The invention provides a method for preparing
biodiesel from microalgae. The method comprises the following steps of: a. changing collected microalgae from the wet
algae into
algae block or
algae powder; b. mixing a catalyst into low-carbon
alcohol, directly adding the algae block or the algae
powder obtained by the step a, and carrying out ester exchange reaction to prepare the
biodiesel; c. after the reaction is stopped, adding an
organic solvent for extracting reaction solution which is divided into
organic solvent phase used for extraction, low-carbon
alcohol water-adding phase and algae mud; and d. after the extraction is completed, collecting the
organic solvent phase used for extraction, removing the organic
solvent by
distillation, and obtaining oily liquid, namely crude products of the
biodiesel. After preparing the biodiesel, the steps that the low-carbon
alcohol water-adding phase is used circularly after dewatered by a
solid drying agent, and the produced algae mud is used for producing
biogas by biological
fermentation are added. The invention completes the oil extraction of microalgae and
biodiesel production by one step, simplifies the technique steps and equipment, saves cost; the sulphuric acid and low-carbon alcohol used for production can be recovered, then dewatered by
drying, then utilized repeatedly, the cost is reduced, the final product is neutral, does not need washing and reduces the
downstream processing pressure; and simultaneously,
chlorophyll is mainly concentrated in the low-carbon alcohol, reduces the interference of the
chlorophyll to the color of the product and does not need the step of decoloring.