Isothermal torrefaction kinetics of hemicellulose, cellulose, lignin and xylan using thermogravimetric analysis

In recent years, torrefaction, a mild pyrolysis process carried out at the temperature range of 200-300 °C, has been considered as an effective route for improving the properties of biomass. Hemicellulose, cellulose, lignin and xylan are the basic constituents in biomass and their thermal behavior is highly related to biomass degradation in a high-temperature environment. In order to provide a useful insight into biomass torrefaction, this study develops the isothermal kinetics to predict the thermal decompositions of hemicellulose, cellulose, lignin and xylan. A thermogravimetry is used to perform torrefaction and five torrefaction temperatures of 200, 225, 250, 275 and 300 °C with 1 h heating duration are taken into account. From the analyses, the recommended values of the order of reaction of hemicellulose, cellulose, lignin and xylan are 3, 1, 1 and 9, respectively, whereas their activation energies are 187.06, 124.42, 37.58 and 67.83 kJ mol⁻¹, respectively. A comparison between the predictions and the experiments suggests that the developed model can provide a good evaluation on the thermal degradations of the constituents, expect for cellulose at 300 °C and hemicellulose at 275 °C. Eventually, co-torrefaction of hemicellulose, cellulose and lignin based on the model is predicted and compared to the thermogravimetric analysis.     

Torrefaction and co-torrefaction characterization of hemicellulose, cellulose and lignin as well as torrefaction of some basic constituents in biomass

Torrefaction is a thermal pretreatment process for biomass where raw biomass is heated in the temperatures of 200-300 °C under an inert or nitrogen atmosphere. The main constituents contained in biomass include hemicellulose, cellulose and lignin; therefore, the thermal decomposition characteristics of these constituents play a crucial role in determining the performance of torrefaction of lignocellulosic materials. To gain a fundamental insight into biomass torrefaction, five basic constituents, including hemicellulose, cellulose, lignin, xylan and dextran, were individually torrefied in a thermogravimetry. Two pure materials, xylose and glucose, were torrefied as well for comparison. Three torrefaction temperatures of 230, 260 and 290 °C, corresponding to light, mild and severe torrefactions, were taken into account. The experiments suggested the weight losses of the tested samples could be classified into three groups; they consisted of a weakly active reaction, a moderately active reaction and a strongly active reaction, depending on the natures of the tested materials. Co-torrefactions of the blend of hemicellulose, cellulose and lignin at the three torrefaction temperatures were also examined. The weight losses of the blend were very close to those from the linear superposition of the individual samples, suggesting that no synergistic effect from the co-torrefactions was exhibited.     

Experimental study on the ignition characteristics of cellulose,hemicellulose, lignin and their mixtures

Ignition behaviour of biomass is an essential knowledge for plant design and process control of biomass combustion. Understanding of ignition characteristics of its main chemical components, i.e. cellulose, hemicellulose, lignin and their mixtures will allow the further investigation of ignition behaviour of a wider range of biomass feedstock. This paper experimentally investigates the influences of interactions among cellulose, hemicellulose and lignin on the ignition behaviour of biomass by thermogravimetric analysis. Thermal properties of an artificial biomass, consisting of a mixture of the three components will be studied and compared to that of natural biomass in atmospheres of air and nitrogen in terms of their ignition behaviour. The results showed that the identified ignition temperatures of cellulose, hemicellulose and lignin are 410 °C, 370 °C and 405 °C, respectively. It has been found that the influence of their interactions on the ignition behaviour of mixtures is insignificant, indicating that the ignition behaviour of various biomass feedstock could be predicted with high accuracy if the mass fractions of cellulose, hemicellulose and lignin are known. While the deficiencies of the determined mutual interactions would be further improved by the analytical results of the activation energies of cellulose, hemicellulose, lignin, their mixtures as well as natural and artificial biomass in air conditions.     

Comparative studies on the pyrolysis of cellulose,hemicellulose, and lignin based on combined kinetics

The thermal degradation behavior and pyrolytic mechanism of cellulose, hemicellulose, and lignin are investigated at different heating rates from 10 Kmin^?1 to 100 Kmin^?1 with a step-size of 10 Kmin^?1 using thermogravimetric analysis (TGA) equipment. It is observed that there are one, two, and three stages of pyrolytic reactions takes place in cellulose, hemicellulose, and lignin respectively. Isoconversional method is not suitable to analyse pyrolysis of hemicellulose and lignin as it involves multi-step reactions. The activation energies of the main decomposition stage for cellulose, hemicellulose, and lignin are 199.66, 95.39, and 174.40 kJ mol^?1 respectively. It is deduced that the pyrolysis reaction of cellulose corresponds to random scission mechanism while the pyrolysis reaction of hemicellulose and lignin follows the order based reaction mechanisms.     

Comparison of lignin,cellulose, and hemicellulose contents for biofuels utilization among 4 types of lignocellulosic crops

Lignocellulose crops serve as an excellent feedstock for biofuels because of their reduced costs and net carbon emission, and higher energy efficiency. To estimate more suitable lignocellulosic crops, we compared the contents of lignin, cellulose, and hemicellulose in miscanthus, switchgrass, sorghum, and reed (from 14 accessions according to the collection site) in the leaves and stems and expressed these as % content based on dry weight. This study shows that miscanthus, switchgrass, and sorghum are valuable lignocellulosic crops owing to the significantly lower lignin content than that in reed, among both whole crops as well as specific plant parts. Although switchgrass has been reported to possess the highest polysaccharide content among the crops examined; our results showed no difference at a 5% significance level. Our study also showed that Miscanthus sacchariflorus possesses lower lignin and higher polysaccharide content in its leaves and stalks compared to the other Miscanthus species. Furthermore, M. sacchariflorus also showed lower lignin and higher polysaccharide contents than those in switchgrass. It is possible that M. sacchariflorus is a better resource than switchgrass, although these content assays showed no differences at the 5% significance level. M. sacchariflorus plants collected in Hacheonri, Jejudo, Korea (MFJH), contained 14.12% lignin and 64.23% holocellulose, indicating that Korean miscanthus is a competitive bioenergy crop compared to foreign crops such as switchgrass, which is widely used in the United States.     

Synergistic effect of curcumin and activated carbon catalyst enhancing hydrogen production from biomass pyrolysis

This study observes the synergistic effect of low cost and environmentally friendly catalysts, Activated Carbon and curcumin on the production of hydrogen gas in the biomass pyrolysis process. The Study used turmeric containing curcumin as an anti-oxidant agent added to the activated carbon (AC) catalyst. Biomass from coconut wood was pyrolyzed up to 550 °C using a fixed bed reactor. Both AC and curcumin were combined with a ratio of 1:0, 1:1, 1: 3, 0:1, and 3:1. The addition of AC and curcumin was able to increase the production of hydrogen and methane gas. The combination of AC and curcumin with 1:1 ratio was able to increase hydrogen gas by 25.6%. In addition, this combination was also increase methane gas by 71.8%.Curcumin as an anti-oxidant is able to prevents recombination reactions between radical molecules. Activated carbon surface is more protected from free radicals attacking and sticking to the surface. The phi-phi interaction between the two aromatic rings and the surface of activated carbon produces electrostatic forces on the surface of activated carbon to become stronger therefore it is more reactive in cracking hydrocarbon molecules and producing hydrogen gas. Software simulation, SEM, XRD, and FTIR tests were performed to support the analysis of experimental results.     

Microwave pyrolysis of polystyrene and polypropylene mixtures using different activated carbon from biomass

In this study, microwave pyrolysis was experimented with mixed types of plastic waste. Two different plastic wastes polystyrene waste (PSW) and polypropylene waste (PPW) were used as feedstock. Carbon and activated carbon were synthesized from different biomass; rice husk (RH), corn husk (CH) and coconut sheath (CS) respectively which are used as microwave susceptors. The effect of impregnation on product yields was studied. Microwave pyrolysis at 900 W and with a polymer to an absorbent ratio of 10:1, produced the highest oil yield of 84.30 wt% when coconut sheath activated carbon (CSAC) was used as an absorbent. The reaction time was 10 min for the complete decomposition of polymer mixtures. Oil properties were determined and a high calorific value of 46.87 MJ kg⁻¹ was obtained. These properties were compared to conventional fuel properties and the product oil has a density of 0.76 g ml⁻¹ and viscosity of 2.4 cSt which is an equivalent fraction obtained to that of gasoline. Product oil has a styrene recovery of 67.58% from microwave pyrolysis. The results demonstrate that, microwave pyrolysis has a great potential for energy recovery from mixed plastic waste and the use of agricultural residues as absorbents enhanced the production efficiency of the process.     

Effect of cellulose and lignin content on pyrolysis and combustion characteristics for several types of biomass

Fundamental pyrolysis and combustion behaviors for several types of biomass are tested by a thermo-gravimetric analyzer. The main compositions of cellulose and lignin contents for several types of biomass are analyzed chemically. Based on the main composition results obtained, the experimental results for the actual biomass samples are compared with those for the simulated biomass, which is made of the mixture of the cellulose with lignin chemical. The morphological changes before and after the reactions are also observed by a scanning electron microscope. The main compositions in the biomass consisted of cellulose and lignin. The cellulose content was more than lignin for the biomass samples selected in this study. The reaction for the actual biomass samples proceeded with the two stages. The first and second stage corresponded to devolatilization and char combustion during combustion, respectively. The first stage showed rapid mass decrease caused by cellulose decomposition. At the second stage, lignin decomposed for pyrolysis and its char burned for combustion. For the biomass with higher cellulose content, the pyrolysis rate became faster. While, the biomass with higher lignin content gave slower pyrolysis rate. The cellulose and lignin content in the biomasses was one of the important parameters to evaluate the pyrolysis characteristics. The combustion characteristics for the actual biomass depends on the char morphology produced.     

Gasification of rice husk in two-stage gasifier to produce syngas,silica and activated carbon

Rice husk was utilized in the production of syngas, silica and activated carbon. Experiments were performed in two-stage gasifier for the production of syngas. The syngas is generated with minimum tar yields due cracking of tar at high temperature. Rice husk char obtained from the pyrolysis stage of the reactor was used in the silica extraction process to obtain silica and activated carbon. Using nitrogen as pyrolysis agent high purity (88.46%) silica was obtained with a good quality of syngas as compared to air as pyrolysis agent. Highest surface area of 276.91 m²/gm of silica was found at 500^?C.     

Solar gasification of coal, activated carbon, coke and coal and biomass mixtures

Subbituminous coal, activated carbon, coke and a mixture of coal and biomass were gasified using direct solar irradiation in a 23-kW solar furnace located at the U.S. Army White Sands Missile Range, White Sands, New Mexico. The sunlight was focused directly on the coal (or alternate fuel) bed being gasified through a window in the reactor. Steam or CO₂ (in different experiments) was passed through the solar-heated coal bed where it reacted with the coal and thus formed a combustible product gas that contained the energy content of both the coal and the sunlight. More than 40 per cent of the sunlight arriving at the focus external to the reactor was chemically stored as fuel value in the product gas. Since there were considerable solar losses because of the reflectivity of the window and the window aperture being smaller than the focal-spot size, it is estimated that in excess of 60 per cent of the solar energy that entered the reactor was chemically stored. The product-gas production rate increased with increased solar power, and when steam was used for gasification, the product-gas composition and thus heating value were almost independent of solar power. A typical moisture-free gas composition was 54 per cent H₂, 25 per cent CO, 16 per cent CO₂, 4 per cent CH₄ and 1 per cent higher hydrocarbons. Activated carbon and a uniform mixture of coal and biomass were also gasified with similar efficiencies but slightly different product-gas compositions. Coke showed a lower solar conversion efficiency. Solar gasification offers several advantages over conventional oxygen-blown gasifiers: (1) commercial grade oxygen is not required, (2) almost twice as much gas per ton of coal can be achieved because no coal is burned to provide process heat and because the gas contains energy from both coal and the sun, and (3) the system has very low thermal inertia and is insensitive to thermal shock, making it very adaptable to rapidly changing solar conditions such as passing clouds.     

Glycerol electrooxidation on Pd,Pt and Au nanoparticles supported on carbon ceramic electrode in alkaline media

In the present study, electrooxidation of glycerol was investigated on Au, Pd and Pt nanoparticles modified carbon ceramic electrode (CCE) by using different electrochemical techniques such as: Cyclic voltammetry (CV), Chronoamperometry (CA), Chronopotentiometry (CP) and Electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were also employed to physicochemical survey of the electrocatalysts. The kinetic parameters of glycerol oxidation, i.e. Tafel slope and activation energy (E_a), were determined on the modified electrodes. The Tafel slopes of 166 mV dec⁻¹ on Pt|CCE, 177 mV dec⁻¹ on Au|CCE and 136 mV dec⁻¹ on Pd|CCE were obtained. The lowest E_a value of 11.2 kJ mol⁻¹ was calculated on Au|CCE. In continuation, the reaction orders with respect to the glycerol and NaOH concentrations on Pd|CCE were found to be 0.27 and 0.87, respectively. The CV, CP and CA results showed remarkable electrocatalytic activity and good poisoning tolerance of Au|CCE for glycerol oxidation.     

Effect of hydrogen additive on methane decomposition to hydrogen and carbon over activated carbon catalyst

The effect of H₂ addition on CH₄ decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H₂ to CH₄ changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H₂ flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H₂, and when the H₂ flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H₂ to CH₄ and the catalyst deactivation is restrained. Filamentous carbon is obtained when H₂ is introduced into CH₄ reaction gas compared with the agglomerate carbon without H₂ addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition.     

Thermocatalytic decomposition of methane for hydrogen production using activated carbon catalyst: Regeneration and characterization studies

A series of experiments was conducted to study the deactivation and regeneration of activated carbon catalyst used for methane thermocatalytic decomposition to produce hydrogen. The catalyst becomes deactivated due to carbon deposition and six decomposition cycles of methane at temperatures of 850 and 950 °C, and five cycles of regeneration by using CO₂ at temperatures of 900, 950 and 1000 °C were carried out to evaluate the stability of the catalyst. The experiment was conducted by using a thermobalance by monitoring the mass gain during decomposition or the mass lost during the regeneration with time. The initial activity and the ultimate mass gain of the catalyst decreased after each regeneration cycle at both reaction temperatures of 850 and 950 °C, but the amount is smaller under the more severe regenerating conditions. For the reaction at 950 °C, comparison between the first and sixth reaction cycles shows that the initial activity decreased by 69, 51 and 42%, while the ultimate mass gain decreased by 62%, 36% and 16% when CO₂ gasification carried out at 900, 950 and 1000 °C respectively. Temperature -programmed oxidation profiles for the deactivated catalyst at reaction temperature of 950 °C and after several cycles showed two peaks which are attributed to different carbon characteristics, while one peak was obtained when the experiment was carried out at 850 °C. In conclusion, conducting methane decomposition at 950 °C and regeneration at 1000 °C showed the lowest decrease in the mass gain with reaction cycles.     

Effects of carbon sources and carbonized carbon contents during carbon riveting process on the stability of Pt/C catalyst

Effects of different carbon sources and carbonized carbon contents during carbon riveting process (CRP) on the stability of Pt/C catalysts have been systematically studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammograms (CV), and accelerated potential cycling tests (APCT) have been carried out to characterize the catalysts. Experimental results show that the carbon riveted Pt/C catalysts treated by different carbon sources have different stability due to different properties of Pt and carbon after the CRP. The best carbon source for the carbon riveted Pt/C catalysts is glucose and is ascribed to the most content of Pt (0) and sp³-C after the CRP. APCT results indicate that the stability of Pt/C catalysts carbon-riveted by glucose exhibits the increasing trend with the increase of carbonized carbon contents because of increasing anchor effect to Pt nanoparticles. However, a larger carbon content from the carbonization of glucose can also reduce the electrochemically active specific surface areas (ESA) of the carbon riveted Pt/C catalyst by covering the active sites of Pt nanoparticles. Taking into account both activity and stability of the carbon riveted Pt/C catalysts, 6% carbon from the carbonization of glucose is the optimized content.     

Optimization of content of components over activated carbon catalyst on CO2 reforming of methane using multi-response surface methodology

To accurately and efficiently optimize the component content of the catalyst is one important strategy to fabricate robust catalysts. By multi-response surface methodology (RSM), this study chose promising metal components (Co, Ce, and W) supported over activated carbon as a catalyst to investigate the catalytic activity of CO₂–CH₄ reforming. First, the center point of the center-complex design (CCD) based on RSM was determined by single-factor experiment, Co, W and Ce were loaded with 10.1 wt%, 9.7 wt%, and 9.2 wt%, respectively. Then, the three-factor and five-level CCD was exhibited. Four well-matched quadratic regression models (R² is close to 1) were developed to gain a better understanding of the effects of the individual component content and their interactions on CH₄ conversion, CO₂ conversion, H₂ yield, and CO yield. The results showed that W content was the most important negative parameter affecting the conversion of CH₄ and CO₂, while the Co and Ce content played a significant positive role in the catalyst performance. The interactive effects of all different component content imposed a significant effect on the CO₂ conversion and CO yield. At last, the content optimization suggested that the optimal catalytic activity was achieved at the content of Co, W, and Ce of 10.6 wt%, 6.5 wt%, and 8.6 wt%, respectively, which was validated by a mean error of less than 2.2%.     

Optimization and aging of Pt nanowires supported on single-walled carbon nanotubes as a cathode catalyst in polymer electrolyte membrane water electrolyser

A catalyst material containing platinum nanowires supported on single-walled carbon nanotubes (CNTs) is tested thoroughly for the use as a cathode catalyst for polymer electrolyte membrane water electrolyser (PEMEL). The Nafion ionomer content, the platinum to CNT ratio and the thickness of the catalyst layer (CL) is optimized. Long-term measurement with constant current and start-stop cycling of the optimized CL is performed in order to study the durability of the catalyst material. The CLs are characterized ex-situ with TEM, XRD and Raman spectroscopy. During the constant current operation, platinum experiences Ostwald ripening type of degradation and during the cycling, particle agglomeration. The magnitude of platinum degradation is, however, lower than for a commercial Pt/C type of catalyst. Moreover, the CNTs are subjected to carbon corrosion, but the rate of corrosion is observed to be decreasing. Therefore, carbon nanotubes are considered more suitable support material for the cathode catalyst of PEMELs.     

Synthesis of glycerol-free fatty acid methyl ester using interesterification reaction based on solid acid carbon catalyst derived from low-cost biomass wastes

The current research was aimed to corroborate as well as compare the feasible applicability of waste banana peel and empty fruit bunch (EFB) in synthesising high-performing heterogeneous catalysts. The solid acid catalysts originated from biomass wastes were employed for the synthesis of glycerol-free fatty acid methyl ester (FAME) using catalytic interesterification process pathway. Acetic acid was produced as the by-product instead of glycerol. The heterogeneous acid catalysts were synthesised utilising sulphuric acid through direct sulfonation with thermal treatment. The concentration of the sulphuric acid was manipulated from 2 to 13 mol L^?1 to investigate its effects on the resulting FAME yield while maintaining the sulfonating ratio at 10 mL g^?1. The catalytic performances of the as-synthesised catalysts were studied under reaction conditions of 12 wt % catalyst loading, 50:1 methyl acetate to oleic acid molar ratio for a duration of 8 hours at 60°C. The catalyst produced by activated carbon derived from EFB and sulfonated with 13 mol L^?1 sulphuric acid exhibited the highest FAME yield at 44.3%. The parameter studies on reactant ratio (45:1-70:1), reaction temperature (90°C-130°C) and time (4-24 hours) of interesterification reaction discovered a general increasing trend in the FAME yield up to 52.3% with the optimum conditions of 50:1, 110°C and 8 hours, respectively. The catalyst was recyclable with 82% of the catalytic performance retained after five successive cycles with catalyst reactivation. This study confirmed that the renewable heterogeneous catalyst derived from biomass waste could catalyse the glycerol-free interesterification process via an environmentally benign and promising approach for green fuel production.     

Effect of carbon black additive in Pt black cathode catalyst layer on direct methanol fuel cell performance

Vulcan XC-72R, Ketjen Black EC 300J and Black Pearls 2000 carbon blacks were used as the additive in Pt black cathode catalyst layer to investigate the effect on direct methanol fuel cell (DMFC) performance. The carbon blacks, Pt black catalyst and catalyst inks were characterized by N₂ adsorption and scanning transmission electron microscopy (STEM) with Energy dispersive X-ray (EDX) spectroscopy. The cathode catalyst layers without and with carbon black additive were characterized by scanning electron microscopy, EDX, cyclic voltammetry and current-voltage curve measurements. Compared with Vulcan XC-72R and Black Pearls 2000, Ketjen Black EC 300J was more beneficial to increase the electrochemical surface area and DMFC performance of the cathode catalyst layer. The cathode catalyst layer with Ketjen Black EC 300J additive was kept intimately binding with the Nafion membrane after 360 h stability test of air-breathing DMFC.     

Optimisation of an asymmetric manganese oxide/activated carbon capacitor working at 2 V in aqueous medium

The charge storage mechanism of manganese oxide and activated carbon has been studied in aqueous medium in order to optimise an asymmetric (or hybrid) supercapacitor based on these two materials as positive and negative electrode, respectively. Amorphous manganese oxide can be polarised up to potentials of 1.2 V in neutral medium. Under negative polarisation, a pseudocapacitive behaviour of activated carbon has been demonstrated, that is related with reversible hydrogen adsorption in the pores. It allows carbon to be polarised at potential values far from the thermodynamic decomposition of the electrolyte. Balancing the mass of these two materials with pseudocapacitive properties results in a practical cell voltage of 2 V in aqueous medium, with energy densities close to the values obtained with electric double layer capacitors working in organic electrolytes, while avoiding their disadvantages.     

Effect of temperature on the mechanism of ethanol oxidation on carbon supported Pt,PtRu and Pt3Sn electrocatalysts

The electrochemical oxidation of ethanol on carbon supported Pt, PtRu and Pt₃Sn catalysts was studied in acid solutions at room temperature and in direct ethanol fuel cells (DEFC) in the temperature range 70–100 °C. In all the experiments, an enhancement of the activity for the ethanol oxidation was observed on the binary catalysts. In acid solution the improvement at low current densities was higher on PtRu than on Pt₃Sn. In DEFC tests, at 70 °C the cells with PtRu and Pt₃Sn showed about the same performance, while for T > 70 °C the cells with Pt₃Sn as anode material performed better than those with PtRu as anode material. The apparent activation energy for ethanol oxidation on PtRu catalyst was lower than on Pt₃Sn, particularly at high cell potentials, i.e. at low current densities. At low temperatures and/or low current densities, the positive effect of Ru oxides on the bifunctional mechanism determined the enhancement of activity for the ethanol oxidation reaction, while at high temperatures the positive effect of Sn alloying (enlarged lattice parameter) on CH₃CH₂OH adsorption and C–C cleavage prevails.