6. MODELLING
6.8. M ODELLING RESULTS AND DISCUSSION
The modelling resulted in the following results which gave a performance index of 0.62.
Table 8: Modelling results with reaction rate constants calculated at 160ºC k10
[m3/(kmol.s)] 151.83 E1/R [K] 5121.63 k1 =
[m3/(kmol.s)] 0.72 K0
[m3/kmol] 2385.11 DH/R [K] 79.25 K =
[m3/kmol] 2195 k20
[m3/(kmol.s)] 17.48 E2/R [K] 717.82 k2 =
[m3/(kmol.s)] 8.25 k30
[1/s] 20.69 E3/R [K] 870.05 k3 =
[1/s] 8.33
The values of the reaction rate constant for each step indicated that reaction 1 proceeded slowest while reaction 2 and reaction 3 occurred at more or less the same rate. The large value of K
indicated that reaction 1 occurred more rapidly in the forward direction than in the reverse direction.
This fit may not be the optimal solution as it is a complex problem to find an optimal solution for 8 different variables.
The scatter of the data is shown in Figure 29 and Figure 30
(a) (b) (c)
Figure 29: Comparison of experimentally determined concentration and that determined by the model for (a) furfural, (b) acetic acid and (c) hydrochloric acid
From Figure 29 it was apparent that while reasonable fit of the furfural and acetic acid data could be achieved, the HCl tended to be over-predicted.
Figure 30: Contribution of each run to the total error (performance index)
Figure 30 shows that run 14 made the largest contribution to the error with 14% of the total error attributable to this run.
Run Number
0 1 2 3 4 2
4 6 8 10 12 14
Sampling time [h]
Furfural [g/L]
Run # 1
0 1 2 3 4
1 2 3 4 5 6
Sampling time [h]
Acetic acid [g/L]
Run # 1
0 1 2 3 4
5 10 15 20 25 30
Sampling time [h]
HCl [g/L]
Run # 1
0 1 2 3 4
2 4 6 8 10 12 14
Sampling time [h]
Furfural [g/L]
Run # 2
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Acetic acid [g/L]
Run # 2
0 1 2 3 4
10 20 30 40 50 60
Sampling time [h]
HCl [g/L]
Run # 2
0 1 2 3 4
2 3 4 5 6 7
Sampling time [h]
Furfural [g/L]
Run # 3
0 1 2 3 4
1 2 3 4 5
Sampling time [h]
Acetic acid [g/L]
Run # 3
0 1 2 3 4
0 5 10 15
Sampling time [h]
HCl [g/L]
Run # 3
0 1 2 3 4
1 2 3 4 5
Sampling time [h]
Furfural [g/L]
Run # 4
0 1 2 3 4
0 0.5 1 1.5 2 2.5 3
Sampling time [h]
Acetic acid [g/L]
Run # 4
0 1 2 3 4
0 1 2 3 4 5 6
Sampling time [h]
HCl [g/L]
Run # 4
0 1 2 3 4
0 5 10 15 20
Sampling time [h]
Furfural [g/L]
Run # 5
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Acetic acid [g/L]
Run # 5
0 1 2 3 4
10 20 30 40 50 60
Sampling time [h]
HCl [g/L]
Run # 5
0 1 2 3 4
3 4 5 6 7 8
Sampling time [h]
Furfural [g/L]
Run # 6
0 1 2 3 4
1 2 3 4 5
Sampling time [h]
Acetic acid [g/L]
Run # 6
0 1 2 3 4
2 4 6 8 10 12 14
Sampling time [h]
HCl [g/L]
Run # 6
68
0 1 2 3 4
0 5 10 15
Sampling time [h]
Furfural [g/L]
0 1 2 3 4
0 2 4 6
Sampling time [h]
Acetic acid [g/L
0 1 2 3 4
10 20 30 40
Sampling time [h]
HCl [g/L]
0 1 2 3 4
3 4 5 6 7 8
Sampling time [h]
Furfural [g/L]
Run # 6
0 1 2 3 4
1 2 3 4 5
Sampling time [h]
Acetic acid [g/L]
Run # 6
0 1 2 3 4
2 4 6 8 10 12 14
Sampling time [h]
HCl [g/L]
Run # 6
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Furfural [g/L]
Run # 7
0 1 2 3 4
1 2 3 4 5
Sampling time [h]
Acetic acid [g/L]
Run # 7
0 1 2 3 4
0 5 10 15
Sampling time [h]
HCl [g/L]
Run # 7
0 1 2 3 4
2 4 6 8 10 12 14
Sampling time [h]
Furfural [g/L]
Run # 8
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Acetic acid [g/L]
Run # 8
0 1 2 3 4
0 5 10 15 20 25
Sampling time [h]
HCl [g/L]
Run # 8
0 1 2 3 4
0 2 4 6 8 10 12
Sampling time [h]
Furfural [g/L]
Run # 9
0 1 2 3 4
0.5 1 1.5 2 2.5 3
Sampling time [h]
Acetic acid [g/L]
Run # 9
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
HCl [g/L]
Run # 9
0 1 2 3 4
0 5 10 15
Sampling time [h]
Furfural [g/L]
Run # 10
0 1 2 3 4
0 2 4 6 8 10
Sampling time [h]
Acetic acid [g/L]
Run # 10
0 1 2 3 4
10 20 30 40 50 60
Sampling time [h]
HCl [g/L]
Run # 10
0 1 2 3 4 0
2 4 6 8 10 12
Sampling time [h]
Furfural [g/L]
Run # 11
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Acetic acid [g/L]
Run # 11
0 1 2 3 4
0 5 10 15 20 25
Sampling time [h]
HCl [g/L]
Run # 11
0 1 2 3 4
0 5 10 15 20 25
Sampling time [h]
Furfural [g/L]
Run # 12
0 1 2 3 4
0 2 4 6 8 10
Sampling time [h]
Acetic acid [g/L]
Run # 12
0 1 2 3 4
10 20 30 40 50
Sampling time [h]
HCl [g/L]
Run # 12
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Furfural [g/L]
Run # 13
0 1 2 3 4
1 2 3 4 5
Sampling time [h]
Acetic acid [g/L]
Run # 13
0 1 2 3 4
0 2 4 6 8 10 12
Sampling time [h]
HCl [g/L]
Run # 13
0 1 2 3 4
0 10 20 30 40
Sampling time [h]
Furfural [g/L]
Run # 14
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
Acetic acid [g/L]
Run # 14
0 1 2 3 4
0 5 10 15 20 25 30
Sampling time [h]
HCl [g/L]
Run # 14
0 1 2 3 4
0 1 2 3 4 5 6
Sampling time [h]
Furfural [g/L]
Run # 15
0 1 2 3 4
0.5 1 1.5 2 2.5 3
Sampling time [h]
Acetic acid [g/L]
Run # 15
0 1 2 3 4
0 1 2 3 4 5 6
Sampling time [h]
HCl [g/L]
Run # 15
0 1 2 3 4
3 4 5 6 7 8
Sampling time [h]
Furfural [g/L]
Run # 16
0 1 2 3 4
1 1.5 2 2.5 3 3.5 4
Sampling time [h]
Acetic acid [g/L]
Run # 16
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
HCl [g/L]
Run # 16
70
0 1 2 3 4
0 1 2 3 4
Sampling time [h]
Furfural [g/L]
0 1 2 3 4
0.5 1 1.5 2
Sampling time [h]
Acetic acid [g/L
0 1 2 3 4
0 1 2 3 4
Sampling time [h]
HCl [g/L]
0 1 2 3 4
3 4 5 6 7 8
Sampling time [h]
Furfural [g/L]
Run # 16
0 1 2 3 4
1 1.5 2 2.5 3 3.5 4
Sampling time [h]
Acetic acid [g/L]
Run # 16
0 1 2 3 4
0 2 4 6 8
Sampling time [h]
HCl [g/L]
Run # 16
0 1 2 3 4
2 4 6 8 10 12 14
Sampling time [h]
Furfural [g/L]
Run # 17
0 1 2 3 4
0 2 4 6 8 10
Sampling time [h]
Acetic acid [g/L]
Run # 17
0 1 2 3 4
0 5 10 15 20 25 30
Sampling time [h]
HCl [g/L]
Run # 17
0 1 2 3 4
0 2 4 6 8 10
Sampling time [h]
Furfural [g/L]
Run # 18
0 1 2 3 4
0 1 2 3 4 5
Sampling time [h]
Acetic acid [g/L]
Run # 18
0 1 2 3 4
0 2 4 6 8 10 12
Sampling time [h]
HCl [g/L]
Run # 18
0 1 2 3 4
0 5 10 15 20
Sampling time [h]
Furfural [g/L]
Run # 19
0 1 2 3 4
0 2 4 6 8 10 12
Sampling time [h]
Acetic acid [g/L]
Run # 19
0 1 2 3 4
10 20 30 40 50 60
Sampling time [h]
HCl [g/L]
Run # 19
Figure 31: Comparison of experimentally determined concentration versus time profiles (shown in red) and predicted profiles (shown in green) for furfural, acetic acid and hydrochloric acid for each
run
Figure 29 further demonstrates that different runs gave different qualities of fit of the data. The poor overall fit was most likely attributable to experimental error as a result of inaccuracies in temperature measurement and inaccuracies in the determination of the quantities in the product solution.
The profiles for each component of each run can be found in the Appendix J but the profiles for run 1 are shown in Figure 32 below for discussion purposes:
0 5
0 1 2 3
time, hours
Pentosan (B), kmol/m3
Run # 1
0 5
0 0.2 0.4 0.6 0.8 1
time, hours
B-HCl complex, kmol/m3
0 5
0 0.005 0.01 0.015 0.02
time, hours
P-HCl complex, kmol/m3
0 5
0 20 40 60 80 100
time, hours
Pentosan (B) conversion, %
0 5
0 1 2 3 4 5x 10-5
time, hours
Furfural, kmol/m3
0 5
0 1 2 3 4x 10-5
time, hours
Acetic acid, kmol/m3
0 5
0.0276 0.0277 0.0278 0.0279 0.028 0.0281
time, hours
Water, kmol/m3
0 5
0 1 2 3 4x 10-4
time, hours
HCl, kmol/m3
Figure 32: Concentration profiles
Figure 32 shows that the pentosan (B) undergoes an initial exponential decrease in concentration as the pentosan is complexed with the HCl. The pentosan-HCl (B-HCl concentration increases rapidly following a more or less exponential trend until the concentration reaches a maximum at 0.95 kmol/m3 at which point the rate of increase in concentration starts to decrease. This decrease is a consequence of a reduction in the reactant concentration and as a result the reaction which converts the B-HCl complex to a pentose-HCl (P-HCl) complex begins to dominate over the rate of B-HCl production, eventually leading to a decrease in B-HCl concentration. The concentration of the P-HCl complex followed a similar trend, increasing to a maximum value then dropping off as it was consumed in the production of furfural. The furfural and acetic acid concentrations displayed similar trends to P-HCl and B- HCl respectively as a result of the production rates of these two components being dependent on the reactant concentration. The water concentration depleted rapidly initially as a result of its consumption in the hydrolysis reactions. The reason for the increase in water concentration after this was that as the hydrolysis reaction rate began to decrease and the production of furfural lead to an increase in the water concentration. It should be noted however that the change in water concentrations are very small. The HCl concentration was initially low as a result of the HCl becoming adsorbed onto the pentosan molecules, the value of the HCl increased until the pentosan molecules had reached saturation and thereafter the HCl concentration remained stable.