Table 1. Independent factors used for CCD in the transesterification of enriched glycerol and DMC with the 5%Li/MCM-41 solid catalyst (response variable is the GC yield).

Factor	Unit	Symbols	Coded factor levels
			−2	−1	0	+1	+2
Catalyst loading	wt% relative to the initial amount of enriched glycerol	A	2	3	4	5	6
DMC: enriched glycerol molar ratio	—	B	1 : 1	2 : 1	3 : 1	4 : 1	5 : 1
Reaction temperature	°C	C	70	75	80	85	90
Reaction time	min	D	60	90	120	150	180