CS254005B1 - Process for producing alkene oxides - Google Patents

Abstract

The method of producing alkene oxides with the advantage of propylene oxide by electrolysis is that it is used to influence the size of the ratio of anode space and anode surface by changing the ratio of flowing anolyte and catholyte in the range of 3:1 to 1:6, preferably in the range of 2:1 to 1:2 by weight, while the regulation of the mutual ratio of anolyte to catholyte is ensured by sampling the anolyte in place, where alkenhalohydrin is formed. The mentioned procedure improves the energy balance of the process.

Description

254005

SUMMARY OF THE INVENTION The present invention relates to a process for the preparation of alkene oxides by a known electrolysis process by utilizing the established fact that partial removal of the reaction components from the anode compartment of the cell maintains the concentration of alkene chlorohydrin at a level below the critical concentration of the resulting reactions and reduces the energy efficiency of the process. The use of this finding also makes it possible to increase the electrical load of the electrolytic cell, which is essential for the practice of this process. By producing the alkene oxides of the known state of the art, it is possible to carry out essentially two different technological processes, either by the addition of hypochlorous acid to the alkene followed by dehydrochlorination of the resulting chlorochlorohydrin, or by direct oxidation of alkenes. Direct oxidation in the case of higher alkenes, e.g., propylene, is problematic from the point of view of operation because the extracts are very low. The preparation of alkene oxides by means of chlorohydrin by a non-electrolytic process in two stages also has some deficiencies, especially in terms of ecology, since a large number of chlorides are released by the corresponding hydrochlorohydrin, which are introduced into the water streams and the wastewater resistance increases.

It is advantageous to combine the electrolytic preparative halogenohydrin with its dehydrogenation by the hydroxide formed in the catalyst and to recirculate the electrolyte through the electrolytic cell, practically no waste. This idea is the subject of several patents, but in terms of yields and the selected electrolyser design or structure. hydro-dynamics of electrolyte in electrolytic reaction zones, there is still a wide scope for substantially improving the conditions for utilizing this process.

The electrolytic preparation of ethylene chlorohydrin and the anodic oxidation of ethylene to ethylene glycol have already been reported in the patents of McElvya (U.S. Pat. No. 1,253,615, 1,253,617). Glasstone S. Ind. Chemist 7, 315 (1931) exemplifies the simultaneous chlorination and oxidation of inorganic substances in an electrolyser for the preparation of ethylene chlorohydrin. Patankar et al. (J. Sci.Ind. Res. 11B, 365 [1952]) investigated the current yields of electrolysis of NaCl chlorohydrin solutions and an optimum of 84% found at a flow rate of 22.5 mA / cm 2 with 10% NaCl solution. at 1 ° C. Kalinin and Stender (J. Chim. 19, 1045 [1946]) worked with relatively large current densities and a high NaCl concentration. They used porous diaphragm, graphite anodes. At an initial concentration of NaCl of 2 mol / l, a current density of 74 mA / cm 2 and a temperature of 25 ° C, ethylene chlorohydrin yields a current yield of 86 ppm. At even higher current densities, the current yield decreased. Selvig and Ibl (Chem. Ing. Techn. 42, 4, 180 [1970]) observed current yields depending on the electrolyte concentration, electrolysis size and concentration of chlorohydrin formed. They have found that the reduced anode space volume ratio to the anode flat leads to a deterioration of the current yield relative to the increasing chlorohydrin concentration in the anode compartment.

The electrolytic cell for the electrochemical oxidation of alkenes to alkene oxides may be with a diaphragm, ion exchange membrane, without a diaphragm, or may be of gravity type.

The reactions occurring in the anolyte and resulting in the formation of halohydrin are described, for example, in U.S. Pat. 3 288 692, Brit.pat. 1049 756, Franc. pat. 1,375,298, NSRpat. 1 768 443 and 1 618 405. The term anolyte refers to an aqueous electrolytic medium which is in the vicinity of the electrolyte cell anode, i.e. the portion of the aqueous electrolyte in which the halohydrin is formed. The overall reaction carried out in the anolyte can be summarized as follows:

2 MX -) - C = C - H 2 O 0 where M is an alkali metal X is a halogen.

Zatia! as the reactions in which haloenhydrin is formed near the anode, water is electrolysed on the cathode of the electrolytic cell, forming hydro-C - (- HX + 2M + + 2e ~

X is OH xyl ion and hydrogen. Thus, the cathodic electrolyte is alkaline. When the intermediate halohydrin formed in the anolyte is contacted with an alkaline catholyte, dehydrohalogenation takes place with formation of alkene oxide, water and the halide ion is regenerated. In summary, the reaction taking place in the e-cell can be written: electr. -C = C-h H 2 O --------- energy /

-C-C- "i" H? / UO 254005

However, in addition to the indicated reaction, byproducts are formed in the electrolysis (e.g., dihalo derivatives of alkene by the reaction of halogen with the double carbene of the alkene, the hydroxy compounds due to the hydration of the resulting alkene oxide, and the like). The conditions of electrolysis and subsequent separation of the alkene oxide also affect the formation of byproducts.

The metal halide used as the electrolyte must be water soluble, as well as the corresponding hydroxide. Usually, they use fluorides, chlorides, bromides or iodides of metals of sodium, potassium, lithium, barium, calcium, strontium or magnesium. Most commonly, alkali metal chlorides, especially sodium chlorides, are used because of the good solubility of their hydroxides as well as their availability. The concentration of the solutions may range from 2 to 20% (NSR patent 1 768 443, 1 618 405, 2 020 590). The rate at which the electrolyte is fed to the electrolyser can vary within a wide range of 4 to 80 cm 3 / min (NSR Pat. 1 618 405), 10 to 100 cm 3 / min (NSR Pat. 1 290 926), 20 to 200 cm 3 / min. min (NSR Pat. 1 768 359) on a 1dm2 anode surface.

Examples of suitable organic compounds which can be electrolytically epoxidized are the alkenes of the homologous series CnH2n, such as ethene, propene, butene, pentene, in which " n " the linkage is not a terminal branched chain alkene. The alkene used may not be completely pure and may contain the corresponding alkane such as ethane, propane and the like, which do not interfere with the oxidation reaction. The rate of addition of the alkene depends on the rate of reaction to the corresponding halohydrin or excess alkene is added. The electrolytic cell operates in a wide range of temperatures and pressures. As a rule, the temperature is in the range of 30 to 90 ° C, if it can be atmospheric even up to 2 MPa (U.S. Pat. No. 3,288,692). and lower (German Pat. No. 1,768,443).

The anodes used are electrodes of graphite, platinum, titanium coated with a noble metal layer such as platinum and others (NSR Pat. No. 1,618,405, 2,020,590, 1,290,926).

The cathode may be any free material that is chemically resistant to liquors. It is usually made of steel or stainless steel and can be used with or without a diaphragm. The diaphragm is mostly used in asbestos, polyethylene, polyvinyl compounds and the like.

The description, composition and operation of various types of electrolytic cells are exhaustive in British Patent 1,049,756.

Each of the above mentioned washing problems, characterized by a reduced current yield problem while reducing the volume ratio of the a-node space to the anode flat, has consequently limited the current load.

However, to increase this ratio, i.e., the anode anodic volume by the previously known processes, is carried out so that the inter-electrode distance is increased, which in turn results in increased working tension, which substantially affects the electrolysis energy balance. From the cited literature and patent data, the ratio of efflux of anolyte to catholyte is not defined. NSR Pat. 1 243170, 1 258 856, 2 020 590,1 295 535 disclose only the extreme possibilities, but the entire volume of the anolyte passes through the diaphragm to the cathode space, or when the cathode and anode compartment is completely separated by a membrane, none yes-lyt and the dehydrohalogenation reaction takes place outside the electrochemical cell.

According to the invention, this undesirable effect while maintaining the current yield is eliminated by the fact that from the anode space of the electrolysis load, a certain podielanolyte is continuously withdrawn and mixed with the catholyte outside the electrolysis where the dehydrohalogenation of alkene halohydrin is complete and improved hydrodynamics of e-electrolyte during electrolysis.

A method for producing alkene alcohols from large-scale alkenes! a system comprising an anode, a cathode and a diaphragm, using a halide-containing electrolyte, characterized in that it controls the anolyte / catholyte relative to each other from the electrolytic reaction zone in the range of 3: 1 to 1: 6 by weight, preferably in the range of 2: 1 to 1: 2, wherein the regulation of the α-ololyte to catholyte ratio is provided by the odomanomanolyte at the site where the alkene halohydrin is formed. The advantage of the process according to the invention is that the ratio of flowing anolyte and anolyte flowing through it may seem to increase the ratio of the α-node space to the anode surface without increasing the working capacity of the electrolyser.

The anolyte drain is located at one height with the cathode and the tube is inserted into the reaction zone. It is important to maintain the desired hydrodynamic conditions of the electrolyte in the electrolytic space. The electrolyser is designed so that the respective alkene passes through the porous anode surface, and the anolyte from the bottom of the electrolyser is directed along the α-node surface.

The technological procedure illuminating the essence of the invention is schematically shown in the figure:

The electrolyte is fed through the circulation pump 13 via line 2 to the electrolyser, whereby an electrochemical reaction occurs with the supplied alkene through the inlet 10 to form alkene halohydrin. Part of the electrolyte passes through diaphragm 12 and cathode 11, where the cathode 11 undergoes electrochemical decomposition of water. The resistance of the diaphragms 12 also determines the ratio of effluent anolyte 3 and catalyst 4 from the electrolytic reaction zone. This resistance can be changed by the density of the material

Claims (1)

254 7 lu or a type of diffragm material. The drain through the outlet 3 is fed to a mixer and separator 14a where the hydrogen and the unreacted olefin are separated by the outlet 6. The catholyte is also discharged into the mixer and discharged. In extractors 14b, the desired olefinic oxide 5 is separated. The electrolyte after separation of the reactants is recirculated through the line pump 13 to the process. EXAMPLE 1 Propylene oxide was prepared on an electrolysis machine schematically shown in the figure by the following procedure: A 10% aqueous solution of NaCl was fed into the anode compartment of the electrolysis at 25 ° C at a rate of 35 cm 3 / min. Propene conc. 99.5% was fed through a porous graphite anode at a rate of 0.14 g / min. The current load was 9A, the cell voltage of 3.5V. The anolyte portion did not pass through the cathode, and the cell was discharged outside the electrolysis. The mutual ratio of anolyte to catholyte effluent was 1: 5. After mixing the anolyte streams and the catholyte, propylene chlorohydrin reacted to propylene oxide. From the 2.1 liter reaction mixture, 8.87 gpropylene oxide was obtained by rectification and freeze-drying. Theoretical propylene oxide yield calculated from time and amperes, load was 9.75 g. 90.97% w / w of propylene oxide was obtained. Example 2 Under conditions as in Example 1, an 8.5% solution of NaCl was fed to the electrolytic cell at a rate of 44 cm 3 / min. Propene was dosed at 0.27 g / min. The current load was 17.1 Å, the cell 4 V was equal. The mutual ratio of anolyte effluent to catalyst was 3: 1. Treatment of 3.3 liters of mixed anolyte / catholyte solution yielded 21.97 g of propylene oxide. The theoretical yield, under the stated conditions, of propylene oxide 23.16 g, of which the calculated current yield was 94.86% by weight. EXAMPLE 3 An electrolytic ethylene oxide was produced on the apparatus of the figure as follows: Under conditions such as Example 1, an 8.5% NaCl solution was fed to the electrolysis apparatus at a rate of 40 cm 3 / min. Etene and conc. 99.6% was dosed at 0.16 g / min. The current load was 15A, cell voltage of 3.7V. The ratio of anolyte to catholyte effluent was 2: 1. Treatment of 3.6 liters of mixed anolyte / catholyte solution yielded 16.73g of ethylene oxide. The theoretical yield of ethylene oxide was 18.49grams, of which the calculated yield yielded 90.48% by weight. SUBJECT A method for producing alkene oxides from alkenes of a large-scale system consisting of an anode, a cathode and a diaphragm, using a halide-containing electrolyte, characterized in that the anolyte and catholyte from each other are electrolytically recovered from the reaction zone in the range of 3: 1 to 1: 6 weight, preferably in the range of 2: 1 to 1: 2, wherein the control of the anolyte to catholyte ratio is ensured by collection of the anolyte at the point where alkene halohydrin is formed. 1 sheet of drawings