Patent Description:
Polyether polyols having a relatively high content of primary hydroxyl (OH) groups are desired in many polyurethane applications. Conventionally, these polyether polyols are produced in two-steps. In a first step, all propylene oxide (or a mixture of propylene oxide and ethylene oxide) is polymerized, using a basic catalyst, such as potassium hydroxide, in the presence of a starter compound having active hydrogen atoms. This results in an intermediate polyether polyol having mainly secondary OH groups. In a second step, sometimes referred to as an "EO tip", ethylene oxide is then added to the intermediate polyether polyol, thereby converting the majority of the secondary OH groups into primary OH groups. In this process, the same basic catalyst (for example, KOH) is often used for the propoxylation reaction and for the ethoxylation reaction. Following production of the polyether polyol, the basic catalyst is often neutralized using an acid and the resulting salts are removed from the polyol, such as by filtration.

In many cases it is desirable to produce polyether polyols using double-metal cyanide (DMC) catalysts. This is often because, compared with the conventional production of polyether polyols by means of basic catalysts, use of DMC catalysts can result in a decrease in the content of monofunctional polyethers with terminal double bonds, so-called monols. The polyether polyols thus obtained can be processed to form high-quality polyurethanes (for example, elastomers, foams, coatings). In addition, DMC catalysts can possess an exceptionally high activity, thereby rendering it possible to produce polyether polyols at very low catalyst concentrations so that a separation of the catalyst from the polyol is no longer necessary.

One drawback of using DMC catalysts for the production of polyether polyols has been that with these catalysts, unlike basic catalysts, a direct EO tip can be difficult. This is because when ethylene oxide is added to a poly(oxypropylene) polyol containing a DMC catalyst, the result can be a heterogeneous mixture which consists for the most part of unreacted poly(oxypropylene) polyol (having mainly secondary OH groups) and a small extent of highly ethoxylated poly(oxypropylene) polyol and/or polyethylene oxide. As a result, in many cases, DMC catalyzed polyether polyols having a high content of primary OH groups are produced using a two-step process in which the EO tip is carried out in a second, separate step by means of conventional base catalysis.

One disadvantage of this two-step process is the expensive, energy intensive and time consuming removal of water from the DMC polyether polyol / aqueous basic catalyst mixture. (since the basic catalyst is introduced in the form of an aqueous solution of the catalyst, such as a <NUM>% KOH solution). In addition, storage is required for the intermediate polymer, which involves significant capital and maintenance expense. Further, in order to fully react the water away a separate propylene oxide "drying step" is often needed prior to carrying out the EO tip, otherwise low functionality monol and/or glycol is produced. Such an additional step is, however, time consuming and energy intensive.

As a result, it would be desirable to provide processes and production plants capable of producing DMC-catalyzed polyether polyols having a high content of primary OH groups, in which the efficiency of the water removal process is improved. It would also be desirable to provide such a process that does not require the capacity to store the intermediate DMC-catalyzed polyether polyol prior to producing the final polyether polyol having a high content of primary OH groups. It would also be desirable that the process does not require use of a propylene oxide "drying step" to remove water from the reaction mixture prior to carrying out the EO tip.

<CIT> relates to processes for preparing ethylene oxide (EO)-capped polyols in which removal of catalyst residues or salts formed by the neutralization of the basic catalyst is not required prior to discharging the polyol from the reactor because neutralization occurs during or after the starter charge of a subsequent batch.

<CIT> discloses a process for producing a polyoxyalkylene polyol having a high primary hydroxylation rate of the terminal hydroxyl groups, in spite of a low degree of total unsaturation and a low content of oxyethylene groups.

<CIT> is directed to a process for preparing ethylene oxide-capped polyols which involves combining a double-metal cyanide-catalyzed polyol with a basic catalyst.

<CIT> disclosing a continuous process for the preparation of polyoxyalkylene polyethers using DMC catalysts as the polyoxyalkylation catalyst employs continuous addition of alkylene oxide in conjunction with continuous addition of starter and catalyst to a continuous oxyalkylation reactor.

<CIT> relates to a process for the continuous preparation of polyether alcohols by reaction of alkylene oxides with H-functional starter substances in the presence of DMC catalysts, which comprises, at the beginning of the process a) firstly placing initial charge material and DMC catalyst in a reactor, b) metering in alkylene oxide so that the metering rate which is maintained for continuous operation of the reactor is reached in a time of from <NUM> to <NUM> seconds, c) metering in starter substance during or after step b) so that the metering rate which is maintained for continuous operation of the reactor is reached in a time of from <NUM> to <NUM> seconds, d) after the fill level in the reactor which is desired for continuous operation of the reactor has been reached, taking product off continuously from the reactor while at the same time metering in starter substance and alkylene oxides in such an amount that the fill level in the reactor remains constant and metering in DMC catalyst so that the catalyst concentration necessary for continuous operation of the reactor is maintained in the reactor.

In some respects, this disclosure relates to processes for preparing a polyol. The processes comprise: (a) continuously producing an intermediate polyol in a first reactor by a process comprising: (<NUM>) introducing into the first reactor a mixture comprising a DMC catalyst and an initial starter, wherein the mixture is added in an amount sufficient to initiate polyoxyalkylation of the initial starter after introduction of alkylene oxide into the first reactor; (<NUM>) introducing alkylene oxide to the first reactor; (<NUM>) continuously introducing a continuously added starter into the first reactor; and (<NUM>) continuously introducing fresh DMC catalyst and/or further DMC catalyst/starter mixture to the first reactor such that catalytic activity of the DMC catalyst is maintained; (b) continuously discharging the intermediate polyol from the first reactor; (c) continuously mixing the intermediate polyol with an aqueous solutions of alkali metal to provide a mixture comprising the intermediate polyol, alkali metal and water; (d) continuously dehydrating the mixture comprising intermediate polyol, alkali metal and water, by continuously passing the mixture through one or more packed column, trayed column, falling film evaporator, wiped film evaporator, kettle evaporator, or flash tank, thereby continuously producing a dehydrated mixture comprising the intermediate polyol and the alkali metal; (e) transferring the dehydrated mixture to a second reactor; and (f) producing the polyol in the second reactor by feeding an alkylene oxide to the second reactor to thereby react the intermediate polyol with the alkylene oxide in the presence of the alkali metal, wherein the alkylene oxide fed to the second reactor comprises ethylene oxide in an amount sufficient to provide the polyol with an ethylene oxide cap in which up to <NUM>% by weight of ethylene oxide is added as a cap, based on the total weight of the polyol produced in the second reactor.

In other respect, this specification relates to production plants for preparing a polyol. These production plants comprise: (a) a first reactor comprising: (<NUM>) an inlet in fluid communication with a source of alkylene oxide; (<NUM>) an inlet in fluid communication with a source of starter; (<NUM>) an inlet in fluid communication with a source of DMC catalyst; and (<NUM>) an outlet configured to continuously discharge an intermediate polyol from the first reactor; (b) a source of an aqueous solution of alkali metal in fluid communication with the outlet of the first reactor and configured to continuously add the aqueous solution of alkali metal to the intermediate polyol as it is continuously discharged from the first reactor, thereby producing a mixture comprising the intermediate polymer, the alkali metal and water; (c) a packed column comprising a polyol inlet and a polyol outlet, wherein the polyol inlet is in fluid communication with the outlet of the first reactor, wherein the packed column is configured to continuously remove water from the mixture comprising the intermediate polymer, the alkali metal and water, thereby producing a dehydrated mixture comprising the intermediate polyol and the alkali metal; (d) a second reactor comprising: (<NUM>) an inlet that is in fluid communication with the outlet of the packed column and configured to receive the dehydrated mixture comprising the intermediate polyol and the alkali metal; (<NUM>) an inlet in fluid communication with a source of alkylene oxide; and (<NUM>) an outlet configured to discharge the polyether polyol from the second reactor.

<FIG> schematically represents a production plant in accordance with embodiments of the inventions described in this specification.

Various implementations are described and illustrated in this specification to provide an overall understanding of the structure, function, properties, and use of the disclosed inventions. It is understood that the various implementations described and illustrated in this specification are non-limiting and non-exhaustive. Thus, the inventions are not limited by the description of the various non-limiting and non-exhaustive implementations disclosed in this specification.

In this specification, other than where otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term "about", in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described in the present description should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The grammatical articles "one", "a", "an", and "the", as used in this specification, are intended to include "at least one" or "one or more", unless otherwise expressly indicated. Thus, the articles are used in this specification to refer to one or more than one (i.e., to "at least one") of the grammatical objects of the article. By way of example, "a component" means one or more components, and thus, possibly, more than one component is contemplated and may be employed or used in an implementation of the described implementations. Further, the use of a singular noun includes the plural, and the use of a plural noun includes the singular, unless the context of the usage requires otherwise.

As used herein, the term "functionality" refers to the average number of reactive hydroxyl groups, -OH, present per molecule of the -OH functional material that is being described. In the production of polyurethane foams, the hydroxyl groups react with isocyanate groups, -NCO, that are attached to the isocyanate compound. The term "hydroxyl number" refers to the number of reactive hydroxyl groups available for reaction, and is expressed as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content of one gram of the polyol (ASTM D4274-<NUM>). The term "equivalent weight" refers to the weight of a compound divided by its valence. For a polyol, the equivalent weight is the weight of the polyol that will combine with an isocyanate group, and may be calculated by dividing the molecular weight of the polyol by its functionality. The equivalent weight of a polyol may also be calculated by dividing <NUM>,<NUM> by the hydroxyl number of the polyol - Equivalent Weight (g/eq) = (<NUM> x <NUM>)/OH number.

The processes and production plants of this specification will now be described with reference to <FIG>. As indicated earlier, some embodiments of this specification relate to processes for preparing a polyol, such as a polyether polyol. These processes comprise continuously producing an intermediate polyol in a first reactor. The intermediate polyol can have, for example, a functionality of <NUM> to <NUM>, such as <NUM> to <NUM> or <NUM> to <NUM>, and a hydroxyl number of <NUM> to <NUM> KOH/g, such as <NUM> to <NUM> KOH/g, <NUM> to <NUM> KOH/g, or, in some cases, <NUM> to <NUM> KOH/g.

In the processes of this specification, the intermediate polyol is produced continuously. As used herein, the term "continuous" refers to a mode of addition of a relevant catalyst or reactant that maintains an effective concentration of the catalyst or reactant substantially continuously. Catalyst input, for example, may be truly continuous, or may be in relatively closely spaced increments. Likewise, continuous starter addition may be truly continuous, or may be incremental. Thus, it is possible to incrementally add a catalyst or reactant in such a manner that the added materials concentration decreases to essentially zero for some time prior to the next incremental addition. In some implementations, however, catalyst concentration is maintained at substantially the same level during the majority of the course of the continuous reaction and low molecular weight starter is present during the majority of the process. Incremental addition of catalyst and/or reactant which does not substantially affect the nature of the product is still "continuous" as that term is used herein. It is feasible, for example, to provide a recycle loop where a portion of the reacting mixture is back fed to a prior point in the process, thus smoothing out any discontinuities brought about by incremental additions.

Such continuous intermediate polyol production can be conducted using any of a variety of continuous reactors. For example, in some implementations, continuous intermediate polyol production can take place using a single stage continuous stirred tank reactor ("CSTR").

In particular, as shown in <FIG>, production plant <NUM> may include a first reactor <NUM> that is a single stage CSTR. In this implementation, an inlet of CSTR <NUM> is in fluid communication, via line <NUM>, with a source of alkylene oxide <NUM>, an inlet of CSTR <NUM> is in fluid communication, via line <NUM>, with a source of H-functional starter <NUM>, and an inlet of CSTR <NUM> is in fluid communication, via line <NUM>, with a source of DMC catalyst <NUM>. The various afore-mentioned inlets to CSTR <NUM> may be the same inlet or they may be different inlets (such as is depicted in <FIG>). CSTR <NUM> is configured to continuously discharge the intermediate polyol from CSTR <NUM>. As is apparent, an outlet of CSTR <NUM> is in fluid communication, via line <NUM>, with an inlet of a dehydration apparatus <NUM>, such as packed columns 50a and 50b shown in <FIG>. Also, in this implementation, an outlet of CSTR <NUM> is in fluid communication, via line <NUM>, with intermediate polyol storage vessel <NUM>, which, in turn, is also in fluid communication, via line <NUM>, with an inlet of dehydration apparatus <NUM>. The presence of intermediate polyol storage vessel <NUM> may be particularly desirable in cases where second reactor <NUM> is a batch (or semi-batch) reactor. Further, an inlet of dehydration apparatus <NUM> is in fluid communication with a source of an aqueous solution of basic catalyst <NUM>. In the particular implementation depicted in <FIG>, source of aqueous solution of basic catalyst <NUM> is in fluid communication with line <NUM>, thereby allowing the intermediate polyol being continuously discharged from CSTR <NUM> and/or intermediate polyol being discharged from intermediate polyol storage vessel <NUM> to mix with the aqueous solution of basic catalyst prior to the intermediate polyol entering dehydration apparatus <NUM>. An inlet of dehydration apparatus <NUM> is thus configured to continuously receive a mixture of aqueous solution of basic catalyst and intermediate polyol as intermediately polyol is continuously discharged from CSTR <NUM>. In addition, in this implementation, an inlet of dehydration apparatus <NUM> is configured to continuously receive intermediate polyol from intermediate polyol storage vessel <NUM>. As a result, in operation, dehydration apparatus <NUM> may continuously receive intermediate polyol from CSTR <NUM>, continuously receive intermediate polyol from intermediate polyol storage vessel <NUM>, or may continuously receive intermediate polyol from both CSTR <NUM> and intermediate polyol storage vessel <NUM> simultaneously. In any of these cases, the intermediate polyol can be mixed with aqueous solution of basic catalyst prior to entering dehydration apparatus <NUM>.

Aside from the single stage CSTR depicted in <FIG>, the first reactor may comprise another type of continuous reactor, such as a two stage CSTR, a plug flow reactor, or a loop reactor (i.e., a reactor with internal and/or external recycling of substances, optionally with a heat exchanger arranged in the circulation), such as a stream loop reactor, a jet loop reactor, a Venturi loop reactor, a tube reactors configured in loop form with suitable devices for circulating the reaction mixture, or a loop of several tube reactors connected in series or several stirred tanks connected in series.

Regardless of the specific type of first reactor employed, the processes of this specification comprise continuously producing the intermediate polyol in the first reactor by a process comprising: (<NUM>) introducing into the first reactor a mixture comprising a DMC catalyst and an initial starter, wherein the mixture is added in an amount sufficient to initiate polyoxyalkylation of the initial starter after introduction of alkylene oxide into the first reactor; (<NUM>) introducing the alkylene oxide to the first polyol reactor; (<NUM>) continuously introducing a continuously added starter into the first reactor; and (<NUM>) continuously introducing fresh DMC catalyst and/or further DMC catalyst/further starter mixture to the first reactor such that catalytic activity of the DMC catalyst is maintained.

The starter(s) employed may be any compound having active hydrogen atoms. Suitable starters include, but are not limited to, compounds having a number average molecular weight of <NUM> to <NUM>,<NUM>, such as <NUM> to <NUM>,<NUM>, and having <NUM> to <NUM> hydroxyl groups. Specific examples of suitable starters include, but are not limited to, polyoxypropylene polyols, polyoxyethylene polyols, polytetatramethylene ether glycols, glycerol, propoxylated glycerols, propylene glycol, ethylene glycol, tripropylene glycol, trimethylol propane alkoxylated allylic alcohols, bisphenol A, pentaerythritol, sorbitol, sucrose, degraded starch, water and mixtures thereof.

In certain embodiments, the starter used to prepare the DMC catalyst/starter mixture introduced in the above-mentioned step (<NUM>) is an oligomeric starter, such as an oxyalkylated oligomer based on the same low molecular weight starter whose continuous addition is to be used in the above-mentioned step (<NUM>). For example, where propylene glycol is to be continuously added to the reactor in step (<NUM>), a suitable oligomeric starter useful in preparing the activated catalyst/starter mixture may be a <NUM> Da to <NUM>,<NUM> Da molecular weight polyoxypropylene glycol. The same oligomeric starter would also be suitable for use where dipropylene glycol and/or water are continuously added starters. In another example, where glycerin is a continuously added starter, an oxypropylated glycerine polyol having a molecular weight of <NUM> Da to <NUM>,<NUM> Da may advantageously be used in the above-mentioned step (<NUM>). In some implementations. however, a monomeric starter, such as ethylene glycol, propylene glycol, and the like, may be used. Thus, in some implementations, the starter used to prepare the catalyst/starter mixture in the above-mentioned step (<NUM>) may be the same as the continuously added starter used in the above-mentioned step (<NUM>).

In certain implementations, the continuously added starter may comprise water, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, <NUM>,<NUM>-, <NUM>,<NUM>-, and/or <NUM>,<NUM>-butylene glycol, neopentyl glycol, glycerin, trimethylolpropane, triethylolpropane, pentaerythritol, α-methylglucoside, hydroxymethyl-, hydroxyethyl-, and/or hydroxypropylglucoside, sorbitol, mannitol, sucrose, tetrakis [<NUM> hydroxyethyl and/or <NUM>-hydroxypropyl]ethylene diamine, as well as mixtures of any two or more thereof. Also suitable are monofunctional starters such as methanol, ethanol, <NUM>-propanol, <NUM>-propanol, n-butanol, <NUM>-butanol, <NUM> ethylhexanol, and the like, as well as phenol, catechol, <NUM>,<NUM>' dihydroxybiphenyl, and <NUM>,<NUM>'-dihydroxydiphenylmethane, including mixtures of any two or more of the foregoing.

In some implementations, the continuously added starter comprises a polyoxyalkylene polymer or copolymer or suitable initiator for the production thereof, which has a molecular weight less than the desired product weight. Thus, the molecular weight of the continuously added starter may vary from <NUM> Da (water) to <NUM>,<NUM> Da (high molecular weight polyoxyalkylene polyol). In some implementations, the continuously added starter may comprise a starter having a molecular weight less than <NUM>,<NUM> Da, such as less than <NUM> Da, or less than <NUM> Da.

Alkylene oxides suitable for introduction in the afore-mentioned step (<NUM>) include, but are not limited to, ethylene oxide, propylene oxide, oxetane, <NUM>,<NUM>- and <NUM>,<NUM>-butylene oxide, isobutylene oxide, epichlorohydrin, cyclohexene oxide, styrene oxide, and the higher alkylene oxides such as the C<NUM>-C<NUM> α-alkylene oxides. In some implementations, a mixture of propylene oxide and ethylene oxide may be used, such as those with high ethylene oxide content, i.e., up to <NUM> mol percent. In some implementations, propylene oxide alone or a mixture of propylene oxide with ethylene oxide or another alkylene oxide is used. Other polymerizable monomers may be used as well, such as anhydrides and carbon dioxide.

The process for producing the intermediate polyol may employ any double metal cyanide (DMC) catalyst. DMC catalysts are non-stoichiometric complexes of a low molecular weight organic complexing agent and optionally other complexing agents with a double metal cyanide salt, such as zinc hexacyanocobaltate. Exemplary suitable DMC catalysts include those suitable for preparation of low unsaturation polyoxyalkylene polyether polyols, such as are disclosed in <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>. In some implementations, the DMC catalyst comprises one that is capable of preparing "ultra-low" unsaturation polyether polyols, such as are disclosed in <CIT>, <CIT>, and <CIT>.

The DMC catalyst concentration is desirably chosen to provide adequate control of the polyoxyalkylation reaction under the given reaction conditions. In some implementations, the DMC catalyst is used in an amount of <NUM> to <NUM> % by weight, such as <NUM> to <NUM> % by weight, or, in some cases, <NUM> to <NUM> % by weight, based on the amount of polyether polyol to be produced.

An organic complexing ligand may be included with the DMC catalyst. Any organic complexing ligand may be part of the DMC catalyst, such as those described in <CIT>,<CIT>,<CIT>, <CIT>and<CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. Such organic complexing ligands include water-soluble organic compounds with heteroatoms, such as oxygen, nitrogen, phosphorus or sulfur, which can form complexes with the DMC compound. In some implementations, the organic complexing ligand comprises an alcohol, aldehyde, ketone, ether, ester, amide, urea, nitrile, sulfide, or a mixture of any two or more thereof. In some implementations, the organic complexing ligands comprises a water-soluble aliphatic alcohol, such as, for example, ethanol, isopropanol, n-butanol, iso-butanol, sec-butanol, tert-butanol, or a mixture of any two or more thereof.

The DMC catalyst may contain a functionalized polymer. As used herein, the term "functionalized polymer" refers to a polymer or its salt that contains a functional group, such as oxygen, nitrogen, sulfur, phosphorus, halogen, or a mixture of any two or more thereof. Specific examples of suitable functionalized polymer include, but are not limited to, polyethers, polyesters, polycarbonates, polyalkylene glycol sorbitan esters, polyalkylene glycol glycidyl ethers, polyacrylamides, poly(acrylamide-co-acrylic acids), polyacrylic acids, poly(acrylic acid-co-maleic acids), poly(N-vinylpyrrolidone-co-acrylic acids), poly(acrylic acid-co-styrenes) and the salts thereof, maleic acids, styrenes and maleic anhydride copolymers and the salts thereof, block copolymers composed of branched chain ethoxylated alcohols, alkoxylated alcohols, polyether, polyacrylonitriles, polyalkyl acrylates, polyalkyl methacrylates, polyvinyl methyl ethers, polyvinyl ethyl ethers, polyvinyl acetates, polyvinyl alcohols, poly-N-vinylpyrrolidones, polyvinyl methyl ketones, poly(<NUM>-vinylphenols), oxazoline polymers, polyalkyleneimines, hydroxyethylcelluloses, polyacetals, glycidyl ethers, glycosides, carboxylic acid esters of polyhydric alcohols, bile acids and their salts, esters or amides, cyclodextrins, phosphorus compounds, unsaturated carboxylic acid esters and ionic surface- or interface-active compounds.

In some implementations, where used, functionalized polymer is present in the DMC catalyst in an amount of <NUM> to <NUM> % by weight, <NUM> to <NUM> % by weight, or, in some cases, <NUM> to <NUM> % by weight, based on the total weight of DMC catalyst.

The DMC catalyst may or may not be activated prior to use in the process of preparing the intermediate polyol. Activation, when desired, involves mixing the catalyst with a starter molecule having a desired number of oxyalkylatable hydrogen atoms, and adding alkylene oxide, preferably propylene oxide or other higher alkylene oxide under pressure and monitoring the reactor pressure. The reactor may be maintained at a temperature of, for example, <NUM> to <NUM>, <NUM> to <NUM>, or, in some cases, <NUM> to <NUM>. A noticeable pressure drop in the reactor indicates that the catalyst has been activated. The same alkylene oxide(s) as is to be employed in to produce the intermediate polyol may be used to prepare activated catalyst, or a different alkylene oxide may be employed. With higher alkylene oxides having low vapor pressure, a volatile alkylene oxide such as ethylene oxide, oxetane, <NUM>,<NUM>-butylene oxide, <NUM>,<NUM>-butylene oxide, or isobutylene oxide may be employed in lieu of or in conjunction with the higher alkylene oxide to facilitate pressure monitoring. Alternatively, other methods of measuring alkylene oxide concentration (GC, GC/MS, HPLC, etc.) may be used. A noticeable reduction in free alkylene oxide concentration indicates activation.

In some cases, however, "fresh" DMC catalyst may be employed without activation. "Fresh" catalyst as used herein is freshly prepared, non-activated DMC catalyst, i.e., non-activated DMC catalyst in solid form or in the form of a slurry in low molecular weight starter, polyoxyalkylated low molecular weight starter, or a non-starter liquid. In some implementations, all or a substantial portion of the liquid phase of a fresh DMC catalyst mixture will include the same low molecular weight starter used for continuous starter addition, a polyoxyalkylated low molecular weight starter.

In some implementations, a portion of intermediate polyol may be cycled back to a catalyst activation reactor and employed for catalyst activation.

In preparing the intermediate polyol, according to some embodiments, the addition of starter is continuous in the sense that a concentration of low molecular weight starter and/or its low molecular weight oxyalkylated oligomers is maintained for a substantial portion of the total oxyalkylation. In a tube reactor, for example, starter may be introduced separately at numerous points along the reactor, or dissolved in alkylene oxide and introduced along the length of the reactor. In a CSTR, starter may be added to alkylene oxide, and may be added at numerous locations within the reactor. Low molecular weight starter need not even be present in the catalyst/starter mixture, which may employ a much higher molecular weight starter. By whatever method added, low molecular weight starter should be present for a substantial portion of oxyalkylation, such as <NUM>% of oxyalkylation, <NUM>% of the alkoxylation, or more. In some implementations. a low molecular weight starter concentration is maintained for a portion of the oxyalkylation which is effective to reduce the proportion of high molecular weight tail in the intermediate polyol product as compared what would be produced in a batch process where all starter is added at once.

The amount of continuously added starter may be increased to very high levels without unduly broadening molecular weight distribution. The continuously added starter may represent in excess of <NUM> equivalent percent of total starter, such as where the percentage of continuously added starter is <NUM> to <NUM>+%. Despite the continuous addition of starter, polydispersity is generally below <NUM>, such as below <NUM> to <NUM>, or <NUM> to <NUM>.

In preparing the intermediate polyol, it may desirable to have a small concentration of starter present in the reaction mixture at all times, although a final "cook out" to facilitate complete reaction of alkylene oxide may be performed without starter present. Continuous addition of as little as <NUM>-<NUM> equivalent percent of starter relative to total product weight may be effective to substantially eliminate the high molecular weight tail. However, despite the continuous addition of a very significant, and in some cases, major amount of low molecular weight starter, the molecular weight distribution is usually not significantly broadened and products of very low polydispersity are obtained.

As indicated, in some implementations, the continuous process of preparing the intermediate polyol involves establishing oxyalkylation conditions in a continuous reactor. Thus, when it is stated herein that a mixture comprising a DMC catalyst and an initial starter is introduced into the first reactor "in an amount sufficient to initiate polyoxyalkylation of the initial starter after introduction of alkylene oxide into the intermediate polyol reactor" it merely means that oxyalkylation conditions are established at some point in time. For example, an initial establishing of oxyalkylation conditions does not need repeating. Following establishment of oxyalkylation conditions, only the addition of alkylene oxide, continuously added starter, and further catalyst need be maintained.

Moreover, the term "starter' as employed in the phrase "DMC catalyst/initial starter" refers to an oxyalkylatable molecule of any molecular weight. This oxyalkylatable molecule may be a low molecular weight starter molecule having a molecular weight below about <NUM> Da, such as propylene glycol, dipropylene glycol, glycerin, a three mole oxypropylate of glycerin, etc., or may be a much higher molecular weight molecule, for example the product of desired product molecular weight.

Suitable processes and equipment for continuously producing the intermediate polyol are described in <CIT> at col. <NUM>, line <NUM> to col. <NUM>, line <NUM>.

As previously mentioned, the processes of this specification comprise continuously discharging the intermediate polyol from the first reactor and continuously mixing the intermediate polyol with an aqueous solution of an alkali metal alkoxide and/or an alkali metal hydroxide to provide a mixture comprising the intermediate polyol, an alkali metal, and water. Suitable alkali metal alkoxides include, for example, those that contain <NUM> to <NUM> carbon atoms in the alkyl radical. Specific examples of suitable alkali metal alkoxides are, without limitation, sodium methylate, sodium and potassium ethylate, potassium isopropylate and sodium butylate. Suitable alkali metal hydroxides include, for example, sodium hydroxide, cesium hydroxide, and potassium hydroxide. In some implementations, the amount of alkali metal alkoxide and/or an alkali metal hydroxide in the aqueous solution is <NUM> to <NUM>% by weight, such as <NUM> to <NUM>% by weight, <NUM> to <NUM>% by weight, or <NUM> to <NUM>% by weight, based on the total weight of the aqueous solution, with the remainder of the solution consisting essentially of water.

In some implementations, the aqueous solutions of an alkali metal alkoxide and/or an alkali metal hydroxide catalyst is used in an amount such that alkali metal is present in an amount of <NUM> to <NUM> % by weight, <NUM> to <NUM> % by weight, or, in some cases, <NUM> to <NUM> % by weight, based on the total weight of the polyol produced by the processes of this specification.

As indicated, the intermediate polyol is continuously mixed with the aqueous solution of an alkali metal alkoxide and/or an alkali metal hydroxide to provide a mixture comprising the intermediate polyol, an alkali metal, and water. In some implementations, such as the implementation depicted in <FIG>, such mixing can be achieved by inline mixing of the aqueous solution of an alkali metal alkoxide and/or an alkali metal hydroxide with the intermediate polyol as it is continuously discharged from the first reactor. Such inline mixing may, if desired, be enhanced by the use of a mixing device, such as a static mixer or a jet mixer, that may be present at the injection point of the aqueous solution or downstream therefrom.

The processes of this specification further comprise continuously dehydrating the mixture comprising intermediate polyol, alkali metal, and water, thereby continuously producing a dehydrated mixture comprising the intermediate polyol and the alkali metal, though it should be understood that, while the dehydrated mixture will contain less water than the mixture prior to dehydration, such dehydration may not be complete, so that some water still remains in the mixture following the dehydration process. In some implementations, however, the water content of the dehydrated mixture is no more than <NUM> ppm, sometimes no more than <NUM> ppm.

According to the invention, the foregoing continuous dehydration of the mixture comprising intermediate polyol, alkali metal, and water may be accomplished by continuously passing the mixture through one or more packed columns, such as the two packed columns 50a and 50b arranged in series that is depicted in <FIG>. In addition to packed columns or trayed columns, other dehydration apparatus' suitable for use in the processes of this specification can be readily envisaged, such as falling film evaporator, wiped film evaporator, kettle evaporator, flash tank, etc..

Thus, in some implementation, the dehydration is accomplished by passing a stripping gas through the mixture comprising intermediate polyol, alkali metal, and water, such that water is transferred to the stripping gas. In some implementations, a nitrogen-containing gas, such as nitrogen gas, is a suitable inert stripping gas. As a result, in some implementations, such as the implementation depicted in <FIG>. , an inlet of dehydration apparatus <NUM> is in fluid communication with a source of stripping gas <NUM>, such as a source of N<NUM> gas.

In some implementations, the foregoing dehydration may be accomplished by a desorption process in which water passes into the inert stripping gas because of partition equilibria between gas phase and liquid phase. Thus, in some cases, such desorption involves expelling water in an inert stripping gas stream, such as an N<NUM> gas stream. The stripping gas can, such as is depicted in <FIG>, be fed countercurrent to the mixture comprising intermediate polyol, alkali metal, and water. Water migrates from the liquid phase into the gas phase.

Thus, in some cases, the dehydration of the mixture comprising intermediate polyol, alkali metal, and water is executed by passing the mixture countercurrent, i.e., against the direction of flow of an inert stripping gas through one or more packed columns at, for example, reduced pressure and elevated temperatures. More specifically, in some implementations, the dehydration may be carried out at a temperature of <NUM> to <NUM>, such as <NUM> to <NUM>. In some implementations, the column(s) is operated at a pressure of from <NUM> to <NUM> mmHg (absolute), such as <NUM> to <NUM> mmHg (absolute).

The stripping gas may be fed to the packed column in any suitable amount to accomplish the desired level of dehydration. For example, in some implementations, the stripping gas is fed to the packed column in an amount of <NUM> to <NUM> of stripping gas per kg of the mixture comprising intermediate polyol, alkali metal, and water, such as <NUM> to <NUM> of stripping gas per kg of the mixture comprising intermediate polyol, alkali metal, and water.

Suitable packed columns for use in embodiments of the processes of this specification include any columns having internals with separation activity, such as trays, random packings and structured packings. Specific examples of trays include, but are not limited to, bubble trays, tunnel trays, valve trays, sieve trays, dual flow trays and grid trays.

Random packings include packing elements constructed of, for example, steel, stainless steel, copper, carbon, earthenware, porcelain, glass, plastic, or a combination thereof. Specific examples of suitable random packing structures are Raschig® rings in which small pieces of tube to make a packing bed, Pall® rings which are similar to Raschig® rings but also include support structures and external surfacing texture within the ring walls, saddle rings, such as Berl® saddles and Intalox® saddles that are shaped like saddles, Lessing® rings, which are made of ceramic and have internal partitions to increase surface area and enhance efficiency, and, Tri-Packs that has a spherical shape and interior ribs to maximize surface area and wetting.

As will be appreciated by the ordinary skilled artisan, structured packing is a type of packing that channels a liquid into a specific shape. Structured packing utilizes discs made of, for example, metal, plastic or porcelain, with the discs having an internal structure arranged into a type of honeycombed shape. Unlike random packing, structured packing are constructed of large pieces of material that contains holes, grooves, corrugation and other textured elements. Specific types of structured packing, which are suitable for use in the inventions of this specification include, but are not limited to, knitted wire structured packing, fabric packings, and corrugated sheet metal structured packing.

In some implementations, the foregoing dehydration may further comprise passing the mixture through an in-line molecular sieve that is arranged downstream of the packing column(s). As will be appreciated, molecular sieves are often constructed of zeolite, i.e., microporous aluminosilicates.

As indicated earlier, the processes of this specification further comprise transferring the dehydrated mixture to a second reactor and producing the polyether polyol in the second reactor by feeding an alkylene oxide to the second reactor to thereby react the intermediate polyol with the alkylene oxide in the presence of the alkali metal.

As shown in <FIG>, in some implementation, an outlet of dehydration apparatus <NUM> is in fluid communication, via line <NUM>, with dehydrated mixture storage vessel <NUM>, which, in turn, is also in fluid communication, via line <NUM>, with an inlet of second reactor <NUM>. The presence of dehydrated mixture storage vessel <NUM> may be particularly desirable in cases where second reactor <NUM> is a batch (or semi-batch) reactor. In the particular implementation depicted in <FIG>, therefore, dehydrated mixture discharged from dehydration apparatus <NUM> and/or dehydrated mixture from dehydrated mixture storage vessel <NUM> may be fed to second reactor <NUM>. As a result, in operation, second reactor <NUM> may receive dehydrated mixture continuously from dehydration apparatus <NUM>, receive dehydrated mixture from dehydrated mixture storage vessel <NUM>, or may receive dehydrated mixture from both dehydration apparatus <NUM> and dehydrated mixture storage vessel <NUM> simultaneously.

As a result, according to the processes of this specification, the intermediate polyol is used as a starter in preparing the polyol produced in the second reactor. In some implementations, the polyol produced in the second reactor is a "long chain" polyol that has a functionality of <NUM> to <NUM> and an equivalent weight of <NUM> to <NUM> Da, such as a functionality of <NUM> to <NUM> and an equivalent weight of <NUM> to <NUM> Da.

If desired, in addition to the intermediate polyol, other starters may be used to prepare the polyol produced in the second reactor. Such other starters may include, without limitation, low molecular weight starters such as glycerin, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol, trimethylolpropane, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, pentaerythritol, sorbitol, sucrose, ethylenediamine, and toluene diamine, among others, as well as combinations of two or more of the foregoing.

Suitable alkylene oxides that may fed to the second reactor according to implementations of the processes of this specification include, but are not limited to, ethylene oxide, propylene oxide, oxetane, <NUM>,<NUM>- and <NUM>,<NUM>-butylene oxide, isobutylene oxide, epichlorohydrin, cyclohexene oxide, styrene oxide, and the higher alkylene oxides such as the C<NUM> -C<NUM> α-alkylene oxides. In some implementations, propylene oxide, ethylene oxide, or a mixture of propylene oxide with ethylene oxide is used as the alkylene oxide fed to the second reactor. According to the invention, sufficient ethylene oxide is fed to the second reactor to provide the resulting polyol with an ethylene oxide "cap" in which up to <NUM>% of ethylene oxide, such as <NUM> to <NUM>% of ethylene oxide is added as a cap, such weight percents being based on the total weight of the final polyol produced in the second reactor.

In some implementations, the processes of this specification do not include a propylene oxide drying step to remove water from the reaction mixture prior to making the polyol in the second reactor.

The processes conditions used to make the polyol in the second reactor can vary. In some implementations, the dehydrated mixture described above is added to the second reactor and is heated to the desired reaction temperature, such as a temperature of <NUM> to <NUM>, and the alkylene oxide is added to the second reactor. In some implementations, the alkylene oxide is fed over <NUM> to <NUM> hours depending on the configuration and heat removal capabilities of the second reactor. After the total amount of alkylene oxide is fed, the reactor contents may be allowed to react further until the pressure in the reactor is level indicating no further change in the amount of oxide present. The final polyol is then refined to remove the alkali metal, such as by acid neutralization followed by filtration, treatment with solid adsorbents, treatment with solid inorganic compounds and treatment with ion exchanges resins.

The second reactor may be of any configuration, such as batch, semi-batch, or a continuous reactor. In some implementations, however, the second reactor is, as is illustrated in <FIG>, a batch.

In particular, as shown in <FIG>, production plant <NUM> may include a second reactor <NUM> that is a batch reactor. In this implementation, an inlet of reactor <NUM> is in fluid communication, via line <NUM>, with a source of alkylene oxide <NUM>, an inlet of reactor <NUM> is in fluid communication, via line <NUM>, with an outlet of dehydration apparatus <NUM>, and, in some cases, an inlet of reactor <NUM> is in communication with a source of H-functional starter <NUM> (the source of H-functional starter <NUM> may be the same as source of H-functional starter <NUM> or it may be a different source of H-functional starter). The various afore-mentioned inlets to reactor <NUM> may be the same inlet or they may be different inlets (such as is depicted in <FIG>). reactor <NUM> is configured to discharge polyol from reactor <NUM>. As is apparent, an outlet of reactor <NUM> is in fluid communication, via line <NUM>, with an inlet of a polyol work-up system <NUM>. Polyol work-up system <NUM> includes means for removing alkali metal from the polyol exiting reactor <NUM>, such means may include, for example, treatment with an ion-exchange resin, liquid-liquid extraction, or treatment with an absorbent, such as magnesium silicate. Suitable methods for working-up the polyol exiting reactor <NUM> are described in <CIT>; <CIT>; <CIT>; <CIT> and <CIT>. Polyol work-up system <NUM> can be in fluid communication with polyol storage <NUM>.

Claim 1:
A process for preparing a polyol, comprising:
a) continuously producing an intermediate polyol in a first reactor by a process comprising:
(<NUM>) introducing into the first reactor a mixture comprising a DMC catalyst and an initial starter, wherein the mixture is added in an amount sufficient to initiate polyoxyalkylation of the initial starter after introduction of alkylene oxide into the first reactor;
(<NUM>) introducing alkylene oxide to the first reactor;
(<NUM>) continuously introducing a continuously added starter into the first reactor; and
(<NUM>) continuously introducing fresh DMC catalyst and/or further DMC catalyst/further starter mixture to the first reactor such that catalytic activity of the DMC catalyst is maintained;
b) continuously discharging the intermediate polyol from the first reactor;
c) continuously mixing the intermediate polyol with an aqueous solution of alkali metal to provide a mixture comprising the intermediate polyol, alkali metal, and water;
d) continuously dehydrating the mixture comprising intermediate polyol, alkali metal, and water, by continuously passing the mixture through one or more packed column, trayed column, falling film evaporator, wiped film evaporator, kettle evaporator, or flash tank, thereby continuously producing a dehydrated mixture comprising the intermediate polyol and the alkali metal;
e) transferring the dehydrated mixture to a second reactor; and
f) producing the polyol in the second reactor by feeding an alkylene oxide to the second reactor to thereby react the intermediate polyol with the alkylene oxide in the presence of the alkali metal, wherein the alkylene oxide fed to the second reactor comprises ethylene oxide in an amount sufficient to provide the polyol with an ethylene oxide cap in which up to <NUM>% by weight of ethylene oxide is added as a cap, based on the total weight of the polyol produced in the second reactor.