Polyether alcohol production

Abstract

The present invention provides a process for the production of polyether alcohol comprising the steps of: i. preparing a crude polyether alcohol by reacting a starter compound having one or more active hydrogen atoms with an alkylene oxide in a reactor in the presence of a composite metal cyanide complex catalyst; ii. subsequently subjecting the crude polyether alcohol to a stripping step at temperatures in the range of from 90 °C to 160 °C under reduced pressure, using an inert stripping agent, wherein the crude polyether alcohol is contacted with water and a solid acid catalyst at a temperature in the range of from 90 to 160 °C and any volatile substances are concurrently removed via concerted distillation.

Description

[0001]SP3184 - 1 - POLYETHER ALCOHOL PRODUCTION Field of the Invention The present invention is directed to a method for the production of polyether alcohols, to the polyether alcohols produced by said method and to the use of said 5 polyether alcohols in the preparation of polyurethane foams. Background of the Invention Polyether alcohols are well known. They are used for many purposes. The polyether alcohols can be used for 10 preparing polyurethanes by reacting them with polyisocyanates under appropriate conditions. Polyurethane products that can be made include polyurethane foams, coatings, elastomers, sealants and adhesives. Polyether alcohols are typically obtained by 15 reacting a starter compound or initiator having one active hydrogen atom or a plurality of active hydrogen atoms, such as glycerol, with one or more alkylene oxides, such as ethylene oxide and propylene oxide. Known suitable catalysts for this reaction include potassium hydroxide 20 (KOH). Other catalyst, for example phosphazene catalysts, have also been reported for this use. However, composite metal cyanide complex catalysts have been considered a more attractive catalyst for use in the production of many polyether alcohols. These catalysts are frequently also 25 referred to as double metal cyanide (DMC) catalysts. Advantages associated with DMC-catalysed production of polyether alcohols is that it is faster and more efficient than the traditional process using potassium hydroxide as catalyst. Further, the DMC-catalysed process 30 is more environmentally friendly and has a decreased carbon (CO2) footprint. As with all industrial processes, by-products are produced in the production of polyether alcohols and it is desirable to minimize their presence in the product. Many by-products, for example free aldehydes, are removed 5 during the usual manufacturing processes. However, other by-products may be retained in the standard finished products. An example of this is latent aldehyde / ketone. This term refers to aldehyde content which is incorporated in the polyether alcohol structure and may subsequently be 10 released during further processing and / or use. The presence of latent aldehydes in a polyether alcohol can result in the undesirable presence of volatile aldehydes in polyurethane foams made therefrom. Such volatile compounds are undesirable, particularly in home and 15 automobile applications. The removal of aldehydes from crude polyether alcohols produced via a KOH-catalysed route is described in US20190309120. In this document, crude polyether alcohol is contacted with an acidic catalyst and then a 20 volatile compound containing an aldehyde is removed. Similar methods directed to the production of polymer polyols are described in JP2019143137 and JP2019026840. The processes described in these documents add a number of extra steps to the process of producing a polyol suitable 25 for conversion into a polyurethane. It remains desirable to develop a process for the production of polyether alcohol with reduced latent aldehyde content preferably without adding extra process steps to the overall process. 30 Summary of the Invention The present invention provides a process for the production of polyether alcohol comprising the steps of: i. preparing a crude polyether alcohol by reacting a starter compound having one or more active hydrogen atoms with an alkylene oxide in a reactor vessel in the presence of a composite metal cyanide complex catalyst; ii. subsequently subjecting the crude polyether alcohol 5 to a stripping step at temperatures in the range of from 90 °C to 160 °C under reduced pressure, using an inert stripping agent, wherein the crude polyether alcohol is contacted with water and a solid acid catalyst at a temperature in the 10 range of from 90 to 160 °C and any volatile substances are concurrently removed via concerted distillation. Also provided is a polyether alcohol obtainable by said process. Also provided is a process for preparing a 15 polyurethane foam comprising reacting a polyether alcohol and a polyisocyanate in the presence of a blowing agent, wherein the polyether alcohol is obtained by said process. Detailed Description of the Invention One or more specific embodiments of the present 20 disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the 25 specification. When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and 30 “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. In the context of the present invention, in a case where a composition comprises two or more components, 5 these components are to be selected in an overall amount not to exceed 100 wt%. The polyether alcohol in the process of the present invention is prepared by reacting a starter compound having one or more active hydrogen atoms with an alkylene 10 oxide in the presence of a composite metal cyanide complex catalyst (the DMC catalyst). Preferably, the starter compound used in preparing the polyether alcohol is a polyfunctional alcohol, generally containing from 1 to 8 or 2 to 6 or 2 to 415 hydroxyl groups. Examples of such alcohols comprise n- butanol, allyl alcohol, glycols, glycerol, pentaerythritol, trimethylolpropane, triethanolamine, sorbitol, mannitol, sucrose and low molecular weight polyether alcohols. Preferably, the starter compound is 20 selected from the group consisting of glycols, glycerol, pentaerythritol, trimethylolpropane, triethanolamine, sorbitol, mannitol and low molecular weight polyether alcohols. Advantageously, monopropylene glycol (MPG), glycerol, a low molecular weight (e.g. no more than 25 1000g / mol) polyether alcohol or any combination thereof may be used as starter compound. Further, the alkylene oxide used in preparing the polyether alcohol may comprise one or more of propylene oxide, ethylene oxide and butylene oxide. Preferably the 30 alkylene oxide comprises propylene oxide and / or ethylene oxide. Most preferably the alkylene oxide comprises a mixture of propylene oxide and ethylene oxide. The polyether alcohol to be treated in the process of the present invention, comprises polyether chains preferably containing propylene oxide content, optionally butylene oxide content and optionally ethylene oxide content. The terms “ethylene oxide content” and “propylene 5 oxide content”, respectively, in relation to a polyether alcohol refer to those parts of the polyether alcohol which are derived from ethylene oxide and propylene oxide, respectively. Said contents may also be referred to as oxyethylene content and oxypropylene content, 10 respectively. Further, said contents are based herein on total alkylene oxide weight. The ethylene oxide content may be determined according to ASTM D4875. The propylene oxide content of the polyether alcohol may be at least 10% or at least 20 wt.% or at least 30 15 wt.% or at least 40% or at least 50 wt.% or at least 60 wt.% or at least 70 wt.% or at least 80 wt.% or at least 90 wt.% or at least 95 wt.% or at least 99 wt.%. Further, the propylene oxide content of the polyether alcohol may be at most 100 wt.% or at most 90 wt.% or at most 80 wt.% 20 or at most 70 wt.% or at most 60 wt.% or at most 50 wt.% or at most 40 wt.% or at most 30 wt.% or at most 20 wt.%. The ethylene oxide content of the polyether alcohol may be 0 wt.% or at least 3 wt.% or at least 5 wt.% or at least 10 wt.% or at least 12 wt.% or at least 15 wt.% or 25 at least 20 wt.% or at least 30 wt.% or at least 40% or at least 50 wt.% or at least 60 wt.% or at least 70 wt.% or at least 80 wt.% or at least 90 wt.%. Further, the ethylene oxide content of the polyether alcohol may be at most 90 wt.% or at most 80 wt.% or at most 70 wt.% or at 30 most 60 wt.% or at most 50 wt.% or at most 40 wt.% or below 30 wt.% or at most 25 wt.% or at most 20 wt.% or at most 15 wt.% or at most 12 wt.%. The term “primary hydroxyl content” (or “PHC”) is used herein to refer to the relative proportion (in %) of primary hydroxyl groups in a polyether alcohol based on total number of hydroxyl groups including primary and 5 secondary hydroxyl groups. The primary hydroxyl content may be determined according to ASTM D4273. The polyether alcohol may comprise primary hydroxyl groups. The primary hydroxyl content of the polyether alcohol may be 0% or at least 1% or at least 3% or at least 5% or at least 10% or 10 at least 20% or at least 30%. Further, the primary hydroxyl content of the polyether alcohol may be at most 90% or at most 80% or at most 70% or at most 60% or at most 50% or at most 40% or at most 30% or at most 20% or at most 15% or at most 10% or at most 5%. 15 The term “functionality” or “hydroxyl (OH) functionality” of a polyether alcohol refers to the number of hydroxyl groups per molecule of polyether alcohol. The nominal functionality of a polyether alcohol is the same as that of its starter compound (initiator). Unless 20 indicated otherwise, functionality refers to the actual average functionality which may be lower than the nominal functionality and is determined by the number average molecular weight of the polyether alcohol divided by the equivalent weight of the polyether alcohol. The polyether 25 alcohol may have a functionality of from 0.8 to 8, preferably of from 1 to 8, more preferably of from 2 to 6, more preferably of from 2 to 4, more preferably of from 2.5 to 3.5, most preferably of from 2.7 to 3.3. The term “hydroxyl (OH) value” or “hydroxyl (OH) 30 number” is used herein to refer to the milligrams of potassium hydroxide equivalent to the hydroxyl content in one gram of polyether alcohol determined by wet method titration. Hence, said OH value or number is expressed in mg KOH / g. The hydroxyl number may be determined according to ASTM D4274. The hydroxyl number of the polyether alcohol may vary within wide ranges and may be of from 5 to 500 mg KOH / g. In particular, the polyether alcohol may have a hydroxyl number of greater than 115 mg KOH / g, 5 suitably greater than 120 mg KOH / g. The hydroxyl number of the polyether alcohol may be at least 120 mg KOH / g or at least 130 mg KOH / g or at least 140 mg KOH / g or at least 160 mg KOH / g or at least 180 mg KOH / g or at least 200 mg KOH / g or at least 220 mg KOH / g. Further, the hydroxyl 10 number of the polyether alcohol may be at most 500 mg KOH / g or at most 450 mg KOH / g or at most 400 mg KOH / g or at most 350 mg KOH / g or at most 300 mg KOH / g or at most 280 mg KOH / g. The term “molecular weight” (or “MW”) is used herein 15 to refer to number average molecular weight, unless otherwise specified or context requires otherwise. The number average molecular weight of a polyether alcohol can be measured by gel permeation chromatography (GPC) or vapor pressure osmometry (VPO). In the present invention, 20 the polyether alcohol to be treated may have a number average molecular weight of at most 10,000 g / mol, suitably of from 200 to 8,000 g / mol, more suitably of from 300 to 7,000 g / mol, most suitably of from 400 to 6,000 g / mol. Said molecular weight is preferably at least 100 g / mol, 25 more preferably at least 200 g / mol, more preferably at least 300 g / mol, more preferably at least 400 g / mol, more preferably at least 500 g / mol, more preferably at least 550 g / mol, most preferably at least 600 g / mol. Further, said molecular weight may be at most 10,000 g / mol, 30 preferably at most 8,000 g / mol, more preferably at most 7,000 g / mol, more preferably at most 6,000 g / mol, more preferably at most 5,000 g / mol, more preferably at most 4,000 g / mol, more preferably at most 3,000 g / mol, more preferably at most 2,000 g / mol, more preferably at most 1,500 g / mol, more preferably at most 1,200 g / mol, more preferably at most 1,000 g / mol, more preferably at most 800 g / mol, most preferably at most 750 g / mol. In the process of the present invention, the polyether alcohol is prepared using a composite metal cyanide complex catalyst. Composite metal cyanide complex catalysts are frequently also referred to as double metal cyanide (DMC) catalysts. A composite metal cyanide complex catalyst is typically represented by the following formula (1): (1) M1a[M2b(CN)c]d.e(M1fXg).h(H20).i(R) wherein each of M1and M2is a metal, X is a halogen atom, R is an organic ligand, and each of a, b, c, d, e, f, g, h and i is a number which is variable depending upon the atomic balances of the metals, the number of organic ligands to be coordinated, etc. In the above formula (1), M1is preferably a metal selected from Zn(II) or Fe(II). In the above formula, M2is preferably a metal selected from Co(III) or Fe(III). However, other metals and oxidation states may also be used, as is known in the art. In the above formula (1), R is an organic ligand and is preferably at least one compound selected from the group consisting of an alcohol, an ether, a ketone, an ester, an amine and an amide. As such an organic ligand, a water-soluble one may be used. Specifically, one or more compounds selected from tert-butyl alcohol, n-butyl alcohol, iso-butyl alcohol, tert-pentyl alcohol, isopentyl alcohol, N, N-dimethyl acetamide, glyme (ethylene glycol dimethyl ether), diglyme (diethylene glycol dimethyl ether), triglyme (triethylene glycol dimethyl ether), ethylene glycol mono-tert-butylether, iso-propyl alcohol and dioxane, may be used as organic ligand(s). The dioxane may be 1,4-dioxane or 1,3-dioxane and is preferably 1,4- dioxane. Most preferably, the organic ligand or one of the organic ligands in the composite metal cyanide complex catalyst is tert-butyl alcohol. Further, as an alcohol organic ligand, a polyol, preferably a polyether alcohol 5 may be used. More preferably, a poly (propylene glycol) having a number average molecular weight in the range of from 500 to 2,500 Dalton, preferably 800 to 2,200 Dalton, may be used as the organic ligand or one of the organic ligands. Most preferably, such poly(propylene glycol) is 10 used in combination with tert-butyl alcohol as organic ligands. The composite metal cyanide complex catalyst can be produced by known production methods. The reactor vessel in which the crude polyether alcohol is prepared may comprise any suitable reactor 15 vessel typically used in the preparation of polyether alcohols. The preparation of the crude polyether alcohol may be carried out in a batch, semi-continuous or continuous process. Regardless of the reactor vessel type or continuous / batch nature of the process, the crude 20 polyether alcohol is subjected to a stripping step after the reaction is complete. Optionally before and / or after the stripping step, the crude polyether alcohol may be subjected to further purification steps, such as filtration, as well as cooling 25 or heating. The temperature in the stripping step is in the range of from 90 to 160 °C. Preferably, the temperature in the stripping step is no lower than 100 °C, more preferably no lower than 110 °C and preferably no higher 30 than 155 °C. The stripping step is carried out at reduced pressure. By “reduced pressure”, is meant that the pressure in the stripping step is lower than atmospheric pressure. Preferably, the pressure in the stripping step is in the range of from 0.5 to 5.0 kPa. More preferably, the pressure in the stripping step is in the range of from 2.0 to 5.0 kPa. An inert stripping agent is used to facilitate the stripping step. Said stripping agent is preferably N2 gas 5 or steam. The stripping step may be carried out by one of the methods described below: 1) In a batch process, the stripping step may be carried out in the reactor vessel in which the crude polyether 10 alcohol has been prepared by subjecting the reactor vessel to the conditions required for the stripping step. 2) The stripping step may be carried out in a separate reactor vessel. In this method the crude polyether alcohol is removed from the reactor vessel in which it has been 15 prepared and is placed into a new reactor vessel. In the new reactor vessel, the crude polyether alcohol is subjected to the conditions required for the stripping step. 3) The stripping step may be carried out in a packed bed 20 column. In this method, the crude polyether alcohol is fed to the packed bed column which is operated under the conditions required for the stripping step. As part of the process of the present invention, the crude polyether alcohol is contacted with water and the 25 solid acid catalyst at a temperature in the range of from 90 to 160 °C and any volatile substances are concurrently removed via concerted distillation. Such concerted distillation may also be termed reactive distillation and requires a catalytic chemical reaction and distillation to 30 take place in a single apparatus. The crude polyether alcohol is preferably contacted with water and the solid acid catalyst at a temperature greater than 120 °C, more preferably greater than 125 °C, more preferably greater than 130 °C, most preferably at least 135 °C. Further, the crude polyether alcohol is preferably contacted with water and the solid acid catalyst at a temperature lower than 155 °C, more preferably lower than 150 °C, more preferably at most 145 °C. 5 A number of methods are known for reactive distillation, including, but not limited to, those described in A. Kiss & M Johnson, Chemical Engineering Transactions, 69, 553-558. These include, the use of reactive dividing-wall columns, reactive heat integrated 10 distillation columns, reactive cyclic distillation or reactive HiGee distillation. In any of the described methods, the crude polyether alcohol may be contacted with water and the solid acid catalyst before, after, or concurrently to it being 15 subjected to the stripping step in step ii). For example, if the stripping step is carried out in reactor vessels, solid acid catalyst may be added to the reactor vessel with the crude polyether alcohol. Alternatively, the crude polyether alcohol may be contacted with water and the 20 solid acid catalyst at a temperature in the range of from 90 to 160 °C, and any volatile substances are concurrently removed via concerted distillation in the reactor vessel, with a stripping step subsequently being carried out in another reactor vessel or in a packed bed column. 25 In one embodiment, the stripping step is carried out in a packed bed column and the trays present in said column are filled with packing material. Preferably, the stripping step is carried out in a packed bed column and the packing material in the trays comprises the solid acid 30 catalyst. Thus, the crude polyether alcohol is contacted with water and the solid acid catalyst at a temperature in the range of from 90 to 160 °C and any volatile substances are concurrently removed via concerted distillation at the same time as the stripping step. This embodiment has the added advantage of overall process simplification and may simply be retro-fitted into existing process line-ups by replacing at least a portion of the packing material in the stripping column with the solid acid catalyst. 5 Regardless of where and how the crude polyether alcohol is contacted with water and the solid acid catalyst, said solid acid catalyst is preferably insoluble in the polyether alcohol and other materials present in the crude polyether alcohol. Further, preferably, the 10 solid acid catalyst comprises solid that possess Brønsted or Lewis acidic properties on their surfaces which function as catalysts. Suitable solid acid catalysts include, but are not limited to, crystalline zeolite material with H+ or metal exchanged counter ion, natural 15 and modified clays, amorphous silica alumina, a crystalline silica alumina phosphate (SAPO), ion exchange resins, immobilised Bronsted or Lewis acid on metal oxide support(sulphated zirconia, heteropoly acid supported metal oxides) etc. Metal oxides used for immobilisation 20 can be alumina, silica, zirconia, titania and mixtures or combinations thereof. In the process of the present invention, when contacting the crude polyether alcohol with the solid acid catalyst the crude polyether alcohol is concurrently also 25 contacted with water. It is preferred that the amount of water is in molar excess over the amount of latent aldehyde and ketone contents in the polyether alcohol. For example, the amount of water, based on the amount of polyether alcohol, may be of from 0.05 to 2 wt.% or of 30 from 0.10 to 1 wt.% or of from 0.15 to 0.75 wt.% or of from 0.20 to 0.50 wt.% or of from 0.20 to 0.40 wt.% or of from 0.20 to 0.30 wt.%. The process of the present invention provides a polyether alcohol with reduced latent aldehyde content and optionally reduced latent ketone content, wherein water, in combination with the solid acid catalyst, has hydrolysed latent aldehydes and optionally latent ketones thereby releasing free aldehydes and optionally free 5 ketones. Latent aldehyde content is aldehyde content available to be released from aldehyde precursor moieties incorporated in the polyether alcohol polymer structure. For example, latent aldehyde content may be incorporated by the reaction of a polyether alcohol with free aldehyde,10 or a masked version thereof (such as a geminal diol e.g. - C(OH)2-), or derivative thereof such as a hemiacetal e.g. - COR(OR')-). Alcohol groups of a polyether alcohol may react with aldehyde functional groups (or masked versions thereof) to form labile chemical bonds. Such labile 15 chemical bonds may include ether and / or ester bonds. However, it is possible that latent aldehyde content may be available from precursor moieties incorporated into a polyether alcohol structure by other means. The latent aldehyde content of the polyether alcohol 20 may be determined by capillary gas chromatography with flame ionisation detection, by the method described in WO2017001543, after freeing the aldehyde from bound moieties of the polyether alcohol under acidic conditions (e.g. a pH below 3), in particular with strong acid, more 25 in particular phosphoric acid. To determine the latent aldehyde content it may be necessary to subtract free aldehyde content from a sum of the free aldehyde content and the latent aldehyde content determined after freeing aldehyde from bound moieties of the polyether alcohol. 30 Alternatively, free aldehyde content may be stripped from the polyether alcohol before latent aldehyde content is determined. The latent aldehyde content of the polyether alcohol may be taken to comprise or consist of one or more aldehydes available from bound moieties in the polyether alcohol (i.e., aldehydes freed under said acidic conditions). The latent aldehyde content does not necessarily represent the total latent aldehyde content of 5 the polyether alcohol. However, in some embodiments of the invention, the latent aldehyde content consists of all aldehydes available from bound moieties in the polyether alcohol, i.e., the latent aldehyde content is the total latent aldehyde content of the polyether alcohol. 10 The latent aldehyde content may, for example, be taken to comprise or consist of linear, branched or cyclic aldehydes freed from the polyether alcohol under said acidic conditions. Suitably, the latent aldehyde content may comprise or consist of one or more aldehydes 15 containing from 2 to 12 carbon atoms, preferably 2 to 6 carbon atoms, and most preferably 2 or 3 carbon atoms. The latent aldehyde content may optionally comprise an aldehyde with a plurality of aldehyde functional groups. In an embodiment, the latent aldehyde content comprises or 20 consists of propionaldehyde (PA) and acetaldehyde (AA) freed from the polyether alcohol under said acidic conditions. In an embodiment, the latent aldehyde content comprises or consists of PA freed from the polyether alcohol under said acidic conditions. In an embodiment, 25 the aldehyde content comprises or consists of AA freed from the polyether alcohol under said acidic conditions. The present invention also relates to a polyether alcohol obtainable by the above-mentioned process. The present invention further relates to a process 30 for preparing a polyurethane foam comprising reacting a polyether alcohol and a polyisocyanate in the presence of a blowing agent, wherein the polyether alcohol is a polyether alcohol obtained or obtainable by the above- mentioned process. In the above-mentioned process for preparing a polyurethane foam, the polyether alcohol is reacted with a polyisocyanate in the presence of a blowing agent. The polyisocyanate may comprise an aromatic 5 polyisocyanate or an aliphatic polyisocyanate, preferably an aromatic polyisocyanate. The aromatic polyisocyanate may for example comprise tolylene diisocyanate (TDI) or polymeric TDI, xylylene diisocyanate, tetramethylxylylene diisocyanate, methylene 10 diphenyl diisocyanate (MDI) or polymeric MDI (i.e. polymethylene polyphenyl isocyanate), or a modified product thereof. Preferably, the aromatic polyisocyanate comprises tolylene diisocyanate (TDI), i.e. non-polymeric TDI. The TDI may be a mixture of 80 wt.% of 2,4-TDI and 20 15 wt.% of 2,6-TDI, which mixture is sold as “TDI-80”. Further, the aliphatic polyisocyanate may for example comprise hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, lysine diisocyanate or isophorone diisocyanate, or a modified product thereof. 20 Further, the polyisocyanate may comprise any mixture of two or more of the polyisocyanates mentioned above. For example, the polyisocyanate may comprise a mixture of TDI and MDI, in particular a mixture wherein the weight ratio of TDI:MDI varies from 10:90 to 90:10. 25 The blowing agent may comprise a chemical blowing agent and / or a physical (non-chemical) blowing agent. Within the present specification, by “chemical blowing agent” reference is made to a blowing agent that may only provide a blowing effect after it has chemically reacted 30 with another compound. In case the blowing agent comprises a chemical blowing agent, said chemical blowing agent preferably comprises water. Water reacts with isocyanate groups of the polyisocyanate, thereby releasing carbon dioxide which causes the blowing to occur. However, other suitable blowing agents, such as for example, acetone, gaseous or liquid carbon dioxide, halogenated hydrocarbons, aliphatic alkanes and alicyclic alkanes may be employed additionally or alternatively. 5 Due to the ozone depleting effect of fully chlorinated, fluorinated alkanes (CFC’s) the use of this type of blowing agent is generally not preferred, although it is possible to use them. Halogenated alkanes, wherein at least one hydrogen atom has not been substituted by a 10 halogen atom (including the so-called HCFC’s) have no or less ozone depleting effect and therefore are the preferred halogenated hydrocarbons to be used in physically blown foams. One suitable HCFC type blowing agent is 1-chloro-l,1-difluoroethane. Another suitable 15 halogenated alkane of this type for use as a blowing agent, is methylene chloride (dichloromethane). The above blowing agents may be used singly or in mixtures of two or more. The amount of the blowing agent(s) is determined by 20 the desired density of the polyurethane foam to be prepared. For example, a relatively low density can be obtained by using a relatively high amount of the blowing agent(s), and vice versa. A skilled person can readily determine the amount of blowing agent (physical and / or 25 chemical blowing agent) needed to obtain a desired foam density. Water may be used as a blowing agent in an amount which is at least 0.1 part per hundred parts by weight of polyether alcohol (pphp) or at least 0.5 pphp or at least 30 1 pphp. Further, water may be used as a blowing agent in an amount which is at most 10 parts per hundred parts by weight of polyether alcohol (pphp) or at most 5 pphp or at most 3 pphp or at most 2 pphp. In case of halogenated hydrocarbons, aliphatic alkanes and alicyclic alkanes, the amount of the blowing agent may be of from 1 to 50 parts per hundred parts by weight of polyether alcohol (pphp), suitably of from 1 to 5 30 pphp, more suitably of from 1 to 20 pphp. Further, preferably, the polyurethane foam which may be prepared is a flexible polyurethane foam. Further, said flexible polyurethane foam is suitably a slabstock foam. Within the present specification, by “slabstock foam” 10 reference is made to a foam that is made by applying a free rise (unconstrained rise) of the foam. The isocyanate index (or NCO index) may vary within wide ranges and may be of from 60 to 120. In particular, the isocyanate index may be at most 120, more suitably at 15 most 110, more suitably at most 100, most suitably at most 90. Further, the isocyanate index is preferably higher than 60 and may be at least 70 or at least 80 or at least 90. Within the present specification, “isocyanate index” 20 is calculated as 100 times the mole ratio of —NCO groups (isocyanate groups) to NCO—reactive groups in the reaction mixture. In other words, the isocyanate index is defined as: [(actual amount of isocyanate) / (theoretical amount of isocyanate)]*100, wherein the “theoretical amount of 25 isocyanate” equals 1 equivalent isocyanate (NCO) group per 1 equivalent isocyanate-reactive group. Such “isocyanate-reactive groups” as referred to above include for example OH groups from the polyether alcohol and from any water that may be used as a blowing agent. 30 Isocyanate groups also react with water. Additionally, other components may also be present during the above-mentioned polyurethane foam preparation process, such as one or more polyurethane catalysts, surfactants and / or cross-linking agents. Polyurethane catalysts are known in the art and include many different compounds. Suitable catalysts include tin-, lead- or titanium-based catalysts, preferably tin-based catalysts, such as tin salts and 5 dialkyl tin salts of carboxylic acids. Specific examples are stannous octoate, stannous oleate, dibutyltin dilaureate, dibutyltin acetate and dibutyltin diacetate. Other suitable catalysts are tertiary amines, such as, for instance, bis(2,2'-dimethylamino)ethyl ether, 10 trimethylamine, triethylamine, triethylenediamine and dimethylethanolamine (DMEA). Examples of commercially available tertiary amine catalysts are those sold under the tradenames Niax, Tegoamin and Dabco (all trademarks). The catalyst is typically used in an amount of from 0.01 15 to 2.0 parts by weight per hundred parts by weight of polyether alcohol (php). Preferred amounts of catalyst are from 0.05 to 1.0 php. The use of foam stabilisers (surfactants) is well known. Organosilicone surfactants are most conventionally 20 applied as foam stabilisers in polyurethane production. A large variety of such organosilicone surfactants is commercially available. Usually, such foam stabiliser is used in an amount of from 0.01 to 5.0 parts by weight per hundred parts by weight of polyether alcohol (pphp). 25 Preferred amounts of stabiliser are from 0.25 to 2.0 pphp, more preferably of from 0.75 to 1.5 pphp. The use of cross-linking agents in the production of polyurethane foams is also well known. Polyfunctional glycol amines are known to be useful for this purpose. The 30 polyfunctional glycol amine which is most frequently used and is also useful in the preparation of polyurethane foams, especially flexible polyurethane foams, is diethanolamine, often abbreviated as DEOA. A cross-linking agent may be applied in amounts up to 2 parts by weight per hundred parts by weight of polyether alcohol (pphp), but amounts in the range of from 0.01 to 0.5 pphp are most suitably applied. In addition, other well-known auxiliaries, such as 5 colorants, flame retardants and fillers, may also be used during the above-mentioned polyurethane foam preparation process. Said polyurethane foam preparation process may involve combining the polyisocyanate, the polyether 10 alcohol, the blowing agent, a catalyst and optionally surfactant, crosslinker, flame retardant, colorant and / or filler, in any suitable manner to obtain the polyurethane foam. For example, said process may comprise mixing the polyether alcohol, the blowing agent, a catalyst and any 15 other optional component(s) except the polyisocyanate, and then adding the polyisocyanate. Further, the above-mentioned polyurethane foam preparation process may comprise forming the foam into a shaped article before it fully sets. Suitably, forming the 20 foam may comprise pouring the liquid mixture containing all components into a mould before gelling is complete. Further, the present invention relates to a polyurethane foam obtainable by the above-mentioned process for preparing a polyurethane foam, and to a shaped article 25 comprising a polyurethane foam obtained or obtainable by said process. The invention is further illustrated by the following Examples. Examples 30 Reference Example 1 and Example 2 In Reference Example 1, a polyether alcohol was mixed with 1 wt.% of an acid, which was a mixture of 75 wt.% phosphoric acid (H3PO4) and 25 wt.% water, in a 30 ml headspace vial and the vial was agitated using a vortex mixer or ultrasonic bath. The closed vial was heated in an oven at a temperature of 120 °C. In Example 2, the same procedure was followed except that instead of above- mentioned acid, 0.75 wt.% of a solid acid catalyst (“Beta 5 Zeolite”) and 0.25 wt.% of water were used, and that the temperature was 140 °C (not 120 °C). Said amounts of acid, catalyst and water are based on the amount of polyether alcohol. The following materials were used in the Examples: 10 Table 1 Polyether Caradol SC56-16S molecular weight 3000, alcohol functionality of 2.80, EO content 7.8wt%. Beta Beta Zeolite sourced from Zeolyst and having a Zeolite silica alumina ratio of 75 After vapour-liquid equilibrium was reached, the headspace in the vial was analysed using capillary gas chromatography with flame ionization detection. The 15 volatile components were quantified using the External Standard Technique – “Calibration Curve Method”. Table 2 shows the amounts of aldehydes and ketones (based on the amount of polyether alcohol) released from the latent aldehyde and ketone contents in the polyether alcohol. 20 Table 2 ACH freed PA freed Acetone freed from from from latent latent ACH latent PA acetone (ppmw) (ppmw) (ppmw) 1 H3PO4 REF 16 144 7 2 Beta Zeolite extrudates 17 1076 22 ACH = acetaldehyde; PA = propionaldehyde The results demonstrate an excellent and improved removal of the latent carbonyl compound content from the 25 crude polyether alcohol in accordance with the present invention using a solid acid catalyst and water, as compared to the reference using an acid and water instead. In these examples the aldehydes and ketones freed from the polyether alcohol are found in the headspace above the 5 polyether alcohol. By carrying out this process within a vacuum stripper, such compounds would be readily and concurrently removed without requiring extra process steps or a change in conditions.

Claims

SP3184 - 22 - C L A I M S 1. A process for the production of polyether alcohol comprising the steps of: i. preparing a crude polyether alcohol by reacting a starter compound having one or more active hydrogen 5 atoms with an alkylene oxide in a reactor vessel in the presence of a composite metal cyanide complex catalyst; ii. subsequently subjecting the crude polyether alcohol to a stripping step at temperatures in the range of 10 from 90 °C to 160 °C under reduced pressure, using an inert stripping agent, wherein the crude polyether alcohol is contacted with water and a solid acid catalyst at a temperature in the range of from 90 to 160 °C and any volatile substances are 15 concurrently removed via concerted distillation.

2. A process as claimed in claim 1, wherein the starter compound is selected from monopropylene glycol (MPG), glycerol, a polyether alcohol with a molecular weight of no more than 1000g / mol or any combination thereof. 20 3. A process as claimed in claim 1 or claim 2, wherein the alkylene oxide comprises a mixture of propylene oxide and ethylene oxide.

4. A process as claimed in any one of claims 1 to 3, wherein the stripping step is carried out in a reactor 25 vessel, wherein said reactor vessel is the same or a different reactor vessel to the one in which the polyether alcohol is prepared.

5. A process as claimed in any one of claims 1 to 3, wherein the stripping step is carried out in a packed bed 30 column comprising packing material in trays.

6. A process as claimed in claim 5, wherein the packing material in the packed bed column comprises the solid acid catalyst and the crude polyether alcohol is contacted with water and the solid acid catalyst at a temperature in the 5 range of from 90 to 160 °C and any volatile substances are concurrently removed via concerted distillation in the packed bed column during the stripping step.

7. A process as claimed in any one of claims 1 to 6, wherein the solid acid catalyst is selected from the group 10 consisting of crystalline zeolite materials with H+ or metal exchanged counter ion, natural and modified clays, amorphous silica alumina, a crystalline silica alumina phosphate, ion exchange resins and an immobilised Bronsted or Lewis acid on a metal oxide support. 15 8. A process as claimed in any one of claims 1 to 7, wherein the crude polyether alcohol is contacted with water and the solid acid catalyst at a temperature greater than 120 °C, preferably a temperature of at least 125 °C.

9. A polyether alcohol obtainable by the process of any 20 one of Claims 1 to 8.

10. A process for preparing a polyurethane foam comprising reacting a polyether alcohol and a polyisocyanate in the presence of a blowing agent, wherein the polyether alcohol is obtained by the process of any one of Claims 1 to 8.