Preparation of Vanillin from Sulphite Waste Liquor. Part. 1

Abstract

Oxidation process of sulphite waste Liquor to produce vanillin has been investigated about four samples, which were produced from Pinus densiflora Sieb. et Zucc. through various degree of cooking. The oxidation was carried out at a temperature range of 80 to 170°C and under the normal as well as a high pressure.Sulphite waste liquor, in which the concentration of cuastic soda was controlled to be 8 g per 75 cc, was brought into an autoclave, into which oxygen was introduced under a pressure of 10 atm., and heated at a temperature of 170°C. for three hours under rotation. The yield of vanillin thus obtained was 19.4 per cent with respect to the amounts of lignin in the waste liquor used. The later was about 5g per 75cc of it.Next, the whole process was divided into two steps, one is heating process and the other oxidation process, and the waste liquor is subjected to this two processes one after another, Thus waste liquor in the autoclave, into which oxygen was introduced under a pressure of 10 atm., was caused to be oxidized at a temperature of 90 to 95°C under catalytic action of nickel gauze and then heated at a temperature of 170°C after oxygen was removed. The yield of vanillin obtained by this method was 12.65 per cent. On the other hand, the yield of vanillin was 9.3 per cent when waste liquor was firstly heated at a temperature of 150°C for half an hour and then, as the second step, oxidized at a temperature of 100°C in the presence of cupper wire as a catalyst by introducing oxygen under the normal pressure. The same result was also attained when the first heating process was carried out at a temperature of 170°C for five minutes and was followed by the same treatment as above. However, the yield was about 7 per cent when the first heating process at a temperature of 150°C was followed by the oxidation process by cupric oxide at a temperature of 90°C under a normal pressure. In oder to keep effective contact of oxygen with the reaction solution, a new design of apparatus for oxidation process by oxygen was deviced, which might be very interesnitgf rom the industrial point of view. Nickel and cupper proved to be superior catalysts for oxidation by oxygen.The yield of vanillin obtained from sulphite waste liquor which had been produced through lower degree of cooking was larger than that of vanillin from waste liquor produced through higher degree of cooking. This suggests the facts that the degree of cooking of pulp has influence on the yield of vanillin prepared from waste liquor of it.When Tomlinson-Hibbert's method was applied to the sulphite waste liquor employed in this investigation, the yield of vanillin was only 1.5 per cent.