WO2021037572A1

WO2021037572A1 - Process for treating wastewater from an aldolization process

Info

Publication number: WO2021037572A1
Application number: PCT/EP2020/072716
Authority: WO
Inventors: Petra Deckert; FRANK Huetten; Rainer Papp
Original assignee: Basf Se
Priority date: 2019-08-23
Filing date: 2020-08-13
Publication date: 2021-03-04

Abstract

Process to reduce the contamination with C₁₂-compounds and/or C₁₅-compounds of wastewater from an aldolization process for the preparation of 2-ethylhexenal and/or for the preparation of 2-propylheptenal comprising a) acidification of the wastewater to a pH of 0 to 6 and b) separation of the formed organic phase from the aqueous phase, wherein the process does not comprise any liquid-liquid extraction of the wastewater and/or of the aqueous phase and wherein the C₁₂-compounds are C₁₂-hydroxycarboxylic acids, salts of C₁₂-hydroxycarboxylic acids, C₁₂-lactones or mixture of two or more of these compounds and wherein the C₁₅-compounds are C₁₅-hydroxycarboxylic acids, salts of C₁₅- hydroxycarboxylic acids, C₁₅-lactones or mixtures of two or more of these compounds.

Description

PROCESS FOR TREATING WASTEWATER FROM AN ALDOLIZATION PROCESS

Description

Base-catalyzed aldolization reactions, for example aldol additions and aldol condensations, have attained considerable importance in the industrial preparation of alcohols. Merely by way of example, mention may be made of the preparation of neopentyl glycol in which formaldehyde is added onto isobutyraldehyde to form 2,2-dimethyl-3-hydroxypropanal in a first step of the syn thesis. The preparation of the plasticizer alcohols 2-ethylhexanol and 2-propylheptanol is carried out on a far larger scale in a process in which two molecules of n-butyraldehyde or n- valeraldehyde are condensed in an aldol condensation with elimination of water to form the un saturated aldehyde 2-ethylhexenal or 2-propylheptenal in the first step of the synthesis and this unsaturated aldehyde is subsequently hydrogenated to give the respective plasticizer alcohol (cf Weissermel, Arpe; Industrielle Organische Chemie; 4th Edition, pp. 150-152, 231-232,

Wiley- VCH, Weinheim 1994).

The base-catalyzed aldol addition of aldehydes to form b-hydroxyaldehyde adducts or the aldol condensation of two aldehydes to form the respective a,b-unsaturated aldehydes, also referred to as enalization, or the aldol condensation of aldehydes with ketones which is in each case either catalyzed by means of an aqueous base, e.g. sodium hydroxide, or requires a hydrolysis step or an extraction with water to remove the base from the product during the work-up results in considerable amounts of wastewater which is heavily contaminated with water-soluble organic compounds and organic compounds dispersed in water. Thus, it is important to ensure that biodegradability of the wastewater introduced into a conventional wastewater plant is as high as possible to facilitate the further work-up of the wastewater before it is discharged, for example into rivers.

In course of diligent research, it was now found that Ci2-compounds and/or Cis-compounds, show remarkably low biodegradability according to the Zahn-Wellens-EMPA-Test (OECD 302 B) and thus have a major effect on the biodegradability of the wastewater from an aldolization process for the preparation of 2-ethylhexanal or 2-propylheptenal. Ci2-compounds with low biodegradability are especially Ci2-lactones, Ci2-hydroxycarboxylic acids and/or salts of C12- hydroxycarboxylic acids, for example sodium and/or potassium salts. Cis-compounds with low biodegradability are especially Cis-lactones, Cis-hydrocarboxylic acids and/or salts of C15- hydrocarboxylic acids for example sodium and/or potassium salts. For the purpose of clarification, wastewater from an aldolization process for the preparation of 2-ethylhexenal contains Ci₂-compounds, while wastewater form an aldolization process for the preparation of 2-propylheptenal contains Cis-compounds. The wastewater from an aldolization process for the preparation of 2-ethylhexenal contains one or more of the aforementioned C₁₂- compounds, preferably Ci₂-lactones. The wastewater from an aldolization process for the prep aration of 2-propylheptenal contains one or more of the aforementioned Cis-compounds, prefer ably Ci5-lactones. Wastewater from an aldolization process for the preparation of 2-ethylhexenal can be combined with wastewater from an aldolization process for the preparation of 2 propylheptenal and the resulting wastewater contains Ci2-compounds and Cis-compounds, preferably Ci₂-lactones and Ci ₅-lactones.

In consequence to the findings of our research, removing one or more of the aforementioned C₁₂- compounds and/or Cis-compounds, especially Ci2-lactones and/or Cis-lactones from the wastewater presents an efficient method to increase the biodegradability of the wastewater. It is important that the wastewater meets certain limit values regarding its biodegradability because otherwise it cannot be introduced into a conventional water treatment plant for further work-up.

If these limit values are not met, the biodegradability has either to be increased by investment in costly water treatment operations and/or equipment before the wastewater can be introduced into a conventional water treatment plant, or in the worst case, the wastewater has to be dis posed by other means, like concentrating and depositing or thermal treatment.

Some prior art documents disclose processes to lower the contamination of wastewater from aldolization processes that comprise acidification of the wastewater to a pH of 0 to 6 and sepa ration of the formed organic phase from the aqueous phase. For instance, CN 108 128982 A discloses a process for lowering the COD (chemical oxygen demand) value of wastewater but is silent with respect to biodegradability. The process taught by EP 838435 L1 is not even con cerned with lowering the COD US 6 139747 A, US 7943047 B2 and US 6358419 B1 comprise a liquid-liquid extraction step.

CN 102 730 894 A relates to a process comprising atmospheric stripping, low pressure evapo ration, acidifying phase separation, rectification of the organic phase and concentrating the aqueous phase by evaporation of water EP 2995 591 A1 discloses a process involving evapo rative concentration of wastewater comprising non-biodegradable organic compounds, separat ing the supernatant and partly using it as energy source by incineration.

Thus, it was an object of the present invention to increase the biodegradability of a wastewater from an aldolization process which is contaminated with one or more of the aforementioned C₁₂- compounds, especially Ci₂-lactones from the preparation of 2-ethyl hexenal and/or contaminated with one or more of the aforementioned Cis-compounds, especially Cis-lactones from the prepa ration of 2-propylheptenal by reducing the C₁₂- and/or Cis-compound contamination, especially C₁₂- and/or Cis-lactone contamination in the wastewater.

The object of the present invention is solved by a process to reduce the Ci₂-compound and/or Cis-compound contamination of wastewater from an aldolization process for the preparation of 2-ethylhexenal and/or for the preparation of 2-propylheptenal comprising a) acidification of the wastewater to a pH of 0 to 6 and b) separation of the formed organic phase from the aqueous phase, wherein the process does not comprise any liquid-liquid extraction of the wastewater and/or of the aqueous phase and wherein the Ci2-compounds are Ci₂-hydroxycarboxylic acids, salts of Ci₂-hydroxycarboxylic acids, Ci2-lactones or mixture of two or more of these compounds and wherein the Cis-compounds are Cis-hydroxycarboxylic acids, salts of C₁₅- hydroxycarboxylic acids, Cis-lactones or mixtures of two or more of these compounds..

In addition to increasing the biodegradability of the wastewater, the inventive process also de creases the total organic carbon value (TOC) of the wastewater in an efficient manner. By de creasing the TOC value of the wastewater, work-up of the wastewater in a conventional water treatment plant is further facilitated.

The inventive process can be run in a continuous or discontinuous mode.

The wastewater from an aldolization processes to be treated according to the invention is formed in the aldol condensation of n-butyraldehyde to form 2-ethylhexenal or the condensation of n-valeraldehyde to form 2-propylheptenal, in the presence of an aqueous alkali metal hydrox ide solution as catalyst. For each reaction, after leaving the aldol condensation reactor, the aqueous-organic reaction product mixture is subjected to a phase separation in which an organ ic phase consisting essentially of the desired aldol condensation products and an aqueous phase are formed. While the organic phase is processed further to obtain the desired end prod ucts, for example in the case of the production of 2-ethylhexenal by hydrogenation to give 2- ethylhexanol or in the case of the production of 2-propylheptenal by hydrogenation to give 2- propylheptanol, the aqueous phase which is contaminated with organic impurities is regarded as wastewater and treated according to the present invention. After treatment of the wastewater according to the present invention, the so treated wastewater may be introduced into a conven- tiona! water treatment plant for further work-up. Wastewater from an aldolization processes for the preparation of 2-ethylhexenal or for the preparation of 2-propylheptenal can be treated indi vidually or combined in the inventive process.

Depending on their water solubility, the organic impurities present in the wastewater from an aldolization process for the preparation of 2-ethylhexenal and/or 2-propylheptenal can be com pletely or partly present in solution and/or in the form of finely dispersed, microscopically small droplets or particles.

Beside one or more aforementioned C₁₂- and/or Cis-compounds, especially C₁₂- and/or C₁₅- lactones, the organic impurities present in the wastewater from an aldolization process for the preparation of 2-ethylhexenal and/or 2-propylheptenal may comprise one or more of generically disclosed compounds in the following, non-exhaustive listing: o isomers of the carbonyl compounds (aldehydes, ketones) used in the aldol condensation, in particular branched aldehydes; o reduced compounds of the carbonyl compounds used in the aldol condensation reaction, in particular straight-chain and branched alcohols; o lactones other than C₁₂- and/or Ci₅-lactones having a number of carbon atoms corre sponding to the number of carbon atoms of the carbonyl compounds used in the aldol condensation reaction, or having a multiple of the carbon atoms of the carbonyl com pounds used in the aldol condensation reaction, or a number of carbon atoms correspond ing to the number of the carbon atoms of the main product of the aldol condensation reac tion; o alcohols which have one carbon atom more than the carbonyl compound used in the aldol condensation reaction and/or alcohols having twice the number of carbon atoms as the carbonyl compounds used in the aldol condensation reaction; o salts, in particular alkali metal salts, of carboxylic acids having a number of carbon atoms corresponding to the number of carbon atoms of the carbonyl compounds used in the al dol condensation reaction and/or corresponding to the number of carbon atoms of the main products of the aldol condensation reaction, and/or salts of hydroxycarboxylic acids formed by alkaline hydrolysis of the lactones; o saturated aldehydes having a number of carbon atoms corresponding to the number of carbon atoms of the main product of the aldol condensation reaction; o carboxylic esters formed from the abovementioned carboxylic acids and alcohols; o acetals and/or hemiacetals formed from the abovementioned carbonyl compounds and alcohols. Of course, carbonyl compounds which have been used in the aldol condensation reaction but have not reacted can also be present as organic impurities in the aqueous phase.

Owing to the high alkalinity of the wastewater, the abovementioned salts, are present therein in dissolved form. Owing to their sometimes long alkyl chains, these salts can act as solubilizers for other sparingly soluble by-products and thus increase their content in the wastewater, whether in dissolved or dispersed form.

The wastewater from the aldolization process is brought to a pH from 0 to 6, preferable to a pH from 1 to 3. The acidification of the wastewater can be carried out using any strong protic acids, preferably strong mineral protic acids such as hydrochloric acid, sulfuric acid or nitric acid, par ticularly preferably sulfuric acid. If desired, wastewater from other processes which is contami nated with organic substances, for example the aqueous phase which separates off after con densation of the overhead product from the distillation of n-butanol, isobutanol, pentanol, 2 ethylhexanol and/or 2-propylheptanol, can be added for further treatment to the wastewater from the aldolization process for the preparation of 2-ethylhexenal and/or 2-propylheptenal be fore the combined wastewater is acidified.

By means of acidification the salts of C₁₂- and/or Cis-hydrocarboxylic acids which may be pre sent in the wastewater are protonated and their solubility in the organic phase is increased. The protonated C₁₂- and/or Cis-hydrocarboxylic acids present in the wastewater can undergo, at least partly acid-catalyzed, lactonization reactions to form C₁₂- and/or Cis-lactones. For the avoidance of doubt, Ci₂-hydrocarboxylic acids can undergo acid-catalyzed lactonization reac tions to from Ci₂-lactones, while Cis-hydrocarboxylic acids can undergo acid-catalyzed lactoni zation reactions to form Cis-lactones. The solubility of C12- and/or Cis-compunds in an aqueous phase decreases in the following order: salts of hydroxycarboxylic acids > hydroxycarboxylic acids > lactones. The lactonization reaction is schematically shown for a Ci₂-hydroxycarboxylic acid salt and applies mutatis mutandis to Ci₂-hydroxycarboxylic acids.

The use of strong acids has the advantage that the amount of wastewater is kept at a minimum level. The acidification of the wastewater can be carried out in any apparatuses suitable for mix- ing two liquids, for example in stirred vessels or static mixers, preferably in a stirred vessel. The pH of the wastewater can be measured, for example, by means of a glass electrode.

The temperature of the wastewater during acidification is preferably from 5 to 150°C, more pref erably from 10 to 60°C, particularly preferably from 15 to 55°C. The acidification of the wastewater is preferably conducted under a pressure from 0,1 to 10 bar abs, more preferably from 0,5 to 1,5 bar abs and particularly preferably under atmospheric pressure.

After acidification of the wastewater, an organic phase separates out from an aqueous phase. The organic phase is separated from the aqueous phase as C12- and/or Cis-compounds are now predominantly present in the organic phase. Beside C12- and/or Cis-compounds other or ganic impurities are also present in the organic phase and removed together with the C12- and/or Cis-compounds. Thus, the TOC of the wastewater, respectively the aqueous phase ob tained after phase separation, is reduced in addition to higher biodegradability.

The temperature of the wastewater during phase formation of a separate organic and aqueous phase is preferably from 5 to 80°C, more preferably from 10 to 60°C, particularly preferably from 15 to 55°C. It is preferred to keep the temperature of the wastewater during phase formation and phase separation as low as possible, as lower temperatures bring the advantage that the solubility of the C12- and/or Cis-compounds in the aqueous phase is reduced. The formation of separate organic and aqueous phase can be supported by thorough mixing of the wastewater during the acidification step, by an exact adjustment of the pH of the wastewater within the de fined range during the acidification step, by an appropriate residence time of the wastewater during phase formation, or by a combination of two or more of the aforementioned means. An appropriate residence time is preferably between 0.1 to 30 minutes, preferably 1 to 20 minutes, and more preferably 5 to 15 minutes.

The separation of the organic phase from the aqueous phase can be carried out in a continuous or dis-continuous mode in any apparatus suitable for liquid-liquid phase separation, for example in a settler. Suitable settlers are for example gravity settlers with or without coalescence- promoting internals, likewise centrifugal separators or coalescence filters and combinations of these apparatuses. Separation of the organic phase from the aqueous phase is preferably car ried out with one or more coalescence filters. If more than one coalescence filter is used, the coalescence filters can be arranged in parallel and/or in series connection.

Gravity settlers with or without coalescence-promoting internals and their mode of operation are known to the person skilled in the art (see for example Ullmanns’ Encyclopedia of Industrial Chemistry, Liquid-Liquid-Extraction, 4. Phase-Separation Equipment, DO!:

10.1002/14356007. b03_06.pub2). Centrifugal separators and their mode of operation are also well known to the person skilled in the art (see for example Ullmanns’ Encyclopedia of Industrial Chemistry, Liquid-Liquid-Extraction, 3.1.4. Mixer-Settler or 3.1.5 Centrifugal Extractors DOI:

10.1002/14356007. b03_06.pub2). Coalesence filters and their mode of operation are known as well (see for example Chemie - Technik 18 (1989), 14 - 21).

The temperature of the wastewater during phase separation is preferably from 5 to 80°C, more preferably from 10 to 60°C, particularly preferably from 15 to 55°C.

In an advantageous embodiment the acidification of the wastewater is carried out in a stirred vessel. Fresh wastewater is introduced into a stirred vessel and the pH of the wastewater is set to 0 to 6, preferably to 1 to 3 by addition of strong protic acids. A stream of the acidified wastewater is withdrawn from the stirred vessel and introduced into a settler for formation and separation of the organic phase from the aqueous phase. After phase formation, the organic phase is at least widely withdrawn from the settler, preferably at least 95 vol.% of the organic phase are withdrawn form the settler and more preferred at least 99 vol.% of the organic phase are withdrawn from the settler. The organic phase withdrawn from the settler is at least partly reintroduced into the stirred vessel together with fresh wastewater. The volume of the organic phase reintroduced into the stirred vessel is preferably 20 to 50 vol.% with regard to the volume of the wastewater freshly introduced into the stirred vessel. Preferred embodiments in the con text of this invention, like temperature of the individual steps, means of acidification and/or resi dence times are either individually or in combinations of two or more also valid for this advanta geous embodiment.

The organic phase obtained after phase separation is generally not worked up further in the process of the invention but is instead utilized, for example, for energy generation. However, the organic phase can, if desired, also be hydrogenated and worked up to produce products of val ue In such a hydrogenation, the by-products from the aldolization which are comprised in the organic phase are essentially hydrogenated or hydrogenolyzed to form alcohols. For example, the organic phase can be combined with the organic phase which consists essentially of 2 ethylhexenal or 2-propylheptenal and which was separated off earlier and the so obtained or ganic phase can be hydrogenated to the respective alcohols.

The aqueous phase obtained after phase separation can be introduced into a conventional wa ter treatment plant for further work-up. As the aqueous phase may still contain C12- and/or C15- compounds and/or other organic impurities it may be preferable to further reduce the content of Ci2- and/or Cis-compounds and/or other organic impurities in the aqueous phase before the aqueous phase is introduced into a conventional water treatment plant. To further reduce the content of C12- and/or Cis-compounds and/or other organic impurities in the aqueous phase, especially organic impurities with high volatility, it is preferred that the aqueous phase is at least partly introduced into the upper part of a distillation column and a stripping medium which is introduced into the lower part of the column or is generated there is conveyed in countercurrent to the downward-flowing aqueous stream. The stripping medium is preferably an inert gas under the conditions prevailing in the distillation column, e.g nitrogen; particular preference is given to using steam as stripping medium. Distillation, respectively stripping is preferably carried out at temperatures of from 50 to 150° C. and a pressure of from 0 1 to 4 bar abs, more preferably from 0.5 to 1.5 bar abs. The vapor leaving the top of the distillation column is condensed and the condensate is separated into an organic phase and an aqueous phase in a phase separa tor, while incondensable gases can be disposed of, e.g. via a flare. The aqueous phase which has been separated out in this way can advantageously be recirculated to the upper part of the distillation column. The organic phase which has been separated out in this way can be utilized for energy generation or be worked up by hydrogenation to obtain products of value. The aque ous phase taken off from the bottom of the distillation column, and after cooling, can be passed to the water treatment plant. The heat of the hot aqueous phase taken off from the bottom of the distillation column can be utilized for heating the aqueous phase which is fed to the distillation column in a heat exchanger.

In a preferred embodiment, the process does not comprise a dedicated step of concentrating the aqueous phase by evaporating water. For clarification; This does not exclude evaporation of water that happens simply because of the temperature of the aqueous phase it may have in the process or in the stripping step described above. In a preferred embodiment, the process does not comprise any other process steps than those explicitly described herein.

The distillation column is preferably equipped with structured and/or random packings.

If desired, other wastewater contaminated with organic constituents can be fed to the distillation column together with the aqueous phase obtained after phase separation of the acidified wastewater for the purpose of stripping. Examples are wastewater contaminated with n-butanol, iso-butanol, n-pentanol, 2-methyl- 1 -butane-ol , 2-ethylhexanol and/or 2-propylheptanol.

Wastewater contaminated with n-butanol, iso-butanol and/or 2-ethylhexanol can be obtained during distillation, respectively with steam stripping, of the hydrogenation product obtained after hydrogenation of an organic phase consisting essentially of 2-ethylhexenal, by condensation and phase separation of the low boiler fraction. The respective organic phase can be obtained by aldol condensation of n-butyraldehyde.

Wastewater contaminated with n-butanol and/or iso-butanol can be obtained during distillation, respectively with steam stripping, of the hydrogenation product obtained after hydrogenation of an organic phase consisting essentially of n-butanal and/or iso-butanal, by condensation and phase separation of the low boiler fraction. The respective organic phase can be obtained by hydroformylation of propene.

Wastewater contaminated with n-pentanol and/or 2-methyl-1 -butane-ol can be obtained during distillation, respectively with steam stripping, of the hydrogenation product obtained by hydro genation of an organic phase consisting essentially of n-pentanal and/or 2-methyl-1-butane-al, by condensation and phase separation of the low boiler fraction. The respective organic phase can be obtained by hydroformylation of n-butene.

Wastewater contaminated with n-pentanol, 2-methyl- 1 -butane-ol and/or 2-propylheptanol can be obtained during distillation, respectively with steam stripping, of the hydrogenation product obtained after hydrogenation of an organic phase consisting essentially of 2-propylheptenal, by condensation and phase separation of the low boiler fraction. The respective organic phase can be obtained by aldol condensation of n-valeraldehyde.

In an advantageous embodiment the aqueous phase obtained after phase separation of the acidified wastewater is at least partially fed to the distillation column together with wastewater contaminated with n-butanol and/or iso-butanol. The total butanol contamination of the wastewater contaminated with n-butanol and/or iso-butanol is from 1 to 10, preferably from 7 to 9 weight percent with regard to the total weight of the wastewater contaminated with n-butanol and/or iso-butanol. The weight-ratio of wastewater contaminated with n-butanol and/or iso butanol to the aqueous phase may vary over a wide range and is preferably from 005 to 1.0 and more preferably from 0 1 to 0.25 The combined aqueous phases are introduced into the upper part of a distillation column and a stripping medium which is introduced into the lower part of the column or is generated there is conveyed in countercurrent to the downward-flowing aqueous stream. The stripping medium is preferably an inert gas under the conditions prevailing in the distillation column, e.g. nitrogen; particular preference is given to using steam as stripping medium. Distillation, respectively stripping is preferably carried out at temperatures of from 50 to 150°C. and a pressure of from 0.1 to 4 bar abs, more preferably from 0.5 to 1.5 bar abs. The vapor leaving the top of the distillation column is condensed and the condensate is separated into an organic phase and an aqueous phase in a phase separator, while incondensable gases can be disposed of, e.g. via a flare. The aqueous phase which has been separated out in this way can advantageously be recirculated to the upper part of the distillation column. The organic phase which has been separated out in this way can be utilized for energy generation or be worked up by hydrogenation to obtain products of value. The aqueous phase taken off from the bottom of the distillation column, and after cooling, can be passed to the water treatment plant. The heat of the hot aqueous phase taken off from the bottom of the distillation column can be utilized for heating the aqueous phase which is fed to the distillation column in a heat exchang er. This embodiment has the advantage that in addition to a high biodegradability, the TOC val ue of the aqueous phase taken from the bottom of the distillation column is remarkably reduced.

The process principle of an advantageous embodiment is illustrated below by way of example with the aid of the schematic drawing FIG 1 without this illustrative exposition implying any re striction in respect of the use and/or configuration of the process of the invention.

The aldolization process wastewater goes via line 1 into the static mixer 3 where it is mixed with a mineral protic acid, for example sulfuric acid, fed in via line 2 and is brought to the desired pH. The acidified aldolization process wastewater is conveyed via line 4 to the mixer 5, in the pre sent drawing a stirred vessel.

The acidified aldolization process wastewater/organic phase mixture obtained in the mixer 5 is transferred via line 8 to the phase separator 7, in the present drawing a gravity phase separator with integrated coalescence-filter, and separates there into an aqueous phase and an organic phase.

The organic phase is disposed of via line 8, for example to energy generation, while the aque ous phase is removed via line 9. The aqueous phase can be sent to water treatment plant or fed via line 11 into the upper part of a distillation column 12.

The distillation column 12 is heated by means of the circulation vaporizer 13 and for this pur pose an aldolization process wastewater stream is circulated via line 14, the vaporizer 13 and line 15 to the column. The steam generated by the vaporizer 13 strips organic impurities from the aldolization process wastewater present in the column 12 and these are discharged from the top of the column 12 via line 16 The vapor comprising steam and stripped organic compo nents is condensed in the condenser 17 and separated an organic phase and an aqueous phase in the phase separator 18 The incondensable constituents of the vapor are disposed of via line 19, for example to a flare or another incineration apparatus. The organic phase is re- moved via line 20 The aqueous phase is recirculated via line 21 to the upper part of the distilla tion column 12 and together with aldolization process wastewater fed in via line 11 is stripped in countercurrent by the steam generated by the vaporizer 13 In the steady state of the process, a substream of the stripped aldolization process wastewater taken off from the bottom of the col umn via line 14 is branched off via line 22, and passed, if optionally after further cooling, to the water treatment plant.

If the stripping column 13 is also to be utilized for stripping wastewater from other processes which comprises volatile organic constituents and does not require acidification, this wastewater is advantageously added to the aldolization process wastewater in line 10

The inventive process has several advantages over processes known in art.

In accordance to the inventive process it is possible to improve the biodegradability and to lower the TOC-value of the wastewater introduced into a conventional water treatment plant by simple means, namely acidification and phase-separation. This facilitates the work-up of the wastewater in a conventional water treatment plant as no invest in specific water treatment op erations, equipment and/or capacity expansion is needed. Additionally, the inventive process does not require any liquid-liquid extraction step of the wastewater or the aqueous phase which is obtained after phase separation. This eliminates the necessity to handle and to work-up the extraction medium which reduces the overall waste streams originating from the inventive pro cess In addition, no invest and/or equipment for liquid-liquid phase extraction and handling of contaminated extraction medium is needed.

The following embodiments are within the scope of the invention but do not limit the scope of the invention:

1 Process to reduce the contamination with Ci₂-compounds and/or Cis-compounds of wastewater from an aldolization process for the preparation of 2-ethylhexenal and/or for the preparation of 2-propylheptenal comprising a) acidification of the wastewater to a pH of 0 to 6 and b) separation of the formed organic phase from the aqueous phase, wherein the process does not comprise any liquid-liquid extraction of the wastewater and/or of the aqueous phase and wherein the Ci₂-compounds are Ci₂-hydroxycarboxylic acids, salts of Ci₂-hydroxycarboxylic acids, Ci₂-lactones or mixture of two or more of these compounds and wherein the Cis-compounds are Cis-hydroxycarboxylic acids, salts of C15- hydroxycarboxylic acids, Cis-lactones or mixtures of two or more of these compounds. 2. The process according to embodiment 1, wherein Ci2-compounds are C12- hydroxycarboxylic acids, salts of Ci2-hydroxycarboxylic acids, Ci2-lactones or mixture of two or more of the aforementioned compounds.

3. The process according to embodiment 2, wherein salts of Ci2-hydroxycarboxylic acids are sodium and/or potassium salts of Ci2-hydroxycarboxylic acids.

4. The process according to any one of the previous embodiments, wherein the temperature of the wastewater during acidification is 5 to 150°C, preferably from 10 to 60°C and more preferably from 15 to 55°C.

5. The process according to one of the previous embodiments, wherein the acidification of the wastewater is conducted under a pressure from 0,1 to 10 bar abs, preferably from 0,5 to 1 ,5 bar abs and most preferably under atmospheric pressure.

6. The process according to any one of the previous embodiments, wherein the temperature of the wastewater during formation of a separate organic and aqueous phase is from 5 to 80°C, preferably from 10 to 60°C and more preferably from 15 to 55°C.

7. The process according to any one of the previous embodiments, wherein the separation of the organic and the aqueous phase is carried out at a temperature from 5 to 80°C, preferably 10 to 60°C and more preferably from 15 to 55°C.

8. The process according to any one of the previous embodiments, wherein the residence time of the acidified wastewater for formation of the separate phases is from 0.1 to 30 minutes, preferably from 1 to 20 minutes and more preferably from 5 to 15 minutes.

9. The process according to any one of the previous embodiments, wherein the acidification of the wastewater is to a pH of 1 to 3.

10. The process according to any one of the previous embodiments, wherein the wastewater is acidified with strong pro tic acids, preferably with strong mineral protic acids and more preferably with hydrochloric acid, sulfuric acid, or nitric acid and particularly preferable with sulfuric acid. 11. The process according to any one of the previous embodiments, wherein the acidification is carried out in one or more stirred vessels.

12. The process according to any one of the previous embodiments, wherein the phase sepa ration is carried out in one or more settlers.

13. The process according to any one of the previous embodiments, wherein the phase sepa ration is carried out in one or more coalescence filters.

14. The process according to any one of the previous embodiments, wherein the acidification of the wastewater is carried out in a stirred vessel, a stream of the acidified wastewater is withdrawn from the stirred vessel and introduced into a settler, after phase formation in the settler the organic phase is at least widely withdrawn from the settler, preferably at least 95 vol.% of the organic phase are withdrawn from the settler and more preferred at least 99 vol.% of the organic phase are withdrawn from the settler and at least partly rein troduced into the stirred vessel together with fresh wastewater.

15. The process according to embodiment 14, wherein the volume of the organic phase is 20 to 50 vol.% with regard to the volume of the wastewater freshly introduced into the stirred vessel.

16. The process according to any of the previous embodiments, wherein the aqueous phase is at least partially introduced into a distillation column, wherein the distillation column is operated at a temperature from 50 to 150°C and at a pressure of 0,5 to 1.5 bar abs.

17. The process according to embodiment 16, wherein the aqueous phase is stripped in the distillation column with a stripping medium containing steam.

18. The process according to embodiment 17, wherein the stripping medium is steam

19. The process according to embodiment 16, 17, or 18, wherein the aqueous phase is com bined with another wastewater contaminated with n-butanol and/or iso-butanol before the combined wastewater is introduced into the distillation column.

20. The process according to embodiment 19, wherein the total butanol contamination of the wastewater contaminated with n-butanol and/or iso-butanol and to be combined with the aqueous phase is from 1 to 10, preferably from 7 to 9 weight percent with regard to the to- tal weight of the wastewater contaminated with n-butanol and/or iso-butanol and to be combined with the aqueous phase, and the weight ratio of the wastewater contaminated with n-butanol and/or iso-butanol and to be combined with the aqueous phase to the aqueous phase is from 0.05 to 1.0 and preferably from 0.1 to 0.25.

Examples

The following examples illustrate the invention without restricting the scope of the invention. The TOC value was determined in the following examples in accordance with EN 1484-H3 of 1997.

GC-Method for detection of C12- and/or Cis-compounds:

Example 1:

1070 g wastewater (pH 12.8) from an aldolization process for the preparation of 2-ethylhexenal with a TOC value of 12000 mg/I (biodegradability of 70% determined by Zahn-Wellens-EMPA, TOC value of Ci2-compounds 10000 mg/I) was acidified with 53 g concentrated sulfuric acid to a pH of 2. An organic phase formed and the sample was heated to 50°C. The organic phase was separated from the aqueous phase by means of coalescence filter.

The separated organic phase (10 g) contains predominantly Ci2-lactones.

The separated aqueous phase (1103 g) with a TOC value of 4700 mg/I contained 120 mg/I C12- lactones with a biodegradability of 98% determined by Zahn-Wellens-EMPA

Example 2:

1070 g wastewater (pH 12.8) from an aldolization process for the preparation of 2-ethylhexenal with a TOC value of 12000 mg/I (biodegradability of 70% determined by Zahn-Wellens-EMPA) was acidified with 53 g concentrated sulfuric acid to a pH of 2. An organic phase formed and the sample was heated to 50°C. The organic phase was separated from the aqueous phase by means of coalescence filter. The separated organic phase (10 g) contains predominantly Ci₂-lactones.

The separated aqueous phase (1103 g) with a TOC value of 4700 mg/I contained 120 mg/i C12- lactones with a biodegradability of 98% determined by Zahn-Wellens-EMPA.

The separated aqueous phase was stripped batch wise in a distillation column operated at 99 to 102 °C and at ambient pressure with steam as stripping medium.

The aqueous phase taken from the bottom of the distillation column had at TOC value of 1600 mg/I.

Example 3:

1070 g wastewater (pH 12 8) from an aldolization process for the preparation of 2-ethylhexenal with a TOC value of 12000 mg/I (biodegradability of 70% determined by Zahn-Wellens-EMPA) was acidified with 53 g concentrated sulfuric acid to a pH of 2 An organic phase formed and the sample was heated to 50°C. The organic phase was separated from the aqueous phase by means of coalescence filter.

The separated organic phase (10 g) contains predominantly Ci2-lactones.

The separated aqueous phase was mixed with 430 g of wastewater containing 34 g of n-butanol The so obtained mixture was stripped batch wise in a distillation column operated at 99 to 102°C and at ambient pressure with steam as stripping medium.

The aqueous phase taken from the bottom of the distillation column had at TOC value of 190 mg/l

Claims

1. Process to reduce the contamination with Ci2-compounds and/or Cis-compounds of wastewater from an aldolization process for the preparation of 2-ethylhexenal and/or for the preparation of 2-propylheptenal comprising a) acidification of the wastewater to a pH of 0 to 6 and b) separation of the formed organic phase from the aqueous phase, wherein the process does not comprise any liquid-liquid extraction of the wastewater and/or of the aqueous phase and wherein the Ci2-compounds are C12- hydroxycarboxylic acids, salts of Ci2-hydroxycarboxylic acids, Ci2-lactones or mixture of two or more of these compounds and wherein the Cis-compounds are C15- hydroxycarboxylic acids, salts of Cis-hydroxycarboxylic acids, Cis-lactones or mix tures of two or more of these compounds.

2. The process according to claim 1 , wherein the acidification of the wastewater is to a pH of 1 to 3.

3. The process according to claim 1 or 2, wherein a strong protic acid is used for the acidifi cation of the wastewater.

4. The process according to any one of the previous claims, wherein the temperature of the wastewater during formation of a separate organic and aqueous phase is from 5 to 80°C.

5. The process according to any one of the previous claims, wherein the residence time of the acidified wastewater for formation of the separate phases is from 0.1 to 30 minutes.

6. The process according to any one of the previous claims, wherein the acidification is car ried out in one or more stirred vessels.

7. The process according to any one of the previous claims, wherein the acidification of the wastewater is carried out in a stirred vessel, a stream of the acidified wastewater is with drawn from the stirred vessel and introduced into a settler, after phase formation in the settler the organic phase is at least widely withdrawn from the settler and at least partly re introduced into the stirred vessel together with fresh wastewater.

8. The process according to claim 7, wherein the volume of the organic phase is 20 to 50 vol.% with regard to the volume of the wastewater freshly introduced into the stirred vessel.

9. The process according to any one of the previous claims, wherein the aqueous phase is at least partially introduced into a distillation column, wherein the distillation column is op erated at a temperature from 50 to 150°C and at a pressure of 0.5 to 1.5 bar abs.

10. The process according to claim 9, wherein the aqueous phase is stripped in the distillation column with steam or with a stripping medium containing steam.

11. The process according to claim 9 or 10, wherein the aqueous phase is combined with another wastewater contaminated with n-butanol and/or iso-butanol before the combined wastewater is introduced into the distillation column.

12. The process according to claim 11 , wherein the total butanol contamination of the wastewater contaminated with n-butanol and/or iso-butanol and to be combined with the aqueous phase is from 1 to 10 weight percent with regard to the total weight of the wastewater contaminated with n-butanol and/or iso-butanol and to be combined with the aqueous phase, and the weight ratio of the wastewater contaminated with n-butanol and/or iso-butanol and to be combined with the aqueous phase to the aqueous phase is from 005 to 1.0.

13. The process according to any of the previous claims, wherein the phase separation is carried out in one or more settlers, in one or more coalescence filters, or in any combina tion of two or more of the aforementioned apparatuses.