WO1995035161A1

WO1995035161A1 - A membrane reactor

Info

Publication number: WO1995035161A1
Application number: PCT/AU1995/000348
Authority: WO
Inventors: Alastair Mcindoe Hodges; Anton Launikonis; Albert Wai-Hing Mau
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 1994-06-17
Filing date: 1995-06-16
Publication date: 1995-12-28
Also published as: AUPM631494A0

Abstract

A membrane reactor (10) for gas or gas/liquid reaction comprising a reaction chamber (12), a permeable membrane (14) in the reaction chamber, a catalyst supported in the permeable membrane, a gaseous reactant inlet (46) to the reaction chamber opening to one side of the membrane and a liquid inlet (16) to the reaction chamber opening to the other side of the membrane, means (52) to supply pressurized gaseous reactant to the gaseous reactant inlet, a supply line (30, 32, 34) for the liquid connected to the liquid inlet, and wherein the pressurized gaseous reactant supply means (52) is also connected (54) to the liquid supply line whereby to pressurize the liquid and at least substantially balance the pressure across the membrane (14). The invention also extends to a method of conducting gas or gas liquid reaction in a membrane reactor wherein the liquid supplied to the other side of the membrane (14) is pressurized by the pressurized gaseous reactant which is supplied to the one side of the membrane to at least substantially balance the pressure across the membrane.

Description

A MEMBRANE REACTOR

Field of the Invention

This invention relates to a reactor for carrying out chemical reactions that use a gas reactant, a liquid which may be a reactant, and a catalyst and is particularly concerned with such a reactor in which it is desirable to work at pressures greater than atmospheric. In the reactor, the catalyst is immobilized in a membrane, with the liquid contacting one side of the membrane and the gaseous reactant contacting the other side. Gas and liquid diffuse into the membrane and come into contact with the catalyst where reaction takes place.

Background of the Invention

Carrying out chemical reactions in which three phases, gas, liquid and solid, have to be maintained in intimate contact on a continuous basis presents many problems. In fixed bed type reactors it is difficult to maintain the correct flow patterns because chamielling of the gas and liquid can occur as well as clumping of the catalyst and catalyst loss from the support surface due to abrasion. These difficulties can be overcome by using a membrane impregnated with the catalyst and permeable to the gas and liquid as a combined phase contactor and catalyst support.

There have been many proposals concerning catalytic membrane reactors, in which the reactors are either run in batch mode, with the liquid reservoir in contact with the membrane, semi-batch mode where a circulation pump is used or a continuous mode where separate liquid and gas feeds are supplied to opposite sides of the membrane.

It is often desirable to run a membrane reactor using a gas pressure substantially higher than atmospheric pressure in order to increase the rate of reaction. In a conventional membrane reactor the membrane must be strong enough to withstand the pressure difference between the gas and liquid streams, which limits the choice of membrane material and the pressure that can be used. For example, Japanese Patent Sho 54-29423 describes a reactor consisting of a carbon cloth membrane, impregnated with a noble metal catalyst and coated with a resin layer to prevent liquid leakage but allow gas to pass through. This reactor can only be run at pressures close to atmospheric. It would be desirable to be able to run a membrane reactor at high pressure with a small or zero hydrostatic pressure differential across the membrane, allowing a much greater range of membrane materials to be used and a pressure range limited only by the rating of the membrane housing and associated equipment.

Summary of the Invention

According to the present invention, there is provided a membrane reactor for gas or gas /liquid reaction comprising a reaction chamber, a permeable membrane in the reaction chamber, a catalyst supported in the permeable membrane, a gaseous reactant inlet to the reaction chamber opening to one side of the membrane and a liquid inlet to the reaction chamber opening to the other side of the membrane, means to supply pressurized gaseous reactant to the gaseous reactant inlet, a supply line for the liquid connected to the liquid inlet, and wherein the pressurized gaseous reactant supply means is also connected to the liquid supply line -whereby to pressurize the liquid and at least substantially balance the pressure across the membrane.

Further according to the present invention, there is provided a method for conducting gas or gas /liquid reaction in a membrane reactor comprising a permeable membrane having a catalyst supported therein, the method comprising supplying a pressurized gaseous reactant to one side of the membrane and supplying liquid to the other side of the membrane whereby the gaseous reactant reacts at the membrane, optionally with the liquid if the liquid is a reactant, and wherein the liquid supplied to the other side of the membrane is pressurized by the pressurized gaseous reactant to at least substantially balance the pressure across the membrane. By the present invention, the membrane reactor is such that there need be no or substantially no hydrostatic pressure gradient across the membrane so that relatively mechanically weak membranes can be used even at high pressures.

The reactor can be used in a semi-batch or continuous mode by utilising in either case a reservoir of the liquid. In a semi-batch mode the reservoir can be isolated from the membrane while it is pressurized by the gaseous reactant. In a continuous mode, the gaseous reactant may continuously pressurize the reservoir while the liquid is supplied to the membrane. A level sensor may be provided in the reservoir to actuate a liquid supply pump for the reservoir. This type of continuous mode operation is particularly advantageous in that the reservoir may act as an accumulator damper, lessening pulsations in the liquid supply line to the membrane.

The membrane used in the present invention can be made of any material which has the required properties and is sufficiently stable under the required process conditions. In the present invention, the membrane material should be permeable to both the gas and the liquid and capable of containing the reaction catalyst. For example, such a material can be an ionomer such as perfluorocarboxylate polymer (e.g. Flemion) and perfluorosulfonate polymer (e.g. Nafion), other ion exchange materials (such as Amberlyst, Amberlite, zeolites) or other material that is capable of being formed into a permeable membrane and capable of containing the catalyst. The membrane can also be fabricated from a composite material such as one combining one or more materials, for instance polymers, with other types of materials, for example a ceramic or glass material. The said membrane can be in any convenient form, such as for example in the form of a film, a sheet in for example the form of a pillow, or tubular for example in the form of hollow fibres or a tube, as is well known to those skilled in the technology of membranes. (Remion is the registered trade mark of Asahi Glass Co. Ltd., Japan; Nafion is the registered trade mark of E. I. DuPont de Nemours & Co., U.S_A; Amberlyst and Amberlite are registered trade marks of Rohm and Haas Co. U.SA.).

The catalyst supported in the membrane can be either ionic or solid particles. Ionic catalysts can be directly ion-exchanged into an ionomeric membrane such as a perfluorosulfonate polymer while solid paniculate catalysts can be formed by introducing the ions into an ionomeric membrane and reacting them to produce the particles. The catalyst selected will be dependent upon the reaction to be performed.

Brief Description of the Drawing

One embodiment of a membrane reactor in accordance with the invention will now be described by way of example only, with reference to the accompanying drawing which is a schematic representation of the membrane reactor.

Detailed Description of the Drawing

The membrane reactor 10 comprises a housing 12 in which is supported a coiled tubular reactor membrane 14 of gas and liquid permeable material. The membrane 14 comprises a tube of polyperfluorosulfonic acid ionomer (Nafion) and has a catalyst such as platinum metal supported in the ionomer. Such membranes have previously been described and for convenience only will not be described further herein except insofar as they are described in the Examples. Other membrane materials and catalysts are suitable for use in the membrane reactor. The tubular membrane 14 has an inlet 16 and an outlet 18 at respective ends.

Connected to the outlet 18 is an outlet line 20 having a flow sensor 22, a let-down valve 24 and a shut-off valve 26 therein. The flow sensor measures the liquid flow through the outlet line 20 and therefore through the tubular membrane 14. The let¬ down valve 24 drops the pressure in the outlet line 20 from the reactant pressure to an appropriate output pressure. Other pressure reducing means may be adopted. The flow sensor 22 and let-down valve 24 are connected to an electronic process controller 28 and together these components can form a feedback loop to regulate the flow of liquid through the tubular membrane. However, it is to be understood that this type of flow regulation is not essential to the invention and may not be necessary in practice.

A liquid supply line 30 is connected to the membrane inlet 16. The supply line 30 leads from a liquid reservoir 32 which is batch filled via a fill tube 34. Valves 36 and 38 are provided in the supply line 30, respectively upstream and downstream of the reservoir 32. Valve 36 is opened and valve 38 closed during batch filling of the reservoir, and valve 36 is closed and valve 38 opened to supply the liquid from the reservoir 32 to the interior of the tubular membrane 14.

For continuous operation, the reservoir 32 must be continuously filled and, in a modification, a pump 40 is shown connected to the reservoir 32 along a dashed line 42. The connection is shown schematically only since in practice the pump 40 would not be connected to the outlet from the reservoir, but to a separate inlet via appropriate valves. The pump 40 is connected to a storage vessel 44 for the liquid and would be controlled in well-known manner by a level sensor (not shown) in the reservoir 32. The pump 40 will have a capacity such that the liquid can be pumped from the storage vessel 44 at a rate sufficient to maintain the requisite level in the reservoir 32.

As explained in detail hereinafter, the reservoir 32 is pressurized to the operating pressure of the membrane reactor, and in the continuous operation mode the reservoir also acts as an accumulator damper, lessening pressure pulsations in the liquid supply line 30.

Gas reactant is supplied to the reactor housing 12 exteriorly of the tubular membrane 14 through an inlet 46 by way of a control valve 48 in a gas reactant supply line 50. The supply line 50 is connected at 52 to a source (not shown) of the gas reactant at the requisite operating pressure of the membrane reactor. Thus the source may comprise a pressurized storage vessel and controllable pressure reduction means and/or appropriate means to increase the storage pressure to the desired pressure in a controlled manner. The pressurized gas reactant supply line 50 is also connected to the liquid reservoir 32 by way of a branch line 54 having a control valve 56 and a vent valve 58 therein. By this means it is possible to ensure that the gas reactant and the liquid are at substantially the same pressure so that the pressure across the tubular membrane 14 in use is at least substantially balanced. This has the substantial advantage that the operating pressure of the membrane reactor 10 is not limited by the strength of the reactor membrane 14 and high pressures, for example over 6900 kPa, can be used.

The membrane housing 12 and liquid reservoir 32 can be heated, for example externally by a heating jacket (not shown). A thermocouple sensor 61 measures the temperature inside the housing 12. A thermocouple sensor 60 measures the temperature of the liquid in the liquid supply line 30 at the inlet end of the tubular membrane 14. The liquid supply line 30 may also be heated.

In a preferred use, pressurized liquid reactant from the reservoir 32 flows through the supply line 30 and the tubular membrane 14. In the membrane it comes into contact with the catalyst supported therein as well as with gaseous reactant supplied to the membrane housing 12 through the inlet 46. The pressurized gaseous and liquid reactants diffuse into the membrane to contact the catalyst therein, where the desired reaction occurs. The product of the reaction passes through the bore of the membrane to the outlet 18 from where it passes through the let-down valve 24 for collection. Liquid leakage through the membrane 14 is minimized as an equilibrium vapour pressure of the liquid components is maintained in the membrane housing, removing any driving force for diffusion. Any liquid that does collect in the membrane housing 12 can be drained through a drain valve 62.

Examples

The foUowing examples were performed in the described membrane reactor 10 under the specified conditions. Example 1

Cyclohexene, 25 wt% in methanol, was converted to cyclohexane using hydrogen as the reactant gas at 22 ^βC, 1920 kPa and at a flow rate of 0.2 ml/min. A tubular membrane of polyperfluorosulfonic acid 3 mm in diameter, 500 mm in length and loaded with 1 wt% platinum was used as the catalytic membrane. The rate of reaction was 0.45 mmoles/min giving a conversion of 96%.

Example 2

Cyclohexene, 25 wt% in methanol, was converted to cyclohexane using hydrogen as the reactant gas at 60.6 °C, 2830 kPa and at a flow rate of 0.75 ml/min. A tubular membrane of polyperfluorosulfonic acid 3 mm in diameter, 500 mm in length and loaded with 0.5 wt% platinum was used as the catalytic membrane. The rate of reaction was 1.46 mmoles/min giving a conversion of 82%.

Example 3

Cyclohexene, 25 wt% in methanol, was converted to cyclohexane using hydrogen as a reactant gas at 22 °C, 3170 kPa and at a liquid flow rate of 0.51 ml/min. A composite tubular membrane 3 mm in diameter and 200 mm long was used as the catalytic membrane. The composite membrane consisted of a porous teflon tube with 55 milligram of polyperfluorosulfonic acid deposited on its inner surface by solvent casting. The polyperfluorosulfonic acid contained 3 wt% platinum. The rate of reaction was 0.20 mmoles/min giving a conversion of 17.1% and a turnover frequency (moles of product per mole of platinum per second, TOF) of 0.41 sec ^'**.

Example 4

Cyclohexene, 25 wt% in methanol, was converted to cyclohexane using hydrogen as a reactant gas at 60 °C, 2760 kPa and at a liquid flow rate of 0.67 ml/niin. A polyperfluorosulfonic acid membrane in the form of a hollow fibre 0.3 mm in internal diameter and 520 mm long and containing 0.5 wt% platinum was used as the catalytic membrane. The rate of reaction was 0.36 mmoles/min giving a conversion of 23.3% and a TOF of 1.52 sec^"1.

Example 5

Ethylene gas was reacted to a mixture of products consisting mainly of 1-butene, trans-2-butene and cis-2-butene at 60 °C, 2690 kPa and with water flowing through the tube bore at a rate of 0.6 to 1.0 ml/min. A composite tubular membrane 3 mm in diameter and 200 mm long was used as the catalytic membrane. The composite membrane consisted of a porous teflon tube with 80 rnilligram of polyperfluorosulfonic acid deposited on its inner surface by solvent casting. The polyperfluorosulfonic acid contained 0.25 wt% Pd(phen)₂ ^2' as catalyst. The rate of formation of butenes was 0.025 mmoles/min giving a conversion of 12.3% and a TOF of 0.13 sec^'1 .

Example 6

Methyl cyclohexanone 5 wt% in methanol, was converted to methyl-6-oxoheptanoate plus other uncharacterised products using oxygen as a reactant gas at 60 °C, 1620 kPa and a liquid flow rate of 0.43 ml/mm.. A tubular membrane of polyperfluorosulfonic acid 3 mm in diameter and 400 mm in length and loaded with 2.2 wt% ferric ion as the catalyst. The rate of reaction was 0.010 mmoles/min giving a conversion of 8.3% and a TOF of 2.0 x 10^{' 1}.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within its spirit and scope.

Claims

CLAIMS:-

1. A membrane reactor for gas or gas /liquid reaction comprising a reaction chamber, a permeable membrane in the reaction chamber, a catalyst supported in the permeable membrane, a gaseous reactant inlet to the reaction chamber opening to one side of the membrane and a liquid inlet to the reaction chamber opening to the other side of the membrane, means to supply pressurized gaseous reactant to the gaseous reactant inlet, a supply line for the liquid connected to the liquid inlet, and wherein the pressurized gaseous reactant supply means is also connected to the liquid supply line whereby to pressurize the liquid and at least substantially balance the pressure across the membrane.

2. A membrane reactor according to claim 1 wherein the liquid supply line includes a reservoir for the liquid which is connected to the pressurized gaseous reactant supply means.

3. A membrane reactor according to claim 2 which includes means in the liquid supply line between the reservoir and the liquid inlet to isolate the reservoir from the liquid inlet.

4. A membrane reactor according to claim 2 including a pump for supplying the liquid to the reservoir.

5. A membrane reactor according to claim 1 wherein the membrane comprises an ionomeric material.

6. A membrane reactor according to claim 5 wherein the ionomeric material is selected from perfluorocarboxylate polymer and perfluorosulfonate polymer.

7. A membrane reactor according to claim 1 wherein a liquid outlet from the reaction chamber is connected to means for reducing the pressure of the liquid.

8. A membrane reactor according to claim 7 wherein the pressure reducing means comprises a let-down valve.

9. A membrane reactor according to claim 8 wherein the liquid outlet is connected to a flow sensor, and the flow sensor and let-down valve are connected to an electronic process controller to form a feedback loop for regulating the flow of liquid through the reaction chamber.

10. A membrane reactor according to claim 1 wherein the membrane is tubular, the one side of the membrane is the exterior surface of the tubular membrane and the other side of the membrane is the interior surface of the tubular membrane.

11. A membrane reactor according to claim 1 wherein a temperature sensor is provided in the reaction chamber.

12. A membrane reactor according to claim 1 wherein the pressurized gaseous reactant supply means comprises a pressurized storage vessel.

13. A method for conducting gas or gas/liquid reaction in a membrane reactor comprising a permeable membrane having a catalyst supported therein, the method comprising supplying a pressurized gaseous reactant to one side of the membrane and supplying liquid to the other side of the membrane whereby the gaseous reactant reacts at the membrane, optionally with the liquid if the liquid is a reactant, and wherein the liquid supplied to the other side of the membrane is pressurized by the pressurized gaseous reactant to at least substantially balance the pressure across the membrane.

14. A method according to claim 13 wherein the liquid is a reactant.

15. A method according to claim 13 wherein the supply of liquid is intermittent whereby the reaction is performed in semi-batch mode.

16. A method according to claim 13 wherein the supply of liquid is continuous whereby the reaction is performed in continuous mode.

17. A method according to claim 16 wherein the liquid is pressurized in a reservoir which acts as an accumulator damper.

18. A method according to claim 13 wherein the liquid is passed through a tubular membrane.