Formation Of Solid Residue Research Articles

Advancing Renewable Energy: The Prospects of Hydrothermal Liquefaction (HTL) for Biomass into Bio-oil Conversion

Hydrothermal liquefaction (HTL) offers a promising approach to convert biomass into bio-oil, contributing to sustainable energy solutions and reducing dependence on fossil fuels. HTL mimics natural geological processes by decomposing biomass at high temperatures (200–350°C) and pressures (10–25 MPa) in a water-based environment, producing bio-oil that can be refined for various energy applications. Despite its potential, several technical challenges limit the efficiency and scalability of HTL. The high energy requirements for maintaining these conditions also pose economic challenges, making HTL less competitive against traditional energy sources. HTL is the complex composition of bio-oil, which contains a mix of organic compounds that make refining and upgrading challenging. This complexity also affects bio-oil’s stability, requiring advanced purification techniques to ensure quality and usability. Solid residue formation during HTL reduces bio-oil yields and increases processing costs. Recent advances aim to address these limitations. New catalysts, such as metal oxides, improve bio-oil yield and reduce oxygen content, enhancing fuel quality. Innovations in reactor design, including continuous flow and microwave-assisted reactors, improve heat transfer and operational stability. Integrating HTL with other biomass conversion technologies, like anaerobic digestion, also offers pathways to increase efficiency and energy recovery. Advances in analytical techniques, like gas chromatography and mass spectrometry, are also improving bio-oil characterization, informing more effective upgrading strategies. While challenges remain, ongoing research in catalyst development, reactor optimization, and process integration strengthens HTL’s potential as a sustainable energy solution, supporting its role in advancing bio-oil production for a cleaner, renewable future.

Towards harmonization of metal(loid)s determination in conventional and compostable plastics: Comparison of acid digestion protocols in LDPE and PBAT/TPS blends

The determination of metal-containing additives in plastic materials via acid digestion protocols has attracted growing interest to address potential environmental implications. However, the lack of protocol harmonization hinders data comparability within the literature. Here, six acid digestion protocols were employed to determine the metal(loid) content in plastics: these included three different acid mixtures (HNO3 combined with H2SO4, HCl or H2O2) for microwave-assisted digestion, with or without an additional room-temperature digestion step with H2O2.Each protocol was first validated for seven metal(loid)s (As, Cd, Cr, Pb, Sb, Sn and Zn) using a low-density polyethylene (LDPE) certified reference material (ERM®-EC681m). Then, validated protocols were applied on end-use materials, including conventional (i.e., LDPE) and compostable (i.e., PBAT/TPS) plastics.The combination of H2SO4 and HNO3 with a further digestion step with H2O2 was the most suitable protocol: it successfully passed validation thresholds for all metal(loid)s (recoveries in the range 98.6–101.0 %) and yielded the highest concentrations in end-use materials. All other protocols resulted in a less efficient digestion of the sample matrix, leading to lower recoveries and the formation of solid residues. Notably, end-use plastics showed a great variability in metal(loid) concentrations, likely due to their additive-rich composition, in contrast to the minimal content of acid-soluble additives of the reference material.This study represents an initial step towards the harmonization of acid digestion protocols and highlights new challenges in accurately analyzing end-use plastic materials, due to their complex additive composition.

Hydrothermal liquefaction of composite household waste to biocrude: the effect of liquefaction solvents on product yield and quality.

The hydrothermal liquefaction (HTL) of composite household waste (CHW) was investigated at different temperatures in the range of 240-360 °C, residence times in the range of 30-90 min, and co-solvent ratios of 2-8 ml/g, by utilising ethanol, glycerol, and produced aqueous phase as liquefaction solvents. Maximum biocrude yield of 46.19% was obtained at 340 °C and 75 min, with aqueous phase recirculation ratio (RR) of 5 ml/g. The chemical solvents such as glycerol and ethanol yielded a biocrude percentage of 45.18% and 42.16% at a ratio of 6 ml/g and 8 ml/g, respectively, for 340 °C and 75 min. The usage of co-solvents as hydrothermal medium increased the biocrude yield by 35.30% and decreased the formation of solid residue and gaseous products by 19.82% and 18.74% respectively. Also, the solid residue and biocrude obtained from co-solvent HTL possessed higher carbon and hydrogen content, thus having a H/C ratio and HHV that is 1.01 and 1.23 times higher than that of water as hydrothermal medium. Among the co-solvents, HTL with aqueous phase recirculation resulted in higher carbon and energy recovery percentages of 9.36% and 9.78% for solid residue and 52.09% and 56.75% for biocrude respectively. Further qualitatively, co-solvent HTL in the presence of obtained aqueous phase yielded 33.43% higher fraction of hydrocarbons than the pure water HTL and 7.70-17.01% higher hydrocarbons when compared with ethanol and glycerol HTL respectively. Nitrogen containing compounds, such as phenols and furfurals, for biocrudes obtained from all HTL processes, were found to be present in the range of 8.30-14.40%.

Synergistic Effect Between Empty Fruit Bunch and HDPE on Products Yield and Functional Group Content in Bio-fuels Produced from Co-liquefaction Process Under Supercritical Methanol Condition

Synergism between biomass and plastic waste during co-processing reported to produce higher products yield with enhanced quality which thereby solving the problems of high oxygenated compounds and low yields with high viscosity in oil from its individual processing. However, study on synergistic effect (SE) between these feedstocks is considered lacking. In this study, the SE of co-liquefying empty fruit bunch (EFB) and high-density polyethylene (HDPE) in sc-MeOH was investigated using a high-pressure, high-temperature batch-wise reactor system at 260 °C for 30 minutes and at various EFB-HDPE ratios to determine the best ratio for bio-fuel yield and its functional group content. It was found that 25% EFB:75% HDPE (wt/wt %) provides the most significant SE (≈ 8 wt%) for bio-fuel yield and the most considerable reduction in solid residue formation under the studied conditions. The presence of hydroxyl groups from EFB and aliphatic hydrocarbons from HDPE, along with new carbonyl compounds, further highlights the SE resulting from the combined processing of these materials. The findings suggest that optimizing the ratio of biomass to plastic waste in co-liquefaction can significantly enhance the efficiency and yield of bio-fuels while minimizing waste, providing a promising approach for sustainable energy production and waste management.

Decomposition of benzene vapour using non-thermal plasmas: The effect of moisture content on eliminating solid residue

This study investigated the effect of power, carrier gases and moisture content on the removal of benzene in dry air and humidified air in a DBD plasma reactor. The influence of plasma power, carrier gases and humidity on benzene conversion and product selectivity were explored. The main decomposition products were CO, CO2, lower hydrocarbons (C1-C5) and solid residue in the reactor. This study reveals that benzene removal efficiency and the selectivity to CO2 increased with power in both dry and humidified air. In contrast, the selectivity to lower hydrocarbons decreased. The most important finding of this study was that the formation of solid residue in the plasma reactor can be removed in humidified air. As the amount of water vapour increased from 0% to 35% at 20 ℃, the benzene removal efficiency and CO2 selectivity increased; O3 decreased from 7.3 ppm to 0.5 ppm; NOx and solid residue were eliminated. These effects are probably due to OH radicals, and the mechanism for the various effects are proposed. The maximum benzene removal efficiency observed was 93.7%, and the maximum selectivity to CO2 was 82.4% (both at a relative humidity of 35% at 20 ℃ and 10 W). This study demonstrated that plasma-assisted benzene remediation operating in a humid condition can overcome the major drawback of plasma-assisted VOC conversion in the air by eliminating the solid residues in the reactor.

Influence of Crystallite Size of Nickel and Cobalt Ferrites on the Catalytic Pyrolysis of Buckwheat Straw by Using TGA-FTIR Method

Pyrolysis of buckwheat straw with or without catalysts was investigated using the TGA-FTIR method to determine the influence of nickel and cobalt ferrites on the distribution of pyrolysis products. According to the obtained results, the overall shape of the thermogravimetric and derivative thermogravimetric curves is unchanged in the presence of nickel and cobalt ferrites but different weight losses were observed. All catalysts contribute to the formation of solid residue from BWS pyrolysis. The presence of cobalt ferrites exhibited the highest bio-oil yields, whereas the highest non-condensable gas yield and the lowest bio-oil yield was obtained with the addition of NiFe2O4 (1) catalyst. According to the obtained results, the ability of nickel and cobalt ferrites to catalyze deoxygenation reactions depends on the crystallite size. The nickel or cobalt ferrites with smaller crystallite size (15-22 nm) show a higher ability to catalyzed dehydration reaction than catalysts with larger crystallite size (45-54 nm).

Removal of benzene as a tar model compound from a gas mixture using non-thermal plasma dielectric barrier discharge reactor

In the present work, the decomposition of benzene as a tar model compound was studied in a gas mixture (CO2, H2, CO, and CH4) using a dielectric barrier discharge (DBD) non-thermal plasma reactor. The combined effect of temperature and power was studied to investigate the performance of the DBD reactor. The decomposition of tar compound increased from 49.9 to 96% with increasing specific input energy (SIE) from 2.05 to 16.4 kWh/m3. The major products were lower hydrocarbons (C2–C5) and solid residues. The higher temperature (400 °C) in the presence of plasma (40 W), decreased the conversion of tar compound from 96 to 78%. However, the selectivity of lower hydrocarbons increases substantially to 52%, and the formation of solid residues is significantly reduced. Hence, the problematic solid residues formation can be controlled at a higher temperature during the treatment of gasifier product gas using non-thermal plasma.

Removal of cyclohexane as a toxic pollutant from air using a non-thermal plasma: Influence of different parameters

Non-thermal plasmas (NTPs) are a promising technique for abatement of volatile organic compound (VOC) emissions. In this study, the removal of cyclohexane as a toxic pollutant from ambient air was investigated in a dielectric barrier discharge (DBD) reactor at ambient temperature and atmospheric pressure. The effect of specific input energy (SIE) (1.2–3 kJ/L), carrier gases, residence time (1.2–2.3 s) and concentration (220–520 ppm) was evaluated. This work demonstrated that the removal efficiency of cyclohexane increased with increasing specific input energy and residence time. The removal of cyclohexane decreased with increasing concentration at constant SIE and residence time. The main decomposition products were CO2, H2, and lower hydrocarbons (C1–C4). The maximum removal efficiency (98.2%) was achieved at a specific input energy of 3 kJ/L and a residence time of 2.3 s in humidified air. Moreover, maximum O3 concentrations (<10ppm) were observed at 3.0 kJ/L SIE in dry air. NOX was not detected, in any carrier gas. The effect of the presence of water vapour was investigated to determine whether it would reduce the formation of solid residue in the DBD reactor. One of the key findings was that humidification of the air at 25% entirely prevented the formation of solid deposits in the reactor. Humidification not only improved the removal efficiency of cyclohexane, but also increased the yield of H2 and CO2 selectivity. This was due to the formation of potent OH. radicals. In general, this study demonstrates that cyclohexane vapour in air can be almost 100% decomposed to smaller molecules by a non-thermal plasma DBD reactor by optimizing specific input energy (SIE), residence time, humidity, reactor configuration and plasma properties.

Synthesis, Characterization and Catalytical Effects of Fe Contents on Pyrolysis of Cellulose with Fe2O3/SBA-15 Catalysts

Abstract In this study mesoporous SBA-15 was synthesized under acidic conditions using triblock copolymer Pluronic P123 as template and tetraethyl orthosilicate as a silica source. SBA-15 was modified by different iron loading (1.8 %, 5 % and 10 %) via post-synthesis impregnation with Fe(NO3)3·9H2O. The obtained catalysts were characterized using XRD analysis, WDXRF spectroscopy and N2 adsorption-desorption analysis. Pyrolysis of cellulose with and without the catalyst was investigated using TG-FTIR. It was found that the presence of the synthesized catalysts affects formation of solid residue and significantly alters the composition of the other pyrolysis products. All catalysts considerably reduced the fraction of compounds containing hydroxyl group. Fe (10 %)/SBA-15 exhibited the highest deoxygenation ability. SBA-15 showed the highest catalytic selectivity for synthesis of olefins, while Fe (1.8 %)/SBA-15 showed the highest catalytic selectivity for synthesis of aromatic hydrocarbons.

Kraft lignin depolymerisation in sub- and supercritical water using ultrafast continuous reactors. Optimization and reaction kinetics

Kraft lignin was rapidly depolymerised in a continuous reactor using sub- and supercritical water. The reaction yielded an aromatic oil rich in high value aromatic monomers such as guaiacol, vanillin, acetovanillone and homovanillic acid. Different temperatures between 300 and 400 °C and reaction times from 60 ms were studied. An increment in reaction time at every temperature studied promoted secondary reactions of repolymerisation of the lignin products. Those undesired reactions were more relevant as temperature increased. An optimal temperature of 386 °C at a reaction time of 170 ms was found, with a maximum yield in phenolic compounds obtained. At those conditions, a bio-oil containing low molecular weight compounds was obtained with a yield of 44.6 %. A selectivity to the four cited monomers of 9.9 % was achieved, with little formation of solid residue (3.5 %). A simple kinetic model was proposed to describe the yield for the different fractions and fitted to experimental data.

Facile biphasic catalytic process for conversion of monoterpenoids to tricyclic hydrocarbon biofuels

Terpenoids have drawn much attention to scientists in synthesizing high-performance bio- jet fuels due to their ring structures, which feature potential high densities. Here, a facile biphasic catalytic process has been developed for the production of high-density tricyclic hydrocarbon biofuels from a monoterpenoid, 1,8-cineole, using sulfuric acid (H2SO4) as the homogeneous catalyst. A ~100% conversion of 1,8-cineole and a > 40% carbon yield of cyclic dimers were achieved at 100 °C within two hours. The mechanism for the acid-catalyzed conversion of 1,8-cineole to cyclic hydrocarbon dimers were explored. In particular, the formation of the diene intermediates and the following dimerization of dienes was essential to synthesize tricyclic terpene dimers. The biphasic catalytic process accelerated the deoxygenation rate and enabled the dimerization with the aid of organic solvent while controlling the reaction rates to avoid the formation of solid residues. Moreover, this process also facilitated the product separation by organic solvent extraction while enabling easy recycle of the homogenous catalysts.

Solvent-free catalytic conversion of xylose with methane to aromatics over Zn-Cr modified zeolite catalyst

One-pot catalytic co-conversion of xylose and methane to aromatics was investigated under solvent-free conditions. Aromatics are the major liquid products from xylose conversion. 57.6% yield of aromatics with 63.1% selectivity of BTEX, and 10.9% yield of solid residue are achieved over HZSM-5 modified with Zn and Cr species. It’s evidenced that methane presence could effectively improve the yield of aromatics and the selectivity of BTEX, and greatly reduce the formation of solid residue. The results of pyridine absorption and NH3-TPD measurements indicate that the distribution of Bronsted and Lewis acidic sites over the catalyst has a negligible effect on xylose conversion to aromatics. More acidic sites with higher ratio of weak acid sites could benefit the formation of aromatics with high BTEX selectivity during the xylose conversion. The possible reaction pathway involved in xylose conversion to aromatics is proposed based on pseudo-situ investigations. The findings in this work lead to a better understanding of the chemistry involved in xylose conversion, which could potentially contribute to the cost-efficient utilization of natural gas and biomass.

Formation of solid residues in combustion of boron-containing solid propellants

Boron-containing solid propellants are promising propellants for ducted rockets. The experimental data show that combustion of boron-containing propellants is accompanied by an intense conglomeration of the boron particles near the burning surface. As a result, the boron particles conglomerates which are the branched coral structures composed of sintered boron particles are formed in combustion of boron-containing solid propellants. This results in decrease in combustion efficiency of ducted rockets. To calculate the ignition and combustion of a conglomerate in the secondary combustor of a ducted rocket, it is necessary to know the size, structure and shape of the boron particle conglomerates that can significantly affect these processes. In this paper, we consider a model and a method for calculating the boron particles conglomeration in combustion of the boron-containing solid propellants. The process of the boron particles conglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between the contacting boron particles and rupture of these bonds under the action of the aerodynamic detached force from the side the flow of gaseous combustion products of solid propellant. The criterion of formation of residues (slag) on the burning surface of boron-containing propellants is considered. It is shown that depending on the propellant burning rate law, two different types of propellants with different conglomeration behavior can exist. The results of calculations of the boron particles conglomeration which demonstrate the slag formation are shown.

Hydrothermal liquefaction of cellulose in ammonia/water

In order to obtain the N-containing organics from cellulose under mild conditions, hydrothermal liquefaction of cellulose in the presence of ammonia was conducted in this study. The results showed that the increasing reaction temperature and prolonging time facilitated the conversion of cellulose in hydrothermal liquefaction (HTL) with NH3·H2O and decreased the amount of solid residue. Reaction temperature showed more influence than reaction time on solid residue formation. The components of bio-oil were significantly affected by reaction temperature and reaction time. Electrospray ionization-Fourier transform-ion cyclotron resonance-mass spectrometry (ESI FT-ICR MS) provided an insight for understanding the distribution of the different kinds of N-heterocycle compounds in the bio-oil. The possible reaction pathway of N-heterocycle compounds formation from cellulose during hydrothermal liquefaction with NH3·H2O was proposed.

Decomposition of benzene as a tar analogue in CO2 and H2 carrier gases, using a non-thermal plasma

Cracking of benzene in a non-thermal plasma (NTP) dielectric barrier discharge reactor (DBD) was investigated in CO2 and H2 carrier gases. Benzene was acting as an analogue for gasification tar, and CO2 and H2 are abundant in gasifier product gas. A parametric study in terms of specific input energy (SIE), residence time, concentration and temperature was performed to determine the optimal conditions for tar conversion. It was found that almost complete removal of benzene (36 g/Nm3) was observed in each carrier gas above 30 kJ/L and at 4.23 s. Lower hydrocarbons (<C6) (LHC) and solid residue were common products in both carrier gases. The selectivity to LHC in H2 carrier gas was higher (12%) than CO2 (2%) carrier gas, and CO was the major gaseous product in CO2 carrier gas. However, the problem of solid formation in the reactor was completely eradicated by operating at elevated temperatures in H2 carrier gas. The selectivity to lower hydrocarbons increased with increasing temperature. At 400 °C in H2 carrier gas, the selectivity to LHC reached 91% with no formation of solid residue. The major lower hydrocarbons at these conditions were CH4 (82%) and C2 (C2H6 + C2H4) 6.6%.

Advanced models for the prediction of product yield in hydrothermal liquefaction via a mixture design of biomass model components coupled with process variables

Hydrothermal liquefaction (HTL) has recently attracted great interest as a thermochemical conversion technique for biofuels production, however, suffers a lack of broadly applicable models for the prediction of product yield. This study developed a unique model for the prediction of HTL products yield via a mixture design of biomass model components coupled with process variables. The model compounds used in this study were soya protein for a protein representative, a mixture of cellulose and xylan for a saccharide representative, alkaline lignin for a lignin representative and soybean oil for a lipid representative. Reaction temperature (270–320 °C), time (5–20 min) and mass ratio of water/feedstocks (6:1–12:1) were chosen as the process variables of interest. The developed predictive models for biocrude yield and solid residue yield showed accuracy of (R2adj 94.6% and 93.2%, respectively), and were further validated using modelled feedstock and actual feedstock. These models can be used either to optimize HTL conditions when feedstock is known, or to optimize the composition of feedstock when reaction conditions are given. It was also observed that within the experimental design range, relatively mild HTL conditions eliminated alkaline lignin-lipid interaction and protein-lipid interaction, and thus enhanced biocrude formation; while more severe HTL conditions were preferred to reduce solid residue formation through promoting protein-saccharide interaction and saccharide-alkaline lignin interaction.

Plasma-assisted decomposition of a biomass gasification tar analogue into lower hydrocarbons in a synthetic product gas using a dielectric barrier discharge reactor

Cleaning product gas from biomass gasification is one of the major challenges for the application of biomass as a renewable energy source for power generation and value-added chemical synthesis. Non-thermal plasmas are a novel alternative technology for decomposing such tar compounds. In this research, the use of a dielectric barrier discharge (DBD) reactor was investigated for the decomposition of toluene (a tar surrogate) in a synthetic product gas containing H2, CO and CO2. The effect of residence time (0.95–2.82 s), plasma power (5–40 W), concentration (20–82 g/N m3), and temperature (ambient −400 °C) were investigated. It was demonstrated that the percentage removal of tar increased with increasing plasma power and residence time. 99%+ removal of toluene was observed at a plasma power of 40 W (the highest power used) and a residence time of 2.82 s (the highest residence time used). At ambient temperature, the toluene decomposition products include CO, lighter hydrocarbons, and solid residue. Unfortunately, at low temperatures, there was substantial solid residue formation. The synergetic effect of temperature and plasma was investigated to determine whether it could decrease residue formation. It was found that the solid residue completely disappeared at 400 °C. Furthermore, the selectivity and the yield of lower hydrocarbons increased with operating temperature. However, the yield of CO decreased due to the termination of radicals through the combination of CO and O at higher temperatures. Overall, this work demonstrates that toluene can be almost completely converted to smaller molecules by a DBD non-thermal plasma, and that a degree of control can be established by varying power, residence time and temperature, including eliminating the problem of solid residue formation.

Role of CO2 in the Conversion of Toluene as a Tar Surrogate in a Nonthermal Plasma Dielectric Barrier Discharge Reactor

The decomposition of toluene (a model tar compound) in CO2 was investigated at ambient and elevated temperatures in a dielectric barrier discharge (DBD). The effects of reaction parameters, such as the residence time (0.47–4.23 s), plasma power (5–40 W), toluene concentration (20–82 g/Nm3), and temperature (20–400 °C), were investigated. The DBD was shown to be an effective technique for tar removal. The percentage removal of tar increased with increasing the plasma power and residence time (to as high as 99% at the residence time of 4.23 s). The maximum selectivity to the two major gaseous products, CO and H2, was 73.5 and 21.9%, respectively. Solid residue formation was also observed inside the reactor. The synergetic effect of the temperature and plasma power was studied. As temperature increased, the decomposition of toluene decreased slightly from 99 to 88% (from ambient to 400 °C at 40 W) and the selectivity of CO and H2 decreased as a result of the increased rate of recombination of CO and O. The selectivity to lower hydrocarbons increased with the temperature.

Mechanism Study on Depolymerization of the α-O-4 Linkage Lignin Model Compound in Supercritical Ethanol System

The aim of this study was to explore the conversion mechanism of α-O-4 linkage lignin dimer model compound (monobenzone) in supercritical ethanol. The decomposition processes of monobenzone were investigated at different reaction time (0–12 h), conversion temperature (250–310 °C) and initial concentrations (0.01–0.03 g/mL). The reaction mechanism and pathways were proposed based on the distribution of products, the bond dissociation energies and the free radical theory. The results showed almost complete degradation was achieved in supercritical ethanol system. A higher temperature, a longer reaction time and a higher initial concentration significantly promoted the formation of solid residue due to the condensation reactions of the degradation intermediates/products. Based on the formation mechanism of products, the conversion products were classified into three types: (1) its own fragmentation compounds, (2) condensation compounds of its intermediates and (3) the second fragmentation compounds of its intermediates. A depolymerization reaction mechanism of monobenzone that primarily involved homolytic cleavage of the Cα–O linkage was proposed. In addition, the bibenzyl were an important and unstable intermediate product, it can continue to produce many different radical species that can participate in a variety of reaction mechanisms, resulting in complex reaction pathways and products distribution, even forming higher-molecular weight solid residue.

A generalized model of flame to surface heat feedback for laminar wall flames

In this work, experimental measurements of flame heat flux and sample mass loss rate are obtained as a diffusion flame spreads vertically upward (in the direction opposed to the vector of gravity) over the surface of seven commonly used polymeric materials, two of which are glass reinforced composites. Using these measurements, a previously developed empirical flame model specific to poly(methyl methacrylate) is generalized such that it can predict (flame to material surface) heat feedback from 3 to 20cm tall flames supported by a wide range of materials. Model generalization is accomplished through scaling on the basis of a material's gaseous pyrolyzate heat of combustion, which can be measured using mg-sized material samples in a microscale combustion calorimeter. For all seven materials tested in this work, which represent diverse chemical compositions and burning behaviors including polymer melt flow, sample burnout, and heavy soot and solid residue formation, model-predicted flame heat flux (to a water-cooled heat flux gauge) is shown to match experimental measurements taken across the full length of the flame with an average absolute error of 3.8kWm−2 (approximately 10–15% of peak measured flame heat flux). Coupled with a numerical pyrolysis solver, this generalized wall flame model provides the framework to quantitatively study material propensity to ignite and support early fire growth in a range of common scenarios with a level of accuracy and reduced computational cost unmatched by other currently available modeling tools.