Conversion Profiles Research Articles

2-D CFD modeling of gasification of a large biomass char particle in CO2 environment

There is a dearth in the literature of simple but robust models for gasification of large biomass particles that can address all important aspects of the reaction. A transient two-dimensional single-particle model of biomass gasification in the CO2 environment was developed in this work that incorporates chemical kinetics and heat transfer resistances, mass transfer inside the particle and boundary layer, non-equimolar counter diffusion including Knudsen diffusion, spatiotemporal variation in specific char surface area and thermophysical properties. The model was validated extensively with experimental results. Detailed simulation was carried out at reactor temperatures of 923–1123 K) using COMSOL Multiphysics software for two biomass samples – casuarina and acacia. Simulated conversion, reaction rate, temperature and gas composition profiles revealed that the reactions initially followed a shrinking core model, shifting subsequently to a shrinking reactive core model. Sensitivity analysis identified the sensitivities of process parameters as: reactor temperature > particle diameter (constant length) > initial specific char surface area > porosity > pore parameter > particle diameter (constant volume). Casuarina was found to be a more reactive and better-suited biomass than acacia for gasification applications. The work has furnished important guidelines for selecting suitable biomass type and process parameters to design an appropriate gasifier for industrial use.

LED lighting affects maturation, conversion and metabolic profile of somatic embryos derived from Kelussia odoratissima Mozaff

LED lighting affects maturation, conversion and metabolic profile of somatic embryos derived from Kelussia odoratissima Mozaff

Free radical copolymerization kinetics of bio-based dibutyl itaconate and n-butyl acrylate

The free radical copolymerization of dibutyl itaconate (DBI), a monomer derived from renewable resources, and n-butyl acrylate (BA) is investigated to explore the potential of incorporating itaconate monomers into commercial acrylic resins to enhance the sustainability of coating materials. Batch experiments were conducted at 50 °C and 80 °C, varying initial monomer and initiator concentrations as well as monomer compositions, with proton NMR and size exclusion chromatography used to analyze monomer conversion profiles and polymer molar mass distributions (MMDs). The data were analyzed using a kinetic model developed to guide the experimental studies and estimate key kinetic parameters controlling copolymer composition, polymerization rate and polymer MMDs. The use of the more reactive BA as comonomer significantly increases the conversion and molar mass of the resulting copolymer. Furthermore, semi-batch operating conditions similar to current industrial practice can incorporate a substantial fraction of DBI into acrylic copolymer resins, thus enhancing their sustainability profile.

National trends in using revisional surgeries post-sleeve gastrectomy due to reflux and weight recurrence: a matched case-control analysis

BackgroundSeveral options exist for surgical conversion after sleeve gastrectomy (SG), but a definitive safety profile for each option by indication for conversion remains unclear. ObjectivesTo determine and compare 30-day risk profiles of SG conversion to Roux-en-Y gastric bypass (RYGB), biliopancreatic diversion with duodenal switch (BPD-DS), and single-anastomosis duodenoileostomy (SADI). MethodsMetabolic and Bariatric Surgery Accreditation and Quality Improvement Program national database entries from 2020 to 2022 were used to identify 25,760 adult patients who underwent SG conversion to RYGB, BPD-DS, or SADI. Subgroup analyses were performed among 6106 conversions completed for weight-related complications (RYGB: 3053 patients; BPD-DS: 1826 patients; SADI: 1227 patients). Multivariable analysis and 1:1 nearest-neighbor matching were used to further characterize the 30-day risk profile of each conversion. ResultsPatients with RYGB conversions had a lower preoperative body mass index compared with those with BPD-DS + SADI conversions (39.8 versus 46.1, P < .001) and significantly lower rates of medical comorbidities. The distribution of conversion indication for each MBS configuration varied, where most RYGB conversions were for reflux (56.1%) whereas most BPD-DS + SADI conversions were for weight-related complications (87.3%; P < .001). On 1:1 matched analysis of conversions for weight recurrence, odds of 30-day complications (odds ratio .73, P = .019) and readmission (odds ratio .77, P = .031) were lower in BPD-DS + SADI conversions compared with RYGB. There were no significant differences in odds of 30-day reintervention or reoperation between conversion to RYGB and BPD-DS + SADI. Major differing drivers of complications between conversion types included hemorrhage (RYGB 1.98% versus BPD-DS + SADI .87%; P = .001). ConclusionsFor weight recurrence after SG, conversion to BPD-DS + SADI does not have greater 30-day complications than RYGB and may be a safe conversion option.

Effect of binary porogen mixtures on polymer monoliths prepared by gamma-radiation initiated polymerization

Gamma-radiation initiated polymerization is an easy-to-use and simple technique for the preparation of porous polymer monoliths widely used as active materials in separation columns. Herein, binary porogen mixtures of ethyl acetate/acetone/acetonitrile with methanol were used to synthesize diethylene glycol dimethacrylate monoliths with this technique. Systematic studies have been performed to determine the effect of the composition of the solvent mixture on the morphology and the reaction kinetics, including the growth mechanism and the growth rate. The irradiation dose-dependent conversion profiles showed that with binary solvents the polymerization is much faster than with the same compounds used as single solvents. Depending on the type and the composition of the solvent one-, two- and three-dimensional, and fractal growth mechanisms were identified.

Co‐Pyrolysis and Pyrolysis of Corn‐Cob Biomass and Waste Plastic: Comprehensive Study Based on Kinetic and Thermodynamic Approach

AbstractThis study focuses on the utilization of agro‐residual corn‐cob biomass, waste plastic and the combination of both for pyrolysis reaction using thermal analysis. Circular bioeconomy is assured by closing all the resource materials loops through co‐pyrolysis process. The conversion profiles of corn cob pyrolysis at various heating rates reveal a three‐stage decomposition process, and plastic waste exhibits single stage degradation. Due to the interaction between the blended materials, additional degradation peaks arise during the co‐pyrolysis of waste plastic (PET bottles) and biomass (corn cobs). The apparent activation energy fluctuates in the range of 120–260 kJ/mol with the conversion, according to Flynn‐Wall‐Ozawa (FWO) and Kissinger‐Akahira‐Sunose (KAS) kinetic methods. Notably, for co‐pyrolysis the apparent activation energy is lower (168 kJ/mol using FWO) than the individual biomass (179 kJ/mol using FWO) and plastic (175 kJ/mol using FWO), suggesting a positive synergistic effect during charring. The liquid crude and char product analysis from corn cob pyorlysis through FTIR and XRD confirms the application of the products in energy and chemical processes. The results obtained in this study can be utilized for co‐pyrolysis reactor analysis specifically using waste plastic bottles that are accumulating in the environment.

Modulation of Solid-state Thermal Reaction of Iron(III)Citrate by a Co-precursor Studied using Thermogravimetry: Evaluation of Kinetic and Thermodynamic Parameters and Nucleation Rate

Background: Solid state reaction of iron(III)citrate leads to a range of ironbased oxides by varying the reaction conditions, e.g., the presence of co-precursor. The influence of reaction conditions on the kinetics of the solid-state reaction of iron(III)citrate needs to be investigated. Objective: Kinetic analysis of the solid-state reaction of iron(III)citrate in the presence of a co-precursor has been explored to realize the influences of the co-precursor on the reaction process as well as decomposed material. Method:: Non-isothermal thermogravimetry profiles are deconvoluted to individual reaction steps. The model-free kinetic methodology is utilized to estimate step-wise activation energy and, hence, the reaction mechanism along with the reaction rate. Conversiondependent thermodynamic parameters and nucleation rate are estimated. XRD analysis has been used to characterize the decomposed material. Results: Thermogravimetry profiles obtained for an iron(III)citrate and malonic acid mixture are deconvoluted into six steps. The decomposed nanomaterial is identified as magnetite (size 10 nm). The observed reaction mechanisms associated with each step are different, where the activation/reaction rate is conversion-dependent. A good fit between the experimental and reverse-constructed conversion profiles is obtained. The nucleation rate at higher temperatures is affected by both the extent of conversion and the heating rate. A possible reaction pathway is proposed. The study elucidates the role of malonic acid as a co-precursor in modifying the thermal reaction of iron(III)citrate and product formation. Conclusion: This investigation proposes the applicability of suitable co-precursors as a potential controlling factor for preparing iron oxides from iron-based compounds.

Design and simulation of a novel reactor for the H2 storage mechanism in methylcyclohexane

The present study addresses the modeling and simulation of an intensified dehydrogenation reactor-heat exchanger system designed for a H2-based 2.0 MW mobile power plant. The reactor consisted of a multiple triple-tube system where the catalyst was packed in the middle tube while hot exhaust gases passed through the innermost and outermost tubes. A basecase design was defined and the reactor was simulated using the rigorous kinetics developed elsewhere for the MCH dehydrogenation. The parabolic differential equations of mass and heat energy were solved and the axial and radial conversion and temperature profiles were computed. Moreover, the effects of the number of longitudinal fins on the reactor tubes as well as the flow direction were also studied. With 12 number of fins on the reactor tube, the MCH conversion increased from 70.8% to 81.8%, with a corresponding increase in the average bed temperature from 569.3 K to 577.6 K and hydrogen yield from 37.05 kmol h−1 to 42.79 kmol h−1.

A Numerical Model to Predict the Relaxation Phenomena in Thermoset Polymers and Their Effects on Residual Stress during Curing, Part II: Numerical Evaluation of Residual Stress.

This article proposes a numerical routine to predict the residual stresses developing in an epoxy component during its curing. The scaling of viscoelastic properties with the temperature and the degree of conversion is modeled, adopting a mathematical formulation that considers the concurrent effects of curing and structural relaxation on the epoxy's viscoelastic relaxation time. The procedure comprises two moduli: at first, the thermal-kinetical problem is solved using the thermal module of Ansys and a homemade routine written in APDL, then the results in terms of temperature and the degree of conversion profiles are used to evaluate the viscoelastic functions, and the structural problem is solved in the mechanical module of Ansys, allowing the residual stresses calculation. The results show that the residual stresses mainly arise during cooling and scale with the logarithm of the Biot number.

Controlling photopolymerization reaction in layer‐by‐layer photopolymerization in 3D printing

AbstractToday, controlling the photopolymerization process during the 3D printing in vat photopolymerization is a key challenge. In this work, it is shown that using a relatively limited set of parameter, it is possible to estimate key factors involved in such process. On the basis of 16 formulations containing different concentrations of photoinitiator and UV filter, attempt was made to rationalize the photonic parameters used in the 3D printing process, that is, the depth of penetration Dp and the critical energy Ec. It is shown that the experimental Dp values can be correlated with calculated ones from Bouguer–Beer–Lambert law. Real‐time Fourier‐transform infrared spectroscopy (RT‐FTIR) experiments were performed under similar conditions as in 3D printing. The conversion profiles were used to estimate the Ec values. The limits of this approach was discussed as a function of the UV filter concentration. Finally, the RT‐FTIR curves are exploited to predict the in‐depth conversion of the different 3D printed layers and compared to experimental results obtained by confocal Raman microscopy.

Co-combustion characteristics and reaction mechanism of coal slime and sewage sludge using a novel multilateral double volumetric parallel model and dendrite neural network

The co-combustion of coal slime (CS) and sewage sludge (SS) presents an effective method for significantly reducing solid waste on large-scale. This study conducted experimental research to investigate the combustion and co-combustion characteristics of CS and SS, focusing on exploring the synergistic effects and mechanisms during co-combustion processes. Novel multilateral double parallel models (Multi-DPM) were proposed to analyze the contributions of volatile and char components in CS/SS mixtures across different ratios during co-combustion. The effects of temperature, mixing ratio, and heating rate on the co-combustion process were evaluated using a new novel dendrite neural network (DD-NN) model. The results revealed varyied degrees of interaction between CS and SS during co-combustion. Kinetic and thermodynamic analyses revealed that the most significant enhancement in the CS/SS mixing ratio of 6:4. Both the double parallel volumetric model (DPVM) and the newly proposed multilateral double parallel volumetric models (Multi-DPVM) demonstrated the best fit with experimental conversion and proved their suitability for analyzing the co-combustion process of CS and SS. These models were further employed to predict the combustion kinetic parameters and conversion profiles of total volatiles and total char of single and mixed materials, as well as the volatiles and char of the individual CS and SS materials within the mixture. The obtained conversion data and activation energy values from the DPVM and Multi-DPVM were used to assess the best fit reaction mechanism using the master-plots method. This validation underscored the reliability of the DPVM and Multi-DPVM based on integral fitting model solution. Moreover, the application of the new DD-NN model demonstrated good predictive performance for the co-combustion process of CS and SS, identifying key transfer functions influencing the co-combustion process. Overall, this study provides valuable insights into comprehensively understanding the co-combustion mechanism of CS and SS, providing crucial information for industrial product design.

Decomposition mechanism of lumpy dolomite particles

Cylindrical cm-sized dolomite particles were decomposed using the two steps decomposition scheme. Several studies on dolomite decomposition have been done using µm- to mm-sized samples over the years. However, these sizes are too small for industrial kiln application and ignore the influence of important parameters, e.g. thermal conductivity, on the decomposition process. In this work, the decomposition behavior of lumpy dolomite particles in each step was investigated. Experimentally measured sample temperature and conversion profiles in steps 1 and 2 are respectively similar to those obtained for the decomposition of pure magnesite and limestone. To measure the core temperature and conversion is to essentially analyze the decomposition behavior. The thermophysical material properties of the decomposition product in each step as a function of temperature was estimated using the shrinking core model. Finite difference method was employed in solving the 1D heat equation describing the process. The reaction rate coefficient in step 1 is shown to have a weak temperature dependence, the thermal conductivity of the product, MgO∙CaCO3, slightly increases with temperature but the permeability is not dependent. In step 2, the reaction coefficient and MgO∙CaO thermal conductivity and pore diffusivity do not show a clear temperature dependence. Finally, the sensitivity of the material and transport properties on the decomposition process was studied under shaft kiln condition. Thermal conductivity is observed to have the highest influence on decomposition with a value of up to 60 % at 1400 °C and for 120 mm particles.

Soft-sensor estimation via parameter fitting and dynamic optimization in an experimental batch butadiene homopolymerization reactor

In this work, we address modeling and experimental tasks to develop an industrial process for the anionic polymerization of butadiene, which is a key compound used in the production of high-performance tires. The aim of this study was to determine the processing conditions that lead to the efficient manufacturing of polybutadiene. Accordingly, an experimental polymer reaction facility was constructed to record both butadiene conversion and temperature profiles. A first-principles dynamic mathematical model was developed to track the measurement variables as best as possible. To improve the tracking of recorded variables, some process variables were deployed as manipulated variables. Because good experimental tracking was not acceptable, we used the soft-sensor approach to estimate some additional degrees of freedom. The estimation task was performed by describing the problem as a dynamic optimization problem. The results clearly show that the optimization and control tasks of butadiene polymerization reaction facilities are demanding and require good experimental information to develop reliable mathematical models that can be leveraged to speed up the development of such industrial polymerization systems.

Kinetically Controlled Site-Specific Self-assembly of Hairy Colloids.

The solvophobicity-driven directional self-assembly of polymer-coated gold nanorods is a well-established phenomenon. Yet, the kinetics of this process, the origin of site-selectivity in the self-assembly, and the interplay of (attractive) solvophobic brush interactions and (repulsive) electrostatic forces are not fully understood. Herein, we use a combination of time-resolved (vis/NIR) extinction spectroscopy and finite-difference time-domain (FDTD) simulations to determine conversion profiles for the assembly of gold nanorods with polystyrene shells of distinct thicknesses into their (tip-to-tip) self-assembled structures. In particular, we demonstrate that the assembly process is highly protracted compared with diffusion-controlled rates, and we find that the assembly rate varies for different thickness values of the polymer shell. Our findings were rationalized using coarse-grained molecular dynamics simulations, which also corroborated the tip-to-tip preference in the self-assembly process, albeit with a uniform polymer coating. Utilizing the knowledge of quantified conversion rates for distinct colloidal species, we designed coassembling systems with different brush thicknesses, featuring "narcissistic" self-sorting behavior. This provides new perspectives for high-level supracolloidal self-assembly.

Process simulation of methanol production via carbon dioxide hydrogenation

The performance of a packed bed reactor for CO2 conversion to methanol was investigated. Because of the exothermic reaction, temperature and concentration gradients happen along the reactor. A 2D packed-bed reactor model was applied for numerical investigations, coupled with detailed reaction kinetics and transport phenomena. The effect of feed inlet pressure and temperature on CO2 conversion and temperature profiles along the reactor was evaluated. The results showed that firstly increase in the temperature in the reactor because of the presence of exothermic reactions and then slight decrease in the temperature at top section of the reactor. Pressure was decrease from 55 bar to around 54 bar along the reactor. It was found that the CO2 conversion at outlet of reactor was 18.18 % at T = 475 K and it was increased to 23 % at temperature of 498 K and 555 K. The CO2 conversion was reached its maximum at short distance from the reactor entrance at T = 555 K. Also, the outlet temperature of gas mixture was increased from 522.53 K to 534.56 K with increasing feed inlet pressure from 35 bar to 55 bar. The CO2 conversion was 18.12 %, 20.77 %, and 22.96 % at pressures equal to 35, 45, and 55 bar respectively.

High-pressure study of the conversion of NH3/H2 mixtures in a flow reactor

Carbon free fuels such as hydrogen (H2) and ammonia (NH3) will probably play a fundamental role owing to their potential for clean combustion without CO2 emissions. To contribute to the knowledge and development of technologies based on carbon free combustion, the present work deals with an experimental and kinetic analysis of ammonia oxidation in its mixtures with hydrogen at high pressure (up to 40 bar), in the 250–1250 K temperature range using a quartz tubular reactor and argon as bath gas. The impact of temperature, pressure, stoichiometry and H2/NH3 ratio on the concentrations of NH3, NO, NO2, N2O, and N2 obtained as main products of oxidation has been analyzed. The main results indicate that either increasing pressure, H2/NH3 ratio or oxygen availability results in a shift of NH3 and H2 conversion to lower temperatures. The NH3 and H2 consumptions are promoted by the reactions that produce NH2, H, OH, O, HO2 and HNO species. The pressure effect is particularly significant in the low range of pressures studied. The main ammonia oxidation nitrogen products are N2 and N2O, while NO and NO2 concentrations are below the detection limit under all considered conditions. N2O formation is favored by increasing stoichiometry, pressure and H2/NH3 ratio. The experimental results are simulated and interpreted in terms of a literature detailed chemical kinetic mechanism, which, in general, is able to describe quite well both the H2 and NH3 conversion profiles under the studied conditions.

Formic Acid Decomposition Using Palladium-Zinc Preformed Colloidal Nanoparticles Supported on Carbon Nanofibre in Batch and Continuous Flow Reactors: Experimental and Computational Fluid Dynamics Modelling Studies

The need to replace conventional fuels with renewable sources is a great challenge for the science community. H2 is a promising alternative due to its high energy density and availability. H2 generation from formic acid (FA) decomposition occurred in a batch and a packed-bed flow reactor, in mild conditions, using a 2% Pd6Zn4/HHT (high heated treated) catalyst synthesised via the sol-immobilisation method. Experimental and theoretical studies took place, and the results showed that in the batch system, the conversion was enhanced with increasing reaction temperature, while in the continuous flow system, the conversion was found to decrease due to the deactivation of the catalyst resulting from the generation of the poisoning CO. Computational fluid dynamics (CFD) studies were developed to predict the conversion profiles, which demonstrated great validation with the experimental results. The model can accurately predict the decomposition of FA as well as the deactivation that occurs in the continuous flow system. Of significance was the performance of the packed-bed flow reactor, which showed improved FA conversion in comparison to the batch reactor, potentially leading to the utilisation of continuous flow systems for future fuel cell applications for on-site H2 production.

Virtual Volumetric Additive Manufacturing (VirtualVAM)

AbstractTomographic volumetric additive manufacturing (VAM) produces arbitrary 3D geometries by exposure of a rotating volume of photopolymer resin to tomographically‐patterned illumination. This enables high speed, layer‐less printing of parts from a wide range of photopolymers not amenable to layer‐by‐layer processes. Since the entire geometry is produced at once over the course of a few seconds to minutes, molecular diffusion length scales become significant to the printing process. Understanding these molecular reaction and diffusion processes is imperative for advancing VAM to a usable technology. These processes are experimentally very difficult to monitor and measure. Herein, VirtualVAM ‐ a simulation framework for modeling the tomographic VAM process, is developed and experimentally validated. VirtualVAM simulates reaction, diffusion, and heat generation processes over the course of a print with single‐voxel resolution. From a few experimentally‐determined input parameters and a set of images for projection, VirtualVAM is able to generate a large spatio‐temporal data set for any given tomographic VAM print. Using VirtualVAM, a number of experimentally‐unattainable aspects of the VAM process are investigated such as single‐voxel conversion profiles, effect of molecular oxygen, and stopping time determination. VirtualVAM also enables the optimization of exposure patterns to further improve contrast between in‐part and out‐of‐part delivered dose.

From waste to food and bioinsecticides: An innovative system integrating Tenebrio molitor bioconversion and pyrolysis bio-oil production

To achieve a waste-free clean production, the present study aimed to valorize an underused agroindustrial byproduct (rice bran) by mealworms bioconversion and produce bio-oil from pyrolysis of insect excreta (frass) as bioinsecticide. To reach the first goal, the suitability of rice bran (RB) versus standard diet, wheat bran (WB), was examined by determining feed conversion, growth performance, and nutritional profile of T. molitor larvae. RB diet was an appropriate feed substrate for breeding mealworms, as evidenced by their high survival rates, optimal feed conversion parameters, and its capability to support the growth and life cycle of this insect. Besides, RB did not affect soluble larval protein content but modified crude fat content and fatty acid profile. In order to address the second aim, egested frass from RB and WB were subjected to pyrolysis to obtain bio-oils. The main compound was acetic acid (≈37%) followed by 1,6-anhydro-β-d-glucopyranose (from 16 to 25%), as measured by GC-MS analysis. Nitrogen-containing chemicals accounted for ≈10%. Frass bio-oils could represent a novel source of bioinsecticides due to their bioeffectiveness in insect pests of economic importance (Plodia interpunctella and Tribolium castaneum) and medical interest (Culex pipiens pipiens). For P. interpunctella adults, frass bio-oils produced insecticidal activity by fumigant and contact exposure whereas for T. castaneum adults, just fumigant. By a miniaturized model that simulates semireal storage conditions, it was seen that, on T. castaneum, frass RB bio-oil generated higher repellent effect than frass WB. Finally, bio-oils proved to have larvicidal activity against Cx. p. pipiens.

Thermochemical behavior and kinetics study of algae pyrolysis using iron oxide catalyst

AbstractThe shift in emphasis from fossil fuel‐derived energy to waste‐to‐energy technologies has widened the possibility for environmentally sustainable methods such as pyrolysis. Algae collected from local sources that grow in wastewater using atmospheric CO2 is a potential feedstock for pyrolysis. Thus, the work focuses on studying the pyrolysis reaction of macroalgae sourced from regional sources in the presence of Fe2O3 catalyst using the thermogravimetric analysis, followed by kinetic analysis using iso‐conversional methods of Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink methods, and model free Kissinger method. The kinetic model was developed using master plot method. XRD analysis of the Fe2O3 catalyst confirms the presence of the maghemite and hematite phases in the sample. Based on the conversion profile, DTG trend, and kinetic parameter variation, the overall pyrolysis process can be divided into three different stages of dissociation reactions. The apparent activation energy calculated from different models varies in the range: stage I (∼268 kJ/mol), stage II (∼261 kJ/mol), and stage III (∼328 kJ/mol), respectively. Master plot analysis of the kinetic data confirms the best fit of the nucleation model (A2) to experimental data in stage II. Further, the thermodynamic properties of the reaction, such as change in enthalpy (ΔH), change in Gibbs free energy (ΔG), and change in entropy (ΔS) range between 206 and 405 kJ/mol, 189 and 651 kJ/mol, −450 and 27 J/mol/K, respectively, corroborates the complexity of the reaction. Kinetics and thermodynamic property analysis of complex reactions like pyrolysis is essential for pilot plant design.