Carbon black preparation by partial oxidation of spent tyre pyrolysis oil - Influence of temperature, residence time and oxygen to feed ratio.

Preparation of carbon black (CB) by partial oxidation of the spent tyre pyrolysis oil (STPO) and its heavy residue fraction (HRF) was systematically studied using a lab-scale drop tube furnace. The effect of furnace operating temperature (T: 1100 to 1400 °C), residence time (tr: 5 to 60 s) and oxygen to feed ratio (O/F: 174 to 732) on the yield and quality of CB was examined using the response surface methodology (RSM). T was shown to have the most significant influence on CB yield and properties. While the CB yield was also influenced by tr, the quality was more sensitively dependent on T and O/F. The predicted optimal tr and O/F were approximately the same for both feedstocks (60 s and 174, respectively). However, T was higher for the HRF feedstock (1368 °C) than the STPO feedstock (1331 °C) due to the abundance of more viscous heavy hydrocarbons in HRF. Validation experiments under the aforementioned conditions demonstrated the models' ability to predict responses accurately. The CB from both feedstocks had low contents of ash (<0.03%), volatiles (∼0.5%), sulphur (<0.7%), and high carbon (≥95%). The BET surface area and average primary particle size for CB from STPO and HRF were comparable to those of commercial CBs from fossil fuel feedstock. The CB from HRF had a higher carboxyl oxygen functional group (18%) compared to the CB from STPO (∼13%) and commercial CB (<5%).

An Experimental and Density Functional Theory Simulation Study of NO Reduction Mechanisms over Fe0 Supported on Graphene with and without CO.

NO reduction over highly dispersed zerovalent iron (Fe0) supported on graphene (G), with and without the presence of CO in the reacting stream, was systematically studied using a fixed-bed reactor, and the reaction mechanism was examined with the aid of in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. The in situ FTIR results showed that NO adsorbed on the Fe0 site is reduced to form active surface oxygen species (O*), which is then reduced by carbon in graphene to form CO2. The presence of CO in the reacting stream helps to reduce the oxidized Fe(O) sites to regenerate Fe0 sites, making NO reduction easier. It was revealed that NO and CO2 are easily adsorbed on the active surface oxygen species (O*) to form nitrate and carbonate, inhibiting their reduction by CO and deactivating the catalyst. The DFT calculations results suggest that the role of Fe is to reduce the energy barrier of the NO adsorption and decomposition, which controls the formation of active surface oxygen species and N2. The combined FTIR and DFT results offer new insights into the possible mechanism of catalytic NO reduction over graphene loaded with Fe, with and without CO.

More from less: improving solar steam generation by selectively removing a portion of evaporation surface.

Using minimal photothermal material to achieve maximum evaporation rate is extremely important for practical applications of interfacial solar evaporation technology. In this work, we found that with the increase in the size of evaporation surfaces, the evaporation rate decreased. Both experimental and numerical simulation results confirmed that when the evaporation surface size increased, the middle portion of the evaporation surface acted as a "dead evaporation zone" with little contribution to water evaporation. Based on this, the middle portion of the evaporation surface was selectively removed, and counterintuitively, both the evaporation rate and vapor output were increased due to the re-configured and enhanced convection above the entire evaporation surface. As such, this work developed an important strategy to achieve a higher evaporation rate and increased vapour output while using less material.

Emerging technologies for PFOS/PFOA degradation and removal: A review.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are highly recalcitrant anthropogenic chemicals that are ubiquitously present in the environment and are harmful to humans. Typical water and wastewater treatment processes (coagulation, flocculation, sedimentation, and filtration) are proven to be largely ineffective, while adsorption with granular activated carbon (GAC) has been the chief option to capture them from aqueous sources followed by incineration. However, this process is time-consuming, and produces additional solid waste and air pollution. Treatment methods for PFOS and PFOA generally follow two routes: (1) removal from source and reduce the risk; (2) degradation. Emerging technologies focusing on degradation are critically reviewed in this contribution. Various processes such as bioremediation, electrocoagulation, foam fractionation, sonolysis, photocatalysis, mechanochemical, electrochemical degradation, beams of electron and plasma have been developed and studied in the past decade to address PFAS crisis. The underlying mechanisms of these PFAS degradation methods have been categorized. Two main challenges have been identified, namely complexity in large scale operation and the release of toxic byproducts. Based on the literature survey, we have provided a strength-weakness-opportunity-threat (SWOT) analysis and quantitative rating on their efficiency, environmental impact and technology readiness.

An investigation into the preparation of carbon black by partial oxidation of spent tyre pyrolysis oil.

To promote the use of recycled waste materials as an industrial feedstock, this study examined the preparation of carbon black (CB) by partial oxidation of a spent tyre pyrolysis oil using a drop tube furnace. The effect of reaction temperature, the residence time of gas in the reactor and inlet gas oxygen concentration on the yield and properties of the CB were evaluated. The surface chemistry, chemical composition, morphological and thermal properties of the CB samples were characterised using XPS, EA, TEM, BET, and TGA, respectively. The CB yield increased with increasing reaction temperature but decreased as the residence time or oxygen concentration increases. The CB primarily consisted of C (90.5-98.6%) and O (0.9-7.4%), with small traces of S (<1%), Si (<1%) and H (<2%). Hydroxyl, carbonyl, and carboxyl are the key functional groups found on the CB surface, with the hydroxyl groups being dominant. The CB were highly graphitic with a lattice spacing in the range of 0.338-0.350 nm and had BET surface areas of 4-22 m2g-1. The mean primary particle size ranged from 92 to 176 nm and decreased with increasing reaction temperature and oxygen concentration. The CB aggregate configuration became more complex with increasing reaction temperature, residence time and oxygen concentration. The results were not only comparable with commercial CB products from fossil fuel feedstocks but are expected to provide the needed motivation to move towards circular economy strategies, which have positive impacts from a sustainability perspective.

Performance of activated carbons prepared from spent tyres in the adsorption of rhodamine B in aqueous solutions.

Activated carbons were produced from spent tyre pyrolysis char by steam or CO2 activation and evaluated for their performance in rhodamine B (RhB) adsorption in aqueous solutions. The effect of RhB starting concentration (80-150 mg L-1), contact time (0-80 min), temperature (298-318 K) and initial pH on the adsorption process was examined. Pseudo-first-order and pseudo-second-order models were carried out to fit the experimental data to derive RhB adsorption kinetics. Langmuir, Freundlich and Temkin isotherm models were applied to depict RhB adsorption behaviour of the prepared activated carbons. Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were calculated. It has been found that the activated carbons can effectively adsorb RhB due to high mesoporosity and RhB equilibrium adsorption capacity (qe) increased almost linearly with increasing total mesopore volumes, regardless of the activation agents. When BET surface areas are similar, CO2-activated carbon obtained higher qe than steam due to higher mesoporosity of CO2-activated carbon. The results show that pseudo-second-order well fitted the experimental data. RhB starting concentration increased from 80 to 150 mg L-1 causing qe increased from 158 to 251 mg g-1 but RhB removal decreased from 99.7 to 84.5%. The RhB adsorption process follows the Langmuir model and thermodynamic calculation, indicating RhB adsorption is an endothermic, spontaneous process, dominated by both chemisorption and physisorption.

Utilisation of spent tyre pyrolysis char as activated carbon feedstock: The role, transformation and fate of Zn.

Utilisation and minimisation of spent tyre stockpiles has been made more viable by pyrolysis and activation to produce low-cost activated carbons. The unique chemical composition of spent tyre pyrolysis chars (STPC), particularly the high Zn content, has been shown to affect their activation and subsequent utilisation. Nonetheless, little research has examined exactly how these additives affect activation and, ultimately, what becomes of Zn during the activation process. This paper presents a systematic study of the effect of Zn, ZnO and ZnS on the physical properties of STPC and their transformation mechanisms during CO2 activation. Samples of acid-washed STPC with and without ZnO and ZnS addition were activated using a fixed-bed reactor in 66.7%v/v CO2 for 3 h at 850, 950, 1000 and 1050 °C. Under these conditions, both ZnO and ZnS were found to act as a catalyst during activation, increasing surface area, pore volume and burn-off. During the activation, ZnO was reduced by C to form elemental Zn and ZnS was thermally decomposed to release Zn and S. Thermogravimetric analysis of Zn and its compounds above 600 °C, separately and mixed with acid-washed char, under CO2 confirms that ZnO and ZnS dissociate to release Zn(v) that further reacts with CO2 or S to reform ZnO or ZnS. However, Zn is progressively removed from activated carbon at temperatures between 950 °C and 1050 °C. These results have direct implications for the utilisation of SPTC as a feedstock for activated carbon, and the production of Zn-loaded activated carbons.

Minimum ignition energies and laminar burning velocities of ammonia, HFO-1234yf, HFC-32 and their mixtures with carbon dioxide, HFC-125 and HFC-134a.

Given the safety issues associated with flammability characteristics of alternative environmentally-friendly refrigerants, it is vital to establish measurement systems to accurately analyse the flammability of these mildly flammable refrigerants. In this study, we used a customised Hartmann bomb analogue to measure the minimum ignition energy (MIE) and laminar burning velocity (BV) for refrigerant/air mixtures of pure ammonia (R717), R32, R1234yf and mixtures of R32 and R1234yf with non-flammable refrigerants of R134a, R125 and carbon dioxide (R744). The MIEs of R717, R32, and R1234yf were measured at an ambient temperature of 24 °C to be (18.0 ± 1.4), (8.0 ± 1.5) and (510 ± 130) mJ at equivalence ratios of 0.9, 1.27 and 1.33, respectively. Adding the non-flammable refrigerants R134a, R125 and R744 along with R32 at volumetric concentrations of 5% each to R1234yf reduced the latter compound's flammability and increased its MIE by one order of magnitude. The laminar burning velocities of pure R717 and R32 were measured at an equivalence ratio of 1.1 using the flat flame method and found to be 8.4 and 7.4 cm/s, respectively. Adding 5% R1234yf to R32 decreased the laminar burning velocity by 11%, while a further 5% addition of R1234yf resulted in a decrease of over 30% in the laminar burning velocity.

Effect of biochar addition on microbial community and methane production during anaerobic digestion of food wastes: The role of minerals in biochar.

The effect of biochar addition on the microbial community and methane (CH4) production during anaerobic digestion was experimentally investigated, focusing on the role of minerals in biochar. The biochar was prepared from pine sawdust by pyrolysis at 650 °C and 900 °C, respectively, and a subsample was leached with citric acid. The cultures with the addition of biochar, leached biochar, Fe, and leached biochar combined with Fe, respectively, were placed in bench-scale bioreactors for anaerobic digestion. Daily biogas production was measured by volume displacement method and analysed for CH4 concentration, which allowed the cumulative CH4 yield (YM) and daily CH4 production rate (RM) to be determined. Culture samples were also taken daily for volatile fatty acids (VFAs) and microbial community analysis. Compared to the control without biochar addition, the addition of raw biochar significantly increased YM by 46.9% and RM by 43.0%, while leached biochar only increased the YM by 33.2% and RM by 18.2%, respectively. The Fe-containing minerals in biochar were found to enhance VFA degradation and increase population of Clostridia and Methanosaeta, improving the CH4 production.

Inhibition of Arabidopsis chloroplast ß-amylase BAM3 by maltotriose suggests a mechanism for the control of transitory leaf starch mobilisation.

Starch breakdown in leaves at night is tightly matched to the duration of the dark period, but the mechanism by which this regulation is achieved is unknown. In Arabidopsis chloroplasts, ß-amylase BAM3 hydrolyses transitory starch, producing maltose and residual maltotriose. The aim of the current research was to investigate the regulatory and kinetic properties of BAM3. The BAM3 protein was expressed in Escherichia coli and first assayed using a model substrate. Enzyme activity was stimulated by treatment with dithiothreitol and was increased 40% by 2-10 µM Ca2+ but did not require Mg2+. In order to investigate substrate specificity and possible regulatory effects of glucans, we developed a GC-MS method to assay reaction products. BAM3 readily hydrolysed maltohexaose with a Km of 1.7 mM and Kcat of 4300 s-1 but activity was 3.4-fold lower with maltopentaose and was negligible with maltotetraose. With maltohexaose or amylopectin as substrates and using [UL-13C12]maltose in an isotopic dilution method, we discovered that BAM3 activity is inhibited by maltotriose at physiological (mM) concentrations, but not by maltose. In contrast, the extracellular ß-amylase of barley is only weakly inhibited by maltotriose. Our results may explain the impaired starch breakdown in maltotriose-accumulating mutants such as dpe1 which lacks the chloroplast disproportionating enzyme (DPE1) metabolising maltotriose to glucose. We hypothesise that the rate of starch breakdown in leaves can be regulated by inhibition of BAM3 by maltotriose, the concentration of which is determined by DPE, which is in turn influenced by the stromal concentration of glucose. Since the plastid glucose transporter pGlcT catalyses facilitated diffusion between stroma and cytosol, changes in consumption of glucose in the cytosol are expected to lead to concomitant changes in plastid glucose and maltotriose, and hence compensatory changes in BAM3 activity.

Characterization of hard- and softwood biochars pyrolyzed at high temperature.

A wide range of waste biomass/waste wood feedstocks abundantly available at mine sites provide the opportunity to produce biochars for cost-effective improvement of mine tailings and contaminated land at metal mines. In the present study, soft- and hardwood biochars derived from pine and jarrah woods at high temperature (700 °C) were characterized for their physiochemical properties including chemical components, electrical conductivity, pH, zeta potential, cation-exchange capacity (CEC), alkalinity, BET surface area and surface morphology. Evaluating and comparing these characteristics with available data from the literature have affirmed the strong dictation of precursor type on the physiochemical properties of the biochars. The pine and jarrah wood feedstocks are mainly different in their proportions of cellulose, hemicellulose and lignin, resulting in biochars with heterogeneous physiochemical properties. The hardwood jarrah biochar exhibits much higher microporosity, alkalinity and electrostatic capacity than the softwood pine. Correlation analysis and principal component analysis also show a good correlation between CEC-BET-alkalinity, and alkalinity-ash content. These comprehensive characterization and analysis results on biochars' properties from feedstocks of hardwood (from forest land clearance at mine construction) and waste pine wood (from mining operations) will provide a good guide for tailoring biochar functionalities for remediating metal mine tailings. The relatively inert high-temperature biochars can be stored for a long term at mine closure after decades of operations.

Effect of biochar addition on hydrogen and methane production in two-phase anaerobic digestion of aqueous carbohydrates food waste.

Effect of biochar addition on hydrogen and methane production in two-phase anaerobic digestion of aqueous carbohydrates was studied using bench-scale bioreactors. The cultures with biochar additions were placed in 100ml reactors and incubated at 35°C and pH 5 for hydrogen production. The residual cultures were then used for methane production, incubated at 35°C and pH 7. Daily yields of hydrogen and methane and weekly yield of volatile fatty acids (VFA) were measured. The hydrogen and methane production potentials, rate and lag phases of the two phases were analysed using the Gompertz model. The results showed that biochar addition increased the maximum production rates of hydrogen by 32.5% and methane 41.6%, improved hydrogen yield by 31.0% and methane 10.0%, and shortened the lag phases in the two phases by 36.0% and 41.0%, respectively. Biochar addition also enhanced VFA generation during hydrogen production and VFA degradation in methane production.

Interactions of coal gangue and pine sawdust during combustion of their blends studied using differential thermogravimetric analysis.

The interactions between coal gangue and pine sawdust during the combustion process were studied using thermogravimetric analysis. The effect of the blending ratio, oxygen concentration and heating rate on the weight loss (TG) and differential thermogravimetric (TGA) profiles was examined. The TG and DTG curves of the blends were not additives of those of the individual materials, suggesting that interactions between coal gangue and pine sawdust had occurred during the combustion, especially in the temperature range of 400-600°C. Kinetic analysis confirmed that the combustion of coal gangue, pine sawdust and their blends was chemical reaction controlled. Further analysis revealed that the interactions between coal gangue and pine sawdust were primarily due to thermal effects rather than structural changes, with the thermal inertia of coal gangue dominating over the behaviour of the blends. The interactions decreased with decreasing the coal gangue ratio in the blend, oxygen concentration and heating rate.

Copper and zinc adsorption by softwood and hardwood biochars under elevated sulphate-induced salinity and acidic pH conditions.

Biochar adsorption may lower concentrations of soluble metals in pore water of sulphidic Cu/Pb-Zn mine tailings. Unlike soil, high levels of salinity and soluble cations are present in tailing pore water, which may affect biochar adsorption of metals from solution. In the present study, removal of soluble copper (Cu) and zinc (Zn) ions by soft- (pine) and hard-wood (jarrah) biochars pyrolysed at high temperature (about 700 °C) was evaluated under typical ranges of pH and salinity conditions resembling those in pore water of sulphidic tailings, prior to their direct application into the tailings. Surface alkalinity, cation exchange capacity, and negative surface charge of biochars affected Cu and Zn adsorption capacities. Quantitative comparisons were provided by fitting the adsorption equilibrium data with either the homogeneous or heterogeneous surface adsorption models (i.e. Langmuir and Freundlich, respectively). Accordingly, the jarrah biochar showed higher Cu and Zn adsorption capacity (Qmax=4.39 and 2.31 mg/g, respectively) than the softwood pine biochar (Qmax=1.47 and 1.00 mg/g). Copper and Zn adsorption by the biochars was favoured by high pH conditions under which they carried more negative charges and Cu and Zn ions were predicted undergoing hydrolysis and polymerization. Within the tested range, salinity had relatively weak effects on the adsorption, which perhaps influenced the surface charge and induced competition for negative charged sites between Na(+) and exchangeable Ca(2+) and/or heavy metal ions. Large amounts of waste wood/timber at many mine sites present a cost-effective opportunity to produce biochars for remediation of sulphidic tailings and seepage water.

Process modelling of biomass conversion to biofuels with combined heat and power.

A process model has been developed to study the pyrolysis of biomass to produce biofuel with heat and power generation. The gaseous and solid products were used to generate heat and electrical power, whereas the bio-oil was stored and supplied for other applications. The overall efficiency of the base case model was estimated for conversion of biomass into useable forms of bio-energy. It was found that the proposed design is not only significantly efficient but also potentially suitable for distributed operation of pyrolysis plants having centralised post processing facilities for production of other biofuels and chemicals. It was further determined that the bio-oil quality improved using a multi-stage condensation system. However, the recycling of flue gases coming from combustor instead of non-condensable gases in the pyrolyzer led to increase in the overall efficiency of the process with degradation of bio-oil quality.

A preliminary assessment of the potential of using an acacia--biochar system for spent mine site rehabilitation.

Mining activities result in extensive soil degradation by removing the top soil, disturbing soil structure and altering microbial communities. Rehabilitation of spent mine sites through revegetation thus requires proper soil amendments. In this study, a pot trial was conducted to investigate the effects of a jarrah biochar on the growth and nutrient status of a native legume, Acacia tetragonophylla, grown in a mixture of topsoil and mine rejects. Two biochar application rates (37 and 74 t ha(-1)) and two types of biochar, namely nutrient-enriched and non-enriched, were tested. We measured the soil pH and electrical conductivity, the carbon (C) and nitrogen (N) contents and C and N isotope composition (δ(13)C and δ(15)N) of soil and plants, the foliar phosphorus content and the growth and leaf biomass of the plants. Whilst no significant effect of biochar was observed on plant growth, biochar amendment affected soil properties and plant nutritional status. The highest rate of biochar application increased soil pH, C content and C/N ratio, and decreased soil δ(13)C. Biochar application also enhanced photosynthetic N use efficiency, as showed by the increase in foliar C/N ratio, and biological N fixation rates, as indicated by foliar δ(15)N. These positive effects were not observed when biochar was nutrient-enriched due to the associated increase in soil N. Revegetation of mine sites with acacia in combination with biochar amendment constitutes a plausible alternative to the wide use of N fertiliser through the supply of additional N to the system, even though other nutrients may be required in order to enhance plant early growth.

A phenomenological investigation into the opposing effects of fluid flow on sonochemical activity at different frequency and power settings. 2. Fluid circulation at high frequencies.

Sonochemical activity is dependent on flow patterns within the reactor and either no affect or a decrease in activity was observed at 376, 995, and 1179 kHz from overhead stirring. The interaction of fluid flow with ultrasound was further investigated in this study with circulatory flow. The effect of fluid circulation on radical production was investigated at two circulation speeds, with and without surface stabilisation. The sonochemical activity was determined by the yield of hydrogen peroxide, measured by iodide dosimetry. The sonochemically active region was pictured using sonochemiluminescence imaging and the flow fields were visualised with dyed flow videos. At 376 and 995 kHz, an increase in sonochemical activity was observed with the slower flow rate; however at 1179 kHz, the sonochemical activity was either not affected or decreased. The observed changes in sonochemical activity were attributed to an increase in asymmetry of the bubble collapse brought about by fluid motion.

A phenomenological investigation into the opposing effects of fluid flow on sonochemical activity at different frequency and power settings. 1. Overhead stirring.

The effect of flow in an ultrasonic reactor is an important consideration for practical applications and for the scale-up of ultrasonic processing. Previous literature on the influence of flow on sonochemical activity has reported conflicting results. Therefore, this work examined the effect of overhead stirring at four different frequencies, 40, 376, 995 and 1179 kHz, in two different reactor configurations. Comparable power settings were utilised to elucidate the underlying mechanisms of interactions between the flow and sonochemical activity. The sonochemical activity was determined by the yield of hydrogen peroxide, measured by iodide dosimetry, and the active region was visualised with sonochemiluminescence imaging. The overhead stirring in the low frequency reactor altered the yield of hydrogen peroxide so it produced the maximum yield out of the four frequencies. The increase in hydrogen peroxide yield was attributed to a reduction in coalescence at 40 kHz. However at the higher frequencies, coalescence was not found to be the main reason behind the observed reductions in sonochemical yield. Rather the prevention of wave propagation and the reduction of the standing wave portion of the field were considered.

Manipulation of ultrasonic effects on lignocellulose by varying the frequency, particle size, loading and stirring.

The parameters, including ultrasonic frequency, still versus stirring, biomass particle size and biomass loading were concurrently investigated for the ultrasonic treatment of wheat straw. Experiments were conducted at three different frequencies; 40, 376, and 995 kHz using three different solid to liquid ratios, 1/50, 1/20, and 1/15(g/ml), with and without mechanical stirring. Additional treatments in different particle size ranges, 0-0.5, 0.5-1, and 1-2mm were performed at the solid to liquid ratio of 1/20(g/ml). Fractionation was improved at 40 and 995 kHz via different mechanisms. Delignification was favored at the ultrasonic treatment frequency of 40 kHz, biomass loading 1/20(g/ml) with stirring and particle size range of 0.5-1mm. However at 995 kHz carbohydrate solubilization was favored, especially in the particle size range of <0.5mm. The treatment efficacies highlighted the use of ultrasound for physical and chemical effects at different frequencies.

Insight into the mechanism of selective catalytic reduction of NO(x) by propene over the Cu/Ti(0.7)Zr(0.3)O2 catalyst by Fourier transform infrared spectroscopy and density functional theory calculations.

The mechanism of selective catalytic reduction of NOx by propene (C3H6-SCR) over the Cu/Ti0.7Zr0.3O2 catalyst was studied by in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. Especially, the formation and transformation of cyanide (-CN species) during the reaction was discussed. According to FTIR results, the excellent performance of the Cu/Ti0.7Zr0.3O2 catalyst in C3H6-SCR was attributed to the coexistence of two parallel pathways to produce N2 by the isocyanate (-NCO species) and -CN species intermediates. Besides the hydrolysis of the -NCO species, the reaction between the -CN species and nitrates and/or NO2 was also a crucial pathway for the NO reduction. On the basis of the DFT calculations on the energy of possible intermediates and transition states at the B3LYP/6-311 G (d, p) level of theory, the reaction channel of -CN species in the SCR reaction was identified and the role of -CN species as a crucial intermediate to generate N2 was also confirmed from the thermodynamics view. In combination of the FTIR and DFT results, a modified mechanism with two parallel pathways to produce N2 by the reaction of -NCO and -CN species over the Cu/Ti0.7Zr0.3O2 catalyst was proposed.