Department of Chemical Engineering
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Item Sustainable use of rice husk for the cleaner production of value-added products(Elsevier, 2022-02) Kuncharam, Bhanu Vardhan Reddy; Srinivas, AppariThis paper covers a comprehensive review of the thermochemical conversion of rice husk (RH) into value-added products. RH is an organic residue and is produced in large quantities in China, India, Indonesia, and Bangladesh and appears to be a viable source for value-added products from thermochemical processes. The RH properties and operating conditions affect the quality and yield of the bio-oil, gaseous, and biochar products. The conversion techniques such as gasification, slow and fast pyrolysis, and product distribution are systematically reviewed. The literature shows that the Ni-based catalysts demonstrated high activity towards cracking of tar compounds and hydrocarbons, upgraded gas quality, and yielded high hydrogen production. Zeolite-based systems are promising catalysts for the upgradation of bio-oils. Due to the structured porosity and higher acidity, the metal-loaded zeolites catalysts have shown high removal efficiency towards the oxygenated compounds. RH ash is also used as an alternative cementitious material in the construction sector. The optimum level of cement replacement with RH ash in concrete is 15–20%, and higher compressive strength is witnessed for RH ash used concrete than conventional cement concrete. RH ash utilization for soil remediation and blended cement production are also discussed. A sustainable framework has been proposed for the utilization of RH in the chemical and construction sectors.Item A mechanistic study on the reaction pathways leading to benzene and naphthalene in cellulose vapor phase cracking(Elsiever, 2014-10) Srinivas, AppariThe reaction pathways leading to aromatic hydrocarbons such as benzene and naphthalene in gas-phase reactions of multi-component mixtures derived from cellulose fast pyrolysis were studied both experimentally and numerically. A two-stage tubular reactor was used for evaluating the reaction kinetics of secondary vapor phase cracking of the nascent pyrolysates at temperature ranging from 400 to 900 °C, residence time from 0.2 to 4.3 s, and at 241 kPa. The products of alkyne and diene were identified from the primary pyrolysis of cellulose even at low temperature range 500–600 °C. These products include acetylene, propyne, propadiene, vinylacetylene, and cyclopentadiene. Experiments were also numerically validated by a detailed chemical kinetic model consisting of more than 8000 elementary step-like reactions with over 500 chemical species. Acceptable capabilities of the kinetic model in predicting concentration profiles of the products enabled us to assess reaction pathways leading to benzene and naphthalene via the alkyne and diene from primary pyrolysates of cellulose. C3 alkyne and diene are primary precursors of benzene at 650 °C, while combination of ethylene and vinylacetylene produces benzene dominantly at 850 °C. Cyclopentadiene is a prominent precursor of naphthalene. Combination of acetylene with propyne or allyl radical leads to the formation of cyclopentadiene. Furan and acrolein are likely important alkyne precursors in cellulose pyrolysis at low temperature, whereas dehydrogenations of olefins are major route to alkyne at high temperatures.Item Chemical structures and primary pyrolysis characteristics of lignins obtained from different preparation methods(J-Stage, 2014) Srinivas, AppariThis work aims at investigating correlations between primary pyrolysis characteristics of lignin and chemical structure of lignin feedstock. Three different types of lignin samples were prepared through enzymatic hydrolysis, organosolv extraction, and Klason procedure. Analysis by FT-IR and solid state 13C-NMR revealed that the lignin samples exhibited different contents of aromatic carbons, connection carbons, methoxyl carbons, and aliphatic side chains. The three lignin samples were pyrolyzed in a two-stage-tubular reactor at 650 ℃, and pyrolysis products were analyzed with gas chromatographs on-line. More than fifty compounds including inorganic gases, light hydrocarbons (LHs), aromatic hydrocarbons (AHs), phenol derivatives and light non-phenolic oxy-compounds (NPOCs) were gaschromatographically separable and quantified. The influence of the lignin structures on the pyrolysis characteristics was studied, and the correlation of product distribution and lignin chemical structures was examined. The total carbon selectivity into char and tar was increased with increasing lignin aromaticity. Methoxyl group and aliphatic substituents likely contributed for enhancing char formation, while hydrogen in lignin enhanced tar formation. Yields of LHs and NPOCs were increased with increasing aliphatic carbons of the lignin samples. AHs were formed from gas-phase recombination of LHs such as olefins, diolefines and alkynes, rather than directly from aromatic structures in the original lignin likely because of high energy required to cleavage carbon-oxygen bond existed in major structural units such as syringols or guaiacols.Item A circular framework for the valorisation of sugar industry wastes: Review on the industrial symbiosis between sugar, construction and energy industries(Elsiever, 2018-12) Srinivas, AppariThis paper provides a comprehensive review of literature on the properties of sugar industry waste, their varied uses in energy and construction sector, performance and limitations. An efficient upcycling of sugar industry waste in energy production would help the energy sector to reduce its dependency on non-renewable fossil fuels. Literature demonstrates that in the recent years there has been an increased research interest in thermochemical conversion of sugarcane bagasse to produce cleaner energy, rather than its landfilling or combustion. On the other hand, utilisation of secondary by-products from sugar industry in the production of cement, bricks, paver blocks, activated binder and other construction products helps to cut down the carbon footprint of the construction industry, while improving the properties of the final products. From the perspective of the sugar industry, such an arrangement eliminates disposal problems and creates additional revenue. Although independent research studies investigating the use of sugar industry by-products exist, few studies consider these valorisation options together to minimise waste and to create an efficient material flow chain. This study identifies various material and energy recovery pathways from published literature and connects the materials and processes to form a continuous material supply chain with minimum wastage. From the findings, a symbiotic framework has been developed with primary and secondary by-products from the sugar industry serving as source materials for energy production and sustainable construction products.