Methanol is commonly used in the transesterification step in the production of biodiesel. In this process, the methanol is reacted with vegetable or animal fats to produce a usable fuel. Methanol can become saturated with water in this process. To keep costs down and lower waste, it is important to dehydrate the methanol in order to produce reusable methanol. This mixture frequently must go through a methanol dehydration step in order to be reused.
Dehydration of methanol is performed by molecular sieve dehydration units (MSDUs). The wet methanol passes through a vessel filled with molecular sieve beads. Each bead is covered with small pores on its surface. The pore sizes (usually 3A) are small enough to allow water (2.6A) to pass through but not methanol (~4.5A). The sieves absorb the water and allow the methanol to pass through the bed.