The transesterification unit is designed to produce ASTM grade biodiesel by reacting low FFA oil or preesterified oils with excess methanol in the presence of a sodium methylate catalyst.
An oil drying system (Evaporator not shown) removes water and methanol after the esterification unit but prior to the transesterification system. The recovered water and methanol is condensed and sent on to further methanol recovery. This step assures that water does not get in the Biodiesel transesterification process as water leads to soap formation and other purification problems.
Transesterification Reactor Section
The transesterification reaction takes place in two stages with the glycerol by-product removed after each stage via gravity settling. Each stage features the Shockwave Power® Reactor by Hydrodynamics, as shown in the above image. Two liquid phases form during each gravity settling step. The upper layer contains biodiesel with some methanol. The lower phase contains the glycerol by-product, methanol, and catalyst.
The biodiesel purification train consists of a distillation column where the methanol is removed, followed by ion exchange, where any remaining catalyst and soaps are removed. The product is now ASTM grade biodiesel. The glycerol by-product is purified via distillation. The excess methanol is recovered from the biodiesel. The glycerol distillation columns is distilled again to remove water and recycled for use in the process.
The temperature of the preheater is controlled by sensing the oil stream exit temperature and throttling a steam flow control valve prior. The three (3) component mixture is fed to the first stage reactor where 95 wt% of the oil is converted to biodiesel.
The first stage reactor exit stream is fed to a heat exchanger which cools the biodiesel and glycerol to an appropriate temperature that facilitates good phase separation in the gravity settler where the bottom liquid phase containing glycerol, methanol, catalyst, and trace amounts of water is taken off to storage for further processing. The liquid level in the first gravity settler is controlled by sensing a signal from a level transmitter associated and the liquid phase being controlled. By adjusting a corresponding flow control valve on the appropriate drain leg such that the interface level is maintained at the desired set point.
The top phase from first settler contains biodiesel and is mixed inline with additional methanol and catalyst prior to being fed to the second heater and second stage reactor. The temperature of the preheater is controlled by sensing the multi-component exit temperature and throttling a steam flow control valve to maintain the exit temperature at the desired set point.
The second stage reactor exit stream is fed to a second gravity settler, where the bottom liquid phase containing glycerol, methanol, catalyst, and trace amounts of water and unreacted oil if present is taken off and combined with the glycerol stream from the first settler prior to being sent to the glycerol distillation column to be purified. The liquid levels in the gravity settler are controlled by sensing a signal from a level transmitter associated with the liquid phase being controlled and adjusting a corresponding flow control valve on the appropriate drain leg such that the interface level is maintained at the desired set point.
The top phase from the second stage settler is biodiesel and is sent to the biodiesel purification section.