NL8202272A - Benzene prodn. by reforming - using intermediate pore size zeolite(s) free of acidity - Google Patents

Abstract

A prod. having a substantial benzene content is prepd. from normal and slightly branched hydrocarbons by (a) contacting the feed, having a boiling range of 40-200 (esp. 60-120) deg. C, with a conversion catalyst (I) which comprises an intermediate pore size zeolite and pt. cpd., the zeolite being free of acidity; and (b) recovering benzene contg. effluent. Also claimed is a method of upgrading reformer effluent by contact with (I). High-benzene reformate is recovered (from light straight-run naphthas) which need not be fractionally distilled, solvent extracted or dealkylated. In fact, the reformate produced is suitable for purificn. as it is.

Description

Έ Έ.0. 31 133 1

Process for the preparation of benzene.

Benzene is one of the basic raw materials of the chemical industry. It is used for the preparation of rubber products, dyes and detergents and is also used as a solvent and as an additive to gasoline, which increases the octane content. Benzene is usually prepared from hydrocarbonaceous feed materials as a mixture with toluene, the xylenes and higher aromatic hydrocarbons by reforming reactions such as cyclization, dehydrogenation and isomerization. A conventional reforming process uses directly obtained naphtha feeds and platinum-containing catalysts.

Recovery of purified benzene from the benzene-toluene-xylene mixture requires some further treatment, for example some combination of fractionation, solvent extraction and adsorptive extraction. The efficiency of these separating steps 15 increases as the benzene content of the reformate increases. However, there is no particularly efficient process for the preparation of a high benzene reformate which does not need to be fractionally distilled, solvent extracted or dealkylated to obtain a high benzene feedstock which is suitable for subsequent purification steps.

The object of the present invention is to provide such a method.

It has been found that intermediate pore size zeolites can be used for the conversion of light, directly obtained naphthas (and similar mixtures) into mixtures with a high aromatics content. Very surprisingly and unlike the product of conventional reforming processes, the main component of these aromatic mixtures is benzene. The benzene synthesis using the present process becomes much more efficient than according to known processes. The importance of this development can hardly be overestimated in view of the increasing demand for benzene from the chemical and motorized transport industries and in view of the declining volumes of petroleum supplies available on the world market.

A number of U.S. patents pertain to 8202272 i-2 - for the preparation of benzene / toluene / xylene (BTX) mixtures from various feeds.

U.S. Patent 3,756,942 describes the preparation of BTX from a feed up to 125 ° C using ZSM-5.

U.S. Pat. No. 3,760,024 describes the preparation of C 4+ aromatics from alkanes or olefins having 2 to 4 carbon atoms using ZSM-5 *

U.S. Pat. No. 3 * 775 * 501 describes the BTX 10 preparation from olefins using ZSM-5 in the presence of oxygen.

U.S. Patent 3 * 813 * 330 describes the aromatization of olefins in the presence of easily cracked alkanes for the preparation of BTX using 15 ZSM-5 *

U.S. Pat. No. 3 * 827 * 968 describes a two-stage process for the preparation of BTX from olefins using ZSM-5 * Alkenes of 2 to 5 carbon atoms are oligomerized to olefins of 5 to 9 carbon atoms, which are then flavored turn into.

U.S. Patent 3 * 843 * 740 describes the preparation of BTX using a two-step process and ZSM-5 *

In US patent 3 * 945 * 913 the preparation of BTX is described from alkyl groups containing aromatics with 9 or more carbon atoms.

U.S. Patent 4,060,568 describes the preparation of low molecular weight olefins and p-xylene from alcohols using ZSM-5-30 U.S. Patent 4,097 * 367 describes the preparation of BTX from ethylenically unsaturated naphthas and pyrolysis of gasoline using ZSM-5 *

U.S. Patent 4,120,910 describes the preparation of aromatics and BTX by aromatization of ethane.

U.S. Patent 4 * 157 * 293 describes a process for preventing the loss of zinc from Zn-ZSM-5 during the preparation of BTX from alkanes and olefins of 2 to 10 carbon atoms.

40 An overview of the prior art does not teach the method of the present invention. The content of the BTX products is usually much less than 50%.

The present invention is embodied in a process for the selective preparation of a product having a substantial benzene content from a normal and slightly branched chain characterized by: (a) Contacting a hydrocarbonaceous feed containing hydrocarbons with normal contains a slightly branched chain and has a boiling range above about 40 ° C and below about 200 ° C, with a conversion catalyst containing an intermediate pore size zeolite and a Group YIII metal compound of the periodic table and wherein the zeolite is substantially free is of acidity and (b) recovering a benzene-containing effluent.

Feeds suitable for the process contain normal and slightly branched chain alkanes or olefins or both. The feeds may also contain naphthenes. Since the intermediate pore size zeolites used in the process are selective, the conversion efficiency will be greater as the ratio in the feed of molecules that can be added within or in part within the zeolites is greater.

Conventional hydrocarbonaceous feeds suitable for use have a boiling range above about 40 ° C and below about 200 ° C, preferably above about 60 ° C and below about 120 ° C. Typical feedstocks for benzene refinery production include light fractions obtained directly and light naphthas. Alkane-like feeders which are not efficiently cyclized according to conventional reforming processes with hydrogen extraction, can be conveniently processed using the present invention. Whatever the feed source, the greater the ratio of Cg and higher alkanes and olefins in the feed, the greater the efficiency of the process and the higher the benzene content of the effluent. The most preferred feeds mainly consist of hydrocarbons 55, not 6 to 8 carbon atoms.

A particularly useful application of the present process is the improvement in the quality of the effluent produced by the reforming. In conventional reforming processes operating with conventional reforming feeds, the n-alkanes are not converted. By using the effluent from the reformer as a feed in the present process for the preparation of benzene, the aromatics content of the final reformate product can be significantly increased or the initial classification of the product increases when n- low octane alkanes 5 are converted to high octane benzene.

The intermediate pore size zeolites used in the process are crystalline aluminosilicate zeolites having a silica to alumina molar ratio which is greater than 10: 1 and preferably greater than about 40: 1.

These zeolites have a suitable activity even at high silica: alumina mole ratios such as 1000 to 2000: 1.

By "intermediate pore size" as used herein is meant an effective pore opening in the range of about 0.5 nm to 0.65 nm when the zeolite is in the H form. Zeolites with pore openings in this range provide unique molecular sieving properties. Unlike small pore zeolites such as erionite, they will allow hydrocarbons with some branching into the cavities of the zeolite. Unlike large-pore zeolites such as the faujasites, they can differentiate between n-alkanes and slightly branched alkanes on the one hand and larger branched alkanes with, for example, quaternary carbon atoms.

The effective pore size of the zeolites can be measured using standard adsorption techniques and hydrocarbonaceous compounds of known minimum kinetic diameters. See Breek, Zeolite Molecular Sieves, 1974 (especially chapter 8) and Anderson et al., J, Catalysis 58, (1979) 114.

H-form intermediate pore size zeolites will usually admit molecules with kinetic diameters from 0.5 to 0.6 nm with little hindrance. Examples of such compounds (and their kinetic diameters in nm) are: n-hexane (0.43) »3-methylpentane (0.55)» benzene (0.585) and toluene (0.58). Compounds with kinetic diameters from 0.6 to 55 0.65 nm can be admitted into the pores depending on the particular zeolite, but they do not penetrate as quickly and are effectively excluded in some cases (e.g. 2,2-dimethylbutane outside H- ZSM-5 closed). Compounds with kinetic diameters in the range of 0.6 to Q, 65 nm include: 40 cyclohexane (θ, 6θ), 2,3-dimethylbutane (0.6l), 2,2-dimethylbutane 8202272. V% - 5 - (0.62), m-xylene (0.6l) and 1,2,3,4-tetramethylbenzene (0.64)

Generally, compounds with kinetic diameters greater than about 0.65 nm cannot penetrate the pore openings and cannot be adsorbed into the interior of the zeolite. Examples of such larger compounds include: o-xylene (0.68), hexamethylbenzene (0.71), 1,3,5-trimethylbenzene (0.75) and tributylamine (0.81).

The preferred effective pore size range is from about 0.53 to about 0.62 nm. For example, ZSM-5 »ZSM-11 10 and silicalite fall within this range.

Standard techniques are used when performing adsorption measurements to determine the pore size. It is expedient to consider a particular molecule to be excluded if it does not reach at least 95% of its equilibrium adsorption value on the zeolite in less than about 10 minutes (P / Po = 0.5, 25 ° C).

Examples of intermediate pore size zeolites include silicalite and members of the ZSM series such as ZSM-5, ZSM-11, ZSM-12. ZSM-21, ZSM-23, ZSM-35 and ZSM-38. " ZSM-5 is described in U.S. Pat. Nos. 3,702,886 and 3 * 770,614; ZSM-11 is disclosed in U.S. Patent 3,709,979 »ZSM-12 is disclosed in U.S. Patent 3 * 832,449, ZSM-21 is disclosed in U.S. Patent 3,948,758, and silicalite is disclosed in U.S. Patent 4 * 061,724 The preferred zeolites are silicalite, ZSM-5 and ZSM-11.

The conversion catalyst must contain a Group YIII metal compound of the periodic table with sufficient activity for technical use. Group 30 YIII metal compound is here understood to mean the metal itself or a compound thereof.

The noble metals of group YIII and their compounds, platinum, palhdium and iridium, or combinations thereof, can be used.

The most preferred metal is platinum. The Group YIII metal component can be impregnated into the zeolite after it is formed, or the metal can be incorporated into the reaction mixture from which the zeolite is hydrothermally crystallized. It is highly desirable for the metal component to be uniformly dispersed throughout the zeolite, for example, by inclusion in the hydrothermal crystallization mixture. The amount of Group YIII metal present in the conversion catalyst should be within the normal use range of reforming catalysts from about 0.8 to 1.0 wt%, preferably 0 , 2 to 0.8 wt% and most preferably 0.2 to 0.6 wt%.

Reforming catalysts containing platinum are usually subjected to halogen or halide treatments to achieve or maintain a uniform metal dispersion and they also contain a halide component (especially a chlorine compound). The catalysts of the present invention may be subject to similar treatments are subjected without decreasing the catalytic specificity for the benzene synthesis. The halide treatment does not seem to have a significant effect on the benzene yield.

The intermediate pore size / metal zeolite of Group VIII conversion catalyst can be used without binder or matrix. The preferred inorganic matrix when one is used is a silica-based binder such as Cab-O-Sil or Ludox. Other matrices such as magnesium oxide and titanium oxide can be used. The preferred inorganic matrix is not acidic.

It is critical for the selective preparation of benzene in useful amounts that the conversion catalyst be substantially free of acid, eg upon poisoning the zeolite with a basic metal compound, eg alkali metal compound. Intermediate pore size zeolites are usually prepared from mixtures containing alkali metal hydroxides and thus have an alkali metal content of about 1 to 2% by weight. These high levels of alkali metal, usually sodium or potassium, are unacceptable for most catalytic applications because they cause a high rate of fouling. Usually, the alkali metal is removed to lower levels by ion exchange with hydrogen or ammonium ions. Alkali metal compound, as used herein, is understood to mean elemental or ionic alkali metals or their basic compounds.

Surprisingly, unless the zeolite itself is substantially free of acid, the basic compound is required in the present process to direct the synthetic reactions to the benzene production.

The amount of alkali metal necessary to make the zeolite substantially free of acid can be calculated using standard techniques based on 8202272 *> ν 'based on the aluminum content of the zeolite. Under normal conditions, the zeolite, as prepared and without ion exchange, will contain sufficient alkali metal to neutralize the acidity of the catalyst. When a zeolite free from alkali metal is the starting material, alkali metal ions in the zeolite can be ion-exchanged to substantially eliminate the acidity of the zeolite. An alkali metal content of about 100% or more of the acid sites calculated on a molar basis is sufficient.

When the basic metal content is less than 100% of the acid sites on a molar basis, the following test can be used to determine when the zeolite is essentially free of acid. The test method is as follows: 0.1- 0.5 g of catalyst is mixed with 1 g of acid washed and neutralized alundum and filled into a 4.8 m stainless steel reactor tube with the remaining space filled with alundum. The reactor contents are calcined at 450 ° C for 1 hour. The reactor is then placed in a gripper oven and the reactor outlet is connected to the inlet of a gas chromatograph.

20 The inlet is connected to the carrier gas pipe of the gas chromatograph. Helium is passed through the system at 30 cm / min. Bumps of 0.04 microliters of n-decane are injected through a septum over the reactor and the reaction products are determined by standard gas chromatographic analysis. Blank tests not alundum should not show conversion under the experimental conditions, nor should a 100% Catapal alumina catalyst. **

A pseudo first order cracking rate constant, k, is calculated using the formula 1 1 3.0 k = In _ A 1 ~ x where A is the weight of zeolite in grams and x is the fractional conversion to products below decane Cook. The zeolite is substantially free of acid when the value for ln k is less than about -3.8.

The preferred alkali metals are sodium and potassium. The zeolite itself can be substantially free of acid only at very high silica: alumina mole ratios; 8202272-8 - "zeolite consisting essentially of silicon oxide" means a zeolite substantially free of acid without base poisoning.

The reaction conditions for the process usually include pressures ranging from atmospheric to 10 bar and space velocities ranging from 0.1 to 15. If desired, hydrogen can be mixed with the feed to reduce the catalyst's tendency to fouling, but hydrogen does not have to be used. The reactions can take place at temperatures above 480 ° C. Successfully, the method is most efficient at relatively high temperatures above 510 ° C to about 595 ° C.

Substantial amount of benzene is understood to mean a benzene content of the produced C 2+ aromatics greater than about 50 wt% of the C 2+ aromatics, preferably greater than about 60 wt%, and most preferably greater then about 75 wt%.

The following examples illustrate the invention. All percentages are weight percentages unless otherwise indicated.

Two light directly obtained feeds were used in Runs 20.

Supply 1

Density, ° API 79

Nitrogen, ppm <0.1

Sulfur, ppm <0.2 Yol. % alkanes 83.6

Distillation (D86) ° Cj

Start / 5 47 / 50.6 10/30 52.2 / 57.2 50 61.7 50 70/90 68.9 / 80.6 9 5 Apt. 90.0 / 147.2 8202 272 4 - 9 -

Supply 2

Density, ° API 75

Nitrogen, ppm 0.1

Sulfur, ppm 0.2 5 VdL% alkanes 77> 2

Distillation (D86) ° C:

Start / 5 48.9 / 56.2 10/30 57.63.9 50 69.4 10 70/90 76.7 / 92.2 95 / kpt. 102.2 / 123.3 7 ear-rounded I.

A series of experiments were conducted to illustrate the need to use a zeolite substantially free of acid * for the preparation of benzene. In the first set of experiments, a zeolite prepared according to U.S. Patent No. 4-061,724 and having a silica: alumina molar ratio of 892.1 was used. No inorganic matrix was used. The feed 2 was used under the following conditions: space velocity = 1, no hydrogen, 3.4 bar and 538 ° C. Calculations show that 0.16% sodium would saturate the acidic (aluminum) sites.

Catalyst A B C

Ha content,% 0.017 0.99 4.12 Pt content,% 0.33 0.38 0.44

Product C + +,% of feed 56.88 79.69 85.59

Aromatics,% of C ^ + 91.60 66.43 42.57

Benzene,% of aromatics 8.81 65.45 65.89 JO These data show that as the sodium content increased (when the zeolite acidity decreased and neutralized) the C + fraction yield increased and the benzene content of the aromatics fraction increased significantly.

A second set of experiments also showed the surprising effect of an acid-free zeolite on the benzene specificity.

8202272 - 10 -

Again using the feed 2, space velocity = 1, H2 = 1> 1.65 t> ar and 538 ° C along with zeolites showing the ZSM-5 X-ray diffraction pattern and with a silica: alumina molar ratio of 121: 1 (D and E) and 5 "prepared according to U.S. Patent 4,061,724 (E; silica: alumina mole ratio of 938: 1) obtained the following results:

Catalyst I) E ff

After content 2.05 0.005 1.14 Et% 0.44 0.34 0.36

Re% 0.42 0.37 0

Cl% 0.49 <0.05 0

Product C ^ +,% of feed 52.67 37.54 48.55 15 Aromatics,% of C ^ + 88.63 92.05 92.82

Benzene,% of aromatics 89.14 34.12 94.76

These data also illustrate the substantial selectivity to the benzene preparation of the present invention.

Further experiments to demonstrate the selective preparation of benzene in the aromatics fraction and the effect of alkali metal poisoning were performed using a zeolite prepared according to U.S. Patent 4,073,865 with an aluminum content of 950 ppm. The reactions were carried out on feed 2 at a space velocity of 1, no hydrogen, 3 3 bar and 538 ° C.

Catalyst Q g

Na% 2.82 <0.005 Pt% 0.49 0.24

Product% of supply 83.55 43.61

Aromatics% of C 15 + 15.47 63.43

Benzene,% of 35 aromatics 62.44 7.91 8202 272 - 11 -

Although the aromatic fraction of the C + product of G is low, it has a high benzene content and based on converted feed G gave considerably more benzene (about 8%) than H (about 2.5%).

Example II.

Experiments were conducted to demonstrate the need for the presence of a Group VIII metal to achieve not only benzene selectivity but reasonable yields on aromatics. The feed 2 was used together with a space velocity of 1.3 bar, no hydrogen and 538 ° C.

The zeolites of I showed the X-ray diffraction pattern of ZSM-5, while the zeolite of J was prepared according to U.S. Patent 4,061,724. The zeolites were not composed of an inorganic matrix.

15

Catalyst I__J

SiO 2 * Al 2 O 5 67.4 892

Ha% 1.02 0.99

Pt 96 0 0.58

Product 20 ° C +>% of feed 95.84 79.89

Aromatics,% of 5.24 66.43

Benzene,% of aromatics 49.89 65.45

These data demonstrate that the Group VIII metal, platinum in this case, is necessary not only to provide a high benzene fraction of the aromatics formed, but also to yield practical amounts of an aromatic fraction. Example III.

The preceding examples show that benzene can be selectively prepared with high yields from zeolites with a wide range of silica: alumina mole ratios. Several other tests were also performed to illustrate this activity. The K catalyst was prepared according to U.S. Patent 4,061,724, while the L catalyst showed the ZSM-5 X-ray diffraction pattern. The reaction conditions included 1.6 bar, Ε ^ / Ε0 = 1, space velocity = 1, and 538 ° C.

8202272 - 12 -

Supply No. 1 No. 2

Catalyst g ^

Silicon Oxides Aluminum Oxide 938 121

Ha% 1.14 2.03 5 pt% 0.35 0.44

Re% 0.54 0.42 d% 0.75 0.49

Product C *,% of Feed 47.43 52.67 ^ 4 · 10 Aromatics,% of 100 88.63

Benzene,% of aromatics 87.73 89.14

Example 17.

Feed No. 2 was processed with a platinum (0.36%), sodium 15 ("1.14%) zeolite prepared according to U.S. Patent 4,061,724 and with a silica: alumina mole ratio of 958: 1. The reaction conditions included a space velocity of 1.65 bar, Hg / HCl and 538 ° C. The products were compared at the beginning and at the end of the test.

20 Start End (after 1 hour ') (after 20 hours) C5 +,% of supply 57.63 80.48

Aromatics,% of C ^ + 87.30 57.78

Benzene,% of aromatics 85.2 75.2 25% of feed 42.86 35.89

Caromatics,% of feed 7.45 11.60 unreacted feed 7.05 33.97

These data illustrate the surprising result that as the catalyst foules, the Cc + efficiency increases, benzene remains a major constituent of the O aromatics, benzene remains a major product, and non benzene-like aromatics remain a minor part of the product. The sites, which have undesirable cracking activity, become polluted faster than the benzene synthesis sites.

35 Example V.

According to the dehydro closure mechanism according to which 8202272-15 a a conventional reforming proceeds, an n-heptane feed would yield a product which is primarily toluene, with only small amounts of benzene and other aromatics. An experiment was carried out using an n-heptane feed, a platinum, sodium ZSM-5 zeolite and a space velocity, 1.65 bar, Hg / lCl and 558 ° C. The data from the beginning and end of the experiment show that significant amounts of benzene have been produced from n-heptane.

Start End ”* 0 (after 1 hour) (after 20 hours) cc +>% of supply 58.98 69.26

"I

Aromatics,% of 94.87, 84.32

Benzene,% of feed 39.40 21.99 0γ aromatics% of feed 16.56 36.41 * 5 unreacted feed 1.92 3 .5

Example 71.

An experiment was conducted using feed No. 2 and a zeolite showing the ZSM-5 X-ray diffraction pattern. The alkali metals were sodium (in m) and potassium (in M).

The reaction conditions included 3.3 "bar, no hydrogen, a space velocity of 1 and 538 ° C.

Catalyst ΜN

Cation content,% 0.99 1.46

Pt,% 0.58 0.54 C5 +,% of feed 79.69 68.59

Aromatics,% of C + 66.43 40.08

Benzene,% of aromatics 65.45 76.67

Closure 98.77 89.50

The data indicate that a high benzene aromatic fraction can be prepared from a zeolite whose acidity is neutralized by various alkali metals. Example YII.

An experiment was conducted using feed No. 1 and a zeolite prepared according to U.S. Pat. No. 4,061,724 to demonstrate the effect of halide on the content of the gas having 1 to 4 carbon atoms. The catalysts 8202272 * 14 were unbound.

Catalysts 0 P

Cl,% 0.75

Pt,% 0.35 0.48 Re,% 0.54 0.70

Na,% 1.14 1.14

Product yield C5 +,% 47.43 70.18

Aromatics,% of C ^ + 100 52.22 10 Benzene,% of C aromatics 5 87.73 77.10

Methane, wt% of feed 55.82 11.98 C2 0 4.97 C5 0 5.35 15 C 0 7.24 4

The test shows the selective preparation of methane in contrast to the other light gases.

8202272

Claims (13)

1. Process for the selective preparation of a product having a substantial content of normal and slightly branched chain hydrocarbons, characterized in that (a) a hydrocarbonaceous feed containing normal and slightly branched chain hydrocarbons and has a boiling range above about 40 ° C and less than about 200 ° C, contacts a conversion catalyst containing an intermediate pore size zeolite 10 and a Group YIII metal compound of the periodic table, and wherein the zeolite is substantially free is of acid and (b) gains a benzene-containing effluent. 2. Process according to claim 1, characterized in that an intermediate pore size zeolite is used with pore openings in the range from about 0.5 nm to about 0.65 nm. Process according to claim 1 or 2, characterized in that ZSM-5 »ZSM-11 and / or silicalite 20 are used as zeolite. 4. Process according to claims 1 to 5, characterized in that a zeolite is used which contains a sufficient amount of an alkali metal compound to be substantially free of acid. The process according to claim 4, characterized in that a zeolite is used with an alkali metal content of 100-6 or more of the acidic sites in the zeolite on a molar basis. 6. Process according to claim 5, characterized in that an alkali metal selected from potassium and sodium is used. Process according to claims 1 to 6, characterized in that a zeolite is used, which mainly consists of silicon oxide. 8. Process according to claims 1 to 7, characterized in that platinum is used as metal of group YIII of the periodic table. 9. Process according to claims 1 to 8, characterized in that a feed is used with a boiling range 40 above about 60 ° C and below about 120 ° C. 8202272 Τ '- 16 - 10. Process according to claim 9, characterized in that a feed is used which mainly consists of hydrocarbons with 6 to 8 carbon atoms. 11. Process according to claims 1 to 10, characterized in that the contact is made at a temperature above about 480 ° C. Process according to claim 11, characterized in that the contact is made at a temperature above about 510 ° C. Process according to claims 1 to 12, characterized in that a conversion catalyst is used, which further contains a halide component. A method for improving the quality of an effluent from a reforming device, characterized in that (a) a reforming feed is reformed into an effluent from a reforming device and 00 produces a quality-improved reformate with an increased benzene concentration through the effluent of the reformer with a conversion catalyst containing an intermediate pore size zeolite and a Group YIII metal compound of the periodic table and wherein the zeolite is substantially free of acid. - 8202272