1. The transesterification process: overview
Biodiesel is chemically a mixture of fatty acid methyl or ethyl esters (FAME or FAEE), obtained by reacting an oil or fat with an alcohol — usually methanol — in the presence of a catalyst, often alkaline (sodium or potassium hydroxide).
The reaction is transesterification: a triglyceride, the main component of oils and fats, reacts with three methanol molecules and releases three methyl ester molecules (the biodiesel) and one glycerol molecule.
In a process using water washing, the reaction uses excess methanol to shift the equilibrium toward the products. Glycerin separation by settling or centrifugation is followed by biodiesel washing to remove impurities and drying. Obtain the process and operating conditions for each step from the plant: do not select every pump using only the finished biodiesel description.
From a pumping standpoint, the process goes through several distinct points: feeding vegetable oil or tallow to the reactor; dosing methanol and catalyst solution; reactor recirculation; transferring the reaction product to the decanter or centrifuge; crude glycerin transfer; transferring washed biodiesel to drying; methanol recovery and return to the process; transferring finished biodiesel to storage and loading; and effluent drainage. Each point has its own material, flow, temperature and safety requirements.
2. Feedstock feeding: heated vegetable oil and tallow
Feedstock feeding is the first point of the process. Vegetable oils and animal fats have a viscosity that falls with heating, and fats such as tallow solidify below a temperature that depends on the batch composition. Use the viscosity × temperature curve and the melting point supplied by the feedstock supplier instead of generic values.
Heating of lines and pump must keep the product above that point along the whole route, including the worst ambient temperature case at the site. On the FBE, the heating chamber (CA execution) is available from 1.1/2" to 6".
Once heated, oils and fats can be pumped with the same technology; selection considers viscosity at the real pumping temperature.
For this feed, the FBE is the usual option: a positive displacement pump whose flow changes little with discharge pressure — in the 2026 table (viscosity below 1,000 SSU), the FBE 2" goes from 200 to 186 L/min between 0 and 14 kgf/cm² at 1,150 rpm — which helps dosing when reactor pressure changes along the cycle. Speed is chosen by viscosity (FBE 2026 catalog, p.5), and VFD control must respect the model speed range.
The FBCN can also be evaluated when the heated oil has low viscosity and flow is high.
3. Methanol and catalyst: volatility and classified-area operation
Methanol requires specific attention to flammability and exposure. According to NIOSH, it has a flash point of 52 °F (about 11 °C), below usual ambient temperature, a boiling point of 147 °F (about 64 °C), flammability limits of 6% to 36% in air and toxicity by inhalation, skin absorption and ingestion, with risk of optic nerve damage (blindness). A leak can form a flammable atmosphere and expose people.
The specification of methanol pumps therefore starts from the area classification and the product safety data sheet: motor and instruments with Ex certification for the zone, gas group and temperature class defined by the project; sealing chosen for containment; and equipotential grounding. When the specification requires containment, the options include a double mechanical seal with a barrier fluid defined with the seal manufacturer and, on the FBE, the magnetic coupling described in manual MTEC-01/01 for applications that allow no leakage.
On the FBCN, manual MTEC-03/00 provides an A743 CF8M stainless casing and mechanical seals according to the application, plus seal chamber execution S1, with clean liquid from an external source, indicated for toxic, aggressive or malodorous fluids. The assembly is quoted with a motor certified by the motor manufacturer according to the stated classification.
FB Bombas does not publish a single standard configuration for methanol: the arrangement is defined in the proposal, based on the product data sheet and the classification.
Warning
A methanol leak is a serious fire and exposure risk. Treat the methanol pump as a safety item: area classification, motor Ex certification, sealing arrangement with containment and maintenance procedure must be part of the specification before quotation.
4. Crude glycerin and washing: alkaline chemistry and emulsions
After the reaction, the product is a two-phase mixture: biodiesel (methyl ester) in the upper phase and crude glycerin in the lower phase, where most of the residual catalyst, soaps and excess methanol concentrate. Separation is done by decanting or by continuous centrifugation.
Crude glycerin composition, pH and viscosity vary with the process and temperature; ask for the product analysis. With an alkaline catalyst it tends to be alkaline, and the methanol it carries requires the same attention to area classification.
For crude glycerin transfer, the FBE is the usual option because of viscosity. The 2026 catalog lists an A743 CF8M stainless casing and AISI 316L stainless shafts and gears among the options, and speed follows the viscosity table.
Water washing of the biodiesel — sometimes slightly acidified to neutralize soaps — is followed by decanting and vacuum drying. The wash water pump can be an FBCN, with material defined by the water chemistry; transfer of washed and dried biodiesel can use FBE or FBCN, depending on flow, pressure and suction, with a motor suited to the area classification.
5. Methanol recovery: distillation and return to process
Excess methanol used in the reaction is recovered by distillation — usually from the biodiesel phase and the glycerin phase — and returns to the process. As methanol boils at about 64 °C at atmospheric pressure, the columns work at moderate temperature and may run under partial vacuum.
Recovered methanol is condensed, stored in a dedicated intermediate tank and re-injected into the process together with makeup methanol.
Pumps in this section follow the same safety criteria as the previous section. In condensate, reflux and bottoms of columns under vacuum, NPSH available deserves attention: the liquid is close to its boiling point, and vapor pressure at the real temperature must enter the calculation, together with the model NPSH required curve. The FBOT does not apply to these services: it is dedicated to thermal oil circulation.
6. Storage and loading of finished biodiesel
Finished biodiesel has an ANP specification — with limits such as ester content, water, contaminants, flash point and oxidation stability — that must be preserved during storage and loading. Pump and piping must not introduce water, solids or incompatible cleaning residues; check the resolution in force for the values.
Pumps at this stage handle purified product, usually at ambient temperature, without the chemistry of the previous stages.
For storage and loading, FBE and FBCN can be evaluated according to flow, pressure and suction. The area is classified by the project, considering the product and the other substances in the installation; the motor is quoted according to that classification. The configuration is similar to diesel terminals, covered in the fuel transfer guide.