Method for circulating preparation of biodiesel

Abstract

The present invention discloses a method for circulating preparation of biodiesel. The method comprises that: (a) glycerol and a free fatty acid are subjected to an esterification reaction under a high temperature and low pressure environment so as to obtain a glyceride mixture; (b) the glyceride mixture, low carbon alcohol and an alkaline catalyst are mixed and are subjected to a transesterification reaction, and phase separation is performed after completing the reaction so as to obtain a biodiesel solution and a glycerol solution; (c) an acid solution is adopted to neutralize the glycerol solution so as to produce salt precipitate; (d) the glycerol solution obtained in the step (c) is filtered to remove the salt precipitate; and (e) the glycerol solution obtained in the step (d) is heated to remove the low carbon alcohol and the water so as to obtain the purified glycerol product. According to the present invention, the esterification reaction can be performed without additionally addition of the acid catalyst, and the glycerol product can be recovered to carry out circulating preparation of the biodiesel so as to reduce the biodiesel production cost.

Description

technical field [0001] The invention relates to a method for preparing biodiesel in circulation, in particular to a method for preparing biodiesel by using oil with high free fatty acid content as raw material and glycerol as alcohols for esterification reaction. Background technique [0002] The price of raw materials is the main factor affecting the cost of biodiesel (biodiesel). Waste cooking oil and non-edible animal and vegetable oils have become biodiesel raw materials with development prospects due to their low cost. However, these low-cost raw materials usually contain high free fatty acids (FFAs), and cannot be directly subjected to alkali-catalyzed transesterification (transesterification). At present, a two-stage process is commonly used to produce biodiesel from high-content free fatty acids: first, acid esterification, and then alkali-catalyzed transesterification. The acid-catalyzed esterification method uses a homogeneous liquid acid catalyst or a heterogeneo...

AI Technical Summary

Problems solved by technology

In summary, the prior art all carries out the esterification process with acid catalysts, yet, there are some disadvantages in the preparation of biodiesel by acid catalysts for esterification: (1) use homogeneous acid catalysts (such as sulfuric acid, hydrochloric acid and p- Toluene sulfonic acid, etc.), has problems such as difficult separation of catalyst and product, difficulty in catalyst recovery and treatment, corrosion of equipment, waste water treatment, environmental pollution, etc.; (2) If a solid acid catalyst is used instead of a liquid acid catalyst, although it can improve corrosion, pollution, and Separation and other issues

But the disadvantage is that the life of the catalyst is not long, the production cost is high, and if it is used in oil products with poor quality, the catalyst will easily lose its activity.

(3) Carry out the esterification reaction with methanol as the alcohol of the esterification reaction. It is difficult to remove water during the reaction process, so a large amount of methanol is required to facilitate the reaction and the reaction time is longer

In addition, it is not easy to recover the remaining methanol from the reaction, which will consume a lot of energy and time

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