Pulsed electric field pretreatment of lignocellulose biomass for maximum fermentable sugar yield

The utilization of lignocellulosic biorefinery processes holds great promise for the production of biofuels and biochemicals. Lignocellulosic biomass, which includes materials such as plant straw, chaff, various grasses, sawdust, soft and hard woods, tree leaves, and paper waste, represents an abundant resource. However, these materials possess tough cell walls and bonding structures that restrict enzyme accessibility during hydrolysis, leading to a reduced yield of fermentable sugars. Numerous pretreatment methods have been explored to address the recalcitrance of lignocellulosic biomass. However, many of these methods are either costly or environmentally harmful due to their substantial energy or chemical consumption and waste generation. Pulsed electric field pretreatment (PEF) has emerged as a promising method thought to enhance biomass permeability. In this particular study, a PEF pretreatment system was designed, simulated, constructed, and tested specifically for treating flax straw. This system has the capacity to deliver up to 120,000 pulses, with a field strength of up to 8 kV/cm and a pulse width of up to 100 μs. Simulation outcomes highlighted that a design employing two MOSFETs connected in parallel was the most optimal alternative, effectively delivering all applied energy to the biomass while keeping the current within the switch's maximum rating. Nonetheless, perfect synchronization of the metal-oxide-semiconductor field-effect transistors (MOSFETs) was necessary to prevent short circuit. Alternatively, a design featuring a single MOSFET addressed the synchronization issue but encountered MOSFET overheating at high pulse counts and field strengths. Attaching a heat sink to the MOSFET and using a fan helped cooling down of the MOSFET. The PEF pretreatment was performed using a single MOSFET PEF system within a field strength range of 1.54-8 kV/cm, delivering pulses between 500 and 120,000 with pulse widths from 75 to 100 μs. Subsequent analysis of the pretreated flax straw aimed to assess change in its structure and investigate the yield of fermentable sugars compared to untreated flax straw. At 20,000 pulses, 1.54 kV/cm, and 100 μs, glucose yield saw an 18.8% increase over that of untreated flax straw. The impact of pulse count was negligible beyond 20,000 pulses. Increasing the field strength to 8 kV/cm and employing 120,000 pulses at 100 μs resulted in enhanced yields: 25% for glucose, 67% for cellobiose, and 12% for xylose, relative to untreated flax straw. Analysis via ATR-FTIR indicated no change in the composition of the flax straw pre and post-pretreatment, while crystallinity index measurements revealed unchanged cellulose crystallinity due to PEF pretreatment. Scanning electron microscopy (SEM) images displayed a more porous surface in the pretreated flax straw. BET analysis demonstrated a 91% increase in the surface area of the flax straw pretreated at 8 kV/cm and 120,000 pulses compared to raw flax straw. Field strength proved effective at two key levels—1.54 and 8 kV/cm—indicating their critical significance among the studied parameters. The critical field strength was observed to depend on the pulse count, as 1.54 kV/cm was effective only at 20,000 pulses, whereas 8 kV/cm was effective at 60,000 pulses or higher. This suggests that PEF pretreatment can be optimized for improved performance. This research lays the foundation for further exploration into the feasibility of integrating PEF pretreatment into an ethanol production facility.

Name thesis:degree_name

Master of Applied Science (MASc)

Level thesis:degree_level

Master's

Discipline thesis:degree_discipline

Engineering - Process Systems

Grantor dc:publisher

Faculty of Graduate Studies and Research, University of Regina

Year dc:date.issued

2024

Author dc:creator

• Alawad, Ishag Haroon Mohamad

Advisor dc:contributor.advisor

• Ibrahim, Hussameldin

Committee members dc:contributor.committeemember

• Henni, Amr
• Laforge, Paul

Language dc:language.iso

en

DOI

https://doi.org/10.82465/3958

OAI identifier oai:identifier

oai:uregina.scholaris.ca:10294/16421