Char Properties Research Articles

The importance of inherent inorganics and the surface area of wood char for its gasification reactivity and catalytic activity towards toluene conversion

Gasification char is an effective catalyst for tar reforming because of the abundance of surface active sites, which are available for heterogeneous conversion of hydrocarbons and interactions with the reforming agents. This paper focuses on the importance of certain char properties for the gasification and catalytic reforming. Specifically, the gasification reactivity of spruce char is examined, along with its performance as a catalyst for toluene conversion. The material used for this work was produced via gasification of spruce wood chips in the pilot TwoStage Viking plant (Technical University of Denmark, Risø). To obtain a set of samples with varied surface area characteristics and inorganic content, three pre-treatments were applied to samples of this char: acid washing, steam activation, and high-temperature treatment. The gasification and catalytic experiments performed with the untreated and modified materials revealed that the reactivity of the char during gasification in CO2 depends mostly on the metal content in the sample, whereas the conversion of toluene was insensitive to the char inorganic content, but strongly correlated with the surface area available for heterogeneous reactions with toluene.

Determination of Fuel Properties of Char Obtained during the Pyrolysis of Waste Pharmaceutical Blisters

The research presented in this manuscript is focused on the pyrolysis of waste pharmaceutical blisters, which are a large and neglected group of waste, that could be possibly recovered. The studies were focused on the analysis of the chemical composition, as well as fuel properties of the char generated during the process and its possible applications. The process temperatures (400, 425, and 450 °C) were determined based on the thermogravimetric study that was performed prior to the pyrolysis tests. The selected materials included the pre- and post-consumer waste pharmaceutical blisters in order to determine the possible influence of impurities on the final products. The tests were performed on a laboratory scale fixed bed reactor. The obtained solid fractions (metal and char) were separated. Char was subjected to elemental analysis (C, H, N, Cl, S), as well as the heat of combustion and fuel-related properties (content of flammable, non-flammable, and volatile components) were determined. The results were used to compare the properties of char to the properties of active carbon. The market potential was analyzed.

Lab-Scale Study of Temperature and Duration Effects on Carbonized Solid Fuels Properties Produced from Municipal Solid Waste Components.

In work, data from carbonization of the eight main municipal solid waste components (carton, fabric, kitchen waste, paper, plastic, rubber, paper/aluminum/polyethylene (PAP/AL/PE) composite packaging pack, wood) carbonized at 300–500 °C for 20–60 min were used to build regression models to predict the biochar properties (proximate and ultimate analysis) for particular components. These models were then combined in general models that predict the properties of char made from mixed waste components depending on pyrolysis temperature, residence time, and share of municipal solid waste components. Next, the general models were compared with experimental data (two mixtures made from the above-mentioned components carbonized at the same conditions). The comparison showed that most of the proposed general models had a determination coefficient (R2) over 0.6, and the best prediction was found for the prediction of biochar mass yield (R2 = 0.9). All models were implemented into a spreadsheet to provide a simple tool to determine the potential of carbonization of municipal solid waste/refuse solid fuel based on a local mix of major components.

Characterization of slag from anthracite gasification in moving bed slagging gasifier

Gasification has become an effective way to realize clean and efficient utilization of coal. Anthracite is characterized by low grindability index and low gasification reactivity, which is not suitable for fluidized gasifier and entrained-flow gasifiers for low carbon conversion and high crushing cost. However, due to its high thermal and mechanical strength, it is preferred to be gasified in moving bed slagging gasifier. In this work, three slag samples were collected from pilot plant of moving bed slagging gasifier using anthracite as feedstock, and residual char was found in slag. In order to reveal formation mechanism of slag and residual char in the slags, properties of mineral matter and residual char were analysed. Results showed that slag taken from stable operation condition had low contents of residual char and crystalline phases. However, a lot of residual char particles were found in other two slags. Comparing to coal char prepared at 850 °C, residual chars in slags had higher graphitization degree and surface areas. Besides, it presented a higher gasification activity, which mainly depends on its porous structure and surface areas. In addition, formation of metallic iron, interface of char-slag and invasion of char by slag were observed in slag with residual char. It was found that occurrence of residual char in slag from anthracite gasification in moving bed slagging gasifier was strongly influenced by low reactivity of anthracite, unreacted limestone, high molten slag level.

Effects of Briquetting and High Pyrolysis Temperature on Hydrolysis Lignin Char Properties and Reactivity in CO-CO2-N2 Conditions

Carbonaceous reductants for pyrometallurgical applications are usually obtained from fossil-based sources. The most important properties of the reductants greatly depend on the application and the feeding of the reductant into the process. However, the mechanical strength, calorific value, fixed carbon content, and reactivity of the reductant are the properties that usually define the applicability of the reductant for different processes. The reactivity of the biochars is usually high in comparison to metallurgical coke, which may restrict the applicability of the biochar in reduction processes. One cause of the higher reactivity is the higher surface area of the biochars, which can be suppressed with agglomeration treatment, e.g., briquetting. In this work, hydrolysis lignin was used for slow pyrolysis experiments to produce biochars. The biochars were pyrolyzed in briquetted form and in as-received form at various temperatures. The reactivity values of the biochars were tested in dynamic reactivity tests in a CO-CO2-N2 gas atmosphere at temperatures of up to 1350 °C. It was found that the yield of the hydrolysis lignin char only decreased by 3.36 wt% when the pyrolysis temperature was elevated from 600 to 1200 °C, while a decrease in yield of 4.88 wt% occurred when the pyrolysis temperature was elevated from 450 to 600 °C. The mass loss of hydrolysis lignin biochar in the reactivity experiment in CO-CO2-N2 atmosphere was significantly decreased from 79.41 wt% to 56.80 wt% when the hydrolysis lignin was briquetted before the slow pyrolysis process and the temperature of the pyrolysis process was elevated from 600 to 1200 °C. This means that the mass loss of the material was suppressed by 22.61 wt% due to the higher pyrolysis temperature and briquetting process.

Adsorption of Organic Compounds by Biomass Chars: Direct Role of Aromatic Condensation (Ring Cluster Size) Revealed by Experimental and Theoretical Studies.

Biomass chars are a major component of the soil environmental black carbon pool and prepared forms are a potentially useful tool in remediation. A function critical to the roles of both environmental and prepared chars is sorption of organic compounds. Char properties known to control sorption include surface area, porosity, functional group composition, and percent aromatic carbon. Here, we show that sorption affinity (but not maximum capacity) of organic compounds is directly related to the degree of condensation of the aromatic fraction. The Dubinin-Ashtakov characteristic sorption energy (EDA, kJ mol-1) of 22 compounds on a thermoseries of bamboo chars correlates strongly with the DP/MAS-13C NMR-determined bridgehead aromatic carbon fraction (χb), which relates to the mean ring cluster size. Density functional theory-computed binding energy (Ebd) for five of the compounds on a representative series of polybenzenoid hydrocarbon open-face sheets also correlates positively with χb, leveling off for rings larger than ∼C55. The Ebd, in turn, correlates strongly with EDA. An increase in Ebd with cluster size is also found for sorption, both monolayer and bilayer, between parallel sheets representing slit micropores. The increasing sorption energy with cluster size is shown to be due to increasing cluster polarizability, which strengthens dispersion forces with the sorbate. The findings underscore a previously overlooked explicit role of aromatic condensation in sorption energy, and illustrate the utility of EDA-Ebd comparison for predicting sorption.

Effects of volatile matter and oxygen concentration on combustion characteristics of coal in an oxygen-enriched fluidized bed

Oxygen-enriched combustion in fluidized bed is a promising clean coal combustion technology which can efficiently control the emission of coal-fired pollutants, especially CO2. In this paper, by using several judging methods, the combustion characteristics of five kinds of coal under four different oxygen concentrations (20.9%, 27.8%, 40.7% and 52.7%, CO2 as equilibrium gas) were measured in the small-scale fluidized bed reactor with electric heating in detail. The oxygen consumption and volatile release characteristics were explored online. The influence of coal types, volatile matter and oxygen concentration on coal combustion characteristics was analysed. It’s found that the higher the bed temperature was, the faster the reaction rate was and the more oxygen consumption was. At a certain oxygen concentration and proper bed temperature, the separated combustion of volatile and char were observed. When the oxygen concentration was high, the separation phenomenon was more obvious. High-volatile, a certain bed temperature and oxygen concentration were the basic factors for the formation of separated combustion. The total volatile matter is not comprehensive as the index of reaction combustion characteristics and the effect of combustible components should be specifically considered. It’s found that for the coal with high combustible components, the separated combustion is more obvious. Volatile matter plays a dual role in the ignition and combustion of coal. The volatile matter (lower volatile matter) of some coals has a great promoting effect on coal combustion at higher temperature, while that (higher volatile matter) of other coals is not, which is closely related to the properties of char and the diffusion of volatile matter in pores.

State-of-the-Art Char Production with a Focus on Bark Feedstocks: Processes, Design, and Applications

In recent years, there has been a surge of interest in char production from lignocellulosic biomass due to the fact of char’s interesting technological properties. Global char production in 2019 reached 53.6 million tons. Barks are among the most important and understudied lignocellulosic feedstocks that have a large potential for exploitation, given bark global production which is estimated to be as high as 400 million cubic meters per year. Chars can be produced from barks; however, in order to obtain the desired char yields and for simulation of the pyrolysis process, it is important to understand the differences between barks and woods and other lignocellulosic materials in addition to selecting a proper thermochemical method for bark-based char production. In this state-of-the-art review, after analyzing the main char production methods, barks were characterized for their chemical composition and compared with other important lignocellulosic materials. Following these steps, previous bark-based char production studies were analyzed, and different barks and process types were evaluated for the first time to guide future char production process designs based on bark feedstock. The dry and wet pyrolysis and gasification results of barks revealed that application of different particle sizes, heating rates, and solid residence times resulted in highly variable char yields between the temperature range of 220 °C and 600 °C. Bark-based char production should be primarily performed via a slow pyrolysis route, considering the superior surface properties of slow pyrolysis chars.

Characterisation of charred organic matter in micromorphological thin sections by means of Raman spectroscopy

Burned or charred organic matter in anthropogenic combustion features may provide important clues about past human activities related to fire. To interpret archaeological hearths, a correct identification of the organic source material is key. In the present work, Raman spectroscopy is applied to characterise the structural properties of char produced in laboratory heating- and open-fire experiments. This reference data set is compared to analyses of three different archaeological sites with Middle Palaeolithic combustion contexts. The results show that it is possible to determine whether a charred fragment is the product of burning animal-derived matter (e.g. meat) or plant-derived matter (e.g. wood) by plotting a few Raman spectral parameters (i.e. position of G and D bands, and intensity ratios HD/HG and HV/HG) against one another. The most effective parameters for discriminating animal- from plant-derived matter are the position of the G band and the HV/HG intensity ratio. This method can be applied on raw sample material and on uncovered micromorphological thin sections. The latter greatly compliments micromorphology by providing information about char fragments without any clear morphological characteristics. This study is the first of its kind and may provide archaeologists with a robust new method to distinguish animal- from plant-derived char in thin sections.

Char Production from Cassava Rhizome Mixed Soil Improvement by Fast Pyrolysis in a Free-Fall Reactor

This research is to study the pyrolysis process of cassava rhizome (CR) in a free-fall reactor. The objective was to study the effect of mixed soil improvement on the properties of bio-oil and char products. The rhizome cassava mixed soil improvement was 200 g / hr. Mixing ratio of cassava rhizome and soil improvement is 50 to 50 by weight. The mixed soil improvement were granular pH11 plus soil conditioner (L11), volcanic rock (VR), TPI pelletized organic fertilizer (OF) and super dolomite (SD). Temperature pyrolysis was at 500 degrees Celsius. The results showed that bio-oil yield and gas yield decreased while char yields increased. For mixed soil improvement, made higher heating value in bio-oil increased, while the char properties of higher heating value decreases.

Kinetic and structural changes during gasification of cashew nut shell char particles

AbstractCashew Nut Shell (CNS), an abundant waste from the cashew nut production, could become a promising material for gasification. Nevertheless, engineering data regarding this technology is still small and fragmented. In this study, the evolution of the char textural properties during gasification, as well as the effect of operating conditions on char gasification kinetics were extensively investigated and quantified. The textural properties of cashew nut shell char changed significantly following different pathways between CO2 and H2O gasification. Micropores and mesopores were well developed along with the conversion in the case of H2O gasification instead of only micropores in the case of CO2 gasification. Regarding char gasification kinetics, an increase of the temperature from 800 to 1000°C enhanced five times the conversion rate under an H2O atmosphere and 15 times under a CO2 atmosphere. The conversion rate increased two times when the concentration of reacting gases changed from 20 to 60 vol % for both atmospheres. Similarities in terms of gasification kinetics between CNS chars and wood chip chars were found in this range of operating conditions.

Experimental Study of Thermal Pyrolysis of Avocado Seed for Liquid Fuel Production

Bio-waste which is available in large quantities worldwide is rich in biodegradable organic matter. By utilizing from bio-waste as feedstocks to attain valuable bio-based products, resource and waste problems will be solved as being “double green”. The bio-waste utilization aids decrease pollution while providing renewable energy and bio-based chemicals for the upcoming utilizations. Consequently, bio-waste resource utilization has involved growing attention in scientific and industrial societies. The characteristic of avocado seed as a bio-waste was analysed using elemental analysis resulted as 39.89% C, 5.43% H, 0.43% N, 45.2% O content. The higher heating value was calculated using Dulong Formula as 13.70 MJ/kg. The raw milled bio-waste was characterized by FT-IR containing the wavenumbers in the range of 4000-400 cm-1. The spectra bands for bio-waste demonstrated characteristic peaks of cellulose, hemicellulose and lignin. The mean moisture and ash contents of the “as-received” avocado seeds employed in this study were 6.54 wt% and 2.42 wt.%, respectively. Pyrolysis of avocado seed was carried out in a Heinze reactor at 500°C with a heating rate of 10°C/min and retention time of 20 min. The pyrolysis experiment yielded the liquid product (32%), solid product “char” (34%) and non-condensable gas (34%) with biomass conversion of 67%. Based on the results, it was confirmed that avocado seed can be utilized as a potential bio-waste according to pyrolysis results but liquid properties as a bio-fuel oil and solid product char properties as an activated carbon should be evaluated in detail.

Low temperature co-pyrolysis of food waste with PVC-derived char: Products distributions, char properties and mechanism of bio-oil upgrading

The main components of municipal solid waste (MSW) include food waste (FW) and polyvinyl chloride (PVC), which present an opportunity to convert energy or value-added products through low-temperature synergetic pyrolysis. In this study, the characteristics of char and bio-oil derived from MSW, FW and PVC feedstocks via pyrolysis at relatively low temperatures (200–300 °C) for 60 min were investigated. The results revealed that the transformation of PVC to HCl gas production started at a temperature of ＞ 200 °C. The oxygenated carbon groups on the char surface were decomposed at elevated reaction temperatures. The relative molecular mass of bio-oil derived from FW increased when PVC-derived char was used as a catalyst at 250 °C. In addition, active functional groups and pore structures were formed through synergistic pyrolysis. This work provides information regarding the possible route underlying the network of char and bio-oil production from the synergistic conversion of FW and PVC-derived char.

Slow Pyrolysis of Sugarcane Bagasse for the Production of Char and the Potential of Its By-Product for Wood Protection

Sugarcane bagasse was pyrolyzed using a laboratory fixed bed reactor to produce char and its by-product (pyrolysis liquid). The pyrolysis experiments were carried out using different temperatures (400°C and 500°C), heating rate (1 °C/min and 10 °C/min), and holding time (30 min and 60 min). Char was characterized according to its thermal properties, while the pyrolysis liquid was tested for its anti-fungal and anti-termite activities. Pyrolysis temperature and heating rate had a significant influence on the char properties and the yield of char and pyrolysis liquid, where a high-quality char and high yield of pyrolysis liquid can be obtained at a temperature of 500°C and a heating rate of 10 °C/min. The yield of char and pyrolysis liquid was 28.97% and 55.46%, respectively. The principal compounds of pyrolysis liquid were water, acetic acid, glycolaldehyde, 1-hydroxy-2-propanone, methanol, formic acid, levoglucosan, furfural, followed by some phenol compounds and guaiacol derivatives. Pyrolysis liquid at a concentration of 0.20% and 0.25% (v/v) caused a 100% inhibition of Coniophora puteana and Trametes versicolor, respectively, when performing inhibition growth tests in Petri dishes. Filter paper treated with 10% of pyrolysis liquid caused 100% of termite mortality, while only 5.65%–7.03% of the treated filter papers consumed by termites at such concentration. Pyrolysis liquid is potentially effective to be used in the formulation of wood protection against fungi and termites.

CO2 Gasification of Sugarcane Bagasse Char: Consideration of Pyrolysis Temperature, Silicon and Aluminum Contents, and Potassium Addition for Recirculation of Char

In sugarcane bagasse gasification, char recirculation to the gasifier improves the syngas quality and process efficiency. To determine the effect of char properties on the reaction kinetics, in thi...

Preparation and characterization of chars and activated carbons from wood wastes

Preparation of activated carbons from wood waste including northern hardwood pins-fines and wood dust was conducted and then compared through the following methods: physical pyrolysis and CO2 activation, vacuum pyrolysis and CO2 activation, CO2 gasification, and vacuum CO2 gasification processes. Experimental results show that chars and activated carbons with high surface area and pore volume are produced from wood waste through a vacuum CO2 pyrolysis/gasification process. The effects of operation variables of vacuum pyrolysis/gasification on the properties of chars and activated carbons were investigated to identify and optimize the temperature, heating time, and heating rate. The optimized vacuum CO2 gasification conditions were found to be a temperature of 800 °C, a heating rate of 20 °C/min, and a holding time of 2 h respectively. The prepared wood-chars and activated carbons were characterized by nitrogen physisorption, scanning electron microscopy (SEM). Fourier transform infrared (FTIR) spectra determined any changes in the surface functional groups produced during different preparation stages.

Assessment of Graphitized Coal Ash Char Concentrates as a Potential Synthetic Graphite Source

Coal ash char concentrates from four countries (Portugal, Poland, Romania, and South Africa) were prepared, characterised, and graphitized under the scope of the Charphite project (Third ERA-MIN Joint Call (2015) on the Sustainable Supply of Raw Materials in Europe). Coal ash chars may be a secondary raw material to produce synthetic graphite and could be an alternative to natural graphite, which is a commodity with a high supply risk. The char concentrates and the graphitized material derived from the char concentrates were characterised using proximate analysis, X-ray fluorescence, X-ray diffraction (structural), Raman microspectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy, and petrographic analyses to determine if the graphitization of the char was successful, and which char properties enhanced or hindered graphitization. Char concentrates with a lower proportion of anisotropic particles and a higher proportion of mixed porous particles showed greater degrees of graphitization. It is curious to see that embedded Al2O3 minerals, such as glass and clay, influenced graphitization, as they most likely acted as catalysts for crystal growth in the basal direction. However, the graphitized samples, as a whole, do not compare well against a reference natural graphite sample despite some particles in select char concentrates appearing to be graphitized following graphitization.

Thermolysis and analysis of TDI char by supercritical methanol using TGA, DSC, IR and SEM

TDI's synthetic plant generates about 5 mass % of tar by phosgenation process, which has been currently a bottleneck needed to be broken through for the worldwide TDI companies. At present, the reduction fraction of TDI tar is up to 48% relative to the mass of tar and renders the residue of solid crust known as TDI char. In this study, a suasive and effective reduction method has been found, the supercritical methanol is executed to depolymerize the TDI char, and in short, the char can be readily methanolyzed at supercritical state of methanol. With the outstanding depolymerization capability than various existing approaches, the destruction fraction can achieve 81 mass % at supercritical point. A best value as high as 95 mass % is first discovered at 270 °C, exceeding the efficiency at supercritical state. Characterizations of the intrinsic properties of raw char and char remnant after methanolysis have been implemented by TGA, DSC, FT-IR and SEM-EDS. For industrial applications, the diverse methodologies for recovering TDI or related components by alkaline hydrolysis, distillation, vacuum distillation and thermolysis are also discussed and compared with methanolysis in order to recognize the optimal abatement technique.

Interaction of the volatiles from co-pyrolysis of pig manure with cellulose/glucose and their effects on char properties

In this study, the co-pyrolysis of pig manure with cellulose and glucose were investigated at various heating rates. The results demonstrated that potential cross-interaction of the volatiles from the co-pyrolysis facilitated the cracking reaction, resulted in the formation of less charry products and less tarry compounds in the co-pyrolysis. The volatiles interaction also enhanced the evolution of the organics with the π-conjugated ring structures in the bio-oil and remarkably affect the char properties. The dehydration and condensation reactions were promoted during the fast co-pyrolysis of manure with cellulose and glucose, leading to the increased carbon content (from 20.0%–46.5 and 43.0 %), the higher thermal stability, and the enhanced crystallinity of carbon structure in the char formed. In addition, the in-situ Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) characterization indicates that the interaction of volatiles in the co-pyrolysis obviously affected the evolution of the functionalities of the char and the reaction network. Additionally, the HHV (37.2 and 37.9 vs 28.0 MJ/Kg) and the energy yield (66.3 and 68.2 vs 66.2 %) of the char from the co-pyrolysis was higher than that of the manure, which was beneficial for the utilize of the char as solid fuel.

The Correlation between Palm Shell Char Properties and the Production of Metallic Iron in EAF Steelmaking Slag Reduction Reaction

Palm shells wastes generated from oil palm processing are in abundance in landfills every year thereby posing environmental problems. Enormous amount of wastes generated by agro-industry has previously studied as carbon source in steelmaking hence providing solution to environmental problems. This paper studied on the conversion of palm shell waste into carbon material via physical and chemical activation method for metallic iron extraction. Physical char was prepared by pyrolyzed in nitrogen atmosphere at 450ºC while chemical char was impregnated in phosphoric acid before pyrolyzed. Composite pellets of EAF slag (43.18 %Fe2O3) with physical and chemical char were rapidly heated at temperature 1550ºC within 20 minutes under argon flow. All reduced samples were analyzed on the weight loss, degree of reduction, iron recovery and phase analysis using X-ray diffraction (XRD). The results indicated that chemical/slag showed higher weight loss (38.8%) and excellent degree of reduction (29.94%) compared to physical/slag due to higher volatile matter content (9.8%) and larger surface area (562.14m2/g). It was found that the production of metallic iron particles after the reduction process and indicated that chemical char achieved higher iron recovery (15.48%) compared to physical char due to higher total carbon content (60.28%). XRD and Rietveld refinement analysis confirmed that the iron phase was a major component in metallic iron particles for physical/slag and chemical/slag samples. This elucidated that the iron oxides in EAF slag was completely reduced into iron by using palm shell chars as carbon materials. This finding indicates that palm shell chars potentially act as carbon materials in steelmaking applications according to their good characteristics.