Raman sensor to measure progress of bioconversion of lignocellulosic sugars to acetic acid by Moorella thermoacetica

Lignocellulosic bioconversion is a rapidly growing field, encompassing production of a wide range of chemicals and products from renewable resources. In order to be competitive with fossil-based fuels and chemicals, maintaining cost-effectiveness is critical. Key biorefinery processes, such as enzymatic hydrolysis and fermentation of lignocellulosic sugars, can be monitored by advanced sensors in real time, providing information about reactant and product concentration as reactions progress.  Current sensors and analytical techniques are costly and require lengthy offline analysis. Raman spectroscopy has the potential to continuously monitor lignocellulosic processes, maximizing efficiency and allowing for improved process control. The objective of this novel research was to study the progress of biomass to products conversion by measuring the concentration of hydrolysis and fermentation products using Raman spectroscopy. We have shown that hydrolysis of steam exploded hybrid poplar with 7.5% consistency to glucose (20-50 g/L) can be accurately monitored by a 785 nm Raman spectroscopy instrument and novel immersion probe. Furthermore glucose and acetic acid in fermentation can be accurately monitored as well. In this fashion, fermentation of 50 g/L of glucose by Moorella thermoacetica to a high acetic acid yield (80% of theoretical) was successfully monitored by Raman spectroscopy. The models have shown very good correlation between the real-time Raman spectra and the offline HPLC validation. It has been demonstrated that this novel Raman sensor is a robust tool for an online monitoring of lignocellulosic bioconversion and is well suited for ensuring optimal production of bio-based chemicals in a future successful biorefinery complex.