GB2023601A

GB2023601A - A process for Hydrolyzing Alkylene Oxides to Alkylene Glycols

Info

Publication number: GB2023601A
Application number: GB7921363A
Authority: GB
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1978-06-20
Filing date: 1979-06-19
Publication date: 1980-01-03
Also published as: GB2023601B; DE2924680A1; IT7923640A0; BE877082A; FR2429196A1; IT1121584B; CA1133522A; JPS552670A; NL7904749A

Abstract

A process for hydrolyzing alkylene oxides to alkylene glycols in the presence of CO2, and a basic non- halogen containing catalyst. The reaction is effected under a carbon dioxide pressure of less than about 350 psig and a reaction temperature between about 85 DEG C and 400 DEG C. The reaction is preferably effected in the presence of an organic solvent.

Description

SPECIFICATION A Process for Hydrolyzing Alkylene Oxides to Alkylene Glycols This invention relates to a process for the manufacture of alkylene glycols, such as ethylene glycol and propylene glycol, by the hydrolysis of the corresponding alkylene oxide, such as ethylene oxide and propylene oxide. More particularly, this invention involves the catalytic hydrolysis of such alkylene oxides in the presence of CO2 via a glycol ester intermediate to the corresponding alkylene glycols. The hydrolysis is preferably carried out in the presence of an organic solvent.

The prior art states that alkylene oxides can be hydrolyzed to produce the corresponding alkylene glycols. For example, German Patent No.2,141,470 reacts ethylene oxide in aqueous streams in the presence of salts of carboxylic acid and CO2 pressures in excess of about 438 psig and up to 730 psig and temperatures in the range of 1 600 to 2000C to give selectivity to monoethylene glycol in the range of 74 to 90 weight percent. The German Patent describes that high CO2 pressures are more favorable towards producing higher quality monoethylene glycol product and these pressures are between 30 and 50 atmospheres (438 to 730 psig) at temperatures in the range of 1 500 to 3000 C.

German Patent No. 2,359,497 hydrolyzes ethylene oxide to monoethylene glycol and concentrates the CO2 in the aqueous stream. The reaction is carried out with CO2 pressures in excess of 400 psig and with dilute solutions of ethylene oxide.

U.S. Patent No. 3,629,343 to Levin et al describes the hydrolysis of ethylene oxide in the presence of carbon dioxide to yield ethylene glycol. Levin et al speculates that hydrolyzing ethylene oxide in the presence of water and carbon dioxide forms, in some instances, a transitory ethylene carbonate intermediate which is hydrolyzed to ethylene glycol. According to this patent, basic compounds such as carbonates, bicarbonates or hydroxides of alkali metals are utilized for the purpose of diminishing "the formation of dialkylene glycols and accelerate the reaction", see column 2, lines 26-30, of U.S. Patent 3,629,343. In the practice of that process, such basic compounds are employed in combination with halo salts of tetralkylammonium compounds.The examples in this patent illustrate the basic compounds as including sodium bicarbonate, potassium bicarbonate, sodium carbonate, and sodium hydroxide. In the examples of this patent, the maximum yield of monoalkylene glycol was 95.5 percent, based on initial alkylene oxide concentration.

The subject matter of this patent has been carefully reviewed by the Stanford Research Institute, in the private report entitled "Ethylene Glycols, Glycol Ethers and Ethanolamines", Process Economic Program, Report No. 70 (1970). In Report No. 70, a careful consideration was given to British Patent No. 338,026, published in 1 970, which corresponds to U.S. Patent 3,629,343. The author of the report notes the postulation of the reactions which take place in the process of the aforementioned British Patent, which is, the reaction of ethylene oxide with carbon dioxide to form ethylene carbonate and the hydrolysis of the ethylene carbonate to form monoethylene glycol.According to the patent, these reactions are effected simultaneously. However,tin a continuous operation employing multiple reactors, the first reactor involves the utilization of a carbonation catalyst and carbon dioxide and the second reactor, in series with the first, employs hydrolysis using various bases. Report No. 70 attempts to characterize a continuous process from the data which is contained in the aforementioned Sntlsh Patent. In characterizing a continuous process, the report points out that the water to oxide feed ratios were 1.04 to 1 and 1.06 to 1 in the two examples demonstrating a continuous process.In the second reactor, in which the base, water and carbon dioxide were provided, the temperature was 2000C and the pressure in the whole system was 25 to 30 atmospheres, that is 367.5 pounds per square inch to 441 pounds per square inch, respectively.

According to the author of the report, it is believed that much of the critical materials of construction will have to be expensive Monel(R) (Registered Trade Mark) clad construction. In characterizing the continuous process that the authors have discussed in the report, there is an assumption that 90% of the catalyst can be recycled which is regarded as economically important. In defining catalyst recycle, the following is stated: "The system for catalyst recycle, based on crystallization from the cooled, heavy ends, with recycle of a thickened catalyst slurry, is quite uncertain, requiring data on solubility relationships and other factors, which are not available".

Thus, the process as described in Levin et al and characterized in the Stanford Research Institute Report is a continuous process which utilizes pressures in excess of 367 pounds per square inch.

Additionally, said process uses halo salts of tetralkylammonium compounds along with the basic catalyst so that halide is present in an aqueous system. The halide creates corrosion problems and thus necessitates the use of reactors made out of costly specialized materials to prevent corrosion. Figure 5.1 of the report schematically illustrates equipment and process design for making "ethylene glycols by carbonation process". Presence of halides in the column bottoms illustrated in Figure 5.1 would result in higher concentrations of heavy residual material. In addition, as the report points out, catalyst recycle would be very difficult.

Literature reports by N.N. Lebedev et al entitled "Kinetics and Selectivity in Ethylene Oxide Hydrolysis when Catalyzed By Salts of Carboxylic Acids", translated from Kinetika i Kataliz, Vol. 1 7, No.

4, pp. 888-892, July-August, 1 976 (hereinafter Report I) and N.N. Lebedev et al, "Selectivity of (E- Oxide Hydrolysis Catalyzed by Carbonates", translated from Kinetika i Kataliz, Vol. 1, No. 3, pp 583588, May-June, 1976, (hereinafter Report II) describe studies wherein glycol esters are produced from ethylene oxide and subsequently hydrolyzed to the glycol.

In Report lit is shown that when ethylene oxide is hydrolyzed in aqueous solutions of carboxylic acid salts, ethylene glycol is formed in quantitative yield. Polyglycols are formed only in parallel alkaline and non-catalytic hydrolysis reactions. Report I then concludes that due to the marked contribution from alkaline hydrolysis (formed from reaction (II), page 775) when carbonate and oxalate (also acetate and formate) ions are used as catalysts, the greatest yield of monoglycol (monoethylene glycol) occurs when bicarbonate ions are used as catalysts.

Report II describes the selectivity of oxide hydrolysis catalyzed by carbonates. Specifically, ethylene oxide is hydrolyzed to ethylene glycol with and without catalyst and with and without CO2 at pressures of 0 to 146 psig. Report II states on page 512: "At high bicarbonate and glycidol concentrations the steady alkali concentration reaches values at which alkaline hydrolysis is fast and leads to an increase in the yield of polyglycerols.

Hydrolysis under the pressure of carbon dioxide promotes the reverse conversion of alkali to bicarbonate and heightens the glycerol yield, the calculated values of the latter coinciding under these conditions with the experimental values (Fig. 3, Table 3). Propylene and ethylene glycol carbonates are hydrolyzed far more rapidly. For this reason, even at high reagent concentrations the steady alkali concentration is low and carbon dioxide has no effect on the distribution of the products of these reactions".

Also, neither of the processes as described in Reports I and li utilize an organic solvent.

The process of this invention is directed to the manufacture of alkylene glycols, such as ethylene and propylene glycol, by the hydrolysis of the corresponding alkylene oxide, such as ethylene or propylene oxide, in the presence of CO2 at a temperature between about 850 and 4000C and pressure of less than about 350 psig, in the presence of selected catalysts. Preferably the reaction is affected in an organic solvent.

It has been discovered that the process of the present invention is very selective toward the formation of monoethylene glycol. Additionally, the process of the present invention does not require the use of a halide ion containing compound, which halide ion necessitates the use of special equipment to prevent corrosion caused by the halide ion. The process of this invention does not suffer from any problem in catalyst recycle and it can be carried out in conventional metal equipment, such as stainless steel. Moreover, the process of the present invention takes place under conditions of temperatures and pressures existing in commercial operations which means that the present process can be used with equipment which is available in existing commercial facilities. This is quite important since little if any investment in new equipment would be required.Moreover, it has been found that the initial concentration of alkylene oxide has no effect on the product distribution so that concentrated alkylene oxide solutions may be treated according to the process of the present invention. Furthermore, the process of the present invention may be utilized to treat the major waste streams emanating from a process in which ethylene oxide is carbonated and subsequently hydrolyzed to monoethylene glycol as set forth in United States Patent No. 4,1 7,250.

Another advantage of the present invention is that the hydrolysis can be utilized using waste water obtained from industrial reactions, such as, the scrubber waters in ethylene oxide production, thereby providing an ecological advantage through the operation of the process.

In the practice of this invention, an alkylene oxide is reacted with CO2 and particular catalyst to form, in situ, a cyclic or acyclic carbonate intermediate. This intermediate is hydrolyzed, using only a small excess of water, to form the alkylene glycol and regenerate CO2. CO2 can function in the reaction as a selective catalyst (it supplies a kinetically preferred reaction path by means of a carbonate intermediate which hydrolyzes to give the desired product) and also CO2 can eliminate free hydroxide ions in solution, which hydroxide ions cause loss in selectivity to monoethylene glycol. The process of the present invention is preferably carried out in the presence of an organic solvent.The organic solvent helps control the hydroxide ions and CO2 in the liquid phase which allows the use of more active catalysts, such as potassium carbonate, lower CO2 reaction pressures, and lower operating temperatures, while producing higher monoethylene glycol yields.

The catalysts which can be used in the present invention are basic compounds suitable for producing a glycol ester intermediate and include the alkali and alkaline earth metal salts of carbonates, bicarbonates, hydroxides, and phosphates. These catalysts include potassium hydroxide, potassium acetate, potassium phosphate, potassium oxalate, and the like.

The catalysts which may be used in the process of this invention include compounds which contain one to three nitrogen atoms, which when incorporated into protic medium under carbon dioxide pressure produce the carbonate salt, including a double salt. These catalysts are fully described in Patent Application Serial No. 917,329, filed on June 20, 1978, in the name of Glenn A. Taylor, titled "Hydrolysis of Aikylene Carbonates to Alkylene Glycols". These catalysts include guanidine carbonate, [[NH2C(=NH(NH)2]H]2co3; substituted guanidine carbonate|[NR2C(=NH)NR2]H]2CO3 wherein R is independently an alkyl radical of 1 to 5 carbon atoms or aryl radical of 6 or 7 carbon atoms; ammonium uranly carbonate, [(NH4)2C03 UO2CO3 xH2O] wherein x is an integer defining the water of hydration and is generally 2; ammonium carbonate, (NH4)2CO3; substituted ammonium carbonate, (RnNH4~n)2CO3 wherein R is as previously defined and n is an integer of 1 to 4.

The catalyst may be added as the salt or it may be formed in situ.

The amount of catalyst which is provided with the initial feed of reactants may range between about 0.10 to about 15.0 weight percent, based on the total weight of initial reactants. Preferably; the amount of the catalyst is about 0.5 to about 10.0 weight percent, and most preferably, the greatest catalytic effect, for the amount of catalyst employed, is achieved when the catalyst amount ranges between 0.5 and about 5.0 weight percent, based on the total weight of initial reactants. In characterizing the catalyst concentration, it has been characterized in terms of its salt.

The temperature which is necessary to hydrolyze the alkylene oxide can be as low as 85 and one might contemplate that the maximum temperature is about 400"C. However, it is preferred that a minimum temperature of 1 000C be employed and that the maximum temperature be kept below 3000C. In the most preferred operation of the reaction, it is desired that the temperature be between about 120 C and about 18000.

The pressure at which the reaction is carried out should be less than about 350 psig. The preferred operating pressure is between about 100 and about 300 psig, and the most preferred operating pressure is between about 1 50 and about 275 psig.

The organic solvent which is used in the practice of the present invention has the following characteristics: high CO2 absorbtivity; high ethylene oxide absorbtivity; inert towards ethylene oxide; totally miscible with the reaction medium; and it should be a solvent which is easily separated from the product. Any liquid at the reaction temperature, which is miscible with the alkylene oxide and the glycol product can be, to the extent that it continues to be miscible in the system a solvent provided that it is not reactive with either the alkylene oxide reactant, the glycol produced or the catalyst employed.

These solvents include ketones, esters, or ethers, such as acetone, alkylene carbonate and dioxane. It is desirable that the alkylene carbonate employed would produce an alkylene glycol the same as the product glycol being produced.

The solvent is added in amounts of from about 5.0 to 60 weight percent, based on the weight of total feed. Preferably, the solvent is added in amounts of from about 10 to 40 weight percent.

The initial mole ratio of water to alkylene oxide which is employed in the hydrolysis reaction, that is, the amount of water which is combined with the alkylene oxide in the reaction zone in order to effect hydrolysis, should be at least one mole of water per mole of alkylene oxide. However, from a practical standpoint, in order to achieve the kind of performance characterized for the process of this invention, one should employ at least about 1.0 mole of water and at most about 20 moles of water for each mole of alkylene oxide. The preferred ratio is about 2.0 to 11 the most preferred 4 to 1 0. The mole ratios of water to alkylene oxide will of course vary when organic solvent is used in the reaction.

The process of this invention may be carried out as a batch reaction or as a continuous process.

The batch reactions may be carried out in pressure resistant vessels suitably constructed to withstand the pressures of this reaction.

The process, as stated, may be employed in a conventional autoclave or can be effected in a glassware type of equipment when operated at moderate pressures. It may also be employed in a plugflow reactor utilizing conventional procedures to effect the process continuously. Solvent may be recycled and catalyst may be recovered. The process is very advantageously employed by concentrating the catalyst over a vacuum evaporator and recycling it to the reaction.

The reaction may be carried out for very short periods of time in terms of fraction of a second and if desired may be carried out over reaction periods amounting to hours, if desired. These conditions of reaction are governed by the amounts of solvent and catalyst employed, the pressure and temperature employed, and like considerations.

The following examples depict various modes in the practice of this invention including those modes which are considered to be best for the practice of this invention. It is not intended that this invention shall be limited by the examples.

Examples 1 to 28 The reactor system was a 300 cc, 31 6 stainless steel, Parr bomb filled with provisions for batchwise charging of reactants, a gas charge tube, thermocouple, stirrer, electric heating mantel and cooling coil.

During operation, the reactor was charged with a mixture of distilled water (mole/l), catalyst (mole/l), and solvent (mole/l) and heated to reaction temperature. When the desired reaction temperature (OC shown in the Table) was reached, either carbon dioxide or nitrogen was sparged into the reactor. The reactor was brought to 100 psig below the desired operating pressure. At this point ethylene oxide (mole/l) was charged to the reactor. The system was brought to operating pressure (psig shown in the Table) and allowed to react for a period of one hour.

Upon completion of the run, the reactor contents were discharged and weighed. The quantity of liquid product was used to estimate the overall reactor mass balance. The liquid product was analyzed for water (weight percent by the Karl Fisher method) and monoethylene glycol, diethylene glycol and triethylene glycol (weight percent by vpc) to determine conversions and efficiency. The vpc employed used a 1D ft by 1/8 inch stainless steel column packed with Tenax-GC.

The following Table lists the catalyst, the atmosphere (CO2 or nitrogen), reaction pressure (P, psig), reaction temperature (T, OC), and the moles per liter of ethylene oxide (EO), water, catalyst and solvent used. The weight percent of monoethylene glycol (MEG), diethylene glycol (DEG) and triethylene glycol (TEG) produced, are set forth in the Table.

The reaction was carried out to at least 94 percent and in most cases' greater than 98 percent conversions of ethylene oxide to glycols as shown in the Table. The differences in percent conversions was due to differences in rates of reaction for the respective catalyst and reaction parameters for that particular experiment.

Table EO Water Catalyst Solvent MEG DEG TEG Example Catalyst Atmosphere P(psig) T( C) (Mole/I) (Mole/I) (Mole/I) (Mole/I) (wt.%) (wt.%) (wt.%) 1 - N2 250 140 2.57 49.25 - - 88.8 11.1 0.10 2 - CO2 250 150 2.57 49.39 - - 90.8 9.1 0.10 3 - CO2 300 150 1.93 50.08 - - 92.8 7.17 0.08 4 KHCO3 N2 250 140 2.75 47.50 0.239 - 94.1 5.9 < 0.01 5 KHCO3 CO2 250 140 2.46 48.19 0.243 - 94.6 5.4 < 0.01 6 K2CO N2 250 140 2.43 47.76 0.241 - 93.0 7.0 < 0.01 7 K2CO3 CO2 250 140 4.58 42.57 0.231 - 95.6 4.1 < 0.30 8 K2CO3 CO2 250 140 2.53 47.53 0.240 - 95.7 4.3 < 0.01 9 K2CO3 CO2 250 140 2.55 30.20 0.263 Acetone 97.15 2.8 < 0.05 10 K2CO3 CO2 250 140 2.81 (5.30) 11 K2CO3 CO2 250 140 2.33 48.30 0.048 - 92.3 7.7 < 0.01 12 KOH CO2 250 140 2.44 44.38 0.712 - 97.7 2.3 < 0.01 13 KOH CO2 150 140 2.62 48.82 0.247 - 94.2 5.8 < 0.01 14 KOH N2 250 140 2.71 48.38 0.244 - 94.7 5.2 0.10 15 CH3COOK N2 250 140 2.50 48.16 0.243 - 72.0 27.0 1.00 16 CH3COOK N2 250 140 3.04 48.11 0.242 - 92.0 8.0 < 0.01 17 Guanidine N2 250 140 2.66 46.82 0.236 - 95.5 4.5 < 0.01 Carbonate 46.68 0.235 - 92.4 7.6 < 0.01 18 Guanidine CO2 250 140 2.65 Carbonate 46.72 0.235 - 96.0 4.0 < 0.01 19 Potassium CO2 250 140 2.56 Phosphate 46.52 0.234 - 95.6 4.4 < 0.01 20 NaHCO3 N2 350 95 2.73 31.59 0.199 Dioxane 89.7 10.3 < 0.01 21 NaHCO3 CO2 350 95 2.74 (3.34) 31.65 0.199 Dioxane 91.6 8.4 < 0.01 22 NaHCO3 CO2 700 90 1.34 (5.30) 34.2 0.039 Dioxane 97.8 2.2 < 0.01 23 Et4NBr/K2CO3(1) CO2 250 140 2.64 (3.65) 47.83 0.117/ - 98.8 1.2 < 0.01 24 Et4NBr/K2CO3 CO2 250 140 2.47 0.118 30.26 0.110/ Acetone 99.5 0.5 0.001 25 Et4NBr/K2CO3 CO2 500 155 1.88 0.110 (5.30) 37.18 0.047/ (A) 96.6 3.4 0.001 0.020 26 KI/NaHCO3 CO2 500 94 2.26 21.73 0.059/ Acetone 97.8 2.2 < 0.01 0.130 (8.42) 27 Et4NBr CO2 250 140 2.63 46.72 0.205 - 92.95 6.90 0.15 28 K2CO3 CO2 254 140 2.53 47.53 0.240 - 95.7 4.3 < 0.001 )Et4NBr=tetraethylammonium bromide A=0.99 moles/liter of MEG and 1.88 moles/liter of EC. (This illustrates treating a waste stream emanating from a process in which ethylene oxide is carbonated and subsequently hydrolyzed to monoethylene glycol.

Claims

1. A process for producing alkylene glycol which comprises hydrolyzing alkylene oxide with water in the presence of carbon dioxide at a carbon dioxide pressure of less than 350 psig and a temperature between about 850C and 4000C and a non-halogen containing catalyst which is suitable for producing a glycql ester intermediate and is an alkali metal carbonate, phosphate or acetate, an alkaline earth metal carbonate, phosphate or acetate, or a guanidine carbonate.

2. A process as claimed in claim 1, wherein the pressure is between about 100 and 300 psig.

3. A process as claimed in claim 2, wherein the pressure is between about 1 50 and 275 psig.

4. A process as claimed in any of the preceding claims, wherein the temperature is between about 100 C and 3000C.

5. A process as claimed in claim 4, wherein the temperature is between about 1200 and 1 800C.

6. A process as claimed in any one of claims 1 to 5, wherein the catalyst is potassium carbonate.

7. A process as claimed in any one of claims 1 to 5, wherein the catalyst is potassium phosphate.

8. A process as claimed in any one of claims 1 to 5, wherein the catalyst is potassium acetate.

9. A process as claimed in any one of claims 1 to 5, wherein the catalyst is guanidine carbonate.

10. A process as claimed in any one of the preceding claims which is effected in the presence of an organic solvent.

11. A process as claimed in claim 10 wherein the organic solvent is selected from ketones, esters or ethers.

12. A process as claimed in claim 11 wherein the solvent is acetone.

13. A process as claimed in claim 11 wherein the solvent is alkylene carbonate.

14. A process as claimed in claim 13 wherein the alkylene carbonate is ethylene carbonate or propylene carbonate.

1 5. A process as claimed in claim 11 wherein the solvent is dioxane.

16. A process as claimed in claim 1 wherein the alkylene glycol is ethylene glycol.

17. A process as claimed in claim 1 wherein the alkylene glycol is propylene glycol.

1 8. A process for producing alkylene glycol substantially as hereinbefore described in any one of the foregoing Examples.

1 9. A process for producing alkylene glycol which comprises hydrolyzing alkylene oxide with water in the presence of carbon dioxide at a carbon dioxide pressure of less than 350 psig and a temperature between about 850C and 4000C and a non-halogen containing catalyst which is suitable for producing a glycol ester intermediate and is an alkali metal carbonate or phosphate, an alkaline earth metal carbonate or phosphate or a guanidine carbonate.

20. Alkylene glycol whenever produced by a process as claimed in any one of claims 1 to 18.

21. Alkylene glycol whenever produced by a process as claimed in claim 19.