Abstract: The present invention relates to a microbiological process for the production of citric acid by assimilation of .alpha.-olefins, normal paraffins and their mixture. This process is carried out by culturing the microorganisms selected from the group of Candida tropicalis, Candida lipolytica, Candida intermedia and Canida brumptii and their mutants and their variants under higher concentration of dissolved oxygen than that in ordinary aeration in the culture medium. The concentration of dissolved oxygen in the culture medium is suitable in the range of from 5 to 40 ppm, preferably from 10 to 30 ppm on the weight basis of said culture medium in this invention.There is many means of which increase the dissolved oxygen in the culture medium.

Abstract: The present invention relates to a suppressing method of iso-citric acid formation in producing citric acid from hydrocarbons by fermentation.This process is carried out by culturing the microorganisms selected from the group belonging to Candida tropicalis, Candida lipolytica, Candida intermedia and Candida brumptii and their mutants and variants in the culture medium containing paraffinic and olefinic hydrocarbons and their mixture as carbon source under aerobic conditions, wherein specific non-ionic surface active agent is added to said culture medium.The specific non-ionic surface active agent added to said culture medium is selected from the group of sorbitan fatty acid esters and polyoxy-ethylene sorbitan fatty acid esters. The amount of specific surface active agent added to said culture medium is enough from 0.005 to 0.5 percent by weight, preferably from 0.02 to 0.2 percent on the weight basis of said culture medium.

Abstract: This invention relates to a process for effectively and completely converting into a useful hydrocarbon oil comprising naphtha, kerosene and gas oil with high cracking rate, the tar-sand bitumen and the vacuum residues from various petroleum or origins which are difficult to treat in comparison with the ordinary crude oil and contain large amount of asphaltenes and resins according to the combined process of the thermal cracking and hydrocracking.The present invention is useful to manufacture the pollution-free product oil from the tar-sand bitumen and the vacuum residues from the various petroleum origins with high desulfurization percentage of more than 90%. The product oil can be used as the superior fuel oil having less sulfur and metal contents and also as the starting material suitable for the secondary processing.