Coupling process for producing biodiesel from waste fog

A coupling process for producing biodiesel from a waste FOG comprising:

• a step S1 of preheating and dissolving a waste FOG charging the dissolved waste FOG into a filter (1) to remove solid impurities, and charging the filtrate and a certain amount of a short-chain alcohol and a liquid acid catalyst into a pre-esterification reactor (2) for a pre-esterification reaction to generate a pre-esterified mixture;
• a step S2 of charging the pre-esterified mixture into a liquid-liquid separator (3) for liquid-liquid separation to separate out an aqueous phase and an organic phase, separating the organic phase using a second flash separator (5) to obtain a pre-esterification product I and an alcohol solvent, and charging the pre-esterification product I into a water scrubber (6) to remove metal ions to obtain an esterification product II;
• a step S3 of pre-hydrogenating the esterification product II, an oil-soluble hydrogenation catalyst, a vulcanizator, and hydrogen gas in a suspended-bed reactor (7) to generate a product I;
• a step S4 of charging the product I into a gas-liquid-solid separator (8), and passing the separated components through a desulfurization adsorption tower (9) and a first pressure swing adsorption tower (10) for recycling and collection of the hydrogen gas and the hydrogenation catalyst, to obtain an oil phase product I;
• a step S5 of mixing the oil phase product I and hydrogen gas, charging the mixture into a fixed-bed reactor (20) for a deep deoxygenation reaction to obtain a mixed product I, and separating the mixed product I using a first gas-liquid separator (30) to obtain an oil phase product II;
• a step S6 of mixing the oil phase product II and hydrogen gas, and charging the mixture into a hydroisomerization reactor (50) for an isomerization reaction under an action of a catalyst, to generate a product II;
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• a step S7 of charging the product II into a second gas-liquid separator (60) to separate out a gas phase and a liquid phase, and charging the liquid phase product into a fractionation tower (80) to separate out isomerized biodiesel and an aviation fuel product.