Patent GB-531001-A (GB)
Title: Improved production of acrolein
IPC: C07C45/28
Filed: 1939-07-07
Abstract: 531,001. Acrolein. ACROLEIN CORPORATION. July 7, 1939, No. 19897. Convention date, July 27, 1938. Drawings to Specification. [Class 2 (iii)] In the production of acrolein by the absorption of propylene in hot, acid mercuric sulphate reagent (Deniges' reagent) and decomposition of the resulting intermediate product formed, a large excess of propylene is reacted in intimate contact with the reagent to form substantially the maximum amount of the intermediate product, the acrolein formed by decomposition of the intermediate product is rapidly removed with a current of propylene and the mixture of acrolein vapour and propylene is subsequently treated to recover the acrolein and to separate the propylene for further use in the process. In a batch process described, two or more reaction chambers are operated alternately or intermittently and the products are worked up in successive batches. Excess propylene is distributed through the body of the reagent heated to a suitable temperature, with the formation of the intermediate product which is kept in a state of suspension along with the reagent by the propylene stream. The acrolein formed by the decomposition of the intermediate product after a short time at the temperature of the reaction, is swept away by the excess propylene and passed up through a packed stripping tower down which cold water is run. The propylene passes out of the top of the tower and may be returned for re-use, while the acrolein dissolved in water is further heated in a stripping or distilling tower, which may be made up of fractionating plates, with the liberation of substantially anhydrous acrolein. Acrolein may also be separated from its mixture with propylene by cooling to liquefy the acrolein. The acid sludge from the reaction chambers is passed into a sufficiently large number of electrolytic cells, which may be operated alternately, to re-oxidize it, and then returned for re-use. By introducing the sludge into the anode chamber of a diaphragm cell and by using a fairly high current density the sludge is oxidized with the conversion of the mercurous sulphate precipitate into mercuric sulphate in solution and at the same time organic matter present is also oxidized; alternatively, mercurous sulphate may be separated from the acid mother liquor and oxidized separately, e.g. with nitric acid or by roasting in the presence of excess oxygen, and then mixed with the separately oxidized acid mother liquor or with fresh sulphuric acid. A continuous process is also described in which the preheated reagent is sprayed into a spraying tower with a concurrent flow of propylene in excess. The acid sludge containing the intermediate product is pumped to the top of a second tower at such a rate that by the time it reaches the tower the acrolein will have been liberated to a large extent, and again sprayed, this time in countercurrent to a rapid stream of propylene which carries off the acrolein which in turn is isolated as described above. The excess propylene from the first spraying tower is scrubbed for acrolein and returned for re-use along with the propylene from purification of the acrolein, while the acid sludge from the second spraying tower is regenerated electrolytically and also recycled. The initial reaction between the propylene and the acid mercuric sulphate reagent can be carried out at atmospheric pressure or somewhat high pressure, e.g. 2 or 3 atmospheres and at temperatures advantageously around 85‹C., but generally not higher than about 105‹C., while the second stage may be carried out at the same or a somewhat lower temperature. Instead of using propylene for sweeping acrolein out of the reaction mixture, any gas or vapour which does not destroy acrolein may be employed, e.g. water vapour, carbon dioxide, nitrogen or suitable hydrocarbons.