The reuse of waste cooking oil and spent bleaching earth to produce biodiesel

Currently, semi-refined and refined vegetable oils are used as a feedstock in biodiesel production. However, criteria such as competition with conventional fossil fuel, economic reasons, shortage supply of food and its social impact on the global scale have somewhat slowed the development of the biodiesel industry. Spent bleaching earth is currently under-utilized by deposition in landfills with no attempt to recover the oil. In this study the waste oil adsorbed on spent bleaching earth, refined soybean oil, and waste cooking oil were evaluated as potential sources of biodiesel production in Iran. Different characteristics of the oil samples, such as fatty acid composition, peroxide, iodine, acid values, etc., were evaluated. A two-step esterification reaction using methanol was conducted to produce biofuel. Subsequently, physicochemical properties of produced biodiesel were analyzed. The oil content in spent bleaching earth was 19.3%, which was lowered to 3.7% using hexane as the solvent. Gas chromatography showed that palmitic, oleic, and linoleic acids were predominantly fatty acids, respectively, and the highest content of saturated acids belonged to waste cooking oil (24%). The acidity of 8.3% was obtained for the oil recovered from spent bleaching earth followed by waste cooking oil (3.6%) and refined soybean oil (0.1%). Totally, the specifications of all biodiesel produced were in the range defined by ASTM D6751 and EN 14214 standards. Since about 2000–3000 tones of spent bleaching earth residual oil is annually dumped and the amount of waste cooking oil produced yearly is 500,000 tones, there is a great potential for Iran to produce biodiesel from waste oils.     

Strength properties and calorific values of sawdust-briquettes as wood-residue energy generation source from tropical hardwoods of different densities

Agricultural and wood residues are principal energy sources for domestic and industrial activities. However, they are often hardly utilized. Conventional wood material for briquetting optimizes combustion and efficient power production. The relationship between strength properties, resistance to humidity and calorific values of sawdust-briquettes from three tropical hardwoods of different densities [Cylicodiscus gabunensis (heavy), Antiaris toxicaria (medium) and Ceiba pentandra (light)] and a Mixed/Composite type was determined. Wood density influenced all the briquette properties and positively correlated with their Calorific Values (CVs) as: C. gabunensis > A. toxicaria > Mixed type > C. pentandra. However, light timber briquettes had greater Compressive Strength, Swelling Value (i.e., less resistance to humidity) and Shatter Index than dense wood briquettes: C. pentandra > Mixed type > A. toxicaria > C. gabunensis. C. gabunensis briquette recorded less elongation value (8.85%) than the standard stipulated (i.e., 20–50%/min.) specifying its quality to resist deterioration on exposure to humidity/water in open sheds. Enormous briquette Swelling Values for A. toxicaria (60.04%), Mixed type (66.16%) and C. pentandra (70.88%) indicate they would deteriorate fast and require great care to store, handle and transport. However, the large Shatter Indices for the Mixed type (98.8%) and C. pentandra (99.16%) denote their high durability to gravitational deterioration. Briquette technology, a “waste-to-energy method”, contributes to offset bio-residue management problems and reduce toxic emissions from its incomplete carbonization. Thus, comprehensive understanding of wood-residue briquette characteristics is significant for fuel-energy generation.     

Hydrometallurgical separation of rare earth elements, cobalt and nickel from spent nickel-metal-hydride batteries

The separation of rare earth elements, cobalt and nickel from NiMH battery residues is evaluated in this paper. Analysis of the internal content of the NiMH batteries shows that nickel is the main metal present in the residue (around 50% in weight), as well as potassium (2.2-10.9%), cobalt (5.1-5.5%), rare earth elements (15.3-29.0%) and cadmium (2.8%). The presence of cadmium reveals that some Ni-Cd batteries are possibly labeled as NiMH ones. The leaching of nickel and cobalt from the NiMH battery powder with sulfuric acid is efficient; operating variables temperature and concentration of H₂O₂ has no significant effect for the conditions studied. A mixture of rare earth elements is separated by precipitation with NaOH. Finally, solvent extraction with D2EHPA (di-2-ethylhexyl phosphoric acid) followed by Cyanex 272 (bis-2,4,4-trimethylpentyl phosphinic acid) can separate cadmium, cobalt and nickel from the leach liquor. The effect of the main operating variables of both leaching and solvent extraction steps are discussed aiming to maximize metal separation for recycling purposes.     

Physicochemical and structural characterization of biochar derived from the pyrolysis of biosolids,cattle manure and spent coffee grounds

In the framework of circular economy, the need of new feedstock materials for the production of alternative new products is of high priority. Biowastes such as manure, sewage sludge (biosolids, BS) and food-waste are used as raw materials for the production of biochar. The present study aims at characterizing biochars produced from three distinct biowastes (i) manure from cattle waste (manure-derived biochar; MDB), (ii) biosolids (BS) from a conventional Urban Wastewater Treatment Plant (UWTP) (biosolids-derived biochar; BDB), and (iii) spent coffee grounds (SCG)-derived biochar (SCGDB). Samples were slowly pyrolyzed in a small-scale kiln with a capacity of 20–24 kg. The samples were heated under nitrogen atmosphere at approximately 6–7 °C min⁻¹ up to the desired temperature (550 °C) and held for 1.5h. The physicochemical characterization of biochars showed the production of alkaline materials with similarities and variations in their characteristics, which depend to the type of feedstock used. The surface area of the raw materials was considerably low (<0.1 m²/g) and increased after pyrolysis to 14.03 m²/g, 3.98 m²/g and 1.53 m²/g for MDB, BDB and SCGDB, respectively. The high %C content, the low H/C ratio and the FTIR adsorption peaks revealed high aromaticity, polymerization and carbonization of the biochars and the presence of several functional groups. These, are some of the biochar properties which could lead to different sorption mechanisms of organic and inorganic contaminants. Also, they presented good stability in soil, which enables to be used as soil amendment and C sequestration mechanism. Finally, the produced biochars showed promising properties for environmental applications.     

Physiochemical characterization and thermal kinetics of lignin recovered from sustainable agrowaste for bioenergy applications

In this study, lignin, one of the commonly occurring natural polymers, is extracted from banana agro-waste. Lignin is recovered from the spent liquor produced during alkaline pre-treatment of agro-waste and precipitated by acidification. This study focuses on the physio-chemical characterization and thermal degradation behaviour of lignin extracted from agro-waste biomass. The extracted lignin yield accounts for nearly 12% of the biomass composition. Spectral analysis, FTIR and NMR explain purity and carbon skeleton characteristics of herbaceous lignin monomers, majorly G and S units. Morphological analysis by SEM showed hollow spherical structures with large surface area for the extracted lignin. The calorific value of extracted lignin was experimentally found to be 21.4276 MJ/kg, which suggests the possible use of extracted lignin as an alternative to sub-bituminous coal. Thermal studies of lignin showed that lignin degrades in a wide temperature range releasing CO₂, CH₄, H₂O, CO and H₂. The volatile content of extracted lignin is found to be 31.42%, which suggests its possibility for gasification process. The overall outcome supported that recovered lignin from agro-waste is a potential resource for bioenergy.     

Production of ethyl ester from esterified crude palm oil by microwave with dry washing by bleaching earth

The production of ethyl ester from a feed material of esterified crude palm oil with 1.7 wt% of free fatty acid (FFA) content using microwave heating was investigated. Parametric studies were carried out to investigate the optimum conditions for the transesterification process (amount of ethanol, amount of catalyst and reaction time). As a result, optimum reaction parameters for the transesterification process aided by microwave heating have been identified: a molar ratio of oil to ethanol of 1:8.5, 1.5 wt% of KOH/oil, a reaction time of 5 min and a microwave power of 70 W. Glycerin from the ester phase was separated by adding 10 wt% of pure glycerin. The ethyl ester was purified with 1.2 wt% of bleaching earth to remove the residual catalyst and residual glycerin. This transesterification process provided a yield of 85 wt% with an ester content of 98.1 wt%. The final ethyl ester product met the specifications stipulated by ASTM D6751-02.     

Study of age and height wise variability on calorific value and other fuel properties of Eucalyptus hybrid, Acacia auriculaeformis and Casuarina equisetifolia

The age and height wise variations in the fuel properties (basic density, calorific value, proximate and elemental parameters) of three short rotation forestry species i.e., Eucalyptus hybrid, Acacia auriculaeformis and Casuarina equisetifolia have been investigated. The fuel properties parameters were evaluated from the test samples of different age from 2 to 6 year and the samples obtained from three different height of trees i.e., stump height, diameter at breast height and top. A marginal increase in the calorific value with the age of tree (2-6 years) was found in all the species, the variation being significant in E. hybrid and C. equisetifolia. The basic density values were also found significantly different in E. hybrid and C. equisetifolia at lower ages (2-6 years). However, when the results were analyzed along the tree height, the calorific values were found to decrease along the stem length towards the tree-top in A. auriculaeformis and C. equisetifolia. The ash content in general was found to be higher in the top portions of the trees, and the same was found significantly higher in case of A. auriculaeformis. There was no particular trend observed for volatile matter content and the fixed carbon content with age. The fuel properties of lower age trees were compared with that of a mature tree (20 years of age) of same species. In general, the fuel properties of mature trees were found to be better than trees of lower age.