Method for preparing biodiesel from waste oil

Abstract

The invention discloses a method for preparing biodiesel from waste grease. The method comprises the following steps: carrying out low-temperature glyceride esterification reaction, transesterification reaction, dealcoholization, glycerol sedimentation and methyl ester rectification on the raw material waste grease to obtain BD100 biodiesel; wherein the low-temperature glyceride esterification reaction procedure and the ester exchange reaction procedure both adopt a composite zinc catalyst, and the composite zinc catalyst can be directly recovered through settling separation; wherein the composite zinc catalyst is obtained by taking a zinc-containing compound, fatty acid and glycerol as reaction raw materials, reacting and then filtering. On the basis of the acid-base homologous active center of zinc, integrated catalysis of glycerol esterification and ester exchange reaction processes is realized, and the method has the characteristics of low raw material requirement, wide application range, high product yield, easiness in glycerol recovery, no generation of solid waste, recyclability and reusability of the catalyst and the like, and is suitable for industrial production. By adopting the method disclosed by the invention, the BD100 biodiesel can be economically, green, efficiently and stably produced.

Description

technical field [0001] The invention belongs to the technical field of oleochemicals, and in particular relates to a method for preparing biodiesel from waste oil. Background technique [0002] Biodiesel is an important green energy and chemical raw material because of its advantages of non-polluting, biodegradable, and wide source of raw materials. Waste oil is one of the important raw materials of current biodiesel enterprises, but the raw materials contain a large amount of free fatty acids, which must be treated to reduce acidity, and then use alkaline catalysts to catalyze transesterification to obtain biodiesel. At present, using waste oil as raw material, concentrated H 2 SO 4 The catalytic esterification method is combined with the KOH (or NaOH) catalytic transesterification method. This method has common problems such as sulfuric acid wastewater, serious equipment corrosion, incomplete acid reduction, and low yield of biodiesel products. [0003] The glycerol est...

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Problems solved by technology

[0004] However, in the actual biodiesel production process, in the glycerol esterification reaction section, higher glycerol esterification reaction temperature (generally 220-240°C) will cause problems such as oil evaporation loss, oil polymerization, glycerin polymerization, etc., resulting in biodiesel Low product yield, high organic matter content in glycerol esterification wastewater, and low glycerin recovery rate; in addition, the use of KOH or NaOH homogeneous alkali catalysts is easy to undergo saponification reaction with residual fatty acids, resulting in difficulty in separating biodiesel from glycerin and reducing Yield of biodiesel and glycerin, increase of asphalt yield, difficulty in catalyst regeneration, etc.

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