(220g) How Detailed Mass Balances in Biomass Biorefining Processes Can Help in the Development of An Efficient Sugar-Platform Biorefinery

A sugar-platform Biorefinery is a facility that integrates fractionation, separation and conversion processes to derive soluble, monomeric sugars from carbohydrate-containing feedstocks such as forest biomass and agricultural residues. The sugar streams are then used as the major raw material for production of a wide range of bioproducts such as biochemicals and transportation liquid fuels. Different technologies and process configurations with varying degrees of maturity and complexity have been proposed to generate sugar intermediate streams. However, biomass pretreatment followed by enzymatic hydrolysis form the key upstream process of a number of pilot, demonstration, and planned commercial biomass-to-bioproducts industries aiming to access and release sugar residues from biomass feedstocks.

While, it is becoming increasingly apparent that sugar recovery yields, chemical composition of the sugar streams as well as chemical/biochemical inputs (e.g. enzyme dosage) all critically affect the techno-economic viability of a sugar-platform Biorefinery operation, determining the optimal upstream process conditions that maximize sugar recovery yield while minimizing biocatalyst input and the formation of byproducts that affect sugar downstream processing has proved challenging. This is primarily because of the mutual interdependence of the pretreatment and enzymatic hydrolysis steps as operating conditions that allow for high sugar recovery yields during pretreatment leads to low sugar yield during enzymatic hydrolysis at low biocatalyst input. Therefore, the upstream pretreatment and enzymatic hydrolysis process steps are essentially a compromise.

Because of the heterogeneous nature of biomass feedstocks and the multitude and complexicity of the biocatalyst mixtures make kinetic studies a difficult task and with limited practical application, it is anticipated that empirical process modeling, despite overlooking parameters related to reaction kinetics and transport phenomena, can provide practical insight for research and development as well as a useful tool for process control and optimization. This presentation will first discuss the accuracy of a series of empirical modeling approaches [1], some derived from pulping processes, to predict sugar recovery yields and the chemical composition of the sugar streams after biomass pretreatment. Modeling the dependence of sugar yields on biocatalyst dosage during enzymatic hydrolysis will be also discussed. In particular, examples will be presented on how detailed mass balances obtained from empirical modelling of the pretreatment and enzymatic hydrolysis steps could help to also assess the impact that industrially relevant process factors might have on the overall sugar yields and biocatalyst input.

[1] Olsen C, Arantes V, Saddler JN. 2012. The use of predictive models to optimize sugar recovery obtained after the steam pre-treatment of softwoods. Biofuels, Bioproducts and Biorefining 6 (5):534-548.