Char Research Articles

Condensed Phase Deactivation of Solid Brønsted Acids in the Dehydration of Fructose to Hydroxymethylfurfural

Catalyst deactivation resulting from the hydrothermal leaching of sulfonic acid residues and the deposition of carbonaceous residues was studied using condensed phase flow reactor experiments along...

Evaluation of the bioenergy potential of invasive Pennisetum purpureum through pyrolysis and thermogravimetric analysis

The use of lignocellulosic biomass in the production of bioenergy is escalating with time due to the increase in energy demand and ecological pollution. The purpose of this study is to examine the opportunities of biofuel production from Pennisetum purpureum which is an invasive perennial grass in Brunei Darussalam. The proximate analysis of the study showed that the proportions of moisture content (MC), volatile matter (VM), fixed carbon (FC), and ash content (AC) were 5.93%, 69.44%, 16.81%, and 7.82%, respectively. Moreover, the ratios of carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O) provided by the ultimate analysis were 43.23%, 5.80%, 1.17%, 0.11%, and 41.76%, respectively. The low moisture content and the higher heating value (18.55 MJ/kg) marked this grass as a potential source of biomass. Fourier transform infrared spectroscopy revealed the strong bonds between O–H, C–H, C–O, C=O, and C=C in the biomass. The thermogravimetric and their derivative results depicted that the highest weight losses occurred at a temperature of 334 °C with a degradation rate of 6.56 °C/min for pyrolysis condition and at a temperature of 312 °C with a degradation rate of 7.66 °C/min in combustion conditions.

The Asphaltene Fraction – Demystified

The asphaltene constituents of crude oil are the highest molecular weight heaviest and most polar constituents in the oil and the fraction is isolated a dark brown to black friable solids that have no definite melting point and usually foam and swell on heating to leave a carbonaceous residue. The fraction is obtained from crude oil by the addition of a hydrocarbon liquid (such as n-pentane or n-heptane). Any molecular models derived for asphaltene constituents must be in keeping with behavioral characteristics. Efforts have been (and continue to be) made without justification to describe the asphaltene fraction in terms of a single, representative asphaltene molecule or molecules incorporating, in the correct proportions, all of the chemical constituents known to be present in a given asphaltenic matrix. Obviously, the chemistry and structural features of the constituents of crude oil asphaltene fractions will be dictated by the distribution of functional and structural type that occur in the fraction. This makes the representation of the structure and functionality of the constituents by so-called average structures very difficult (if not, impossible) to conceive.

Biomacromolecules and Bio-Sourced Products for the Design of Flame Retarded Fabrics: Current State of the Art and Future Perspectives.

The search for possible alternatives to traditional flame retardants (FRs) is pushing the academic and industrial communities towards the design of new products that exhibit low environmental impact and toxicity, notwithstanding high performances, when put in contact with a flame or exposed to an irradiative heat flux. In this context, in the last five to ten years, the suitability and effectiveness of some biomacromolecules and bio-sourced products with a specific chemical structure and composition as effective flame retardants for natural or synthetic textiles has been thoroughly explored at the lab-scale level. In particular, different proteins (such as whey proteins, caseins, and hydrophobins), nucleic acids and extracts from natural sources, even wastes and crops, have been selected and exploited for designing flame retardant finishing treatments for several fibers and fabrics. It was found that these biomacromolecules and bio-sourced products, which usually bear key elements (i.e., nitrogen, phosphorus, and sulphur) can be easily applied to textiles using standard impregnation/exhaustion methods or even the layer-by-layer technique; moreover, these “green” products are mostly responsible for the formation of a stable protective char (i.e., a carbonaceous residue), as a result of the exposure of the textile substrate to a heat flux or a flame. This review is aimed at summarizing the development and the recent progress concerning the utilization of biomacromolecules/bio-sourced products as effective flame retardants for different textile materials. Furthermore, the existing drawbacks and limitations of the proposed finishing approaches as well as some possible further advances will be considered.

Effect of residue formed during the AC and DC dry-band arcing on silicone rubber filled with natural silica

This paper investigates the residue formed on silicone rubber filled with natural silica in the inclined plane tracking and erosion test under AC and DC voltages. Simultaneous thermogravimetric and differential thermal analyses reveal residue formation dependent on volatilization and crosslinking in silicone rubber. Thermo-oxidation of volatiles yields silica-based residue protecting the surface during dry-band arcing; whereas, crosslinking leaves carbonaceous residue leading to more severe dry-band arcing. Volume fraction of natural silica replacing silicone rubber is shown to be a main source of silica residue suppressing carbonaceous residue, thus preventing failure in the inclined plane test. More severe erosion under the equivalent +DC voltages as compared to standard AC and equivalent — DC voltages of the inclined plane test is attributed to more severe dry-band arcing heat promoted by carbonaceous residue. Silicone rubber filled with lower particle sizes of natural silica is demonstrated to deteriorate erosion performance, possibly as result of filler-polymer interactions or lower particle size reducing the integrity of the protective silica residue. The following paper highlights the importance of using critical AC and DC voltages during the inclined plane tracking and erosion tests.

Improvement of proximate data and calorific value assessment of bamboo through near infrared wood chips acquisition

In a previous study, a near infrared (NIR) spectroscopy model was developed using a spectra of ground bamboo samples. Although the previous report on ground bamboo described a good performance, operation in the power plant was found to be inconvenient due to preparation costs and labour required for the necessary preparation of ground samples. Thus, this study presents the comparison of the performance of an NIR model that was developed by direct scanning of bamboo chips to the previously developed model for ground samples. Special emphasis is put on the comparison of the spectral reproducibility. Bamboo chip models were developed based on PLS regression with variable selection methods in order to achieve the optimal model. The moisture content (MC) and ash content (A) of the developed bamboo chip models could be applied toward quality assurance. The volatile matter (VM) and fixed carbon (FC) models could be used for approximating predictions. The gross and net calorific value (GCV and NCV) models could be used for most applications. The root mean square (RMS) value of pre-treated spectra of different particle size had no statistically significant differences. The study’s findings indicate that the model developed using NIR spectroscopy protocol with wood chips spectra can be used as a classification tool and is an effective method for estimating bamboo chip energy quality. The big particle size of wood chips affect negatively the prediction model, however, it could be solved through spectral pre-processing technique, thus eliminating the need for grinding feedstock samples.

Obtaining stable suspensions for washcoating in microchannels: Study of the variables involved and their effects on the catalyst

La0.5Ca0.5CoO3-δ and La0.9Mg0.1Al0.9Ni0.1O3-δ perovskites were prepared for ethanol oxidation reaction and for ethanol steam reforming. The perovskites were mechanically ground and suspensions were subsequently prepared for washcoating. The physical and physicochemical modifications introduced in the mixed oxides after suspension, and their influence on the catalytic activity, were systematically studied in the suspended solids. The deposition of catalysts in metal microchannels was performed by washcoating. The mechanical milling was carried out in a high energy ball mill followed by measurements of particle size and isoelectric point (IEP). The samples were characterized by XRD, BET, TPR, XPS, FT-IR, TGA and catalytic tests. Both catalysts showed an excellent catalytic activity and high stability. In the oxidation reaction, indications of carbonaceous residues were obtained in the sample with organic additive, and the suspension without any additive presented the best stability. The samples that were evaluated in the ethanol reforming with steam showed good catalytic activity and stability. High yield of H2 was obtained and low selectivity values to CO and CH4 were observed. Polyvinyl alcohol was the additive that showed the best results. The catalytic films were characterized by SEM, EDX, and 3D confocal microscopy. Their stability were studied by adhesion test.

Effects of two different agents, H3PO4 and NaCl, to increase the flame-retardant properties of cellulose fibers

After flame-retardant treatment by the two different agents, the thermal behaviors of Lyocell fibers are discussed. In this research, H3PO4 and NaCl reduced the degradation rate and increased the char yield of the Lyocell fibers, and also increased the limiting oxygen index with the char yield increased. After treatment, the integral procedure decomposition temperature and the activation energy of Lyocell fibers are significantly increased by various concentration factors. These phenomena were indicated by the dehydration, rearrangement, formation of carbonyl groups, the evolution of carbon monoxide and dioxide, and carbonaceous residue formation. These effects were indicating the slow pathway of flame retardancy for the Lyocell fibers and are attributed to the two different flame-retardant agent treatments.

Catalytic thermal decomposition of the fungicide chlorothalonil and derivatives over different modified zeolites and metal surfaces

Homogeneous and heterogeneous gas-phase static thermolysis of chlorothalonil (CT, 1) and four derivatives are presented. After thermal decomposition, many interesting products are formed. Chlorothalonil yielded principally carbonaceous residues and dehalogenated compounds, while all the derivatives also afforded a condensed dihydrophenazine (17). Relevant information from pyrolysis states that: CT is quantitatively decomposed when compared to its aromatic derivatives; in all cases some potential toxic compounds (which were detected with the help of NMR, GC–MS and IR) are produced; the best catalysts to perform the decomposition are the acidic zeolite H–Y and metallic Cu; the two zeolites used, (H-ZSM-11 and H–Y) are able to adsorb the substrates, but only H–Y is capable of decomposing CT in carbonaceous residues.

Deactivation of Zeolites and Zeotypes in Methanol-to-Hydrocarbons Catalysis: Mechanisms and Circumvention.

Solid catalysts deployed in industrial processes often undergo deactivation, requiring frequent replacement or regeneration to recover the loss in activity. Regeneration occurs under conditions distinct from, and typically more harsh than, the catalysis, placing strict requirements on physicochemical material properties that divert catalyst optimization toward addressing regenerability over high activity and selectivity. Deactivation arises from mechanical, structural, or chemical modifications to active sites, promoters, and their surrounding matrices, and the prevailing mechanism for deactivation varies with the reaction, the catalyst, and the reaction conditions. Methanol-to-hydrocarbons processes utilize zeolites and zeotypes-crystalline, microporous oxides widely deployed as catalysts in the refining and petrochemical industries-as solid acid catalysts. Deposition and growth of highly unsaturated carbonaceous residues within the micropores congest molecular transport and block active sites, resulting in deactivation. In this Account, we describe studies probing the underlying mechanisms of deactivation in methanol-to-hydrocarbons catalysis and discuss examples of leveraging the acquired mechanistic insights to mitigate deactivation and prolong catalyst lifetime. These fundamental principles governing carbon deposition within zeolites and zeotypes provide opportunity to broaden versatility of processes for C1 valorization and to relax constraints imposed by hydrothermal catalyst stability considerations to achieve more active and more selective catalysis. Methanol-to-hydrocarbons catalysis occurs via a chain carrier mechanism. A zeolite/zeotype cavity hosts an unsaturated hydrocarbon guest to together constitute the supramolecular chain carrier that engages in a complex network of reactions for chain carrier propagation. Productive propagation reactions include olefin methylation, aromatic methylation, and aromatic dealkylation. Methanol undergoes unproductive dehydrogenation to formaldehyde via methanol disproportionation and olefin transfer hydrogenation. Subsequent alkylation reactions between formaldehyde and active olefinic/aromatic cocatalysts instigate cascades for dehydrocyclization, resulting in the formation of inactive polycyclic aromatic hydrocarbons and termination of the chain carrier. Addition of a distinct catalytic function that selectively decomposes formaldehyde mitigates chain carrier termination without disrupting the high selectivity to ethylene and propylene in methanol-to-hydrocarbons catalysis on small-pore zeolites and zeotypes. The efficacy of this bifunctional strategy to prolong catalyst lifetime increases with increasing proximity between the active sites for formaldehyde decomposition and the H+ sites of the zeolite/zeotype. Coprocessing sacrifical hydrogen donors mitigates chain carrier termination by intercepting, via saturation, intermediates along dehydrocyclization cascades. This strategy increases in efficacy with increasing concentration of the hydrogen donor and provides opportunity to realize steady-state methanol-to-hydrocarbons catalysis on small-pore zeolites and zeotypes.

Minerals and microstructure identification using Raman instruments: Evaluation of field and laboratory data in preparation for space mission

AbstractTwo rovers will be launched in 2020 for robotic exploration missions on Mars: the ESA/Roscosmos ExoMars and the NASA Mars 2020 missions. Both missions will include Raman instruments to characterize the habitable of Mars and to search for molecular evidence of past and present life. In preparation for these missions and to characterize the scientific information that will eventually return from Mars, terrestrial analogue samples of rock formations on Mars are studied in detail. During this study, we compared Raman spectra obtained from different samples of geological matrixes, including specimens of silicate, sulfate, carbonates, and sulfurs, with two Raman instruments. Raman data were obtained in the field with a portable instrument operating with a 785‐nm laser. Based on fast data analyses in the field, a selection of samples were collected and were further analyzed using a benchtop confocal instrument operated in the laboratory and with two excitation lasers at 532 and 785 nm. We illustrate the possible interference from sharp fluorescence associated with rare earth element present in trace amount in minerals. In addition, carbonaceous compounds and β‐carotene, a highly Raman‐active biomarker, were also detected by Raman spectroscopy in association with specific minerals. In the context of planetary exploration, we discuss the capacity for specific mineral matrixes to sustain life under extreme conditions. We also discuss that Raman imaging, although not ready yet for space application with miniaturized spectroscopy, could significantly help in discussing the possible biotic origin of carbonaceous residues, especially by the association of molecular signatures with the localized microstructure.

Synthesis and characterization of a new phase of non Na-loaded analcime zeolite by microemulsion technique

The analcime structure zeolite was synthesized in cationic microemulsion at room temperature. An aluminum sulfate hexadecahydrate (Al2(SO4)3.16H2O) and tetraethylorthosilicate (TEOS) with Si/Al ratio of 10/1 were used as aluminium and silicon sources. Microemulsion was formed with the use of a straight-chained surfactant (cetyltrimethylammonium bromide; CTAB) with mixed solvents (butanol, heptane, and water). The purifying technique with ethanol and acetone was successfully employed to eliminate carbonaceous residues below 250 °C. The as-synthesized product was calcined at 550 °C for 5 h. 1H NMR data supported the alignment of chemical reagents. FT-IR spectra demonstrated similar vibrational range of analcime, while results from XRD pattern also strongly supported the analcime solid structure. The as-synthesized zeolite has Langmuir's surface area of 11.29 m2/g, the total pore volume of 0.0172 cc/g, and the average pore diameter of 67 nm.

Rational design of photoelectrodes for photoelectrochemical water splitting and CO2 reduction

Solar energy has promising potential for building sustainable society. Conversion of solar energy into solar fuels plays a crucial role in overcoming the intermittent nature of the renewable energy source. A photoelectrochemical (PEC) cell that employs semiconductor as photoelectrode to split water into hydrogen or fixing carbon dioxide (CO2) into hydrocarbon fuels provides great potential to achieve zero-carbon-emission society. A proper design of these semiconductor photoelectrodes thus directly influences the performance of the PEC cell. In this review, we investigate the strategies that have been put towards the design of efficient photoelectrodes for PEC water splitting and CO2 reduction in recent years and provide some future design directions toward next-generation PEC cells for water splitting and CO2 reduction.

Estimation of the Elemental Composition of Biomass Using Hybrid Adaptive Neuro-Fuzzy Inference System

The application of evolutionary algorithms could be a rapid and acceptable means of predicting the elemental composition of biomass applicable in power generation. This article introduces a hybrid model comprising of adaptive neuro-fuzzy inference system (ANFIS) and particle swarm optimization (PSO) called PSO-ANFIS model. The model is based on the proximate values of biomass materials to predict their corresponding elemental compositions. This intelligent hybrid model was trained with 581 biomass data and further tested with a new 249 biomass data. The carbon, hydrogen, and oxygen contents of solid biomass were predicted based on the ash content (Ash), fixed carbon (FC), and volatile matter (VM) as the inputs. The model was evaluated based on some known performance criteria. A root mean squared error (RMSE), mean absolute deviation (MAD), mean absolute percentage error (MAPE), log of accuracy ratio (LAR), coefficient of correlation (CC), mean absolute error (MAE) value of 3.5816, 2.3279, 4.8521, 0.0012, 0.9329, 0.0227 at computation time (CT) of 47.04 secs for Carbon (C); 0.6383, 0.4047, 10.2187, 0.002, 0.7986, 0.0261 at CT of 35.2 secs for Hydrogen (H); 4.2042, 2.7417, 10.7612,0.0016, 0.9137 at CT of 28.16 secs for Oxygen (O) respectively was obtained. A regression analysis was also carried out to determine the level of correlation between actual and predicted values. The reported indices show that PSO-ANFIS can be used as a novel computation approach for the prediction of elemental compositions of biomass, which is vital to the combustion, thermochemical, gasification, and pyrolysis process toward energy production.

Multifunctional Linear and Hyperbranched Five-Membered Cyclic Carbonate-Based Polymers Directly Generated from CO2 and Alkyne-Based Three-Component Polymerization

Fixing carbon dioxide (CO2) into polymeric materials is a subject of enduring interest but limited to very few efficient polymerizations. In this work, a facile Pd(OAc)2/LiOtBu-catalyzed one-pot, t...

Synthesis of mesoporous MgO–CeO2 composites with enhanced CO2 capture rate via controlled combustion

Abstract MgO–CeO 2 composites with enhanced sorption rate for CO 2 capture were prepared via a sol-gel combustion method. The effects of water, cerium, and citric acid on the sorption performance were investigated systematically to elucidate the role of components. The cerium content substantially lowered the decomposition temperature by 100 °C and the amount of citric acid affected the propagation rate. Controlled combustion led to different pore structures and CO 2 capture performances, and controlling the amount of citric acid was the most effective way to improve the textural properties and performances. The developed MgO–CeO 2 composites consist of nanoparticles covered with a flat plate, and a small amount of residual carbon from citric acid was also observed in the samples. The optimal MgO–CeO 2 composite using the Ce/Mg molar ratio of 0.05 exhibited a high surface area (333 m 2 /g) and enhanced CO 2 capture capacity (10.4 wt%) at 30 °C. All the composites showed a fast sorption rate that reached approximately 70% of the capacity within 3 min. The analysis of the CO 2 -TPD profiles and XPS spectra indicated that even a relatively small amount of carbonaceous residues after calcinations contributed to retaining more amounts of strong basic sites and consequently resulted in the fast sorption rate. In the cyclic test, the sorption capacity is reasonably stable from the 2nd cycle onwards. The simple preparation via cerium doping and the citric acid-assisted sol-gel combustion can contribute to the development of sorbents for post-combustion as well as pre-combustion CO 2 capture.

Torrefaction of biomass macroalga Ulva intestinalis using TGA

The torrefaction of Malaysian marine biomass specie called Ulva intestinalis was studied using thermogravimetric analyser (TGA). The torrefaction temperature and residence time were varied in the range of 200 – 300 °C and 30 – 90 minutes, respectively. The chemical functional groups in the torrefied U. intestinalis were identified by Fourier transform infrared (FTIR). TGA results showed that the torrefaction temperature has a greater influence on the weight loss and changes in the U. intestinalis’s properties after the torrefaction as compared to the torrefaction time. The increased in fixed carbon (FC), and carbon (C) content and decreased in volatile matter (VM), moisture content (MC) and oxygen (O) with the severity of torrefaction reflects the improvement of calorific values for the torrefied U. intestinalis. Analysis of the FTIR showed that the torrefaction decreased the spectra intensity of the main functional groups (O-H, C=C, C-O and C-H) as a consequence of structural alteration within the biomass. The present findings may provide useful information for the development of industrial torrefaction processes to turn U. intestinalis into a carbon enrichment solid fuel.

Differences in Formation and Oxidation of Colombian Coal Chars in Air and Oxy-fuel Atmospheres

The increasing interest towards more efficient and clean technologies, specially paying attention to CO2 neutral processes is encouraging the investigation of coal thermochemical conversion under oxy-fuel atmospheres (i.e. without N2). The process offers many advantages such as easy separation of the CO2 produced and low NOX/SOX emissions. While coal conversion in air is already well understood, full understanding of the influences of CO2-rich atmospheres is still required. A series of experiments in thermogravimetric analyser, drop-tube reactor and flat-flame burner were performed using a mid-range bituminous coal (Colombian coal) to understand the differences in the chars obtained after the pyrolysis step. Comparing the pyrolysis in N2 and CO2 atmospheres, significant differences were observed in the resulting chemical (composition) and physical properties of the chars, whereas mass loss was very similar for short residence times (< 130 ms). Afterwards, the chars obtained were submitted to oxidation and gasification, under several different operating conditions, in order to evaluate the difference in reactivity of these chars. Chars obtained under CO2 atmospheres revealed a lower reactivity, despite their higher surface area. These aspects cannot be explained and captured by a model which does not focus on some important details. In this paper, the results obtained in these experiments are summarized and discussed on the point of view of the POLIMI modelling approach for thermochemical conversion of solids. This model offers several advantages, such as being flexible to improvements, requiring simple experimental data of the fuel and offers an all-in-one solution for describing the kinetics of the whole process. The developments accounted for a wide range of experimental data, which allowed its calibration for several fuels, mostly in air combustion. It was first developed to describe the pyrolysis step, and later char oxidation/gasification was included in a simplified approach. The detailed mechanism of homogeneous gas phase reactions of the volatiles is also coupled. In order to extend the predictive capabilities of the model for oxy-fuel conditions, dedicated experiments must be considered for future improvements. In this work these missing effects are discussed, identifying the main necessary improvements, allowing this model to be extended and applied also for the designing of reactors that use oxy-fuel technologies.

Which One Does Better Predict the Heating Value of Biomass?—Dry Based or As-Received Based Proximate Analysis Results?

Thirty-nine different species of waste biomass materials that include woody or herbaceous resources as well as nut shells and juice pulps were used to develop empirical equations to predict the calorific value based on the proximate analysis results. Ten different linear/nonlinear equations that contain proximate analysis ingredients including or excluding the moisture content were tested by means of least-squares method to predict the HHV (higher heating value). Prediction performance of each equation was evaluated considering the experimental and the predicted values of HHV and the criteria of MAE (mean absolute error), AAE (average absolute error), and ABE (average bias error). It was concluded that the presence of moisture as a parameter improves the prediction performance of these equations. Also, the samples were classified into two subsets according to their fixed carbon (FC)/ash values and then the correlations were repeated for each subset. Both the full set of samples and the subsets showed a similar trend that the presence of moisture in equations enhances the prediction performance. Also, the FC content may be disregarded from the equation of the calorific value prediction when the FC/ash ratio is lower than a given value.

Designing of sustainable, solid-state and photoluminescence switchable electrospun nanofibrous PVA/WTR-CDs hybrid films: A photophysical study

Herein we proposed a sustainable solid-state photoluminescent nanofibrous hybrid films fabricated through electrospining of polyvinyl alcohol (PVA) and carbon dots (CDs). The CDs employed during the fabrication hybrid films were derived from waste and abundantly available carbonaceous waste tea residue (WTR) precursor. More interestingly, the photoluminescent PVA/WTR-CDs hybrid films were able to switch the increased amount of incorporated WTR-CDs simply under UV light. The as prepared nanofibrous PVA/WTR-CDs hybrid films were further characterized by different techniques in order to confirm the successful and homogenous incorporation WTR-CDs into PVA matrix viz.UV–vis spectroscopy, Field emission-scanning electron microscopy (FE-SEM), Fluorescence spectroscopy and microscopy, Fourier transform infra red spectroscopy (FT-IR). The photophysical investigations of all the films (pristine and hybrid) with respect to its liquid solutions revealed that the intrinsic properties of liquid WTR-CDs were well restored in solid-state nanofibrous hybrid films of PVA/WTR-CDs. Furthermore, morphological analysis via FE-SEM showed uniform and smooth nanofibers in a PVA films with average diameter 0.104 μm and were increased with increased amount of WTR-CDs from 0.104 to 0.170 μm and 0.104 to 0.258 μm for PVA-WTR-CDs-1 and PVA-WTR-CDs-10 hybrid films respectively. All these characteristics of designed solid-state photoluminescent nanofibrous hybrid films opens new avenues in the field of optical sensing, optoelectronics, biological, healthcare, food and related multipurpose applications.