Investigating the effects of substrate morphology and experimental conditions on the enzymatic hydrolysis of lignocellulosic biomass through modeling

Background Understanding how the digestibility of lignocellulosic biomass is affected by its morphology is essential to design efficient processes for biomass deconstruction. In this study, we used a model based on a set of partial differential equations describing the evolution of the substrate morphology to investigate the interplay between experimental conditions and the physical characteristics of biomass particles as the reaction proceeds. Our model carefully considers the overall quantity of cellulase present in the hydrolysis mixture and explores its interplay with the available accessible cellulose surface. Results Exploring the effect of various experimental and structural parameters highlighted the significant role of internal mass transfer as the substrate size increases and/or the enzyme loading decreases. In such cases, diffusion of cellulases to the available cellulose surface limits the rate of glucose release. We notably see that increasing biomass loading, while keeping enzyme loading constant should be favored for both small- (R < 300 $$\mu m$$ μ m ) and middle-ranged (300 < R < 1000 $$\mu m$$ μ m ) substrates to enhance enzyme diffusion while minimizing the use of enzymes. In such cases, working at enzyme loadings exceeding the full coverage of the cellulose surface (i.e. eI>1) does not bring a significant benefit. For larger particles (R > 1000 $$\mu m$$ μ m ), increases in biomass loading do not offset the significant internal mass transfer limitations, but high enzyme loadings improve enzyme penetration by maintaining a high concentration gradient within the particle. We also confirm the well-known importance of cellulose accessibility, which increases with pretreatment. Conclusions Based on the developed model, we are able to propose several design criteria for deconstruction process. Importantly, we highlight the crucial role of adjusting the enzyme and biomass loading to the wood particle size and accessible cellulose surface to maintain a strong concentration gradient, while avoiding unnecessary excess in cellulase loading. Theory-based approaches that explicitly consider the entire lignocellulose particle structure can be used to clearly identify the relative importance of bottlenecks during the biomass deconstruction process, and serve as a framework to build on more detailed cellulase mechanisms.

Numerical Simulation of Methane and Propane Reforming Over a Porous Rh/Al2O3 Catalyst in Stagnation-Flows: Impact of Internal and External Mass Transfer Limitations on Species Profiles

Hydrogen production by catalytic partial oxidation and steam reforming of methane and propane towards synthesis gas are numerically investigated in stagnation-flow over a disc coated with a porous Rh/Al2O3 layer. A one-dimensional flow field is coupled with three models for internal diffusion and with a 62-step surface reaction mechanism. Numerical simulations are conducted with the recently developed computer code DETCHEMSTAG. Dusty-Gas model, a reaction-diffusion model and a simple effectiveness factor model, are alternatively used in simulations to study the internal mass transfer inside the 100 µm thick washcoat layer. Numerically predicted species profiles in the external boundary layer agree well with the recently published experimental data. All three models for internal diffusion exhibit strong species concentration gradients in the catalyst layer. In partial oxidation conditions, a thin total oxidation zone occurs close to the gas-washcoat interface, followed by a zone of steam and dry reforming of methane. Increasing the reactor pressure and decreasing the inlet flow velocity increases/decreases the external/internal mass transfer limitations. The comparison of reaction-diffusion and Dusty-Gas model results reveal the insignificance of convective flow on species transport inside the washcoat. Simulations, which additionally solve a heat transport equation, do not show any temperature gradients inside the washcoat.

REQUIREMENTS FOR MAGNESIUM-CARBON REFRACTORIES FOR BOF LINING AND FEATURES OF STEELMAKING TECHNOLOGIES IN ITS USE

The aim of the work is to develop a computer model of BOP-process that takes into account the interrelation of the parameters of steel smelting with the processes of refractories wear and is aimed at improving the conversion efficiency of metal. To achieve this goal, the authors has carried out a theoretical analysis of the patterns of assimilation of refractories by the slag phase formed during BOF smelting, used X-ray structural, spectral and microscopic studies of samples of magnesium-carbon refractories selected from different zones of the converter lining. By the method of regression analysis of the heats, mathematical models have been obtained that describe the features of the destruction of magnesium-carbon refractories. According to the research results, the main factors affecting the internal mass transfer in refractories under the conditions of its contact with the liquid slag melt have been defined. The requirements for the physical and chemical properties of magnesium-carbon refractories of the BOF working layer and for the production conditions have been substantiated. Scientific novelty of the work is the creation of a mathematical model for describing the process of internal mass transfer between the liquid slag phase of BOF and refractory, which takes place in its pores. The influence of the refractory porosity, pore diameter, concentration of the slag components, interfacial tension, wettability of the refractory with the liquid slag phase on the rate of internal mass transfer processes in BOF lining has been determined. The practical significance of the studies is a BOF model developed on a PC and adapted for PJSC “Dniprovsky Metallurgical Plant”, taking into account the interrelation of the parameters of metal conversion with the processes of magnesium-carbon refractories destruction, which allows to predict and optimize the process results.

Requirements for magnesium-carbon refractories for bof lining and features of steelmaking technologies in its use

The aim of the work is to develop a computer model of BOP-process that takes into account the interrelation of the parameters of steel smelting with the processes of refractories wear and is aimed at improving the conversion efficiency of metal. To achieve this goal, the authors has carried out a theoretical analysis of the patterns of assimilation of refractories by the slag phase formed during BOF smelting, used X-ray structural, spectral and microscopic studies of samples of magnesium-carbon refractories selected from different zones of the converter lining. By the method of regression analysis of the heats, mathematical models have been obtained that describe the features of the destruction of magnesium-carbon refractories. According to the research results, the main factors affecting the internal mass transfer in refractories under the conditions of its contact with the liquid slag melt have been defined. The requirements for the physical and chemical properties of magnesium-carbon refractories of the BOF working layer and for the production conditions have been substantiated. Scientific novelty of the work is the creation of a mathematical model for describing the process of internal mass transfer between the liquid slag phase of BOF and refractory, which takes place in its pores. The influence of the refractory porosity, pore diameter, concentration of the slag components, interfacial tension, wettability of the refractory with the liquid slag phase on the rate of internal mass transfer processes in BOF lining has been determined. The practical significance of the studies is a BOF model developed on a PC and adapted for PJSC “Dniprovsky Metallurgical Plant”, taking into account the interrelation of the parameters of metal conversion with the processes of magnesium-carbon refractories destruction, which allows to predict and optimize the process results.