes it desirable to increase the octane values of the individual components of the pool. Although there are various ways of achieving this objective, some necessarily involve compromises which may render them less attractive in a commercial refinery operation. For example, the octane rating of FCC gasoline may be improved by operating the cracker at a higher temperature (conventionally measured at the top of the riser) . Similarly, reformate octane may be increased by operating the reformer at higher severity. H -ever, in both cases, a yield loss will ensue. In the case of by-product gasoline from catalytic dewaxing processes it may be possible to improve octane during the start-up by increasing the temperature rapidly to a value higher than normal, as described in U.S. Patent No. 4,446,007 (Smith). However, the use of higher temperatures in dewaxing processes will also tend to decrease the yield of dewaxed products. Alternative measures for increasing pool octane are therefore still desirable.

Another trend in the petroleum refining industry is towards the reduction of benzene and other lower boiling point aromatics in the gasoline or distillate pool. In the United States, the Environmental Protection Agency (EPA) is considering regulation of the gasoline content and similar measures are being considered in the European Community. Benzene is particularly prevalent in reformer gasoline, being a distinctive product of the reforming process, produced by the dehydrogenation of C_g cycloparaffins, the dehydrocyclization of straight chain paraffins of appropriate chain length (C_g) and dealkylation of other aromatics. It is produced in particularly high concentrations in the continuous catalytic reforming process which is currently replacing the conventional cyclic reforming process in the industry. It would be possible to reduce the benzene content of the reformate by a simple fractionation process but because the boiling point of benzene is close to that of other desirable and unobjectionable components of the reformate, this too would lead to a considerable loss in yield.

Therefore, what is needed is a process for selectively removing certain aromatic components contained in a mixture of aromatic hydrocarbons found in the refinery liquid fuel pool so as to reduce the aromatic content of the gasoline pool and reduce soot formation in the distillate pool.

A hydrogenating process has now been devised which is capable of selectively removing certain aromatic components, based on molecular size, in a mixture of aromatic components which are contained in a refinery gasoline or distillate pool thereby decreasing the aromatic content of the refinery gasoline pool thereby reducing aromatic emissions. Decreased aromatic components in the refinery distillate pool results in a decrease in soot production during combustion when kerosene and jet fuels are produced from the distillate pool.

Accordingly, the invention resides in a process for the shape selective preferential hydrogenation of certain aromatic components in a mixed feed of aromatic hydrocarbonaceous components comprising the step of hydrotreating the feed in the presence of a non-acidic ZSM- 5 catalyst which contains a Group VIII metal and is modified with a metal selected from tin, lead, and indium to convert certain aromatic components in the feed to cycloalkanes and thereby produce an effluent with a reduced aromatic content.

During the hydrogenation process of the invention, only those aromatic components which can enter the Pt/ZSM-5 modified catalyst are converted to cycloalkanes. Generally, aromatic components which enter the pores of the catalyst will comprise benzene, toluene, and xylenes which are collectively referred to as (BTX) . Other representative aromatics of a size sufficient to enter the pores of the catalyst include monoalkylbenzene and beta-alky1- naphthalene. Bulkier polyalkyl aromatics too large to enter the catalyst are not converted.

This process generally comprises contacting the feedstock at a temperature between 100°C (212"F) and 400'C (752^βF), preferably 100 to 325^βC, and a pressure between 100 and 3550 kPa (atmospheric and 500 psig) with the catalyst in the presence of hydrogen, in which the hydrogen-to-feedstock ratio is between 89 and 356 Nm³/m³ (500 and 2,000 standard cubic feet) of hydrogen per barrel of feed. The feedstock is contacted with the catalyst in a fixed bed at a liquid hourly space velocity between 0.1 and 20. In a preferred embodiment, the catalyst is used as a hydrofinishing catalyst for the selective conversion of certain aromatics to cycloalkanes in the hydrotreating (HDT) stage of a lube oil hydroprocessing process. The preferred source of the aromatic component containing fraction is a reformate i.e., a refinery stream which has been subjected to catalytic reforming, preferably over a reforming catalyst containing platinum. Other refinery streams containing significant quantities of aromatics and with a suitable boiling range of about C.. to 400^βF (C to 205^βC), usually C₅ to 330^βF (C₅ to 165"C) may, however, be used. Kerosine distilled from the crude unit is an example of a distillate stream from which certain aromatic hydrocarbons can be converted to cycloalkanes when admixed with bulkier polyalkyl aromatics.

Reformates usually contain C to C_ aromatic hydrocarbons and C_g to C- paraffinic hydrocarbons with the aromatic hydrocarbons being constituted mainly by benzene, toluene, xylene and ethyl benzene. Compositions for reformates which may be used in the present process are shown in Table 1 below:

TABLE 1

Reformate Composition βrpad Intermediate Narrow

Specific Gravity 0.72 to 0.88 0.76 to 0.88 0.76 to 0.83 Boiling Range "F 60 to 400 60 to 400 80 to 390 ^βC 15 to 205 15 to 205 27 to 200 Mole % Benzene 5 to 60 5 to 40 10 to 30 Toluene .... 5 to 60 10 to 40 10 to 40 C_ Aromatic¹ ' 5 to 60 5 to 50 5 to 15

(1) Xylene and ethyl benzene component.

The composition of a typical reformer stream from a platinum reforming process is given in Table 2 below. TABLE 2 Reformate Composition

Mol , . Pet.

0 , . 2

15 . . 5

Benzene 25. . 8 Non-arom. C_ 0 . , 2 Toluene 34 . , 9 C ©_Q aromatics 10. 2

C aromatics 3 . , 0

As may be seen from the above figures, benzene constitutes a significant proportion of the reformate stream and if no measures are taken to remove it, it will pass into the refinery gasoline pool unchanged. The present method provides a convenient way of converting the benzene to cyclohexanes which are not environmentally objectionable and which conversion also increases the yield of the gasoline pool. The catalyst employed in the process of the invention comprises a Group VIII metal and non-acidic microporous ZSM-5 modified with a metal selected from tin, indium and lead.

ZSM-5 and its synthesis are described in, for example, U.S. Patent No. 3,702,886 and RE 29,948. The ZSM-5 employed in the catalyst of the invention does not exhibit any appreciable acid activity and therefore meets the criteria of non-acidic catalysts described by Davis et al. , J. Catal.. 15, 363 (1969) . An additional method of testing the non-acidic character of the catalyst composition of the invention is to add lOOmg of the catalyst to 30ml of distilled, deionized water (with a pH of 7) maintained under an inert atmosphere (i.e., free of C0₂) , such as an argon atmosphere, whereby the water with the catalyst will ahve a PH of at least 6 and preferably at least 7. ZSM-5 free of acidity can be produced by replacing all cation-exchangeable sites of the zeolite with alkali or alkaline earth metal ions.

The amount of Group VIII metal in the non-acidic catalyst composition can range from 0.05 to 10 weight percent and preferably 0.1 to 5 weight percent of the microporous material. In a preferred embodiment, platinum is the Group VIII metal, bot other Group VIII metals including iridium and palladium can also be employed. The Group VIII metal is conveniently incorporated in the catalyst by ion exchange.

The metal modifier content of the ZSM-5 can range from 0.01 to 20 weight percent, and more preferably from 0.1 to 10 weight percent. Incorporation of the modifier metal, indium, tin, or lead, is conveniently accomplished by addng a source of the metal to the synthesis mixture used to produce the ZSM-5.

The non-acidic, metal-modified, Group VIII metal containing ZSM-5 used in the invention can be combined with a matrix or binder material to render it attrition resistant and more resistant to the severity of the conditions to which it will be exposed during use in hydrocarbon conversion applications. The combined compositions can contain 1 to 90 weight percent, preferably 2 to 80 weight percent, of the materials of the invention based on the combined weight of the matrix (binder) and material of the invention. Preferably, the matrix or binder material is non-acidic, such as silica or titania.

EXAMPLES The competitive hydrogenation of an equimolar mixture of ortho- and para-xylene to dimethyleyelohexanes was investigated at 325^βC (617^βF) and 2170 kPa (300 psig) . Platinum was incorporated via ion-exchange with Pt(NH₃).Cl₂, followed by calcination in air to 350"C. Crystal sizes were all about 1 micron. The yields (mol %) of the various dimethylcyclohexanes (DMCH) produced, 1,4-DMCH from para-xylene and 1,2-DMCH from ortho-xylene, as well as the ratio of these products are shown in Table 3 below:

TABLE 3

Catalyst tr-1.4 cis-1.4 tr-1.2 cis-1.2 1,4/1,2

Non-selective

Pt/Si-ZSM-5 18.2 8.0 13.7 6.6 1.3

Pt/Ti-ZSM-5 8.5 6.2 6.0 5.5 1.3

Pt/Zr-ZSM-5 7.9 8.8 4.1 10.3 1.2

Pt/[B]zeolite* 10.6 7.6 7.0 6.7 1.3 beta

Selective

Pt/Sn-ZSM-5 28.2 10.9 1.08 0. ,3228

Pt/Pb-ZSM-5 16.06.7 0.36 0. .1247

Pt/In-ZSM-5 9.9 5.0 2.9 2. .7 2.7

* At 250*C (482'F), 620 kPa (75 psig).

Shape selective preferential hydrogenation of para- xylene was observed for the tin-, lead-, and indium- modified Pt/ZSM-5 catalysts.

The competitive hydrogenation of an equimolar mixture of benzene, toluene, and para-xylene was investigated at 250^βC and 2170 kPa (300 psig) over both a para-selective Pt/[Sn]ZSM-5. The results are shown in Table 4, below:

TABLE 4 Hydrogenation (Hydr) of BTX

Catalyst % Benz Hvdr % Tol Hvdr % Para-Xyl Hvdr

Pt/[Sn]ZSM-5 69 44 17 In both cases, the order of reactivity was benzene > toluene > para-xylene. This order contrasts with that observed over sulfided Ni/W on alumina ( J. L. LePage in a publication entitled "Applied Heterogeneous Catalysis", published by Gulf Publishing Co., Houston, Texas, 1987 on page 371) .

Shape selective hydrogenation of para-xylene relative to ortho-xylene was achieved over tin, lead, and indium modified Pt/ZSM-5 catalysts. The failure to observe similar selectivities for unmodified Pt/ZSM-5 catalysts demonstrates the anchoring effect of these modifiers in suppressing platinum migration out of zeolitic channels.

Claims

CLAIMS :

1. A process for the shape selective preferential hydrogenation of certain aromatic components in a mixed feed of aromatic hydrocarbonaceous components comprising the step of hydrotreating the feed in the presence of a non-acidic ZSM-5 catalyst which contains a Group VIII metal and is modified with a metal selected from tin, lead, and indium to convert certain aromatic components in the feed to cycloalkanes and thereby produce an effluent with a reduced aromatic content.

2. A process as claimed in claim 1 wherein the Group VIII metal is platinum.

3. A process as claimed in claim 1 or claim 2 wherein the metal modifier is tin.

4. A process as claimed in any preceding claim wherein the feed is a refinery reformate stream.

5. A process as claimed in any preceding claim 1 wherein hydrotreating is conducted at a liquid hourly space velocity of 0.5 to 20, a pressure of 100 to 3550 kPa (atmospheric to 500 psig), a temperature of 100° to 400'C, and a once-through hydrogen circulation rate of 89 to 356 Nm³/m³ (500 to 2,000 standard cubic feet) per barrel of feed.

6. A process as claimed in claim 5 wherein the temperature is 100 to 325^βC.