GB761078A - Improvements in or relating to the preparation of alkyl acrylate esters - Google Patents

Abstract

<PICT:0761078/IV(b)/1> Alkyl acrylate esters are obtained by preparing, in the presence of a polymerization inhibitor, a mixture of acrylonitrile and a mineral oxy-acid, said acid having a concentration of from about 50 to 95 per cent and being present in quantities of from about 1.5 to 10 mols. for each mol. of acrylonitrile, continuously feeding said mixture into a primary reaction zone, passing said mixture from said primary zone to a secondary reaction zone or zones, continuously vaporizing an alkanol having from one to eight carbon atoms, and bringing together said vaporized alkanol and said mixture in a molar ratio of at least 1 of alkanol to 1 of acrylonitrile by feeding said alkanol vapour into the secondary reaction zone or zones in a direction counter to the flow of said mixture, and heating said mixture in the primary and secondary reaction zones to maintain the temperature of the mixture in said zones above the boiling-point of said alkanol and the acrylate ester that is formed. The alcohol is preferably blended with water so that a mixture of alcohol and water vapours enters the acrylonitrile oxy-acid reaction product, best yields being obtained by passing vapours containing 75 to 85 per cent alcohol and from 15 to 25 per cent water into the reaction zone. Specified mineral oxy-acids are sulphuric and phosphoric acids, sulphuric acid being preferred. Specified alkanols are methanol, ethanol, propanol, isopropanol, butanol, 2-ethyl-hexanol and n-octanol. Polymerization inhibitors mentioned are hydroquinone, phenyl beta-naphthylamine, tertiary butyl catechol and picric acid. In the Figure an alkanol is passed into a jacketed vaporizer 5 from which the alcohol vapours are passed through a diffusion disc 11 into the bottom of a secondary reaction zone 12 which contains some acrylonitrile-mineral oxy-acid mixture together with some acrylic acid ester. The alcohol vapours react with the acrylonitrile oxy-acid mixture and also strip the ester from the liquid in the reactor. The reactor 12 is jacketed and the spent reaction mixture overflow 20 is throttled by valve 21 to maintain the liquid level in the reactor at a substantially constant level. The temperature in this reactor is kept high enough to maintain the alcohol in the vapour state and to evaporate the acrylate ester formed and the alcohol and ester vapours pass through line 22 and a second diffusion disc 23 into the base of the primary reaction zone 24. The reactor 24 is also jacketed and the temperature of the reaction mixture in this zone is also maintained above the boiling point of the alcohol and acrylate ester and the vapours pass into fractionating column 32 and condenser 23 where they are liquefied and drawn off. In the meantime an acrylonitrile mineral oxy-acid mixture is fed continuously at controlled rates from pre-mix tank 34 into reactor 24 where the acrylonitrile oxy-acid mixture reacts with the unreacted alcohol entering through the diffusion disc 23, the ester formed together with unreacted alcohol passing into the fractionating column and condenser whilst the partially reacted acrylonitrile oxy-acid mixture overflows through pipe 42 and enters the lower portion of reactor 12. Examples are given for the production of ethyl and methyl acrylates using the aqueous alcohol and sulphuric acid. In the case of the C1-C4 alcohols the temperature in the primary reaction zone is preferably 130-155 DEG C. and in the secondary zone or zones is preferably 120-180 DEG C.