Table 1. Experimental Domain with Natural and Coded Values of Independent Variables Used in Box-Behnken Design (BBD) for Transesterification Reaction.

variable	unit	symbol/code	coded variable level
			level 1	level 2	level 3
			–1	0	+1
reaction temperature	°C	A	55	65	75
methanol-to-oil molar ratio		B	10	20	30
catalyst loading	wt %	C	3	6	9