Because LA exists in the form of calcium lactate in the conversion of
glycerol using CaO catalystwithmethanol solvent, the tedious recovery
of LA is still required, and gypsum(CaSO4) will be produced. To recover
the LA and avoid the gypsumproduction, an integrated process for alkyl
lactate production, which includes the glycerol conversion to calcium
lactate and PG in methanol/ethanol solvent and calcium lactate
transesterification with methanol/ethanol and carbon dioxide, was
studied. The refined glycerol and two types of crude glycerol (Table 1)
obtained from biodiesel industry were used as starting materials. The
conversion of glycerol in methanol/ethanol solvent to calcium lactate
and PG was conducted at the optimum condition obtained in
Section 2.3 (230 °C, 240 min, CaO/glycerol = 0.8, CuO/glycerol = 0.2,
andmethanol/glycerol=5). The subsequent calciumlactate conversion
to methyl or ethyl lactate was conducted at 180 °C/240 min or 220 °C/
240 min, respectively, based on our previous study [34]. To reach the
optimum condition, additional methanol or ethanol (molar ratio of
methanol/ethanol to glycerol at 10) were added to the reactor before
the transesterification of calcium lactate. In this study, dry ice was as
the carbon dioxide source and the amount of dry ice added in the
process was about 0.2 g. The autogenous pressure of the process
reached about 10 MPa at the final reaction temperature