Potential of ionic liquids as emerging green solvent for the pretreatment of lignocellulosic biomass

Lignocellulosic biomass is available in abundance as a renewable resource, but the major portion of it is often discarded as waste without utilizing its immense potential as an alternative renewable energy resource. To overcome recalcitrance of lignocellulosic biomass, various pretreatment methods are applied to it, so that the complex and rigid polymeric structure can be broken down into fractions susceptible for enzymatic hydrolysis. Effective and efficient biomass processing is the goal of pretreatment methods, but none of the explored pretreatment methods are versatile enough to fulfil the requirement of biomass processing with greater flexibility in terms of operational cost and desired output efficiency. Deployment of green solvents such as ionic liquids for the pretreatment of lignocellulosic biomass has been a topic of discussion amongst the scientific community in recent times. The presented work provides a detailed overview on the deployment of ionic liquid for the pretreatment of lignocellulosic biomass coupled with a brief discussion on other pretreatments methods. The recyclability and reusability along with other unique properties makes an ionic liquid pretreatment different from the other traditional pretreatment methods. Also, this study explores diverse critical parameters that governs the dissolution process of biomass. Hazardous properties of ionic liquids have also been explored. Future perspective and recommendations have been given for an efficient, effective, and eco-friendly deployment of ionic liquid in biomass pretreatment process.

Advances in phase change materials and nanomaterials for applications in thermal energy storage

Phase-changing materials are nowadays getting global attention on account of their ability to store excess energy. Solar thermal energy can be stored in phase changing material (PCM) in the forms of latent and sensible heat. The stored energy can be suitably utilized for other applications such as space heating and cooling, water heating, and further industrial processing where low-temperature heat energy is required. The presented work attempts to evaluate past, present, and future trends in the development of energy storage materials and their encapsulation techniques for efficient utilization of the available energy. Hybrid PCM with nanoparticles has excellent potential to tailor thermo-physical properties and uplift the efficiency of energy storage systems. Synergistic use of PCM with nanomicromaterial can further improve the capacity of energy storage system along with the charging and discharging efficiencies of the system. Impacts of the size of particle, concentration ratio, and shape of particle have been studied to assess their effectiveness in enhancing storage efficiency of the systems. Waste heat recovered and stored in energy storage materials can undoubtedly improve the total energy availability of the source, thus enhancing the exergy efficiency with simultaneous reduction in the entropy generation rate. Core-shell nanoparticles can further improve the optical absorptance spectra towards an infrared region of thermal energy. Paraffin wax-based NEPCMs with graphene nanoplatelets achieve 2.14 W/(m·K) thermal conductivity, enabling faster and more efficient heat transmission and lowering charging and discharging times for thermal storage devices.

Advancements in solar technologies for sustainable development of agricultural sector in India: a comprehensive review on challenges and opportunities

Agriculture is the main occupation of the majority of people in India. The majority of the population in India is dependent (directly or indirectly) on agriculture as an occupation. The agriculture sector requires more freshwater and power for better yield in the current scenario. Nevertheless, the ever-increasing rate of energy consumption, limited fossil fuels, and rising pollution have made the expansion of renewable resources essential. Due to the suitable solar potential available in India, the deployment of solar energy has been more as compared to other renewable resources. The current study aims to discuss the various technologies, initiatives and policies of solar energy usage in agriculture. This work delivers an assessment of the advancement of solar energy vis-à-vis agricultural applications through the greenhouse concept and photovoltaic approach in India. Various agricultural applications of solar energy, such as solar water desalination system, solar water pumping system, solar crop dryer system for food safety, etc. are discussed as a means to promote solar-based technology. It also highlights the scenario of solar energy in India with important accomplishments, developmental approaches, and future potential. In-depth studies of various policies and government initiatives including those in research and development are also discussed. The current survey on solar technologies will be an aid to agribusiness frameworks to comprehend the statuses, obstructions, and extent of advancement. Finally, some future recommendations for further developments in this approach are discussed. This work sheds light on varied areas of solar energy-assisted agricultural systems as a potentially sustainable and eco-friendly pathway.

Historic review and recent progress in internal design modification in solar stills

Solar still, which uses solar renewable energy sources, especially solar energy, to produce pure water, is a promising technology as it is abundantly available and eco-friendly. Researchers have innovated in internal and external designs to enhance distillate productivity in solar desalination systems. The present review paper discusses the major internal modifications done in history and recent past to enhance the distillate output. Six sub-sections have been developed concerning historic internal modifications that discuss types of basin liners, water depth, stones, dyes, phase change materials, and weirs. It has been found that among all the historic internal modifications, phase change materials were the most effective with distillate yield enhancement of up to 80%. The limitation in distillate yield made the researchers to perform further modifications to enhance the productivity, and hence, recent internal designs have also been discussed. Recent internal modifications have six sub-sections: fins, wicks, nanofluids, nanostructures, dynamic modifications, and natural materials. Among the recent, dynamic modifications were the most efficient with productivity enhancement of up to 300%, with a maximum cumulative yield of 8.78 kg/m2/day for the rotating wick solar still compared to CSS which gave only 2.21 kg/m2/day. Such a kind of review work has not been performed till date, which covers all the internal design modifications in one paper exhaustively. Furthermore, gaps have been identified, and future perspectives have been presented in the conclusion section. It has been observed that nanostructures, nanoparticles, and dynamic modifications are the most promising internal modifications in recent times that can boost distillate productivity to a greater degree.

Thermal plasma gasification of organic waste stream coupled with CO2-sorption enhanced reforming employing different sorbents for enhanced hydrogen production

In the past few years, rising concerns vis-à-vis global climate change and clean energy demand have brought worldwide attention to developing the ‘biomass/organic waste-to-energy’ concept as a zero-emission, environment-friendly and sustainable pathway to simultaneously quench the global energy thirst and process diverse biomass/organic waste streams. Bioenergy with carbon capture and storage (BECCS) can be an influential technological route to curb climate change to a significant extent by preventing CO₂ discharge. One of the pathways to realize BECCS is via in situ CO₂-sorption coupled with a thermal plasma gasification process. In this study, an equilibrium model is developed using RDF as a model compound for plasma assisted CO₂-sorption enhanced gasification to evaluate the viability of the proposed process in producing H₂ rich syngas. Three different classes of sorbents are investigated namely, a high temperature sorbent (CaO), an intermediate temperature sorbent (Li₄SiO₄) and a low temperature sorbent (MgO). The distribution of gas species, H₂ yield, dry gas yield and LHV are deduced with the varying gasification temperature, reforming temperature, steam-to-feedstock ratio and sorbent-to-feedstock for all three sorbents. Moreover, optimal values of different process variables are predicted. Maximum H₂ is noted to be produced at 550 °C for CaO (79 vol%), 500 °C for MgO (29 vol%) and 700 °C (55 vol%) for Li₄SiO₄ whereas the optimal SOR/F ratios are found to be 1.5 for CaO, 1.0 for MgO and 2.5 for Li₄SiO₄. The results obtained in the study are promising to employ plasma assisted CO₂-sorption enhanced gasification as an efficacious pathway to produce clean energy and thus achieve carbon neutrality.

Bioenergy with carbon capture and storage can be an influential technological route to curb climate change to a significant extent by preventing CO₂ discharge.

COVID-19 pandemic and global carbon dioxide emissions: A first assessment

Anthropogenic carbon dioxide emissions are the main cause of global climate change. The COVID-19 pandemic has been one of the worst of its kind in the last century with regard to global deaths and, in the absence of any effective treatment, it led to governments worldwide mandating lock-down measures, as well as citizens voluntarily reducing non-essential trips and activities. In this study, the influence of decreased activity on CO₂ emissions and on the economy was assessed. The US, EU-28, China and India, representing almost 60% of anthropogenic carbon emissions, were considered as reference entities and the trends were extrapolated to estimate the global impact. This study aimed to deduce initial estimates of anthropogenic CO₂ emissions based on the available economic and industrial outputs and activity data, as they could not be directly measured. Sector-wise variations in emissions were modeled by assuming proportionality of the outputs/activities and the resulting emissions. A decline in road traffic was seen up to March 2020 and then a steady growth was observed, with the exception of China where road traffic started to recover by the end of January. The vast majority of passenger flights were grounded and, therefore, global air traffic plummeted by 43.7% from January to May 2020. A considerable drop in coal power production and the annual industrial growth rate was also observed. The overall economic decline led to a drop of 4.9% in annual global gross domestic product (GDP) for Q2 2020. The total global CO₂ emissions reduction for January through April 2020 compared to the year before was estimated to be 1749 Mt. CO₂ (14.3%) with a maximum contribution from the transportation sector (58.3% among total emissions by sector). Like other previous crises, if the economy rebounds as expected the reductions will be temporary. Long-term impacts can be minimized considering the business as well as lifestyle changes for travel, utilizing virtual structures created during this crisis, and switching to sustainable transportation.

Alkali Metal CO2 Sorbents and the Resulting Metal Carbonates: Potential for Process Intensification of Sorption-Enhanced Steam Reforming

Sorption-enhanced steam reforming (SESR) is an energy and cost efficient approach to produce hydrogen with high purity. SESR makes it economically feasible to use a wide range of feedstocks for hydrogen production such as methane, ethanol, and biomass. Selection of catalysts and sorbents plays a vital role in SESR. This article reviews the recent research aimed at process intensification by the integration of catalysis and chemisorption functions into a single material. Alkali metal ceramic powders, including Li₂ZrO₃, Li₄SiO₄ and Na₂ZrO₃ display characteristics suitable for capturing CO₂ at low concentrations (<15% CO₂) and high temperatures (>500 °C), and thus are applicable to precombustion technologies such as SESR, as well as postcombustion capture of CO₂ from flue gases. This paper reviews the progress made in improving the operational performance of alkali metal ceramics under conditions that simulate power plant and SESR operation, by adopting new methods of sorbent synthesis and doping with additional elements. The paper also discusses the role of carbonates formed after in situ CO₂ chemisorption during a steam reforming process in respect of catalysts for tar cracking.