Effect Of Residence Time Research Articles

Optimization of solvothermal liquefaction of water hyacinth over PTFE-acid mediated kaolin catalyst for enhanced biocrude production

The invasive nature of water hyacinth and the need for renewable energy sources have necessitated this research. Catalyst development through enhanced pore structure and process parameters optimization are requirements for effective mass transport during the biomass valorization and improved biocrude formation during solvothermal liquefaction process. In this present study, the effects of temperature (250–340 °C), residence time (10–20 min) and catalyst loading (10–13 wt%) on biocrude, biochar, gas yield, and biomass conversion were optimized using a Box-Behnken experimental design. The developed catalyst through the application of polytetrafluoroethylene (PTFE) for pore structure enhancement was characterized using SEM, BET and XRD techniques. The process optimization found maximum biocrude yield (32.0 wt%), minimum biochar yield (19.4 wt%) and maximum conversion efficiency (80.6%) at 340 °C, 20 min residence time, and 13 wt% catalyst loading. The GC-MS result of the biocrude produced at the optimum conditions (13 wt% catalyst loading) consists of ketones (32.2%), acids (22.3%) and had 65.2% carbon, 7.3% hydrogen, HHV of 29.4 MJ/kg and H/C ratio of 1.34 while an increment in catalyst loading of 20 wt% enhanced the overall biocrude properties with HHV of 35.50 MJ/kg. This result depicts the suitability of the PTFE modified acid treated kaolin for high quality biocrude production through valorization of water hyacinth into a candidate for renewable energy material.

Effect of heat-treatment temperature and residence time on microstructure and crystallinity of mesophase in coal tar pitch

Effect of heat-treatment temperature and residence time on microstructure and crystallinity of mesophase in coal tar pitch

Plasma-catalytic CO2 methanation over Ni supported on MCM-41 catalysts: Effect of metal dispersion and process optimization

Catalytic carbon dioxide (CO2) conversion technologies can be important components in carbon capture, storage and utilization for CO2 mitigation and possible future economic activity and have gained significant attention globally in past decades. Electrified non-thermal plasma (NTP) catalysis enables CO2 hydrogenation into value-added chemicals under mild conditions. If the hybrid process is coupled with renewable energy and green hydrogen, it can be the promising solution to address the energy and carbon emission challenges. To enhance the energy efficiency of NTP-catalytic systems, bespoke catalyst design and process optimization are necessary. Here, using Ni catalysts supported on mesoporous MCM-41 and NTP-catalytic CO2 methanation as the model systems, the effects of Ni metal dispersion, argon (Ar) addition and residence time on the NTP catalysis were also studied. The findings show that (i) increased metal dispersion alone did not lead to significant enhancement in the performance of NTP catalysis (e.g., CH4 production rate: 31.4 × 10−5 mol/(s·gNi) for 42.6 % Ni dispersion vs. 26.8 × 10−5 mol/(s·gNi) for 25.1 % dispersion), (ii) Ar addition to the system led to the decreased methane production rate (e.g., CH4 selectivity decreased by ∼19 % due to the increase in Ar addition to the system from 5 to 50 mL/min), and (iii) optimization of the residence time could improve the performance of NTP-catalytic CO2 methanation (i.e., an extension of the residence time to 0.69 s resulted in the higher CO2 conversion of 72.7 % and CH4 selectivity of 95.9 % at 9.6 kV than that at 0.49 s and 11 kV).

Ultrasonic aerosol agglomeration: Manipulation of particle deposition and its impact on air filter pressure drop

Acoustic agglomeration is a technique that leverages on sound waves to promote the collision of aerosol particulate matter, thus leading to the formation of larger particle agglomerates. In this study, this acoustics-driven phenomenon is demonstrated for its usefulness as an aerosol pre-conditioning method to significantly enhance the efficiency of filtration systems in particle treatment processes. Specifically, favorable changes in pressure drop across the filters are observed as a result of receiving less particle mass, for which filters are shown to be able to have their operational life extended remarkably by more than 50%. The involved ultrasonic aerosol agglomeration mechanisms are unveiled through numerical simulations, and the effects of residence time, sound pressure level, and initial particle number concentration on agglomeration performances are experimentally investigated. In addition, validations and measurements of filter pressure drop are obtained through a series of experiments. This study provides a comprehensive overview to the design and performance characterization of acoustics-agglomeration-enhanced filtration systems, which could potentially derive energy savings for fan power in ventilation systems and be scaled up for applications in industrial plants for reducing carbon emissions.

Effect of Residence Time and Carrier Gas on the Dehydrogenation of n-Hexane over Alumina-supported Chromium Catalyst

CrOx/γ-Al2O3 catalyst was prepared by incipient wetness impregnation method, and the influence of residence time and carrier gas on the dehydrogenation of n-hexane were studied. It is found that n-hexane dehydrogenation over CrOx/γ-Al2O3 catalyst with H2 as carrier gas exhibits totally different catalytic behaviors with that of diluting n-hexane with N2. When diluting feed with N2, the selectivity to dehydrogenation product is promoted while the cracking reaction is exhibited with reducing residence time. However, the selectivity to dehydrogenation product is significantly decreased while the isomerization of n-hexane is promoted when using H2 as carrier gas. It is proposed that H2 undergoes dissociation on the dehydrogenation active site, and further facilitates the olefinic dehydrogenation products to form carbocation, which performing isomerization reaction on the acid site on the γ-Al2O3 surface. Therefore, the isomerization of n-hexane is promoted in cost of the selectivity to dehydrogenation product when using H2 as carrier gas.

Reducing the phytotoxicity of spent mushroom substrate (SMS) for sustainable growing media by superheated steam torrefaction: effects of temperature and residence time

Reducing the phytotoxicity of spent mushroom substrate (SMS) for sustainable growing media by superheated steam torrefaction: effects of temperature and residence time

Discussion on Torrefaction Parameters for Making the Refuse-Derived Fuels by Response Surface Methodology

The torrefaction process is one of the mild pyrolysisor the low-temperature carbonization, which is a thermochemical conversion in which biomass is heated in an inert or nitrogen atmosphere, and the temperature ranges from 200°C to 300°C. It is considered to be an effective pretreatment method to make solid fuels. This study utilizes low-temperature carbonization technology to improve the combustion efficiency of solid-derived fuel (RDF-5) made from biomass. In this experiment, a tubular furnace was used to feed nitrogen gas for 15 min, and four raw materials of pennisetum, rice straw, wood chips and Camellia seed cakes were fed. The analysis was carried out, and the effects of temperature and residence time on the calorific value, energy yield and energy density of the four raw materials were explored using response surface methodology (RSM). It can be seen from the experimental results that among the four raw materials, the carbon content and calorific value of Camellia seed cakes are the highest. Elemental analysis showed that the proportions of nitrogen and sulfur in these four raw materials are very low. These four substances were understood to be suitable to be refuse-derived fuels (RDF-5). Comparing the calorific value of the four kinds of biomass after torrefaction process, the calorific value of pennisetum, Camellia seed cakes, wood chips and rice straw increased by 42.5%, 38.7%, 52.7%, and 18.6%, respectively. These findings revealed that the higher temperature and the longer residence time, the smaller energy yield and the higher energy density.

Valorization of bio-oil distillation residue through co-pyrolysis with moso bamboo to prepare biochar: Optimization study on effects of blend ratio, pyrolysis temperature, and residence time

In view of the high energy consumption and pollutant emissions in the cement production industry, biomass as the renewable carbon-neutrality energy is promisingly conducive to remitting cement carbon dioxide emissions and simultaneously realizing waste-to-energy initiatives. In this study, bio-oil distillation residue (DR), with high carbon content and heat value, is co-pyrolyzed with moso bamboo (MB) to optimize the bulk and combustion properties of biochar, aiming at yielding bio-fuel as an alternative fuel to replace coals for energy and heat supply in cement industry. The impacts of three primary process parameters on the carbonization reaction were investigated, while the parametric interactions were further estimated by using response surface methodology (RSM) to optimize the ultimate, proximate and fuel characteristics of biochars. The results showed the co-pyrolysis synergies between bio-oil distillation residue and moso bamboo endowed the maximum biochar yield of 44.62% and the maximum difference biochar yield of 7.56%. Meanwhile, the experimental carbon content, fixed carbon content and high heat value (HHV) were regulated through coupling parametric distribution and further increased by 1.96%, 2.59% and 1.23 MJ/kg, respectively. The parametric responses on combustion characteristics of biochar based on thermogravimetric analysis were predicted, and the optimal carbonization conditions for biochar production were also summarized. This study would offer an optimal biochar production scheme to adaptively yield coal-like biochar for reducing anthropogenic carbon dioxide emissions in cement industry.

Tempe Wastewater Treatment Using Effective Microorganisms Made from Kepok Banana Peel Waste

Wastewater produced by the tempeh industry contains a high organic content, so it requires serious handling so as not to cause pollution in water bodies. One method that can accelerate the decomposition of the organic substance process is to use Lactobacillus sp. bacteria as effective microorganisms (EM). The material used to manufacture EM is sourced from kepok banana peel waste, which has a carbohydrate content of 9.8%. This study aims to examine the effect of EM concentration and residence time on reducing pollutants in tempeh wastewater using EM made from kepok banana peel waste. The EM concentrations were 0%, 10%, 20%, and 30% successively, with residence times of 0, 4, 8, 12, and 16 days. The researchers used a batch system in a 5-litre plastic tube reactor with an aeration system. The results demonstrated the effectiveness of adding EM from kepok banana peel waste in reducing Chemical Oxygen Demand (COD) levels. Specifically, a 20% dose of EM resulted in a 78.13% removal, a 30% dose of Biological Oxygen Demand (BOD) led to a 78.01% reduction, and a 10% dose of Total Suspended Solid (TSS) resulted in a 66.81% removal over an optimum residence time of 16 days.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge.The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Intensified extraction and stripping of uranium using membrane dispersion microextractor

The extraction and stripping of uranium(VI) using membrane dispersion microextractor were investigated in high phase ratio. The effects of residence time, aqueous phase flowrates and organic phase flowrates, as well as nitric acid and the extractant concentration on the stage efficiency were evaluated. With the increase of aqueous phase flowrate and organic phase, the efficiency firstly decreased and then increased. Both the extraction efficiency and stripping efficiency can reach >90 % at high phase ratio within 10 s. The efficiency decreased with the increase of nitric acid in aqueous phase, whereas the efficiency increased with the increase of tributyl phosphate (TBP) concentration. Finally, mass transfer characteristic in extraction process in membrane dispersion microextractor was discussed. The overall mass transfer coefficient in membrane dispersion microextractor could reach 0.13 s−1 at A:O = 5:1 and 0.058 s−1at high A:O ratio of 40:1.

Hydrothermal carbonisation of mixed agri-food waste: Process optimisation and mechanistic evaluation of hydrochar inorganic chemistry

In this study, low-quality mixed agri-food waste (MAFW) was upgraded into homogenous high-quality solid fuel (i.e., hydrochar) via hydrothermal carbonisation (HTC). Response surface methodology (RSM) and principal component analysis (PCA) were used to study the effect of temperature (190–230 °C), residence time (1–5 h) and solid loading (5–20 %) on hydrochar fuel characteristics and provide mechanistic insights into hydrochar inorganic chemistry. In addition, HTC operating conditions were optimised to maximise hydrochar yield and calorific value and minimise ash content. Results from RSM revealed that reaction temperature and solid loading had most influence on the studied responses. The process optimisation of the HTC of MAFW resulted in hydrochar yield, calorific value and ash content of 52.25 %, 24.56 MJ/kg and 6.20 % (further validated within 3 % error), respectively at optimum operating condition of ⁓212 °C, 5 h and ⁓7.8 % solid loading. Furthermore, analysis by PCA revealed solid loading had a more significant impact on the fate of inorganic elements compared to reaction temperature and residence time. The results also suggests that inorganics are less concentrated in hydrochar at low solid loading and medium reaction severity. Compared to the raw-MAFW, the likelihood of fouling and slagging during combustion was reduced in the hydrochar.

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%).

Changes of C, H, and N Elements of Corn Straw during the Microwave Heating Process

Due to the rapid growth of the global economy, energy consumption has been steadily increasing, leading to increasing issues such as energy shortages and environmental concerns. Biomass energy, a critical renewable energy source, plays a vital role in advancing low-carbon energy development and resource sustainability. In this study, experiments were conducted to study the migration of C, H, and N elements of corn straw during the microwave heating process, and the effects of residence time, heating temperature, and microwave power were also investigated. The results showed that when the temperature rose, both the proportion of C and H elements fluctuated slightly. Specifically, when the temperature rose from 75 °C to 275 °C, there was a 1.02% increase in the proportion of the C element and a 0.25% decrease in the proportion of the H element. Residence time appeared to be a significant factor influencing the changes in C, H, and N elements. For a 40 min residence time, the proportion of the C element increased from 31.77% to 35.36%, while the proportion of the H element decreased from 4.50% to 3.83%. When there was an increase in the microwave power between 160 W and 200 W, higher temperatures were reached in the samples, leading to the carbonization process of corn straw being more complete. Consequently, the proportion of the C element rose with extended residence time, whereas the proportion of the H element decreased as the residence time increased.

Continuous Synthesis of Spherical Polyelectrolyte Brushes by Photo-Emulsion Polymerization in a Microreactor.

Nanosized spherical polyelectrolyte brushes (SPBs) are ideal candidates for the preparation of nanometal catalysts, protein separation, and medical diagnostics. Until now, SPBs have been synthesized by photo-emulsion polymerization in a batch reactor, which remains challenging to scale up. This paper reports a successful continuous preparation of SPBs by photo-emulsion polymerization in a self-made microreactor. The effects of residence time, monomer concentration, and feed ratios on the conversion of monomers and SPB structures are systematically investigated by dynamic lighting scattering and transmission electron microscopy. Poly(acrylic acid) (PAA) SPBs obtained in a microreactor exhibiting a narrow size distribution with a short reaction time are very effective in inhibiting the calcium carbonate scale and are comparable to those produced in a batch reactor. This work confirms the feasibility of continuous preparation and scaled-up production of SPBs.

Production of phenolic monomers from lignin in hydrothermal medium: Effect of rapid heating and short residence time

This study investigates the influence of heating rate and short residence time (1–15 min) on the hydrothermal liquefaction (HTL) of alkali lignin, as a function of reaction temperature (280–320 °C). A novel induction-heating reactor system (IHRS) was designed and was used for rapid heating rate (∼100 °C/min), while a resistive-heating reactor system (RHRS) was used for slow heating rate (∼5.3 °C/min). The experiment using IHRS with a short residence time (1 min) resulted in the highest yield of carbon recovery in biocrude (52.2 ± 0.63 wt%) at 320 °C under autogenous pressure. In contrast, the experiments using RHRS or longer residence time (8–15 min) with IHRS showed lower biocrude yield due to the promotion of gasification and undesired secondary reactions. The detailed characterization of biocrude revealed that rapid heating rate improves the selectivity of compound in biocrude, such as phenol, while slow heating rate produced a broader distribution of compounds, including anisole and alkyl phenols at 320 °C for 1 min residence time. Furthermore, the usefulness of phenol as capping agent during IHRS of lignin was demonstrated in suppressing char formation and increasing biocrude yield.

Synthesis of tapioca starch/palm oil encapsulated urea-impregnated biochar derived from peppercorn waste as a sustainable controlled-release fertilizer

Nutrient leaching and volatilization cause environmental pollution, thus the pursuit of developing controlled-release fertilizer formulation is necessary. Biochar-based fertilizer exhibits slow-release characteristic, however the nutrient release mechanism needs to be improved. To overcome this limitation, the approach of applying encapsulation technology with biochar-based fertilizer has been implemented in this study. Black peppercorn waste was used to synthesize urea-impregnated biochar (UIB). Central composite design was used to investigate the effects of pyrolysis temperature, residence time and urea:biochar ratio on nitrogen content of UIB. The optimum condition to synthesize UIB was at 400 °C pyrolysis temperature, 120 min residence time and 0.6:1 urea:biochar ratio, which resulted in 16.07% nitrogen content. The tapioca starch/palm oil (PO) biofilm formulated using 8 g of tapioca starch and 0.12 µL of PO was coated on the UIB to produce encapsulated urea-impregnated biochar (EUIB). The UIB and EUIB pellets achieved complete release of nitrogen in water after 90 min and 330 min, respectively. The nutrient release mechanism of UIB and EUIB was best described by the Higuchi model and Korsmeyer-Peppas model, respectively. The improvement of water retention ratio of UIB and EUIB pellets was more significant in sandy-textural soil as compared to clayey-textural soil. The EUIB derived from peppercorn waste has the potential to be utilized as a sustainable controlled-release fertilizer for agriculture.

Elucidating dechlorination of waste polyvinyl chloride under high‐temperature catalytic hydrothermal treatment

AbstractThis study focused on evaluating the reduction of chlorine content in waste polyvinyl chloride (WPVC) through high‐temperature catalytic hydrothermal treatment (HTT). Catalytic HTT experiments were carried out to evaluate the effect of noble metal catalysts (Ru/C, Pt/C, and Pd/C), residence time (0.5, 1, 2, and, 4 h), reaction temperature (300, 325, and 350°C), and catalyst loading (0, 5, and 10 wt%). The findings indicated that dechlorination efficiency can be achieved by 99.01% at 350°C and 1 h, with 10 wt% Pd/C loading. Based on chlorine balance, the chlorine content of the solid phase significantly decreased from 568.8 to 5.64 g kg−1 at the same condition. The catalytic HTT solid residue ash has low chlorine content under most operational conditions. These results suggest that catalytic HTT is an effective method to dechlorinate WPVC as a high‐halogenated waste plastic in order to reduce its harmful effect on the environment.

Kinetic Modeling of Cornstalk Cellulose Hydrolysis in Supercritical Water: A Comparative Study of the Effects of Temperature and Residence Time on Derivative Production

Kinetic modeling is essential in understanding and controlling the process of cellulose hydrolysis for producing value-added cellulose derivatives. This study aims to adopt a set of dominate kinetic ordinary differential equations of cornstalk cellulose hydrolysis in supercritical water for mechanism-based prediction of the production of cellulose, glucose, fructose, glyceraldehyde, erythrose, 5-hydroxymethyl furfural, glycolaldehyde, threose, aldose, and other cellulose derivatives from cornstalks under processing conditions with a pressure of 89 MPa and a temperature of 378 °C, as considered in a recent experimental study in the literature. The yield rates of several cellulose derivatives, e.g., glucose, fructose, 5-HMF, and erythrose as predicted by the present model, are close to those of experimental measurements. The model is further used to predict the yield rates of a few new cellulose derivatives, e.g., glycolaldehyde, threose, and aldose, that are potentially generated in cornstalk cellulose hydrolysis in supercritical water. The present model and computational simulations can be utilized as a rational tool to predict, control, and optimize the derivative yields in cellulose hydrolysis in supercritical water via tuning the process parameters, and, therefore, are useful for the optimal production of targeted bio-based fuels and chemicals from cornstalks and other agricultural and municipal wastes.

Optimizing marine macrophyte capacity to locally ameliorate ocean acidification under variable light and flow regimes: Insights from an experimental approach.

The urgent need to remediate ocean acidification has brought attention to the ability of marine macrophytes (seagrasses and seaweeds) to take up carbon dioxide (CO2) and locally raise seawater pH via primary production. This physiological process may represent a powerful ocean acidification mitigation tool in coastal areas. However, highly variable nearshore environmental conditions pose uncertainty in the extent of the amelioration effect. We developed experiments in aquaria to address two interconnected goals. First, we explored the individual capacities of four species of marine macrophytes (Ulva lactuca, Zostera marina, Fucus vesiculosus and Saccharina latissima) to ameliorate seawater acidity in experimentally elevated pCO2. Second, we used the most responsive species (i.e., S. latissima) to assess the effects of high and low water residence time on the amelioration of seawater acidity in ambient and simulated future scenarios of climate change across a gradient of irradiance. We measured changes in dissolved oxygen, pH, and total alkalinity, and derived resultant changes to dissolved inorganic carbon (DIC) and calcium carbonate saturation state (Ω). While all species increased productivity under elevated CO2, S. latissima was able to remove DIC and alter pH and Ω more substantially as CO2 increased. Additionally, the amelioration of seawater acidity by S. latissima was optimized under high irradiance and high residence time. However, the influence of water residence time was insignificant under future scenarios. Finally, we applied predictive models as a function of macrophyte biomass, irradiance, and residence time conditions in ambient and future climatic scenarios to allow projections at the ecosystem level. This research contributes to understanding the biological and physical drivers of the coastal CO2 system.