NOVELTY - In the production of fatty acid esters (FAE) and glycerol (GL), by transesterifying a vegetable or animal oil with an aliphatic monohydric alcohol (MHA) over a solid heterogeneous catalyst to give effluent containing at least FAE, free GL and GL bonded to MHA, at least part of the effluent is treated to separate FAE and bonded GL using membrane(s) permeable to water, MHA, FAE and GL but impermeable (or almost impermeable) to mono-, di- and triglycerides.    USE - The process is useful for converting vegetable or animal oils (e.g. rape, sunflower, soya or palm oil) into lower alkyl esters (FAE) for use as biofuels, especially diesel. Glycerol (GL) is also recovered.    ADVANTAGE - In comparison with the parent process (described in EP1352893), inclusion of the membrane separation stage markedly reduces operating costs by reducing (i) the amount of alcohol (MHA) and/or catalyst required, (ii) the amount of MHA to be evaporated and condensed and (iii) the amount of steam consumed and cooling required in the evaporation and condensation stages.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a plant for carrying out the process, comprising dryer(s) (1) into which the starting oil is introduced; first transesterification reactor(s) (2), having an inlet with dried oil supply line(s) and alcohol (MHA) supply lines; MHA evaporator(s) (3), downstream of the reactor, with an outlet leading to a condenser (4) for evaporated MHA and a line for evacuated of the MHA-depleted phase; separator(s) (6) for the glycerol (GL)-rich and ester (FAE)-rich phases; membrane separation unit(s) (12) downstream of the separator(s), in which the FAE-rich stream is separated into a retentate (E1) comprising mono-, di- and triglycerides and a permeate (E2) comprising MHA, water, FAE and GL; optionally a second transesterification reactor (7) downstream of the membrane separator; collector(s) (5) for fresh and/or recycled MHA; and optionally a purification section comprising an alcohol evaporator (8), insoluble GL separator (10) and/or final purifier (11).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of an oil transesterification procedure, in which retentate obtained by membrane separation is supplied to a first reactor and the permeate is subjected to a second reaction stage.    Dryer (1)    First conversion reactor (2)    Evaporator (3)    Alcohol condenser (4)    Buffer vessel for alcohol storage (5)    Decanter vessel, as phase separator (6)    Second conversion reactor (7)    Alcohol evaporators (8)    Condenser (9)    Decanter, as insoluble glycerol separator (10)    Final purifier (11)    Membrane separation unit (12)    Starting oil (A)    Recycled alcohol introduced before first reactor (B)    Mixture of esters, alcohol, glycerol and glycerides (C)    Liquid concentrated by evaporation (D)    Ester-rich upper phase (E)    Retentate (E1)    Permeate (E2)    Glycerol-rich lower phase (F)    Recycled alcohol introduced before second reactor (G)    Effluent from second reactor (H)    Alcohol-depleted liquid (I)    Glycerol phase (J)    Crude ester phase (K)    Final purified ester stream (L)    Supply of fresh methanol (M)