NOVELTY - Method for converting by-products and intermediates of biodiesel and biobutanol production into fuel mixture involves converting by-products and intermediates of biodiesel and biobutanol production into fuel by an acid-catalyzed acetal-forming reaction. The oxo component of acetal-forming reaction is 2 or more acetone produced in biobutanol production, acetone, aldehyde, acetaldehyde or butyraldehyde obtained by oxidation of alcohol produced in biobutanol production and/or formaldehyde produced in methanol oxidation of waste remained in the biodiesel production.    USE - Method for converting by-products and intermediates of biodiesel and biobutanol production into fuel mixture (claimed).    DETAILED DESCRIPTION - Method for converting by-products and intermediates of biodiesel and biobutanol production into fuel mixture involves converting by-products and intermediates of biodiesel and biobutanol production into fuel by an acid-catalyzed acetal-forming reaction. The oxo component of acetal-forming reaction is 2 or more acetone produced in biobutanol production, acetone, aldehyde, acetaldehyde or butyraldehyde obtained by oxidation of alcohol produced in biobutanol production and/or formaldehyde produced in methanol oxidation of waste remained in the biodiesel production. The alcohol component of acetal-forming reaction is glycerin produced in biodiesel production, ethanol, isopropanol and butanol from alcohol produced in biobutanol production, glycerin-methanol mixture remaining in biodiesel production, fractions or intermediate containing residual alcohol (ethanol and/or butanol) other than oxo compounds, or their mixtures produced in biobutanol production. In acetal-forming reaction, the molar ratio of oxo compound and alcohol is 1:1 or more, and molar ratio of oxo compound and glycerin is 1:1 or less. Strong organic or inorganic catalysts are used as acidic catalysts, preferably sulfuric acid, p-toluenesulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid, sulfonated cation-exchange resin, heteropolyacid or sulfonated inorganic oxide, preferably sulfonated zirconium, cerium or titanium dioxide.