The transesteriﬁcation reaction is accomplished continuously, using three reactors in series operating under mild conditions (i.e.: Temperature = 55°C and Atmospheric Pressure).
The transesteriﬁcation reaction can be presented as follows:
| (catalyst) |
CH-O-CO-R + 3CH3OH → CH-OH + 3CH3-O-CO-R
(Triglycerides) (Methanol) (Glycerol) (Methylester)
Reaction heat is negligible, and a heat supply from outside is necessary in order to keep the reaction mixture at the required temperature. Raw material is continuously fed to the three reaction steps consisting of pump, reaction vessel and relevant piping. The appropriate amount of methanol and catalyst are continuously dosed.
Methanol is fed to the reaction unit in a proper excess with respect to the stoichiometric amount with the aim to maximize the transesteriﬁcation yield and to limit as much as possible the side reaction of saponiﬁcation. Separately obtained glycerine, relatively rich in soap, is directly sent to the glycerine treatment unit. Light phase outgoing from the head of the reactor is transferred to the second reaction loop, after the addition of methanol and catalyst. Working conditions and the reaction volume of the second reactor are identical to the ﬁrst reactor. Light phase coming from the top of the second reactor is transferred to the third reactor, with previous addition of methanol and catalyst. Reaction mixture leaving from the third reactor containing the main product (methylester), the excess of methanol and the glycerine (reaction by-product) and a limited amount of soaps is sent to the methylester puriﬁcation section.
Methylester / Glycerine Separation
Reaction mixture coming from the third reactor and containing the product (methylester), the excess of methanol and the glycerine (reaction by-product) as well as the limited amount of soaps (formed by side-reaction of saponiﬁcation of methylester), is transferred to the gravity separator after a partial removal of the contained methanol. Glycerine (containing glycerine, part of the excess of methanol and almost the total amount of soaps) is sent to the glycerine treatment unit. The methylester phase coming from separator contains glycerine traces, soaps and catalyst; these impurities are removed through washing with water added up with citric acid. Methylester has to be dried to remove the remaining water and methanol.
The product- methylester is transferred to storage through the pump, after being cooled down to 30° – 40°C.
Vent Condensation And Recovery Unit
The unit is designed in order to condense all emergency vents from the upstream production unit.