Please use this identifier to cite or link to this item: http://prr.hec.gov.pk/jspui/handle/123456789/21699
Title: Synthesis and Applications of Ionic Liquids in Biomass Processing
Authors: Asim, Azmat Mehmood
Keywords: Physical Sciences
Chemistry
Issue Date: 2022
Publisher: University of the Punjab, Lahore
Abstract: Life sustainability on the globe relies on the uninterrupted supply of natural resources for food, energy and other necessities. With the increasing population, the consumption of natural reservoirs has also multiplied to an enormous extent. This unwarranted utilization of natural resources through man-made technologies has caused serious concerns about the depletion of these resources and also environmental deterioration. Fossil fuels have been the major source of numerous products including energy, chemicals, plastics and others. But, now, fossil fuels are identified as the most lethal factor in respect of environmental pollution. Therefore, the major challenge before the researchers is to develop novel technologies that could ensure to maintain the life sustainability along with environmental protection. Lignocellulosic biomass is one of the various renewable sources of the above-mentioned products with huge potential. Its cellulosic and lignin components can produce a variety of products at par with fossil fuels if properly used. The utilization of the great potential of lignocellulosic biomass is gravely hindered by its recalcitrant structure wherein cellulosic content is buried within the lignin and hemicellulose network. Previously, researchers have developed certain methods including physical, chemical and biological processes, to fractionate the biomass into its components. Unfortunately, every method bears its own drawbacks in terms of energy intensiveness, environmental contamination and slow processing, which are all undesirable in this era. Alternate technologies are, therefore, needed to fruitfully utilize the huge potential of the biomass through its fractionation. Ionic liquids (ILs) were introduced in biomass processing in the beginning of this century. There has been consistent research in this field for the last two decades. Despite the development of many successful ionic liquid-based methods, much room exists for the research to synthesize more effective, environment-friendly, and cost-effective ILs for this purpose. In this study, various ionic liquids, mainly protic ones (PILs), have been synthesized and evaluated for their efficiencies in biomass fractionation. In the first part, a series of PILs from pyridine and sulfuric acid having clusters on the anion was synthesized and used for the pretreatment and lignin extraction from wheat straw. The PILs exhibited very good pretreatment efficiency with high delignification and saccharification yields. Fairly high lignin yields were obtained under very mild conditions. The optimized pretreatment was achieved with the PIL containing 4 equivalent moles of sulfuric acid at 60 ℃ for 2 hours, biomass loading 20%, and particle sizes in the range 180-800 µm. The delignified pulp from the ionic liquids gave high glucose yields, the maximum being 85%. In the second part, another series, based on pyridine and sulfuric acid and anionic clusters, was synthesized and utilized for lignin extraction from wheat straw and rice husk. In comparison to the sulfuric acid-based PILs, these ILs also showed high efficiencies but under relatively severer conditions. In this case, the optimum yields were obtained at 100 ℃ for pretreatment of 2 hours with 5% biomass loading. The optimum lignin yield was 77% along, whereas the maximum sugar yield was 84%. The third part of the thesis is about synthesizing biocompatible ILs to make the process more and more environmentally safe and sustainable. Highly biocompatible starting reagents choline and lysine were used to synthesize cholinium lysinate ([Ch][Lys]. In view of the food-grade nature of its ingredients, this IL was employed to produce food grade glucose from rice straw and wheat straw. In order to be compatible with the food quality products, food-grade enzymes were used for the saccharification step. This IL was proved to have excellent delignification capability owing to its characteristic structural features which are highly desirable for lignin removal. The peak delignification (87%) was achieved at 120 ℃ after a pretreatment of 8 hours with 20% biomass loading and particle sizes in the range of 180-800 µm. However, the optimum food-grade glucose yield (84%) was obtained from the pulp recovered at 100 ℃ after 8 hours. The results were compared with benchmark IL and non-food-grade enzymes which showed relatively higher yields. In the last part, another IL based on an aliphatic amine (dimethylbutylamine) and sulfuric acid was prepared to be evaluated in biomass processing. The protic IL ([DMBA][HSO4]) was utilized for delignification and cellulose enrichment of bagasse and corn stover. Here, the effect of hemicellulose and lignin removal on the proportion of the cellulose component and subsequent saccharification yields was assessed. Sufficiently high delignification was achieved for both the types of biomass, while for bagasse the yields were better than for corn stover. The peak delignification was 83% at 140 ℃ for 4-hour pretreatment with 20% biomass loading. The extent of hemicellulose removal and cellulose enrichment were substantiated by high glucose but diminished xylose yields. Under the optimum conditions, bagasse produced 91% of glucose while residual xylans produced only 3% xylose. On the other hand, corn stover gave 82% glucose and 7% xylose under similar conditions. The ILs synthesized in this study were characterized through FT-IR and NMR analyses. The compositional analysis of raw and pretreated biomass was performed following NREL protocol consisting of digestion, fractionation, gravimetric measurements, and HPLC analysis. The recovered pulp was further analyzed through FT-IR, SEM, and TGA. The extracted lignin was characterized by FT-IR, HSQC NMR, and GPC analyses. Finally, the potential of the untreated biomass and recovered pulps to produce sugars from saccharification were quantitatively assessed through HPLC analysis. Despite the development of many successful ionic liquid-based methods, much room exists for the research to synthesize more effective, environment-friendly, and cost effective ILs for this purpose. In this study, various ionic liquids, mainly protic ones (PILs), have been synthesized and evaluated for their efficiencies in biomass fractionation. In the first part, a series of PILs from pyridine and sulfuric acid having clusters on the anion was synthesized and used for the pretreatment and lignin extraction from wheat straw. The PILs exhibited very good pretreatment efficiency with high delignification and saccharification yields. Fairly high lignin yields were obtained under very mild conditions. The optimized pretreatment was achieved with the PIL containing 4 equivalent moles of sulfuric acid at 60 ℃ for 2 hours, biomass loading 20%, and particle sizes in the range 180-800 µm. The delignified pulp from the ionic liquids gave high glucose yields, the maximum being 85%. In the second part, another series, based on pyridine and sulfuric acid and anionic clusters, was synthesized and utilized for lignin extraction from wheat straw and rice husk. In comparison to the sulfuric acid-based PILs, these ILs also showed high efficiencies but under relatively severer conditions. In this case, the optimum yields were obtained at 100 ℃ for pretreatment of 2 hours with 5% biomass loading. The optimum lignin yield was 77% along, whereas the maximum sugar yield was 84%. The third part of the thesis is about synthesizing biocompatible ILs to make the process more and more environmentally safe and sustainable. Highly biocompatible starting reagents choline and lysine were used to synthesize cholinium lysinate ([Ch][Lys]. In view of the food-grade nature of its ingredients, this IL was employed to produce food-grade glucose from rice straw and wheat straw. In order to be compatible with the food quality products, food-grade enzymes were used for the saccharification step. This IL was proved to have excellent delignification capability owing to its characteristic structural features which are highly desirable for lignin removal.
Gov't Doc #: 26977
URI: http://prr.hec.gov.pk/jspui/handle/123456789/21699
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

Files in This Item:
File Description SizeFormat 
AZMAT MEHMOOD ASIM chemistry 2022 uop lhr.pdf 24.5.22.pdfPh.D thesis17.15 MBAdobe PDFView/Open


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.