Variables Level -1.414 -1 0 1 1.414 Catalyst amount X1 (°C) 2.17 3 5 7 7.83 Biomass to solvent ratio X2 (w/v, mL) 1:7.93 1:10 1:15 1:20 1:22.07 Exp No. Code value Experimental value     X1 X2 X1 X2   Y (%) 1 -1 1 3 1:20   59.31 ± 2.62 2 1 1 7 1:20   61.56 ± 1.59 3 1 -1 7 1:10   45.14 ± 4.59 4 -1 -1 3 1:10   53.60 ± 1.91 5 0 0 5 1:15   60.77 ± 0.84 6 -1.414 0 2.17 1:15   55.14 ± 3.83 7 0 1.414 5 1:22.07   70.86 ± 4.78 8 1.414 0 7.83 1:15   49.16 ± 3.15 9 0 -1.414 5 1:7.93   52.19 ± 2.77 10 0 0 5 1:15   60.02 ± 3.69 11 0 0 5 1:15   57.25 ± 2.00 12 0 0 5 1:20   59.94 ± 2.52 13 0 0 5 1:20   60.77 ± 0.84

Table 1: Values of independent variables and treatment conditions by the central composite experimental design (% w/w, base on lipid weight).