Kinetic modeling of concentrated acid hydrolysis of walnut green skin

Abstract

The overall goal of this experiment was to detect whether kinetic modeling can explain effects of temperature, acid concentration, time and solid contents on the production of glucose by concentrated acid hydrolysis of walnut green skin. For this purpose, sulfuric acid concentration of 20, 40 and 60% (w/w), processing temperature of 65, 80 and 90°C, reaction time of 120, 180 and 240 min and solid content of 5, 10 and 15% (w/w) were used as hydrolysis conditions. High performance liquid chromatography (HPLC) was used to analyze the products. The process was modeled by first-order irreversible reaction in series and kinetic constant, relating reaction time to glucose released. To relate temperature with kinetic constant and calculate activation energy, Arrhenius equation was employed. Optimal conditions occurred at 40% H 2 SO 4 , 90°C and 15% solid content for 285 min, which yielded a solution with 10.72 g glucose/L. In these conditions, 45% of the cellulose was hydrolyzed.

Unified Kinetic Model for Cellulose Deconstruction via Acid Hydrolysis

“…Experimental batch reactor data for fitting and evaluation of model parameters was obtained from various earlier studies, ,,− ,− corresponding to acid hydrolysis of pure cellulose such as α-cellulose, microcrystalline cellulose, and cellulose extracted from lignocellulosic biomasses such as paper refuse and sugar cane bagasse in the presence of sulfuric acid at different concentrations. The ODEs given by eqs – for n = 0 and 1 for all the species at specific reaction conditions were solved using ODEsolver45 in MATLAB.…”

“…Interestingly, YPW contains 41.9% cellulose, 23.5% hemicelluloses, 26.6% lignin, 3.4% acetyl intermediates, and only 0.6% ash, 39 while WGS contains only 21.5% cellulose, 13.25% hemicelluloses, 18.25% extractives, 26.07% lignin, and 20.93% ash. 15 Thus, the better match of the model predicted cellulose profile with the experimental data of YPW hydrolysis can be attributed to the high content of cellulose and low content of ash in YPW, while the low content of cellulose and high content of ash and extractives in WGS leads to variations between model prediction and experimental data for WGS acid hydrolysis. Moreover, the effect of parameters n and y for dilute-acid hydrolysis of yellow poplar wood at 225 °C and 0.07% (w/w) H 2 SO 4 were found to be the same as that in cellulose hydrolysis.…”

“…It is evident that the model predictions are in good agreement with experiments under all types of reaction conditions. The model was also validated with experimental data of acid hydrolysis of two biomasses, namely walnut green skin (WGS) 15 and yellow poplar wood (YPW), 39 by utilizing the parameters m, n, and y within the uncertainty limits corresponding to concentrated acid−low temperature for WGS and dilute acid−high temperature for YPW. It is clear that the model predicted cellulose profile for YPW hydrolysis matches well with the experimental data while the model predicted glucose profile for WGS hydrolysis captures the experimental trend, albeit with a variation in the initial time period up to 150 min.…”

“…In the above equation, k i 0 is the pre-exponential factor in time –1 , A is the acid concentration, E a i is activation energy in kJ/mol, T is temperature in K, R is the universal gas constant, and m 1 and m 2 are the slopes of cellulose and glucose hydrolysis profiles, respectively. This model was widely used for the kinetic study of the hydrolysis of all types of biomass feedstocks. ,− Table ,,− lists the values of k 10 , k 20 , E a 1 , E a 2 , and m 1 and m 2 observed for acid hydrolysis of cellulose extracted from different literature sources at different acid concentrations and temperatures. It is clear that the pre-exponential factors, activation energies, and acid exponents for cellulose hydrolysis to glucose vary in a very broad range, 10 10 to 10 19 min –1 , 127–188 kJ/mol, and 1.0–6.0, respectively.…”

“…(d) Glucose production from acid hydrolysis of walnut green skin (WGS) (exptl. data: Arastehnodeh et al15 ). (e) Cellulose profile during hydrolysis of yellow poplar wood (YPW) (exptl.…”