NOVELTY - A vessel (200) for forming fatty acid esters comprises sealable input (202) to enter alcohol and lipid-containing substance; body that surrounds an interior, and is robust at a temperature greater than 200 degrees C and a pressure greater than 5 mPa; porous structure (201) that comprises at least one of transition metal, transition metal oxide or silicate, or oxide or silicate of aluminum, silicon, magnesium or calcium; and sealable output (203) to exit glycerol and fatty acid esters. The porous structure occupies more than half of the volume of the interior.    USE - For forming fatty acid esters (claimed) (including esters of valeric acid, caproic acid, enanthoic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptedecylic acid, stearic acid, nonadecanoic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, heptacosanoic acid, montanic acid, melissic acid, lacceric acid, crotonic acid, isocrotonic acid, undecylenic acid, oleic acid, elaidic acid, cetoleic acid, erucic acid, brassidic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, propiolic acid, stearolic acid, nervonic acid, ricinoleic acid, (+)-hydnocarpic acid and (+)- chaulmoogric acid) which are used in fuels such as a fuel for diesel engine, base oil for lubricant oil and additive for fuel oil, and biodiesel.    ADVANTAGE - The vessel is biofuel production vessel; and is economical and environmentally-friendly for handling wastes such as agricultural facility byproducts, livestock production facility waste, livestock processing facility waste and food processing facility waste, while producing a renewable energy source at the same time. This renewable energy source is used as a process load. The energy is generated in quantities sufficient to meet the steam load of a processing plant after start-up, without the need for any added auxiliary fuel. The energy produced can additionally or alternately be commercially sold and/or used to generate electricity. Thus provides operational flexibility. The incorporation of the porous materials in the vessel also allows improvement of product yields compared to operation of the vessels without inclusion of these materials.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method of acquiring fatty acid esters involving introducing alcohol and lipid-containing substance into the vessel, optionally with co-solvent, where the vessel has inner diameter of at least 2 cm and the length-to-width ratio of less than 20 to 1; maintaining the vessel at or near the supercritical conditions of the reactant mixture, where the supercritical conditions react the alcohol and lipid-containing substance to form glycerol and fatty acid esters; and acquiring the fatty acid esters; and    (2) method of producing fatty acid esters involving reacting lipid-containing substance with an alcohol, optionally with co-solvent, in a reaction vessel under near critical or supercritical reaction conditions; and producing fatty acid esters from substances exiting the output of the vessel.    DESCRIPTION OF DRAWING(S) - The figure shows an exemplary vessel of the invention comprising a porous structure.    Vessel (200)    Porous structure (201)    Sealable input (202)    Sealable output (203)    Regulator (204)