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Inexpensive and nontoxic metal-free heteroatom (P, N, and O) enriched high surface area nanoporous materials (CHNM and HNM) as efficient heterogeneous catalysts for the conversion of epoxides to cyclic carbonates by utilizing CO2 is reported. The catalysts were made by condensing the heteroatom enriched precursor with melamine and pyrrole to produce HNM and CHNM, respectively. The catalysis was carried out under mild experimental conditions, i.e. 100 °C reaction temperature and 4 bar CO2 pressure under solvent-free conditions. Almost 100% conversion can be realized using HNM as a catalyst and this superior performance was attributed to the presence of larger heteroatoms as compared to CHNM, although the latter has 159% specific surface area and 115% pore volume as compared to the former. The obtained results are discussed in terms of the Lewis acid–Lewis base interaction, textural properties and the frameworks of the catalysts and the reactants.

The development of green and sustainable processes to synthesize active pharmaceutical ingredients and key starting materials is a priority for the pharmaceutical industry. A green and sustainable protocol for the oxidative cleavage of olefins to produce pharmaceutically and biologically valuable carboxylic acids is achieved. The developed protocol involves 70% aq. TBHP as an oxidant over a heterogeneous vanadium catalyst system. Notably, the synthesis of industrially important azelaic acid from various renewable vegetable oils is accomplished. The catalyst could be recycled for up to 5 cycles without significant loss in yield and the protocol was successfully demonstrated at the gram-scale.

Extractive desulfurization of synthetic and actual gas oil with various solvents was carried out to understand the fruitfulness of studies on solvent screening using synthetic carrier phases. Solvent extraction of various model sulfur compounds from two synthetic carrier phases of different composition was carried out using N,N-dimethylformamide (DMF) solvent to illustrate the effect of the sulfur compound molecular structure on its extractability and interaction with the carrier phase composition. Removal of sulfur compounds from the synthetic carrier phase followed the order: BT ≈ DBT > 4-methyl-DBT > 3-methyl BT ≈ 4,6-dimethyl-DBT > 2-N-octylthiophene ≫ 1-dodecanethiol. Thereafter, extraction of actual straight run gas oil (SRGO), cracked gas oil (CGO), and their mixtures was studied using DMF to understand the effect of their composition on extraction performance. Performance parameters such as yield of raffinate, degree of sulfur removal, distribution coefficient, and performance factor were found to be quite different for different gas oil streams. Thereafter, models were developed for correlating performance of extraction in terms of degree of sulfur removal (Dsr), yield (Y) of extracted gas oil with composition of gas oil and operating conditions. A performance factor (Pf,α) (defined as the summation of Dsr and Y with the weight factor (α) to Dsr) model was used to estimate the optimum operating conditions to maximize the extraction performance. Results indicate that the value of the weight factor (α) affects operating conditions, Dsr and Y, significantly and should be chosen with utmost care in light of downstream process capabilities and overall process economics.

Diethyl carbonate (DEC) is a well-known linear organic carbonate that has wide applications. Besides its use as a fuel additive, DEC is an excellent electrolyte for lithium ion batteries and is used for the production of polycarbonates, which are globally used engineering plastics. The synthesis of DEC from CO2 helps in CO2 mitigation. It was earlier synthesized by phosgenation of ethanol, which is a toxic and dangerous process. Certain non-phosgene routes have been developed in recent years, which include oxidative carbonylation of ethanol, trans-esterification of carbonate, alcoholysis of urea, ethanolysis of CO2 and the ethyl nitrite route for DEC synthesis. This review underlines various non-phosgene methods for the synthesis of DEC by critically evaluating the catalysts used, operating conditions and mechanism of synthesis. The performances of various catalysts have been compared graphically along with the identification of problems and potential solutions. Certain engineering aspects, including kinetics and thermodynamics of the various routes, have also been highlighted. The shortcomings and research gaps have been explicitly mentioned and discussed along with required future developments and research work for DEC synthesis.

In this paper, a series of CexZr1−xO2 solid solution spheres were synthesized by exo- and endo-templating methods and tested for dimethyl carbonate (DMC) synthesis using direct conversion of CO2. The synthesized catalysts were characterized by X-ray diffraction (XRD), N2-physisorption, scanning electron microscopy (SEM), and CO2/NH3-temperature-programmed desorption (TPD). Formation of CexZr1−xO2 solid solutions with tetragonal and cubic crystal structures depending on cerium/zirconium compositions was confirmed by XRD analysis. The specific surface area of the mixed oxide decreased and the average pore diameter increased with an increase in the ceria content, with the exception of the mixed oxides with x = 0.4–0.5 i.e. Ce0.4Zr0.6O2 and Ce0.5Zr0.5O2. The basic and acidic site density of the synthesized catalysts was in the order: ZrO2 < CeO2 < Ce0.5Zr0.5O2, and the basic and acidic site density per unit area followed the same order. The best Ce0.5Zr0.5O2 catalyst was further used for the optimization of reaction conditions such as reaction time, reaction temperature, catalyst dose and reusability for DMC synthesis. Furthermore, study of chemical equilibrium modeling was done using the Peng–Robinson–Stryjek–Vera equation of state (PRSV-EoS) along with the van der Waals one-fluid reaction condition so as to calculate change of Gibbs free energy (ΔG°) and heat of reaction (ΔH°).

The present research deals with the treatment of agri-based pulp and paper mill wastewater by continuous electrocoagulation (CEC) process using iron (Fe) as an electrode material. Effects of flow rates (dm3 h−1): 0.5–4.0 and residence time (τ): 0.5–4.0 h were investigated on degradation of chemical oxygen demand (COD), color, total solid (TS), turbidity, specific energy consumption (SEC), instantaneous current efficiency (ICE) and electrochemical degradation index (EDI). At flow rates of 1.0 and 0.5 dm3 h−1, COD removal efficiency of 78.20 and 82.15%; and color removal efficiency of 79 and 90%, respectively, was achieved. TS concentration of wastewater slurry was also reduced by 65% after 3 h residence time with flow rate of 1 dm3 h−1. The specific energy consumption (kW h per kgCODremoved) was decreased from 16.3 to 14.3 with decrease in τ from 4 to 1 h. At a supply charge concentration of 0.62 A h dm−3, the current efficiency (CE) values were 310% and 274% after τ = 2 and 1 h, respectively. Dissolution and consumption of electrodes were also studied with a change in flow rates. Sludge obtained after the CEC process was analyzed for settling and filterability characteristics, morphology and elemental analysis, point of zero charge, physicochemical and elemental characterization, and TS concentration. The operating cost of the process was also calculated based on the electrical energy and electrode consumption and was found to be 61.0 Indian Rupees (0.9 USD) for the treatment of 1 m3 of wastewater.

In the present study, extraction of sulfur and polyaromatic impurities from actual straight run gas oil (SRGO) containing 1.3 wt% sulfur was studied using various solvents such as acetonitrile, N,N-dimethylformamide, furfural, N,N-dimethylacetamide and dimethyl sulfoxide. Effects of water as antisolvent, extraction conditions and types of extraction operation (batch, single and multi-stage and continuous) have been studied. Performance of solvent extraction process, which is governed by the degree of sulfur removal (Dsr) and yield of extracted SRGO (ESRGO), has been evaluated in terms of a performance factor (Pf,α), which has been defined in terms of weight factor (0 < α < 1) as: Pf,α = αDsr + (1 − α) yield. DMF was found to be a better solvent in terms of Pf,α and regeneration ability. The possibility of utilization of extract as carbon black feed stock (CBFS) has also been discussed based upon the calculated bureau of mines correlation index (BMCI) values.

Many industrial aqueous streams contain nitrogenous aromatic compounds, which need to be removed by an adsorption process, for which it is essential to study the interactive affects of these compounds during their simultaneous adsorption. In the present study, granular activated carbon (GAC) was used for simultaneous adsorption of pyrrole and indole from aqueous solution. First, Taguchi's method (L27 orthogonal array) was applied to optimize various parameters, like initial adsorbate concentration, adsorbent dose, temperature and contact time for their simultaneous adsorption onto GAC. Adsorbent dose and the interaction between initial concentrations were found to be the most significant factors. Indole adsorption onto GAC was found to be higher than that of pyrrole. Thereafter, binary adsorption equilibrium data were generated and modeled by various multicomponent isotherm models. Extended-Langmuir isotherm best represented the isotherm data at 30 °C among various multicomponent isotherm models used in this study.

Recycling of solid wastes (sludge) generated during electrochemical (EC) treatment is one of the biggest technological challenges for scientists. Here we propose a facile approach for the preparation of active aluminium oxide nanomaterials (NMs) in different crystalline forms by recycling the sludge generated during EC treatment of textile dye wastewater. Thermogravimetric (TGA/DTA) analysis, powder X-ray diffraction (PXD), field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray analysis (EDX) analyses of the samples incinerated at different temperatures demonstrate formation of nanocrystalline α-, β- and γ- aluminas (Al2O3). Moreover, FE-SEM together with trans-mission electron microscopy (TEM) and atomic force microscopy (AFM) showed morphological variations of the α-, β- and γ-Al2O3 NMs but largely with uniform size and shape for respective crystallographic forms. Brunauer–Emmett–Teller (BET) surface area measurement indicated fairly good surface areas for the prepared Al2O3 NMs. Catalytic activity tests revealed β-Al2O3 to be most active among all other crystallographic forms reported here. The present study offers a novel and green method for the recycling of sludge (solid waste) into NMs for environmental catalysis applications.

Sulfur compounds represent one of the most common impurities present in the crude oil. Sulfur in liquid fuel oil leads directly to the emission of SO2 and sulfate particulate matter (SPM) that endangers public health and community property; and reduces the life of the engine due to corrosion. Furthermore, the sulfur compounds in the exhaust gases of diesel engines can significantly impair the emission control technology designed to meet NOx and SPM emission standards. The research efforts for developing conventional hydrodesulfurization and alternative desulfurization methods such as selective adsorption, biodesulfurization, oxidation/extraction (oxidative desulfurization), etc. for removing these refractory sulfur compounds from petroleum products are on the rise. Research laboratories and refineries are spending huge amounts of money in finding a viable and feasible solution to reduce sulfur to a concentration of less than 10 mg l−1. This paper reviews the current status in detail of various desulphurization techniques being studied worldwide. It presents an overview of novel emerging technologies for ultra-deep desulfurization so as to produce ultra-low-sulfur fuels.

Herein we report a study on the changes in zeta potential during the electrochemical (EC) treatment of basic green 4 (BG) dye solutions. BG is a basic acrylic dye with a triphenylmethane group. It is extensively used in the textile and other industries. This study was conducted in a batch electrochemical reactor using a sacrificial aluminum anode. Zeta potentials were measured with changes in operating variables such as current density (j), initial pH (pH0), and initial dye concentration (C0). The process performance was analyzed in terms of the chemical oxygen demand (COD), total organic carbon (TOC) and decolorization efficiency along with important cost-related parameters such as electrode and energy consumption. At the optimum conditions, 82.4% COD, 63.5% TOC and 99.4% color removal efficiencies were observed, when C0 = 100 mg L−1, the treatment time was 45 min, with j = 117.64 A m−2 and the initial pH0 = 6.2. The respective electrode and energy consumptions at the optimum conditions were 0.16 kg Al per kg COD removed and 2.48 kW h per kg COD removed. The magnitude of the zeta potential gave an indication regarding the potential stability of the colloidal suspensions of BG dye and aluminum flocs present in the solution over the pH range of 3.2–12.2. It was found that the removal of the cationic dye was maximum when the zeta potential was least negative and that the removal was due to adsorption on neutral aluminum hydroxide. Finally, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), pore size distribution and thermogravimetric analysis (TGA) techniques were used to characterize the solid residues obtained during the EC treatment of aqueous solutions with and without BG dye.