NOVELTY - Producing glycerin from biodiesel feedstock comprises: filtering biodiesel feedstock; separating water from filtrate (105); distilling the dried filtrate (109); distilling the distillate (111); repeating distilling the dried filtrate and distilling the distillate steps, one or more times; passing the final distillate via an ion exchange resin; contacting methanol, a solid heterogeneous esterification or transesterification catalyst; separating water and methanol; contacting at a temperature of less than 102 degrees F (38.89 degrees C); separating water, glycerin and methanol; and distilling the glycerin.    USE - The method is useful for producing glycerin from biodiesel feedstock (claimed).    ADVANTAGE - The method: provides methanol with purity of at least 99.9%; provides esterification reaction product with high yield of greater than 99.8%; and exhibits improved operability, flexibility, and biodiesel and/or glycerin purity in a cost-effective manner.    DETAILED DESCRIPTION - Producing glycerin from biodiesel feedstock comprises: filtering the biodiesel feedstock, and removing from the feedstock solid particles having a diameter of up to 2 microns, to provide a filtrate (105) and a retentate (107); separating water from the filtrate, to provide a dried filtrate (109); distilling the dried filtrate, to provide a distillate (111) and a residue; distilling the distillate to provide a subsequent distillate and optionally a subsequent residue (113); repeating at least one of distilling the dried filtrate and distilling the distillate steps, one or more times, by distilling the subsequent distillate, to obtain a final distillate; passing the final distillate through an ion exchange resin; contacting methanol, a solid heterogeneous esterification or transesterification catalyst immobilized on a solid support and the final distillate, where the contacting step is carried out under conditions to provide an esterification reaction product comprising biodiesel, methanol, water, glycerin, optionally free fatty acids or triglycerides, and a subsequent esterification reaction product; separating water and methanol from the esterification reaction product, where the methanol separated from the esterification reaction products or transesterification reaction products is purified to at least 99.9 wt.%, and is employed in a subsequent esterification, and/or transesterification; contacting at a temperature of less than 102 degrees F (38.89 degrees C); separating water, via distillation, glycerin and methanol from the transesterification reaction product; and distilling the glycerin, and passing through activated carbon, to provide a purified glycerin.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a pretreatment of biodiesel feedstock.    Filtrate (105)    Retentate (107)    Dried filtrate (109)    Distillate (111)    Subsequent residue. (113)