Use of a non-inflammible solvent mixture for the extraction of tung oil
Tung oil, an important drying oil, is used in considerable amounts by the paint and varnish, linoleum, and electrical industries. At present domestic tung oil is obtained by mechanical expression. The cake which remains after expression has an oil content of from four to five per cent. Although the amount of domestic oil produced is a small part of the oil consumed in this country, tung oil shipments from China have ceased and the treatment of present and future domestic tung nut crops to obtain the maximum amount of oil most economically is a problem of considerable importance.
Solvent extraction has proven more efficient and economical ln industries such as soybean and cottonseed oil extraction. It appeared feasible that tung oil might be extracted by analogous methods thus decreasing the loss of oil in the cake and increasing the efficiency and economy of tung oil production in the United States.
First Soxhlet extractions of ground tung kernels were performed with ethyl alcohol, benzene, carbon tetrachloride, chloroform, hexane, and toluene. Of the flammable solvents, benzene extracted the most oil, 51.7 per cent. Hexane was next in oil extraction with 50.8 per cent. In the non-inflammable class, carbon tetrachloride extracted the most oil, 47.8 per cent.
The compositions of non-inflammable mixtures of carbon tetrachloride with hexane and benzene were determined in a Cleveland open cup tester. A non-inflammable mixture of carbon tetrachloride-benzene (70 per cent and 30 per cent by volume respectively) was more economical than either a non-inflammable carbon tetrachloride-hexane mixture or carbon tetrachloride used alone. Consequently the carbon tetrachloride-benzene mixture was selected as the solvent to use in continuing the investigation.
Higher extraction efficiencies were obtained for batch extractions at 22 deg. C. with raw tung kernels than with roasted tung kernels. The highest extraction efficiency was obtained with raw tung kernels at 40 deg. C. for a batch extraction of 90 minutes.
Since the efficiencies of batch extraction are limited, preliminary investigations of the feasibility of using countercurrent extractors were made. These studies showed that the Allis-Chalmers and Ford type extractors were not applicable to the extraction of tung kernels with the carbon tetrachloride-benzene mixture since the tung kernels, as prepared, floated in the solvent mixture. The Allis-Chalmers extractor which depends upon the downward flow of the material being extracted against the upward flow of solvent would therefore not be suitable. Similarly the Ford type extractor would not be applicable because the solvent would have to travel downward against the natural tendency of the oil being extracted and the oil-solvent solution formed to flow upward since they would be lighter than the original solvent mixture.