Multiscale Modeling of Hydrothermal Pretreatment: From Hemicellulose Hydrolysis to Biomass Size Optimization

Abstract

In the general process for lignocellulosic bioconversion to ethanol, pretreatment has been viewed as the main cause of low process yield. Consequently, it is believed that obtaining a better understanding of the hydrothermal pretreatment method would pave the way for overall process optimization. This work focuses on developing a model for a pretreatment process that considers both the chemical and physical natures of the process. The chemical aspect of the process mainly involves the hydrolysis of hemicellulose to monomeric sugars. This paper considers all xylooligomers, with a degree of polymerization up to 30 as soluble, and that the bond breakage is a function of the position in the hemicellulose chain. Also, all of the bonds with the same position undergo breakage at the same time. The physical aspect of the process involves reducing the size of the feedstock as well as heating the feedstock to a desired temperature. For this aspect, we have developed a model to estimate the energy requirements for size reduction and proposed a method to find the optimum chip size for pretreatment. Finally, we performed two sets of sensitivity analysis: first, to compare the dynamic importance of xylooligomer size evolution versus xylose decomposition and, second, to compare the relative importance of kinetic parameters versus the length of particle on the overall process yield. Sensitivity analysis revealed that, at the beginning of the process, the chemical reaction is more important than diffusion; however, as the reaction proceeds, diffusion becomes the determinant factor. It was also shown that the solidphase reaction rate, xylooligomer size evolution, and xylose decomposition are all determinant factors; therefore, any model for hemicellulose hydrolysis should take all three of these factors into account.

The multi-scale challenges of biomass fast pyrolysis and bio-oil upgrading: Review of the state of art and future research directions

“…Hydrothermal pretreatment (also referred to as "wet torrefaction") using compressed hot water or other hydrothermal media, is another emerging technology for fractionating biomass [93,113,114], pretreatment of lignocellulosic biomass (removing the need for the energy-intensive biomass drying stage [115]), liquefaction of lignocellulosic and aquatic biomass (by enzymatic hydrolysis [116][117][118]), or upgrading of pyrolysis oil. The hydrothermal pretreatment process is conducted at saturated vapor pressure in the temperature range of 180-260°C [93,119].…”

Hydrothermal processing, as an alternative for upgrading agriculture residues and marine biomass according to the biorefinery concept: A review

“…Hosseini et al [109] Model for calculating the temperature needed for different particle sizes. Temperature as a function of severity factor and radius in hydrothermal processing.…”

“…Hosseini et al [109] generally used to correlate the effects of operational conditions (i.e., temperature, residence time, particle size, pH) on hemicellulose solubilization. It was initially used to control the pulping process in the paper industry, but it was reintroduced for comparison of hydrothermal processing pretreatment severities on LCMs [110][111][112].…”

Multi-product biorefineries from lignocelluloses: a pathway to revitalisation of the sugar industry?

“…In the context of sugar industry, a biorefinery could be annexed to a sugar mill to increase diversification and support regional and rural development. A number of economic assessments have been published on biofuel production from 2G waste biomass, considering biochemical [ 21 , 22 ] or thermochemical technologies [ 23 – 26 ]. Production of value-added chemicals and polymers from lignocellulosic waste biomass has been also explored in the past few years [ 10 , 27 – 29 ].…”