DSpace Collection:

DIRECT HYDROTHERMAL VALORIZATION OF BIOMASS AND ELECTROPLATING EFFLUENT

2024-08-01T00:00:00Z

Title: DIRECT HYDROTHERMAL VALORIZATION OF BIOMASS AND ELECTROPLATING EFFLUENT Authors: Kumar, Pankaj Abstract: With the global increase in industrial activities and urban expansion, addressing cleaner energy production and wastewater treatment has become a critical aspect of responsible environmental management. Industrial activities, particularly those involving metal processing, contribute significantly to the carbon dioxide emission and contamination of water bodies with heavy metals, presenting significant environmental hazards and potential threats to human health. Heavy metals such as copper, zinc, cobalt, and nickel are a few of the most widely used metals, mainly in the electroplating and mining industries. Fatal consequences may arise if the trace amounts of these metals in the human body exceed the threshold limits. Therefore, these heavy metals must be recovered from the wastewater streams economically and effectively. Moreover, the energy utilized by heavy metal industries is produced from non-renewable sources (coal and oil), contributing to greenhouse gas emissions. The depletion of fossil fuel reservoirs, coupled with the escalating specter of global warming, prompts researchers to shift their attention toward renewable energy alternatives such as biomass. Biomass is a carbon-neutral and environmentally friendly energy resource with significant economic value and abundant reserves. The biomass's thermochemical conversion route (pyrolysis and gasification) encounters limitations attributed to its elevated moisture content, necessitating substantial energy inputs for the drying process. Supercritical water gasification (SCWG) offers a distinct advantage in effectively handling wet biomass to generate a hydrogen-rich fuel gas mixture. In this, supercritical water (SCW) is utilized as a solvent and reaction medium to transform lignocellulosic biomass into a fuel gas rich in high value H2-rich gaseous fuel and biochar. SCW shows improved heat transfer and mass transfer properties with higher solvation properties. To enhance the performance and yield of hydrogen, catalysts were incorporated into the process under controlled operating conditions during SCWG. However, these catalysts are prone to deactivation during the process. Henceforth, this research highlights the in-situ utilization of metal-contaminated wastewater as a catalyst infused with lignocellulosic biomass for the co-synthesis of a hydrogen-rich fuel gas mixture and nanometal carbon hybrid (NCH) via SCWG.

FILM FLOWS INSTABILITIES: EFFECT OF SURFACTANT, IMPOSED SHEAR AND POROUS SUBSTRATE

2024-07-01T00:00:00Z

Title: FILM FLOWS INSTABILITIES: EFFECT OF SURFACTANT, IMPOSED SHEAR AND POROUS SUBSTRATE Authors: Jain, Neha Abstract: Cylindrical liquid film flows present inside or outside of a vertical tube or wire is ubiquitous and garnered a lot of interest in literature due to its applications in industrial, technological and biological processes. These film flows are prone to the disturbances where the amplification of the disturbances over time may distort the interfaces and render it unstable. These instabilities may be desirable for enhanc ing the heat and mass transfer phenomena in the distillation unit, heat exchangers, falling film reactors and also for the formation of liquid drops in microfluidic de vices. There are situations where the perfectly cylindrical interfaces are required such as during the coating of wire. The distortions at the interface creates an un even film thickness which affects the final quality of the product. Therefore, many strategies have been developed to control or manipulate these instabilities such as the use of surface-active agents at the gas-liquid or liquid-liquid interfaces, applica tion of an externally imposed shear stress at the free surface, by replacing the rigid solid wall with the soft or deformable solid substrate, etc. Consequently, the stabil ity of these film flows has been an important area of research both experimentally and theoretically. Cylindrical liquid films present inside or outside of a tube always remain unsta ble due to the surface tension driven capillary instability which is termed as the Rayleigh-Plateau (RP) instability. This RP instability exists even in the absence of inertia. However, the presence of inertia excites an another mode of instability at the free surface that is known as free surface instability, which exists for both planar and cylindrical film flows. Furthermore, for the stationary cylindrical film, the effect of the presence of an insoluble surfactant was found to be stabilising. It decreases the growth rate of the Rayleigh-Plateau instability but could not eliminate it completely (Camapana et al. 2004; Carroll & Lucassen 1974; Cassidy et al. 1999; Halpern & Grotberg 1993). However, in the presence of the basic flow, the RP instability was completely eliminated above a critical value of the Marangoni number (Nair & Sharma 2020). They also investigated that the surfactant mode remains stable in the low wavenumber limit and become unstable for a range of arbitrary wavenumber ii for high Marangoni number. Similar observation of complete suppression of RP instability was made by (Ogrosky 2021) for the liquid film present inside of a tube but did not mention anything about finite wavenumber instability as investigated by (Nair & Sharma 2020). Apart from the effect of presence of surfactant at the free surface (passive gas), number of studies are available where the surfactant loaded gas-liquid interface is subjected to an externally applied shear stress for planar and cylindrical film flows. The presence of an imposed shear was found to be destabilis ing or stabilising (downstream or upstream direction) for the gas-liquid mode. The surfactant mode was found to be unstable solely due to the presence of basic shear (Bhat & Samanta 2019; Wei 2005b; Zhou et al. 2014). The existing literature has explored the effect of the surfactant for the liquid film present inside of a tube using lubrication or the long wave approximation. There fore, in one of the objective of this thesis: (1) We investigated the effect of the surfactant on the liquid film present inside of a vertical tube in presence of the base f low using the long-wave and numerical shooting method. Furthermore, to the best of our knowledge no study has examined the effect of the imposed shear stress at the gas-liquid for the liquid film flowing outside of a vertical fibre. Hence, the second objective is: (2) To examine the effect of an imposed shear stress on the stability of gravity-driven surfactant doped Newtonian liquid film flowing outside of a verti cal rod or fibre. Both the studies were conducted in the limit of vanishingly small Reynolds number (Re “ 0). We carried out the linear stability analysis using the long-wave asymptotic analytical method and further extended our results to finite or arbitrary wavenumbers using the numerical shooting method. In Chapter 2 of this thesis, the stability of the gravity-driven and surfactant-doped Newtonian liquid film present inside of a vertical tube was examined using the lin ear stability analysis in the creeping flow limit. This flow configuration exhibits two normal modes of instability. (i) Surface tension-driven Rayleigh-Plateau mode. (ii) Surfactant mode, which arises due to the gradients of surface tension in presence of surfactant. It has been observed that in the presence of the base flow (character ized by Bond number, Bo), the Rayleigh-Plateau instability can be eliminated com pletely, when the Marangoni number increases above a critical value. In contrast, the surfactant mode which was stable for stationary film now remains unstable for any non-zero value of the Marangoni number, when the base flow was included into iii the stability analysis. This surfactant mode instability was observed to endure for f inite or high wavenumber depending on the liquid film thickness and Bond number. It was noted that the maximum growth rate for the surfactant mode become higher than that of the RP mode for a clean film (Ma=0). Therefore, for moderate and high Bond number, the long-wave nature of instability observed for static film shifts to f inite or short wave surfactant mode instability present into the system. Therefore, the presence of surfactant has an overall destabilizing effect on film flows and the long-wave model is not sufficient to determine the overall stability characteristics of such film flows. In chapter 3 of this thesis, the linear stability of gravity-driven flow of a surfactant laden Newtonian liquid film over a rod is examined in creeping flow limit, in the presence of an externally applied shear stress at gas-liquid (GL) interface. The im posed shear can be applied either in a direction assisting the flow (positive shear stress) or opposite to the direction of the gravity-driven flow (negative shear stress). The two instability modes exist for this flow configuration: (i) Rayleigh-Plateau (RP) mode, and (ii) surfactant mode. Earlier studies revealed that, in absence of im posed shear stress, the surfactant can completely suppress the RP instability above a critical value of Marangoni number. With further increase in Marangoni number to sufficiently high values, the surfactant mode becomes unstable. Hence, there ex ists a window in terms of Marangoni number, where the liquid film remains stable. However, in the presence of imposed shear stress at the gas-liquid interface, the dy namics of the liquid film changes significantly and alters the stability characteristics of the film flow. We first examined the problem using the long-wave asymptotic analysis, it was demonstrated that the positive stress has a stabilizing effect on the RP mode in addition to the stabilizing contribution due to the presence of the sur factant and destabilizing impact on the surfactant mode. Therefore, for any physical situation where the surfactant is present in the sufficiently low concentration (small values of Ma), the application of the suitable magnitude of the positive stress can be used to completely suppress the RP instability. The surfactant mode which remains stable in the absence of an external shear, may become unstable, when the magni tude of the positive stress increases above a threshold value (τ ą τc) and remains stable for τ ă τc. Thus, the effect of increasing the positive shear was found to be destabilizing for the surfactant mode, in contrast to the stabilizing effect for the RP iv mode. It is important to note the the critical value of stress above which surfactant mode destabilises is lower in magnitude to the critical stress required for the sta bilisation of the RP mode. Hence, it is not possible to eliminate the RP instability without triggering the surfactant mode instability. Below this critical value of the stress, long-wave RP instability will be present in to the system whereas above τc, the surfactant mode instability occupies the whole region from low to finite wave perturbations for any value of Marangoni number. Therefore, the positive stress is found to have an overall destabilising effect on the system. However, the extension of the results from low to finite or high wavenumber shows the existence of a stable gap in terms of Marangoni number for small values of the imposed shear stress. This stable gap vanishes, when the shear stress increases beyond the critical value required for the destabilisation of the surfactant mode. For the negative imposed shear stress, the low wavenumber results predicts that for the effect of negative shear stress is destabilizing (stabilizing) for RP (surfac tant) mode, when the magnitude of applied stress is lower than a threshold value (τ ă τc “ 4 d). However, the effect of the imposed shear reverses for both modes when τ ą τc. Note that the critical value of the imposed shear remains same for both the RP or surfactant mode unlike in case of positive shear, where critical stress (τc) was different for both the modes. The analysis concerned with the results of negative shear stress shows that with increase in the magnitude of imposed shear, the finite wavenumber perturbations are destabilised and occupies the whole region in Marangoni versus wavenumber plane. Therefore, it results into the change in stability behavior from long-wave (for stress free interface) to finite wavelength dominated instability. Hence, it is not possible to obtain stable flows when magni tude of shear stress is above a certain value in a similar manner as shown for the positive applied stress. In Chapter 4 of this thesis, we conducted the linear stability analysis of gravity driven Newtonian liquid film flow over a porous inclined plane. The flow in the f luid andporouslayer is modelled with Navier Stokes and volume-averaged Navier Stokes (VANS) equation respectively. In this study, three different modes of insta bility was found: surface mode, shear mode and the porous mode. The surface mode is the long-wave instability mode which triggers due to the deformation of the free surface above a critical value of Reynolds number. In regard of the rigid v plane, it has been observed that for the low angle of inclination, the mode which be come unstable at finite wavenumber was termed as shear or hard mode. However, the porous mode is observed only in the presence of permeable porous substrate instead of rigid plane. The porous mode instability occurs as a results of perme ation of the fluid flow perturbations inside the porous region. We re-examined the research conducted by Camporeale et al. (2013) and made corrections in the pertur bation equations that was initially done by Camporeale et al. (2013). They missed many terms in the boundary condition at the fluid-solid interface (normal stress bal ance) and added an extra term in fourth order ODE for porous layer. It has been observed that the corrected equations significantly change the stability features for the range of parameters typically for large δ. Camporeale et al. (2013) observed that the high wave number porous mode exists with surface and shear for all chosen value of angle of inclination θ. However, such porous mode instability remains ab sent in our analysis. We observed that porous mode do exists but in the range low to finite wavenumber for very small angle 0.03˝ at δ “ 0.02. We also studied the effect of different parameter (d,δ,α,Re,θ) on the flow stability behaviour of the system.

TRI- REFORMING OF METHANE FOR THE PRODUCTION OF SYNTHESIS GAS

2024-07-01T00:00:00Z

Title: TRI- REFORMING OF METHANE FOR THE PRODUCTION OF SYNTHESIS GAS Authors: Pandey, Akansha Abstract: The conversion of the two most problematic gases, i.e., CO2 and CH4, to the valuable synthesis gas via the tri-reforming (TRM) is a very promising route. The TRM with CO2, H2O, and O2 to produce synthesis gas (syngas) with an H2/CO molal ratio of 1.5-2 is highly desirable for the production of important chemicals and fuel additives, including methanol, dimethyl ether (DME), and substitute natural gas (SNG), etc., via the Fischer-Tropsch (F-T) process. In this thesis, a novel nano-nickel metal catalyst dispersed on mesoporous-zirconia is developed for the controlled production of the synthesis gas with an H2/CO mol ratio of 1.5-2 via the TRM. The catalysts were tested in a downflow-fixedbed reactor at 600-850 oC and 1 atm. At the optimum feed (CH4:CO2:O2:H2O:N2) ratio of 1: 0.5: 0.1: 0.0125:1, the maximum CO2 and CH4 conversion was ~28% and ~86%, respectively, over the 5 wt.% Ni/ZrO2. At this condition, the syngas with an H2/CO ratio of ~1.5 was obtained at a lower reaction temperature of 700 oC. The superior activity of this catalyst was due to the presence of highly dispersed and reduced nickel particles over the combined tetragonal and monoclinic phases of mesoporous ZrO2. The basic strength of the catalyst, the nickel particle size, and metal dispersion played a important role in controlling the TRM activity as well as the H2/CO mole ratio. The time-on-stream (TOS) study and the used catalyst characterization results established that the nanosized nickel metal particles dispersed on mesoporous-zirconia were thermally stable and coke-resistant. Further, a series of Zr-MOF were synthesized via the solvothermal method, and an impregnation technique was used to synthesize the nickel impregnated on a MOF-derived ZrO2 catalyst. The catalyst was characterized by various methods, including N2-porosimetry, X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), temperature programmed reduction (TPR), H2-chemisorption, CO2-temperature programmed desorption (CO2-TPD), high-resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy (FE SEM), etc. Characterization results supported the formation of the Zr-MOF and nickel metal dispersed on MOF-derived ZrO2. Further, the TRM activity of the catalyst developed were tested in a downflow-fixed bed reactor. The various catalysts were screened for TRM activity at different temperatures (600-850 oC). Results demonstrated that TRM was highly favorable over the NZ-1000 catalyst due to its desirable physicochemical properties, including nickel metal surface area (2.3 i m2.gcat-1), metal dispersion (7.1%), and nickel metal reducibility (45%), respectively. Over the NZ 1000 catalyst, an optimum H2/CO ratio of ~1.6-2 was achieved at 750 °C, and it was stable for a longer period of time. To understand the kinetic behavior of TRM reaction, the kinetic study was performed over 5 wt.% Ni/ZrO2 catalyst under steady-state condition. The reaction temperature and W/FAo were varied from 650-800 oC and 0.61-3.06 g.min.mol-1 at 1 atm. pressure. The Power law model and Langmuir Hinshelwood-Hougen-Watson (LHHW) model for heterogeneous reaction was proposed. The model equations were solved by using MATLAB. For the Power law model, the calculated activation energy with respect to CH4 and CO2 was 42.31 and 83.31 kJ.mol-1, respectively. For the LHHW model, the POM reaction was not considered due to the complete consumption of O2 during the reaction. Therefore, DRM, SRM, and WGS reaction were used for kinetic study. For deriving the rate expression, the surface reaction was considered as the rate-controlling and irreversible in nature. The rate expressions were solved by an ode23 solver in MATLAB in combination with the genetic algorithm optimization tools for the estimation of kinetic parameters. The obtained activation energy for DRM, SRM, and WGS reaction were 76.29, 117.16, and 67.33 kJ.mol-1, respectively.

CONVERSION OF POLYPROPLENE- RICH DISPOSABLE FACE MASK THROUGH CATALYTIC PYROLYSIS TO PRODUCE HIGH-VALUE HYDROCARBON-OIL

2024-07-01T00:00:00Z

Title: CONVERSION OF POLYPROPLENE- RICH DISPOSABLE FACE MASK THROUGH CATALYTIC PYROLYSIS TO PRODUCE HIGH-VALUE HYDROCARBON-OIL Authors: Hooda, Sanjeevani Abstract: The exponential rise in the global energy demand along with the steep depletion of conventional fossil fuels necessitate an alternative and sustainable energy source. Moreover, the profusion of waste plastic generation (projected to be around 155 to 265 metric tons per year by 2060) without proper disposal methods has led to a global concern that needs a potent solution (Lebreton and Andrady, 2019). Likewise, the upsurge in the waste generation of disposable face masks during the COVID-19 pandemic as well as its persistence in the environment over the years without a proper disposal method has led to a global concern that needs a potent solution. Their non biodegradable nature and prolonged presence in the environment leads to their progressive breakdown into micro and nano-size plastic fragments that can be easily ingested by animals and humans, thus posing a severe threat to the society (X. Chen et al., 2021). A thermochemical conversion approach provides a promising solution for converting waste to energy, meeting the demands of both, the depleting fossil fuel crisis as well as the requirement for proper disposal methods. Different thermochemical processes like pyrolysis, gasification, combustion, hydrothermal liquefaction, etc., are available to convert various feedstocks into high-value products. Amongst these, pyrolysis is preferred because of the cost-efficient, easy-to-use, and environment-friendly nature of the process (Czajczyńska et al., 2017; Praveenkumar et al., 2024). Moreover, the presence of high amount of carbon, hydrogen, and volatile matter in the disposable face mask illustrated by its ultimate analysis (carbon: 77.77%, hydrogen: 13.4%, nitrogen: 0.05%, oxygen: 8.78%) and proximate analysis (volatile matter: 83.35%, ash: 11.95%, fixed carbon: 4.70%) makes it a potential source of energy that can be harvested via pyrolysis technique. Thus, present study explores the feasibility of converting disposable face mask to energy using a low-cost waste (spent aluminium hydroxide/oxide nanoparticle adsorbent) derived catalyst. Subsequently, analysis of the textural and morphological characteristics of the catalyst using different analytical techniques such as XRD, FTIR, BET, FESEM and NH3-TPD demonstrates a mesoporous structure, with a surface area of 161.20 m2 g-1 and total pore volume of 0.25 cm3 g-1. Furthermore, the presence of all three acidic sites denotes to the availability of large number of binding sites, that can enhance the reactivity of the process. Thermogravimetric analysis of the non-catalytic and catalytic pyrolysis (using spent AHNP derived !-Al2O3) of disposable face mask was conducted at varied heating rates of 10oC/min, 20oC/min, 30oC/min, 40oC/min, and 50oC/min, respectively. Iso-conversional methods, Kissinger Akahira Sunose (KAS) and Ozawa Flynn Wall (OFW) were used for the kinetic study. Additionally, the thermodynamic parameters of the process namely Gibb’s free energy (∆G, kJmol-1), enthalpy (∆H, kJmol-1), and entropy (∆S, kJmol-1K-1) were also determined. Results found that addition of catalyst to the process benefits the overall efficacy of the process by reducing the activation energy (Ea) (without catalyst; OFW-Ea: 188.7 kJ/mol, KAS-Ea: 186.2 kJ/mol; with bare alumina (!-Al2O3); OFW-Ea: 183.2 kJ/mol, KAS-Ea: 180.4 kJ/mol) as well as lowering the disordered state of the process. The results illustrated the potential efficacy of utilizing spent aluminium hydroxide/oxide adsorbent based catalyst in place of high-cost commercial catalysts. However, conventional analysis techniques do not provide insights into the influence of characteristics of feedstock on the process kinetics. Therefore, a study was conducted to exemplify the efficacy of using machine learning for the predictive modeling of the pyrolysis process kinetics in order to understand the complexities of the interrelations of predictor variables and their influence on activation energy. The activation energy for pyrolysis of waste plastics was evaluated using machine learning models namely Random Forest, XGBoost, CatBoost, and AdaBoost regression models. Characteristics of the feedstock, types of plastic, conversion values and iso-conversional methods (OFW, KAS, and Friedman (FR)) used for kinetic evaluation, were taken as predictor variables. A total 674 data points were collected from literature as well as the present investigation. Feature selection based on the multicollinearity of data and hyperparameter tuning of the models utilizing RandomizedSearchCV was conducted. Random forest model outperformed the other models with R2 value of 0.941. Shapely additive explanations projected fixed carbon content, ash content, conversion value, and carbon content as significant parameters of the model. Moreover, on comparing the predicted results of activation energy with the results estimated using TGA data through iso-conversional method, an absolute error range of 0.1 to 1.8% (for OFW) and 0.2 to 1.2% (for KAS) in the conversion range of 0.1 to 0.9 was observed. These results further substantiate the reliability and robustness of the model developed using machine learning approach. Subsequently, the modelling and optimization of the catalytic pyrolysis of face masks incorporating a waste-derived catalyst to analyze the effect of process parameters (temperature, feed-to-catalyst ratio, and inert gas flow rate) on the oil yield of the process was conducted. The experimental study was carried out in a semi-batch reactor using spent AHNP derived !-Al2O3 ii as a catalyst. Response surface methodology and machine learning were used for the optimization and modeling of the process. Both response surface methodology (rotational central composite design, R2-0.95) and machine learning (decision trees regression, R2-0.83) demonstrated a higher prediction accuracy and lower error margins. Both the modeling processes provide results with high efficacy. However, the employment of machine learning adds on to the knowledge of the interrelations of the predictor variable with the output of the model by employing the explainable artificial intelligence (XAI). Pyrolysis temperature was spot lighted to be the predominant parameter followed by feed-to-catalyst ratio. Experimental oil yield (13.5%) obtained at optimized parameters (516 oC temperature, 3:1 feed-to-catalyst ratio, and 163 mL/min inert gas flow rate) was compared with those predicted through response surface methodology (13.7%) and decision trees regression (13.12%), showcasing an absolute error range of 0.2-0.4 wt%. Thus, the results highlight the successful modeling and optimization of the catalytic pyrolysis of face masks. Further, at optimized conditions, the effects of metal doped spent AHNP derived !-Al2O3 catalysts on the pyrolysis product distribution and composition were investigated. Monometallic (Ni, Co, Fe impregnated) and bimetallic (Ni-Co, Ni-Fe, Co-Fe impregnated) waste derived alumina catalysts were explored for their catalytic performance to produce commercial range fuels from disposable face mask and further compared with the bare alumina (!-Al2O3) based catalytic as well as non-catalytic processes. Catalysts were used in an ex-situ mode. Characterization of the metal doped catalysts highlighted bi-modal mesoporous structure with surface area in the range of 140.42 to 161.20 m2 g-1 that helps to enhance the stability and activity of the catalysts. Ni-Co/Al and Co-Fe/Al exhibited higher oil production of 14.9 wt% while Fe/Al demonstrated increased non-condensable gas production of 78.8 wt%. Ni/Al showed a higher selectivity for naphthene and paraffins likewise, Fe/Al exhibited a higher selectivity for olefins in the oil. Likewise, different catalysts exhibit distinctive advantages in terms of product distribution and composition due to their individual characteristics. However, in terms of the calorific value of oil, Ni/Al presented the best results with HHV of 44.64 MJ/kg. The present study demonstrates the feasibility of valorizing the face mask into energy-dense oil comparable to commercial range fuel using a spent adsorbent based catalyst. The potential environmental effects associated with the non-catalytic and catalytic pyrolysis of disposable face mask was estimated using life cycle analysis (LCA) and the economic assessment iii of the processes was conducted in terms of operational cost analysis. Mono-/bimetal doped spent adsorbent (aluminium oxide/hydroxide nanoparticles) derived catalysts were utilized in the process and assessed for their impact on the environment. The impact of individual process units on the distinct environmental indices of CML 2001-August 2016 methodology of ‘Sphera’s LCA for experts’ software was assessed. The scenario comprising of recycling the energy produced via combustion of non-condensable gases along with utilizing the excess energy as well as char for energy and coal credits demonstrates a significant reduction in the LCA impact values of the overall process. The sub-processes significantly effecting the environment factors were evaluated to be the pyrolysis process, combustion of hydrocarbon-oil, catalyst, and shredding of the face mask. The lack of bias, robustness, and reliability of the LCA results were further established by the Monte Carlo uncertainty analysis showcasing a standard deviation of less than 10%. Based on the operational cost assessment, the pyrolysis process can be arranged in a sequence as Al < non-catalytic < Fe/Al < Ni-Fe/Al < Ni/Al < Co-Fe/Al < Ni-Co/Al < Co/Al. Additionally, the operational cost of the process presented in the study is significantly lower than the studies utilizing the commercial based catalyst. Thus, the present study highlights the eco-friendly nature of the non-catalytic and catalytic pyrolysis of the disposable face mask utilizing a spent adsorbent derived catalyst and also provides a comprehensive insight for the scale-up of the process following a circular economy approach.