HK1152520B - Process for preparing polyol esters - Google Patents

Description

Process for preparing polyol esters

Technical Field

The invention relates to a method for producing polyol esters from linear or branched aliphatic monocarboxylic acids having 3 to 20 carbon atoms and polyols by converting the starting compounds in the presence of an adsorbent.

Background

Esters of polyhydric alcohols, also known as polyol esters, can be used in industry on a large scale for a variety of purposes, for example as plasticizers or lubricants. The selection of suitable raw materials enables control of physical properties, such as boiling point or viscosity, as well as chemical properties, such as hydrolysis resistance or stability to oxidative degradation. Polyol esters can also be tailored to the solution of specific performance issues. A detailed review of the use of polyol esters can be found, for example, in Ullmann's Encyclopaedia of Industrial chemistry, 5 th edition, 1985, VCH Verlagsgesellschaft, volume A1, page 305-319; 1990, volume A15, page 438-; 1981, Vol.14, pp.496-498.

The use of polyol esters as lubricants is very important industrially, especially for those applications in which the mineral oil-based lubricants do not fully meet the requirements set. Polyol esters are particularly useful as turbine engine oils and instrument oils. Polyol esters for lubricant applications are generally based on 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 2-hexanediol, 1, 6-hexanediol, neopentyl glycol, trimethylolpropane, pentaerythritol, 2, 4-trimethylpentane-1, 3-diol, glycerol or 3(4), 8(9) -dimethylol tricyclo [ 5.2.1.0%^2，6]Decane (also known as TCD alcohol DM) was used as the alcohol component.

Polyol esters are also used to a considerable extent as plasticizers. Plasticizers have many uses in plastics, coatings, sealants and rubber products. Preferably, they physically interact with high molecular weight thermoplastics without undergoing chemical reactions, by virtue of their swelling and dissolving capabilities. This results in a homogeneous system, the thermoplastic range of which is shifted to lower temperatures than the original polymer, one result being that its mechanical properties, such as increased deformability, elasticity and strength, and reduced hardness, are optimized.

In order to develop the widest possible field of application as plasticizers, they must meet a series of criteria. They should ideally be odorless, colorless and light-resistant, cold-resistant and heat-resistant. Furthermore, they are expected to be insensitive to water, relatively non-flammable and not very volatile, and not harmful to health. Furthermore, the production of the plasticizer should be simple and, in order to comply with ecological requirements, waste products, such as by-products which cannot be further utilized and waste water containing contaminants, should be avoided. One particular class of polyol esters (which are referred to simply as G-esters) contain glycols or ether glycols as the alcohol component, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1, 2-propanediol, or higher propylene glycols. They can be prepared in different ways. In addition to the reaction of the alcohol and acid, optionally in the presence of an acidic catalyst, other methods are used in practice to obtain the G ester, including the reaction of the diol with an acid halide, the transesterification of a carboxylic ester with a diol, and the addition of ethylene oxide to a carboxylic acid (ethoxylation). In industrial manufacture, only direct reaction of diols with carboxylic acids and ethoxylation of carboxylic acids have been identified as production methods, and esterification of diols and acids is generally preferred. This is because it is possible to carry out the process with conventional chemical apparatuses without particular complexity and to provide a chemically homogeneous product. In contrast, ethoxylation requires large and expensive technical equipment. Ethylene oxide is a very reactive chemical. Which can polymerize explosively and form an explosive mixture with air over a very wide mixing range. Ethylene oxide stimulates the eyes and respiratory tract, causes chemical burns and causes liver and kidney damage, and is carcinogenic. Its operation therefore requires a great deal of safety measures. Furthermore, strict cleanliness of the storage and reaction devices must be ensured to avoid the formation of unwanted impurities due to side reactions of ethylene oxide with foreign matter. Finally, the reaction with ethylene oxide is not very selective, since it produces a mixture of compounds of different chain lengths.

Direct esterification of alcohols with carboxylic acids is one of the basic operations in organic chemistry. In order to increase the reaction rate, the conversion is usually carried out in the presence of a catalyst. The use of an excess of one of the reactants and/or the removal of the water formed during the reaction ensures that the equilibrium is shifted towards the side of the reaction product (i.e. the ester) according to the law of mass action, which means that high yields are achieved.

Comprehensive information on the preparation of polyol Esters (also including Esters of ethylene glycol and Fatty Acids) and on the properties of selected representatives of these classes of compounds can be found in Goldsmith, polyhydroaliphatic Esters of Fatty Acids, chem. Rev.33, 257 ff. (1943). For example, esters of diethylene glycol, triethylene glycol and polyethylene glycol are prepared at temperatures of 130 to 230 ℃ over reaction times of 2.5 to 8 hours. To remove the reaction water, carbon dioxide was used. Suitable catalysts for the esterification of polyols mentioned are mineral acids, acid salts, organic sulfonic acids, acetyl chloride, metals or amphoteric metal oxides. The water of reaction is removed by means of an entrainer, for example toluene or xylene, or by introducing an inert gas, for example carbon dioxide or nitrogen.

Johnson (ed.), fat Acids in Industry (1989) chapter 9, Polyoxydehtylene esters of fat Acids, discusses the production and properties of Fatty acid esters of polyethylene glycol and gives a series of preparation clues. Higher diester concentrations are achieved by increasing the carboxylic acid/diol molar ratio. Suitable measures for removing the water of reaction are azeotropic distillation in the presence of a water-immiscible solvent, heating while passing an inert gas or carrying out the reaction under reduced pressure in the presence of a drying agent. When the addition of the catalyst is omitted, a longer reaction time and a higher reaction temperature are required. The use of a catalyst allows both reaction conditions to be milder. In addition to sulfuric acid, organic acids, such as p-toluenesulfonic acid and polystyrene-type cation exchangers, are preferred catalysts. The use of metal powders, such as tin or iron, is also described. According to the teaching from US 2,628,249, the color problem in the case of catalysis with sulfuric acid or sulfonic acid can be alleviated when operating in the presence of activated carbon.

Procedures for the preparation of diethylene glycol and triethylene glycol esters with octanoic acid without the addition of a catalyst are known from US 2,469,446. The esterification temperature is 270 to 275 ℃ and the water of reaction is driven off by means of a carbon dioxide stream.

Reaction schemes without catalyst addition are typically run with a molar excess of the particular carboxylic acid (which also acts as a catalyst due to its acidity).

Various methods are known for removing the water of reaction formed when esters are formed from polyols and carboxylic acids. For example, the reaction water formed is distilled out of the reaction vessel together with the excess carboxylic acid and fed to a downstream phase separator, where the carboxylic acid and water are separated according to their solubility properties. In some cases, the carboxylic acids used also form azeotropes with water under the reaction conditions and are capable of removing the water of reaction as an entrainer. Azeotropic distillation in the presence of an added water-immiscible solvent is also used, the reaction mixture is heated while passing an inert gas, and the polyol and the carboxylic acid starting material are reacted under reduced pressure or in the presence of a drying agent. In particular, it has been found that removal of water by azeotropic distillation helps to establish equilibrium during the polyol ester production process. According to the procedure known from DE 19940991 a1, a water-immiscible solvent which acts as an entrainer and should have a boiling point of less than 112 ℃ is added to the reaction mixture only when a temperature of at least 140 ℃ is reached.

The crude ester obtained after removal of the reaction water and excess unconverted starting material (suitably excess added carboxylic acid) may first be treated with an alkaline reagent, e.g. with sodium carbonate or aqueous sodium hydroxide solution, to remove the last residue of acidic components. After washing with water and treatment with bleaching earth and activated carbon, the last traces of coloring and odorous substances can be removed by applying reduced pressure at elevated temperature. A process for working up crude polyol esters is known, for example, from US 2,469,446a 1. In some cases, the treatment with bleach and activated carbon must be repeated more than once to obtain a final product with satisfactory color properties. The crude ester is dried after the base treatment, for example by passing an inert gas over the product or applying a reduced pressure and optionally additionally distilling off under reduced pressure, according to the procedure known from DE 19940991 a 1. In order to improve the color of the polyol ester, WO 94/18153a1 proposes a subsequent treatment with an aqueous hydrogen peroxide solution.

Due to the quality criteria of the polyol esters described at the outset, the process steps in the esterification stage with removal of the reaction water and in the work-up of the crude esters are very important process characteristics, since the adjustment of these process steps significantly affects the organoleptic and optical properties of the end product. More particularly, there are high demands on the color properties of polyol esters, such as low color number and high color stability. In contrast, the structure of the raw materials, polyol and acid, is critical to the mechanical and thermal properties of the polymeric material plasticized with the polyol ester and affects the hydrolytic and oxidative stability of the lubricant.

It has now been found that, surprisingly, polyol esters having excellent color number and color stability can be prepared from polyols and linear or branched aliphatic monocarboxylic acids when the esterification reaction is carried out in the presence of an adsorbent and the steam treatment is carried out in a subsequent work-up of the crude product.

Disclosure of Invention

The invention therefore relates to a process for preparing polyol esters by reacting polyols with linear or branched aliphatic monocarboxylic acids having 3 to 20 carbon atoms and subsequent work-up of the reaction mixture, characterized in that a mixture of starting compounds is reacted in the presence of an adsorbent, unconverted starting compounds are removed, subsequently a steam treatment is carried out and the remaining polyol ester is dried, and the polyol ester is filtered after the end of the reaction or after any other work-up measures.

The new procedure is notable for a high degree of reliability not only in laboratory and experimental operations, but also in industrial installations in particular. Even in a continuous form, it is easy to implement and provides high purity polyol esters. The combination of the presence of the adsorbent in the esterification stage and the steam treatment in the post-treatment stage is crucial to the process of the present invention and results in excellent color properties and significant color stability of the polyol ester.

Detailed Description

The adsorbents used, which are present during the esterification reaction, are porous, large surface area solid materials which are commonly used in chemical practice both in laboratories and in industrial settings. Examples of such materials are high surface area polysilicic acids such as silica gel (silica xerogel), diatomaceous earth, high surface area alumina and hydrated alumina, mineral materials such as clays, carbonates or activated carbon. Activated carbon has been found to be particularly useful. Generally, the adsorbent is suspended in finely divided form in the reaction solution, which is agitated by strong stirring or by the introduction of an inert gas. This achieves intimate contact between the liquid phase and the adsorbent. The mass ratio of liquid phase to adsorbent can be adjusted substantially freely and thus according to the respective requirements. It has been found useful to use from 0.05 to 30, preferably from 0.1 to 5.0, especially from 0.1 to 1.0, parts by weight of adsorbent per 100 parts by weight of liquid phase. After the reaction is complete, the adsorbent can be removed from the process and recycled to the esterification vessel and reused. Can be reused until the decolourisation power of the adsorbent is exhausted. However, it is also possible to leave the adsorbent in the crude product and remove it at any convenient stage during work-up.

The reaction of the polyol and the aliphatic monocarboxylic acid may be carried out without using a catalyst. This reaction variant has the advantage that it avoids the addition of foreign substances to the reaction mixture which would cause undesirable contamination of the polyol ester. However, in this case, it is generally necessary to maintain a higher reaction temperature, since only then is it possible to ensure that the reaction proceeds at a sufficient rate, i.e. an economically acceptable rate. In this context, it should be noted that an increase in temperature can cause thermal damage to the polyol ester. Thus, the use of catalysts to promote the reaction and increase the reaction rate is not always avoided. The catalyst can often be an excess of aliphatic monocarboxylic acid, which is at the same time a reaction component for the polyol, so that the reaction proceeds autocatalytically. In addition, conventional esterification catalysts are suitable for influencing the reaction rate, such as sulfuric acid, formic acid, polyphosphoric acid, methanesulfonic acid or p-toluenesulfonic acid, and combinations of such acids. It is likewise possible to use metal catalysts, such as titanium-containing, zirconium-containing or tin-containing catalysts, for example the corresponding alkoxides or carboxylates. Catalytically active compounds which are insoluble in the reaction system and are solid under the reaction conditions, such as alkali metal or alkaline earth metal hydrogen sulfates, for example sodium hydrogen sulfate, may also be used. The solid catalyst is removed from the reaction mixture after the end of the esterification by simple filtration together with the adsorbent present. The amount of catalyst used can be within wide limits. From 0.001 to 5% by weight of catalyst, based on the reaction mixture, can be used. However, since higher amounts of catalyst have hardly any advantage, the catalyst concentration is generally from 0.001 to 1.0% by weight, preferably from 0.01 to 0.5% by weight, based in each case on the reaction mixture. Suitably, it is decided, optionally by preliminary experiments, for each case whether the catalyst should be used at a relatively high temperature or at a relatively low temperature.

Esterification can be carried out with stoichiometric amounts of polyol and aliphatic monocarboxylic acid. However, it is preferred to react the polyol with an excess of monocarboxylic acid without adding a catalyst, so that the excess monocarboxylic acid itself acts as a catalyst. It is also possible to remove excess monocarboxylic acids from the crude ester by distillation in a simple manner, which generally have a lower boiling point than the polyol used. The aliphatic monocarboxylic acids are used in an excess of from 10 to 50 mol%, preferably from 20 to 40 mol%, per mole of hydroxyl groups of the polyol to be esterified.

The water of reaction formed is distilled off from the reaction vessel during the reaction together with the excess monocarboxylic acid and passed to a downstream phase separator, where the monocarboxylic acid and water are separated off according to their solubility properties. The monocarboxylic acids used can also form azeotropes with water under the reaction conditions and can serve as entrainers for removing the water of reaction. The progress of the reaction can be monitored by the water obtained. The separated water is removed from the process while the monocarboxylic acid from the phase separator is returned to the reaction vessel. The addition of other organic solvents which assume the role of entrainers, such as hexane, 1-hexene, cyclohexane, toluene, xylene or xylene isomer mixtures, is not excluded, but is limited to a few special cases. The entrainer may be added as early as the start of the esterification reaction or at a relatively high temperature. The reaction is terminated by cooling the reaction mixture when the desired theoretical amount of water has been obtained or the hydroxyl number, as measured, for example, according to DIN53240, has fallen below the set value.

The reaction between the polyol and the aliphatic monocarboxylic acid starts in the range of about 120 to 180 ℃ depending on the starting materials and can proceed to completion in different ways.

One configuration of the process of the invention involves first heating from room temperature to a temperature of at most 280 c, preferably at most 250 c, and, while the temperature is kept constant, reducing the pressure in stages starting from the standard pressure to facilitate the removal of the reaction water. The choice of pressure stage (whether one, two or more stages) and the choice of pressure to be established at a particular stage can be varied over a wide range and adjusted according to particular conditions. For example, in the first stage, the pressure may be reduced from the standard pressure to 600hPa, and then the reaction may be carried out to completion at a pressure of 300 hPa. These pressure values are guiding values and can be suitably observed.

In addition to the pressure change, it is likewise possible to change the temperature in one, two or more stages from room temperature during the esterification reaction, so that the temperature rises in stages, generally to a maximum temperature of 280 ℃ under constant pressure. However, it has been found appropriate to heat up to 280 ℃ with a stepwise increase in temperature and to reduce the pressure stepwise. For example, the esterification reaction can be carried out in the first stage at a temperature starting from room temperature up to 190 ℃. Reduced pressure down to 600hPa was also applied to accelerate the expulsion of the reaction water. When the temperature stage of 190 ℃ is reached, the pressure is again reduced to 300hPa and the esterification is carried out to completion at a temperature of at most 250 ℃. These temperature and pressure values are indicative values and can be suitably observed. The temperature and pressure conditions to be established at a particular stage, the number of stages and the specific rate of temperature rise or pressure decrease per unit time may vary within wide ranges and are adjusted according to the physical properties of the starting compounds and the reaction products, the temperature and pressure conditions of the first stage established starting from standard pressure and room temperature. It has been found that a two-stage increase in temperature and a two-stage decrease in pressure is particularly suitable.

The lower pressure limit to be established depends on the physical properties of the starting compounds and the reaction products formed, such as boiling point and vapor pressure, and also on the apparatus set-up. Starting from the standard pressure, it is possible to operate in stages within these limits with a pressure reduction from stage to stage. An upper temperature limit of typically 280 ℃ should be observed to prevent the formation of decomposition products, which adversely affect color and other properties. The lower limit of the temperature stage depends on the reaction rate, which must still be high enough to complete the esterification reaction within an acceptable time. Within these limits, it is possible to operate in stages with a temperature increase from stage to stage.

The reaction mixture obtained after the end of the reaction comprises, apart from the polyol ester as the desired reaction product, possibly unconverted starting materials, in particular aliphatic monocarboxylic acids which are still in excess in the case where an excess of monocarboxylic acid has been used according to the preferred configuration of the process of the invention. The unconverted and excess starting compound is generally distilled off first, where appropriate under application of reduced pressure.

The work-up of the crude ester obtained can be designed in different ways. For example, the adsorbent present may first be removed from the crude ester. The product is filtered in a conventional filtration unit at standard temperature or at a temperature of up to 150 ℃. Filtration may be facilitated by common filter aids such as cellulose, silica gel, diatomaceous earth, wood flour. Any solid catalyst added in the esterification stage or catalyst conversion products that have been separated off are removed together with the adsorbent. Treatment with alkaline agents, for example with aqueous sodium carbonate or sodium hydroxide, can also be provided for the removal of acidic catalysts, such as sulfuric acid (if added in the esterification stage), and for the removal of the final residue of acidic constituents. However, the removal of the adsorbent from the crude esterification product is not absolutely necessary and further work-up can be carried out in the presence or absence of an adsorbent.

Thereafter, the crude ester, which has optionally been treated with a base or filtered, is subjected to a steam treatment, which can be carried out, for example, in simple form by introducing steam into the crude product. One advantage of the steam treatment is that the metal catalyst still present during the process (if added) is destroyed and converted into a hydrolysate which can be effectively filtered off. The steam treatment also helps to improve the color number of the polyol ester. The adsorbent added during the esterification reaction facilitates the separation of the catalyst conversion product while it is still present. The presence of the adsorbent during the steaming process also additionally has a favourable effect on the colour and colour stability of the polyol ester, so its presence is recommended. However, it is also possible to filter off the adsorbent after the esterification reaction has ended and the excess starting compound has been removed, i.e.before the steam distillation has taken place.

The steam treatment is generally carried out at standard pressure, but the use of a slight reduced pressure, suitably as low as 400hPa, is not excluded. The steam treatment is generally carried out at temperatures of from 100 to 250 ℃, preferably from 150 to 220 ℃, in particular from 170 to 200 ℃, and is also governed by the physical properties of the polyol ester to be prepared in each case.

In the steaming process step, it has been found appropriate to proceed in a very gentle manner during heating until the working temperature is reached in order to heat the crude ester to the desired steaming temperature.

The duration of the steaming treatment can be determined by routine experimentation and is typically carried out for 0.5 to 5 hours. Too long a steam treatment causes an undesirable increase in the color number of the polyol ester and should therefore be avoided. Increased degradation of the polyol ester to acidic compounds is also observed, as evidenced by an increase in the neutralization or acid number, for example, as measured according to DIN EN ISO 3682/ASTM D1613. In the case of too short a treatment time, the removal of residual starter compound and water is incomplete and the desired polyol ester still has too high an undesirable acid number and too high a water content. In the case of too short a treatment time, only a very small beneficial effect on the color number of the polyol ester is observed.

The conditions of the steam treatment, such as temperature, pressure and duration, should be adjusted in a controlled manner according to the specific polyol ester in order to achieve the best results in terms of polyol ester color number and to minimize as much as possible the residual content of starting compounds and water while inhibiting degradation reactions.

Especially in the case of polyol esters based on ether glycols, such as triethylene glycol or tetraethylene glycol, the conditions in the steam treatment should be adapted to the specific polyol ester to suppress undesirable degradation of the ether chains.

After the steaming, optionally after filtering the adsorbent, the polyol ester is dried, for example by passing an inert gas over the product at elevated temperature. It is also possible to simultaneously apply reduced pressure and optionally inert gas over the product at elevated temperature. Even without the action of an inert gas, it is possible to operate only at elevated temperatures or only under reduced pressure. The particular drying conditions, such as temperature, pressure and duration, appropriate for a particular polyol ester can be determined by simple preliminary testing. Temperatures of from 80 to 250 ℃, preferably from 100 to 180 ℃ and pressures of from 0.2 to 500hPa, preferably from 1 to 200hPa, in particular from 1 to 20hPa, are generally employed. If the adsorbent added in the esterification stage is still present, the polyol ester is filtered. Filtration is carried out in conventional filtration units at standard temperature or at temperatures of up to 120 ℃. The filtration can be assisted by common filter aids, such as cellulose, silica gel, diatomaceous earth, wood flour. However, its use is limited to special cases.

Whether the adsorbent used in the esterification stage has been filtered off at the beginning of the work-up procedure or after drying, it has been found to be appropriate to subject the polyol ester to a further work-up with an adsorbent. For this aftertreatment, suitable adsorbents are likewise those which are also used in the esterification stage, in particular activated carbon. Finally, the polyol ester is subsequently filtered.

The measures of carrying out the esterification reaction in the presence of an adsorbent have provided a light-colored crude product, the color quality of which can be improved again by steam treatment carried out in a work-up step. The further treatment of the polyol ester with aqueous hydrogen peroxide for color improvement is not excluded, but is limited to special cases.

A light-colored polyol ester is obtained which also meets the remaining specifications such as water content, residual acid content, residual content of catalyst ingredients and residual content of monoester.

The polyols used as starting materials for the process according to the invention correspond to the general formula (I)

R(OH)_n (I)

Wherein R is an aliphatic or alicyclic hydrocarbon group having 2 to 20, preferably 2 to 10 carbon atoms, and n is an integer of 2 to 8, preferably 2, 3, 4, 5 or 6.

Suitable polyols are likewise compounds of the formula (II)

H-(-O-[-CR¹R²-]_m-)_o-OH (II)

Wherein R is¹And R²Each independently of the others is hydrogen, alkyl having 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, or hydroxyalkyl having 1 to 5 carbon atoms, preferably hydroxymethyl, m is an integer from 1 to 10, preferably from 1 to 8, especially 1, 2, 3 or 4, o is an integer from 2 to 15, preferably from 2 to 8, especially 2, 3, 4 or 5.

Suitable polyols which can be converted into the light-coloured polyol esters by the process of the invention are, for example, 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, neopentyl glycol, 2-dimethylolbutane, trimethylolethane, trimethylolpropane, ditrimethylolpropane, trimethylolbutane, 2, 4-trimethylpentane-1, 3-diol, 1, 2-hexanediol, 1, 6-hexanediol, pentaerythritol or dipentaerythritol or 3(4), 8(9) -dimethyloltricyclo [5.2.1.0 ]^2，6]Decane.

Other polyols which may be used include ethylene glycol and 1, 2-propylene glycol, and oligomers thereof, especially ether glycols di-, tri-and tetraethylene glycol or dipropylene glycol, tripropylene glycol or tetrapropylene glycol. Ethylene glycol and propylene glycol are industrially produced chemicals. The base materials used for their preparation are ethylene oxide and propylene oxide, from which 1, 2-ethanediol and 1, 2-propanediol are obtained by heating under pressure with water. Diethylene glycol is obtained by ethoxylation of ethylene glycol. Triethylene glycol is obtained as a by-product in the hydrolysis of ethylene oxide to ethylene glycol, as is tetraethylene glycol. Both compounds can also be synthesized by reacting ethylene glycol with ethylene oxide. Dipropylene glycol, tripropylene glycol, tetrapropylene glycol and higher propoxylated products are obtained by multiple additions of propylene oxide to 1, 2-propanediol.

In order to obtain light-colored polyol esters by the process of the present invention, linear or branched aliphatic monocarboxylic acids having 3 to 20 carbon atoms in the molecule are used. Although saturated acids are preferred in many cases, it is also possible to use unsaturated carboxylic acids as reaction components for the ester synthesis, depending on the particular field of application of the plasticizer or lubricant. Examples of monocarboxylic acids as components of the polyol esters are propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, 2-methylbutyric acid, 3-methylbutyric acid, 2-methylpentanoic acid, n-hexanoic acid, 2-ethylbutyric acid, n-heptanoic acid, 2-methylhexanoic acid, cyclohexanecarboxylic acid, 2-ethylhexanoic acid, n-nonanoic acid, 2-methyloctanoic acid, isononanoic acid, 3, 5, 5-trimethylhexanoic acid, 2-propylheptanoic acid, 2-methylundecanoic acid, isoundecanecarboxylic acid, tricyclodecanecarboxylic acid and isotridecanoic acid. The novel process has been found to be particularly useful for the preparation of monoethylene glycol or oligoethylene glycol and 1, 2-propylene glycol or oligopropylene glycol with C₄-to C₁₃-or C₅-to C₁₀Polyol esters of monocarboxylic acids and for the preparation of polyols based on 1, 3-butanediol, neopentyl glycol, 2, 4-trimethylpentane-1, 3-diol, trimethylolpropane, ditrimethylolpropane, pentaerythritol or 3(4), 8(9) -dimethylol tricyclo [5.2.1.0^2，6]Polyol ester of decane.

Polyol esters of ethylene glycol and its oligomers are outstandingly suitable as plasticizers for all customary high molecular weight thermoplastic materials. They find particular use as additives to polyvinyl butyrals which, in combination with glycol esters, are used as interlayers in the manufacture of multilayer or composite glass. They can likewise be used as coalescents or film-forming assistants in aqueous polymer dispersions which have various uses as coatings. The preparation process according to the invention makes it possible to prepare polyol esters in a simple manner which have excellent color properties and which also meet further quality requirements, such as low odor or low acid number. The process of the invention is particularly suitable for the preparation of triethylene glycol di-2-ethylhexanoate (3G8 ester), tetraethylene glycol di-n-heptanoate (4G7 ester), triethylene glycol di-2-ethylbutyrate (3G6 ester), triethylene glycol di-n-heptanoate (3G7 ester) or tetraethylene glycol di-2-ethylhexanoate (4G8 ester).

The process of the invention can be carried out continuously or batchwise in reaction apparatuses which are typically used in chemical technology. It has been found that useful apparatus are stirred tanks or reaction tubes, with a batch mode being preferred.

The process of the present invention is illustrated in detail in the following examples, but it is not limited to the embodiments.

Example (b):

example 1:

preparation of triethylene glycol di-2-ethylhexanoate (3G8 ester); esterification in the presence of activated carbon

Esterification of triethylene glycol with 2-ethylhexanoic acid was carried out in a heatable 1 l four-necked flask equipped with stirrer, internal thermometer and water separator.

Initially a flask was charged with 250 grams (1.66 moles) of triethylene glycol and 680 grams (4.72 moles) of 2-ethylhexanoic acid and 0.4 weight percent activated carbon based on the total reaction mixture. The mixture was heated to 225 ℃ while stirring and applying a slight reduced pressure of 900 hPa. When this temperature was reached, the pressure was gradually reduced to 400hPa and the reaction water formed was removed on a water separator. The progress of the reaction was monitored by continuously weighing the amount of water discharged via the water separator and by the progress of the hydroxyl number. After a total reaction time of 14.5 hours, the reaction is terminated at a residual hydroxyl number of 4.2mg KOH/g (according to DIN 53240).

Subsequently, the excess 2-ethylhexanoic acid was distilled off at a temperature of 200 ℃ and a pressure of 20hPa for 3.75 hours. Thereafter, the mixture was steam distilled at 200 ℃ and standard pressure for 2.5 hours. After final filtration to remove the activated carbon, light colored triethylene glycol di-2-ethylhexanoate having the index reported in table 1 was obtained.

Example 2 (comparative):

preparation of triethylene glycol di-2-ethylhexanoate (3G8 ester); esterification without addition of activated carbon

The procedure was as in example 1, except that the esterification reaction was carried out without adding activated carbon. Due to the absence of solids, the mixture was not filtered after esterification and work-up. The measured indices are also listed in the table below.

Table 1: index of triethylene glycol Di-2-ethylhexanoate prepared according to examples 1 and 2

Gas chromatography analysis (% by weight):

index:

as shown in the experimental data of table 1, activated carbon needs to be added in the esterification stage to obtain light colored polyol esters. Both the addition of activated carbon in the esterification stage and the steam distillation during work-up are necessary to obtain light-colored polyol esters. Steam distillation alone is not sufficient to obtain a product that meets specifications.

Example 3:

preparation of neopentyl glycol di-2-ethylhexanoate by esterification in the presence of activated carbon

The esterification of neopentyl glycol with 2-ethylhexanoic acid was carried out in a heatable 1 l four-necked flask equipped with stirrer, internal thermometer and water separator.

Initially a flask was charged with 312.8 g (3.0 mol) of neopentyl glycol and 966.9 g (6.7 mol) of 2-ethylhexanoic acid and 1.0 wt.% of activated carbon based on the total reaction mixture. While stirring and applying a slight reduced pressure of 600hPa, the mixture was heated to 200 ℃ and held at this temperature for 2 hours. Subsequently, the pressure was gradually reduced to 500hPa and the reaction water formed was removed on a water separator. The progress of the reaction was monitored by continuously weighing the amount of water discharged via the water separator and by the progress of the hydroxyl number. The reaction was terminated after a total reaction time of 8 hours.

Subsequently, the excess 2-ethylhexanoic acid is distilled off at a temperature of 190 ℃ and a pressure of 95hPa for a further 2 hours, and subsequently at a temperature of 130 ℃ and a pressure of 6hPa for a further 0.5 hour. Thereafter, steam distillation was carried out at 180 ℃ and under standard pressure for 0.5 hour and final drying was carried out at 120 ℃ for 15 minutes. After final filtration to remove the activated carbon, a light-colored neopentyl glycol di-2-ethylhexanoate with the following indices was obtained:

table 2: exponential gas chromatographic analysis (in% by weight) of neopentyl glycol di-2-ethylhexanoate prepared according to example 3:

neopentyl glycol di-2-ethylhexanoate	93.2％
		Neopentyl glycol mono-2-ethylhexanoate	5.8％
Excess material	1.0％

Hazen color number (DIN ISO 6271)

69

Example 4 (comparative):

preparing neopentyl glycol di-2-ethyl hexanoate; esterification without addition of activated carbon

The procedure was as in example 3, except that the esterification reaction was carried out without addition of activated carbon. Due to the absence of solids, the mixture was not filtered after esterification and work-up.

Table 3: exponential gas chromatographic analysis (in% by weight) of neopentyl glycol di-2-ethylhexanoate prepared according to example 4:

neopentyl glycol di-2-ethylhexanoate	92.9％
		Neopentyl glycol mono-2-ethylhexanoate	6.2％
Excess material	0.9％

Hazen color number (DIN ISO 6271)

140

These examples also demonstrate that the performance of the esterification reaction in the presence of an adsorbent has a beneficial effect on the color number of the polyol ester desired.

Claims (28)

1. Process for the preparation of polyol esters by reacting polyols with linear or branched aliphatic monocarboxylic acids having 3 to 20 carbon atoms and subsequent work-up of the reaction mixture, characterized in that a mixture of starting compounds is reacted in the presence of an adsorbent, unconverted starting compounds are removed, a steam treatment is subsequently carried out and the remaining polyol ester is dried, the polyol ester is filtered after the end of the reaction or after any other work-up measure,

wherein the polyol used is a compound of the formula (II)

H-(-O-[-CR¹R²-]_m-)_o-OH (II)

Wherein R is¹And R²Each independently hydrogen, alkyl having 1 to 5 carbon atoms, or hydroxyalkyl having 1 to 5 carbon atoms, m is an integer from 1 to 10, o is an integer from 2 to 15,

the steam treatment is carried out at a temperature of 100 to 250 ℃ for 0.5 to 5 hours.

2. The process according to claim 1, characterized in that the mixture of starting compounds is heated in the presence of the adsorbent to a temperature of at most 280 ℃ and the pressure is reduced in stages while keeping the temperature constant.

3. A process according to claim 2, characterized in that the mixture of starting compounds is heated to a temperature of at most 250 ℃ in the presence of the adsorbent.

4. The process according to claim 1, characterized in that the mixture of starting compounds is heated in stages to a maximum temperature of 280 ℃ in the presence of an adsorbent under constant pressure.

5. The process according to claim 1, characterized in that the mixture of starting compounds is heated in the presence of an adsorbent at a temperature which is raised in stages to a temperature of at most 280 ℃, and the pressure is reduced in stages.

6. A process according to claim 5, characterized in that the mixture of starting compounds is reacted in the first stage at a temperature of at most 190 ℃ and a pressure of at most 600hPa in the presence of the adsorbent, and in the second stage the reaction is brought to completion by raising the temperature to at most 250 ℃ and at a pressure of at most 300 hPa.

7. Process according to any one of claims 1 to 6, characterized in that the adsorbent is used in an amount of 0.05 to 30% by weight per 100 parts by weight of liquid phase.

8. The process according to claim 7, characterized in that the adsorbent is used in an amount of 0.1 to 5.0% by weight per 100 parts by weight of liquid phase.

9. The process according to claim 7, characterized in that the adsorbent is used in an amount of 0.1 to 1.0% by weight per 100 parts by weight of liquid phase.

10. A process according to any one of claims 1 to 6, characterized in that the adsorbent used is silica gel, diatomaceous earth, alumina, hydrated alumina, clay, carbonate or activated carbon.

11. A process according to claim 7, characterized in that the adsorbent used is silica gel, diatomaceous earth, alumina, hydrated alumina, clay, carbonate or activated carbon.

12. The process according to claim 8, characterized in that the adsorbent used is silica gel, diatomaceous earth, alumina, hydrated alumina, clay, carbonate or activated carbon.

13. The process according to claim 9, characterized in that the adsorbent used is silica gel, diatomaceous earth, alumina, hydrated alumina, clay, carbonate or activated carbon.

14. Process according to any one of claims 1 to 6, characterized in that the steam treatment is carried out at a temperature of 150 to 220 ℃.

15. A process according to claim 14, characterized in that the steam treatment is carried out at a temperature of 170 to 200 ℃.

16. Process according to any one of claims 1 to 6, characterized in that the polyol ester is dried after the steam treatment at a temperature of 80 to 250 ℃ and a pressure of 0.2 to 500 hPa.

17. The method according to claim 16, characterized in that the temperature is between 100 and 180 ℃.

18. A method according to claim 16, characterised in that the pressure is 1 to 200 hPa.

19. A method according to claim 17, characterised in that the pressure is 1 to 200 hPa.

20. A method according to claim 18 or 19, characterised in that the pressure is 1 to 20 hPa.

21. A process according to claim 16, characterized in that the polyol ester is dried in the presence of an inert gas.

22. A process according to any one of claims 1 to 6 characterised in that the polyol ester is filtered after the steaming.

23. A process according to any one of claims 1 to 6, characterised in that the polyol ester is filtered after drying.

24. Process according to any one of claims 1 to 6, characterized in that the polyol used is a compound of the general formula (II)

H-(-O-[-CR¹R²-]_m-)_o-OH (II)

Wherein R is¹And R²Each independently hydrogen, methyl, ethyl, propyl or hydroxymethyl, m is an integer from 1 to 8, o is an integer from 2 to 8.

25. A process according to claim 24, characterized in that the polyol used is a compound of the formula (II)

H-(-O-[-CR¹R²-]_m-)_o-OH (II)

Wherein R is¹And R²Each independently hydrogen, methyl, ethyl, propyl or hydroxymethyl, m is 1, 2, 3 or 4, o is 2, 3, 4 or 5.

26. A process according to any one of claims 1 to 6, characterized in that the polyol used is di-trimethylolpropane, dipentaerythritol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol or tetrapropylene glycol.

27. A process according to any one of claims 1 to 6, characterized in that the aliphatic monocarboxylic acid converted is propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, 2-methylbutyric acid, 3-methylbutyric acid, 2-methylpentanoic acid, n-hexanoic acid, 2-ethylbutyric acid, n-heptanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, n-nonanoic acid, 2-methyloctanoic acid, isononanoic acid, 3, 5, 5-trimethylhexanoic acid or 2-propylheptanoic acid.

28. The process of any one of claims 1 to 6 which produces triethylene glycol di-2-ethylhexanoate, tetraethylene glycol di-n-heptanoate, triethylene glycol di-2-ethylbutyrate, tetraethylene glycol di-2-ethylhexanoate, or triethylene glycol di-n-heptanoate.