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Table 3 Equations for the dependent variables (gross calorific value, extraction yield and amount of hemicelluloses extracted) as a function of the independent variables (acid concentration and temperature)

From: Tagasaste, leucaena and paulownia: three industrial crops for energy and hemicelluloses production

Equations R2 Snedecor’s F-value
Tagasaste
 (1) GCV = 19 603.0 + 77.8 XC + 587.5 XT + 212.9 XCXC + 365.9 XTXT 0.99 812
 (2) Yield = 69.3 − 11.4 XC − 3.7 XT − 3.5 XCXC − 3.9 XTXT + 5.8 XCXT 0.99 211
 (3) HE = 62.5 + 10.8 XC + 12.2 XT − 2.1 XCXC + 12.0 XTXT − 8.5 XCXT 0.99 325
Leucaena
 (4) GCV = 19 315.5 + 82.8 XC + 274.8 XT + 218.7 XTXT 0.97 115
 (5) Yield = 66.4 + 5.7 XC − 7.1 XT + 4.7 XCXC − 0.6 XCXT 0.99 1460
 (6) EH = 55.2 − 1.2 XC + 14.8 XT + 7.5 XTXT + 3.5 XCXT 0.99 1633
Paulownia trihybrid
 (7) GCV = 20 186.6 + 318 XC + 480.6 XT + 221.8 XCXC + 77.8 XTXT − 52.2 XCXT 0.99 325
 (8) Yield = 54.5 − 4.5 XC − 4.5 XT − 3.8 XCXC + 5.2 XCXT 0.96 51
 (9) EH = 57.6 + 17.5 XC + 10.8 XT + 16.5 XCXC − 7.7 XCXT 0.98 214
  1. GCV Gross Calorific Value, HE amount of hemicelluloses extracted, XC acid concentration, XT temperature
  2. The differences between the experimental values and those estimated using the equations never exceeded 5% of the former
  3. The independent variables are expressed in coded units (Eq. 1)