Process for manufacturing low-salt polyalkoxylates

Abstract

The present invention deals with a process for manufacturing low-salt polyalkoxylates.

Description

[0001] Process for manufacturing low-salt polyal koxylates

[0002] The present invention deals with a process for manufacturing low-salt poly alkoxy lates, low-salt alkoxylates obtained or obtainable from the inventive process and their uses.

[0003] Polyalkoxylates (herein also referred to as "polyalkylene glycols”, "PAG”), e.g. polyethylene glycols (PEG) or polypropylene glycol, are a well-known class of compounds with many industrial uses. To name just one example, PAGs may be used in detergent compositions.

[0004] US 2016 / 0369051 A1 describes a process for preparing polyols, comprising the steps of adding an alkylene oxide onto a starter compound, neutralizing the alkaline crude polyol by contacting an acid with it, optionally removing water and finally, removing the formed neutralization salts. Preferably, an inorganic mineral acid is used for the neutralization step, e. g. sulfuric acid.

[0005] The crude polyol is a mixed alkylene oxide addition product (EG and PO, blockwise) of a long-chain polyether polyol. Furthermore, Ambosol® (i. e. magnesium silicate based ion exchanger) is used.

[0006] US 8 017 814 B2 discloses a process for the preparation of polyether polyols.

[0007] US 4 507 475 A describes a process for purification of crude polyether polyols.

[0008] US 10 131 743 B2 relates to a method for working up alkaline polyether polyols.

[0009] US 2023 / 0391952 A1 discloses a process for preparing polyether alcohols having a low metal ion content. None of the publications mentioned above disclose or hint at that water may be added in several portions. Furthermore, none of the documents describes turbidity measurements of the reaction mixture or conductivity measurements of the resulting poly alkoxy late . Besides, the publications mentioned above relate to polyether polyols and do not describe the use of starters selected from mono propylene glycol, dipropylene glycol and mixtures thereof.

[0010] The processes known in the art have some disadvantages. For example, most of them need to make use of an ion exchanger and / or require extensive filtering procedures. Separate filtering units are required, and transfer pipes between the reaction vessel and the filtering units are usually needed, which must be regularly flushed and cleaned, leading to loss of product (generally up to 5% by weight of the entire batch). Furthermore, these additional apparatuses are expensive in acquisition and in operation, leading to a less economic manufacturing process. Furthermore, since the processes disclosed in the publications mentioned above refer to certain educt and product types, they may not always be transferred to other educt and product types. For example, a process described for a mixed alkylene oxide (e. g. based on EO and PO) is not directly transferable to a process for a mono-alkylene oxide based product (e. g. based only on PO). In addition, processes disclosed for the production of so-called polyether polyols, which are used for manufacturing polyurethanes, are not generally applicable for the production of other polyalkoxylates, based on different starter molecules. The known processes also mostly lead to products with relatively high levels of salts, e. g. sodium and potassium salts. These salts, e. g. potassium salts, may lead to undesired side reactions when the poly alkoxy lates are converted into amines (e. g. for applications in polyurethane manufacturing).

[0011] Thus, it was an objective of the present invention to overcome the problems and disadvantages resulting from known processes for manufacturing low-salt poly alkoxy lates. For example, it was an objective to avoid or at least reduce the need for filtering operations. It was an objective of the present invention to provide a process for manufacturing low- salt polyalkoxylates which goes without using an ion exchanger and / or which reduces the amount or size of filters needed. Furthermore, it was an objective of the present invention to provide a process for manufacturing low-salt polyalkoxylates based on propylene oxide only. It was also an objective of the present invention to provide a time- and cost-efficient process.

[0012] The inventors have surprisingly found that a process as described in the appended claims and in the present specification is able to reach said objectives. The inventors have found that using phosphoric acid (preferably under certain conditions, as disclosed herein in the claims and the specification) may overcome at least some of the problems mentioned above and has several advantages. For example, low-salt polyalkoxylates may be obtained by the inventive process. Furthermore, the inventive process makes the use of additional ion-exchanger or filtering units unnecessary in most parts.

[0013] Therefore, one object of the present invention is a process for manufacturing low-salt polyalkoxylates by (a) adding an alkylene oxide compound (AO) onto a starter compound (S) having at least one Zerewitinoff-active hydrogen atom in the presence of a basic catalyst (C) to obtain an alkaline crude poly alkoxylate, (b) subsequently neutralizing the alkaline crude poly alkoxy late by contacting phosphoric acid with the alkaline crude poly alkoxy late over a period of time t1, (c) optionally removing water, and (d) removing the neutralization salts formed.

[0014] In the context of the present invention, the term "low-salt” may relate to polyalkoxylates with a conductivity of less than 0.02 piSiemens / cm, determined in 10 wt.% aqueous solution at 25° C. A low conductivity is equivalent to a low content of salts in the poly al koxy I ate, in particular low content of sodium and / or potassium salts.

[0015] Furthermore, in the context of the present invention, the term "low-salt” also relates to polyalkoxylates with a total content of alkali salts (sum of alkali salts) of less than 25 ppm, preferably less than 20 ppm.

[0016] Acid (precipitation agent)

[0017] The acid used in the inventive process in step (b) is phosphoric acid.

[0018] The phosphoric acid may be used as an aqueous solution, for example 40% by weight aqueous solution.

[0019] Alkylene oxide

[0020] The alkylene oxide compound (AO) in step (a) is selected from ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO) and mixtures thereof. In an embodiment of the inventive process, the alkylene oxide compound in step (a) is selected from alkylene oxide mixtures containing at least 50 mole % PO and pure PO, preferably pure PO.

[0021] In a preferred embodiment, only PO is used as alkylene oxide.

[0022] Starter compound

[0023] In a preferred embodiment of the inventive process, the starter compound (S) is selected from the list consisting of mono propylene glycol, di propylene glycol and mixtures thereof. Mono propylene glycol is particularly preferred, in an embodiment of the inventive process.

[0024] Catalyst

[0025] In a preferred embodiment, the basic catalyst (C) is selected from sodium hydroxide and potassium hydroxide. In a particularly preferred embodiment, the basic catalyst is potassium hydroxide.

[0026] Process

[0027] In one embodiment of the inventive process, step (a) may be performed at a temperature of 80 to 180° C, preferably 100 to 160° C.

[0028] In one embodiment of the inventive process, the period of time t1 is between 0.1 seconds to 45 minutes, preferably 1 minute to 30 minutes.

[0029] In another embodiment of the inventive process, the period of time t1 is between 0.1 seconds to 90 minutes, preferably 5 minutes to 80 minutes, more preferably 30 minutes to 80 minutes.

[0030] The acid may be added (in step (b)) in liquid form.

[0031] Furthermore, step (b) is usually performed at a temperature of between 80 to 150°C, preferably 90 to 130°C.

[0032] In an embodiment of the inventive process, step (b) is finished at a degree of neutralization of 60 to 95%, preferably 70 to 90%.

[0033] In the inventive process, water may be added in several portions, preferably in a first portion of 3 to 5 % by weight of water, and subsequently a second portion of 1 to 3 % by weight of water, and optionally subsequently a third portion of 0.5 to 3 % by weight of water, each relative to the reaction mixture present in the reaction vessel at the time of addition of the respective portion of water

[0034] In a preferred embodiment, the whole inventive process is performed in the same reaction vessel. But the inventive process may also involve several reaction vessels, in another embodiment.

[0035] Generally, step (b) is done under stirring. The stirrer may be operated at a speed of 100 to 500 rpm, preferably 200 to 400 rpm. In a further embodiment of the inventive process, step (b) is done under stirring for a certain period of time p1, then the stirrer is stopped and the reaction mixture is allowed to stand for another period of time p2.

[0036] Generally, in the inventive process, there is generally no need to use an ion exchanger (like, e. g., Ambosol®). It is therefore also preferred not to use an ion exchanger in the entire process.

[0037] In a preferred embodiment of the inventive process, after optional step (c) the amount of polyalkoxylate product remaining in the vessel is higher than 95% by weight, relative to the entire amount of polyalkoxylate product. It is preferred in the inventive process that the majority of the product precipitates (e. g. as a film) on the inside (e. g. walls) of the reaction vessel, whereas only a minority (preferably less than 5% by weight, relative to the entire amount of polyalkoxylate product) stays dissolved. This minor part of product which remains dissolved may (or has to be) be removed by using a filter.

[0038] Process according to any one of the preceding claims, wherein after optional step (c) the amount of potassium phosphate remaining in the vessel is more than 90 mole-%, preferably more than 95 mole-% potassium phosphate, relative to the entire amount of potassium phosphate.

[0039] The remaining amount of potassium phosphate will stay in the additional filter which may be used in the inventive process (so-called "police filter”).

[0040] Polyalkoxylate

[0041] The molecular weight Mn of the polyalkoxylate resulting from the inventive process, as determined by GPC, is generally between 100 and 4000 g / mol, preferably 150 and 2500 g / mol.

[0042] In one preferred embodiment, the molecular weight Mn of the resulting polyalkoxylate, as determined by GPC, lies in the range of 150 to 500 g / mol, particularly in the range of 180 to 300 g / mol.

[0043] In a preferred embodiment, the conductivity of the resulting polyalkoxylate product is less than 0.02 piSiemens / cm, in 10 % aqueous solution at 25° C. This shows that the product has a low content of salt (in particular, sodium and / or potassium salts).

[0044] Usually, the OH number of the polyalkoxylate resulting from the inventive process is in the range of 300 to 800 mg KOH / g, preferably 400 to 700 mg KOH / g. In one preferred embodiment, the OH number of the polyalkoxylate resulting from the inventive process is in the range of 450 to 600 mg KOH / g.

[0045] Generally, the turbidity of the polyalkoxylate product, as determined by nephelometric measurement according to DIN EN ISO 7027, is less than 10 NTU, preferably less than 5 NTU. In a preferred embodiment of the inventive process, the APHA color of the resulting polyalkoxylate is lower than 100 Hazen.

[0046] In an embodiment of the inventive process, the resulting polyalkoxylates have a total content of alkali salts (sum of alkali salts) of less than 25 ppm, preferably less than 20 ppm.

[0047] In one embodiment of the inventive process, the resulting polyalkoxylates have a content of sodium of less than 5 mg / kg, preferably less than 2 mg / kg, and / or a potassium content of less than 25 mg / kg, preferably less than 20 mg / kg.

[0048] A further object of the present invention is a low-salt polyalkoxylate, obtained or obtainable according to the inventive process.

[0049] A preferred embodiment of the inventive process is a process for manufacturing low-salt polyalkoxylates by (a) adding an alkylene oxide compound (AO) onto a starter compound (S) having at least one Zerewitinoff-active hydrogen atom in the presence of a basic catalyst (C) to obtain an alkaline crude polyalkoxylate, (b) subsequently neutralizing the alkaline crude polyalkoxylate by contacting phosphoric acid with the alkaline crude polyalkoxylate over a period of time t1, (c) optionally removing water (for example, by distillation), and (d) removing the neutralization salts formed, wherein water is added in several portions in the process.

[0050] In this preferred embodiment mentioned above it is preferred to add water in a first portion of 3 to 5 % by weight of water, and subsequently a second portion of 1 to 3 % by weight of water, and optionally subsequently a third portion of 0.5 to 3 % by weight of water, each relative to the reaction mixture present in the reaction vessel at the time of addition of the respective portion of water.

[0051] The first addition of water may be done before step (c) of the inventive process. Then, according to step (c), water is preferably removed. Then, a second portion of water (and, if applicable, further portions) may be added, each time, preferably, followed by a dewatering step.

[0052] For the addition of water, deionized water is usually used.

[0053] As mentioned above, after the first addition of water, a dewatering step by distillation is usually applied.

[0054] In general, the crude polyalkoxylate is cooled or let to cool down after the first addition of water and dewatering step (and optionally, after the second and further additions of water), preferably to below 100 °C.

[0055] Preferably, the mixture of crude polyalkoxylate and water is stirred, preferably for a minimum of 5 minutes (preferably at least 10 minutes). This is done to ensure thorough mixing and interaction between the water and its precipitate Usually, a second dewatering step by distillation is applied after the second water dosing (and, if applicable, after further water dosings). Thus, a preferred embodiment of the inventive process is also a process for manufacturing low-salt poly alkoxy lates by (a) adding an alkylene oxide compound (AO) onto a starter compound (S) having at least one Zerewitinoff-active hydrogen atom in the presence of a basic catalyst (C) to obtain an alkaline crude poly alkoxy late, (b) subsequently neutralizing the alkaline crude polyalkoxy late by contacting phosphoric acid with the alkaline crude poly alkoxy late over a period of time t1 , (c) optionally removing water, and (d) removing the neutralization salts formed, wherein water is added in several portions in the process, wherein the first addition of water is done before step (c), then water is removed in step (d), and subsequently, a second portion of water is added, followed by a second step of removing water (c2), wherein, preferably, a step of mixing the crude poly alkoxy late and water is applied, preferably for a period of at least five minutes (for example, by stirring for a certain period of time) after each addition of water and before the step of removing water, wherein, preferably, a first portion 3 to 5 % by weight of water, and subsequently a second portion of 1 to 3 % by weight of water, and optionally subsequently a third portion of 0.5 to 3 % by weight of water are added (followed, optionally, by another step of removing water), each relative to the reaction mixture present in the reaction vessel at the time of addition of the respective portion of water.

[0056] Besides, in one embodiment, a polyalkylene glycol (PAG), obtainable or obtained by the inventive process, additionally comprises at least one antioxidation agent, preferably butylated hydroxytoluene (BHT) and / or tocopherol.

[0057] Furthermore, another object of the present invention is also the use of an inventive low-salt poly alkoxy late, or a low- salt poly alkoxy late obtained or obtainable according to the inventive process, for manufacturing reactive intermediate for production of polyurethane thickeners, as a formulation additive in detergent compositions or as a carrier for solid detergent compositions.

[0058] Working example

[0059] Some aspects of the present invention are illustrated by the following, non-limiting working examples.

[0060] Example 1

[0061] A polyalkoxylate was manufactured based on mono propylene glycol. 164.86 mol of mono propylene glycol was alkoxylated with 418.85 mol of propylene oxide under basic catalysis (1.29 mol KOH). The resulting alkaline crude polyalkoxylate had a base number of 1.94 mg KOH / g, a pH (10% dilution in water) of 11.5 and a conductivity (at 20° C) of 624 pS.

[0062] The alkaline crude polyalkoxylate was treated with a 40 % by weight aqueous solution of phosphoric acid until a degree of neutralization of nearly 80 % was reached. Phosphoric acid and water were dosed into the reaction vessel at a temperature of 95° C under stirring. After 15 min of stirring, the temperature was increased to 120° C over a period of three hours, and the water was removed simultaneously. At a pressure of approximately 100 mbara, the product started to precipitate as solid film at the vessel surface. Still at a temperature of 120° C, the mixture was stirred for another one hour, and a pressure of approx. 50 mbara was reached.

[0063] The mixture in the reaction vessel was cooled down to 55° C. The low portion of residue which did not remain in the vessel (e. g. as a film precipitation on the walls of the reaction vessel) was filtered at a pressure of 3.5 bara.

[0064] The resulting poly alkoxy late (which remained in the vessel) was analysed. It had a content of sodium of less than 1 mg / kg and a potassium content of less than 15 mg / kg.

[0065] An additional filtering with, e. g., Ambosol®, is not required.

[0066] A further series of examples was performed to evaluate the effects of dosing water in several portions.

[0067] Example 2

[0068] To minimize the process-related effort involved in desalination at the conclusion of KOH-catalyzed alkoxylation, a very rudimentary filtration system was utilized. This system was solely designed to separate a small residual portion of the crystalline / amorphous potassium phosphate that was produced during the process. A representative example from all experiments was an oligomeric polypropylene oxide characterized by a low molecular weight of 100-1,000 g / mol, as determined using the GPC measurement method. This material was synthesized through the KOH solution-initiated polymerization of propylene oxide on either mono- or dipropylene glycol at temperatures ranging from 120 to 140°C.

[0069] After the first three hours of dewatering (1a; 4.4 wt% water) at 120°C, the raw product was cooled to below 100°C. Following this cooling phase, a second portion (1e; 2.2 wt% water) of deionized water was added to the system. Once the water portion was introduced, the mixture was stirred for a minimum of 15 minutes to ensure thorough mixing and interaction between the water and its precipitate. After this stirring period, the distillation process with a target vacuum of <50 mbar was restarted to facilitate further separation of components based on their boiling points and to enhance the overall yield and purity of the desired product. This methodical approach helped optimize the distillation process by allowing for the removal of impurities and undesired byproducts that may have formed during the initial stages of distillation.

[0070] Table 1 - Filtration with phosphoric acid (1 a / 1 e) Degree of final product filtration time K neutralization water portion conductivity

[0071] [w dso [pm] dw [pm] [Irmin] content

[0072] [%] t.%]

[0073] [MS] filter 20pm final [ppm]

[0074] 1a) 80 4,4 <10 32 9,7 4:20 <10

[0075] 1e) 80 4,4 +2,2 <10 35 13,1 3:34 <10

[0076] It could also be observed that the addition of water in several portions led to a considerably reduced filtering time, thus leading to a more efficient and economical process.

Claims

Patent claims1) Process for manufacturing low-salt poly alkoxy I ates by (a) adding an alkylene oxide compound (AO) onto a starter compound (S) having at least one Zerewitinoff-active hydrogen atom in the presence of a basic catalyst (C) to obtain an alkaline crude polyalkoxylate, (b) subsequently neutralizing the alkaline crude polyalkoxylate by contacting phosphoric acid with the alkaline crude polyalkoxylate over a period of time t1 , (c) optionally removing water, and (d) removing the neutralization salts formed.2) Process according to any one of claims 1 or 2, wherein step (a) is performed at a temperature of 80 to 180° C, preferably 100 to 160° C, and / or wherein the period of time t1 is between 0.1 seconds to 90 minutes, preferably 5 minutes to 80 minutes.3) Process according to any one of the preceding claims, wherein step (b) and optional step (c) are performed, separately from each other, at a temperature of between 80 to 150°C, preferably 90 to 130°C, and / or wherein step (b) is finished at a degree of neutralization of 60 to 95%, preferably 70 to 90%.4) Process according to any one of the preceding claims, wherein the acid is added in liquid form.5) Process according to any one of the preceding claims, wherein water is added in several portions, preferably in a first portion of 3 to 5 % by weight of water, and subsequently a second portion of 1 to 3 % by weight of water, and optionally subsequently a third portion of 0.5 to 3 % by weight of water, each relative to the reaction mixture present in the reaction vessel at the time of addition of the respective portion of water.6) Process according to any one of the preceding claims, wherein the whole process is performed in the same reaction vessel and / or wherein step (b) is done under stirring.7) Process according to any one of the preceding claims, wherein the turbidity of the reaction mixture, as determined by nephelometric measurement according to DIN EN ISO 7027, after step (b) or optional step (c) is less than 10 NTU, prefably less than 5 NTU.8) Process according to any one of the preceding claims, wherein the alkylene oxide compound (AO) in step (a) is selected from ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO) and mixtures thereof.9) Process according to any one of the preceding claims, wherein the alkylene oxide compound in step (a) is selected from alkylene oxide mixtures containing at least 50 mole % PO and pure PO, preferably pure PO.10) Process according to any one of the preceding claims, wherein the starter compound (S) is selected from the list consisting of mono propylene glycol, di propylene glycol and mixtures thereof, preferably selected from mono propylene glycol and di propylene glycol.11) Process according to any one of the preceding claims, wherein the basic catalyst (C) is selected from sodium hydroxide and potassium hydroxide, preferably potassium hydroxide.12) Process according to any one of the preceding claims, wherein no ion exchanger is used.13) Process according to any one of the preceding claims, wherein the conductivity of the resulting polyalkoxylate product is less than 0.02 piSiemens / cm, in 10 % aqueous solution at 25° C.14) Process according to any one of the preceding claims, wherein the molecular weight Mn of the resulting polyalkoxylate, as determined by GPC, is between 100 and 4000 g / mol, preferably 150 and 2500 g / mol, and / or wherein the OH number of the resulting polyalkoxylate is in the range of 300 to 800 mg KOH / g, and / or wherein the APHA color of the resulting polyalkoxylate is lower than 100 Hazen.15) Process according to any one of the preceding claims, wherein after optional step (c) the amount of polyalkoxylate product remaining in the vessel is higher than 95% by weight, relative to the entire amount of polyalkoxylate product.16) Process according to any one of the preceding claims, wherein after optional step (c) the amount of potassium phosphate remaining in the vessel is more than 90 mole-%, preferably more than 95 mole-% potassium phosphate, relative to the entire amount of potassium phosphate.17) Low salt polyalkoxylate, obtained or obtainable according to the process of any one of claims 1 to 16.18) Use of a low salt polyalkoxylate according to claim 17, or obtained or obtainable according to the process of any one of claims 1 to 16, for manufacturing a reactive amine intermediate for production of polyurethane thickeners, as a formulation additive in detergent compositions or as a carrier for solid detergent compositions.