TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The process further comprises allowing the effluent to separate into two phases in a decanter. The heavy phase effluent from the decanter is split into two streams. One of these streams is the recycled catalyst fed to the heater prior to the first biodiesel reactor, where the fresh catalyst use is minimized. The other is sent forward, where it is combined with concentrated acid in order to neutralize the catalyst and convert any soap into fatty acids. The former (recycled catalyst) stream is 25-100 wt.% of this latter (to be neutralized) stream. The top (biodiesel) phase from the decanter is fed to the second biodiesel reactor, where more methanol and catalyst are added to complete the reaction. The effluent from the second reactor is mixed with dilute acid and sent through a mixer in order to neutralize the catalyst and convert any soaps into fatty acids. The mixer's effluent is allowed to separate into two phases in a second decanter. The top (biodiesel) phase is washed with a small amount (3.1-10% of the biodiesel stream) of warm water from the water absorber's sump tank. The water absorber removes virtually all the methanol in the vapor exiting the plant's nitrogen blanketing system, before this vapor is discharged to the atmosphere. The biodiesel and water are separated in a third decanter. The water separated in the decanter is used to dilute (via a mixer) the acid that is added to the second reactor's effluent. The biodiesel layer from the decanter is sent to intermediate storage. From here it is preheated in an economizer, then vacuum distilled to recover the excess methanol and remove water. After vacuum stripping, the biodiesel product is sent to another intermediate storage vessel via heat economization with the feed to the biodiesel vacuum distillation, cooling in a plate cooler with cooling water, and chilling in another plate cooler with chilled fluid. From this intermediate storage, the biodiesel is combined with filter aid and fed to a precoated pressure leaf filter where solid impurities in the biodiesel are removed. The filtrate is a high quality biodiesel product that is sent to bulk storage. The bottom phase from the second decanter is combined (via a mixer) with the neutralized heavy phase from the bottom of the first decanter. The glycerin rich stream is cooled, sent to intermediate storage, and then is vacuum distilled to recover the excess methanol and remove most of the water. The vacuum distillation vessel has a steam sparge at its bottom, where methanol removal is maximized without removing excessive water. The effluent from the vacuum stripping is commodity grade crude glycerin, which is sent to product storage via heat economization with the feed to the glycerin vacuum distillation. The vacuum distillation overheads from the biodiesel and glycerin streams are combined and condensed in condensers (shell and tube or plate construction) with first cooling water, and then chilled fluid. A small cooled recycled water stream from the previously described water absorber sump tank is introduced to the vapor fed to the first (cooling water) condenser via a spray nozzle in order to pre-condense the vapors. The combined condensate from both condensers is sent to intermediate storage prior to processing by the methanol rectification system. Uncondensed vapor leaving the second (chilled fluid) condenser is sent through to the absorber that the incoming triglyceride is fed to. The methanol rectification system is run continuously. Wet methanol feedstock is preheated with a first economizer, and then with steam. The preheated wet methanol is then fed to the middle of the rectification column. In the rectification column, the methanol is purified to at least 99.9% in the structured packing above the feed tray. Water is purified to at least 99.8% in the structured packing below the feed tray. Most of the purified water is circulated through the reboiler and returned to the bottom of the rectification column. The rest of the purified water is cooled and either recycled to the water absorber sump tank described above or sent for use elsewhere. The volatilized purified methanol leaves the top of the rectification column as vapor and is condensed in condensers (shell and tube or plate construction) with first cooling water, and then chilled fluid. A portion of the condensed methanol is returned to top of the rectification column as reflux. The balance of the condensed methanol is cooled and reused in the biodiesel process. Non-condensibles leave the second (chilled fluid) condenser and are sent through the absorber that the incoming triglyceride for the biodiesel plant is fed to.