Process for manufacturing polyalkoxylates

Abstract

The present invention deals with a process for manufacturing polyalkoxylates.

Description

[0001] Process for manufacturing polyalkoxylates

[0002] The present invention deals with a process for manufacturing polyalkoxylates (preferably low-salt polyalkoxylates), polyalkoxylates 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. phosphoric acid or 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] The established alkoxylation processes usually involve alkaline catalysts, in particular potassium hydroxide. Generally, the alkoxylation catalyst has to be separated from the polyalkoxylate product afterwards.

[0007] The potassium present (in the form of potassium hydroxide, with approximately 1, 000-5, OOOppm potassium content in the intermediate form) is preferably used in high concentrations as an alkoxylation catalyst, to carry out the alkoxylation reaction quickly and uniformly.

[0008] Thus, reducing the amount of catalyst can only be minimized up to certain limits, and the catalyst and must, in most cases, be actively removed from the intermediate reaction mixture, usually through desalination by precipitation of potassium salts on an industrial scale.

[0009] A series of precipitation methods are currently established practice, including phosphoric acid, polyphosphoric acid (precipitated as potassium phosphates) or solid ion exchange minerals (Al / silicates e.g. under the trade names Ambosol / Magnesol) that absorb potassium ions efficiently, but slightly increase the sodium concentration by sodium leaching effects. These precipitates must be separated by filtration from the intermediate product and disposed of in solid or dissolved forms in accordance with applicable environmental regulations.

[0010] This is technically feasible for mono- / di- / tri potassium phosphates and / or heterogenic ion exchangers, but requires highly inefficient and costly technical filtration efforts.

[0011] Thus, there is a need in the art for a simpler method of disposal. As set out above, 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. This may also lead to loss of product (which remains in the filter apparatus).

[0012] US 6.342,641 B1 discloses purified bisphenol A ethoxylates and processes of purifying thereof. Neutralization of crude bisphenol A ethoxylate is done with phosphoric acid. It is also mentioned in this patent specification that other methods of catalyst removal, e. g. by passing carbon dioxide through the crude reaction mixture, suffer from some drawbacks. Thus, said U. S. patent publication discourages the person skilled in the art from using CO2 as a precipation agent.

[0013] 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 poly alkoxy lates, 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.

[0014] It may also be desirable in the precipitation / neutralization step to come up with a relatively fine filtrate.

[0015] Thus, it was an objective of the present invention to overcome the problems and disadvantages resulting from known processes for manufacturing poly alkoxyl ates (particularly, polyal koxy lates with a low content of alkali salts). 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 polyalkoxylates (preferably 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 polyalkoxylates (particularly, polyalkoxylates with a relatively low content of alkali salts) based on propylene oxide only.

[0016] Furthermore, manufacturing processes for polyalkoxylates where potassium hydroxide is used as catalyst (which is the most frequent choice of catalyst) and, e. g., phosphoric acid is used as a precipitation agent, may have the disadvantage that potassium phosphate salts are generated. These types of salts may be undesired and are tedious to dispose of.

[0017] As mentioned, the known processes 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 polyalkoxylates are converted into amines (e. g. for applications in polyurethane manufacturing). Thus, one further objective of the present invention was to provide a process for manufacturing poly al koxy lates which avoids the generation of undesired phosphate salts, which would have to be disposed of in a laborious process.

[0018] It was an objective of the present invention to provide a process for manufacturing poly al koxy lates which works (at least) comparably well in established filtering procedures as state of the art processes (for example, similar time needed for filtering operations), while at the same time reduces or avoids the efforts needed for disposal of filter residues

[0019] Furthermore, it was an objective of the present invention to reduce the potassium / sodium ion (salt) content of intermediate products obtained from the direct one-step alkaline propoxylation of the starters: water, mono-propylene glycol, di-propylene glycol, or mixtures thereof to final homo-polypropoxylates through additional post- treatment / desalination process steps, preferably to a maximum ion value of <100ppm, preferably <20 ppm finally.

[0020] 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.

[0021] Precipitation as potassium carbonate by neutralizing the intermediate materials with carbon dioxide surprisingly enables more efficient process windows. The precipitation with carbon dioxide is generally easy to conduct, with less polar and high-molecular-weight poly alkoxy lates as a result.

[0022] Surprisingly, low-molecular-weight hydrophobic polypropylene oxides with a molecular weight <1 ,000 g / mol can also be desalinated in this way, by optimizing the process conditions for each dedicated wet products.

[0023] The inventive process may, furthermore, the advantage that no phosphate salts are generated in the neutralization step. The potassium carbonate salts which are the result of the inventive precipitation (also called neutralization) step are much less problematic in handling and disposal.

[0024] Besides, the precipitate which is generated by the inventive process is generally in the form of a relatively fine precipitate (in some cases also with a relatively uniform particle size distribution), as compared to other, generally known processes with state of the art neutralization agents.

[0025] Therefore, one object of the present invention is a process for manufacturing poly alkoxy lates (particularly, poly alkoxy lates with a low content of alkali salts) 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 carbon dioxide with the alkaline crude polyalkoxylate over a period of time t1 , (c) optionally removing water, and (d) removing the neutralization salts formed. In the context of the present invention, the term "low-salt” may relate to poly alkoxyl ates 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 polyal koxy late, in particular low content of sodium and / or potassium salts.

[0026] Furthermore, in the context of the present invention, the term "low-salt” may also relate to poly alkoxy I ates with a total content of alkali salts (sum of alkali salts) of less than 25 ppm, preferably less than 20 ppm.

[0027] Precipitation agent

[0028] In the inventive process, carbon dioxide is used as precipitation agent. It may also be referred to as neutralization agent.

[0029] The carbon dioxide is usually used in gaseous state. The dosing of carbon dioxide in gaseous state - which is the usual way of dosing carbon dioxide, as mentioned - is quite different from dosing a liquid, e. g. a solution of one of the precipitation agents known in the art (e. g. , phosphoric acid) from a process engineering perspective.

[0030] Furthermore, in general, the crystallites which are formed when neutralizing with CO2 may be different from those which are formed when neutralizing with one of the established precipitation agents.

[0031] In one embodiment of the inventive process, the gaseous carbon dioxide is added to the reaction mixture until saturation pressure is reached.

[0032] In one specific embodiment of the inventive process, phosphoric acid is used as additional precipitation agent, in a subsequent process step after the initial precipitation with carbon dioxide and filtration of the product still containing water.

[0033] Thus, the amount of undesired salts in the polyalkoxylate (e. g. , polypropoxylate) may be even further reduced, while the amount of phosphate salts resulting from the precipitation with phosphoric acid may be considerably decreased as compared to a precipitation with phosphoric acid only.

[0034] Alkylene oxide

[0035] The alkylene oxide compound (AO) in step (a) is selected from ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO) and mixtures thereof.

[0036] 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.

[0037] In a preferred embodiment, only PO is used as alkylene oxide.

[0038] Starter compound 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.

[0039] 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.

[0040] Process

[0041] 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.

[0042] 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.

[0043] In another embodiment of the inventive process, the period of time t1 is between 0.1 seconds to 90 minutes, preferably 1 minute to 80 minutes, particularly 20 to 80 minutes.

[0044] The carbon dioxide may be added (in step (b)) in gaseous form.

[0045] Furthermore, step (b) is usually performed at a temperature in the range of 50 to 150°C, preferably 60 to 130°C.

[0046] In an embodiment of the inventive process, step (b) is finished at a degree of neutralization of 60 to 95%, preferably 70 to 90%.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Generally, in the inventive process, it is not mandatory to use an additional ion exchanger in an additional separation step. However, in one embodiment of the inventive process, an additional separation step using an ion exchanger is performed after step (b).

[0051] In another embodiment of the inventive process, an additional precipitation step (b.2) using phosphoric acid as precipitation agent is performed after step (b). Polyalkoxylate

[0052] 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.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] In an embodiment of the inventive process, the obtained poly alkoxy lates have a dso value (based on volume fraction) of at least 10 m, preferably at least 20 pm, particularly at least 50 pm, as determined by statistic laser scattering, using a Malvern Mastersizer 200 according to European norm ISO 13320 EN. The data were treated according to the Mie-Theory by software using a "universal model" provided by Malvern Instruments (e.g. Fraunhofer model where the refractive index of the continuous media is only taken into consideration).

[0057] In an embodiment of the inventive process, the resulting polyal koxy lates have a total content of alkali salts (sum of alkali salts) of less than 25 ppm, preferably less than 20 ppm.

[0058] In one embodiment of the inventive process, the resulting poly al koxy lates 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.

[0059] A further object of the present invention is therefore also a polyalkoxylate, obtained or obtainable according to the inventive process, preferably a polyalkoxylate with a low content of alkali salts.

[0060] 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.

[0061] Furthermore, another object of the present invention is also the use of an inventive (low-salt) polyalkoxylate, or a (low-salt) polyalkoxylate obtained or obtainable according to the inventive process, for manufacturing reactive amine intermediate for production of polyurethane thickeners, as a formulation additive in detergent compositions or as a carrier for solid detergent compositions. Working examples

[0062] Some aspects of the present invention are illustrated by the following, non-limiting working examples.

[0063] To assess the filterability, the particle size distribution (PSD) was determined using a Malvern Mastersizer 200 according to ISO 13320, and the crystal morphology was examined optically using microscopy. The filter resistance and the filtration duration of the mixture depend primarily on the d50 / d90 value.

[0064] The preferred particle size distribution yielded a d50 or d90 value of >10 m and aggregated particles with a high aspect ratio (average particle length / width >1.5).

[0065] The salt content was analyzed in the laboratory using various methods: acid / base titration with 0.01 molar HOI solution, atomic absorption spectroscopy (AAS) and measurement of conductivity of the intermediate solutions. The phosphorus content was determined by elemental analysis.

[0066] The raw products from the alkoxylation (using propylene oxide as alkylene oxide and mono propylene glycol as starter, and potassium hydroxide as catalyst), including water in different proportions (ranging from 0.1-5 wt.% based on the raw product) were provided.

[0067] Carbon dioxide was added by pressurization until saturation. The pressure in the reactor was approximately 1-20 bara. Precipitation of potassium carbonate began immediately with the pressurization with carbon dioxide. Different temperatures were tested, and a minimum temperature of 60° C was set.

[0068] After the reaction time, filtration was performed in some experiments, followed by drying. Drying was carried out at temperatures of 100-120°C under vacuum (approximately 10 mbara) for a minimum of 15-30 minutes.

[0069] During the experimental series, it was found that using carbon dioxide precipitation, all molecular weights of poly- propoxylates >400 g / mol could be easily desalinated to <10 ppm Na / K content, see below.

[0070] However, raw products of polypropylene oxides with a low molecular weight of <400g / mol could only be desalinated to a residual potassium content of 180 ppm in a single-step process. In such cases, repeating the process through a multi-stage precipitation process, where already filtered raw material is reintroduced into the process, reacted with carbon dioxide again, and filtered once more, proved advantageous. This resulted in salt contents being reduced to a slightly lower value of 011, ranging from 150-190 ppm. Scheme 1: Process parameters for desalination of Polypropylenoxide; M=~250g / mol

[0071] Scheme 2: Process parameters for desalination of Polypropylenoxide; M=~600g / mol Scheme 3 Process parameters for desalination of Polypropylenoxide; M=~2. OOOg / mol

[0072] Residual salt concentrations (>10 ppm) could be reduced further to a limit of <10 ppm by combining filtration method of wet precursor with state-of-the-art known phosphate precipitation techniques or ion exchange methods. In addition, a comparative experiment was performed, wherein, in the first case (inventive example), carbon dioxide was used as neutralization agent and, in the second case (comparative example), neutralization was done with phosphoric acid (40% solution in water).

[0073] The particle size distribution was determined by laser diffraction, using a "Malvern Mastersizer” of Malvern Panalytical company and processing the data according to the Mie theory. The crude poly alkoxy I ate which was used in the experimental set-up was a poly propoxyl ate based on monopropylene glycol with an average molecular weight Mw of around 2500 g / mol (determined by GPC). It was observed that in the inventive example, the precipitate exhibited a particle size distribution with a d50 value of approximately 13 pm, characterized by a relatively broad, bimodal distribution. In contrast, the comparative example demonstrated a particle size distribution with a d50 value of around 32 pm, also featuring a broad, bimodal distribution. This resulted in comparable filtration pressure and filtration time, as the filter cake requires a diverse particle size distribution for optimal performance.

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 carbon dioxide with the alkaline crude polyalkoxylate over a period of time t1 , (c) removing water, and (d) removing the neutralization salts formed.2) Process according to claim 1 , 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 1 minute 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 50 to 150°C, preferably 60 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 carbon dioxide is added in gaseous form.5) 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 and / or wherein step (c) is done at a temperature in the range of 80 to 150 °C, preferably 90 to 140 °C, and / or wherein step (c) is done at vacuum for a period in the range of 5 to 90 minutes, preferably 10 to 60 minutes .6) 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.7) 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.8) 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.9) 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.10) Process according to any one of the preceding claims, wherein an additional separation step (b.1), optionally using an ion exchanger, is performed after step (b) and before step (c).11) Process according to claim 11, wherein an additional precipitation step (b.2) using phosphoric acid as precipitation agent is performed after step (b.1 ) and before step (c).12) 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.13) 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.14) Polyalkoxylate, obtained or obtainable according to the process of any one of claims 1 to 13.15) Use of a polyalkoxylate according to claim 14, or obtained or obtainable according to the process of any one of claims 1 to 13, 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.

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