Numerical investigation of microwave-assisted pyrolysis of lignin

A comprehensive three-dimensional mathematical model is developed for studying the microwave-assisted pyrolysis of biomass. Kraft Lignin is considered as biomass feedstock in the model, and a mixture of lignin and char, is used as the sample for pyrolysis. A lumped kinetic model which considers three lumped pyrolysis products (gas, liquid and remaining solid fractions) is coupled with the governing equations for the microwave field, heat transfer, mass transfer, Darcy fluid flow and a transient numerical analysis is performed. The distribution of electric field in the microwave cavity, and the distribution of electric field, temperature, and pyrolysis products within the lignin sample are presented. The lignin sample is predicted to undergo volumetric heating when subjected to microwave heating. Accordingly the reaction zone extends from the center of the biomass sample bed towards the outer surface. Preliminary evaluation of the applicability of the model for assessing the effect of different parameters on the microwave pyrolysis of lignin is also carried out

Optimal hydrogels for fast and safe delivery of bioactive compounds

The design of injectable, biocompatible hydrogels encapsulating bioactive substances and exhibiting minimal aerosol formation is an important problem and its optimal solution can lead to more effective delivery vehicles in various applications. The delivery rate from such hydrogels is generally slow if one targets minimal aerosol formation. This thesis explores different biomaterials as potential hydrogels for such applications. The design criteria are good extrusion consistency without phase separation, fast release rate of the encapsulated biomolecule and ability to maintain the functionality of the encapsulated entity. In vitro tests were developed to evaluate the hydrogels synthesized. We were able to develop a gel showing good extrusion consistency and fast release rate of an active virus.M.S., Biomedical Engineering -- Drexel University, 200

Fluid model for a partially packed dielectric barrier discharge plasma reactor

In this work, a two-dimensional numerical fluid model is developed for a partially packed dielectric barrier discharge (DBD) in pure helium. In fluence of packing on the discharge characteristics is studied by comparing the results of DBD with partial packing with those obtained for DBD with no packing. In the axial partial packing configuration studied in this work, the electric field strength was shown to be en hanced at the top surface of the spherical packing material and at the contact points between the packing and the dielectric layer. For each value of applied potential, DBD with partial packing showed an increase in the number of pulses in the current profile in the positive half cycle of the applied voltage, as compared to DBD with no packing. Addition of partial packing to the plasma-alone DBD also led to an increase in the electron and ion number densities at the moment of breakdown. The time averaged electron energy profiles showed that a much higher range of electron energy can be achieved with the use of partial packing as compared to no packing in a DBD, at the same applied power. The spatially and time averaged values over one voltage cycle also showed an increase in power density and electron energy on inclusion of partial packing in the DBD. For the applied voltage parameters studied in this work, the discharge was found to be consistently homogeneous and showed the characteristics of atmospheric pressure glow discharge

Lactic acid and biomethane production from bread waste: a techno-economic and profitability analysis using pinch technology

Lactic acid (LA) is a vital platform chemical with diverse applications, especially for biodegradable polylactic acid. Bread waste (BW) is sugar-rich waste biomass generated in large quantities in residential and commercial operations. Recently, we evaluated the potential of BW for LA production by Bacillus coagulans under non-sterile conditions. This work presents a techno-economic and profitability analysis for valorizing 100 metric tons of BW per day to alleviate environmental pollution with concurrent production of LA and biomethane. We compared two fermentation approaches: acid-neutral (Scenario I) and low pH (Scenario II). Traditional esterification with methanol, followed by hydrolysis of methyl lactate, was employed for downstream separation to obtain polymer-grade LA. High-pressure steam was generated from solid debris via anaerobic digestion to complement energy demands partly. Energy consumption was further attenuated by process integration using pinch technology, with around 15% and 11% utility cost savings for Scenario I and II, respectively. These processes were capital-intensive, with 42–46% of LA production cost stemming from direct and indirect costs. Utilities were the major cost-contributing factor (19–21%) due to energy-intensive water evaporation from dilute fermentation broth. Due to additional processing steps, capital investment and operating costs were slightly higher in Scenario I than in Scenario II. LA manufacturing cost was thus more for Scenario I ($2.07 per kg) than Scenario II ($1.82 per kg). The minimum LA selling price for Scenario I and II were $3.52 and$3.22 per kg, respectively, with five-year payback periods and 8.5% internal rates of return. LA was slightly more expensive for decentralized BW processing than the market price

Life cycle analysis of fermentative production of succinic acid from bread waste

According to the US Department of Energy, succinic acid (SA) is a top platform chemical that can be produced from biomass. Bread waste, which has high starch content, is the second most wasted food in the UK and can serve as a potential low cost feedstock for the production of SA. This work evaluates the environmental performance of a proposed biorefinery concept for SA production by fermentation of waste bread using a cradle-to-factory gate life cycle assessment approach. The performance was assessed in terms of greenhouse gas (GHG) emissions and non-renewable energy use (NREU). Waste bread fermentation demonstrated a better environmental profile compared to the fossil-based system, however, GHG emissions were about 50% higher as compared to processes using other biomass feedstocks such as corn wet mill or sorghum grains. NREU for fermentative SA production using waste bread was significantly lower than fossil-based system and about the same as that of established biomass-based processes, thus proving the great potential of waste bread as a valuable feedstock for bioproduction of useful chemicals. The results show that steam and heating oil used in the process were the biggest contributors to the NREU and GHG emissions. Sensitivity analyses highlighted the importance of the solid biomass waste generated in the process which can potentially be used as fish feed. The LCA analysis can be used for targeted optimization of SA production from bread waste, thereby enabling the utilization of an otherwise waste stream and leading to the establishment of a circular economy

Techno-economic viability of bio-based methyl ethyl ketone production from sugarcane using integrated fermentative and chemo-catalytic approach: process integration using pinch technology

Butanediols are versatile platform chemicals that can be transformed into a spectrum of valuable products. This study examines the techno-commercial feasibility of an integrated biorefinery for fermentative production of 2,3-butanediol (BDO) from sucrose of sugarcane (SC), followed by chemo-catalytic upgrading of BDO to a carbon-conservative derivative, methyl ethyl ketone (MEK), with established commercial demand. The techno-economics of three process configurations are compared for downstream MEK separation from water and co-product, isobutyraldehyde (IBA): (I) heterogeneous azeotropic distillation of MEK-water and extractive separation of (II) MEK and (III) MEK-IBA from water using p-xylene as a solvent. The thermal efficiency of these manufacturing processes is further improved using pinch technology. The implementation of pinch technology reduces 8% of BDO and 9–10% of MEK production costs. Despite these improvements, raw material and utility costs remain substantial. The capital expenditure is notably higher for MEK production from SC than BDO alone due to additional processing steps. The extraction based MEK separation is the simplest process configuration despite marginally higher capital requirements and utility consumption with slightly higher production costs than MEK-water azeotropic distillation. Economic analysis suggests that bio-based BDO is cost-competitive with its petrochemical counterpart, with a minimum gross unitary selling price of US$ 1.54, assuming a 15% internal rate of return over five-year payback periods. However, renewable MEK is approximately 16–24% costlier than the petrochemical route. Future strategies must focus on reducing feedstock costs, improving BDO fermentation efficacy, and developing a low-cost downstream separation process to make renewable MEK commercially viable

Integrated biorefinery for bioethanol and succinic acid co-production from bread waste: techno-economic feasibility and life cycle assessment

In this study, an advanced decarbonization approach is presented for an integrated biorefinery that co-produces bioethanol and succinic acid (SA) from bread waste (BW). The economic viability and the environmental performance of the proposed BW processing biorefinery is evaluated. Four distinctive scenarios were designed and analysed, focusing on a plant capacity that processes 100 metric tons (MT) of BW daily. These scenarios encompass: (1) the fermentation of BW into bioethanol, paired with heat and electricity co-generation from stillage, (2) an energy-optimized integration of Scenario 1 using pinch technology, (3) the co-production of bioethanol and SA by exclusively utilizing fermentative CO2, and (4) an advanced version of Scenario 3 that incorporates carbon capture (CC) from flue gas, amplifying SA production. Scenarios 3 and 4 were found to be economically more attractive with better environmental performance due to the co-production of SA. Particularly, Scenario 4 emerged as superior, showcasing a payback period of 2.2 years, a robust internal rate of return (33% after tax), a return on investment of 32%, and a remarkable net present value of 163 M$. Sensitivity analysis underscored the decisive influence of fixed capital investment and product pricing on economic outcomes. In terms of environmental impact, Scenario 4 outperformed other scenarios across all impact categories, where global warming potential, abiotic depletion (fossil fuels), and human toxicity potential were the most influential impact categories (−0.344 kg CO2-eq, −16.2 MJ, and −0.3 kg 1,4-dichlorobenzene (DB)-eq, respectively). Evidently, the integration of CC unit to flue gas in Scenario 4 substantially enhances both economic returns and environmental sustainability of the biorefinery.NER

Bread waste valorization: a review of sustainability aspects and challenges

Bread waste (BW) poses a significant environmental and economic challenge in the United Kingdom (UK), where an estimated 20 million slices of bread are wasted daily. BW contains polysaccharides with great potential for its valorization into building block chemicals. While BW valorization holds tremendous promise, it is an emerging field with low technology readiness levels (TRLs), necessitating careful consideration of sustainability and commercial-scale utilization. This review offers a comprehensive assessment of the sustainability aspects of BW valorization, encompassing economic, environmental, and social factors. The primary objective of this review article is to enhance our understanding of the potential benefits and challenges associated with this approach. Incorporating circular bioeconomy principles into BW valorization is crucial for addressing global issues stemming from food waste and environmental degradation. The review investigates the role of BW-based biorefineries in promoting the circular bioeconomy concept. This study concludes by discussing the challenges and opportunities of BW valorization and waste reduction, along with proposing potential strategies to tackle these challenges

Process optimization for recycling of bread waste into bioethanol and biomethane: a circular economy approach

Bread is the second most wasted food in the UK with annual wastage of 292,000 tons. In the present work, bread waste (BW) was utilized for fermentative production of ethanol by Saccharomyces cerevisiae KL17. Acidic and enzymatic saccharification of BW was carried out resulting in the highest glucose release of 75 and 97.9 g/L which is 73.5 and 95.9% of theoretical yield, respectively. The obtained sugars were fermented into ethanol initially in shake flask followed by scale up in bioreactor in batch and fed-batch mode. In the fed-batch mode of cultivation, the maximum ethanol titers of 111.3, 106.9, and 114.9 g/L with conversion yield and productivity of 0.48, 0.47, and 0.49 g/g, and 3.1, 3.0, and 3.2 g/L.h was achieved from pure glucose, glucose-rich acidic and enzymatic hydrolysates, respectively. Further to improve the process economics, the solid residues after acidic (ABW) and enzymatic (EBW) hydrolysis of BW along with respective fermentation residues (FR) obtained after the ethanol production were pooled and subjected to anaerobic digestion. The solid residue from ABW + FR, and EBW + FR yielded a biochemical methanation potential (BMP) of 345 and 379 mL CH4/g VS, respectively. Life cycle assessment of the process showed that the total emissions for ethanol production from BW were comparable to the emissions from more established feedstocks such as sugarcane and maize grain and much lower when compared to wheat and sweet potato. The current work demonstrates BW as promising feedstock for sustainable biofuel production with the aid of circular biorefining strategy. To the authors knowledge, this is the first time, such a sequential system has been investigated with BW for ethanol and biomethane production. Further work will be aimed at ethanol production at pilot scale and BMP will be accessed in a commercial anaerobic digester

Viscous jets and filaments in electric fields: stability analysis and role of viscoelasticity

Viscous liquid jets and filaments are important in a number of industrial and domestic applications as well as in several natural processes. Application of an electric field is found to have a remarkable effect on the behaviour of these jets, mainly in controlling the propagation of instabilities and breakup dynamics. Such electrified jets have been exploited in a number of industrial applications such as electrospraying, electrospinning, electroseparations, ink-jet printing, etc. This thesis presents five theoretical and computational studies on different electrified viscous jet/filament systems. The first study is on electrospinning, a simple technique to generate polymeric nanofibers by taking advantage of distinctive flow instabilities in electrified jets of polymer solutions. This process, though easy to perform is quite complex to model mainly due to coupling of a number of physics together and the large number of dependent parameters. Here it is attempted to derive a relation between the final fiber diameter and the various process parameters. A scaling analysis of an approximate equation for the motion of a bent jet is performed and two new dimensionless numbers describing viscous moment and surface charge repulsion effects are identified. Experimental data for a wide range of polymer solutions are all shown to have a common slope, when expressed in terms of these new dimensionless ratios. Using this correlation between the dimensionless numbers, a new scaling expression is obtained for the final fiber diameter as a function of various process parameters. In the next study, stability of immersed viscous liquid threads subjected to radial or axial electric fields is investigated using linear stability analysis. Axisymmetric (m = 0) and asymmetric (m = 1) modes of perturbation are studied for arbitrary viscosity ratios. The viscosity ratio, in general, is shown to have a damping effect on the two modes of perturbations, and the effect is more pronounced for the m = 1 as compared to m = 0 perturbation. Investigating the effect of both the electric field and the viscosity ratio simultaneously, an operating diagram is generated, showing the predominance of the two modes at any given value of operating parameters. The above analysis is extended to understand the occurrence of the unique “pearling” stability on lipid bilayer cylindrical vesicles under electric field. It is shown that a certain critical axial electrical field needs to be applied to induce pearls on a bilayer vesicle. The maximum growth rate and the wavenumber of the pearling instability were found to in- crease with increasing electric field. While growth rate continues to increase, the maximum wavenumber reaches a steady value at higher electric fields. Like electric field, viscoelasticity induced by dissolved polymer molecules also plays a significant role in controlling the dynamics of breakup of jets and filaments. In the fourth study, capillary thinning of viscoelastic liquid bridges is investigated using an efficient hybrid method that combines a 1-D slender-filament approximation for the full profile of a liquid bridge with a 0-D stress balance to predict the temporal evolution of the filament “neck”. In addition, an advanced constitutive model for polymeric stresses is used to study the anomalous concentration dependence of break-up dynamics in polymer solutions that are nominally regarded as being dilute. The microstructural constitutive model incorporates changes in the friction coefficient of polymer molecules as they unravel, stretch and begin to experience significant intermolecular interactions in strong extensional flows due to a phenomenon known as “self-concentration”. The hybrid simulation technique is used with this new constitutive model to predict dynamics of liquid-bridge necking that compares well with experimental observations reported in the literature on dilute polymer solutions. In the last study, the importance of relaxation time and self-concentration on electrospinning of dilute polymer solutions is investigated by considering the steady region of an electrified jet of a polymer solution. It is shown that elastic stresses increase exponentially with Deborah number (De). For each concentration there exists a critical De below which the elastic stresses at the end of the steady jet region are insufficient to overcome capillary stresses and lead to an unstable jet in the whipping region. However, above the critical De, the elastic stresses may be sufficiently dominant to lead to more uniform fibers, thus pointing to the possibility of improved “electrospinnability” even with dilute polymer solutions. Also, it is suggested that self-concentration may play an important role in electrospinning of polymer solutions with higher relaxation time and high conductivity.Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia