Continuous enzymatic hydrolysis of lignocellulosic biomass with simultaneous detoxification and enzyme recovery

Effects of Mixing and Particle Size on the Kinetics and Dynamics of Enzymatically Treated Cotton Cellulose (MCC) in Continuous Flow Reactor

Enzymatic hydrolysis (EH) of cellulosic biomass needs tremendous technological advancement so as to efficiently convert cellulosic biomass into renewable fuels and commodity chemicals. Therefore, development of highly improved process engineering techniques is inevitable to reduce the processing cost of the fluids in the reactor. In this investigation, effect of mixing and particle size on the EH of microcrystalline cotton cellulose (MCC) has been investigated by using a spatially averaged low-dimensional two-mode mixing (TMM) model. The model simulations were carried out for the average particle sizes of MCC ranging from 0.78 to 25.52 μm and mixing speed of η → 0 (very high) to η → 1000 (very low). The effects of mixing and particle size on the formation of glucose and reducing sugar (RS) have been quantified by exploiting the rigorous multistep reaction kinetics and TMM model. To access the bond-breaking ability, its effects on the degree of polymerization (DP) was also analyzed. The results deduced that increase in mixing limitations and reduction in particle size imparts a significant increase in glucose and RS yield while decreasing the DP drastically. Thus, our simulations reveal that while η → 1000 economizes the process by reducing the energy requirements, reduction in particle size can be beneficial for reducing the residence time in the depolymerization of MCC to fuels and chemicals.

A two-phase substrate model for enzymatic hydrolysis of lignocellulose: application to batch and continuous reactors

BACKGROUND

Enzymatic hydrolysis continues to have a significant projected production cost for the biological conversion of biomass to fuels and chemicals, motivating research into improved enzyme and reactor technologies in order to reduce enzyme usage and equipment costs. However, technology development is stymied by a lack of accurate and computationally accessible enzymatic-hydrolysis reaction models. Enzymatic deconstruction of cellulosic materials is an exceedingly complex physico-chemical process. Models which elucidate specific mechanisms of deconstruction are often too computationally intensive to be accessible in process or multi-physics simulations, and empirical models are often too inflexible to be effectively applied outside of their batch contexts. In this paper, we employ a phenomenological modeling approach to represent rate slowdown due to substrate structure (implemented as two substrate phases) and feedback inhibition, and apply the model to a continuous reactor system.

RESULTS

A phenomenological model was developed in order to predict glucose and solids concentrations in batch and continuous enzymatic-hydrolysis reactors from which liquor is continuously removed by ultrafiltration. A series of batch experiments were performed, varying initial conditions (solids, enzyme, and sugar concentrations), and best-fit model parameters were determined using constrained nonlinear least-squares methods. The model achieved a good fit for overall sugar yield and insoluble solids concentration, as well as for the reduced rate of sugar production over time. Additionally, without refitting model coefficients, good quantitative agreement was observed between results from continuous enzymatic-hydrolysis experiments and model predictions. Finally, the sensitivity of the model to its parameters is explored and discussed.

CONCLUSIONS

Although the phenomena represented by the model correspond to behaviors that emerge from clusters of mechanisms, and hence a set of model coefficients are unique to the substrate and the enzyme system, the model is efficient to solve and may be applied to novel reactor schema and implemented in computational fluid dynamics (CFD) simulations. Hence, this modeling approach finds the right balance between model complexity and computational efficiency. These capabilities have broad application to reactor design, scale-up, and process optimization.

Biotechnological route for sustainable succinate production utilizing oil palm frond and kenaf as potential carbon sources

Due to the world's dwindling energy supplies, greater thrust has been placed on the utilization of renewable resources for global succinate production. Exploration of such biotechnological route could be seen as an act of counterbalance to the continued fossil fuel dominance. Malaysia being a tropical country stands out among many other nations for its plenty of resources in the form of lignocellulosic biomass. To date, oil palm frond (OPF) contributes to the largest fraction of agricultural residues in Malaysia, while kenaf, a newly introduced fiber crop with relatively high growth rate, holds great potential for developing sustainable succinate production, apart from OPF. Utilization of non-food, inexhaustible, and low-cost derived biomass in the form of OPF and kenaf for bio-based succinate production remains largely untapped. Owing to the richness of carbohydrates in OPF and kenaf, bio-succinate commercialization using these sources appears as an attractive proposition for future sustainable developments. The aim of this paper was to review some research efforts in developing a biorefinery system based on OPF and kenaf as processing inputs. It presents the importance of the current progress in bio-succinate commercialization, in addition to describing the potential use of different succinate production hosts and various pretreatments-saccharifications under development for OPF and kenaf. Evaluations on the feasibility of OPF and kenaf as fermentation substrates are also discussed.