Optimization of Process Variables in the Synthesis of Tributyl Citrate Using a Polyvinylpolypyrrolidone-Supported Brønsted Acidic Ionic Liquid Catalyst

Table 3

Experimental design and the results of the Box-Behnken design for the optimization process.

Number	Variable and level				TBC yield (%)
	1	−1	1	0		0	89.81
2	−1	−1	0	0	85.23
3	−1	0	0	−1	88.27
4	−1	0	1	0	88.57
5	−1	0	−1	0	86.52
6	−1	0	0	1	88.90
7	0	0	1	−1	89.10
8	0	0	1	1	91.93
9	0	1	0	−1	90.91
10	0	0	−1	−1	87.72
11	0	1	−1	0	90.05
12	0	1	1	0	91.79
13	0	1	0	1	91.44
14	0	−1	0	−1	87.15
15	0	0	−1	1	88.45
16	0	−1	1	0	88.20
17	0	−1	0	1	88.30
18	0	−1	−1	0	85.80
19	1	−1	0	0	89.92
20	1	0	−1	0	90.12
21	1	0	0	−1	90.22
22	1	1	0	0	91.23
23	1	0	1	0	91.42
24	1	0	0	1	91.61
25	0	0	0	0	92.05
26	0	0	0	0	92.43
27	0	0	0	0	92.70
28	0	0	0	0	92.24
29	0	0	0	0	92.60