Method for pretreating waste fat, oil and grease and co-producing first-generation biodiesel

A method for pretreating waste fat, oil and grease (FOG) and co-producing a first-generation biodiesel, comprising:

• S1, feeding waste FOG, a liquid acid catalyst, and methanol at a certain proportion into a pre-esterification reactor, and conducting pre-esterification reaction to obtain a pre-esterification mixed liquid;
• S2, removing waste residues from the pre-esterification mixed liquid after the pre-esterification reaction through a filter to obtain a filtrate, and separating the filtrate by a liquid-liquid separator to obtain an organic phase and an aqueous phase;
• S3, introducing the organic phase after the pre-esterification reaction into a methanol recovery tower I and conducting separation to obtain a pre-esterification product and crude methanol;
• introducing the aqueous phase into a methanol recovery tower II and conducting another separation to obtain a liquid acid catalyst and crude methanol;
• and purifying the crude methanol through a methanol refining tower;
• and
• S4, separating the pre-esterification product through a biodiesel refining tower to obtain a first-generation biodiesel product, and a pretreated waste FOG at a tower bottom.