WO2023158327A1

WO2023158327A1 - A process for obtaining a polyether polyol with a low content of alkali metal ions

Info

Publication number: WO2023158327A1
Application number: PCT/PL2023/050009
Authority: WO
Inventors: Jerzy WACEK
Original assignee: Pcc Rokita Spółka Akcyjna
Priority date: 2022-02-18
Filing date: 2023-02-15
Publication date: 2023-08-24
Also published as: HUP2200443A1; PL440409A1

Abstract

The invention relates to a process for obtaining a poly ether polyol with a low content of alkali metal ions, comprising the following steps: (a) a polyaddition reaction of at least one alkylene oxide to a starter containing at least two active hydrogen atoms in the presence of a catalyst being an alkali metal hydroxide or alkoxide thereof; (b) neutralisation of the crude polyether polyol obtained in step (a) by the addition of sodium acid pyrophosphate (Na2H2P2O7) and water to the reaction mixture; (c) reducing the water content of the mixture obtained in step (b) to less than 0.1% by weight through distillation under reduced pressure; (d) removal of alkali metal salt crystals from the mixture obtained in step (c) by filtration to obtain a polyether polyol with a content of alkali metal ions of not more than 5 ppm. The inventive process allows for obtaining polyether polyols with a low content of alkali metal ions, which allows for significantly reducing side reactions in polyurethane plastics production processes.

Description

A PROCESS FOR OBTAINING A POLYETHER POLYOL WITH A LOW CONTENT OF ALKALI METAL IONS

Field of the Invention

The invention relates to a process for obtaining a polyether polyol with a low content of alkali metal ions, wherein the crude polyether polyol obtained by the polyaddition reaction of at least one alkylene oxide to a starter containing at least two active hydrogen atoms in the presence of a catalyst being an alkali metal hydroxide or alkoxide thereof is subjected to the steps of neutralisation, water content reduction and filtration to obtain a polyether polyol with a content of alkali metal ions of not more than 5 ppm. Polyether polyols obtained by the inventive process may be used to produce polyurethane plastics.

Prior Art

The process for obtaining polyol polyethers using an alkali catalyst requires alkali metal ions to be removed from the final product for two reasons:

• Na⁺, K⁺ ions catalyse the reaction of isocyanates with hydroxyl groups;

• Na⁺, K⁺ ions catalyse the trimerisation reaction of isocyanate groups into isocyanurates, which are particularly undesirable in the production of prepolymers and flexible foams.

The content of alkali metal ions in the product depends on the efficacy of the crude polyether polyol purification process conducted by way of neutralising alkali metal ions using acids, adsorbents, acidic inorganic salts and ion exchange resins. Another important factor contributing to the alkali metal ion content of the product is the concentration of the alkali metal-based catalyst used for the polymerisation reaction. In industrial practice, the concentration of such a catalyst is 2000 to 3000 ppm per product. A higher catalyst concentration accelerates the polymerisation reaction, while rendering purification problematic and resulting in higher product losses in the filtration process due to the larger volume of the filter cake. Then, lower catalyst concentrations makes the reaction rate decrease significantly, thus reducing the efficiency of the production plant.

Patent US 4,855,509 describes a method for removing alkali metal ions from polyols involving contacting a polyol for a period of 0.5 hours to 3 hours at a temperature below 100°C with a mono- or dihydrogen phosphate, in particular MgHPCU used in an amount of 0.5 to 3 wt% relative to the weight of the polyol to be purified.

Patent US 3,000,963 discloses a method for removing alkali metal ions from polypropylene glycols) by adding to the product a solid organic acid, insoluble in the product, in an amount from 10% to 200% in excess relative to the alkali equivalent in the unpurified product, followed by, once the acid has reacted with the alkali ions, producing a salt insoluble in the product, which is filtered off. The organic acids used in the aforementioned invention include a group of acids such as oxalic, diglycolic, benzoic, citric, succinic, fumaric, itaconic, phthalic, isophthalic and terephthalic acid.

Patent US 3,833,669 describes a method for purifying polyether polyols using 1 to 100 parts of alkaline magnesium salt and 1 to 20 parts of carbon dioxide for each part of magnesium salt over a temperature range of 20 to 150°C, for a period of 0.5 hours to 2 hours. Said alkaline magnesium salt is selected from magnesium hydroxide, magnesium oxide, magnesium carbonate, alkaline magnesium carbonate and mixtures thereof. The process is conducted in the presence of 1 to 10 parts of water for every part of alkaline magnesium salt added.

Further, US application 2003/0158450 describes a process for obtaining polyether polyols containing up to 20 ppm of Na⁺ and /or K⁺ ions, which includes the following steps:

(a) reacting an initiator having active hydrogen atoms with at least one alkylene oxide in the presence of a catalyst comprising an alkali metal hydroxide,

(b) neutralising the polyether polyol obtained in step (a) by contacting the reaction product with an acid with a pKa of less than 5 and water, wherein the acid and water are added such that, following the addition, the water content is 2% by weight or less relative to the weight of the polyether polyol, and the molar ratio of acid to hydroxide is in the range of 0.3 to 1,

(c) optionally, reducing the water content of the reaction mixture to less than 2% by weight of the polyether polyol,

(d) removing salt crystals from the polyether polyol and obtaining a neutralised poly ether polyol containing up to 20 ppm of sodium and/or potassium ions.

Patent US 8,017,814 describes a process for obtaining polyether polyols containing up to 15 ppm of sodium and potassium ions, wherein the process comprises:

(a) reaction of an initiator having active hydrogen atoms with at least one alkylene oxide in the presence of a catalyst containing an alkali metal hydroxide,

(b) neutralisation of the polyether polyol obtained in step (a) by contacting the reaction product with phosphoric acid and water,

(c) removal of salt crystals from the polyether polyol and obtaining a neutralised poly ether polyol containing up to 15 ppm of sodium and/or potassium ions, with no adsorption agent or metal phosphate hydrate used either before, during or following neutralisation.

Patent EP 2855559 describes a method for removing an alkali catalyst from polyether polyols comprising the following steps:

(a) mixing crude poly ether polyol with acid and water;

(b) partial removal of water, preferably by distillation, so that the water content of the mixture constitutes no more than 5% by weight, wherein the mixture contains neutralised polyether polyol, water and salt crystals produced by the reaction of the alkaline catalyst and the acid added in step (a);

(c) redissolving at least part of said salt by adding water;

(d) partial removal of water, preferably by distillation, to obtain a dehydrated mixture of neutralised polyether polyol and crystals of said salt;

(e) removal of crystals of said salt, preferably by filtration, to obtain the polyether polyol.

The recrystallisation process allows for obtaining larger salt crystals and easier filtration of the product.

Although the prior art methods described above allowed for reducing the sodium and potassium ion content of polyether polyols to no more than 20 ppm and even no more than 15 ppm, there still remains a real need to provide even more efficient methods for reducing the content of said ions, as this directly contributed to the reduction of side reactions in polyurethane plastics production processes.

Summary of the Invention

The invention relates to a process for obtaining a polyether polyol with a low content of alkali metal ions, comprising the following steps:

(a) a polyaddition reaction of at least one alkylene oxide to a starter containing at least two active hydrogen atoms in the presence of a catalyst being an alkali metal hydroxide or alkoxide thereof;

(b) neutralisation of the crude polyether polyol obtained in step (a) by adding sodium acid pyrophosphate (Na2H2P2O?) and water to the reaction mixture;

(c) reducing the water content of the mixture obtained in step (b) to less than 0.1% by weight through distillation under reduced pressure; (d) removal of alkali metal salt crystals from the mixture obtained in step (c) by filtration on a pressure filter to obtain a polyether polyol with a content of alkali metal ions of not more than 5 ppm.

Preferably, the polyaddition reaction in step (a) is conducted at a temperature of 100 to 150°C, preferably 110 to 130°C.

Preferably, the polyaddition reaction in step (a) is conducted in a pressure reactor equipped with mixing elements, preferably selected from static mixers, mechanical mixers, jet mixers, diffusers and pumps for circulating the reaction fluid.

Preferably, the polyaddition reaction in step (a) is conducted in the presence of nitrogen, the concentration of which in the gas phase is maintained at a level of at least 60% by vol.

Preferably, the starter is selected from glycerol, trimethylolpropane (TMP), propylene glycol, dipropylene glycol or mixtures thereof.

Preferably, the alkylene oxide is selected from ethylene oxide, propylene oxide and butylene oxide.

Preferably, the catalyst is selected from NaOH, KOH, CsOH or sodium, potassium and caesium alkoxides.

Preferably, the polyaddition reaction in step (a) is conducted under energetic stirring with simultaneous nitrogen bubbling.

Preferably, the volatile components in the reaction mixture from step (a) are degassed before being transferred for neutralisation in step (b).

Preferably, in step (b), part of the reaction mixture from step (a) is transferred to a separate mixer and sodium acid pyrophosphate is added thereto and mixed until a slurry is obtained, which in turn is added to the remaining part of the reaction mixture from step (a) temporarily placed in the neutraliser, followed by adding water in an amount of 0.5 - 1 wt%. of the total weight of the neutralised poly ether polyol, preferably 0.7 - 0.8 wt%.

Preferably, in step (c), distillation under reduced pressure is conducted with simultaneous nitrogen bubbling of the mixture.

Preferably, at least one antioxidant, preferably selected from spatially substituted phenols, diphenylamines and lactone polymers, is added to the polyether polyol with low content of alkali metal ions obtained in step (d). Preferably, the antioxidant concentration ranges from 400 to 5000 ppm, depending on the specific polyether polyol and its intended use. The antioxidant is added in order to stabilise the purified polyether polyol during storage and processing into polyurethane plastics. The inventive process allows for obtaining polyether polyols with the content of alkali metal ions, in particular K⁺ and Na⁺ reduced to less than 5 ppm, thus minimising side reactions in the manufacture of polyurethane plastics using these polyether polyols.

Detailed description of the invention

The first step of the inventive process for obtaining a polyether polyol with a low content of alkali metal ions involves the polyaddition reaction of at least one alkylene oxide to a starter containing at least two active hydrogen atoms in the presence of a catalyst which is an alkali metal hydroxide or alkoxide thereof.

In a preferable embodiment of the inventive process, a catalyst, such as KOH, is added to the starter, after which such a mixture is heated to 110-130°C for several (1- 5) hours and, with inert gas, e.g. nitrogen bubbling, the excess water from the starter and from the alkoxide formation reaction is removed according to the following diagram:

R-OH *KOH - ► R-QK + H₂Q

The alkoxide forms at 100-130°C under reduced pressure and with a reaction time of 0.5-6 hours, e.g. with glycerine as the starter at 120°C and full vacuum, approx. 75% of glycerine reacts with potassium hydroxide to form the alkoxide, while for the same process conditions approx. 90% of the propoxylated glycerine with a molecular weight of 560 Da reacts to form the alkoxide. In the process of starter catalysis, it is important to remove the water both present in the 50% aqueous solution of KOH catalyst used and that produced during the reaction of alkoxide formation, since the water in the polymerisation reaction with the alkylene oxide increases the polyglycol content, which, for triols, causes the polyurethane foams obtained by the use of the polyether polyols thus obtained to have a lower hardness.

The resulting starter-catalyst mixture, dried to a water content of less than 0.05% by weight, is transferred to a reactor and subjected to a polyaddition reaction with at least one alkylene oxide, preferably selected from ethylene oxide (EO), propylene oxide (PO) and butylene oxide (BO), in block(TP-TE, TE-TP, TP-TB, TB-TP, TE-TB, TB-TE), statistical (TP/TE, TP/TB, TE/TB), mixed block- statistical (TP-TP/TE, TP-TE/TB, TE- TP/TE, TE-TB/TE, TB-TP/TE, TB-TB/TE) or statistical-block (TP/TE-TB, TE/TB-TP, TP/TE-TE, TB/TE-TE, TP/TE-TB, TB/TE-TB), composite (e.g. TP-TP/TE-TE, TP- TE-TP/TE, TP-TE-TP, TP-TB-TE, TP-TE/TP-TP) sequences, as required for specific product properties: or, if only EO, PO or BO is used, a homopolymer (TP, TE, TB), to obtain a specific molecular weight, wherein TE denotes a block formed exclusively from EO monomers, TP - a block formed exclusively from PO monomers, and TB - a block formed exclusively from BO monomers.

The reaction of the polyaddition of alkylene oxides to a starter containing active hydrogen atoms takes place at an elevated temperature, preferably selected from the range of 110-130°C, and under a pressure of up to 10 bar under nitrogen, the content of which in the gas phase is not less than 60% by volume. Example starters that can be used in the inventive process include glycerol, trimethylolpropane (TMP), propylene glycol, dipropylene glycol, ethylene glycol, diethylene glycol, sorbitol.

Once the starter, catalyst and the required amount of alkylene oxides have been introduced into the pressure reactor, digestion takes place, during which unreacted oxides bound to the polymer, which may be observed as a decreasing pressure in the reactor maintained at a constant reaction temperature. Once the pressure in the reactor has stabilised, thus indicating that the alkylene oxides have reacted, the liquid reaction mixture, which is then directed to the process to remove alkali metal ions from the catalyst, is being degassed.

Part of the reaction mixture from reaction step (a) is transferred to a separate mixer and sodium acid pyrophosphate is added thereto under energetic stirring to prevent precipitation of the solid pyrophosphate. The resulting suspension is added to the remainder of the reaction mixture from step (a) temporarily placed in the neutraliser. Water is then added with energetic stirring in an amount of 0.5%-l% by weight of the total mass of the neutralised polyether polyol, preferably in an amount of 0.7%-0.8% by weight. The neutralisation is deemed to be complete following a positive test of the colour of the acidity indicator (2:1 isopropanol-water solution with bromothymol blue) changing to yellow.

In the next step (c), the water content of the mixture obtained in step (b) of the neutralisation is reduced to less than 0.1 wt.%, preferably less than 0.05 wt.%, by distillation under reduced pressure, preferably with simultaneous nitrogen bubbling.

The mixture obtained in step (c) is then filtered on a pressure filter. To prepare the filter for filtration, a suspension of the filter aid (diatomaceous earth) is made in dehydrated poly ether poly glycol in a mixer and applying the filtration layer onto the filter elements, followed by filtration of the polyether polyglycol to an alkali metal ion content of no more than 5 ppm.

Alkali metal ions, preferably K⁺ and Na⁺, were determined using BWB-XP flame photometer (from BWB Technologies UK Ltd.). It is a multi-channel, low-temperature flame photometer for the simultaneous determination of Na, K, Li, Ca, Ba. Polyether polyols of the diols type obtained by the inventive method have a weight average molecular weight Mw typically in the range of 1000 to 4000 Da. Now, polyether polyols of the triols type obtained by the inventive method have a weight average molecular weight Mw typically in the range of 1000 to 6000 Da.

Examples

Example 1

0.77 kg of glycerine and 0.19 kg of a 50% KOH solution were added to the preparator. After flushing the reaction vessel with nitrogen under continuous stirring, the contents were heated to 110°C for 3 hours and then, after starting the nitrogen bubbling and connecting to the vacuum system, the water was distilled to 0.04 wt%. The starter and catalyst mixture thus prepared was transferred to a reactor previously flushed with nitrogen, nitrogen was added to achieve a pressure of 1 bar and 3.9 kg of propylene oxide was added at a temperature of 115°C. Once the pressure was stabilised, 26.8 kg of propylene oxide/ethylene oxide mixture was added in an 85: 15 wt% ratio at 130°C. After digestion, the crude polyether polyol was transferred to a neutraliser and degassed under vacuum from the volatile components. Part of the polyether polyol (10 wt.%) was transferred to a separate mixer, to which 0.225 kg of sodium acid pyrophosphate (Na2H2P2O?)was added. The resulting pyrophosphate suspension was transferred to the neutraliser with the remaining polyether polyol. Following energetic mixing, 0.25 kg of demineralised water was dosed in. The neutralised polyether polyol was distilled under reduced pressure to remove water to 0.04 wt.% in the product, followed by, having prepared a suspension of filter aid (Dicalite) in the polyether polyol in a mixer and placing the filter layer on a filter, the product was filtered to obtain a polyether polyol with a hydroxyl number LOH = 47 [mg KOH/g] containing 2 ppm of K⁺ and Na⁺ ions. To the purified product, 4000 ppm of Irgastab® PUR 55 antioxidant (BASF SE) (a mixture of diphenylamines with C6-C9 side chains at the phenyl ring and phenols with steric bases in the form of Cs-Cio ester side chains) was added.

Example 2

2 kg of propoxylated glycerine with an average molecular weight of Mw = 560 Da and 0.13 kg of a 50% KOH solution were added to the preparator. After flushing the reaction vessel with nitrogen under continuous stirring, the contents were heated to 110°C for 2 hours and then, after starting the nitrogen bubbling and connecting to the vacuum system, the water was distilled to 0.05 wt%. The starter and catalyst mixture thus prepared was transferred to a reactor previously flushed with circulation reactor nitrogen, nitrogen was added to achieve a pressure of 1 bar and 20 kg of propylene oxide was added at a temperature of 115°C. Following pressure stabilisation, degassing and repeated nitrogen processing, 3.7 kg of ethylene oxide was added at 130°C. After digestion, the crude poly ether polyol was transferred to a neutraliser and degassed under vacuum from the volatile components. Part of the polyether polyol (10 wt.%) was transferred to a separate mixer, to which 0.2 kg of sodium acid pyrophosphate was added. The resulting pyrophosphate suspension was transferred to the neutraliser with the remaining polyether polyol. Following energetic mixing, 0.2 kg of demineralised water was dosed in. The neutralised polyether polyol was distilled under reduced pressure to remove water to 0.05 wt.% in the product, followed by, having prepared a suspension of filter aid (Dicalite) in the polyether polyol in a mixer and placing the filter layer on a filter, the product was filtered on a plate filter to obtain a poly ether polyol with a hydroxyl number LOH = 27.4 [mg KOH/g] containing 1 ppm of K⁺ and Na⁺ions. 4000 ppm of Irgastab® PUR 55 antioxidant was added to the purified product.

Claims

Claims A process for obtaining a polyether polyol with a low content of alkali metal ions, characterised in that it comprises the following steps:

(c) reducing the water content of the mixture obtained in step (b) to less than 0.1% by weight through distillation under reduced pressure;

(d) removal of alkali metal salt crystals from the mixture obtained in step (c) by filtration on a pressure filter to obtain a polyether polyol with a content of alkali metal ions of not more than 5 ppm. The process according to claim 1, characterised in that the polyaddition reaction in step (a) is conducted at a temperature from 100 to 150°C, preferably from 110 to 130°C. The process according to claim 1 or 2, characterised in that the polyaddition reaction in step (a) is conducted in a pressure reactor equipped with mixing elements, preferably selected from static mixers, mechanical mixers, jet mixers, diffusers and pumps for circulating the reaction fluid. The process according to any one of claims 1 to 3, characterised in that the poly addition reaction in step (a) is conducted in the presence of nitrogen, the concentration of which in the gas phase is maintained at a level of at least 60% by volume. The process according to any one of claims 1 to 4, characterised in that the starter is selected from glycerol, trimethylolpropane (TMP), propylene glycol, dipropylene glycol or mixtures thereof. The process according to any one of claims 1 to 5, characterised in that the alkylene oxide is selected from ethylene oxide, propylene oxide and butylene oxide. The process according to any one of claims 1 to 6, characterised in that the catalyst is selected from NaOH, KOH, CsOH or alkoxides of sodium, potassium and caesium. The process according to any one of claims 1 to 7, characterised in that the poly addition reaction in step (a) is conducted under energetic stirring with simultaneous nitrogen bubbling. The process according to any one of claims 1 to 8, characterised in that the volatile components in the reaction mixture from step (a) are degassed before being transferred for neutralisation in step (b). The process according to any one of claims 1 to 9, characterised in that a part of the reaction mixture from step (a) is transferred to a separate mixer and sodium acid pyrophosphate is added thereto and mixed until a slurry is obtained, which in turn is added to the remaining part of the reaction mixture from step (a) temporarily placed in the neutraliser, followed by adding water in an amount of 0.5 - 1 wt%. of the total weight of the neutralised polyether polyol, preferably 0.7 - 0.8 wt%. The process according to any one of claims 1 to 10, characterised in that in step (c) the distillation under reduced pressure is conducted with simultaneous nitrogen bubbling of the mixture. The process according to any one of claims 1 to 11, characterised in that at least one antioxidant is added to the polyether polyol with low content of alkali metal ions obtained in step (d). The process according to claim 12, characterised in that the antioxidant concentration is from 400 to 5000 ppm. The process according to claim 12 or 13, characterised in that the antioxidant is selected from spatially substituted phenols, diphenylamines and lactone polymers.