Response Surface Methodology for Biodiesel Production Using Calcium Methoxide Catalyst Assisted with Tetrahydrofuran as Cosolvent

Table 1

Reaction condition variables and levels for CCD.

Reaction condition variables	Symbol code	Range and levels
		−2	−1	0	+1	+2
Methanol-to-oil molar ratio		6	8	10	12	14
Catalyst concentration (wt%)		1.5	2	2.5	3	3.5
Reaction time (min)		30	60	90	120	150
THF in methanol (% v/v)		4.5	6	7.5	9	10.5