WO1998007676A1

WO1998007676A1 - Process for separating 2-butyl-2-ethyl-1,3-propanediol from reaction mixtures containing the same

Info

Publication number: WO1998007676A1
Application number: PCT/FI1997/000485
Authority: WO
Inventors: Hannu Holma; Rami Haakana; Kalevi Heinola; Esko Karvinen; Lea Rintala; Lea Parkkinen; Eija Kuisma
Original assignee: Neste Oyj
Priority date: 1996-08-19
Filing date: 1997-08-19
Publication date: 1998-02-26
Also published as: AU3943897A; FI963244A; FI102830B1; FI963244A0; FI102830B

Abstract

The invention concerns a process for separating 2-butyl-2-ethyl-1,3-propanediol from a reaction blend, which has an organic phase containing BEPD, and an aqueous phase, and which has been produced by allowing 2-ethylhexanal and formaldehyde to react in a reactor in the presence of a hydroxide compound, whereby the hydroxide compound has been fed into the reactor principally during the whole time of reaction. A characterizing feature of the invention comprises allowing the reaction blend to phase into an organic phase and an aqueous phase and removing the aqueous phase immediately from the reactor, i.e. within ca. 0.1 minute to 2 hours from the completion of the input of the hydroxide compound. The organic phase is washed with an aqueous solution to remove impurities and BEPD is recovered by submitting the water washed organic phase to distillation. By the invention the number of process steps is reduced, and the raw material costs decrease, because the usual addition of sulphuric acid is not needed.

Description

Process for separating 2-butyl-2-ethyl-l,3-propanediol from reaction mixtures containing the same

The present invention concerns a process according to the preamble of claim 1 for separating 2-butyl -2-ethyl-l,3-propanediol from reaction mixtures. These reaction mixtures comprise an aqueous phase and a BEPD-containing organic phase. They originate in a reaction performed in a reactor, in which 2-ethylhexanal and formaldehyde are reacted with each other in the presence of a hydroxide compound. The hydroxide compound is fed to the reactor essentially throughout reaction.

The substance 2-butyl-2-ethyl-l,3-propanediol. in the following also denoted as BEPD. is known per se and it is being used for example in the manufacturing of polyester and in the paint industry as a component of powder paints. The excellent UV-protection provided by BEPD, and its very low water adsorption, are some of the advantages of said compound.

BEPD is manufactured from 2-ethylhexanal and formaldehyde in a single-step process through aldol addition, immediately followed by a Cannizzaro reaction. In the first reaction of the process, i.e. the aldol reaction, a basic alkali metal hydroxide or an alkali earth metal hydroxide is usually used as a catalyst. In the second phase of the process, said hydroxide acts as a reactant, reacting with the BEPD-aldol. an intermediate product of the aldol reaction. The hydroxide compound is fed to the reaction mixture in the form of an aqueous solution, whereby a two-phase product mixture is obtained when the reaction is complete. The organic phase of the mixture contains BEPD and the aqueous phase contains an alkali metal or alkaline earth metal formate.

According to the prior art, the reaction product containing BEPD is purified through a multi-phase cleansing method. Thus, the reaction mixture is first neutralized with (concentrated) sulphuric acid to set the pH value to about 5 to 7. Then, the reaction mixture is mixed for 1 to 60 minutes, typically 5 to 30 minutes, after which the phases are allowed to separate, the aqueous phase is removed and the organic phase is washed twice while it is being mixed, first with water containing sodium hydroxide, yielding a pH value around 12 to 14, whereafter it is washed for the second time with acidified water (sulphuric acid) to adjust the pH to at least approximately neutral (about 6 to 7). After each washing, the phases are allowed to separate and the aqueous phase is removed. The purpose of the alkaline wash is to separate the acid fractions, which may disturb the distillation of BEPD and give rise to problems with corrosion. The obtained raw BEPD product is distilled at low pressure. Salts may be recovered from the aqueous phase separated from the product mixture, and further processed.

Some considerable draw-backs are connected with the known methods. The cleansing method is very complicated and it consists of several stages and the pH value of the organic phase is first to be adjusted to the acid range, then to the alkaline, and finally to the neutral range. The sulphuric acid and the sodium hydroxide used to control the pH value increase the costs of the raw material. Furthermore the cleansing result of the known methods is not even always very good.

It is an object of the present invention to eliminate the problems of the known technique and to achieve a new process for the separation and recover}' of BEPD from reaction mixtures containing said compound.

The present invention is based on the concept of separating the process water, i.e. the aqueous phase of the reaction mixture, immediately after the reaction phase and stabilizing it through acid addition. The organic phase is washed with water and its pH value is adjusted, if necessary, prior to the recovery of BEPD by distillation. Thus the washing and recovery of BEPD may be simplified considerably, and the result of the cleansing of the product may be improved to yield a washing efficiency of over 90 %, preferably over 92

%, considering the sodium ion concentration.

More specifically, the process according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.

The invention provides considerable advantages compared to traditional washing alternatives. For instance, the number of processing stages decreases, because no addition of sulphuric acid is needed. The product phase may be washed with clean water instead of water containing lye, because there is no need to shift the pH value back to the neutral range. The raw material costs decrease, because no sulphuric acid or lye is needed in connection with the washing. A better washing result is achieved, since the ion concentration of the product is not increased during the washing. The concentrations of ion in the process and washing waters decrease as a result of the afore-mentioned reasons, whereby the environmental loading decreases. Acid fractions can be avoided in the distillation of the product (less problems of corrosion). If necessary, the product can be washed in one single step.

The washing and separation process according to the invention is connected with the production of BEPD, in particular by a one-step method from 2-ethylhexanal and formaldehyde in the presence of a hydroxide compound. The manufacture of BEPD is described in more detail in the following:

The production is carried out as a batch, semi-batch or continuous process. According to one embodiment, the method can be performed in a semi-batch reactor equipped with efficient mixing, whereby the calculated amount of 2-ethylhexanal and formaldehyde is first fed into the reactor, forming the reaction mixture, whereafter a suitable hydroxide compound is added to the reaction blend. Hydroxide is continuously fed into the mixture in order to control the heat of reaction. The reaction mixture is agitated throughout the reaction. After the reaction, the two-phase reaction mixture is separated. The organic phase of the blend contains BEPD, possibly together with some organic impurities. The water phase contains alkali metal or alkaline earth metal salts.

The hydroxide compound may be fed at constant rate throughout the reaction. More preferably, however, the feed is carried out incrementally so that the hydroxide compound is fed with at least two or three different rates, so as to obtain a heat production of the reaction of 2-ehtylhexanal and formaldehyde with is at least approximately the same immidately after each increase of the feeding rate. The feeding rate of the hydroxide compound is increased each time the rate is changed, so that the latter feeding rate is always ca 10-100 %, preferably ca 20-80 % higher tnan the former feeding rate. In the alternative of continuous feeding, the feeding rate of the hydroxide compound is continuously increased. Most preferably the amount of hydroxide compound fed into the reaction per unit time is increased at least by a factor of 1.5 or 2 during the reaction.

The amount of hydroxide compound to be fed depends on the amount of 2-ethylhexanal. According to the invention, it has been found preferable to keep the molar ratio of the total input of hydroxide compound (i.e. the total amount of hydroxide fed into the reaction blend) and 2-ethylhexanal at a value, which is slightly larger than 1 , preferably ca 1.01 to 1.5, preferably 1.02 to 1.25 and 1.2 at the most.

In the invention, 2-ethylhexanal is preferably used in the form of as pure as possible a solution (purity most preferably > 90 %, preferably over 95 %). Formaldehyde and the hydroxide compound are used in the form of aqueous solutions, preferably as strong aqueous solutions, whereby the concentration of formaldehyde in the aqueous solution is 30-50 weight-%. This aqueous solution contains most preferably 2-20 wt-% some lower alcohol, such as methanol. Methanol or a corresponding alcohol stabilizes the formaline solution and prevents the dimerization of formaldehyde. The hydroxide compound is most preferably used in the form of as strong as possible an aqueous solution or suspension, the concentration of e.g. sodium hydroxide being preferably over 40 %, in particular over 45 %. In addition to sodium hydroxide, other alkali metal hydroxides can be used as hydroxide compounds, for instance potassium or lithium hydroxide, and alkaline earth metal hydroxides, such as calcium and magnesium hydroxide. The molar ratio of formaldehyde to 2-ethylhexanal is ca 2.1 - 5, preferably 2.3 - 3.0, in particular at the most a slight excess of preferably less than 50 % of the formaldehyde is used. The corresponding molar ratio with respect to the hydroxide compound is 1.5 - 3, preferably ca 1.9 - 2.1.

It should be mentioned, that besides the formaline solution, paraformaldehyde may also be used, which decomposes in the reaction blend, forming formaldehyde.

The temperature of the reaction is kept at 40 to 80 °C at least essentially during the reaction. The reaction time varies with the production process, i.e., it depends on whether it is a batch, semi-batch or continuous process. In addition, the reaction time varies to some extent depending on the amounts of reactants, the reaction temperature and especially with the amount of hydroxide compound input. Typically the reaction time is about 1 to 24 hours, preferably ca 4 to 12 hours. In the examples described below. 6 hour reaction times were used. The 2-ethylhexanal used as feedstock reacts usually completely within 4 hours; and the concentration of the BEPD-aldol that is formed as an intermediate product is at its highest (ca 50 %) after ca three hours.

After the reaction is completed, the yield of BEPD calculated from ethylhexanal is over 90 %. The reaction mixture is removed from the reactor, the blend is washed, and BEPD is separated from the organic phase by low pressure distillation. By washing the BEPD the alkali metal or alkaline earth metal salts, formed in the reaction, are substantially separated from the product. Heavy organic impurities are removed from BEPD in connection with the distillation.

In the preferred washing alternative according to the invention, the reaction blend is not neutralized by sulphuric acid after the completion of the feed of the catalyst. Instead, the produced mixture is allowed to separate into phases, and the aqueous phase is removed from the reactor as soon as possible after the completion of the catalyst feed. This takes typically 0.1 minutes to 2 hours, preferably ca 1-30 minutes, after the completion of the reaction. The time depends on the temperature of the reaction mixture. The higher the temperature, the more rapidly the product becomes coloured. Thus, at a temperature of 50 to 80 °C, the aqueous phase is preferably separated within 1 to 20 minutes from the completion of the reaction. Because the aqueous solution is very alkaline, it is stabilized, by adding sulphuric acid, to the pH value 6 to 8. after which it can be postprocessed to recover the salts. By making the aqueous phase acidic after the separation sodium hydroxide is neutralized which prevents colourization from taking place.

The organic phase containing BEPD is then washed in the reactor in one or two steps with pure water. The washing may be performed in an intermediate vessel or holding tank. instead of in the reactor. The mass of the washing water in relation to the mass of the organic phase is 0.2 to 1.0, preferably 0.4 to 0.5. in the first step, and 0.2 to 1.0, preferably 0.2 to 0.4 in the second step, if a two-step washing is used. In the case of single-step wash. the corresponding ratio is 0.5 to 1.2. In the purification of the product, a washing efficiency of up to 94 to 96 % is attained, including the concentration of the sodium (or corresponding alkali metal or alkaline earth metal) ion. If necessary, the pH value is controlled in connection with the latter washing, by adjusting the pH value to about 6 to 7. using an aqueous solution containing sulphuric acid. The produced raw BEPD product is distilled in reduced pressure at about 100 to 150 °C (5 to 15 mmHg).

The following non-limiting working examples illustrate the invention.

Example 1 (two-step wash)

BEPD was prepared by a semi-batch process out of 2-ethylhexanal (2-EH). having a purity of over 90 weight-%, and formaline. The concentration of the aqueous formaline solution was 37 weight-% HCHO and it contained 10 weight-% CH₃OH. First, 1207 g (9.225 moles) of 2-EH and 191 1 g (23.546 moles) of HCHO were fed into the reactor to make up the reaction blend, after which 927g (11.125 moles) in total of sodium hydroxide was fed into the reaction blend. The concentration of the sodium hydroxide aqueous solution was 48 weight-%, and it was fed for 6 hours at three input rates, namely 93 g/h (1.1 161 moles per hour) during the first hour of the reaction, 135 g/h (1.6201 moles/h) of NaOH during the following two hours and. finally, 188 g/h (1.2562 moles/h) during the third to the 6th hour.

After the reaction, the reaction blend was allowed to separate into phases , and the process water was separated. 272.4 g of the organic phase was taken and washed with pure water (136.2 g) at 60 °C. In the beginning, the Na-concentration was 4,200 ppm, after washing 330 ppm. The washing was repeated with 81.7 g of water, yielding a Na-concentration of 175 ppm. The total efficiency of the wash was thus 95.8 %.

Example 2 (single step wash)

After the reaction phase according to Example 1 , the reaction blend was allowed to separate into phases and the process water was separated. 297.7 g of organic phase was taken and washed with pure water (148.8 g) at 60 °C. In the beginning, the Na- concentration was 4200 ppm, after washing 300 ppm. The washing efficiency was thus 92.7 %.

Claims

Claims:

1. A processfor separating 2-butyl-2-ethyl-l ,3-propanediol from reaction blends, which have an organic phase containing BEPD and an aqueous phase, and which have been produced by reacting 2-ethylhexanal and formaldehyde in a reactor, in the presence of a hydroxide compound, the hydroxide compound having been fed into the reactor essentially during the whole time of reaction, c h a r a c t e r i z e d by the combination of the following steps:

- allowing the reaction blend to separate into phases comprising an organic phase and an aqueous phase, and the aqeous phase is removed from the reactor immediately after the completion of the feed of the hydroxide compound,

- washing the organic phase with an aqueous solution to remove water soluble impurities, and

- recovering BEPD by submitting the water-washed organic phase to distillation.

2. The process according to claim 1, wherein the aqueous phase is removed from the reactor within about 0.1 minutes to 2 hours from the completion of the feed of the hydroxide compound.

3. The process according to claim 1 or 2, wherein the organic phase is washed in the reactor, in an intermediate vessel or a holding tank.

4. The process according to claim 1, 2 or 3, wherein the organic phase is washed with pure water.

5. The process according to one of claims 1 to 4, wherein the mass of the washing water is 0.4- to 2-fold relative to the mass of the organic phase.

6. The process according to one of the claims above, wherein the organic phase is washed in two steps, whereby the mass of water used in the first step is 0.2-1.0-fold, preferably 0.4-0.5-fold, relative to the mass of the organic phase, and in the second step the mass of water is 0.2-1.0-fold, preferably 0.2-0.4-fold relative to the mass of the organic phase.

7. The process according to any of claims 1-5, wherein the organic phase is washed in a single step, whereby the mass of the water is 0.5- to 1.2-fold relative to the mass of the organic phase.

8. The process according to any of the preceding claims, wherein the pH of the organic phase is adjusted to a value of 6 - 7 prior to distilling the BEPD.

9. The process according to one of the preceding claims, wherein the aqueous phase is treated with acid addition and, optionally, submitted to post-processing to recover the compounds present in the aqueous phase.

10. The process according to any of the preceding claims, in which a reaction blend, obtained by using sodium hydroxide as hydroxide compound, is processed, c h a r a c t e r i z e d in that the washing efficiency of the purification of the product is over 90 %, preferably over 92 %, including the concentration of the sodium ion.

11. The process according to any of the preceding claims, wherein the molar ratio of sodium hydroxide to 2-ethylhexanal is over 1 and smaller than 1.5, preferably 1.02 to 1.25.