Hydrogenolysis of polyalkylene glycols to produce monoethylene glycol monoalkyl ethers, monoethylene glycol and ethanol
This application is a continuation of prior U.S. application Ser. No. 307,224, filed Sept. 30, 1981, now abandoned. 
    
    
     BRIEF SUMMARY OF THE INVENTION 
     1. Technical Field 
     This invention relates to a process for selectively cleaving a polyalkylene glycol, e.g., diethylene glycol, containing at least one ether group therein at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating the polyalkylene glycol with molecular hydrogen in the presence of a hydrogenation catalyst containing iridium to produce at least one of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. Monoethylene glycol monoethyl ether can be produced in significant amounts by employing the process of this invention. 
     2. Background Art 
     It is known that monoethylene glycol is commercially produced by the hydrolysis of ethylene oxide which in turn is generated by the oxidation of ethylene, typically by the reaction of ethylene and oxygen over a silver containing catalyst. Other processes (noncommercial) for making monoethylene glycol involve reactions of carbon monoxide with hydrogen or formaldehyde, typically in the presence of a certain precious metal catalyst. Major by-products of the commercial oxide/glycol process are diethylene glycol and higher polyalkylene glycols in amounts up to 10 percent by weight of the total product mixture. However, diethylene glycol may or may not be a commercially desirable by-product. For instance, considerably more diethylene glycol by-product may be produced from the commercial oxide/glycol process than can be utilized profitably. In those instances where the production of diethylene glycol is commercially undesirable, any process capable of efficiently converting this by-product to monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol, ethanol or other valuable products would be highly desirable. 
     It has been found as a result of the present invention that polyalkylene glycols, e.g., diethylene glycol, can be selectively cleaved at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating the polyalkylene glycol with molecular hydrogen in the presence of a hydrogenation catalyst containing iridium to efficiently produce at least one of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. 
     The following prior art references describe processes involving hydrogenolysis or cleaving with molecular hydrogen in the presence of a hydrogenation catalyst: 
     Japanese Patent Publication No. 25,246/74 describes selectively cleaving polyalkylene glycols, e.g., diethylene glycol, and polyalkylene glycol monoalkyl ethers at a carbon-to-carbon covalent bond by heating with molecular hydrogen in the presence of a nickel or palladium catalyst to give alkylene glycol monoalkyl ethers, e.g., monoethylene glycol monomethyl ether, polyalkylene glycol monoalkyl ethers, alkylene glycol dialkyl ethers and polyalkylene glycol dialkyl ethers. Lower polyalkylene glycols, monoethylene glycol, dimethyl ether and methane are described as being coproduced by this cleaving process. However, this patent does not disclose or teach the co-production of ethanol and monoethylene glycol monoethyl ether resulting from the hydrogenolysis of a polyalkylene glycol. 
     German Pat. No. 2,900,279 describes selectively cleaving polyalkylene glycols, e.g., diethylene glycol, or monoethylene glycol monoalkyl or monoaryl ethers including their homologs at a carbon-to-carbon bond with molecular hydrogen in the presence of a catalyst consisting of a support material, onto which at least one of the elements palladium, platinum, ruthenium, rhodium or iridium are applied in the form of a compound to give dimethyl ethers, methylalkyl ethers or methylaryl ethers. When a polyalkylene glycol is used as the starting reactant, its terminal hydroxymethyl groups are cleaved to produce the dimethyl ether of a glycol. Monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol are not produced from the hydrogenolysis of a polyalkylene glycol according to the teachings of this patent. 
     French Pat. No. 2,447,363 describes selectively cleaving polyalkylene glycol monoalkyl ethers at a carbon-to-oxygen covalent bond with molecular hydrogen in the presence of a nickel and barium catalyst to give alkylene glycol monoalkyl ethers and polyalkylene glycol monoalkyl ethers having one less ethylene group, e.g., diethylene glycol monoethyl ether is cleaved to give monoethylene glycol monoethyl ether. When hydrogenolysis of polyalkylene glycol monoalkyl ethers is not complete, small quantities of ethanol may be detected in the reaction mixture. This patent does not describe the hydrogenolysis of a polyalkylene glycol to produce each of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. 
     U.S. Pat. No. 3,833,634 describes a process for the preparation of polyfunctional oxygen-containing compounds such as ethylene glycol and/or derivatives thereof by reacting an oxide of carbon with hydrogen using a rhodium complex catalyst in combination with carbon monoxide at elevated temperature and pressure. Example 23 describes the production of ethylene glycol by hydrogenolysis of open chain glycol ethers, e.g., tetraethylene glycol dimethyl ether. 
     Japanese Public Disclosure No. 109,908/79 describes selectively cleaving an alkylene oxide, e.g., ethylene oxide, with molecular hydrogen in the presence of a hydrogenation catalyst and solvent having low polarity. The reaction is carried out in the liquid phase to give alkylene glycol alkyl ethers, e.g., monoethylene glycol monoethyl ether. Ethanol is produced as a by-product. This patent does not describe the hydrogenolysis of a polyalkylene glycol to produce each of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. 
     U.S. Pat. No. 1,953,548 describes a process for producing n-propyl alcohol by passing propylene oxide vapor over a contact catalyst containing alumina at elevated temperature and immediately thereafter, in the presence of hydrogen, over a hydrogenation catalyst containing reduced nickel. 
     U.S. Pat. No. 3,975,449 describes a hydrogenolysis process for producing a primary diol and/or triol from an epoxide by contacting the epoxide with molecular hydrogen and a solid catalyst comprising nickel or cobalt at elevated temperature and pressure. 
     Davidova and Kraus, Journal of Catalysis, 61, 1-6 (1980) describe cleaving of 1,2-epoxybutane with molecular hydrogen in the presence of a supported platinum catalyst at elevated temperature and atmospheric pressure to give oxygenated products, e.g., 2-butanone, 1-butanol and 2-butanol. 
     German Pat. No. 2,434,057 describes a hydrogenolysis method for producing glycol dimethyl ethers by cleaving the formals of the corresponding glycol monomethyl ethers with molecular hydrogen in the presence of catalysts composed of oxide mixtures of silicon and aluminum and/or rare earths and additionally containing the metals nickel, cobalt or copper. 
     German Pat. No. 2,716,690 describes a hydrogenolysis method for producing glycol dimethyl ethers by cleaving the formals of the corresponding glycol monomethyl ethers with molecular hydrogen in the presence of catalysts composed of oxide mixtures of silicon and aluminum and/or rare earths as well as metallic nickel and/or cobalt and/or copper, characterized by the fact that the catalysts additionally contain metallic palladium and/or rhodium and/or platinum as the promoter. 
     However, none of these references and no prior art is currently known to us which discloses or teaches a process for selectively cleaving a polyalkylene glycol at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating with molecular hydrogen in the presence of a hydrogenation catalyst containing iridium to produce at least one of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. 
     DISCLOSURE OF INVENTION 
     The present invention provides a process for selectively cleaving a polyalkylene glycol, e.g., diethylene glycol, containing at least one ether group therein at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating the polyalkylene glycol with molecular hydrogen in the presence of a hydrogenation catalyst comprising iridium to produce at least one of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. Monoethylene glycol monoethyl ether can be produced in significant amounts by employing the process of this invention. 
     In copending U.S. patent application Ser. No. 307,226 filed on an even date herewith, there is described the manufacture of monoethylene glycol monomethyl ether, monoethylene glycol and ethanol by the hydrogenolysis of a polyalkylene glycol, e.g., diethylene glycol. The polyalkylene glycol is selectively cleaved at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating with molecular hydrogen in the presence of a hydrogenation catalyst comprising nickel to produce at least one of monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. Monoethylene glycol monomethyl ether can be produced in predominant amounts by employing the process disclosed in this copending application. 
     Copending U.S. patent application Ser. No. 307,225, filed on an even date herewith, describes a process for selectively cleaving a polyalkylene glycol, e.g., diethylene glycol, at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating with molecular hydrogen in the presence of a hydrogenation catalyst comprising ruthenium to produce at least one of monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. The production rate of each of said monoethylene glycol monomethyl ether, monoethylene glycol and ethanol is at least about 10 moles/kilogram ruthenium/hour. 
     In copending U.S. patent application Ser. No. 307,210 filed on an even date herewith, there is described the manufacture of monoethylene glycol and ethanol by the hydrogenolysis of a polyalkylene glycol, e.g., diethylene glycol. The polyalkylene glycol is cleaved at a carbon-to-oxygen covalent bond by heating with molecular hydrogen in the presence of a hydrogenation catalyst, e.g., copper chromite, to produce at least one of monoethylene glycol and ethanol. The selectivity of the monoethylene glycol and ethanol may approach or exceed 95 molar percent using copper chromite as the hydrogenation catalyst. 
     It has been surprisingly found as a result of the present invention that when a composition containing iridium is used as the hydrogenation catalyst in a process for hydrogenolyzing polyalkylene glycols, at least one of monoethylene glycol monomethyl ether, monoethylene glycol and ethanol is produced in addition to significant amounts of monoethylene glycol monoethyl ether. In a preferred aspect of this invention, the selectively to monomethylene glycol monoethyl ether is at least about 35 molar percent. 
     DETAILED DESCRIPTION 
     Hydrogenolysis of polyalkylene glycols may proceed according to different cleavage pathways. For example, as illustrated in the present invention, polyalkylene glycols may be cleaved at either a carbon-to-oxygen covalent bond or a carbon-to-carbon covalent bond to give different products. The cleavage pathways are influenced or varied, to a certain extent, by choice of hydrogenation catalyst, concentration of active metal in hydrogenation catalyst, pressure provided by molecular hydrogen and other factors. When a hydrogenation catalyst containing iridium is used in the hydrogenolysis of a polyalkylene glycol, e.g., diethylene glycol, according to the present invention, the cleavage pathway may be directed toward a carbon-to-oxygen terminal hydroxy bond resulting in the production of monoethylene glycol monoethyl ether, a carbon-to-oxygen ether bond resulting in the production of monoethylene glycol and ethanol, and a carbon-to-carbon covalent bond resulting in the production of monoethylene glycol monomethyl ether. Because of the high bond energy required to cleave a carbon-to-oxygen terminal hydroxy bond in comparison with the lower bond energies required to cleave a carbon-to-oxygen ether bond and a carbon-to-carbon covalent bond, it is surprising indeed that monoethylene glycol monoethyl ether may be produced in significant amounts by using a hydrogenation catalyst containing iridium in accordance with the hydrogenolysis process of the instant invention. As a preferred embodiment of the present invention, at least one of monoethylene glycol monomethyl ether, monoethylene glycol and ethanol is produced in addition to significant amounts of monoethylene glycol monoethyl ether. 
     The preferred hydrogenation catalysts which can be used to catalyze the hydrogenolysis process of this invention are well known in the art and include compositions containing iridium. The preferred hydrogenation catalysts may also include, as an additional ingredient, a promoter or promoters for increasing the activity of the hydrogenation catalysts. Suitable catalyst promoters may include barium, calcium, magnesium, manganese, strontium, zirconium, titanium, hafnium, potassium, lithium, sodium, rubidium, cesium, molybdenum, chromium, tungsten, zinc and the like. Certain metals such as copper, chromium, molybdenum, tungsten, iron, cobalt, ruthenium, rhodium, palladium, platinum, nickel, rhenium, tantalum, vanadium, niobium, zinc and the like may act as co-catalysts in combination with iridium. It is noted that molybdenum, chromium, tungsten and zinc may act as either a co-catalyst or promoter. Reference to the hydrogenation catalysts, promoters and co-catalysts as containing the above-described metals is meant to include the metal in the compound form as well as the elemental form, for example as a metal oxide or sulfide or as a metal hydride, or as the reduced elemental metal or as mixtures of the foregoing. The hydrogenation catalysts may be employed in the presence or absence of a catalyst support. Suitable catalyst supports include silica gel, aluminum oxide, magnesium oxide, titanium dioxide, magnesium aluminate, zirconium dioxide, silicon carbide, ceramic, pumice, carbon, diatomaceous earth, kieselguhr and the like. Illustrative of the preferred hydrogenation catalysts useful in the process of this invention include compositions containing iridium on a suitable catalyst support, e.g., iridium on silica gel, iridium on kieselguhr and the like. The compositions containing oxides may be totally or partially reduced in situ during reactor heat-up. The most preferred hydrogenation catalysts of this invention include compositions containing at least about 5 percent by weight iridium on a suitable catalyst support, and are prepared by known methods detailed hereinbelow. 
     The hydrogenation catalysts useful in the process of this invention can be employed in any form. They may be present in the reaction mixture as finely divided powders, porous tablets, pellets, spheres, granules and the like. It is desirable that the hydrogenation catalysts possess a high surface area. The preferred surface area ranges from about 0.5 m 2  /gm to about 300 m 2  /gm and even greater. Most preferably, the surface area of the hydrogenation catalysts ranges from about 10 m 2  /gm to about 300 m 2  /gm. The average pore diameter of the hydrogenation catalysts is not narrowly critical. Hydrogen diffusion appears to be rate limiting in catalysts having very small pores. It appears that a very small average pore diameter and/or a large catalysts particle diameter are detrimental to high monoethylene glycol monoethyl ether-monoethylene glycol monomethyl ether-monoethylene glycol-ethanol selectivities and/or polyalkylene glycol conversion rates. In general, for obtaining desirable monoethylene glycol monoethyl ether-monoethylene glycol monomethyl ether-monoethylene glycol-ethanol selectivities, it is believed that catalysts having an average pore diameter of at least about 150 Å, preferably at least about 250 Å, and a particle diameter of less than 10 millimeters, preferably 5 millimeters or even less, are useful in the hydrogenolysis process of this invention. 
     The quantity of the hydrogenation catalysts which is employed is not narrowly critical and can vary over a wide range. In general, the process of this invention is desirably conducted either continuously or batchwise in the presence of a catalytically effective quantity of the hydrogenation catalysts which gives a suitable and reasonable reaction rate, e.g., from about 1 to about 100 moles/kilogram catalyst/hour. The reaction proceeds when one employs as little as about 0.01 weight percent, or even a lesser amount of catalyst based on the total quantity of the reaction mixture under batch conditions. The upper concentration of the hydrogenation catalyst can be quite high, e.g., about 50 weight percent of catalyst based on the total quantity of reaction mixture. Higher concentrations may be used if desired. However, the upper concentration appears to be dictated by economics in terms of the cost of certain hydrogenation catalysts to achieve the given reaction and by ease of handling of the reaction mixture during the course of the reaction. Depending on various factors, such as the total operative pressure of the system, the operative temperature and other considerations, a concentration of between about 0.1 and about 30 weight percent hydrogenation catalyst based on the total quantity of the reaction mixture is generally suitable in the practice of this invention. 
     The preferred polyalkylene glycols which can be used in the practice of the process of this invention are well known in the art and include: diethylene glycol, triethylene glycol, tetraethylene glycol and the like. In the most preferred embodiment of this invention, diethylene glycol formed as a by-product of the commercial oxide/glycol process described hereinabove, is selectively cleaved at a carbon-to-oxygen covalent bond and independently at a carbon-to-carbon covalent bond by heating with molecular hydrogen in the presence of a hydrogenation catalyst containing iridium to produce at least one of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. By utilizing the preferred catalysts and reaction conditions of the present invention, higher polyalkylene glycols such as triethylene glycol and tetraethylene glycol may be selectively cleaved to give at least one of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. These polyalkylene glycols are prepared by methods well known in the art. 
     The relative amounts of polyalkylene glycol and molecular hydrogen which are initially present in the reaction mixture can be varied over a wide range. In general, the molar ratio of molecular hydrogen to polyalkylene glycol is in the range of between about 1:20 and about 2000:1, preferably between about 1:2 and about 500:1 and most preferably, between 1:1 and about 200:1. It is to be understood, however, that molar ratios outside the stated broad range may be employed. However, very high molecular hydrogen-to-polyalkylene glycol molar ratios are economically unattractive, and very low molecular hydrogen-to-polyalkylene glycol molar ratios will result generally in low conversions and lower product selectivities. When operating in the continuous mode, molecular hydrogen and polyalkylene glycol may be fed either concurrently or countercurrently over the hydrogenation catalyst using either upward, downward or horizontal flow with concurrent downward flow being preferred. The gas hourly space velocity (GHSV) of molecular hydrogen and the liquid hourly space velocity (LHSV) of polyalkylene glycol may be varied over a wide range utilizing the continuous process. The gas hourly space velocity of molecular hydrogen may range from about 100 hr -1  or less to greater than 100,000 hr -1 , preferably from about 1,000 hr -1  to about 100,000 hr -1 , and most preferably from about 2,000 hr -1  to about 75,000 hr -1 . The liquid hourly space velocity of polyalkylene glycol may range from about 0.01 hr -1  or less to about 100 hr -1  or greater, preferably from about 0.1 hr -1  to about 25 hr -1 , and most preferably from about 0.25 hr -1  to about 10 hr -1 . The higher GHSV and LHSV values generally tend to result in uneconomically low conversion of polyalkylene glycol, and the lower GHSV and LHSV values generally tend to decrease the selectivity of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. The intended purpose is to provide a sufficient quantity of polyalkylene glycol and molecular hydrogen in the reaction mixture to effect the desired production of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. 
     The process of this invention can be effected over a wide temperature range. In general, the process is conducted at a temperature of between about 150° C. and about 350° C. Lower temperatures generally give improved product selectivity, but often at economically unfavorable rates. Higher temperatures generally increase total productivity but tend to increase by-product formation. Operating the process at temperatures lower than 150° C. will not produce the desired products at optimum rate so that the reaction will typically be operated over an extended period of time and/or excessive quantities of catalyst must be employed in order to obtain the desired production of reaction products at reasonable rates. When operating the process at temperatures higher than 350° C. there is a tendency for the organic materials contained in the reaction mixture to decompose. In most cases when operating at the lower end of the temperature range, it is desirable to utilize pressures in the higher end of the pressure range. The preferred temperature range is between about 200° C. and 300° C., while the most preferred temperature range is between about 225° C. and 265° C. However, there are occasions when a preferred temperature range may include any of the more desirable ranges as well as the broadest range such that the process may be operated at a temperature of between 175° C. and 300° C. as well as between about 150° C. and 325° C. 
     The process of the present invention is effected under atmospheric or superatmospheric pressure conditions. In a preferred embodiment of the present invention, the pressure is produced almost exclusively by the molecular hydrogen provided to the reaction. However, suitable inert gaseous diluents may also be employed if desired. Actual operating pressures (initial pressures under batch operating conditions) of between about atmospheric and about 10,000 psig represent an operative limit for producing the monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol products. The preferred actual operating pressure conditions for the production of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol range from about 100 psig to about 4000 psig and, most preferably, from about 250 psig to about 2000 psig. When operating the process at lower pressures, the rate of reaction becomes slower and therefore the reaction period must be extended until the desired amount of reaction products are produced. When operating the process at higher pressures, the rate of production of the desired products will generally be increased. Higher pressures generally tend to increase the selectivity of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol but very high pressures can also increase by-product formation through secondary hydrogenolysis reactions. Lower pressures generally tend to increase the formation of by-products such as 2-oxodioxane and decrease the selectivity of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol. 
     The process of this invention is effected for a period of time sufficient to produce the desired monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol products. In general, the reaction time can vary from a fraction of a second to several hours, i.e., from 0.1 second and shorter to approximately 10 hours, and longer. If more sluggish reaction conditions are selected, then the reaction time will have to be extended until the desired products are produced. It is readily appreciated that the required residence period, i.e., reaction time, will be influenced by reaction temperature, concentration and choice of hydrogenation catalyst, total pressure, concentration (molar ratio) of polyalkylene glycol and molecular hydrogen and other factors. When operating the hydrogenolysis process of this invention under continuous conditions, the reaction time or residence period may generally range from a fraction of a second to several minutes or more whereas the residence period under batch conditions may generally range from a few minutes to several hours. The synthesis of the desired products from the hydrogenolysis of a polyalkylene glycol is suitably conducted under operative conditions which give reasonable reaction rates and/or conversions. 
     The process of this invention can be carried out in a batch, semi-continuous or continuous manner in either a liquid phase, vapor phase or a combination liquid-vapor phase. The reaction may be conducted in fixed-bed, slurry-phase, trickle-bed or fluidized-bed reactors or the like using a single reaction zone or in a plurality of reaction zones, in series or in parallel. The reaction may be conducted intermittently or continuously in an elongated tubular zone or a series of such zones. The material of construction of the equipment should be such so as to be inert during the reaction. The equipment should also be able to withstand the reaction temperatures and pressures. The reaction zone can be fitted with internal and/or external heat exchangers to control undue temperature fluctuations caused by the moderate exothermic nature of the reaction. In a preferred embodiment of the present invention, agitation means to ensure complete mixing of the reaction mixture should be used in reaction systems not employing a fixed-bed catalyst. Mixing induced by magnetic stirrer, vibration, shaker, rotating, sparging with gas, oscillation, etc. are all illustrative of the types of agitation means which are contemplated herein. Such agitation means are available and well known to the art. 
     The polyalkylene glycol, molecular hydrogen and hydrogenation catalyst ingredients may be initially introduced into the reaction zone batchwise. Alternatively, the polyalkylene glycol, molecular hydrogen and hydrogenation catalyst ingredients may be introduced into the reaction zone continuously or intermittently during the course of the synthesis reaction. Means to introduce the ingredients into the reaction zone during the course of the reaction and/or means to adjust the ingredients in the reaction zone during the reaction, either intermittently or continuously, can be conveniently utilized in the process to maintain the desired molar ratios of ingredients and to maintain the pressure exerted by hydrogen. 
     The operative conditions of the present process may be adjusted to optimize the selectivities and conversion rates of the desired products and/or the economics of the process. For example, it may generally be preferred to operate at relatively low conversion rates, which tends to increase selectivities of monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol due to reduced by-product formation. Lower conversions also tend to increase the monoethylene glycol/ethanol molar ratio by reducing secondary hydrogenolysis of monoethylene glycol. Recovery of the desired monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol and ethanol can be achieved by methods well known in the art, such as by distillation, fractionation, extraction, and the like. Typically, in carrying out the process, the product contained in the reaction mixture would be withdrawn from the reaction zone and distilled to recover the desired products. For reactors not employing a fixed-bed catalyst, a fraction comprising the hydrogenation catalyst and by-products can be removed for recovery or regeneration of the catalyst. Fresh hydrogenation catalyst can be intermittently added to the reaction stream or it can be added directly to the reaction zone, to replenish any catalyst which is lost in the process. 
    
    
     Although this invention has been described with respect to a number of details, it is not intended that this invention should be limited thereby. The examples which follow are intended solely to illustrate the embodiments of this invention which to date have been determined and are not intended in any way to limit the scope and the intent of this invention. 
     As used in the Examples appearing hereinafter, the following designations, terms and abbreviations have the indicated meanings: 
     psig: pounds per square inch gauge pressure 
     rpm: revolutions per minute 
     kg: kilogram 
     lbs.: pounds 
     cu.: cubic 
     ft.: foot 
     cat.: catalyst 
     hr.: hour 
     cc: cubic centimeter 
     m 2  : square meter 
     gm: gram 
     conv.: conversion 
     DEG: diethylene glycol 
     hr -1  : reciprocal hour unit for GHSV and LHSV 
     % or percent: percent by weight unless otherwise specified. 
     ratios: are on a weight basis unless otherwise specified. 
     temperatures: are given in °C. unless otherwise specified. 
     ND: not detected 
     selectivity: calculated according to the formula, 
     
         % Selectivity i=.sup.r i×100/.sup.r DEG conv. 
    
     where i is the individual component, i.e., monoethylene glycol monoethyl ether, monoethylene glycol monomethyl ether, monoethylene glycol, ethanol or by-products and r is the rate in moles/kg cat/hr. 
     The catalysts used in the Examples are identified as follows: 
     Catalyst I 
     A composition containing 5 percent by weight iridium on silica gel; the silica gel is commercially available from Davison Specialty Chemical Company as Grade-59; and having a surface area of 275 m 2  /gm, a bulk density of 25 lbs./cu. ft., the particle size is powder after grinding and a pore volume of 1.2 cc/gm. 
     Catalyst II 
     A composition containing 5 percent by weight iridium and 0.2 percent by weight calcium on silica gel; the silica gel is commercially available from Davison Specialty Chemical Company as Grade-59; and having a surface area of 275 m 2  /gm, a bulk density of 25 lbs./cu. ft., the particle size is powder after grinding and a pore volume of 1.2 cc/gm. 
     Catalysts I and II were prepared in the laboratory in accordance with the following general procedure: 
     The silica gel support, prewashed with hot oxalic acid solution to reduce impurities, was impregnated under vacuum with an aqueous solution of appropriate precursors denoted in Table A below. The solution volume was just sufficient to fill the catalyst pores, and the salt concentration was adjusted to give the desired weight percent in the finished catalyst. After standing 30 minutes at room temperature, the impregnated support of Catalyst I was dried in stages as follows: 85° C. for 1 hour, 110° C. for 2 hours, 150° C. for 2 hours and 200° C. for 2 hours; and the impregnated support of Catalyst II was dried in the following stages: 85° C. for 1 hour, 110° C. for 2 hours and 150° C. for 3  hours. The dried material was transferred to a quartz tube and reduced by heating (Catalyst I was reduced by heating to 400° C. and Catalyst II was reduced by heating to 500° C.) at a rate of 100° C. per hour under flowing hydrogen. The temperature was held at 400° C. (Catalyst I) or 500° C. (Catalyst II) for 1 hour and then the system was cooled to 80° C. in hydrogen. The hydrogen was displaced with nitrogen and the catalyst cooled to room temperature. 
     
                       TABLE A                                                     
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Catalyst Identification                                                   
                    Catalyst Precursors                                   
______________________________________                                    
I                   IrCl.sub.3                                            
II                  IrCl.sub.3, Ca(NO.sub.3).sub.2                        
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     EXAMPLES 1 AND 2 
     Examples 1 and 2 were conducted batchwise in a 300-milliliter stainless-steel autoclave reactor equipped with a magnetic stirrer in accordance with the following procedure. Prior to each of the Examples the magnetic stirrer was disassembled and all components washed thoroughly to remove residual catalyst powder. All parts and internals of the reactor were similarly cleaned, rinsed with acetone and dried. The reactor was charged with a mixture of 50 grams of diethylene glycol and 1 gram of a finely pulverized (-200 mesh) catalyst specifically identified for each Example in Table I below. The reactor was then sealed, purged twice with 500 psig of molecular hydrogen and, after pressure testing, charged with an initial amount of molecular hydrogen. The initial molecular hydrogen pressure for each Example is given in Table I. The magnetic stirrer was started and adjusted to 1000 rpm, and the reaction system was then heated to a temperature specified for each Example in Table I. After a six-hour reaction period the reactor was cooled, stirring was discontinued and the pressure vented slowly. During the venting step, a sample of product gas was collected for analysis by gas chromatography. The remaining liquid contents of the reactor were then removed, weighed and analyzed by gas chromatography. The performance of catalysts tested in Examples 1 and 2 is given in Table I. 
     
                       TABLE I                                                     
______________________________________                                    
POLYALKYLENE GLYCOL HYDROGENOLYSIS                                        
(BATCH PROCESS)                                                           
PRODUCT DATA                                                              
EXAMPLE               1         2                                         
______________________________________                                    
Catalyst Identification                                                   
                      I         II                                        
Temperature, °C.                                                   
                      250       250                                       
Initial Pressure (H.sub.2), psig                                          
                      1800      2000                                      
Reaction Rate (moles/kg cat./hr) to:                                      
Monoethylene Glycol   4.61      1.35                                      
Ethanol               4.13      1.55                                      
Ethane                1.62      .171                                      
Monoethylene Glycol Monomethyl Ether                                      
                      .164      .082                                      
Monoethylene Glycol Monoethyl Ether                                       
                      4.25      1.00                                      
Methanol              .378      .050                                      
Dioxane               .682      ND                                        
2-Oxodioxane          ND        ND                                        
1,2-Butanediol        ND        ND                                        
Others.sup.(a)        .107      .171                                      
Selectivity (mole percent)                                                
Monoethylene Glycol Monoethyl Ether                                       
                      41        38                                        
Monoethylene Glycol Monomethyl Ether                                      
                      2         3                                         
Monoethylene Glycol   44        51                                        
Ethanol               40        58                                        
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 .sup.(a) Includes diethyl ether and unknowns.                            
 
    
     Examples 1 and 2 illustrate the effectiveness of compositions containing iridium as the hydrogenation catalyst of this invention. When a composition containing at least 5 percent by weight iridium is used as the hydrogenation catalyst, the selectivity of monoethylene glycol monoethyl ether may exceed 40 molar percent (see Example 1) in addition to the co-production of monoethylene glycol and ethanol in near equimolar amounts and monoethylene glycol monomethyl ether in lesser amounts.