1,720,984 research outputs found
Greener and sustainable approach for the synthesis of commercially important epoxide building blocks using polymer-supported Mo(VI) complexes as catalysts
No full textThe growing concern for the environment, increasingly stringent standards for the release of chemicals into the environment and economic competitiveness have prompted extensive efforts to improve chemical synthesis and manufacturing methods as well as development of new synthetic methodologies that minimise or completely eliminate pollutants. As a consequence, more and more attention has been focused on the use of safer chemicals through proper design of clean processes and products. Epoxides are key raw materials or intermediates in organic synthesis, particularly for the functionalisation of substrates and production of a wide variety of chemicals such as pharmaceuticals, plastics, paints, perfumes, food additives and adhesives. The conventional methods for the industrial production of epoxides employ either stoichiometric peracids or chlorohydrin as an oxygen source. However, both methods have serious environmental impact as the former produces an equivalent amount of acid waste, whilst the later yields chlorinated by-products and calcium chloride waste. Hence, a greener and efficient route for catalytic epoxidation that could improve manufacturing efficiency by reducing operational cost and minimising waste products is highly desired. In this chapter, a greener alkene epoxidation process using molybdenum (Mo) based heterogeneous catalyst and tert-butyl hydroperoxide (TBHP) as an oxidant has been presented. A polystyrene 2-(aminomethyl)pyridine supported molybdenum(VI) complex, i.e. Ps.AMP.Mo and a polybenzimidazole supported Mo(VI) complex, i.e. PBI.Mo have been successfully prepared and characterised. The catalytic activities of the polymer supported Mo(VI) complexes have been evaluated for epoxidation of 1-hexene and 4-vinyl-1-cyclohexene (4-VCH) in a batch reactor. Experiments have been carried out to study the effect of reaction temperature, feed molar ratio of alkene to TBHP and catalyst loading on the yield of epoxide for optimisation of reaction conditions in a batch reactor. The long term stability of the polymer supported Mo(VI) catalysts have been evaluated by recycling the catalysts several times in batch experiments using conditions that form the basis for continuous epoxidation studies. The extent of Mo leaching from each polymer supported catalyst has been investigated by isolating any residue from reaction supernatant studies after removal of heterogeneous catalyst and using the residue as potential catalyst for epoxidation. The efficiency of Ps.AMP.Mo catalyst has been assessed for continuous epoxidation of 1-hexene and 4-vinyl-1-cyclohexne with TBHP as an oxidant using a FlowSyn reactor by studying the effect of reaction temperature, feed molar ratio of alkene to TBHP and feed flow rate on the conversion of TBHP and the yield of epoxide. The catalysts were found to be active and selective for batch and continuous epoxidation of alkenes using TBHP as an oxidant. The continuous epoxidation in a FlowSyn reactor has shown considerable time savings, high reproducibility and selectivity along with remarkable improvement in catalyst stability compared to the reactions carried out in a batch reactor
Direct Air Capture of Carbon Dioxide from the Atmosphere and Sequestration: Developing A new Class of Regenerable Hybrid Ligand Exchanger
No full textClimate change is a major obstacle to sustainable development, and the suffering inflicted on marginalized populations is disproportionately high in both the developed and developing world. As a result of global warming, it is anticipated that the frequency, intensity, and consequences of some types of extreme weather events, such as ice melting, water scarcity, and sea level rise, would increase. The elevated atmospheric CO2 concentration from anthropogenic emissions is singularly responsible for global warming and is regarded as humanity\u27s worst existential threat. The magnitude of the crisis is enormous, with approximately 36.3 Gt/year of global CO2 emission, necessitating urgent actions from tens of countries for carbon mitigation. Direct air capture (DAC) is important to achieve net-zero greenhouse gas emissions by 2050. However, the ultra-dilute atmospheric CO2 concentration (~ 400 ppm) poses a formidable hurdle for high CO2 capture capacities using sorption-desorption processes. Therefore, for increased uptake, point-source flue gas streams with orders of magnitude higher CO2 concentrations have been desirable targets for enhanced CO2 removal. Previous studies have demonstrated that the overall economics and energy efficiency of DAC are greatly enhanced when the sorbent exhibits a high sorption capacity and can be regenerated efficiently. In this study, we present for the first time a Lewis acid-base interaction derived hybrid sorbent with a polyamine-Cu(II) complex enabling over 5.0 moles CO2 capture per kilogram of the new sorbent, nearly 2-3 times greater capacity than most of the DAC sorbents reported to date. The hybrid sorbent is mechanically strong, chemically stable, and like other amine-based sorbents, is amenable to thermal desorption at less than 90 °C. Additionally, seawater was validated as a viable regenerant, and the desorbed CO2 is simultaneously sequestered as innocuous, chemically stable alkalinity (NaHCO3). The dual-mode of regeneration offers an unprecedented flexibility in using oceans as decarbonizing sinks to widen DAC application opportunities. Furthermore, this study reveals for the first time that seawater has the potential to be used both as a regenerant and a sink for direct air capture of CO2 and thus can eliminate the need for underground geological storage simultaneously in agreement with the recent National Academies of Sciences (NAS) recommendations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Advancement of the Hybrid Ion Exchange Nitrogen and Phosphate (HIX-NP) Recovery from Waste Water and a New Approach to Brine-Free Nitrate Removal
No full textDue to rapid declining freshwater reserves worldwide, societies are reexamining approaches to maintain potable and industrial water supplies to meet the current and future demands. By utilizing wastewater, an impaired water resource that is large, resili
Development of Hybrid Ion Exchange Processes Driven by Carbon Dioxide (HIX-CO2)
No full textFreshwater scarcity is severely faced by humans even though our planet is full of water,being more than 97% of the water is salty water such as seawater or brackish water. Andsome of the brackish water is impaired by various of contaminants, such as nitr
Hybrid Ion Exchange Processes for Sustainable Softening and Marcellus Flowback Treatment
No full textHybrid ion exchange technology has been applied in many environmental aspects nowadays due to its high treatment efficiency, reusability, customizable selectivity, operational stability, and low cost. Under certain circumstances, ion exchange technology is a favorable substitute for traditional treatment process, and its applications in industries are continually growing.Water hardness is a concern for many industrial and municipal unit operations, which could result in surface scaling of heat transfer equipment or membranes. Sodium exchange softening, although commonly used, has caused serious pollution to local ecological and water environments due to its discharge of high salinity spent regenerant. Many arid areas are banning such softening processes as a result of the detection of increasing salinity in local water resources. The additional sodium ion introduced into the softened water also induces a health concern when the water is used for drinking or cooking. A more efficient hardness removal technology that does not add sodium ions to treated water is urgently inquired. Al3+ is an optimal regenerant considering its higher affinity to cation exchangers than calcium and magnesium at most water conditions. Furthermore, Al3+ will precipitate during the service cycle thus eliminating the addition of sodium or aluminum to the effluent. Experimental results indicated that calcium is persistently removed for multiple cycles using a stoichiometric amount of aluminum chloride as the regenerant. The process operates at nearly 100% thermodynamic efficiency, where one equivalent of Al3+ was consumed to remove one equivalent of Ca2+. Nevertheless, partial desalination is attained during hardness removal. The hardness removal capacity of the aluminum cycle process is slightly reduced from 1.4 meq/g to 1.2 meq/g compared with the sodium cycle process. However, at steady state, other contaminants, namely fluoride, phosphate, and silica, could be simultaneously removed as a consequence of Lewis acid and base reactions. It is noteworthy that the major components and setup are nearly the same as a traditional sodium cycle softening process, which eradicates the major difficulty to retrofit continuing softening systems.Wastewater produced from Marcellus Shale activities and acid mine drainage (AMD) are two major concerns of Pennsylvania for their environmental impact on surface and groundwater resources, aqueous ecosystems, and human health. Reuse of flowback and produced water represents one of the innovative technologies which could significantly reduce the environmental impacts of the activity. However, about 20% of injected water will return to the surface with high salinity. Both treatment techniques and makeup water resources are needed to fulfill this goal. Acid mine drainage (AMD) water, which is available in the vicinity of shale gas wells, could be utilized to alleviate the fresh water demand, reduce environmental impacts for both flowback and AMD, cut down the cost for transportation and leakage risk, trim the greenhouse gas emissions2, and diminish the cost and impact for wastewater treatment. Several researchers already inspected this possible technology genuinely. However, some issues remain unresolved such as the demand for large volume reactors and stirrers, long hydraulic retention time (HRT), haphazardly mixing, and uncertain mixing ratios. Radium, barium, and strontium, which induce precipitation on the piping and are regulated in water resources, are major concerns for either recycle or final disposal of flowback water. To remove these divalent ions, the addition of sulfate salt or mixing with sulfate-containing water are two widely studied processes. Huge amounts of salt addition could cause a TDS increase and a removal efficiency decrease. On the other hand, directly mixing with AMD water will cause significant volume increase of treated water. Ion exchange technology, which can selectively exchange sulfate with chloride, is an ideal process to treat flowback water without a TDS and final volume increase. Experimental data demonstrates that such technology can use sulfate ions in acid-mine drainage to treat Marcellus flow back waste water to remove radium, barium and strontium and without increasing the volume of waste water or adding excess sodium. Over 200 bed volumes of AMD water is treated and the effluent sulfate concentration is lower than 100 ppm, which is an ideal fresh water resource for hydrofracking. Moreover, there are no additional chemicals needed for such ion exchange processes to treat flowback water with AMD. Radium, barium, and strontium are removed over 90% in the treated flowback without any volume increase. The treated solids after evaporation are suitable for landfill disposal. Compared with current technology used at a flowback treatment factory, the reactor volume is reduced from 100 m3 to about 5 m3 to achieve the same treatment capacity
A new class of sorbents for the selective removal of arsenic(V) and selenium(IV) oxy-anions
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