Method for making three-phase catalytic processes

 

(57) Abstract:

The invention relates to chemistry, namely the three-phase catalysis processes "gas-liquid-solid". The technical result is overcoming called diffusion inhibition of activity limitations and selectivity without the use of finely dispersed catalysts. In the present invention the process is carried out in the mode of forced flow of reactants through the homogeneous catalytic macroporous membranes with a pore diameter of not less than 50 nm when the volume of pores of not less than 0.05 cm3/cm3. 2 C.p. f-crystals, 2 Il.

The invention relates to the field of chemistry, namely the three-phase catalysis processes "gas-liquid-solid".

Three-phase catalytic processes of "gas-liquid-solid" is traditionally carried out in reactors of periodic action, where the reaction between the gas and liquid flows on the suspended powdered catalyst with vigorous stirring of the reaction mixture / G. C. Bond, Heterogeneous Catalysis: Principles and Applications, Clarendon, Oxford, 1987/. This process is caused by the need to reduce the negative influence of external and internal diffusion of reactants on the activity and selectivity of the reaction.

Suntastic catalysts from the reaction mixture after the reaction.

One of the possible ways of intensification of interfacial mass transfer is to provide forced (under the influence of pressure gradient) flow of reaction mixture through a homogeneous catalytic pores of the membrane. This situation is fundamentally unattainable, if the media used traditional granular porous materials: in the latter case, the transport of the reactants inside the porous grain is purely diffusive (Fig. 1). The different nature of the transport of substances in the pores of the membrane and granular catalyst may lead to differences in the conditions of mass - and heat transfer with forced flow through the porous catalytic membrane capable of providing higher coefficients of mass transfer and heat. If interdiffuse braking on granular catalyst latter circumstance opens the possibility of more effective implementation of the response observed with increasing activity and selectivity in the presence of the porous catalytic membrane.

In Fig. 1 shows a schematic diagram of a mass transfer in a flow of substance through the porous membrane (a) and the layer of the heterogeneous catalyst (B).

Catalytic membranes is about the use of non-porous / U.S. Patent N 3290406, 1966/, mesoporous /J. Peureux, M. Torres, H. Mozzanega, Nitrobenzene liquid-phase hydrogenation in a membrane reactor. Catalysis Today, 25 (1995) 409-415/ and microporous /C. Lange, S. Storck, B. Tesche, J. Catalysis, 175 (1998) 280/ catalytic membranes in heterogeneous catalytic processes.

A common shortcoming of the aforementioned analogues is the need to use expensive metal or ceramic composite membranes, as well as small catalytically active surface of the membrane, close to its geometric outer surface.

Famous work /C. Lange, S. Storck, B. Tesche and W. F. Maier, J. Catalysis, 175 (1998) 280/. Catalytic membrane is anisotropic microporous structure with selective separating layer (nominal pore diameter of about 0.5-1 nm, the thickness of the selective layer of the order of 0.2-0.5 µm), and a catalytically active component (Pt) is located in this layer. These features contribute to the following disadvantages: high hydraulic resistance of catalytic membrane penetrating through the flow of the reaction mixture (hydrocarbons diluted with hydrogen); a small amount of catalytically active component in the membrane (about 110-7mol Pt in the membrane mass around 4-5 g), resulting in a low catalytic activity of HB gaseous and liquid media for solid-phase catalysts in the form of a porous catalytic membrane /Patent RF 2073559 C1, IPC 7 B 01 J 12/00, 1997/. The flow of gas or liquid is directed to the catalytic unit, representing layers spaced corrugated and flat panels coated with the catalyst, with a flat panel made of a porous permeable material. The disadvantage is the high hydraulic resistance of catalytic membrane penetrating through it flow the reaction mixture and low catalytic activity per unit mass of the membrane.

The task to be solved by the invention is the development of the method of performing three-phase catalytic processes, free from the above disadvantages and to overcome caused by diffusion inhibition of restriction activity and selectivity.

To solve this problem is proposed to implement a three-phase catalytic processes in the mode of forced flow of reactants through the homogeneous catalytic macroporous membranes with a pore diameter of at least 50 nanometers when the volume of pores of not less than 0.05 cm3/cm3while catalytic membranes divide the reactor into several areas.

On the basis of application of such membranes mass exchange between reactant which may lead to an increase in the observed activity and selectivity of catalysts.

In the present invention the membrane, has developed a uniform macroporous structure, evenly applied catalytically active component. The membrane has a low hydraulic resistance penetrating through the flow of the reaction mixture, and may contain high (up to several percent relative to the weight of the membrane), the amount of catalytically active component. Catalytic membrane installed in the reactor so that the reaction mixture passes through the pores of the membrane under the action of excess pressure of the reaction gas and, if necessary, recycle.

The invention is illustrated by the following examples:

Example 1.

The oxidation of sulfide ions by oxygen in the water

The oxidation reaction of sulfide ions is carried out in aqueous solutions at room temperature in the presence of a catalyst is a sodium salt of tetrachlorosilane cobalt (Na-TSFC) deposited on a polymeric microfiltration membrane mifil (thickness of the membrane 120 μm, a pore diameter of 0.4 μm, specific surface area of 24 m2/g). Catalytic oxidation of sulfide ions proceeds according to the equation (A):

S2-+O2--->S,SO32-, S2O

The deposition of catalyst on the membrane is carried out by adsorption of Na-TSFC from aqueous solutions at room temperature, receiving a catalytically active macroporous membranes with the content of Na-TSFC 0.2 to 60 mg per 1 g of the membrane carrier.

Sample catalytic membranes prepared as described above and containing adsorbed Na-TSFC in the amount of 2.6 mg/g, is placed in a constant-temperature membrane reactor with a magnetic stirrer (Fig. 2) where is poured 250 cm3aqueous solution of Na2S with a concentration of 0.04 mol/l Solution pH is 13. After that, the vacuum reactor, and then it serves oxygen at a pressure of 0.12 MPa. An aqueous solution of Na2S under the action of excess pressure of oxygen permeates through the membrane and recycle in the system (the valve at the outlet of the reactor is open). In Fig. 2. principle diagram of the catalytic membrane reactor.

The catalyst in the solution before and after the membrane is absent, indicating a strong adsorption on the membrane. Catalytic conversion of S2-with the passage of the solution through the membrane is 15% at the time of the con is the thief Na2S through catalytic membrane (valve at the outlet of the reactor is closed). Duration of experience 3 hours. Catalytic oxidation of S2-does not leak.

Example 3 (comparative).

Catalytic membrane tested in examples 1 and 2, cut into pieces of size 2 x 2 mm and tested in conditions similar to example 2. Duration of experience 3 hours. Catalytic oxidation of S2-does not leak.

Example 4.

The reaction of hydrogenation of sunflower oil

The reaction of hydrogenation of sunflower oil flows Nickel and palladium catalysts according to the following scheme:

< / BR>
The target reaction - sequential hydrogenation of the double bond C=C in the triglycerides of polyunsaturated fatty acids is accompanied by undesirable side processes, the most important of which is the isomerization of the initial CIS-form to TRANS-form. The presence of TRANS-isomers in Margarines and cooking fats increases the risk of coronary cardiovascular disease, and therefore should be minimized. The purpose of this step is to reduce the output of the TRANS-isomers in the hydrogenation of sunflower oil on palladium catalysts.

Catalytic membrane containing 2 wt.% palladium is prepared by adsorption of palladium from the benzene solution Pd3(OAc)6at room temperature the membrane mifil. The dried samples restored in aqueous solution KBH4, washed with distilled water and dried in vacuum at room temperature.

Catalytic membrane, prepared as described above, is installed in the reactor, similar to those shown in Fig. 2. The reaction of hydrogenation of sunflower oil is carried out in the mode of oil flow through the membrane at a temperature K and hydrogen pressure of 0.35 MPa, analyzing the concentration of CIS - and TRANS-isomeric triglycerides of fatty acids 18: 1 when changing the degree of conversion of the original triglyceride 18:2 (CIS-form). PR is CLASS="ptx2">

Example 5 (comparative).

The same procedure used for the preparation of palladium rolled congestion on granular carbon media Sibunit /Patent RF N 1706690, IPC B 01 J 20/20, publ. 23.01.92, BI N 3/ with an average radius of pores of 40 nm. The catalyst containing 2 wt.% palladium. Before use in the reaction of hydrogenation of sunflower oil the Pd/C catalyst is crushed to particles less than 10 microns.

The reaction of hydrogenation of sunflower oil in the presence of Pd/C catalyst, prepared as described above is carried out in a static laboratory reactor with stirring at a temperature of C and hydrogen pressure of 0.35 MPa.

When the degree of conversion of the original triglyceride (CIS-18:2) 63 % receive a hydrogenation product containing 31% of the CIS isomer and 18% TRANS-isomeric triacylglycerols 18:1.

Example 6.

The reduction of nitrate ions by hydrogen in water

The reduction of nitrate ions by hydrogen in water in the presence of bimetallic palladium-copper catalysts flows through the series-parallel scheme

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Catalytic membrane is prepared by impregnation of the ceramic membrane carrier (disk with a diameter of 45 mm and a thickness of 4.6 mm, dia is it drying at room temperature, oxidation by air at K and recovery aqueous solution of NaBH4at room temperature.

In terms of solution flow NaNO3through catalytic membrane (valve at the outlet of the reactor is open). 90% conversion of NO3-reach for 110 minutes.

Example 7 (comparative).

Catalytic membrane containing 1.6 wt.% palladium and 1.2 wt.% copper, are placed in a reactor similar to those shown in Fig. 2, and experience in the reduction reaction of the nitrate ions. To do this, poured into the reactor an aqueous solution of sodium nitrate and serves hydrogen. In the first experiment the valve at the outlet of the reactor was closed, resulting in a porous space of the membrane with the active component Pd-Cu, located on the pore walls is available for the reactants only due to diffusion.

At a temperature of 298K, hydrogen pressure = 1.1 ATM, initial concentration of nitrate-ions = 200 mg/l and the volume of solution 100 cm3that is a 90% conversion of NO3-was achieved at 1100 minutes.

Thus, the proposed method of implementation of the three-phase catalytic processes in the mode of forced flow of the reaction solution through the catalytic macroporous membrane leads to mnogo the th industry.

1. Method for making three-phase catalytic processes in the presence of the porous catalytic membrane, wherein the process is carried out in the mode of forced flow reactor through a homogeneous catalytic macroporous membrane.

2. Method for making three-phase catalytic processes under item 1, characterized in that the use of membranes with a pore diameter of not less than 50 nm when the volume of pores of not less than 0.05 cm3/cm3.

3. Method for making three-phase catalytic processes for PP.1 and 2, characterized in that the catalytic membranes divide the reactor into several zones.

 

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5 cl, 1 dwg

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