NL8003528A - PROCESS FOR PREPARING ETHYLENE GLYCOLESTERS. - Google Patents

Description

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Process for preparing ethylene glycol esters.

The invention relates to an improved process for the preparation of ethylene glycol esters by oxidation of the olefin ethylene with molecular oxygen or a molecular oxygen-containing gas in acetic acid at a temperature of about 125-200 ° C in the presence of a tellurium catalyst combination and a suitable source of bromine, whereby a high reaction speed and a low formation of polymeric and other heavy by-products are obtained * By an appropriate control of the acetoxylation reaction at a partial oxygen pressure of 0.14-0.7 kg / cm absolute at a reactor outlet, a 1 800 3 5 28 ethylene partial pressure of 1.05-3.5 kg / cm at the reactor outlet with a total concentration of tellurium per se in the reaction system between about 0.1 and 0.5 wt .% was found to have a high ratio, compared to the total tellurium cation in solution, of a highly active organic complex tellurium oxidation catalyst compound, which meets certain analytical specifications, is shaped and maintained, providing the specified process benefits.

Numerous processes have already been described and proposed for the preparation of glycol esters, including ethylene glycol esters, by oxidation with molecular oxygen of olefins, such as ethylene, in the presence of a carboxylic acid, such as acetic acid, and in the presence of a tellurium catalyst and a halogen -source. Such tellurium-catalyzed processes described in the patent literature, while providing feasible methods for the acetoxylation of olefins in the liquid phase, do not yield both high reaction rates and high selectivity over the glycol esters with an associated reduction in yield. unwanted high molecular by-products, which lead to a decrease in yield and poor practicality.

U.S. Pat. Nos. 3,479,395 and 3,637,515 disclose that olefins can be oxidized to glycols and glycol esters in the liquid phase with a tellurium dioxide catalyst having a source of halide ion, preferably chloride.

US patent 3,668,239 describes the oxidation of olefins with a special catalyst combination of tellurium and a form of bromine, which imparts a pH to the reaction medium of less than 2.0 at 25 ° C upon dilution with water in a weight ratio of 10: 1.

US Patent 3,689,535 describes a process for preparing ethylene glycol esters by contacting a mixture of ethylene, bromine or chlorine and oxygen in the presence of a carboxylic acid and a metal cation of variable valence of Te, Ce, Sb , Mn, V, Ga, As, Co, • ·

Cu, Se or Ag.

Other US patents describing the preparation of glycol esters by molecular oxidation of an olefin in a carboxylic acid medium using a tellurium catalyst in combination with halogen using varying oxidation, recovery and purification methods are the US patents 3,715,388, 3,715,389, 3,743,672, 3,789,065, 3,907,874, 3,985,795, 4,045,477 and 4,073,876.

The ethylene glycol esters obtained by the process of the invention find many important applications, for example as solvents and plasticizers, and for the preparation of ethylene glycol or vinyl acetate.

Surprisingly and in contradiction to the already known processes for the tellurium-catalysed acetoxylation of ethylene or other oxidation procedures, it has now been found that within the reaction system to which the invention relates, higher reaction rates are obtained and the formation of undesirable, the yield adversely affecting by-products 800 3 5 28 * 3 is kept as small as possible when the reaction is carried out under low oxygen pressure, i.e. a partial oxygen pressure of 0.14-0.7 kg / cm absolute and a partial ethylene pressure of 1.05-3.5 kg / cm at the reactor outlet while maintaining a total concentration of tellurium in the reaction between about 0.1 and 0.5 wt%. Appropriate control of these reaction parameters maximizes in the reaction system the formation and ratio, compared to the total amount of tellurium in solution in all forms, of a highly active oxidation catalyst, with the highly active oxidation Catalyst includes an organic complex tellurium compound, which gives a differential polarographic pulsation peak at -0.7 volts in the analysis with 1 normal KCl-NH 2 OH buffer solution.

In addition, it was found that outside of the specified reaction conditions and parameters of the invention, for example, at partial oxygen pressures above 0.7 kg / cm at the reactor outlet. +4 late, other tellunum catalysts, such as TeBr, or Te and +2. ^

Compounds that are too complex are predominantly present, resulting in an excessive yield of high molecular materials, a yield loss, slower reaction rates and generally poor process feasibility. The predominant Te + ^ catalyst gives a differential polarographic pulsation peak at -0.98 volts in the analysis with 1 normal KCl-NH ^ 0H buffer solution. The phenomena due to the low oxygen pressure contradict what might be expected when compared to the known oxidation processes, in particular those described in the prior art for the oxidation of olefins, and these phenomena show the differences between the method according to the invention and those described in the literature.

The object of the invention is to provide an improved process for the preparation in the liquid phase of ethylene glycol esters and in particular the diacetate from ethylene at higher reaction rates and selectivities with respect to the esters, while avoiding the difficulties of implementation known in the art processes.

800 3 5 28 4

Another object of the invention is to provide a specific process for the preparation of ethylene glycol esters using low oxygen pressures which will control the catalyst form of the tellurium in the reaction system and which will achieve the maximum reaction rate with minimal by-product formation and other difficulties of operation. .

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These and other objects and advantages of the invention will become apparent from the description below.

According to the invention, ethylene glycol esters 10 are prepared by liquid phase reaction under oxidative conditions of ethylene, molecular oxygen and acetic acid at a temperature of about 125-200 ° C, preferably 140-175 ° C, in the presence of an effective amount of a combination Option catalyst system containing tellurium and a bromine source which forms bromide ions during the reaction, maintaining a partial oxygen pressure of about 0.14-0.7 kg / cm 2 and a partial ethylene pressure of about 1.05-3.5 kg / cm at the reactor outlet and a total concentration of tellurium per se in the reaction system between about 0.1 and 0.5 wt.%, based on the total reaction mixture, and under maximization of the formation and presence, compared to the total amount of tellurium as such in solution in the reaction system, of an organic complex tellurium oxidation catalyst compound, which provides for analysis in the differential polarographic pulse pulsation at -0.7 volts with a 1 N KCl-NH 2 OH buffer solution.

In the method according to the invention it was found that the concentration of the active organic complex tellurium catalyst compound, which gives a differential polarographic pulsation peak at -0.7 volts with an IN in the analysis. KCl-NH ^ OH buffer solution, is influenced by or correlates with the reaction rate (grammes of ethylene, consumed per hour per liter of reaction medium in the liquid phase) and experimentally the results indicated below were obtained: 35 800 3 5 28 y5 t5

Rate Organic Tecone, of soluble complex at bar Te (wt%) _ -0.7 v (wt%) Total_ A 0.11 <0.04 0.84 5 B 0.48 0.17 0.62 C 0.95 0.35 0.55

In addition, it was demonstrated experimentally that the active organic complex tellurium catalyst compound indicated above was maximized when the oxygen partial pressure was low: 10 Oxygen outlet pressure Organic Te complex at __ -0.7 v (wt%) _ A 0.14 kg / cm2 0 , 31 B 0.56 kg / cm2 0.17 C 1.82 kg / cm2 0.02 15 The formation of heavy compounds (high molecular weight glycolic acid ethylene glycol ester, polymeric by-products and other heavy materials) has been found to be influenced by the concentration of the total soluble tellurium as such in the reaction, as indicated below.

20 Total Soluble Molded Heavy Materials

Too conc. (wt%) (wt%) _ A 0.2 0.4 B 0.5 1.2 C 1.0 2.5 25 In addition, the high ethylene pressure at the reactor outlet also minimizes the formation of heavy materials at constant oxygen pressure, as evidenced by the results indicated below.

outlet 02 “outlet pressure Formation of pressure 2 heavy materials 30 (kg / cm; (kg / cm) _ (wt.) _ A 0.49 0.42 1.3 B 1.47 0.91 0.9 C 3 24 1.68 0.6 D 0.70 0.28 1.2 35 In order to avoid yield loss and other operational difficulties associated with the formation of a large amount of heavy materials, it is therefore evident that it is necessary to add the total amount of keep tellurium at a low value and maintain the ethylene partial pressure at the reactor outlet at a value of 2 over 1.05 kg / cm 2.

The reaction between ethylene, oxygen and acetic acid can be carried out in an autoclave or any other pressure reactor. Although the order of addition of the reactants and the components constituting the catalyst combination or catalyst mixture may vary, a general procedure involves the addition of acetic acid and the catalyst components to the reaction vessel, the subsequent addition from the appropriate amount of ethylene and oxygen (with or without an inert diluent gas, such as nitrogen) to the desired reaction pressure and the subsequent heating of the mixture to the desired temperature for the appropriate period of time. The reaction can be carried out according to a preferred batch or continuous process, and the order of addition of the reactants can also be varied to suit the particular equipment used. Acetic acid in the required amount is added to the reaction system. Oxygen and ethylene can be continuously supplied during the course of the reaction. The reaction products are recovered and treated by any conventional method, such as distillation, etc., to effect separation of the ethylene glycol esters from the unreacted materials, catalyst and by-products. The unreacted materials, by-products, and intermediate products, for example, ethylene bromide, ethylene glycol derivatives, glycolic acid, acetic acid, etc., can optionally be recycled into the reaction system to act as a catalyst or to obtain a further amount of ester.

The ethylene used in the process of the invention at a partial pressure greater than 1.05 kg / cm at the reactor outlet is generally the commercially available ethylene and may contain other inert materials such as ethane which may generally present in commercially available ethylene.

The acetic acid (methanecarboxylic acid), which is used as a solvent in the process of the invention and 800 3 5 28 7 also serves to provide the ester portion to the glycol ester to form, for example, the ethylene glycol mono- or diacetate for which the method according to the invention can be applied is preferably glacial acetic acid of 99.4 (minimum) 5% by weight, but may also comprise the technical or aqueous diluted qualities of 90% by weight or higher, i.e. with no more than 10 wt% water. When the acetic acid is used as a solvent as well as to provide the acid portion, it is used in excess of the stoichiometric amount required for the reaction.

If desired, the reaction can be carried out in the presence of an inert organic solvent in addition to the acetic acid used as the reaction component. Suitable solvents are, for example, benzene, t-butylbenzene, ethylene glycol diacetate, t-butanol, etc. When an inert solvent is used, the acetic acid must be used in at least the stoichiometrically equivalent amount necessary for the preparation of the ester from ethylene.

The tellurium used in the catalyst system is 20 in. combination with a source of bromine, and suitable for use in the method of the invention, includes, for example, tellurium as such or a tellurium compound. As chemical forms of tellurium compounds, which can be used as such or as mixtures, mention may be made of tellurium carbonate, oxide, hydroxide, bromide, lower alkoxide, phenoxide, carboxylate, etc. The tellurium can be oxidation zone are added as a powder or it can be added in any form, which may be partially or completely soluble under the reaction conditions to form at least a small amount of soluble tellurium cations. The tellurium is preferably in the form of its oxide. Tellurium or tellurium compounds recovered from the reaction system can also be used as catalysts, with or without further alteration or purification. The reaction will proceed with small amounts of the tellurinm catalyst described above and these are used in the reaction system to provide a total 800 3 5 28 8 concentration of tellurium in the reaction system of about 0.5 wt%, based on the total reaction mixture.

The source of bromine, which must be non-basic, used in combination with the tellurium or tellurium compound-5 catalyst, may be any compound or mixture of compounds which may form bromide ions in solution under the acetoxylation reaction. circumstances. For example, bromine itself can be used, while c; source may also be hydrobromic acid, tellurium tetrabromide (which is both a source of Te and Br), an organic bromide or a metal bromide with the exception of the basic alkali metal or earth alkali metal bromides. Organic bromides include the bromine derivatives of ethylene being oxidized, and the reaction products, for example, 2-bromoethyl acetate, 1,2-dibromoethane, ethylene-15-bromohydrin, and other bromine-containing derivatives of ethen and including higher molecular ethers and the like. The bromine or the bromide compounds are used in the reaction to provide a total concentration of bromine in the acetoxylation system between about 2.0 and 12% by weight and preferably between 4.0 and 8.0 wt% based on the total reaction mixture.

The molecular oxygen used in the process of the invention at a partial pressure of less than 0.7 kg / cm at the reactor outlet may be in the concentrated form or in the form of an oxygen-containing gas such as air or oxygen, diluted with an inert gas, such as nitrogen or carbon dioxide, etc.

The acetoxylation reaction will proceed at temperatures of about 125-200 ° C, and preferably temperatures of about 140-175 ° C are used to obtain the optimum reaction rate. Heating and / or cooling means can be used inside and / or outside the reaction system to maintain the temperature within the desired range.

The molar ratio of oxygen to ethylene in the reaction to provide the above benefits and also to maintain a partial pressure of oxygen between 0.14 2 2 and 0.7 kg / cm and a partial pressure of ethylene between 1.05 and 3, 5 kg / cm 800 3 5 28 9 at the reactor outlet is essential and will vary between 0.04: 1 and 0.67: 1. The reaction time generally depends on the catalyst used, the temperature, the pressure and the type of the equipment used. Generally, about 0.5-4 hours are required to obtain the desired degree of reaction, but shorter or longer reaction times can be used. The reaction times will also vary depending on whether the process is carried out semi-continuously or discontinuously.

Although the exact mechanism of preparation or the identity of the highly active organic complex tellurium oxidation catalyst compound that meets the above analytical specifications, and maximized in the reaction system by the reaction parameters of the invention, is not known with certainty. it is known that the complex catalyst provides the surprising results obtained by using the process of the invention.

It is the unexpected and surprising finding of this invention that the tellurium, bromine source, oxygen and ethylene reaction parameters can be weighed out in an acetoxylation process to provide the high reaction rate and low by-product formation.

The invention is further illustrated but not limited by the examples below.

In the examples below, the reactions were performed in a 300 ml titanium autoclave equipped with a liquid and vapor inlet and outlet vents and a stirrer, to which the feed reaction components and catalyst were added. Oxygen diluted with nitrogen and ethylene were continuously fed and the reactor was heated to the desired temperature over a 4 hour reaction period. Samples were taken at intervals during each run to determine the heavy by-product materials, yield and catalyst composition. The reaction rates were calculated from the ethylene consumption via the inlet and outlet gas compositions.

After the completion of the reaction, the pressure on the system is released and the reaction mixture cooled. A gas-liquid chromatographic analysis can be used for the determination of ethylene glycol diacetate and its precursors.

Example I

A continuous run was conducted in which a liquid mixture containing 64.0 wt% acetic acid (99.5%), 10.0 wt% diethylene glycol diacetate, total 7.0 wt% water, 3.3 wt. % ethylene glycol diacetate, 14.7 wt% 2-bromoethyl acetate and 1.0 wt% hydrobromic acid, were fed to the autoclave 10 together with 1 wt% tellurium as tellurium dioxide. The oxidation reactor was heated to 149 ° C and a gas mixture of ethylene and oxygen, diluted with nitrogen, was continuously fed through the inlet opening (nozzle) within the autoclave to maintain 0.3 kg oxygen outlet pressure. / cm and an ethylene outlet pressure of 1.17 15 kg / cm. The reaction temperature was maintained at 149 ° C for a reaction period of 4.0 hours. Analysis of the ethylene at the inlet and outlet showed that the reaction rate (grams of ethylene consumed per hour per liter of liquid reaction medium within the oxidation zone) was 0.60 moles / hour / liter. 20 samples taken every hour during the run show that the concentration of the active organic complex tellurium compound, which gave a differential polarographic pulsation peak at -0.7 volts with an IN, buffer solution of KCl-NH ^ OH, 0.29 wt% with a total tellurium as such in solution of 0.56 wt%.

The amount of heavy by-product materials formed was only 1.3% by weight.

Examples II-V

In Examples II-V below, unless otherwise specifically indicated, the liquid mixture used in Example I was fed to the autoclave together with 1 wt% tellurium as tellurium dioxide. The oxidation reactor was heated to 149 ° C and a gas mixture of ethylene and oxygen, diluted with nitrogen, was continuously fed at varying partial pressures at the outlet. The reaction conditions and results are shown in Table A below.

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Claims (8)

A process for the liquid-phase oxidative preparation of ethylene glycol esters by reaction of ethylene, molecular oxygen or an oxygen-containing gas and acetic acid 5 in the presence of tellurium or a tellurium compound and a source of bromine which provides bromide ions during the reaction wherein this reaction is carried out within an oxidation zone at a temperature of about 125-30 ° C, characterized in that the oxidation reaction is carried out at a partial oxygen pressure of about 0.14-0.7 kg / cm at the reactor outlet 2 and a ethylene partial pressure of about 1.05-3.5 kg / cm at the reactor outlet at a total concentration of tellurium-cat ion in the reaction system of about 0.1-0.5 wt% based on the total reaction mixture, resulting in higher reaction rates and lower formation of polymers and other heavy by-products. 2. Process according to claim 1, characterized in that the reaction is carried out at a temperature of 140-175 ° C. 3. A method according to claim 1, characterized in that the tellurium compound is tellurium dioxide. Process according to claim 1, characterized in that the source of bromine is hydrobromic acid. 5. Process according to claim 1, characterized in that an inert organic solvent is used in the oxidation reaction. 6. Process according to claim 1, characterized in that the ratio of oxygen to ethylene in the reaction, in order to provide a partial outlet pressure of oxygen between 2 2 0.14 and 0.7 kg / cm and of ethylene between 1, 05 and 3.5 kg / cm, 30 is in the range of about 0.04: 1 and 0.67: 1. 7. Process for the oxidative preparation of ethylene glycol diacetate in the liquid phase by reaction of ethylene, molecular oxygen and acetic acid in the presence of tellurium dioxide and hydrobromic acid, to form bromide ions during the reaction, this reaction being carried out within an oxidation zone at a temperature of about 800 35 28 140-175 ° C, characterized in that the oxidation is carried out at 2 a partial oxygen pressure of 0.14-0.7 kg / cm and a partial 2 ethylene pressure of 1.05-3.5 kg / cm at the outlet of the oxidation reactor with a total concentration of tellurium cation in solution between about 0.1 and 0.5% by weight, based on the total reaction mixture, resulting in higher reaction rates and lower formation of polymeric and other heavy by-product materials are obtained. 8. Methods as described in the description and / or examples. 800 35 28