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Poly(ethylene terephthalate) (PET) is the most common plastics produced for applications in food and drinking containers. It is degraded to valuable product by several methods. Glycolysis of PET gains bis(2-hydroxyethylene) terephthalate (BHET) as the main product utilized as plasticizer. Calcium catalysts, Ca2+ and Ca(OH)2∙2H2O were explored to study the mechanism of PET cleavage by DFT calculations at B3LYP/6-311++G** level. Two possible pathways, coordination, and non-coordination of ethylene glycol on the calcium in glycolysis reaction, have been investigated. In addition, poly(ethylene furanoate) (PEF), considered as a sustainable polymer with the similar functional properties, was chose for the comparison of conformational structures with PET. The understanding of the relationship between PET (and PEF) structures and calcium catalysts is useful for the future development of linear sustainable polyesters.

A one-pot, four-component strategy for the synthesis of trifluoromethylated, and other fully-substituted pyrroles is reported using minimum loading of calcium catalyst at room temperature. A variety of arenes, α-keto aldehydes, amines, and activated alkynes took part in the reaction to produce high-yielding products. Friedel–Crafts arylation and aza-Michael addition are the key reactions in this approach. [ABSTRACT FROM AUTHOR]

Biodiesel can substitute for conventional diesel fuel and contribute to the decarbonization of the transportation sector. To improve biodiesel sustainability and decrease production costs, low-grade fats such as non-edible animal fats must be used. Animal fats are mixed with tissues which must be removed before alcoholysis to avoid biodiesel contamination with nitrogen and phosphorus-containing compounds. Biodiesel was produced by the methanolysis of beef tallow and beef tallow/soybean oil mixtures over calcium heterogeneous catalysts obtained by the calcination of scallop shells. The tallow from fatty bovine tissues was extracted using boiling water, dry microwave treatment, and acetone extraction. The thermal stability and the moisture content of the extracted fats were evaluated by thermogravimetry. The thermograms of fats revealed that microwave treatment, which was faster (3 min instead of 40 min for boiling water and 240 min for acetone extraction) and had the lowest energy consumption, led to a dry fat with a thermal stability analogous to that of fats extracted with boiling water and acetone. All the extracted fats behaved similarly in the methanolysis reaction over calcium catalyst, with biodiesel yield (61–62%) being 30% lower than the analogous obtained from soybean oil (88%). Co-processing the extracted tallow with soybean oil overcomes the drawback related to the low-grade fats. [ABSTRACT FROM AUTHOR]

Coal or coal char/pyrocarbon gasification is a viable way to produce cheaper hydrogen. The gasification of three different lignites and their pretreated samples showed that either the intrinsic calcium in lignite or the extrinsic calcium added by ion exchange had high catalytic activity. It was proven that most of the calcium in the lignite was organically associated, which was mainly bound to carboxyl groups and highly dispersed at an atomic level. Furthermore, Yuxi lignite was demineralized to investigate the catalytic characteristics of calcium and potassium catalysts on steam gasification. The changes of gasification rate, gas compositions and oxygen chemisorption capacity with carbon conversion hinted that the catalytic mechanism of calcium was different from that of potassium. X-ray absorption near edge structure (XANES) analysis revealed that carboxyl-bound calcium was the active form of the catalyst, and the deactivation of the calcium catalyst in the gasification process was due to the transformation of carboxyl-bound calcium to other chemical forms. The organically bound calcium also led to the porous char structures at the early gasification stage, which improved the catalytic activity. Image 1 • Insightful characterization of lignite char gasification catalyzed by calcium/potassium. • Quantitative analysis of organically bound active calcium in char. • Detailed explanations of the active sites and deactivation of the calcium catalyst. • Proposal of an active site/intermediate mechanism for calcium catalysis. [ABSTRACT FROM AUTHOR]

The use of vegetable oils to produce biodiesel raises several sustainability issues, namely the fuel/food conflict. The high cost of vegetable oils and an expensive homogeneous base catalyzed process encourages the search for alternative raw materials and more efficient production processes. Biodiesel from beef tallow, a non-edible fat, was produced by methanolysis over calcium based heterogeneous catalyst. The catalyst was prepared by calcination of scallop shells at 800 ​°C. To overcome the undesired effect of the tallow acidity (3.9 mgKOH/gfat), mixtures of tallow and soybean oil (SBO) (0.6 mgKOH/gfat) were processed and alcohol co-solvents (isopropanol, 1-propanol, and isobutanol) and biodiesel itself, as a solvent, were used to improve the miscibility of the reaction mixture. Processing of neat tallow promotes an important decay of the catalytic activity due to the partial neutralization of the basic catalyst. Co-processing mixtures of tallow/SBO allowed minimizing the acidity effect. Alcohol co-solvents harmed the biodiesel yield due to competitive adsorption of alcohols with methanol on catalyst active sites but protected the catalyst against adsorption of the reaction mixture species. Biodiesel used as a solvent had an almost null effect on the esterification reaction yield, thus showing the absence of mass transfer limitation.Co-processing low-grade fat with vegetable oil seems to be a feasible strategy to process low-grade fats using basic heterogeneous catalysts, thus contributing to improving the sustainability of biodiesel production.

Due to sustainability issues, biodiesel must be produced from low-grade fats and the conventional homogeneously-catalyzed processes must be replaced by more efficient and more profitable production processes such as heterogeneous ones. Biodiesel (fatty acids methyl esters, FAME) was produced from a mixture (50 wt%) of soybean oil and non-edible beef tallow over heterogeneous calcium-based catalysts obtained by calcination of scallop shells. In order to improve the catalytic performances, solvent assisted methanolysis was conducted using alcohols (ethanol, 1-propanol, isopropanol and isobutanol), acetone, methylcyclohexane, and tetrahydrofuran (THF) with Vmethanol/Vsolvent = 2.8. Catalytic data revealed that alcohol solvents adsorb competitively with methanol on the catalyst active sites reducing the FAME yield due to their slower alcoholysis rates. Hexane and methylcyclohexane are inadequate for methanolysis reactions since they are immiscible with methanol. THF and acetone are immiscible with the co-produced glycerin, which favors methyl esters formation by displacing the chemical equilibrium towards reaction products. Acetone performs better than THF (FAME yield gain of 14% against 3%) because of its higher miscibility with methanol. THF was the most effective solvent to avoid fat adsorption on the catalyst surface, a key factor for catalyst stability, and to improve the glycerin purity. [ABSTRACT FROM AUTHOR]

Ethanolysis of soybean oil was carried out over lime catalyst produced by calcination of scallop shells food wastes. The as prepared catalyst showed XRD lines belonging to lime, whereas post reaction samples presented XRD pattern belonging to Ca(OH)2 overlaid with lines of calcium diglyceroxide. The catalyst dynamics during ethanolysis was similar to that reported for methanolysis, being hydration and consequent diglyceroxide formation the main transformations of CaO catalyst during reaction. The influence of the reaction parameters, such as ethanol:oil molar ratio (10:1–14:1), catalyst loading (10–15%, based in oil weight) and time reaction (6–10 h), on the FAAE (fatty acids ethyl esters) yield was analyzed by response surface methodology. A polynomial model was fitted using Minitab software, showing a correlation between predicted and experimental FAEE yields of 0.921. The maximum FAEE yield of 99.2% was computed for optimal reaction parameters of 11:1 ethanol:oil molar ratio; 13.8% catalyst loading and 9.1 h of reaction time. The fitted model was verified for the optimal conditions, using three replicas, given 99.0% of FAEE yield instead of the 99.2% predicted. [ABSTRACT FROM AUTHOR]

Individual and mixed plastics consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) were decomposed at 600 °C in the presence and absence of either calcium oxide (CaO) or calcium hydroxide (Ca(OH) 2 ) under a steam atmosphere. In the presence of CaO, steam cracking was enhanced, increasing gas and liquid yields and decreasing the wax content derived from PE and PP. The production of sublimating substances from PET was also reduced. However, the presence of CaO and steam had a negative influence on PS degradation, reducing the oil yield. In addition, synergistic effects were observed in plastic mixtures. PET enhanced gasification, PS and PET reduced wax production from PE and PP, and mixing all four plastics enhanced oil production in the presence of CaO and steam. Both CaO and Ca(OH) 2 enhanced the total gas and oil yield of mixed plastics, achieving a maximum oil yield of 52.2 wt% in the presence of steam. Furthermore, solids were almost completely decomposed at 700 °C, with only 0.2 wt% of residue remaining. [ABSTRACT FROM AUTHOR]

Decomposition of NH3 to N2 with Fe and Ca catalysts supported on brown coal chars has been studied with a cylindrical quartz reactor from a viewpoint of hot gas cleanup. The catalyst is prepared by pyrolyzing a brown coal with Fe or Ca ions added. In the decomposition of 2000 ppm NH3 diluted with He at 750 °C and at a space velocity of 45,000 l/h, 2–6 wt% Fe catalysts are more active than not only 6 wt% Ca catalyst but also 8 wt% Fe catalyst loaded on a commercial activated carbon. The transmission electron microscope observations show that fine iron particles with the sizes of 20–50 nm account for the higher catalytic performances. When reaction temperature is increased to 850 °C, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH3. The co-feeding of H2 with 2000 ppm NH3 improves the performance of the 2% Fe catalyst at 750 °C, but contrarily the coexistence of syngas (CO/H2=2) deactivates it remarkably, whereas the addition of CO2 to syngas restores the catalytic activity of the Fe to the original state without syngas. The powder X-ray diffraction and temperature programmed desorption measurements strongly suggest that the Fe and Ca catalysts promote NH3 decomposition through cycle mechanisms involving the formation of N-containing intermediate species and the subsequent decomposition to N2. [Copyright &y& Elsevier]

Poly (ϵ-caprolactone) (PCL) and poly (l-lactide) (PLA) were prepared by ring-opening polymerization catalyzed by organic amino calcium catalysts (Ca/PO and Ca/EO) which were prepared by reacting calcium ammoniate Ca(NH3)6 with propylene oxide and ethylene oxide, respectively. The catalysts exhibited high activity and the ring-opening polymerization behaved a quasi-living characteristic. Based on the FT-IR spectra and the calcium contents of the catalysts, and based on the 1H NMR end-group analysis of the low molecular weight PCL prepared using catalysts Ca/PO and Ca/EO, it was proposed that the catalysts have the structure of NH2–Ca–O–CH(CH3)2 and NH2–Ca–O–CH2CH3 for Ca/PO and Ca/EO, respectively. The ring-opening polymerization of CL and LA follows a coordination-insertion mechanism and the active site is the Ca–O bond. [Copyright &y& Elsevier]

Triblock copolymer PCL–PEG–PCL was prepared by ring-opening polymerization of ϵ-caprolactone (CL) in the presence of poly(ethylene glycol) catalyzed by calcium ammoniate at 60 °C in xylene solution. The copolymer composition and triblock structure were confirmed by 1H NMR and 13C NMR measurements. The differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed the micro-domain structure in the copolymer. The melting temperature Tm and crystallization temperature Tc of the PEG domain were influenced by the relative length of the PCL blocks. This was caused by the strong covalent interconnection between the two domains. Aqueous micelles were prepared from the triblock copolymer. The critical micelle concentration was determined to be 0.4–1.2 mg/l by fluorescence technique using pyrene as probe, depending on the length of PCL blocks, and lower than that of corresponding PCL–PEG diblock copolymers. The 1H NMR spectrum of the micelles in D2O demonstrated only the –CH2CH2O– signal and thus confirmed the PCL-core/PEG-shell structure of the micelles. [Copyright &y& Elsevier]