Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
  • C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
  • C07C29/86—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by liquid-liquid treatment
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/25—Preparation of halogenated hydrocarbons by splitting-off hydrogen halides from halogenated hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/38—Separation; Purification; Stabilisation; Use of additives
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C21/00—Acyclic unsaturated compounds containing halogen atoms
  • C07C21/02—Acyclic unsaturated compounds containing halogen atoms containing carbon-to-carbon double bonds
  • C07C21/19—Halogenated dienes
  • C07C21/20—Halogenated butadienes
  • C07C21/21—Chloroprene

Definitions

• the present invention relates to the production of chloroprene from 3,4-dichlorobutene-1 in a two phase mixture of water and alcohol, and to the recovery of alcohol from other organic materials present in organic phases from the dehydrochlorination reaction.
• 3,4-dichlorobutene-1 with alkali in a two phase mixture of water and an alcohol at elevated temperatures is disclosed in United States patent specification 3 079 446, The chloroprene is distilled off from the reaction mixture as it is formed.
• the dehydrochlorination of 3,4-dichlorobutene-1 to give chloroprene at temperatures in the range of 40 to 70oC is disclosed in German patent specification 2 707 073.
• the process for the recovery of alkanol contained in an organic phase resulting from the dehydrochlorination of 3,4-dichlorobutene to give chloroprene is a reaction medium which is a two phase liquid mixture of water and an alcohol in the presence of a alkali is characterised by subjecting the organic phase to an extraction step with water and separating an aqueous phase containing the alcohol from the organic phase, acid being added to the extraction step in a quantity sufficient to reduce the pH of the aqueous phase to below 5.
• the reaction medium must consist of two liquid phases and the alcohol employed must be such as to give with the water two liquid phases under the reaction conditions used.
• suitable alcohols are higher alkoxyalkanols and unsubstituted alkanols for example those containing 3 to 8 carbon atoms in the molecule.
• An example of a suitable alkoxyalkanol is 2-butoxyethanol.
• Preferred unsubstituted alkanols are those containing 3 to 5 carbon atoms e.g. propanol-1 .
• the ability to form a separate liquid phase will depend on the nature of the alcohol, the relative quantities of alcohol and water, and the concentration of dichlorobutenes and chloroprene in the organic phase and of alkali metal hydroxide and alkali metal chloride in the aqueous phase, but for any given reaction mixture a suitable alcohol can be selected by simple test.
• an alcohol which, when shaken with a saturated brine solution containin 22% wt/wt NaOH at a volume ratio of alcohol to aqueous phase corresponding to that to be used in the dehydrochlorination process, forms a separate phase, which phase contains at. least 0.1% wt/wt NaOH.
• An example of a volume ratio of alcohol to aqueous phase at which the test may be carried out is 3:1. It is particularly preferred to use alcohols which give a separate phase containing at least 0.5% wt/wt NaOH in order to obtain a fast reaction rate.
• butanol-2 is not a preferred solvent, while n-butanol and 2-butoxyethanol are preferred solvents. It is particularly preferred to use 2-butoxyethanol.
• the dehydrochlorination step is usually carried out with alkaline dehydrochlorination agents and traces of these may remain in the organic phase recovered from the dehydrochlorination reaction and give rise to subsequent problems during extraction with water.
• alkaline dehydrochlorination agents does not inevitably lead to emulsification problems however, particularly if the alkali concentration in the organic phase recovered from the dehydrochlorination step is low. It is believed that problems with emulsification; are particularly likely if the organic phase has been heated to temperatures greater than 100oC, particularly 105oC, in the presence of alkali before the extraction step is carried out.
• Heating at such temperatures may occur during the dehydrochlorination step particularly if chloroprene is distilled off from the reaction mixture which is formed. Such a heating in the presence of alkali may also take place if the dehydrochlorination step is carried out at temperatures below 100oC e.g. at 40oC to 70oC and a liquid organic phase containing chloroprene is removed from the dehydrochlorination reaction and is subsequently distilled to separate the chloroprene from the other constituents of the organic phase prior to extraction with water.
• Alkali may be present during this distillation because of alkali carried over from an alkaline dehydrochlorination agent. However alkali may also be added during the distillation to protect the distillation column against corrosion.
• the present invention is particularly suitable for recovering alkanol from a bleed stream taken from the organic phase to prevent the concentration of high boiling material in the organic phase becoming excessive.
• the acid is most conveniently added to the extraction step by introducing it into the water used to carry out the extraction step. Alternatively the acid may be added to the mixture during the extraction step.
• suitable acids are strong mineral acids. such as HCL, H 3 PO4 as well as organic acids e.g. acetic.
• the nature and quantity of acid added must be sufficient to decrease the pH of the aqueous extract to below 5, preferably to below 2.
• Addition of acid may take place continuously so as to maintain the pH below 5 or may be carried out discontinuously, addition only taking place when a problem of emulsion formation arises.
• the process of the present invention may be combined with the process of our copending application (Case 4723/2727) which describes a process for the dehydrochlorination of 3, 4-dichlorobutene-1 to give chloroprene in a two phase liquid mixture of water and an alkanol in the presence of an alkali in which a bleed is taken from the organic phase and is subjected to extraction with water, the volume ratio of water and organic phase brought into contact at the first extraction step is not less than 15:1 or if the bleed is substantially free drom chloroprene, not less than 6:1.
• Figure 1 is a diagrammatic representation of apparatus suitable for carrying out the process of the invention when dehydrochlorination is carried out under conditions such that chloroprene is distilled from the reaction mixture as it is formed.
• Figure 2 is a diagrammatic representation of apparatus suitable for carrying out the process of the invention when the dehydrochlorination is carried out at temperatures such that chloroprene is retained in the liquid withdrawn from the reactor, and the chloroprene is subsequently recovered by distillation from an organic phase separated from the reaction mixture.
• a mixture of nitrogen and nitric oxide, sodium hydroxide solution, and 3,4-dichlorobutene-1 are introduced into reactor 1, provided with stirrer 2, through pipes 3, 4, and 5 respectively.
• the reactor contains a mixture of water and alkanol (e.g. 2-butoxyethanol).
• the reactor 1 is heated by heating means (not shown) to maintain the contents at a temperature such that chloroprene will distill off from the reaction mixture as it is formed. (Examples of suitable temperatures are those in in the range 90 to 105oC). Vapour passes through pipe 6 into distillation column 7 and condensate returns through pipe 8. Chloroprene is removed overhead at 9.
• the reactor 1 is provided with a stand pipe 10 through which the liquid contents of reactor 1 overflow into decanter 11, where they separate into lower aqueous phase containing dissolved NaCl, and an upper organic phase.
• the aqueous phase is discarded through pipe 12.
• the organic phase consisting of unreacted dichlorobutenes, chloroprene, and high boiling impurities is recycled through pipe 13 to the reactor.
• a bleed is taken through pipe 14 to a distillation column 70 in which the residual chloroprene is distilled overhead at 90.
• the material from the base of the distillation column is passed through line 140 to a stirred vessel 15 to which water is introduced through pipe 16.
• the resulting mixture passes through pipe 18 to decanter 17 from which a lower organic phase is separated and discarded through pipe 19.
• the upper aqueous phase containing the extracted alkanol is returned through pipe 20 to the reactor 1.
• the dehydrochlorination reactor is operated at a temperature such that the chloroprene produced does not boil off from the reaction mixture (Examples of suitabl e temperatures are 50oC to 70oC).
• Example A is a comparative Example not according to the invention. The arrangement used was thus substantially that illustrated by Figure 1. Examples 3 and 4 differ from the arrangement shown in Figure 1 in having two stages of mixing and separation instead of only one. In the Examples all the extractions were carried out at ambient temperature. Example A
• Example 2 A sample of the bleed used in Example A was washed with 12 volumes of water containing ca 0.4% by weight of hydrogen chloride and no emulsification occurred. The aqueous phase contained ca 83% of the butoxyethanol in the system and had a pH of 1.8.
• Example 2
• Example 3 Another sample of the same organic bleed as in Example A was extracted with 12 volumes of water containing 0.01% by weight of hydrogen chloride and no emulsion was produced. The separated aqueous phase pH was about 4.5.
• Example 3 Another sample of the same organic bleed as in Example A was extracted with 12 volumes of water containing 0.01% by weight of hydrogen chloride and no emulsion was produced. The separated aqueous phase pH was about 4.5.

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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (3)

• 1980
  • 1980-03-04 WO PCT/GB1980/000038 patent/WO1980001911A1/en not_active Application Discontinuation
  • 1980-03-04 JP JP50053180A patent/JPS56500098A/ja active Pending
  • 1980-09-24 EP EP80900416A patent/EP0024404A1/en not_active Withdrawn

Patent Citations (3)

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