BACKGROUND OF THE INVENTION

The present invention relates to a process for the removal of a pH-basic material from a polyether polyol.

Polyether polyols are reacted with polyisocyanates to produce polyurethanes. These polyether polyols are produced by polymerization reactions catalyzed by alkaline materials such as potassium hydroxide. These alkaline materials must be removed or at least substantially removed from the product polyether polyol to avoid adverse effects upon the characteristics of polyurethane plastics and foams produced from the polyol. These alkaline materials are often removed by simply adding acid to the polyol polymerizate containing alkali metal catalyst to neutralize the alkaline catalyst. An insoluble salt is formed. This insoluble salt may then be removed from the polyol by filtration.

U.S. Patent 3,582,491 discloses a method for removing inorganic catalyst from polyols in which a mixture of water, water- insoluble polyether, and a solvent which is substantially immiscible in water is subjected to electrostatic coalescence. Two phases are generated. The first phase is an aqueous phase containing water -soluble materials such as the inorganic catalyst present in the polyol. The second phase is an organic phase in which both the polyether and the water-immiscible solvent are present. This second organic phase must be further treated (e.g., by distillation or vacuum distillation) to remove the organic solvent from the polyether polyol.

U.S. Patent 3,715,402 discloses a process for the removal of catalysts from polyols in which a mixture of water, polyether, a solvent in which the polyether is soluble and an acid is subjected to electrostatic coalescence or centrifugation. Two streams are recovered by this process. The first stream is an aqueous stream in which the water soluble materials, including the catalyst, are present. The second stream is a solution of the polyether polyol in the solvent. This second stream must be further treated (e.g., by distillation or vacuum distillation) to separate the polyether polyol from the solvent. U.S. Patent 4,029,879 discloses a process for the removal of catalysts from polyether polyols in which from 1 to 5% (based on polyether polyol) of water, is added to an adsorbent synthetic magnesium silicate-polyol mixture. The resultant mixture is heated for at least one hour at a temperature of from about 80 to about 130 ^β C and then filtered to remove the adsorbent which contains the catalyst. The polyol is then stripped of water and other volatile materials by heating at 80 to 130°C (1 to 10 mm mercury pressure).

U.S. Patent 4,129,718 also discloses a process for removal of catalysts from polyether polyols. In this disclosed process, crude polyol, an adsorbent and water are mixed at a temperature of from about 80 to 130°C for at least 45 minutes and treated with carbon dioxide just prior to filtration. After filtration, the polyol is stripped of water and other volatile materials present.

Each of these known procedures is disadvantageous in that a significant amount of neutralization salt or adsorbent-containing alkaline catalyst must be disposed of as waste. These procedures also reduce the yield of polyol because residual polyol present in the neutralization salt or on the adsorbent is lost. The polyether polyol must also be further treated to remove solvent.

U.S. Patent 4,482,750 discloses a process for removing alkaline catalysts from polyether polyols in which water and optionally an inert organic solvent are added to an alkaline polyether polyol to form an emulsion. The emulsion is maintained at a temperature of at least 70°C for at least 30 minutes with little or no stirring in order to destabilize the emulsion. The destabilized emulsion is then passed through a sheet-formed structure made of fine fibers to separate the aqueous phase from the organic phase. Residual alkaline material is then removed from the organic phase by, for example, adding an acid or adsorbent to the organic phase and then distilling off any solvent or water which is still present. One of the disadvantages of this process is that it requires a significant amount of time to destabilize the emulsion prior to separation of the organic and aqueous phases. Another disadvantage of this disclosed process is that only certain types of polyether polyols may be treated effectively.

Devices for separating mixtures such as the polyether polyol poiymerizates discussed above are also known. These devices generally require specialized media, electricity or complicated flow paths. U.S. Patent 3,919,081, for example, discloses a process for separating an emulsion of water and an insoluble hydrocarbon in which a tank having a solid medium in granular form is employed. The solid medium disclosed in this patent is activated carbon.

U.S. Patent 4,661,227 discloses an apparatus for the removal of inorganic aqueous solutions from organic solvents in which a coalescer is employed. The coalescer is a vertical housing having a central electrode which is constructed of conical members that define a tortuous flow path.

A process for removing a pH-basic material from a polyether polyol in which large amounts of neutralization salt are not generated, organic solvents are not needed, specialized adsorbent materials are not required and simple, standard coalescers could be used would, therefore, be an improvement over the current commercial processes.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for removing a pH-basic material, particularly an alkaline catalyst, from a polyether polyol. It is another object of the present invention to provide a process for removing a pH-basic material from a polyether polyol in which significantly less solid waste is generated than in prior art processes.

It is a further object of the present invention to provide a process for the removal of alkaline materials from polyether polyols in which 90% or more of the residual pH-basic material is removed prior to addition of a neutralizing acid.

It is another object of the present invention to provide a process for removing alkaline materials from polyether polyols in which the polyol/water emulsion need not be destabilized prior to passage through the coalescer.

It is also an object of the present invention to provide a polyether polyol having improved color characteristics in which substantially all pH-basic material has been removed prior to traditional purification treatments.

These and other objects which will be apparent to those skilled in the art are accomplished by combining (a) a polymerizate made up of a polyether polyol and a pH-basic material with (b) water and, if the difference in specific gravity of the organic phase and the aqueous

phase is less than 0.1, (c) an inorganic salt (preferably in the form of an aqueous solution of the inorganic salt) at a temperature of from about 90 to about 150°C under conditions such that an emulsion forms. This emulsion is then passed directly through a coalescer at a rate which ensures the formation of two phases. The optimum residence time in the coalescer will vary depending on specific process conditions and the type of polyether polyol used. For most of the common commercial polyether polyols, a residence time of at least 30 minutes is required. The two phases formed in the coalescer are (1) an aqueous phase containing the pH-basic material and (2) an organic phase containing the polyether polyol. These phases exit the coalescer at different points and are directed to different retaining vessels. The polyether polyol-containing phase may then be further treated with an acid to precipitate out an insoluble salt of the pH-basic material.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of the process of the present invention.

Figure 2 illustrates one arrangement of equipment useful for the practice of the present invention in which the coalescer is a vertical packed column.

Figure 3 illustrates an arrangement of equipment suitable for the process of the present invention in which the coalescer is a T- shaped, two-stage coalescer. DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to a process for removing a pH- basic material, particularly an alkaline catalyst, from a polyether polyol polymerizate in which the amount of solid waste product to be disposed of is significantly reduced. In this process, a polyether

polyol polymerizate in which a pH-basic material is still present is combined with water and, if the difference between the specific gravity of the organic phase and the specific gravity of the aqueous phase is less than 0.1, an inorganic salt in a manner such that an emulsion forms. If used, the inorganic salt is preferably used in the form of an aqueous solution.. The emulsion is then passed directly through a coalescer to cause separation into two phases. One phase is an aqueous phase containing a substantial amount of the alkaline catalyst. The second phase is an organic phase containing the polyether polyol. No organic solvent is added to the polyether polyol polymerizate either prior to formation of the emulsion or passage through the coalescer.

Polyether polyols are generally produced by adding alkylene oxides, particularly propylene oxide and/or ethylene oxide, to a starting material having acidic hydrogen atoms (e.g., water, polyalcohols or polyamines) in the presence of a pH-basic catalyst (generally, an alkali metal hydroxide). The amount of catalyst generally used in such processes is from about 0.1 to about 1.0%, by weight. Upon completion of the alkoxylation reaction, the polyether polyol polymerizate is treated to remove as much of the basic catalyst as possible. Usually, about 0.0005% (5 ppm) or less of the catalyst remains after such treatment.

In many of the known procedures, the basic catalyst is removed by (a) neutralization of the polyether polymerizate with a dilute acid, (2) distilling off water, (3) precipitation of the inorganic salts formed by the acid-base reaction, and (4) filtering off the precipitated salt.

In the process of the present invention, the polyether polyol polymerizate is emulsified and the resultant emulsion is passed

through a coalescer to separate off an aqueous layer containing 90% or more of the pH-basic catalyst which was initially present in the polyether polyol polymerizate. The organic phase recovered from the coalescer may then be treated by known techniques. For example, dilute acid may be added to the polyether polyol recovered as the organic phase from the coalescer to neutralize any remaining pH- basic material. Water present in the polyether polyol/acid mixture may then be distilled off and the precipitated salt removed by filtration. The amount of polyether polyol lost through distillation and precipitation is substantially reduced by this process. The amount of solid waste generated by this process is also significantly reduced.

In the process of the present invention, a polyether polyol polymerizate containing a pH-basic material is combined with water and optionally, a minor amount of an inorganic salt. The inorganic salt is used when the difference between the specific gravity of the organic phase and the specific gravity of the aqueous phase is less than 0.1. An inorganic salt may also be added to polyether polyol polymerizates in which the specific gravity differential between the polyol phase and aqueous phase is greater than 0.1, but such addition of salt is not required. Because most of the commercially produced polyether polyols do not have a specific gravity which is sufficiently higher or lower than the specific gravity of the aqueous phase of the polymerizate, an inorganic acid salt will generally be added to a polymerizate treated in accordance with the process of the present invention.

Any inorganic salt which is capable of producing an aqueous solution having a specific gravity greater than the density of water is suitable. An inorganic salt which forms an insoluble salt when reacted with any acid to be used in subsequent treatments is preferred. For

practical reasons, it is most preferred that the inorganic salt be the same as the pH-basic catalyst which was used in the alkoxylation reaction to produce the polyether polyol. Examples of useful inorganic salts include: sodium chloride, potassium chloride, potassium sulfate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, barium hydroxide, and strontium hydroxide. The preferred inorganic salts include: sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, barium hydroxide and strontium hydroxide. Potassium hydroxide is the most preferred inorganic salt.

When an inorganic salt is used, the inorganic salt is generally added to water prior to combination with the polyether polyol polymerizate. However, the inorganic salt may be added simultaneously with or subsequent to addition of the water to the polyether polyol polymerizate. The amount of inorganic salt to be added depends on the stability of the emulsion generated when combining the aqueous phase and the polyol polymerizate. If the specific gravity differential between the polyol polymerizate and water is sufficient to allow easy phase separation, little, if any, salt will be required. Where the specific gravities of the polyol polymerizate and water are close, larger amounts of salt will be needed to aid coalescence and phase separation. The inorganic salt may be used in amounts of from 0 weight % up to saturation, based on the amount of water added to the polyether polyol polymerizate. For most of the commercially produced polyether polyols, from about 1 to about 15 weight % inorganic salt are preferred. Amounts of from about 2 to about 6 weight % of inorganic salt are most preferred.

The amount of water to be added to the polyether polyol polymerizate depends on the amount of pH-basic catalyst to be removed from the polymerizate. It is preferred that the minimum amount of water necessary to remove almost all of the pH-basic catalyst be used. Use of only the necessary amount of water minimizes the amount of water which must be removed by distillation after coalescence. Amounts of from about 5 to about 65% by weight, based on the weight of the total weight of the emulsion are generally useful, with amounts of from about 12 to about 26% by weight being preferred.

The water, polyether polyol polymerizate, and any inorganic acid salt are combined under conditions such that an emulsion is formed at a temperature of from about 80 to 100°C, preferably from about 90 to 100°C, and most preferably about 95°C. The emulsion is then heated to a temperature of from about 90 to 150°C, preferably from about 115 to about 130°C, and most preferably about 130°C before entering the coalescer.

In a preferred embodiment of the invention, an aqueous solution of the inorganic salt is heated to a temperature of from about 80 to 100°C, preferably from about 90 to 100°C, and most preferably about 95°C before it is combined with the polymerizate which is maintained at a temperature within the same preferred ranges. The emulsion is then heated to a temperature of from about 90 to 150°C, preferably from about 115 to about 130°C, and most preferably about 130°C before entering the coalescer.

Any of the known techniques for generating an emulsion may be used in the practice of the present invention. It is, however, preferred that both heating and mixing be done in-line, particularly where the process is to be conducted as a continuous flow process.

The time necessary to heat the materials to the necessary temperature will be dependent upon the flow rate and starting temperatures of the streams being fed to the coalescer. Mixing is preferably achieved using a static mixer. An example of a suitable static mixer is a portion of piping equipped with inserts designed to induce turbulence and mixing. Such static mixers are commercially available from Koch Engineering Company, Chemineer, Inc., TAH Industries and Sulzer Brothers, Ltd.

It is preferred, that the water, inorganic salt and polyether polyol polymerizate be combined in a static mixer under conditions such that the shear force will generate an emulsion.

Examples of other devices for generating emulsions which could be used in the process of the present invention include: pin mixers, stirred tanks, in-line agitators, impingement mixers, sonic mixers, orifice or nozzle mixers, and centrifugal pumps.

The emulsion is then passed directly through a coalescer to cause the separation of (1) an aqueous phase containing the pH- basic catalyst and added inorganic salt and (2) an organic phase which is made up primarily of polyether polyol. Any of the known coalescing devices may be used in the practice of the present invention. Specific examples of commercially available coalescers which may be used in the practice of the present invention include those available from: Otto York, Inc.; ACS Industries, Inc.; Fluid Technology Group of Facet Enterprises, Inc.; and Osmonics, Inc.

Any of the known coalescing media or packing materials having (1) a high surface area or a high surface area to volume ratio and (2) sufficient surface activity that the formation of droplets during the coalescing process is not impeded may be used in the practice of the

present invention. Coalescing media which are resistant to degradation under the highly pH-basic conditions of the process of the present invention are preferred. A coalescer in which a metal mesh coalescing medium (or packing material) is present has been found to be particularly useful. It is preferred that the metal mesh be made of stainless steel or of stainless steel through which a fibrous material such as polytetrafluoroethylene or a polyester (such as that which is commercially available under the name Dacron) is interwoven. Traditional coalescing materials having the required surface area and surface activity such as activated carbon may also be used in the practice of the present invention. The coalescer used in the process of the present invention may have one, two or more beds of coalescing medium present therein.

The emulsion is generally passed through the coalescer at a rate such that the emulsion will separate into two phases. The specific rate to be used will be dependent upon the particular coalescer being used. Suitable rates may be readily determined by those skilled in the art.

Some polyether polyols (e.g., those made from propylene oxide only) will require a very short residence time in the coalescer (e.g., 5- 10 minutes). However, most of the commonly used polyether polyols will require an average residence time of at least 30 minutes. An average residence time of from about 35 to about 420 minutes is generally sufficient. The preferred average residence is from about 50 to about 240 minutes, most preferably about 60 minutes. The emulsion is maintained at a temperature of from about 90 to about 150°C, preferably from about 90 to about 130°C, and most preferably about 130°C as it is passed through the coalescer.

In a coalescer having a metal mesh packing material, the mesh provides a high surface area medium on which the water is forced together (i.e., coalesced) to form droplets. These water droplets have a density which is sufficiently different from that of the polyol to induce their separation from the emulsion by gravity. The small amount of polyol which is soluble in the aqueous phase is also coalesced into droplets which separate by gravity. For example, in a system where potassium hydroxide is the pH-basic catalyst to be removed and also the inorganic salt added to the polyether polyol polymerizate, the aqueous potassium hydroxide (at a concentration of 4%) will have a density of 0.97 g/ml compared to the polyol density of 0.94 g/ml (at approximately 130°C). The aqueous potassium hydroxide phase would, therefore, exit the coalescer at the bottom and the less dense polyether polyol phase would exit the coalescer at some point above the phase interface level.

The volume in the coalescer downstream of the mesh may be used as a settling chamber. The interface level between the two phases is generally maintained at a level which provides optimum residence time for each phase. This level may be monitored by an ultrasonic or capacitance instrument and controlled by restriction of the flow out of the bottom of the coalescer.

In one embodiment of the present invention, further separation may be achieved by means of additional beds of coalescing medium (preferably high surface area mesh material) located at points above and below the first bed of mesh material through which the emulsion is initially passed. Each of the separated phases would then be subjected to a second coalescing step. This embodiment is schematically illustrated in Figure 3 which will be discussed in greater detail below.

The pressure in the coalescer is maintained above atmospheric pressure to insure that the boiling point of the aqueous phase is greater than the operating temperature of the coalescer. This prevents boiling in the coalescer that would cause undesirable mixing of the aqueous and polyol phases and disrupt the phase separation. The pressure is maintained using restrictions in the lines by which the aqueous phase and the polyether leave the coalescer. For example, at an operating temperature of 130°C, the pressure in the coalescer is advantageously maintained at a level of from about 45 to about 55 psig.

Polyether polyol leaving the coalescer may be further treated to remove any residual pH-basic catalyst by, e.g., acid neutralization and filtration to remove precipitated salt. The aqueous phase containing 90% or more of the pH-basic catalyst and any other inorganic material leaving the coalescer may be used, for example, to neutralize acidic solutions. In a preferred embodiment of the present invention, the aqueous phase exiting the coalescer is diluted with water until it has an inorganic salt concentration corresponding to that of the inorganic salt solution added to the polymerizate to be coalesced. The diluted aqueous phase may then be recycled into the process. This recycled stream may replace or supplement the aqueous solution of inorganic salt to be mixed with the polyol polymerizate to form an emulsion.

The process of the present invention may be carried out batchwise or on a continuous basis. It is preferred that this process be carried out on a continuous basis.

Figure 1 illustrates the embodiment of the present invention in which water (stream 2) is combined with a solution of inorganic salt (stream 3) in mixer A to generate a dilute solution of inorganic salt (stream 4). The polyether polyol polymerizate (stream 1) is combined

with the dilute solution of inorganic salt (stream 4) as both streams are fed to static mixer B. The resulting emulsion (polymerizate/salt stream) exiting mixer B (stream 5) is then passed through coalescer C. The less dense phase exiting coalescer C (stream 6) is the polyether polyol phase. The more dense phase exiting coalescer C (stream 7) is the aqueous phase.

Figure 2 illustrates an embodiment of the present invention in which the polyether polyol polymerizate (stream 21) is combined with an aqueous solution of inorganic salt (stream 22) to form stream 23. Stream 23 is then passed through static mixer B to form an emulsion (stream 24). Stream 24 is then passed through coalescer C which is equipped with coalescing medium 25. The coalesced stream 26 is then separated into its aqueous phase (stream 28) and polyether polyol phase (stream 27). Figure 3 illustrates an embodiment of the present invention in which the polyether polyol polymerizate (stream 31) is combined with an aqueous solution of inorganic salt (stream 32) to form stream 33. Stream 33 is then passed through static mixer B to form the emulsion (stream 34). Stream 34 is then passed through coalescer C which is equipped with three separate beds of coalescing medium 35. The polyol phase exits coalescer C as stream 36. The aqueous phase exits coalescer C as stream 37.

The process of the present invention generally removes at least 90% of the pH basic catalyst which was initially present in the polyether polyol polymerizate. In many cases, 95% or more of the pH basic catalyst is removed.

Having thus described our invention, the following Examples are given as being illustrative thereof. All parts and percentages

given in these Examples are parts by weight and percentages by weight, unless otherwise indicated.

EXAMPLES Example 1-1Q Figure 1 shows the general configuration of the equipment and process materials used in each of these Examples.

Stream 1 was a polyether polyol alkaline polymerizate which had been prepared by the reaction of ethylene and/or propylene oxide with a starting material containing active hydrogen (starter) under potassium hydroxide (KOH) catalysis. The nominal temperature of stream 1 was 95°C. Stream 2 was water at ambient temperature. Stream 3 was a 45% aqueous solution of potassium hydroxide at ambient temperature.

Streams 2 and 3 were combined in mixer A at a controlled ratio to provide a dilute potassium hydroxide solution (stream 4). The ratio was varied over a range of from about 74:1 to about 10:1 parts of stream 2 to parts of stream 3. The dilute KOH solution (stream 4) was heated to 90°C and combined with stream 1 , the alkaline polyether polymerizate. This mixture (stream 5) was emulsified by passing it through static mixer B. Stream 5 was heated to the final operating temperature and then passed through the coalescer C. As coalescing took place, the more dense material (usually the aqueous phase) settled to the bottom of the coalescer C while the less dense material (usually the polyether) rose to the top. A phase interface was formed and the more dense phase (stream 7) exited the coalescer at an outlet below the interface level. The less dense phase (stream 6) exited above the level of the interface. The polyether polyol, usually stream 6, was then further processed using techniques common to commercial polyether production. The finished

product was a polyether polyol suitable for use in reactions with isocyanates to form polyurethanes. This process can be run continuously for a long period of time. For the specific examples characterized by the data in the table below, run times of from about 90 to 900 minutes were used.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.