Effects of microwave activation conditions on the properties of activated oil sands coke (2023)

Conventional thermochemical conversion techniques for biofuel production from lignocellulosic biomass is often non-selective and energy inefficient. Microwave assisted pyrolysis (MAP) is cost and energy-efficient technology aimed for value-added bioproducts recovery from biomass with less environmental impacts. The present review emphasizes the performance of MAP in terms of product yield, characteristics and energy consumption and further it compares it with conventional pyrolysis. The significant role of biochar as catalyst in microwave pyrolysis for enhancing the product selectivity and quality, and the influence of microwave activation on product composition identified through sophisticated techniques has been highlighted. Besides, the application of MAP based biochar as soil conditioner and heavy metal immobilization has been illustrated. MAP accomplished at low temperature creates uniform thermal gradient than conventional mode, thereby producing engineered char with hotspots that could be used as catalysts for gasification, energy storage, etc. The stability, nutrient content, surface properties and adsorption capacity of biochar was enhanced by microwave activation, thus facilitating its use as soil conditioner. Many reviews until now on MAP mostly dealt with operational conditions and product yield with limited focus on comparative energy consumption with conventional mode, analytical techniques for product characterization and end application especially concerning agriculture. Thus, the present review adds on to the current state of art on microwave assisted pyrolysis covering all-round aspects of production followed by characterization and applications as soil amendment for increasing crop productivity in addition to the production of value-added chemicals, thus promoting process sustainability in energy and environment nexus.

In this paper, pyrolysis of Indonesian oil sands (IOS) was investigated by two different heating methods to develop a better understanding of the microwave-assisted pyrolysis. Thermogravimetric analysis was conducted to study the thermal decomposition behaviors of IOS, showing that 550°C might be the pyrolysis final temperature. A explanation of the heat–mass transfer process was presented to demonstrate the influence of microwave-assisted pyrolysis on the liquid product distribution. The heat–mass transfer model was also useful to explain the increase of liquid product yield and heavy component content at the same heating rate by two different heating methods. Experiments were carried out using a fixed bed reactor with and without the microwave irradiation. The results showed that liquid product yield was increased during microwave induced pyrolysis, while the formation of gas and solid residue was reduced in comparison with the conventional pyrolysis. Moreover, the liquid product characterization by elemental analysis and GC–MS indicated the significant effect on the liquid chemical composition by microwave irradiation. High polarity substances (ε>10 at 25°C), such as oxy-organics were increased, while relatively low polarity substances (ε<2 at 25°C), such as aliphatic hydrocarbons were decreased, suggesting that microwave enhanced the relative volatility of high polarity substances. The yield improvement and compositional variations in the liquid product promoted by the microwave-assisted pyrolysis deserve the further exploitation in the future.

Overburden and tailings materials from oil sands production were used as construction materials as part of a novel attempt to create a self-sustaining, peat accumulating fen-upland ecosystem. To evaluate the potential for elemental release from the construction materials, total elemental concentrations in the tailings sand, petroleum coke and peat used to construct a fen ecosystem were determined using microwave-assisted acid digestions and compared to a leaching experiment conducted under environmentally-relevant conditions. A comparison of solid phase to aqueous Na, Ca, S and Mg concentrations showed they were highly leachable in the materials. Given that the concentrations of these elements can affect plant community structure, it is important to understand their leachability and mobility as they migrate between materials used to construct the system. To that end, a mass balance of aqueous Na, Ca, S and Mg was conducted based on leaching experiments and materials analysis coupled with existing data from the constructed system. The data indicate that there is a large pool of leachable Na, Ca, S and Mg in the system, estimated at 27t of Na, 14t of Ca, 37.3t of S and 8.8t of Mg. Since recharge mainly drives the fen-upland system water regime, and discharge in the fen, evapo-accumulation of these solutes on the surface may occur.

In this work, a microwave planar resonator sensor with boosted quality factor is proposed for the non-contact detection and classification of particles of different diameters in gaseous and aquatic environments. This approach can be applied to rapid particle counting, particle size sensing and classification in lossy and non-lossy medium. The presented sensor operates based on variations in the dielectric properties of materials in the vicinity of a planar open-ended microstrip resonator device. Finite Element Method (FEM) analysis is performed to study the effect of particle size on the transmission response profile of the sensor. Verification of the established FEM model and the functionality of the sensor are investigated by experiment. The resolution of the sensor may be adjusted by changing the quality factor of the resonator, which is directly related to the direct current bias voltage of the active device in the local feedback loop. The initial results show the sensor to be capable of detecting the resonant frequency variations of 1kHz over 1.5GHz, which corresponds to a detectable frequency resolution better than 1 part per million (PPM). The reported sensor operates at 1.42GHz and demonstrates particle classification capability within an overall 500kHz resonant-frequency shift for different bead-diameter sizes (40–400μm) at a distance of 5mm, in both air and water (ε’=78 and tanδ=0.15) using petroleum coke beads as a test material.

Pomegranate peel was converted into activated carbon using microwave induced and KOH activation techniques. The prepared activated carbon (PPAC) was characterized using FTIR, TGA, SEM, and nitrogen-adsorption surface area (BET). BET measurements gave remarkable increase in both the surface area (941.02m²/g) and total pore volume (0.470cm³/g). Various operational parameters such as pH, initial dye concentration, contact time and solution temperature in batch systems were investigated on the use of PPAC in the adsorption of remazol brilliant blue reactive (RBBR) dye. At pH 2, the optimum dye removal was 94.36%. The amount of dye removed was dependent on initial dye concentration and solution temperature. Adsorption kinetics was found to follow pseudo-second-order kinetic model. Experimental data were analyzed using eight model equations: Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Radke Prausnite, Sips, Viet–Sladek and Brouers – Sotolongo isotherms and it was found that the Freundlich isotherm model fitted the adsorption data most with the highest correlation (R²≥0.99) and lowest normalized standard deviation, ∆q_e. Both intra-particle and film diffusion governed the adsorption process. Thermodynamic parameters, such as standard Gibbs free energy (∆G⁰), standard enthalpy (∆H⁰), standard entropy (∆S⁰), and the activation energy (E_a) were calculated. The adsorption of RBBR dye onto PPAC was found to be spontaneous and exothermic in nature. This study shows that the adsorption follows physisorption mechanism.

In this study, microwave-assisted KOH activation was adopted for preparation of a microporous activated carbon from an agricultural waste, Siris seed pods. Carbon with high BET surface area of 1824.88m²/g and 0.782cm³/g total pore volume has been obtained from these precursors. The influences of radiation time, radiation power, and impregnation ratio on yield and iodine number of prepared carbon have been studied and the best conditions were determined. The sorption mechanisms of a nitroimidazole antibiotic, metronidazole (MNZ), onto such carbon have been investigated. The adsorption data of MNZ were analyzed by Langmuir, Freundlich, and Temkin isotherms and the best correlation was achieved by the Langmuir isotherm with maximum capacity of 196.31mg/g. The analyses of kinetic data showed that the adsorption of MNZ on prepared carbon follow closely the pseudo-second order model. Results of thermodynamic studies showed endothermic and spontaneous natures of MNZ adsorption under examined conditions.

Journal of Water Process Engineering, Volume 23, 2018, pp. 207-216

The aim of this work was to determine the optimal Photoperoxi-Electrocoagulation (PPEC) process experimental conditions for the treatment of a tannery industrial wastewater (TIW). The lab-scale PPEC-reactor comprises a pair of iron-flat plates, resulting in a contact effective area of 58.5 cm²; the PPEC reaction was conducted by electrochemical phenomenon associated to a Fenton’s reaction based on the H₂O₂ concentrations added, the solar UV–vis light was exposed, as well as iron ion dissolved original plate deterioration, resulting in a production of an efficient hydroxyl radical (OH). An optimising analysis using a response surface methodology was performed; the optimum conditions of the PPEC process were attained at a solution pH of 4, current density of 34.2 mA cm⁻², 6 g H₂O₂ L⁻¹ and an electrolysis time of 120 min. The effects on the removal of chromium and COD were evaluated, suggesting satisfactory results for the PPEC reaction. Based on the low calculated median lethal dose (LD₅₀) values from a lettuce-seed-based ecotoxicity test, untreated TIW samples were completely lethal for doses with 100%, except for samples taken after 90 and 120 min. The PPEC process could be applied as an efficient low-cost alternative treatment for the removal of pollutants from TIW with a low environmental impact.

Journal of the Taiwan Institute of Chemical Engineers, Volume 60, 2016, pp. 383-393

The present research work is based on degradation of major pollutants of purified terephthalic acid (PTA) wastewater by electrocoagulation (EC) process. Terephthalic acid (TPA), benzoic acid (BA) and para-toluic acid (p-TA) are the major pollutants of PTA wastewater. A central composite design (CCD) has been developed for maximum removal of TPA, BA, p-TA, COD and minimum consumption of energy. Effects of various process parameters viz. pH: (5–13), current density: (49.5–255.5A/m²), supporting electrolyte concentration, NaCl: (0.25–2.25g/L) and electrolysis time: (15–95min) are studied on removal efficiencies of responses. Aluminium (Al) and iron (Fe) were selected as electrode materials. Maximum percentage removal of TPA: 56.21, 54.10; BA: 59.52, 53.84; p-TA: 45.71, 39.91, and COD: 49.91, 42.95 are achieved at optimum operating conditions by Al and Fe electrodes respectively. Operating cost of the process was calculated based on energy consumption, electrode consumption, sludge disposable, and transportation costs and found $13.64 and $14.46 per kg of COD removed by Al and Fe electrodes respectively. Sludge residues obtained after EC treatment at optimum operating conditions are analyzed by settling, sludge volume index (SVI), XRD, SEM/EDX, point of zero charge (PZC), FTIR and DGA/TGA.

Applied Energy, Volume 137, 2015, pp. 126-133

Chemical Engineering Journal, Volume 310, Part 1, 2017, pp. 226-239

In-situ Gasification Chemical-Looping Combustion (iG-CLC) burning coal is achieving a great interest due to the possibility of using low cost oxygen carriers such as CaSO₄. The Limestone Chemical Looping Combustion process (LCL-C™) registered by Alstom Power Inc. proposes the use of a continuous CaCO₃ feeding together with coal to produce CaSO₄ as an oxygen carrier via sulphur retention. The operation is similar to what happens in a circulating fluidized bed boiler burning coal. In the present research work, the study of thermodynamic equilibrium limitations together with mass and enthalpy balances have been carried out for a CLC system in order to investigate whether the LCL-C™ process is a promising and energy efficient option to carry out the coal combustion with CO₂ capture and in-situ desulphurisation. So, no limitations were found to transfer the required oxygen from air to fuel using sulphated limestone as oxygen carrier for whatever coal used. The selection of a suitable oxygen carrier to fuel ratio mainly depends on the sulphur content of the coal used. In addition, no drawback referred to thermal integration in the system has been detected. Thus, operation at 950°C in the fuel reactor to avoid SO₂ release via side reactions, and 1050°C in the air reactor is feasible. Likewise, experimental tests have been performed in a thermogravimetric analyser to evaluate the capability of a limestone to be sulphated and to transfer oxygen. A value of the oxygen transport capacity of about 16.7wt.% was obtained. This value is four times higher than that of others typical inexpensive oxygen carriers published in literature.

Fuel, Volume 148, 2015, pp. 160-167

International Journal of Hydrogen Energy, Volume 41, Issue 43, 2016, pp. 19570-19578

The graphitisation of ordered mesoporous carbons (CMK-3) was carried out by thermal treatments under different conditions of temperature and heating rate. The electrochemical characterization in acidic medium of the graphitised CMK-3 showed that such a thermal treatment is effective to decrease the carbon oxidation rate (corrosion) while preserving a good porosity in terms of capacitance. Besides, the graphitisation degree and, in consequence the electrochemical corrosion resistance, can be modulated by an appropriate choice of thermal treatment conditions, where the heating rate and temperature appear as critical parameters. Under certain graphitisation conditions, the carbon corrosion of CMK-3 can be minimized showing lower rates compared to a commercial carbon black (Vulcan XC-72R). Palladium nanoparticles were supported on the most promising graphitised CMK-3 and Vulcan using a method based on impregnation and reduction with borohydride, resulting in suitable metal crystallite sizes. The electrocatalytic activity towards the oxidation of carbon monoxide and formic acid were assessed in aqueous sulphuric acid electrolyte for application at the anode of direct formic acid fuel cells (DFAFCs). The best activity results were obtained for the Pd catalyst supported on a graphitised CMK-3.