Bioconversion of crude glycerols to biofuels and value-added bioproducts
SUPERVISOR: Dr. Wensheng Qin (Biology)
ABSTRACT: Biodiesel-derived crude glycerol, a core by-product of biodiesel production process is becoming of great environmental and economical concern for growth of biodiesel industries due to its ever-growing over supply problem. Therefore, biotransformation of crude glycerol to renewable energy would lead to both environmental and economic dividends of biodiesel plant. In this study, numerous bacterial strains isolated from environmental samples were screened for their capability of converting glycerol to 2,3-BD, a high worth green product uses as a liquid fuel or fuel additive. Moreover, high productions of 2,3-BD were reported using two mutant strains of newly isolated Klebsiella variicola SRP3 and K. pneumoniae SRP2 respectively. However, Real-time qPCR and glycerol dehydrogenase (GDH) enzyme activity assay revealed that the overexpression of GDH gene resulted in an increased GDH enzyme activity, led to a markedly boosted 2,3-butanediol (2,3-BD) production.
Kinetic and thermodynamic studies on pyrolysis of waste HDPE polymers
SUPERVISOR: Dr. Siamak Elyasi (Chemical Engineering)
ABSTRACT: Pyrolysis is a promising technology for converting waste plastic into high-value hydrocarbons, which can help to protect the environment and improve the waste management industry. Available methods for finding kinetic parameters and heat of solid state reactions are not compatible with the complexity of pyrolysis reactions, and do not give reliable parameters to design an industrial pyrolysis reactor. This work developed two new techniques to determine kinetic parameters and heat of solid state reactions with high-certainty. The proposed kinetic study method is a differential isoconversional technique that finds activation energy and pre-exponential factor at different extents of reaction using isothermal Thermogravimetric Analysis (TGA) datasets. Employing this method, kinetic parameters of pyrolysis of high-density polyethylene (HDPE) were determined at different reaction conversions. The obtained apparent activation energy values were obtained in the range of 270 to 290 kJ/mol. The developed method for finding heat of reaction employs Differential Scanning Calorimetry (DSC) technique at constant temperatures. This method involves a new procedure to find heat loss from the DSC instrument as function of temperature and sample weight. The method was employed to find heat of cracking of HDPE at constant temperature of 400, 410, 420 and 430 °C, and the average heat of reaction was determined to be 1375±233 kJ/kg. Based on available recommendations in the literature for using ZSM-5 catalysts in polymer pyrolysis, catalytic cracking of high-density polyethylene was studied using three ZSM-5 catalysts with different Si/Al ratios of 25, 38 and 80. Using a TGA instrument and altering the variables such as temperature and the catalyst to HDPE ratio, catalytic activity of the catalysts was investigated, and proper operating conditions were estimated. ZSM-5 catalysts with Si/Al ratios of 25 and 38 at constant temperatures of 330, 340, 350, 360 and 370 °C, and cat/HDPE ratio of 15 % III showed considerably high catalytic activity in cracking of HDPE (especially the ZSM-5 with Si/Al ratio of 25). Using the developed kinetic study method, kinetic parameters of catalytic cracking of HDPE were determined at the aforementioned conditions, and apparent activation energy values were dropped dramatically to the range of 20 to 90 kJ/mol. In addition, catalytic activity, deactivation behavior, regenerability and reuse of the ZSM-5 catalyst with Si/Al ratio of 25 in consecutive cracking tests were also investigated. When activity of the used catalyst dropped to 20% of its initial value, a catalyst regeneration at 480 °C for 5 h was conducted; however, due to dealumination reactions occurred in the regeneration step, the initial catalytic activity could never be recovered. After catalyst regeneration, the regenerated catalyst was used in the same cracking tests. With 10 regeneration cycles, the ZSM-5 was used in 54 cracking tests. The effect of calcination temperature on the activity of ZSM-5 in cracking of high-density polyethylene was then explored. Calcination at 600 and 700 °C reduced acidity and activity of the ZSM-5 mainly due to catalyst dealumination. On the contrary, no drop in activity of the 500 °C-calcined catalyst was detected. Overall, the findings of this study can be employed to design an industrial reactor for pyrolysis of waste polymers. Additionally, the methods developed in this study for obtaining kinetic parameters and heat of pyrolysis can be used in any other solid state reactions.
Conversion of Crude Glycerol from the Biodiesel Industry to Value-added Products
SUPERVISOR: Dr. Sudip Rakshit (Chemical Engineering)
ABSTRACT: Crude glycerol is a major by-product of the biodiesel industries. For every 100 kg of biodiesel produced, approximately 10 kg of the byproduct glycerol is generated. With large increase in biodiesel production, there is a glut in the glycerol produced. Presently crude glycerol is purified to its purer marketable form, burnt as a fuel or mixed with animal feed. However, none of these options contribute considerable revenues to the concerned biodiesel industry. Additionally, some of these routes are not environmentally friendly. It has thus become imperative to find ways to convert crude glycerol to some value-added products. Bioconversion of crude glycerol to microbial lipids is one possible way to valorize it. However, impurities like methanol, salts and soap present in crude glycerol inhibit the growth of microbes used for such conversions. The research work carried out in this thesis addressed these issues and developed tangible alternatives to overcome these problems. Initially the possible use of a heterogeneous catalyst Calcium oxide (CaO) attached to support alumina (Al2O3) for the production of biodiesel was studied. We found that the use of such a catalyst improves the purity of biodiesel and the glycerol produced. Crude glycerol obtained using such insoluble catalysts contained lower levels of impurities and can be converted relatively easily to other useful products. With CaO anchored on Al2O3 as catalyst, the purity of biodiesel and glycerol were found to be 97.66% and 96.36% respectively. The unanchored heterogeneous catalyst CaO resulted in purities of 96.75% and 92.73% respectively. As the byproduct glycerol containing smaller amount of impurities, the use of anchored heterogeneous catalyst is recommended. The potential use of ash from various sources as a cheap alternative heterogeneous catalyst was also studied. With the use of ash from birch bark and fly ash from wood pellets as catalysts, biodiesel and glycerol with purity in the ranges of 88.06%-99.92% and 78.18%-88.23% respectively were obtained. Since such catalysts are cheap and reusable, their application can reduce expenses and the use of environmentally unsafe compounds. The crude glycerol used in all experiments was obtained from a biodiesel producer in Ontario (Canada). It was found to contain 44.56 wt.% glycerol and many impurities including 13.86 wt.% methanol, 32.97 wt.% soap and 4.38 wt.%. After the characterization of the samples it II was converted to microbial lipids using an oleaginous yeast Rhodosporidium toruloides ATCC 10788. When this strain was grown on crude glycerol, double the biomass (21.16 g/L) and triple the lipid concentration (11.27 g/L) was obtained compared to growth on pure glycerol media. The capacity of this strain to grow on crude glycerol with high levels of impurities and produce large amounts of lipids proves its robustness. Investigation of the effect of individual components on the lipid production ability of this strain showed it to be capable of using soap as a sole carbon source. This was also the reason for enhanced lipid production even in the presence of other impurities present in crude glycerol. The lipids obtained were rich in oleic acid (47.16%), a mono-unsaturated fatty acid (MUFA). Feedstock rich in MUFA are considered suitable for biodiesel production. Thus, the process of conversion of crude glycerol to microbial lipids can be integrated to existing biodiesel plants. This will help in the management of crude glycerol produced during biodiesel production, save transportation and disposal costs and contribute to the revenues of such industries. The possible applications of microbial lipids obtained from oleaginous (oil producing) microbes depends on its fatty acid composition. Most reports suggest the potential use of microbial lipids for biodiesel production. However, tailoring lipids obtained from these microbes, by changing the fatty acid composition, can make it suitable for use in various biotechnology, pharmaceutical and food industries. The possible use of essential oils from plant sources to change the fatty acid profile of the lipids obtained from R. toruloides ATCC 10788 was studied. The addition of seven types of essential oils into the growth medium resulted in lipids with seven different fatty acid profiles. Most of the essential oils tested enhanced the stearic acid content of the lipids. The latter has numerous applications in food, pharmaceuticals and cosmetic industries. Additionally, specific levels of these essential oils in the media changed the metabolic pathways of lipids production resulting in unique fatty acids compositions. For instance, use of 2 g/L of orange essential oil in the growth medium produced lipids with fatty acid composition similar to mahua butter which has a number of food, cosmetic and medical applications. Addition of origanum (0.3 g/L) or pine essential oil (3 g/L) into the media improved the oleic acid content of the lipid by 17.90% and 14.35% respectively. This study also provides an insight into the ability of these essential oils to affect the activity of enzymes involved in fatty acid biosynthesis metabolism of R. toruloides ATCC 10788. Most of the essential oils used were found to inhibit Δ9 and Δ12 desaturase enzymes present in the fatty acids biosynthesis metabolic pathways of this strain. This in turn increased the amounts of stearic acids in most of the lipids obtained. Further investigations showed that mono-terpenoids in the essential oils played a major role in bringing about such changes in the fatty acids composition and that the effect of essential oils are specific to the microbial species under study. Subsequently, the possible use of microbial lipids obtained from crude glycerol for polyol production was studied. Polyol is a precursor to the production of polyurethane foams. In order to produce large quantities of lipids, fermentation of crude glycerol was carried out in a 1L bioreactor. This resulted in 27.48 g/L of biomass and 18.69 g/L of lipids at the end of 168 h. The lipids obtained were then converted to polyol using epoxidation and oxirane ring opening reactions. For comparison, polyols from commonly used vegetable oils (i.e. canola and palm oil) were also produced under similar reaction conditions. The hydroxyl numbers of polyols from canola, palm and microbial oil were found to be 266.86, 222.32 and 230.30 (mg KOH/g of sample) respectively. These values are within the range required for polyurethane production. We subsequently converted the polyols obtained from these oils into rigid and semi-rigid types of polyurethanes. Polyurethanes produced can potentially be used for various commercial applications. In this way, we have been successful in demonstrating the possible use of microbial lipids in biopolymer industries. The use of a robust microbial strain capable of growing on crude glycerol and the conversion of the lipids obtained to bioplastics can not only help fix the carbon produced (leading to reduction in GHG emission obtained by its combustion), but also potentially bring revenues to industries that integrate such processes into existing facilities.
Nanomaterials-based electrochemical approaches for biosensing and bacterial disinfection
SUPERVISOR: Dr. Aicheng Chen (formerly with Chemistry)
ABSTRACT: Electrochemical approaches to myriad medical and environmental challenges are highly attractive due to their strong potential for extensive and green applications. Point of care diagnostics through the electrochemical monitoring of clinically and environmentally relevant molecules are gaining attraction due to their low cost and simple fabrication procedures. The development of highly stable and sensitive electrochemical sensors/biosensors, for a wide variety of biomolecules in actual samples, makes these methods alternative analytical tools in different pharmaceutical and hospital laboratories. Electrochemical biocatalysis is an additional promising area to address the removal of bacteria for the generation of safe potable water. As the world’s population is dealing with lack of access to safe drinking water, photoelectrocatalysis has been investigated as a very efficient technique for the destruction of pathogenic bacteria in water. Nanomaterials with dimensions of less than 100 nm have great potential to enhance the performance of electrochemical methods, due to their excellent electronic, mechanical, and thermal properties. These materials have the capacity to greatly enhance biocatalytic activity, and thus greatly improve the performance of electrochemical sensors/biosensors. This remarkable improvement in bacterial catalysis has been studied using a novel synergistic approach, which incorporates both photocatalysts and electrocatalysts. For my PhD thesis, we designed a high-performance electrochemical sensor based on graphene for the sensitive detection of acetaminophen, valacyclovir, and mixtures thereof. This sensor was fabricated through the concurrent electrochemical reduction and deposition of graphene oxide (GO) onto a glassy carbon electrode (GCE) using cyclic voltammetry (CV). The electrocatalytic properties of the electrochemically reduced graphene (ERG) for the oxidation of acetaminophen were analyzed via cyclic voltammetry (CV), differential pulse voltammetry, (DPV) and chronoamperometry. For comparison, various ERG/GCEs were prepared under different electrodeposition cycles to optimize the required quantity of ERG. Our experimental results indicated that the optimized ERG/GCE possessed robust activity toward the electrochemical oxidation of acetaminophen, valacyclovir, and their mixture, leading to the development of a highly sensitive electrochemical sensor for its detection. An extremely low detection limit of 2.13 nM for acetaminophen, and 1.34 nM for the exclusive detection of valacyclovir was achieved. A wide linear detection range of from 5.0 nM to 800 μM was II achieved via the combination of an amperometric technique and DPV. The developed electrochemical sensor was further employed for the determination of acetaminophen, valacyclovir, and their mixture in human serum, with excellent recovery, ranging from 96.08% to 103.2%. The fabricated electrochemical sensor also demonstrated high selectivity, stability and reproducibility. We investigated a novel enzyme entrapment approach utilizing a cationic polymer for the detection of ethanol. Entrapment is one of the primary approaches for enzyme immobilization; however, it suffers from a few critical drawbacks, including leakage and high mass transfer resistance to substrates. To address these challenges, herein we report on a new facile and effective enzyme entrapment platform utilizing a special cationic polymer, poly(2-(dimethylamino)ethyl methacrylate) (MADQUAT) on a nanohybrid single-wall carbon nanotube/reduced graphene oxide (SWCNT–rGO) thin film. The ethanol biosensor developed in this study exhibited rapid response, wide linearity range, high sensitivity (26.27 μA mM−1 cm−2), a remarkably low limit of detection (0.16 μM), high selectivity, and high stability. The optimized biosensor was further tested with actual samples including wine, beer, and blood alcohol, and demonstrated promising analytical and biomedical applications. The increasingly serious issue of lack of access to clean potable water globally is of great concern. The high costs associated with the purchase and operation of water treatment facilities hinders access to clean water for entire populations. Herein, we report on an efficient and cost-effective approach for the remediation of E. coli (as model organism), through a combination of photochemistry and electrochemistry enabled by a bifunctional electrode. The bifunctional electrode utilizes titanium (Ti) as the substrate, nanoporous TiO2 as a photocatalyst, and RuO2 nanoparticles as an electrocatalyst. A high disinfection rate at 0.62 min-1, with >99.999% of bacterial removal within 20 min has been achieved using this TiO2/Ti/RuO2 bifunctional electrode. Complete bacterial disinfection was attained within a 30 min electrochemical treatment, as assessed by a spread plate method. Further, the bifunctional disinfection mechanism was investigated through protein concentration leakage, total organic carbon mineralization, and metabolomics analysis. A major loss of vital metabolites occurred over a period of 20 to 30 min, which suggested the mass inactivation of E. coli within this treatment duration. The novel strategy for the integration of advanced electrochemical oxidation and photochemical degradation via the bifunctional electrode system developed in this study has III strong potential to be utilized as an environmentally compatible technology for water purification and wastewater treatment. Simple and robust electrochemical approaches utilizing novel nanomaterials have been developed for the sensing of biomolecules and water disinfection. Carbon based nanomaterials and nanocomposites were employed to develop sensitive electrochemical sensor/biosensors, and nanoporous TiO2/RuO2 bifunctional materials were utilized for the design of a high-performance bacterial disinfection technology.
New generation of dispersants by grafting lignin or xylan
SUPERVISOR: Dr. Pedram Fatehi (Chemical Engineering, Biorefining Research Institute)
ABSTRACT: Synthetic dispersants are commonly used in the stabilization of various colloidal suspensions. However, their non-biodegradable and toxic natures hamper their industrial use. The use of natural polymers as dispersants for various colloidal suspensions has been reported in the past, but the incentive for producing highly efficient natural polymeric dispersants is high. Lignin and xylan are the most abundant and sustainable natural polymers on earth, which are produced as by-products of pulping and cellulosic ethanol industries. These chemicals can be considered as the raw materials for producing value added products such as dispersants. In this dissertation, the anionic modification of kraft lignin and xylan via carboxymethylation, sulfomethylation and oxidation were comprehensively investigated and the applications of the products as dispersants in kaolin and coal suspensions were systematically assessed. The influence of reaction conditions on charge density and solubility of kraft lignin or xylan were systematically investigated. The anionic products obtained were characterized using NMR, FTIR, TGA, molecular weight and elemental analyses. The adsorption of anionic lignin or xylan on kaolin and coal particles and their effect on zeta potential of the suspensions was comprehensively assessed. The relative turbidity and viscosity analyses of colloidal suspensions confirmed the better dispersion performance of the products compared with commercial ones. The impact of dispersant dosage, pH of the suspension and time of mixing on dispersant performance of anionic lignin or xylan in kaolin and coal suspensions was also studied. The dispersion efficiency of suspensions found to increase with anionic lignin or xylan dosage and time of mixing. The dispersion efficiency of anionic lignin or xylan was at maximum under neutral conditions. The influences of molecular weight and charge density on the dispersant performance of anionic lignin in kaolin suspensions were also studied. The results showed that a highly charged anionic lignin adsorbed more compared with the low charged ones, and an increase in the molecular weight of anionic lignin showed no significant effect on its adsorption performance. Both charge density and molecular weight had an influence on dispersant activity of anionic lignin in kaolin suspensions. The dispersion studies of anionic kraft lignin or xylan in kaolin and coal suspensions showed that the increase in the dispersibility of these colloidal suspensions depends on adsorbed amount of anionic lignin or xylan on kaolin and coal particles, but not on the unadsorbed amount present in the suspensions. In the presence of anionic lignin or xylan dispersants, the zeta potential of kaolin or coal particles cannot determine directly the stability of colloidal suspensions. The adsorbed anionic lignin or xylan on kaolin and coal particles induced electrostatic repulsion between the particles and thereby improved the dispersibility of suspensions. The results obtained in this work confirms the possibilities for use of kraft lignin or xylan as dispersants in kaolin and coal suspensions and provides more insights on how the dispersability of these suspensions will be impacted by the properties of the produced dispersants. The results of this thesis contributed to knowledge on the chemical modification of lignin and xylan, characterization of modified products and to the fundamentals associated with the performance analysis of dispersion systems.