Table 2.

BBD and the response values for the PA yields

Run	X1 (Acid solution/raw material, mL/g)	X2 (HCl concentration, mol/L)	X3 (Extraction time, h)	Response (PA yield, %)
1	−1	−1	0	1.86
2	0	−1	1	2.11
3	−1	1	0	1.94
4	0	0	0	2.14
5	−1	0	−1	1.92
6	1	0	−1	2.01
7	0	0	0	2.13
8	1	−1	0	2.01
9	0	1	−1	2.04
10	0	0	0	2.13
11	1	1	0	2.09
12	0	1	1	2.06
13	0	0	0	2.14
14	0	−1	−1	1.94
15	0	0	0	2.14
16	1	0	1	2.05
17	−1	0	1	2.01