J. Weineck (specification No. 1289 of 1881) avoids the use of both chloride and sulphate of sodium in soapmaking as follows: - He exposes fats in a cylindrical wrought-iron vessel, fitted with a stirring gear, and provided with a jacket which is filled with hot water. At 113° F. (45° C), the tallow (when that fat is used) melts, and then 20 per cent, of a 2 per cent, solution of soap at the same temperature is added to the fats, stirring meanwhile. When the mass is perfectly emulsified, caustic lye of the same temperature is added. When well mixed, the temperature is raised to ahout 194° F. (90° C), and the stirrer is kept at work until saponification is completed. After some hours, the spent lye is let off, and registers 5° to 10° B. Operating thus, he claims to utilize some chemical heat evolved in the action of the lye upon the emulsified fats, and by saponifying the fats in this globular state he says he saves fuel, time, labour, cost on plant, and, above all, obtains lyes free from any large amount of salts. But even in this process, assuming it works otherwise satisfactorily, it would appear that the alkaline lye must be neutralized with an acid before concentration, otherwise the glycerine would suffer decomposition.
Perhaps in such a case, however, carbonic anhydride could be profitably employed.
The most curious specification is that (No. 2176 of 1881) of P. J. Baptiste Depoully and Leon Droux, of Paris. These gentlemen neutralize the spent lyes with any acid, filter, evaporate, remove the deposited salts, and heat the mother-liquor in contact with oleic acid or other fatty acids at a temperature of 338° to 347° F. (170° to 175° C.) In this way they reproduce fats which are washed, and subsequently decomposed by means of lime, or by superheated steam, with or without the aid of sulphuric acid. When lime is employed, the soap thus produced is afterwards decomposed by the agency of an acid; or, instead of using free fatty acids, the patentees employ neutral fats and oils in their process, thus giving rise to the formation of diacid and monacid glycerides. In brief, the whole of their proposals are based upon the well-known classical investigation of Berthelot, but it is not easy to see in what precise manner they can be economically carried out in commercial practice.
Reviewing these various specifications, the different processes described therein are designed to effect the following objects: -
1. To remove or destroy albuminous and resinous matters, together with any residual soap contained in spent soap-lyes.
2. To facilitate the removal of tbe salt, either by employing means to diminish the solubility of chloride of sodium, in cases where that substance is used, or to substitute for it another, which may be more readily and profitably removed.
3. To economise the cost of concentrating the purified lyes to that point at which the glycerine may be at once employed for certain purposes in its then crude condition, or still further purified by distillation.
Kingzett very much questions whether the alkali, utilized by the carbonic anhydride process would pay for the cost of the gas necessary to be employed, except, perhaps, in conjunction with Wei neck's process; and he equally doubts whether the cost and trouble of increasing the insolubility of chloride of sodium in glycerine liquors, by the employment of hydrochloric acid, would even be balanced by the effect produced. Speaking generally, therefore, and after giving a considerable amount of practical attention to this subject, the soapmaker who wishes to recover the glycerine from spent lyes cannot do better at present, it would appear to Kingzett, than proceed to evaporate the water from the neutralized liquor in the most economical manner available, with the dual object of getting rid, by deposition and crystallization, of as much salts as possible, and of preparing the crude glycerine for distillation, and surely he can do all this without the use or infringement of any patented process - indeed, it is being done on a large scale. But there is another way of dealing with the production of glycerine already known and practised, and which will, Kingzett feels sure, be much more widely adopted in the course of time.
At present the soapmaker saponifies neutral fats and oils with caustic lye, and then, at an expensive rate, seeks to recover the glycerine left in the lees; but, theoretically speaking, he would be better advised to decompose the fats and oils, in the first place, in the manner that is practised by the candlemaker, viz., by the agency of superheated steam, with or without the assistance of sulphuric acid or lime, using the fatty acids for saponification with alkali, and obtaining comparatively pure glycerine in this direct manner. The practical objection to this procedure is that the existing plant of soapmakers is not adapted to the process, and, moreover, they cannot produce such good-coloured soaps from the fatty acids as result from the direct saponification of fats. But this is largely a sentimental objection, the soap being really equal in quality, and, so far as the objection is sound, Eingzett is confident that at the right time it will be overcome. (Jl. Soc. Chem. Ind.)
It may be remarked that Clolus's process has been in successful operation for some time at his works at Billan-court, near Paris, while additional works have been erected at Marseilles, Runcorn, and Glasgow.
H. Fleming, of Kalk, near Cologne (German patent No. 13,953 of 1880), proposes to subject the soap lyes to dialysis. In an article in the Seifen-fabricant, he points out that 4 works in the town of Neuwied alone run to waste about 1500 tons of lye per annum, which contain 75 tons of glycerine, worth about 7500/. Lyes contain between .92 and 7.8 per cent, of glycerine. Before being able to recover the latter, it is necessary to remove the sodium chloride, which is best done by osmosis. The lyes are first evaporated by steam until the liquor contains at least 20 per cent, of glycerine. It is then neutralized with sulphuric acid. The quantity of the acid required varies much, as the liquors contain from 1.9 to 19.9 per cent, of sodium carbonate. Where soda ash has been used instead of sodium chloride for the purpose of salting out, as much as 31 per cent, of alkali has been found in the lye after evaporation. It is advisable to use a slight excess of sulphuric acid, afterwards to let the liquors stand to crystallize, and then to neutralize them with lime; after settling, they are further evaporated. They should now contain no less than 40 per cent, of glycerine, but may contain as much as 66 per cent. The specific gravity is about 1.28; the ashes about 13 to 16 per cent.