Determination of saccharides and ethanol from biomass conversion using Raman spectroscopy: Effects of pretreatment and enzyme composition

This dissertation focuses on the development of facile and rapid quantitative Raman spectroscopy measurements for the determination of conversion products in producing bioethanol from corn stover. Raman spectroscopy was chosen to determine glucose, xylose and ethanol in complex hydrolysis and fermentation matrices. Chapter 1 describes the motives and main goals of this work, and includes an introduction to biomass, commonly used pretreatment methods, hydrolysis and fermentation reactions. The principles of Raman spectroscopy, its advantages and applications related to biomass analysis are also illustrated. Chapter 2 and 3 comprise two published or submitted manuscripts, and the thesis concludes with an appendix. In Chapter 2, a Raman spectroscopic protocol is described to study the efficiency of enzymatic hydrolysis of cellulose by measuring the main product in hydrolysate, glucose. Two commonly utilized pretreatment methods were investigated in order to understand their effect on glucose measurements by Raman spectroscopy. Second, a similar method was set up to determine the concentration of ethanol in fermentation broth. Both of these measurements are challenged by the presence of complex matrices. In Chapter 3, a quantitative comparison of pretreatment protocols and the effect of enzyme composition are studied using systematic methods. A multipeak fitting algorithm was developed tomore » analyze spectra of hydrolysate containing two analytes: glucose and xylose. Chapter 4 concludes with a future perspective of this research area. An appendix describes a convenient, rapid spectrophotometric method developed to measure cadmium in water. This method requires relatively low cost instrumentation and can be used in microgravity, such as space shuttles or the International Space Station. This work was performed under the supervision of Professor Marc Porter while at Iowa State University. Research related to producing biofuel from bio-renewable resources, especially bioethanol from biomass, has grown significantly in the past decade due to the high demand and rising costs of fossil fuels. More than 3 percent of the energy consumption in the U.S. is derived from renewable biomass, mostly through industrial heat and steam production by the pulp and paper industry, and electricity generation from municipal solid waste (MSW) and forest industry residues. The utilization of food-based biomass to make fuels has been widely criticized because it may increase food shortages throughout the world and raise the cost of food. Thus, nonfood-based and plentiful lignocellulosic feedstocks, such as corn stover, perennial grass, bagasse, sorghum, wheat/rice straw, herbaceous and woody crops, have great potential to be new bio-renewable sources for energy production. Given that many varieties of biomass are available, there is need for a rapid, simple, high-throughput method to screen the conversion of many plant varieties. The most suitable species for each geographic region must be determined, as well as the optimal stage of harvest, impacts of environmental conditions (temperature, soil, pH, etc.). Various genetically modified plants should be studied in order to establish the desired biomass in bioethanol production. The main screening challenge, however, is the complexity of plant cell wall structures that make reliable and sensitive analysis difficult. To date, one of the most popular methods to produce lignocellulosic ethanol is to perform enzymatic hydrolysis followed by fermentation of the hydrolysate with yeast. There are several vital needs related to the field of chemistry that have been suggested as primary research foci needed to effectively improve lignocellulosic ethanol production. These topics include overcoming the recalcitrance of cellulosic biomass, the pervasiveness of pretreatment, advanced biological processing and better feedstocks. In this thesis, a novel approach using Raman spectroscopy has been developed to address important issues related to bioethanol generation, which will aid the research aimed to solve the topics mentioned above.« less