DD291937A5 - CATALYST FOR THE PREPARATION OF DIMETHYL ETHER OF SYNTHESEGAS - Google Patents

Abstract

The invention relates to a catalyst for the preparation of dimethyl ether (DME) from a mixture of gases consisting essentially of carbon monoxide and hydrogen (methanol synthesis gas). The catalyst, consisting of a hydrogenation component and a dehydration component, is characterized by a high activity and selectivity. It makes it possible to achieve a high yield of DME even at relatively low temperatures of about 210C. The dehydration component used is a ZSM-5 type zeolite {heterogeneous catalysis; dimethyl ether; Carbon monoxide / hydrogen; Hybrid catalyst; hydrogenation; Dehydratisierungskomponente; zeolite}

Description

Field of application of the invention

The invention relates to a catalyst for the preparation of dimethyl ether (DME) from a mixture of gases consisting essentially of carbon monoxide and hydrogen (methanol synthesis gas). The catalyst, consisting of a hydrogenation component and a dehydration component, is characterized by a high activity and selectivity. It makes it possible to achieve a high yield of DME even at relatively low temperatures of about 210 ^° C. The dehydration component used is a zeolite of the ZSM-5 type.

The DME produced with the catalyst object of the present invention has gained increasing interest in recent years as a propellant for the aerosol technology because, in contrast to the CFCs still in use, it is not harmful to the environment. Because of the good miscibility with water, in particular water-soluble substances can be readily converted into aerosols. Furthermore, dimethyl ether can serve as starting material for the preparation of amines or of dimethyl sulfate. In the context of the synthesis of gasoline hydrocarbons by the MTG process or of olefins by the MTO process (Mobil Oil Corp.) dimethyl ether is an important intermediate.

Characteristic of the known technical solution

The gross reaction of synthesis gas to DME proceeds according to the following simplified scheme:

CO + 2H ₂ »CH ₃ OH (hydrogenation)

2CH ₃ OH> CH ₃ -O-CH ₃ + H ₂ O (dehydration)

and optionally:

CO + H ₂ O> CO ₂ + H ₂ (CO conversion)

Usually DME is prepared by dehydration of methanol on acidic catalysts. As by-product, it is involved in isobutyl oil synthesis.

Since methanol is mainly produced from synthesis gas, DME can also be obtained by adding the dehydration component to the methanol contact under the conditions of the methanol process. In this way, methanol formed on the hydrogenation component is continuously removed from equilibrium by the subsequent dehydration reaction. As a result, the reaction in accordance with the law of mass action in the direction of the target product DME is favored. This procedure also has the advantage that only one process stage is required for the production of DME compared to two process stages in the production from methanol, since the dehydration reaction must take place in a second reactor, which operates in contrast to Methanolhersteliung at atmospheric pressure. As the dehydrating agent, oxides or salts of Al, Cr, La, Mg, Cu or Zn are mainly used (GB 2099327 (1982)). However, modifications of the alumina are predominantly used (US Pat. No. 4,375,424 (1983)) Patent DD-AP 208973 uses crystalline silicic acid as the dehydrating agent in which some Si atoms are replaced by Al.

The dehydration activity (DHA) of the dehydration contacts based on Y-Al ₂ O ₃ described hitherto in the literature, including its modifications by doping with other metals, is unsatisfactory. In most cases, sufficient DHA can only be achieved at elevated temperatures at which the hydrogenation component is already aging considerably. Thus, a satisfactory DHA is only achieved at 280 ⁰ C in U.S. Patent 4,521,540 (1985), which is too high for a methanol contact for use in the low temperature methanol process. Similar conditions can be found in DE-Offenlegungsschrift 2363944 (1978). In US-Fatent 4375424 (1983) even reaction temperatures of about 300 ° C are required when using Y-Al ₂ O ₃ as DHA to obtain good DME yields. However, these high temperatures affect the life of cryogenic Methcnolkatalysatoren whose optimum reaction temperature is 210-25O ⁰ C.

Object of the invention

The aim of the invention is a catalyst for the preparation of dimethyl ether with a very active dehydrating component which, when mixed with a known methanol contact, produces a high DME yield at relatively low reaction temperatures when using synthesis gas and produces little methanol and hydrocarbons.

Explanation of the essence of the invention

The object of the invention is to find a catalyst which consists of a hydrogenation component and a dehydration component and which has the following properties:

high hydrogenation and dehydration activity (DHA)

high ratio of formed dimethyl ether to methanol,

- low by-product formation

- low reaction temperatures.

High DHA makes it possible to increase the proportion of methanol contact for the available catalyst volume. The amount of methanol remains low due to the high DHA of the dehydration component. The result is an increase in the DME productivity of the reactor. The formation of hydrocarbons is undesirable because their distillative separation is difficult.

According to the invention, a catalyst for the preparation of dimethyl ether (DME) from carbon monoxide and hydrogen, consisting of a mixture of a hydrogenation component in the form of a methanol contact z. Example, from oxides of Cu, Zn and Al, and a dehydrating component, which is characterized in that the dehydration component is a zeolite of type ZSM-5 having a Si-Al atomic ratio in the crystal lattice of 12 to 100. With the catalyst according to the invention, a higher DME selectivity and a higher DME yield can be achieved than is the case with the use of the dehydration components described in the literature. The catalytic activity of the dehydration component according to the invention is higher than that of the dehydration components described in the literature at the same temperature. With the catalyst according to the invention, reaction temperatures of 210 to 250 ° C. are possible, which are suitable for use as hydrogenation component a mixture of CuCVZn (VAI ₂ O ₃ or CuO / ZnO / Cr ₂ O ₃ or CuO / ZnO / AljOs / CrjOj Hydrogenation components enable a high yield of intermediate methanol.

As the dehydrating component, a ZSM-5 type zeolite is used, e.g. Example, the zeolite HS30 (Si / Al ratio 12-16, manufacturer: VEB Chemical Combine Bitterfeld), which was converted with 0.5-N HNO ₃ at 8O ⁰ C in the H ⁺ -form. This zeolite is prepared template-free, ie without the use of expensive quaternary ammonium bases (template). To achieve higher Si / Al ratios, the zeolite is dealuminated by treatment with steam (F. Asinger, Methanol-Chemie und Energierohstoff, Akademieverlag Berlin, 1987, p.81).

After mixing with amorphous SiO ₂ as a binder, for example Aerosil (DEGUSSA) in a mass ratio of zeolite: SiO ₂ = 65:35, deformation takes place (2 mm strand diameter).

embodiments

A series of experiments was carried out with the catalyst according to the invention and with a comparative catalyst based on Al ₂ O ₃ , as described, for example, in the patent GB 2093365. First, by varying the mixing ratios of hydrogenation component and Y-Al ₂ O ₃ as the dehydration component (reference catalyst mixture), the optimum mass fraction of dehydration component at a load of 2000 V / Vh was found to be 60%. With this mixing ratio and the catalysts of the invention were used. The remaining reaction conditions listed below were the same for the reference catalyst and catalysts according to the invention:

Reactor type: Differential circulation reactor with minimized dead space

Reactor volume: 7.8ml

Grain diameter: 2-4mm (chippings)

Formation: 9 hours with 2% H ₂ in N ₂ at atmospheric pressure

Reaction temperature: 210 to 230 ⁰ C

Gas load: approx. 2000V / Vh

Input gas: 15% CO, 85% H ₂

Working pressure: 5MPa

Hydrogenation component: standard methanol contact from oxides of Cu, Zn, Al; Asinger, 1987

In preliminary experiments, it was found that the mechanically produced catalyst mixture has a greater abrasion resistance with respect to the mixture produced by grinding and pre-pressing with comparable activity. It has been found that the aging resistance of the Aerosil bound catalyst over other binders, eg. As alumina, is considerably larger.

Table 1

VNr. A B C D e F G H 1 Y-Al ₂ O ₃ 0.6 210 1942 37.8 52.1 0.9 57.3 2 Y-Al ₂ O ₃ 0.6 230 1942 56.7 59.3 1.9 97.9 3 69 0.6 210 1931 28.4 84.2 5.6 70.2 4 69 0.6 230 1931 56.6 70.3 7.4 116.9 5 52 0.6 210 1928 26.5 80.8 3.4 62.8 6 52 0.6 230 1928 55.4 69.6 6.3 112.8 7 36 0.6 210 1926 27.3 87.5 8.4 69.9 8th 36 0.6 230 1926 58.5 66.9 5.4 114.9 9 98 0.6 210 1931 23.7 87.3 13.5 60.8 10 98 0.6 230 1931 54.2 68.8 9.3 109.6

A = dehydration component (γ-ΑΙ ₂ Ο ₃ or zeolite, which is characterized by its Sl / Al ratio).

B = mass fraction Dehydration Comp. at the overall mix

C = reaction temperature ( ⁰ C)

D = gas load (at 22 ° C)

E = CO conversion C / o)

F = DME selectivity (%) = 100% -n ₀ ME-2 / (n _C oE - ncoA)

η = molar flows of DME, CO input gas,

CO residual gas (mol / h)

G = selectivity ratio DME to methanol H = space-time yield (RZA) to DME (g / [l.h])

From Table 1 it can be seen that the RZA (column H) obtained with the catalyst according to the invention are significantly higher than d for both reaction temperatures (column C) ^; e RZA obtained with Y-Al ₂ O ₃ as a dehydrating agent. In addition, the selectivity ratio DME to (the unwanted) methanol (column G) when using the catalyst according to the invention is much greater than when using Y-Al ₂ O ₃ .

However, the dehydration activity of both systems as a function of the reaction temperature can be different. This was taken into account by measurements at 21O ⁰ C and 23O ⁰ C. For both temperatures, the higher dehydration activity of the catalyst according to the invention over the Y-Al ₂ O ₃ becomes clear.

The mass fraction of dehydration component of 0.6 given in Table 1 is based on a Y-Al ₂ O ₃ proportion optimized for the stated reaction conditions in order to obtain a basis of comparison for the contact according to the invention. Due to the higher DHA of the zeolites used, their mass fraction in the catalyst mixture can be lowered, whereby the respective optimum proportion for the specific reaction conditions must be determined by experiments. Thus, for zeolite Zeo 52 for a load of 2000 V / Vh, a temperature of 23O ⁰ C, a pressure of 5 MPa and the specified synthesis gas composition an optimum proportion of dehydration component of 0.2 was determined. Although zeolites are used in the dehydration of methanol, but lead to saturated and unsaturated hydrocarbons, while the DME formation is insignificant. It was therefore surprising that when using synthesis gas in which methanol is formed only as an intermediate, DME is produced as the main product, while no hydrocarbon formation takes place. It was also surprising that the use of a non-aluminated zeolite ZSM-5, which has a Si / Al ratio of 12 to 16, yielded high DME yields with low hydrocarbon formation. For the comparison of the non-dealuminated zeolite with a dealuminated (Zeo 52), the 20% dehydration component determined by optimization was used (Table 2).

Table 2

Dehydratisierungskomponente Zeo 52 23O ⁰ C Zeo 52 A B C D e F G H (Mass fraction = 0.2) HS30 HS30 21O ⁰ C HS 30 2000 38 134.8 5.1 67.2 0.1 0.0 68.5 HS30 2000 41 139.8 4.7 65.6 0.0 0.0 66.2 2000 39 163.7 3.5 66.0 0.1 0.0 84.7 1000 50 99.5 5.2 68.5 0.4 1.9 90.2 2000 42 176.9 4.7 67.8 0.2 0.5 81.1 3600 47 255.5 3.3 64.4 0.3 0.8 66.4

A = gas load (V / Vh)

B = test number

C = space-time yield (RZA) of DME (g / [l.hj]

D = selectivity ratio of DME to methanol

E = selectivity DME (%)

F = selectivity C ₂ compounds (%)

G = selectivity C ₃ compounds (%)

H = CO conversion (%)

Higher RZA and more favorable DME / MeOH ratio are also obtained at higher temperatures. The then reduced life of the hydrogenation component applies to both the dehydrating agent according to the invention and for Y-Al ₂ O ₃ . The reduced life of the catalyst is due in both cases to aging of the hydrogenation.

Claims (2)

1. Catalyst for the preparation of dimethyl ether (DME) from carbon monoxide and hydrogen, consisting of a hydrogenation component in the form of a methanol contact, for. Example, of oxides of Cu, Zn and Al, a dehydrating component with a suitable binder, characterized in that the dehydration component is a zeolite of the type ZSM-5 having a Si-Al atomic ratio in the crystal lattice of 12 to 100. 2. Catalyst according to item 1, characterized in that the dehydration component is prepared without a template.