DE10302095A1 - Production of propene oxide, used as chemical intermediate, involves passing nitrogen-hydrogen-oxygen-propene mixture over catalyst in ceramic membrane reactor and removing product from permeation side with inert sweep gas - Google Patents

Abstract

Propene oxide (I) production involves passing nitrogen/hydrogen/oxygen/propene gas mixture (II) over catalyst at 25-250 degrees C on porous membrane forming hydrophilic top layer of porous, asymmetric ceramic ultrafiltration support with pore size under 1 nm. (I) is removed continuously from permeation side with inert sweep gas stream (III) and residual gas (IV) on inlet side. (I)/(IV) separation factor is 4-50. (III) and (II) have same pressure in 1-9 bar range. An Independent claim is also included for the membrane reactor used in this process.

Description

The invention relates to a method for the production of propene oxide from propene using a catalytic Membrane reactor.

With 4.5 million t / a production, propene oxide is one of the largest chemical intermediates with an annual increase in demand of around 4%. The production of propene oxide is mainly based on 3 technologies: [i] the chlorohydrin process, [ii] the indirect oxidation process via peroxides (Halon process) or H ₂ O ₂ and [iii] via direct oxidation.

• [i] More than 50% of propene oxide production takes place via the multi-stage chlorohydrin process, which is due to the use of chlorine and the resulting saline wastewater as environmentally unfriendly is to be assessed.
• [ii] In the two-stage process, propene is oxidized indirectly using H ₂ O ₂ or organic peroxides (halon process). Disadvantages of these processes are the high H ₂ O ₂ costs and the fact that the plant sizes have to be limited for safety reasons. Processes for the direct oxidation of propene in methanol with 30% H ₂ O ₂ in the liquid phase with catalysts such as titanium silicalite (TS-1), titanium-modified HZSM-5 or platinum-impregnated TS-1 are currently under development. Yields of propene oxide up to 67% with selectivities of 97% are achieved.
• [iii] Processes of propene oxide production by direct oxidation are sought which are more economical and environmentally friendly than previous ones and which can be implemented in one step if possible. Such processes are possible by catalytic direct oxidation of propene with oxygen or by direct oxidation of propene with H ₂ O ₂ . These processes could advantageously be implemented using membrane reactors because propene oxide can be separated off at the same time.

The synthesis of propene oxide from propene and oxygen in the presence of hydrogen and nitrogen can be carried out on gold catalysts on TiO ₂ -SiO ₂ supports, titanium silicalite (TS-1) and MCM-41 in the temperature range 25–100 ° C in the gas phase. Previous attempts to produce propene oxide in one step, the catalytic direct oxidation of propene with oxygen in the gas phase, did not meet the requirements for technical processes with regard to propene yield and service life of the catalysts. It is known from the literature that high selectivities (99%) but only low yields (2%) are achieved when using gold catalysts and that the catalytic activities already decrease after a short time [TA Nijhulus, BJ Huizinga, M. Makkeee, JA Moulijin, Ind. Eng. Chem. Res. 38 (1999) 884-891; T. Hayashi, K, Tanaka, M. Haruta, Am. Chem. Soc., Div. Pet. Chem. 41 (1996) 71].

Little information is available for separation of propenoxides with membranes. M. Kobayashi, J. Togawa, T. Kanno, J. Horiuchi, K. Tada [Desalination 144 (2002) 399-403] through a microporous inorganic glass membrane with embedded catalyst the reaction gas and received through this driving style due to the short dwell time a higher one on the catalytic converter selectivity compared to a diffusion or grafting style. The porous Glass membrane did not allow any product separation.

From the DE 26 58 189 A1 the electrochemical production of propene oxide by reacting a chlorohydrin solution on the anode and an alkaline solution on the cathode side of a porous membrane is known. Propene oxide is isolated on the cathode side and released with the re-formation of alkali chloride.

In the US 5,141,530 are selectively separated with semi-permeable polycarbonate, polyester and polyester carbonates with a non-ionic surface and pores of 10 to 500% gas mixtures, including oxo compounds, but not mentioning propene oxide in particular.

The invention is based on the object Propene through one-step direct oxidation and simultaneous separation of the gas mixture used with high selectivity and yield manufacture.

According to the invention, the method consists in passing a gas mixture consisting of nitrogen, hydrogen, oxygen and propene over a catalyst layer which is arranged on a supported, porous membrane, the propene oxide formed after permeating through the hydrophilic membrane and the carrier on the permeation side by means of a inert sweep gas stream is continuously removed from the membrane support, and the other reaction products and unreacted gases are removed from the inlet side of the reactor, the membrane forming the top layer of a porous ceramic ultrafiltration support with an asymmetrical layer structure and a pore size of <1 nm and a separation factor for propene oxide / residual gases in the range from 4 to 50,
and wherein the sweep gas flow has the same pressure as the gas mixture on the inlet side of the membrane, but has a different - preferably lower - partial pressure as the inlet-side gas mixture, and pressures are in the range from 1 to 9 bar and the catalyst temperature in the range from 25 to 250 ° C.

The used in the invention Membranes essentially consist of four layers of oxide Materials with different porosity and a selectively separating Membrane layer through which propene oxide and water are preferred over the permeate other reaction products. The catalyst is in place as a layer or fill on or in the membrane. The feed gas mixture, consisting of propene, oxygen, hydrogen and an inert gas as a thinner, e.g. Nitrogen. Resulting products, propene oxide and water, permeate through the near the catalyst membrane. Unreacted reactants in the Retentate coming out of the reactor can feed the feed gas again added become. This enables a circular procedure to be implemented. By the Use of membranes in tube-capillary geometry or as a hollow fiber is the formation of large-scale technical Modules possible.

The carrier is selected from Al ₂ O ₃ , TiO ₂ , SiO ₂ , ZrO ₂ and mixtures thereof.

The catalyst is selected from Au-TiO ₂ -SiO ₂ or Au-titanium silicalite.

In the process, the pore size is asymmetrical carrier from the permeation side to the input side from 3000 nm to 5 nm decreasing. In this context, "asymmetrical layer structure" means a structure that starting from the large-pored body has a decreasing pore size towards one side, so that the pores on the surface of the innermost layer have the smallest diameter. This innermost layer also represents the functional side of the body, on which the membrane is located or installed. On this innermost layer is also the deposition of the molecular sieve membrane, the pore sizes <1 nm, preferably in the range 0.3-0.8 nm can have.

The ratio of " Composition of components A and B in the permeate relative to the composition ratio understood these components in the retentate. The separation factor at method according to the invention is preferably in the range 5-30, with separation factors> 30 being particularly preferred are.

The pressure is advantageous with the method according to the invention depending on the membrane type. It ranges from 1 to 8 bar.

Preferred temperatures are in Range of 50-200 ° C, advantageous 140-180 ° C, especially 165-185 ° C.

The ratio of the gases in the supplied gas mixture (feed gas) is advantageously in the range of N ₂ : H ₂ : O ₂ : propene = 60-80: 5-15: 5-15: 5-15, in particular 65-72: 8-12 : 6-10: 6-10.

Through membrane-supported reaction control, propene oxide and water of reaction formed on the catalyst are removed through the permselective membrane, so that propene oxide can be formed again on the catalyst. The driving force for the permeative transport of propene oxide and water through the membrane is the small partial pressure difference to the permeate side. The direct removal of the propene oxide formed from the vicinity of the catalyst largely prevents the further reaction of propene oxide to CO _x and oligomers which are adsorbed on the catalyst surface and are the cause of the deactivation of the catalyst.

• – in situ-Hydrolyse von Tetraalkylorthosilicaten, z. B. Tetraethylorthosilikat (TEOS) in den Poren eines Ultrafiltrations-Keramikträgers mit definierten Wassermengen (hydrothermal) [gemäß DE 18722902 A1 ] und zusätzlich unter Autoklavbedingungen [gemäß DE 10021580 A1 ].
• – durch Aufbringen einer Gelschicht auf Keramikträger. Das Gel wird durch Hydrolyse von Metallalkoholaten oder Salzen Metalloxidsole unter stark sauren Bedingungen bei Wasserdefizit hergestellt. Eine ultramikroporöse Membranschicht bildet sich durch Vernetzung während der Trocknung/Kalzinierung aus.
• – Durch Kristallisation von (a) Silikalith-Schichten durch SiO₂-in situ-Kristallisation oder (b) Al-reicher ZSM-5-Schichten mit Hilfe von Impfkristallen (Seeds) auf Keramiken.

The membranes for the reactor can be produced in various ways. Asymmetrical ceramic carriers are used. These are inert to organic solvents and temperature resistant up to at least 300 ° C. By chemically modifying the surface, pore sizes and interactions in the pores can be set, which enable separations down to the molecular level. SiO ₂ -modified ceramics or zeolite membranes are particularly advantageous. These are prepared by:

• - In situ hydrolysis of tetraalkyl orthosilicates, e.g. B. tetraethyl orthosilicate (TEOS) in the pores of an ultrafiltration ceramic support with defined amounts of water (hydrothermal) [according DE 18722902 A1 ] and additionally under autoclave conditions [according to DE 10021580 A1 ].
• - by applying a gel layer on a ceramic substrate. The gel is produced by hydrolysis of metal alcoholates or salts of metal oxide sols under strongly acidic conditions with a water deficit. An ultramicroporous membrane layer is formed by crosslinking during the drying / calcination.
• - By crystallization of (a) silicalite layers by SiO _{2 in} situ crystallization or (b) Al-rich ZSM-5 layers with the aid of seed crystals on ceramics.

The latter process is carried out in such a way that a pretreatment of the carrier is carried out by applying seed crystals of the appropriate molecular sieve type and then - after the seed-coated carrier has been heated at 400 to 600 ° C. - from aqueous diluted gels to the seed-loaded carriers the method explained below is carried out. The advantage of carriers with seed crystals is the targeted phase-pure crystal growth on the carrier with largely un suppression of secondary nucleation in the volume phase. A limited influence on the crystal orientation in the layer and the formation of thin crystal layers is possible. This subsequent process consists in bringing the asymmetric carrier with the seed crystals into contact with a liquid composition suitable for molecular sieve synthesis in a closed system in such a way that there is a repeated change of liquid and vapor phases at least for the area of the functional surface, steam and the liquid phase are in a thermodynamic equilibrium, and the treatment period is in the range of 8 to 100 hours at a temperature of 80 to 200 ° C and at a pressure from atmospheric to autogenous pressure of the system.

The repeated change from liquid and Vapor phase for the surfaces to be treated is advantageously carried out 0.2 to 15 times per minute, preferably 1 to 10 times, especially 3 to 5 times per minute. Such a change can, for example, by installing the closed container a tumbler take place who performs this very slow movement, whereby the wobble movement by rotating the container its longitudinal axis with approx. 1 rpm superimposed can be so that all parts of the tube alternate evenly in the liquid or vapor phase. The container is about 30 to 90% of its size free volume filled with the synthesis gel.

The membranes used for the selective separation of propene oxide and water were preferably obtained by in situ hydrolysis of tetraethyl orthosilicate (TEOS) in the γ-Al ₂ O ₃ layer of an ultrafiltration (UF) support or by applying SiO ₂ polymer sols thereon Prepared layer.

Special advantages for separation problems, such as occur in chemical reactions, for example inorganic membranes due to their resistance to organic Compounds, including propene oxide as well as their high thermal load capacity> 300 ° C.

An essential feature of the invention is that a membrane reactor to carry out the Process of propene oxide synthesis is used. This exists from a porous ceramic ultrafiltration carrier with an asymmetrical layer structure, the carrier being a hydrophilic membrane layer on the input side with pore size in the range from 0.3 to 0.8 nm contains and a separation factor for Propene oxide / residual gases up to> 30 has and that on the membrane layer a catalyst layer on the input side is arranged with a layer thickness of 0.1 to 1.5 mm.

• – [F. Bocuzzi, A. Chlorino, S. Tsubota, M. Haruta, J. Phys. Chem. 100 (1996) 3625] Am Au/TiO₂-Katalysatorsystem besteht ein Gleichgewicht Ti⁴⁺O-Au ↔ Ti³⁺O-Au⁺ an der Oberfläche. Molekularer Sauerstoff wird am den Ti³⁺-Kation zum negativ geladenen O-Spezies. Mit der Anlagerung von H₂ entstehen Hydroperoxo- oder Peroxid-Spezies, die mit an Ti adsorbiertem Propen zu Propenoxid reagieren. Die Schlüsselrolle des Au erscheint als Bindungsvermittler für C₃H₆ und vermeidet den direkten Elektronentransfer von H₂ und O₂.
• – Im Modell von Olivera et al. [P.P. Oliveri, E.M. Patrito, H. Sellers, Surf. Sci. 313 (1994) 25] für Au/Ti-Silikalith der folgende Mechanismus angenommen. Au auf der Oberfläche generiert aus H₂ und O₂ in situ H₂O₂. Dieses reagiert auf isolierten Ti⁴⁺-Zentren und dann mit adsorbiertem Propen auf der SiO₂-Matrix. Die Menge an Ti-Atomen in Ti-Silikatlith ist strukturbedingt gering, die Au- und Ti-Atome sind in der SiO₂-Matrix dispers verteilt und voneinander isoliert. Die hohe Dispersion von Ti-Atomen, das mesoporöse Netzwerk der SiO₂-Matrix bewirkt die Stabilisierung von Propenoxid und erlaubt Reaktionen bei höherer Temperatur.

In membrane reactors, a remarkable increase in performance with regard to the propene oxide yields and conversions of propene can be achieved using the catalysts mentioned in the literature [TA Nijhulus, BJ Huizinga, M. Makkeee, JR Moulijin, Ind. Eng. Chem. Res. 38 (1999) 884-891; T. Hayashi, K, Tanaka, M. Haruta, Am. Chem. Soc., Div. Pet. Chem. 41 (1996) 71]. It is essential for the increase in performance that the propene oxide formed can be removed from the catalyst environment via the membrane. The partial oxidation of propene to propene oxide is a unidirectional reaction. Controlling the reaction as in equilibrium reactions by subtracting a component is therefore not possible. The mechanism of the epoxidation of propene on Au catalysts has not yet been clarified. It is assumed that the reactions can take place according to the following models:

• - [F. Bocuzzi, A. Chlorino, S. Tsubota, M. Haruta, J. Phys. Chem. 100 (1996) 3625] On the Au / TiO ₂ catalyst system there is an equilibrium of Ti ⁴⁺ O-Au ↔ Ti ³⁺ O-Au ⁺ on the surface. Molecular oxygen becomes a negatively charged O species on the Ti ³⁺ cation. The addition of H ₂ produces hydroperoxo or peroxide species, which react with propene adsorbed on Ti to form propene oxide. The key role of Au appears as a binding mediator for C ₃ H ₆ and avoids the direct electron transfer of H ₂ and O ₂ .
• - In the model by Olivera et al. [PP Oliveri, EM Patrito, H. Sellers, Surf. Sci. 313 (1994) 25] for Au / Ti silicalite the following mechanism was adopted. Au on the surface generated from H ₂ and O ₂ in situ H ₂ O _2. This reacts on isolated Ti ⁴⁺ centers and then with adsorbed propene on the SiO ₂ matrix. The amount of Ti atoms in Ti silicate lithium is small due to the structure, the Au and Ti atoms are dispersed in the SiO ₂ matrix and isolated from one another. The high dispersion of Ti atoms and the mesoporous network of the SiO ₂ matrix stabilize propene oxide and allow reactions at higher temperatures.

Particularly preferred membrane reactors are those in the form of a pipe, a multi-channel pipe, a system of capillaries, a closed module or a combination from that. A tube is particularly preferred.

The invention is intended below Examples closer explained that are not considered a limitation of Invention can be seen. The following examples show which Improvements in propene oxide separation through the use of membranes or can be achieved by membrane reactors.

example 1

A membrane reactor in tube geometry is used to solve the problem, as in P. Kölsch, M. Noack, R. Schäfer, G. Georgi, R.Omorjan, J. Caro, J. Membr. Sci. 198 (2002) 119-128. Via a multifunction valve, samples can be discharged to an online connected GC and analyzed. With the analysis data, material balances of the reaction are possible.

The propene oxide yield, selectivity and separation factor (Propene oxide / residual gases) were passed through in the membrane reactor TEOS membrane determined in situ hydrolysis. Compared but also yields and selectivities in the co-feed reactor, which the Corresponds to the tubular reactor. A co-feed reactor is present when sweep gas input and permeate outlet of the membrane reactor are closed and the Membrane layer has a dense structure, so that no gas flow or gas exchange can take place. Such a co-feed reactor corresponds with that in approximation a tubular reactor.

The results for the catalyst 1 of the Au-TiO ₂ -SiO _{2 type} are shown in Table 1. It becomes clear that the yields are 3-5 times higher and the selectivities are about 2-3 times higher in the membrane reactor than in the co-feed reactor. Higher pressure also increases yield and selectivity. The test conditions were the same, but the sales achieved were different.

Table 1: propene yield Y (PO) and selectivity S (PO) in the co-feed and membrane reactor, separation factors determined in the membrane reactor (membrane γ-121, catalyst 1)

Test conditions: 180 ° C, feed - 30ml / min N ₂ : H ₂ : 0 ₂ : propene = 70; 10: 10: 10, membrane reactor: 2 outputs, sweep gas: 40m1 / min argon;

Example 2

With a membrane reactor which was comparable to that in Example 1, measurements were carried out to separate propene oxide from the remaining reaction gases (propene, H ₂ , O ₂ , N ₂ ) with the catalyst 2, likewise of the Au-TiO ₂ -SiO _{2 type} , which, however, provided a lower propene oxide yield and selectivity. The example shows that the reproducible preparation of the catalysts of the Au-TiO ₂ -SiO _{2 type} has not yet been solved. Depending on the pressure, the propene oxide yields and selectivities determined in Table 2 were determined. Both in the yields and in the selectivities, better results are obtained with this procedure with the membrane reactor compared to the co-feed reactor, which corresponds to a tubular reactor.

Table 2: Pressure influence on the propene oxide yield Y (PO) and propene oxide selectivity S (PO), (membrane γ-121, catalyst 2)

Test conditions: Feed: 21 ml / min N ₂ , 3 ml / min O ₂ , propene, H ₂ , 140 ° C, in the membrane reactor 40 ml / min Ar sweep gas

Example 3

With a membrane reactor that is comparable with that of Example 1, measurements were made to separate Propene oxide from the reaction gases, in this case in the reactor an inert substance was present instead of the catalyst. It was done thus no reaction in the reactor, was tested in these experiments Separation effect of the membrane.

Permeative characterization was carried out with gas mixtures of the composition N ₂ : H ₂ : propene: O ₂ : propene oxide = 70: 10: 7.5: 7.5, which are similar to the composition of the gases after reaction in the syntheses of propene oxide from propene of the membranes with regard to the separation selectivity and the flows on ceramic membranes, which were prepared by in situ hydrolysis of tetraethyl orthosilicate. The same membrane as that described in Examples 1 and 2 was used here.

On the membranes produced by TEOS in situ hydrolysis on UF-Al ₂ O ₃ supports, propene oxide / residual gas separation factors of> 30 and at flows of 240 were used at pressures from 0.25 to 4 bar with a 500 ml / min sweep gas purge l / m ² h at 25 ° C (with low pressure drops across the membrane) determined.

Example 4

In an apparatus as described in Example 3, the permeative selectivity and achievable flows of the 5iO ₂ membrane for the gas mixture of the composition N ₂ : H ₂ : propene: O ₂ : propene oxide = 70: 10: 7, 5: 7, 5 , which are similar to the composition of the gases after reaction in the syntheses of propene oxide from propene. Propene oxide / residual gas separation factors of up to 28 and flows of up to 90 l / m ² h were obtained on membranes produced by polymeric SiO ₂ sol gel coating of UF-Al ₂ O ₃ supports; the separation factors drop sharply at higher pressures (> 1 bar).

Example 5

In an apparatus as described in Example 3, the permeative selectivity and achievable flows of a zeolite membrane for the gas mixture of the composition N ₂ : H ₂ : propene: O ₂ : propene oxide = 70:10: 7, 5: 7, 5 , which are similar to the composition of the gases after reaction in the syntheses of propene oxide from propene. Permeation measurements of up to 8 bar pressure difference on the membrane were carried out on MFI membranes at temperatures of 25-150 ° C; Separation factors (propene oxide / residual gas) 4 to 5 were found. The flow rates of these membranes were up to 68 l / m ² h.

Claims (14)

Process for the preparation of propene oxide from propene, characterized in that a gas mixture consisting of nitrogen, hydrogen, oxygen and propene is passed over a catalyst layer which is arranged on a supported, porous membrane, the propene oxide formed after permeating through the hydrophilic membrane and continuously removes the carrier from the membrane carrier on the permeation side by means of an inert sweep gas stream, and the other reaction products and unreacted gases upstream from the reactor, the membrane forming the top layer of a porous ceramic ultrafiltration support with an asymmetrical layer structure and having a pore size of <1 nm and a separation factor for propene oxide / residual gases in the range from 4 to 50, and the sweep gas stream having the same pressure like the gas mixture on the inlet side of the membrane, but has a different partial pressure as the inlet gas mixture, and the pressure is in the range from 1 to 9 bar, and the catalyst temperature is in the range from 25 to 250 ° C. A method according to claim 1, characterized in that the carrier is selected from Al ₂ O ₃ , TiO ₂ , SiO ₂ , ZrO ₂ and mixtures thereof. A method according to claim 1, characterized in that the catalyst is selected from Au-TiO ₂ -SiO ₂ or Au-titanium silicalite. A method according to claim 1, characterized in that the pore size of the asymmetrical carrier decreasing from the permeation side to the input side from 3000 nm to <1 nm is set. A method according to claim 1, characterized in that the pressure is set in a range from 1 to 8 bar and dependent of the membrane types used. A method according to claim 1, characterized in that nitrogen or argon is used as the sweep gas. A method according to claim 1, characterized in that the temperature is in the range of 140 to 185 ° C. A method according to claim 1, characterized in that the ratio N ₂ : H ₂ : O ₂ : propene is in the range 60-80: 5-15: 5-15: 5-15. A method according to claim 1, characterized in that the separation factor is in the range of 5 to 30. Membrane reactor for performing the method according to claim 1, consisting of a porous ceramic Ultrafiltration carrier with asymmetrical layer structure, characterized in that the carrier has a hydrophilic membrane layer on the feed input side with a pore size <1 nm, the one Separation factor for Propene oxide / residual gases in the range of 5 to 50 are reached and that feed side a catalyst layer or catalyst grain in a layer thickness is arranged from 0.1 to 1.5 mm. Membrane reactor according to claim 10, characterized in that the membrane layer is made by hydrothermal in situ hydrolysis a tetraalkyl orthosilicate under autoclave conditions at 150-450 ° C. Membrane reactor according to claim 10, characterized in that the membrane layer is made by applying one of the hydrolysis of metal alcoholates or salts of metal oxide sols gels and crosslinking produced under strongly acidic conditions of the gel when drying and calcining. Membrane reactor according to claim 10, characterized in that the membrane layer is produced by crystallization of silicalite layers by SiO _{2 in} situ crystallization or of aluminum-rich ZSM-5 layers in each case with the aid of seed crystals in a closed system with a suitable for molecular sieve synthesis liquid composition with repeated alternation of liquid and vapor phase for the wearer at 80-200 ° C for 8-100 hours. Membrane reactor according to claim 10, characterized in that the layer thickness of the catalyst in the range of 0.3 to 0.5 nm lies.