NOVELTY - Biodiesel reactor system comprises: either reactor (10) having reactor bottom discharge and top inlet, reactor recirculation line (34), reactor recirculation pump (36), and reactor nozzle (35); or reactor, pretreatment tank, line connecting reactor to pretreatment tank, pretreatment recirculation line, pretreatment recirculation pump, and pretreatment nozzle; or reactor having headspace, catch basin positioned in the headspace, alcohol drain line connected to catch basin drain, and heat exchanger connected to the alcohol drain line.    USE - The biodiesel reactor system is useful to produce biodiesel fuel.    ADVANTAGE - The biodiesel reactor has improved split efficiency and the overall yield of the biodiesel reaction due to the presence of the conical section on the bottom of the reactor. The biodiesel reactor provides a controlled cavitation, operate at relatively low pressure resulting in fewer maintenance issues and low energy usage, thus it is a simple and inexpensive.    DETAILED DESCRIPTION - Biodiesel reactor system comprises: either (a1) a reactor having a reactor bottom discharge and a reactor top inlet; (b1) a reactor recirculation line extending from the reactor bottom discharge to the reactor top inlet, where the reactor recirculation line includes a reactor recirculation line discharge; (c1) a reactor recirculation pump connected to the reactor recirculation line; and (d1) a reactor nozzle connected to the reactor recirculation line discharge, where the reactor nozzle provides backpressure to the reactor recirculation pump such that cavitation occurs in the reactor recirculation pump; or (a2) a reactor; (b2) a pretreatment tank including a pretreatment bottom outlet and a pretreatment top inlet; (c2) a line connecting the reactor to the pretreatment tank; (d2) a pretreatment recirculation line extending from the pretreatment bottom outlet to the pretreatment top inlet; (e2) a pretreatment recirculation pump connected to the pretreatment recirculation line; and (f2) a pretreatment nozzle connected to the pretreatment recirculation line discharge, where the pretreatment nozzle provides backpressure to the pretreatment recirculation pump such that cavitation occurs in the pretreatment recirculation pump; or (a3) a reactor having a headspace; (b3) a catch basin positioned in the headspace, where the catch basin includes a catch basin drain; (c3) an alcohol drain line connected to the catch basin drain, where the alcohol drain line is at least partially positioned external to the reactor vessel; and (d3) a heat exchanger connected to the alcohol drain line. An INDEPENDENT CLAIM is also included for a method of producing biodiesel comprising: (a) charging an oil feedstock to a reactor; (b) recirculating the oil feedstock in the reactor using a reactor recirculation line and a reactor recirculation pump such that the reactor recirculation pump cavitates while recirculating; (c) charging a catalyst and an alcohol to the reactor; (d) allowing the oil feedstock to split after step (c); and (e) splitting a glycerol layer from a biodiesel layer formed during step (c).    DESCRIPTION OF DRAWING(S) - The figure shows a side view schematic of the reactor with certain internal parts.    Reactor (10)    Reactor heater (22)    Recirculation line (34)    Reactor nozzle (35)    Recirculation pump (36)