Process for the preparation of ethylene glycol

Ethylene glycol is an important commercial product that is used in liquids for antifreeze and antifreeze, in hydraulic fluids, in the manufacture of alkyd resins. Solvents and polyester fibers is used.

In DE-OS 27 21 734 a process of oxidative carbonylation of an alcohol with oxygen and carbon monoxide in the presence of a particular catalyst system for the preparation of Oxalsäureesiern is described. Oxalic acid esters are used commercially as solvents and as starting materials for dyes and in the production of pharmaceuticals, but there is no reference in the literature to the possibility of converting oxalic acid esters in the vapor phase into the industrially valuable ethylene glycol.

From Helvetica Chimica Acta, 1955, page 978, last sentence, it is apparent that the reduction of oxalic acid esters by means of hydrogen in the presence of copper-containing catalysts leads to ethylene glycol. In general, however, such reductions are carried out in the liquid phase and under high pressure, namely generally under hydrogen pressures of over 200 bar.

In Organic Reactions, Vol. VIII, Chap. 1, John Wiley and Sons, Inc., New York, 1954, pages 1-27, a general mechanism for the liquid phase hydrogenation of esters to alcohols is given, it being noted that diethyl oxalate in the liquid phase provides a good yield of ethylene glycol , but only if it is carried out at a pressure which is much higher than the usual liquid phase hydrogenation pressures, ie higher than 280 bar.

From US-PS 23 05 104 a process for the vapor phase hydrogenation of alkyl esters of hydroxyacetic acid is known, in which a fed with a double catalyst reaction zone at temperatures between 150 and 300 ° C and pressures of 10 to 1000 bar or more is used.

In GB-PS 5 55 240 and GB-PS 5 75 380 are processes for the catalytic vapor phase hydrogenation of hydroxyacetic acid and its derivatives (esters) or an ester of glycolic acid at temperatures of 150 to 300 "C and pressures of 10 to 1000 bar to Production of ethylene glycol indicated.

From US-PS 20 60 880 a process for the preparation of ethylene glycol is known, which consists in subjecting a Oxalsäuredialkylester at a pressure of about about 200 bar of a catalytic hydrogenation. Preferably, this method is included

Jo pressing above about 400 bar and temperatures of 200 to 275 ° C performed. As Example 1 of this PS shows, the yields of ethylene glycol when working at pressures below about 200 bar are very low, with the essential products being ethanol, diethyl ether and the like. In order to achieve high product yields, it is therefore imperative that

■ are operated with high pressure, which is associated with all known disadvantages of high pressure systems. A successful Niederdruckhydrierung of Oxalsäuredialkylestem to ethylene glycol should therefore not be possible thereafter.

From the above, it can be seen that there is hitherto no feasible at relatively low hydrogen pressures process for the production of ethylene glycol by reduction of a corresponding Oxalsäuredialkylesters containing the desired product with minimal side reactions and long-term retention of the activity of the hydrogenation catalyst used for this purpose in high yield and high Conversion degree results.

The invention therefore has the object to remedy this situation and to provide a corresponding new production process for ethylene glycol, which does not know the above-mentioned disadvantages of the known modes of operation. This object is achieved according to the invention by the method resulting from the claims.

The reaction taking place in the process according to the invention can be represented by the following equation:

ROCCOR + 4H₂ HIGH₂CH₂OH + 2ROH / _ + pressure

Oxalsäureester

ethylene glycol

alcohol

Therein, R represents an optionally substituted alkyl or aralkyl group which may contain other substituents, for example, alkoxy, amino, carboxy and cyano groups which do not interfere with the reaction of the present invention. The alcohol formed by the hydrogenation of the oxalic acid ester in addition to the desired ethylene glycol can be separated off from the reaction mixture without difficulty and converted back into an oxalic acid ester Hi by the oxidative carbonylation reaction, for example according to DE-OS mentioned above.

The vapor phase catalytic hydrogenation process of the invention may be carried out in any suitable reactor, for example a tubular reactor, wherein an oxa-acid ester to be hydrogenated, which is heated to vapor or gaseous state, together with hydrogen at the desired pressures and temperatures via a hydrogenation catalyst is passed, which may be in the form of a fixed bed, a fluidized bed or a moving bed. Since vapor phase hydrogenation reactions are generally exothermic, cooling means may be employed in and / or outside the reactor to maintain the temperature within the desired range. The vaporous reaction products leaving the hydrogenation reactor can be recovered by any known method, for example by condensation, and then subjected to fractional distillation to separate ethylene glycol and alcohol from readily reacted material and by-products. The reaction is generally carried out in a cyclic or continuous mode, and appropriate recycling of excess or unreacted hydrogen or oxalic acid ester can be employed.

The oxalic acid esters which can be used in the process according to the invention correspond to the general formula already mentioned. The esters preferably used in the hydrogenation process for producing ethylene glycol are those in which R represents an alkyl group having 1 to 8 carbon atoms, for example, oxalic acid dimethyl, diethyl, dibutyl and di-amyl esters. The esters are preheated and evaporated, which can be determined by their vapor pressure, to ensure that virtually all of the ester is in the vapor state when passed over the catalyst bed along with hydrogen. The catalyst bed is maintained at a temperature at which condensation of the oxalic acid ester or ethylene glycol formed is prevented. Temperature and pressure of the reaction are chosen so that the reaction products emerging from the reaction zone are present in the gas phase.

In the hydrogenation of oxalic acid esters, hydrogen is generally used in excess of the stoichiometrically required amount for the conversion of the oxalic acid ester into ethylene glycol and the corresponding alcohol. The preferred molar ratio of hydrogen to oxalic acid ester entering the reaction section is 30: 1. Higher or lower ratios of hydrogen to oxalic acid ester may also be employed in the process as long as the ester is in the vapor state and the hydrogen is used in at least the stoichiometric amount of 4: 1.

The hydrogenation catalysts that can be used in the process of the invention. are described in the literature, and any known hydrogenation catalyst or a mixture of such catalysts, which are suitable for the conversion of esters in alcohols, can be used. Thus, one can use catalysts which are described together with their preparation in US-PS 20 94 611.23 05 104 and 33 74 184. In general, hydrogenation catalysts containing copper in elemental form or in combination with oxygen, as well as other hydrogenation metal oxides used in conjunction with copper, can be used with or without carriers. Particularly preferred catalysts are the copper-zinc chromite or copper chromite catalysts, which may be reinforced with barium or sodium hydroxide and reduced in hydrogen. Examples other than the above hydrogenation catalysts suitable for the purposes of the present invention include zinc / copper / cadmium / chromium, copper ammonium chromium. Many well-suited hydrogenation catalysts are commercially available, for example, the copper-zinc chromite catalyst (Girdler T-359), copper barium chromite (Harshaw Cu 1107) catalysts, and the sodium hydroxide-reinforced copper chromite catalyst (Houdry 536 CP).

The hydrogenation catalysts can be prepared by any suitable methods, for example by precipitation or fusion. The preferred copper chromite and copper-zinc chromite catalysts are precipitated catalysts and can be prepared by the method given in British Pat. No. 5,755,380 and then reduced to hydrogen. A copper chromium hydrogenation catalyst can be prepared, for example, by neutralizing 1 mole of chromium trioxide and 1 mole of copper (U) nitrate trihydrate in aqueous ammonium carbonate to a pH of 7. The precipitate is washed and dried and then at 400⁰C calcined. The calcined catalyst is then made to particle sizes corresponding to 2057 to 1204 microns or 2057 to 500 microns mesh, and reduced in hydrogen, for example, at 200 ° C for 17 hours.

The gas-phase hydrogenation catalysts used in the process of the invention are known to lose activity or degrade in a short time, due to a number of different factors and conditions which must be limited, controlled or eliminated in order to increase the economics of the process. In such reactions, catalyst poisoning and consequent loss of catalyst activity is apparently due to uncontrolled or erroneous distribution of the heat of reaction, causing hydrogenolysis of the ethylene glycol formed and other chemical-type factors, for example, in the hydrogenation of diethyl oxalate, the formation of copper salts (oxalates and Glycolates), 2-ethoxyethanol, ethyl glycolate and polymeric esters, for example polyglycolates or polymers! Ethylene oxalate which, when deposited on the catalyst surface, reduces the hydrogenation activity of the catalyst. Oxalic acid esters themselves polymerize neither in the preheater nor in the reactor nor on the catalyst surface. Other factors include catalyst poisons such as sulfur or halogen compounds.

conditions which may come into contact with the introduced hydrogen or the oxalic acid ester to be hydrogenated with the catalyst, for example hydrogen sulfide and organic sulfates, as well as a combination of the factors mentioned above and other causes. The amount of by-products formed in the reaction is generally indicative of catalyst degradation.

Hydrogenolysis and the concomitant byproduct formation on the catalyst surface as well as poisoning and deterioration of the catalyst by materials contained in the feed and loss of catalyst activity are minimized by the procedures of the present invention. Hydrogenation catalyst activity r can be increased considerably by a number of variables , namely by

(1) prereduction of the hydrogenation catalyst, reduction or prevention of oxidation of the oxidation, and enhancement of the hydrogenation activity of the quaternaryator,

(2) removal of sulfur from the oxalic acid ester to be introduced, preferably up to less than 0.4 ppm sulfur,

(3) use of a practically sulfur and halo ^2d hydrogen-free,

(4) Use of a catalyst bed diluted or mixed with inert carriers such as tabular alumina, silica and glass beads, whereby the distribution of the ^{J ()} Improved reaction heat and local overheating in the bed can be reduced or avoided, thereby limiting the extent of hydrogenolysis, and

(5) Purification of the Reaction Catalyst System of ^{J :)} If necessary, with hydrogen during an interruption of the operation to decompose impurities, especially copper (II) oxalate, which may have accumulated on the catalyst surface. Purification with hydrogen can be carried out at reaction temperatures (catalyst bed temperatures) and reaction pressures, and generally takes 5 to 20 hours.

The prereduction of the hydrogenation catalysts, such as copper chromite or copper zinc chromite, is carried out to substantially reduce the copper compounds, such as copper oxide to metallic copper. So is most conveniently effected with hydrogen in a suitable device. The specific reduction measures used are well known and may vary from catalyst to catalyst. Reductions with hydrogen are generally carried out at a temperature of 100 to 450 ° C with hydrogen pressures of 0.01 to 9.8 bar. All copper oxides formed in the reaction are rapidly reduced to metallic copper in the presence of hydrogen.

Sulfur may usually be present in the form of an organic sulfate such as ethyl hydrogen sulfate, diethyl sulfate and di-n-butyl sulfate as an impurity in the corresponding oxalic acid dialkyl ester to be hydrogenated. Since such sulfur, which may be present in the oxalic acid ester in amounts up to 700 ppm, will rapidly poison the hydrogenation catalyst, particularly copper chromite, it must be removed from the feed oxalate as much as possible, preferably to levels less than 0.4 ppm. An example of a convenient method of reducing the sulfur content of diethyl oxalate is by treating the ester with sodium ethoxide (sodium ethylate) at a temperature of 80 ° C and optionally thereafter neutralizing any unreacted sodium ethoxide with acetic acid and distilling the oxalate solution. the resulting non-volatile sodium sulfate remaining. To avoid the possible formation of mixed esters and other side reactions, sodium methylate and sodium butylate, for example, may likewise be used to treat the particular oxalic acid dialkyl ester.

Hydrogen sulfide and / or hydrogen chloride, which can be an impurity in the hydrogen feed and cause catalyst poisoning, can be completely or substantially removed by any of the conventional gas scrubbing systems. Convenient methods are to pass the gas through a bed of a mixture of Fe 2 O 3 with fly ash or through a bed of CuO / ZnO.

In carrying out the process of the present invention, a substantially sulfur-free, vaporized oxalic acid ester is generally added along with virtually zero sulfur hydrogen over a prereduced hydrogenation catalyst operating at a reaction (catalyst bed) temperature of 150 to 300⁰C, preferably between 200 and 230⁰C, is maintained at a hydrogen pressure of 0.98 to 68.6 bar, preferably 9.8 to 32.4 bar. and a flow rate (the volumes of the gaseous mixture of oxalic acid ester and hydrogen calculated at ordinary temperature and pressure conducted per hour over one volume of the hydrogenation catalyst bed) are passed from 3,000 to 20,000 hours - 'preferably 8,000 to 15,000 hours' , The liquid and hourly flow rate of the oxalic acid ester (calculated as the liquid volume of the ester per unit volume of the hydrogenation catalyst), which is passed over the catalyst in vapor form, is from 0.001 to 5.0 hours in the inventive process, preferably from 1.0 to 3.5 hours¹.

The invention is further illustrated by the following examples.

In all of these examples, the hydrogenation experiments are carried out in a straight tubular reactor having an inner diameter of 25 mm and a length of 91 cm, which is provided with a heating jacket to bring the catalyst bed to the reaction temperature. A hydrogenation calcine sorbitol (100 mL) (with or without inert diluent) is placed in the center of the reaction tube and held in position with glass wool plugs. A metal spiral passage for the distribution and circulation of vapors is attached to the top of the catalyst bed. To evaporate the oxalic acid ester and preheat the hydrogen prior to entering the hydrogenation reactor, a glass tube filled with glass beads is used. The gaseous products and by-products leaving the reactor are introduced into a straight water-cooled tube cooler and then into a liquid-gas separator. The reaction products are analyzed for ethylene glycol, alcohol, unreacted oxalic acid ester and by-products by gas-liquid chromatography (glc) and NMR spectra. The ethylene glycol and the corresponding alcohol can then pass through

fractional distillation are separated from the condensate.

example 1

The hydrogenation reactor is charged with 100 ml of a copper-zinc chromite catalyst (Girdler T-359) prereduced at 0.23 bar hydrogen at 213 ° C without inert diluent. 260 ppm of sulfur containing diethyl oxalate and hydrogen become 19O⁰C preheated, whereby the Diethyloxalat is evaporated. The gaseous mixture of vaporized oxalate and hydrogen is introduced into the reactor and over the catalyst at 215 ° C under a hydrogen pressure of 68.6 bar at a flow rate (SV) of about 4900 hours and a liquid hourly throughput rate (LHSV). of 0.3 hour 'passed. The release of heat of reaction is noted. The reaction is continued for a total of 9 hours and fluid samples are taken continuously. The gas-liquid sig-Ch^rThe liquid product chromatography gives 11.7 to 18.9 weight percent ethylene glycol. 44.5 to 62.7 weight percent ethanol and 6.4 to 30.9 weight percent unreacted diethyl oxalate besides 9.7 to 22.6 weight percent indefinite byproducts. Analysis of the catalyst reveals the presence of 0.14 weight percent sulfur versus 0.09 weight percent sulfur on the catalyst prior to use, and the presence of copper oxalate.

Example 2

The procedure described in Example 1 is repeated using a prereduced barium-reinforced copper chromite catalyst (Harshaw Cu 1107) 3>. The reaction is continued for a total of 18 hours and samples of liquid product are taken continuously. Analysis of these samples gives 5.0 to 12 weight percent ethylene glycol, 21 to 42 weight percent ethanol, and 29.1 to 40.9 weight percent unreacted diethyl oxalate. The deterioration of the catalyst is in turn caused by the sulfur content of the diethyl oxalate feed. The theoretical yield of ethylene glycol and the corresponding ethanol by catalytic hydrogenation of diethyl oxalate using stoichiometric amounts of the reactants is 40 and 60 weight percent, respectively

B e 1 s ρ ie I 3

The hydrogenation reactor is charged with 50 milliliters of a nairium hydroxide reinforced copper chromite catalyst pre-reduced in 4.5 hours at 225 C with 70 liters per hour of hydrogen hydrogenated in Example 4 of US Pat. No. 3,374,184 (commercially available as Houdry 536 CP Catalyst available). The catalyst is mixed in the ratio of 50 ml to 50 ml with tabular alumina having a particle size corresponding to the sieve openings of 2057 to 1204 microns ω diethyl oxalate is prepared by reaction with sodium ethoxide at 8O⁰C subsequent neutralization of the unreacted ethoxide with acetic acid and distillation of the diethyl oxalate descentrifuged to a sulfur content of 17 ppm, preheated together with hydrogen to 200 ° C and into the reactor and the catalyst at a temperature of 215 ° C under a hydrogen pressure of 3, 1 bar with an SV based on the volume of the catalyst bed of 100 ml of 5000 hour and a LHSV of diethyl oxalate of 0.5 hour- 'passed. The release of heat of reaction is observed, which travels down the bed from the beginning of the experiment as the gaseous mixture of diethyl oxalate and hydrogen contacts the catalyst bed. Liquid samples are withdrawn every 15 minutes, and the reaction is carried out for 10 hours, at which time the catalyst activity apparently decreases as a result of sulfur poisoning. Gas-liquid chromatography of the samples taken shows yields of 20 to 37.5 weight percent ethylene glycol, 30 to 34 weight percent ethanol and 100 percent conversion of diethyl oxalate. The diluted with inert alumina catalyst reduces the intensity of the released heat of reaction and limits the extent of hydrogenolysis.

Example 4

The procedure described in Example 3 is carried out using a catalyst of the same kind. The 17 hours under 0.98 bar hydrogen at 200⁰C, and from diethyl oxalate desulfurized to less than 0.2 ppm sulfur content with sodium methoxide as described in Example 3. Prior to preheating and mixing with the vaporized diethyl oxalate, the feed hydrogen is passed through a sulfide scrubber containing a mixture of FejCh and flyash. The reaction conditions are as follows: catalyst bed temperature 200 ° C, 31 bar hydrogen pressure, steam flow rate 3000 hour, and LHSV 0.2 to 0.5 hour. The hydrogenation is continued for 95 hours, after which the catalyst appears unimpaired, which results from a stable position of the released heat of reaction at less than Vj of the length of the catalyst bed and the consistently high selectivity to ethylene glycol with 100% conversion of diethyl oxalate. Samples of the condensed liquid reaction product are withdrawn every 15 minutes and analyzed by gas-liquid chromatography. These analyzes of samples yield 36.2 to 40 weight percent ethylene glycol, water concentrations of 0.6 to 1.7 weight percent 0 weight percent diethyl oxalate (100 percent conversion of diethyl oxalate). and trace amounts of ethyl glycolate and diethylene glycol.

Example 5

The hydrogenation reactor is charged with 53 ml of copper chromite catalyst having a particle size, the mesh sizes are from 20: 7 to 1204 microns diluted with 50 ml of tabular alumina charged with the same particle size. The catalyst is prepared by neutralizing a solution of 1 mole of chromium trioxide and 1 mole of copper (II) nitrate trihydrate in 2 liters of room temperature water with a solution of ammonium carbonate made up to a pH of 7. The precipitate is washed and dried and at a temperature of 400⁰C calcined and brought to a particle size by milling and sieving corresponding to sieve openings of 2057 to 1204 microns. The catalyst then becomes 200 hours at 038 bar hydrogen for 54 hours⁰C completely reduced Diethyl oxalate desulfurized by treatment with sodium ethoxide to less than 0.4 ppm sulfur and hydrogen becomes 200⁰C preheated

to evaporate the diethyl oxalate. The mixture containing the vaporized diethyl oxalate and hydrogen is introduced into the reactor and over the catalyst at 220 ° C⁰C under a hydrogen pressure; of 31 bar at a throughput rate of 10,000 hours and a LHSV of 1.5 hours. The reaction is continued for 460 hours, with only a slight deterioration of the catalyst observed. Only after llOstündigem use of the catalyst is the formation of trace amounts of nonselective by-products, ie observed by 2-ethoxyethanol, ethyl glycolate and diethyl ether. Liquid samples of the reaction product are taken every 30 minutes and analyzed by gas-liquid chromatography. Analyzes of the samples provide greater than 95 percent selectivity to ethylene glycol at 100 percent conversion of the diethyl oxalate and yields of 36.8 to 39.6 weight percent ethylene glycol, 0.83 to 1.58 weight percent water, 0 weight percent unreacted diethyl oxalate, and trace amounts of 2-ethoxyethanol. Ethyl glycolate and diethyl ether, and ethanol as the remainder.

Example 6

The hydrogenation reactor is charged with the mixture of copper chromite catalyst and aluminum oxide described in Example 5 in the amount also indicated there. Diethyl oxalate with a sulfur content of less than 0.2 ppm and hydrogen are used to evaporate the diethyl oxalate to 200⁰C heated The gas mixture oxalate / hydrogen is introduced into the reactor and at 232⁰C catalyst bed temperature) was passed over the catalyst under a hydrogen pressure of 13.7 bar with an SV of 12,000 hours and a LHSV of 1.8 hours, with the diethyl oxalate feed being about 2.8 mole percent. The reaction is continued for 14 hours and samples of the condensed reaction product are taken every 15 minutes. Analysis of the liquid samples gives on average 34% by weight of ethylene glycol, 52% by weight of ethanol, 3% by weight of water, 0% by weight of diethoxalate and trace amounts of ethyl glycolate.

Example 7

The reactor is charged with the mixture of copper chromite and Al 2 O 3 described in Example 5 in the amount indicated there. Di-n-butyloxalate having a sulfur content of less than 0.4 ppm and hydrogen are heated to 200⁰C is heated, and the gaseous mixture of oxalate and hydrogen is introduced into the reactor and at a temperature of 230⁰C under 31 bar hydrogen pressure with an SV of 12,000 hours - 'and a LHSV of 2.0 hours - passed over the catalyst bed During the reaction, the release of heat of reaction is observed, which raises the temperature to about 255 ° C. The reaction is continued for 12 hours and samples of the condensed liquid product are removed every 15 minutes. Gas-liquid chromatography of the samples taken gives 24.6 to 27.3 weight percent ethylene glycol, 59.3 to 71.5 weight percent Butano L 035 to 1.76 weight percent water, and traces of ethanol and butyl glycolate upon conversion of the di-n-one. Butyloxalate of 100%.

Example 8

The procedure described in Example 7 is repeated using the same prereduced catalyst: Reaction conditions: temperature of the catalyst bed 230⁰C, 13.7 bar hydrogen pressure, steam SV 12,000 hour, LHSV 0.3 hour, di-n-butyl oxalate concentration 2.9 mole percent. There is an exothermic reaction. The hydrogenation becomes 18

1 hour, and fluid samples are taken every 15 minutes. Gas-liquid chromatographic analysis of the samples of the reaction product yields 22.5 to 26.2 weight percent ethylene glycol, 53 to 63.5 weight percent butanol, 1.35 to 1.81

Γι weight percent water, 1.0 to 2 weight percent ethanol and 0 weight percent unreacted di-n-butyloxalat. The theoretical yield of ethylene glycol and butanol in the catalytic hydrogenation of di-n-butyloxalate using stoichiometric

2 »amounts of reactants is 29.5 weight percent ethylene glycol and 70.5 weight percent butanol.

Example 9

The reactor would be the same amount and the

J) same type pre-reduced dilute catalyst as described in Example 5, charged. Diisobutyl oxalate with a sulfur content of less than 0.3 ppm and hydrogen become 200⁰C heated. The vaporous oxalate-hydrogen mixture is introduced into the reactor and at a catalyst bed temperature of 220 ° C⁰C under a hydrogen pressure of 13.7 bar with a throughput rate of 12,000 hours 'and a fluid-related throughput rate of 3.0 hour' passed over the catalyst. Due to the onset of exothermic reaction, the temperature is increased to 260 ° C. The reaction is continued for 25 hours and samples of the condensed liquid product are taken every 15 minutes. The gas-liquid-chromium

The results of the samples taken are 23.9 to 27.8 percent by weight of ethylene glycol, 57.2 to 70.9 percent by weight of isobutanol, 0.90 to 1.65 percent by weight of water and trace amounts of ethanol and isobutyl glycolate at 100 percent conversion of the

• Γ) diisobutyl oxalate.

Example 10

Using the same amount and the same kind of pre-reduced diluted catalyst

As in Example 9, a dimethyloxalate melt and hydrogen is heated to 200⁰C heated The vapor mixture containing less than 0.2 ppm sulfur is introduced into the reactor and heated at a temperature of 225 ° C under a hydrogen pressure of 20.8 bar at a throughput rate of 15 000 hours.¹ and a liquid flow rate of 3.0 hours' passed over the catalyst. The release of heat of reaction is to be tested. The reaction is continued for 36 hours and samples of the condensed liquid product are taken every 15 minutes. Gas-liquid chromatographic analysis of the samples yields 36.5 to 473 weight percent ethylene glycol, 353 to 46.1 weight percent methanol, 0.48 to 1.02 weight percent water, and trace amounts of ethanol and methyl glycolate at 100 percent conversion of dimethyloxalate.