AU1750895A - Polyglycol finishing process - Google Patents

Description

POLYGLYCOL FINISHING PROCESS

RAP flRODWD OF THE TrJVRNTTON The present invention relates to the field of polyglycol finishing processes. More particularly, it relates to a polyglycol finishing process having reduced amounts of solid or liquid wastes.

Processes for preparing and finishing polyglycols are numerous in the art. Commonly a catalyst is used in the polyglycol preparation process, and such catalyst is typically a basic catalyst such as KOH or another alkali metal hydroxide. It can be desirable to remove the catalyst or neutralize it with an acid before using the polyglycol for a final purpose, since the basicity in the polyglycol may adversely affect the reaction or reactivity of the composition of the final purpose. Such is especially true when a polyglycol is to be used to prepare a polyurethane related product, since the presence of unneutralized catalyst may result in over-catalysis of the reaction desired, e.g., a polyurethane-forming reaction. Weak acids and dilute acids can be used for the neutralization and the resultant salts left in the polyglycol in some cases, but the salts tend to act as catalysts when the polyglycol is used in certain reactions, such as for polyurethane formation, and can enhance the rate of reaction to an undesirable or unacceptable extent.

To counter the undesirable effects of leaving the resultant salts in the polyglycols, various means for their removal have been developed. For example, processes combining crystallization and filtration allow for removal of the salts. Other known means of removing salts include extraction, for example, washing, and adsorption using various adsorbents including, for example, ion exchange media.

However, each of these conventional means of removal have some significant disadvantage. One disadvantage is that they require one, or more, separate removal steps following the neutralization, which involves, in many cases, additional time, equipment expense, solvent expense and the like. Accordingly, it would be desirable in the art to have a means of "finishing" a polyglycol that would preferably reduce processing steps and reduce waste products that must be removed.

SUMMARY OF THE INVENTION

The present invention is an improvement in a process for finishing a crude polyglycol prepared with a basic catalyst, the process including at least the step of contacting the polyglycol with an acid, the improvement comprising using hypophosphorous acid as the acid and filtering the resulting solids.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment, the present invention is an improvement in a process for preparing and finishing a polyglycol. For the purposes of the present invention, polyglycols, sometimes also referred to as polyols, polyether polyols, or just polyethers, can include a wide range of commonly and conventionally known hydroxy-functional polyethers. These include, for example, polyalkylene polyethers having at least one hydroxyl group, preferably, polyalkylene polyether polyglycols. These polyethers include the polymerization products of oxiranes or other oxygen-containing heterocyclic compounds, such as tetramethylene oxide prepared in the presence of a catalyst and/or initiated by water, and polyhydric alcohols having from two to eight hydroxyl groups, amine groups, or other active hydrogen sites. Preferably, the polyethers have at least some oxypropylene units produced from propylene oxide. As is known to those skilled in the art, propylene oxide can be homopolymerized or copolymerized with one or more other oxiranes or other oxygen-containing heterocyclic compounds. The oxygen-containing heterocyclic compounds are preferably alkylene oxides.

The oxygen-containing heterocyclic compounds, hereinafter exemplified by but not limited to alkylene oxides, are suitably reacted either in mixture or sequentially. When more than one alkylene oxide is used, resulting polyethers can contain random, block, or random-and-block distributions of monomers. Mixtures of alkylene oxides most often produce randomly distributed alkylene oxide units. Sequential addition of different alkylene oxides most often produces blocks of the alkylene oxide segments in a polyether chain.

Exemplary oxiranes suitable for preparation of polyethers include ethylene oxide, propylene oxide, butylene oxide, amylene oxide, glycidyl ethers such as t-butyl glycidyl ether, phenyl glycidyl ether and the like. Other suitable oxiranes include 1,2-butylene oxide, 1,2-hexylene oxide, 1,2-decene oxide, 2-methoxy propylene oxide, methoxy ethylene oxide, 2,3-butylene oxide, 2,3-hexylene oxide, 3,4-decene oxide, 1,1,l-trifluoromethyl-2,3-epoxyoctane, and the like. The polyethers are also prepared from starting materials such as tetrahydrofuran copolymerized with alkylene oxide; epihalohydrins such as epichlorohydrin, epiiodohydrin, epibromohydrin,

3,3-dichloropropylene oxide, 3-chloro-1,2-epoxypropane,

3-chloro-1,2-epoxybutane, 3,4-dichloro-1,2-epoxybutane,

3,3,3-trichloropropylene oxide and the like; arylalkylene oxides such as styrene oxide; and the like. Preferably, the polyethers are prepared from alkylene oxides having from two to six carbon atoms such as ethylene oxide, propylene oxide, and butylene oxide.

For the purposes of the present invention, the polyethers, when prepared by the process described above, are prepared from at least 10, more preferably at least 50, and even more preferably at least 80 percent of an alkylene oxide selected from the group consisting of propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide or mixtures thereof. Most preferably, propylene oxide is selected. Homopolymers of propylene oxide, or copolyethers of propylene oxide with ethylene oxide, butylene oxide and mixtures thereof are preferred for use in the practice of the invention.

Illustrative alcohols suitable for initiating formation of a polyalkylene polyether include glycerine, ethylene glycol, 1, 3-propylene glycol, dipropylene glycol, 1,2-propylene glycol. 1,4-butylene glycol, 1,3-butylene glycol, 1, -butylene glycol, 1,5-pentane diol, 1,7-heptane diol, 1,1,l-trimethylolpropane, 1,1,1-trimethylolethane, hexane-l,2,6-triol, alpha-methyl glucoside, pentaerythritol, erythritol and sorbitol, as well as pentols and hexols. Sugars such as glucose, sucrose, fructose, maltose and the like and compounds derived from phenols such as

(4,4' -hydroxyphenyl) ,2-propane, bisphenols, alkylphenols such as dodecylphenol, octylphenol, decylphenol and mixtures thereof and the like are also suitable for forming polyether polyols useful in the practice of the invention. Mono-alcohols, preferably mono-alcohols having from 1 to 18 carbon atoms and alkoxy-substituted mono-alcohols, including methanol, ethanol, isomers of propyl alcohol, isomers of butyl alcohol, and ethers thereof, are also suitable for forming the hydroxy-functional polyethers.

Amines suitable for reaction with oxiranes to form polyethers include aliphatic and aromatic mono- and polyamines, optionally having substituents such as alkyl, carboxyl, carboalkoxy groups and the like. Exemplary aromatic amines include aniline, o-chloroaniline, p-phenylene diamine, 1,5-diaminonaphthalene, methylene dianiline, the condensation products of aniline and formaldehyde, 2,4-diamino toluene, ethylene diamine, toluene diamine and the like. Exemplary aliphatic amines include methylamine, triisopropanolamine, isopropanolamine, diethanolamine, triethanolamine, ethylenedia ine, 1, 3-propylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, mixtures thereof and the like. Amine based polyglycols are disclosed in further detail in, for example, U.S. Patent 4,358,547.

Polyethers preferably can have an average of from 1 to 8, preferably from 2 to 4, hydroxyl groups per molecule. The polyethers also are preferably of relatively high molecular weight, having molecular weights ranging from 88 to 50,000, preferably from 1,000 to 7,500. The polyethers may also preferably be capped, for example, with ethylene oxide used to cap propylene oxide, as is well-known to those skilled in the art. The polyethers used in the present invention can be prepared by processes known to those skilled in the art, and are further discussed in, for example, Encyclopedia _£ Chemical Technology. Vol. 7, pp. 257-2e2, Interscience Publishers (1951); M. J. Schick, Nonionic Sur ctants. Marcel Dekker, New York (1967); British Patent 898,306; and U.S. Patents 1,922,459; 2,871,219; 2,891,073; and 3,058,921. One or more catalysts are advantageously used in the preparation of the hydroxy-functional polyether. Conventional catalysts include alkali or alkaline earth metals or their corresponding hydroxides and alkoxides, Lewis acids, protonic acids, coordination compounds and the like.

Thus, such catalysts preferably contain a Group IA or Group IIA metal ion. One skilled in the art can readily determine suitable amounts of alkylene oxides, initiators, catalysts and adjuvants as well as suitable processing conditions for polymerizing the alkylene oxides. Additional sources of detail regarding polymerization of alkylene oxides include, e. g., R. A. Newton, "Propylene Oxide and Higher 1,2-Epoxide Polymers" in Encyclopedia __L Chemical Technology. 3rd ed. , Vol. 10, R. Kirk and D. F. Othmer, John Wiley _ Sons, New York (1982,) p. 633; D. J. Sparrow and D. Thorpe, "Polyols for Polyurethane Production" in Telechelic Polymers: Synthesis and pplica ion. E. J. Goethals, CRC Press, Inc., Boca Raton, Florida (1989), p. 181; J. Furukawa and T. Saegusa, Polymerization o_£ Aldehydes and Oxides. Interscience, New York (1963), pp. 125-208; G. Odian, Principles __ Polymerization. John Wiley _ Sons, New York (2nd ed. 1970) pp. 512-521; J. McGrath, ed. , Ring-Opening Polymerization. Kinetics Mechanisms. and Synthesis. American Chemical Society, Washington, D.C. (1985) pp. 9-21, 137-147 and 204-217; and U.S. Patents 2,716,137; 3,317,508; 3,359,217; 3,730,922; 4,118,426; 4,228,310; 4,239,907; 4,282,387; 4,326,047; 4,446,313; 4,453,022; 4,483,941 and 4,540,828.

Preferred catalysts for polyglycol production are basic catalysts, more preferably hydroxides and alkoxides of alkali metals: lithium, sodium, potassium, rubidium, and cesium. Potassium hydroxide is preferred. When alkoxides are used as catalysts, the alkoxy groups advantageously contain from one to 36 carbon atoms. Exemplary of such alkoxides are alkoxides having anions of propylene glycol, glycerine, dipropylene glycol, propoxylated propylene or ethylene glycols and the like.

Embodiments of the present invention include processes wherein KOH is used as a catalyst for preparing polyglycols and some portion of the KOH is residual in the crude polyglycol . For purposes of the present invention, the term "crude polyglycol" means a polyglycol which, during the process of being prepared, has achieved substantially all of the molecular weight intended, but has not been finished by removal of residual catalyst.

In practicing embodiments of the present invention, preferably the crude hydroxy-functional polyether is pre-treated to remove excess catalyst. Removal of excess base catalyst is typically desirable because residual catalyst concentrations in the unfinished polyether are generally high, i.e., more than 500 ppm, since such concentrations are needed to provide the desired rate of alkoxylation in preparing the hydroxy-functional polyether. To simply neutralize such a high level of catalyst may be too expensive or cause technical problems. Therefore, it is commercially preferred to use means other than neutralization to remove most of the initial amount of catalyst prior to finishing the polyether according to the process of the present invention. Typically such means employed include centrifugation, water-washing, extraction, the use of ion exchange resins, and the like, as are known to and practiced by those skilled in the art. In a preferred embodiment, the excess catalyst is removed to a level of less than or equal to 100 ppm, more preferably less than or equal to 50 ppm, and most preferably less than or equal to 25 ppm, prior to treatment with hypophosphorous acid.

The present invention can be practiced in processes wherein the polyglycol contains some oxyethylene structures. But oxyethylene structures within a polyglycol can affect the amount of water that remains entrapped within a polyglycol prior to and after dewatering. Polyglycols which can be used with the present invention are those having less than 40 weight percent, preferably less than 30 weight percent, and even more preferably less than 25 weight percent oxyethylene groups. After dewatering, preferably the polyglycol has less than 0.20, more preferably less than 0.15 percent, and even more preferably less than 0.10 percent water remaining within the polyglycol prior to contacting the polyglycol with hypophosphorous acid. Residual water can be dissolved, or dispersed within the polyglycol or, more likely, both.

Hypophosphorous acid is advantageously used in the process of the present invention for at least two reasons. Surprisingly, hypophosphorous acid - alkali metal salts (hereinafter alkali metal hypophosphites) are very insoluble in some polyglycols. The polyglycols useful with the present invention include those having hydroxy equivalent weights of 700 to 10,000 preferably 800 to 8,000 and even more preferably 1,000 to 7,000. It is these polyglycols in which alkali metal hypophosphites are very insoluble.

The alkali metal hypophosphites, when precipitated from polyglycols useful with the present invention, can be in the form of long branching crystals and can have diameters of from 0.001 to 0.006 mm. Such large crystals are advantageously easy to filter. As a result of the easy filtration of alkali metal hypophosphites crystals and the very low level of solubility of alkali metal hypophosphites, very low residual levels of catalyst cations in the finished polyglycols can result from the finishing process of the present invention. Polyglycols prepared with a KOH catalyst and finished by the process of the present invention can have a potassium concentration of less than 20 ppm, preferably less than 10 ppm and even more preferably less than 5 ppm.

In the practice of the present invention, hypophosphorous acid can be added to a crude polyglycol in any way known to be useful to one skilled in the art of finishing polyglycols. Hypophosphorous acid can be obtained as an oily liquid, deliquescent crystals or an aqueous solution. Preferably, the hypophosphorous acid is added to a polyglycol in the form of a 50 weight percent aqueous solution and admixed until all of the residual basic catalyst is neutralized. Preferably, the crude polyglycol is maintained at a temperature of from 90°C to 140°C during this process.

One important factor in practicing the method of the present invention is promoting large crystal growth. If too little acid is added, then residual catalyst will remain in the polyglycol after finishing which can be undesirable. If too much acid is added, then undesirable side reaction can occur within the polyglycol upon storage. End uses could also be restricted if acid levels in the polyglycol are too high. Preferably, the amount of residual basic catalyst in the crude polyglycol is determined and sufficient hypophosphorous acid is added to the polyglycol to achieve a molar ratio of hypophosphorous acid to basic catalyst of from 0.95 to 1.15, more preferably 1.00 to 1.12 and most preferably 1.05 to 1.10.

The alkali metal hypophosphite crystals formed in practicing the process of the present invention are easily filterable with any suitable conventional filter apparatus. For example, the polyglycol can be passed through a filter bed composed of diato aceous earth, entrapping the salt crystals. Also usable with the present invention are paper and cloth screen filters. Metal screen filters are also known to be used with polyglycols. Combinations of all or part of these filtering means can also be used with the present invention. Any filtering means which is compatible with polyglycols and has a porosity sufficient to pass the polyglycol and trap the alkali metal hypophosphite crystals can be used with the process of the present invention.

The following examples are provided ro illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated. EXAMPLE 1

A propylene oxide polyglycol having a nominal hydroxy functionality of 3 was prepared by admixing a 450 molecular weight glycerine initiated propylene oxide polyglycol with propylene oxide in the presence of KOH under a nitrogen pad, the KOH being at a concentration of 3 percent by weight. The reaction was carried out at from 110°C to 120°C and at from ambient pressure to 80 psig (551 KN/m²) . The resultant crude polyglycol had 3,500 ppm KOH which was lowered to 63 ppm by water-washing. The water content was then lowered to less than 1.5 percent by dewatering. The polyglycol was next neutralized using a 50 weight percent aqueous solution of hypophosphorous acid at a molar ratio of 0.97:1 or a weight ratio of 2.3:1 of hypophosphorous acid to residual KOH. The resulting polyglycol was then filtered through a filter using DietE as filtration media. DietE is a diatomaceous earth having a bulk density of 260 g/1 and 10 percent residual through mesh, of 325 Tyler (0.044mm) . The properties of the polyglycol, and sold wastes generated were measured and are listed below in the Table.

COMPARATIVE EXAMPLE 2

A polyglycol was prepared and finished substantially identically to Example 1 except that instead of being treated with hypophosphorous acid, the crude polyglycol was filtered through a bed of magnesium silicate. Resultant waste volumes were calculated and using magnesium silicate resulted in an 1200 percent increase in waste volume. The properties of the polyglycol were measured and are listed below in the Table.

Table

Example S/Finishing Example 1/ Comparative 2/ Type H₃P0₂ MagSil

OH Number^{1 m}9 KOH/g 56.76 56.43

OH Percent² 1.72 1.71

Water Percent³ 0.056 0.043

PH⁴ 8.5 8.2

Acid No.^{5 m}eq g <0.01 <0.01

Unsaturation⁶ <0.05 <0.05

Color, APHA⁷ 0/5 10

Viscosity⁸ ®100°F 237 236 (37.8°C) cST

[K+] 9ppm 3 0.25

Appearance¹⁰ CLEAN CLEAN

1. ASTM D-4274

2. ASTM D-4274

3. ASTM D-4672

4. ASTM E-70

5. ASTM D-4662

6. ASTM D-4671

7. ASTM D-1209

8. ASTM D-445

9. ASTM D-4668

10. ASTM D-4670

COMPARATIVE EXAMPLE 3

A polyglycol was prepared and finished substantially identically to Example 1 except that instead of being treated with hypophosphorous acid, the crude polyglycol was treated with orthophosphoric acid. No filterable salt crystals were observed.

Claims (1)

1. WHAT IS CLAIMED IS:

   1. In a process for finishing a crude polyglycol prepared with a basic catalyst, the process including a step of contacting the crude polyglycol with an acid, the improvement characterized as using hypophosphorous acid as the acid and filtering the resulting solids.

   2. The process of Claim 1 wherein the crude polyglycol has an hydroxy equivalent weight of from 700 to 10,000.

   3. The process of Claim l wherein the concentration of residual basic catalyst is determined and the polyglycol is then contacted with hypophosphorous acid at a molar ratio of hypophosphorous acid to basic catalyst of from 0.95 to 1.15.

   4. The process of Claim 3 wherein the molar ratio is 1.00 to

   1.12.

   5. The process of Claim 1 wherein the solids are filtered using a bed of diatomaceous earth.

   6. The process of Claim 1 wherein the solids are filtered using a screen filter.

   7. The process of Claim 6 wherein the screen filter is a cloth covered screen filter.

   8. A polyglycol prepared by the process of Claim 1.