Characteristics of hydrochar and liquid fraction from hydrothermal carbonization of cassava rhizome

Hydrothermal carbonization (HTC) of cassava rhizome (CR) was performed to investigate the effect of process parameters including temperature, time, and biomass to water ratio (BTW) on characteristics of hydrochar and liquid fraction products. The effect of temperature was two-fold. First, an increase in reaction temperature from 160 to 180 °C decreased hydrochar yield from 54 to 51%, however, a further increase of temperature from 180 to 200 °C saw an increase in the hydrochar yield to 58%. This was associated to degradation, polymerization, and condensation reactions during HTC. The hydrogen/carbon and oxygen/carbon atomic ratios decreased from 1.4 and 0.6 at 160 °C to 1.2 and 0.4 at 200 °C, respectively. The liquid fraction contained various valuable chemical species including, glucose, furan compounds, (furfural, furfuryl alcohol, hydroxymethylfurfural), volatile fatty acid (succinic acid, lactic acid, formic acid, acetic acid, levulinic acid, and propionic acid) with their highest yields (wt.% dry raw material) of 4.5, 18.5, and 24.3, respectively.     

Optimization of furfural production from millet husk using response surface methodology

Biomass has been recognized as a viable source for energy and bio-based chemicals. This study reported furfural production from millet husk via simultaneous hydrolysis and dehydration processes. Effect of reaction variables such as temperature (120–200°C), resident time (15–45 min), and acid concentration (5–10%) was studied using central composite design. Furfural yield (71.55%) was achieved at 184°C, 39 min, and 9% acid concentration. FT-IR spectrum of the produced furfural showed absorption at 1,697 and 2,880 cm^?1 indicating a conjugated carbonyl functional group and aldehydic hydrogen. The results revealed that millet husk could be a potential substrate for furfural production.     

Sludge stabilization and energy recovery by hydrothermal carbonization process

Hydrothermal carbonization (HTC) is a thermal conversion process that converts high-moisture biomass into hydrochar. HTC was applied to stabilize and process sludge collected from septic tanks into hydrochar for practical energy recovery. Experiments were conducted with a 1-L high-pressure reactor operating at different temperatures and reaction times in which the sludge was mixed with catalysts and biomass at different ratios. The effects of catalysts (i.e., acetic acid, lithium chloride, borax, and zeolite) and biomass (i.e., cassava pulp, dried leaves, pig manure, and rice husks) mixing with sludge for hydrochar production were investigated. The experimental data showed acetic acid and cassava pulp to be the most effective catalyst and biomass, respectively, increasing energy contents to the maximum value of 28.5 MJ/kg. The optimum HTC conditions were as follows: sludge/acetic acid/cassava pulp mixing ratio of 1/0.4/1 (by weight), at a temperature of 220 °C, and reaction time of 0.5 h. The relatively high energy contents of the produced hydrochar suggest its applicability as a solid fuel.     

Effects of hydrothermal carbonization on products from fast pyrolysis of cellulose

In the first step of this study, the hydrothermal carbonization (HTC) of cellulose was performed at 225 and 250 °C for 4, 8 and 12 h. The effect of temperature and residence time on hydrochar (HC) yields and characteristics was investigated, and the highest hydrochar yield had a heating value of 21.06 MJ/kg. In the second step, cellulose and hydrochar-derived cellulose was subjected to fast online pyrolysis at 500, 600 and 700 °C, using a pyrolysis-gas chromatography-mass spectrometry system. The HTC process significantly affected the pyrolysis products. The major decomposition product resulting from the fast pyrolysis of cellulose was levoglucosan, but at all tested temperatures, 2-methylfuran was the major product from hydrochars. Increasing the pyrolysis temperature caused a decrease in the relative yield of 2-methylfuran. Another prominent compound observed in pyrolyzates was 2,5-dimethylfuran. The relative yields of these two compounds decreased when the residence time of the HTC process was increased. The highest 2-methylfuran selectivity was 67.4%, while the highest 2,5-dimethylfuran selectivity among the furanic compounds was 24.0%. This study demonstrated that, by combining HTC and pyrolysis processes, fine chemicals can be produced from cellulose.     

Technological aspects of sunflower biomass and brown coal co-firing

The technological problems occurring in the co-firing of biomass and brown coal (lignite) prompted this research project. During the fuel preparation, accidental self-ignition and explosions were several times reported by power plants operators. The aim of this study was to evaluate brown coal, sunflower husks and sunflower husk pellets as fuels for co-firing in energetic boilers. Sunflower husk had a lower ash content and calorific value than the pellets. The range of the combustion temperatures of the biomass (200–300 °C) was narrower than that of brown coal (200–800 °C). The formation of highly alkaline ash from the biomass resulted in the formation in boiler of agglomerates of ash. The elemental composition, thermogravimetric and biological analyses suggested that the pellets contained synthetic additives difficult to identify. The biological method was proposed for evaluating biomass additives. The use of additional agents in the pelletizing process may influence on the combustion parameters. Mixing biomass with brown coal may occasionally result in self-ignition in the logistic chain. Plastic additives and biological activity may contribute to self-ignition.     

Thermodynamic investigation on gasification performance of sewage sludge-derived hydrochar: Effect of hydrothermal carbonization

Compared with the conventional thermal drying process, hydrothermal carbonization (HTC) can reduce the energy cost of water removal from sewage sludge prior to its steam gasification. However, less attention is paid on the interactions between HTC and gasification. In this study, the thermodynamic evaluation on hydrochar gasification performance under different operating conditions including HTC duration (τ), HTC temperature (T_HTC), gasification temperature (T_g), and steam/hydrochar mass ratio (S/C ratio) is performed. Two indicators including carbon conversion rate (CC) and cold gas efficiency (CGE) are used to assess the gasification performance. The results show that elevating both gasification temperature and S/C ratio can enhance the H₂ production, which also result in the increase of CC and CGE. The content and gasification activity of fixed carbon increase under moderate HTC duration and temperature, favoring the H₂ formation despite of the apparent loss of volatiles species in the hydrochar. Longer HTC duration or higher HTC temperature declines the H₂ production due to the sharp reduction of carboxyl and hydroxyl groups, weakening water gas reaction and on-site reforming reaction of tar occurred on the hydrochar surface. In terms of the values of CC = 93.9% and CGE = 64.38%, the optimum HTC conditions of τ = 30min and T_HTC = 200 °C can be determined. The data provided here favor guiding HTC treatment of sewage sludge targeting gasification and thus promoting the development of this promising waste-to-energy technology.     

Thermo-chemical conversion of waste rubber seed shell to produce fuel and value-added chemicals

Rubber seed shell (RSS), comprises of 96.67 wt% organic content and 38.6% crystallinity index, was used for the production of biofuel and value-added chemicals through semi-batch pyrolysis. Thermogravimetric analysis (TGA) of RSS at heating rate of 20 °C/min showed R50 value as 12.72%/min at 376.5 °C. The gaseous product evolved during the decomposition of RSS were analyzed through inline Fourier transform infrared (FT-IR) coupled with TGA instrument. The effects of pyrolysis temperatures (350°C-600 °C) and heating rates (10°C/min–40 °C/min) on the product distribution (liquid, gas and bio-char) were investigated. The maximum yield of liquid product (46.14 wt%) and the carbon-rich bio-char (31.92 wt%) were obtained at 550 °C temperature for heating rate of 30 °C/min. The fuel characteristics of produced bio-char such as higher calorific value (34.5 MJ/kg), higher fixed carbon (79.74 wt%), lower ash (1.87 wt%) and lower moisture content (2.11 wt%) suggested its potential to be used as solid fuel. Value-added organic compounds such as acetic acid, phenolic compounds, creosol, pilocarpine, benzene and levoglucosan were identified in the liquid product using gas chromatography. The pH values of liquid products (2.55–3.0) support the presence of organic acids and phenolic fraction. The presence of various functional groups was also identified using FT-IR spectroscopy. In depth analysis of physico-chemical-thermal properties of RSS and obtained products (liquid and bio-char) suggested that RSS can be considered as a suitable feedstock for the production of value added chemicals including fuel.     

Cascaded production of biogas and hydrochar from wheat straw: Energetic potential and recovery of carbon and plant nutrients

The increasing interest in biogas production has brought notable attention to lignocellulosic wastes as a promising and yet unexploited feedstock. As these materials are usually highly recalcitrant the energetic efficiency of biogas production, however, is comparatively low. With the aim to overcome this drawback, a novel cascaded approach was investigated that combines anaerobic digestion with hydrothermal carbonization (HTC). The latter is used to convert the digestate into a carbon-rich product termed hydrochar. An energetic evaluation of this cascaded treatment shows that the energy recovery can be nearly doubled compared to single anaerobic digestion.Furthermore, systematic HTC experiments with both fresh and digested wheat straw and with reaction temperatures of 190 °C, 210 °C, 230 °C, and 250 °C revealed an effect of reaction temperature on carbon, nitrogen, and phosphorus concentration in the final hydrochar. Carbon, nitrogen and phosphorus are primarily retained in the hydrochar, which could favor its use as soil ameliorant instead of an energy carrier.     

Hydrothermal carbonization: Fate of inorganics

Hydrothermal carbonization (HTC) is a pretreatment process for making a homogenized, carbon rich, and energy-dense solid fuel, called biochar, from lignocellulosic biomass. Corn stover, miscanthus, switch grass, and rice hulls were treated with hot compressed water at 200, 230, and 260 °C for 5 min. Mass yield is as low as 41% of the raw biomass, and decreases with increasing HTC temperature. Higher heating values (HHV) increase up to 55% with HTC pretreatment temperature. Up to 90% of calcium, magnesium, sulfur, phosphorus, and potassium were removed with HTC treatment possibly due to hemicellulose removal. At a HTC temperature of 260 °C, some structural Si was removed. All heavy metals were reduced by HTC treatment. The slagging and fouling indices are reduced with HTC treatment relative to that of untreated biomass. Chlorine content, a concern only for raw and HTC 200 switch grass, was reduced to a low slagging range at 230 °C, and 260 °C. Alkali index was medium for raw biomass but decreased by HTC.     

Comprehensive performance enhancement of polybenzimidazole based high temperature proton exchange membranes by doping with a novel intercalated proton conductor

On the study of high temperature proton exchange membrane (HTPEM), the trade-off between proton conductivity and physico-chemical property (such as mechanical strength, dimensional stability and methanol resistance) remained a main obstacle for comprehensive performance enhancement. To address this issue, novel HTPEM was prepared by doping phosphotungstic acid intercalated ferric sulfophenyl phosphate (FeSPP-PWA) into polybenzimidazole (PBI) via hot pressed method. Intense hydrogen bonding network was built between PBI and FeSPP-PWA, rendering construction of proton channels and reinforcement of physico-chemical property. As a novel proton conductor, FeSPP-PWA facilitated formation of efficient proton transfer pathway. The layered morphology and inorganic intrinsity of FeSPP-PWA also improved the mechanical and dimensional stability while reducing the methanol permeability of the PBI/FeSPP-PWA membranes. The composite membrane exhibited good thermal stability up to 200 °C. The proton conductivity of PBI/FeSPP-PWA (30 wt%) reached 110 mS cm^?1 at 170 °C and 100% RH, and was 69.3 mS cm^?1 at 180 °C and 50% RH. The PBI/FeSPP-PWA also showed low methanol permeability and high membrane selectivity for application in direct methanol fuel cells.     

Biohydrogen production from Imperata cylindrica bio-oil using non-stoichiometric and thermodynamic model

This paper presents a non-stoichiometric and thermodynamic model for steam reforming of Imperata cylindrica bio-oil for biohydrogen production. Thermodynamic analyses of major bio-oil components such as formic acid, propanoic acid, oleic acid, hexadecanoic acid and octanol produced from fast pyrolysis of I. cylindrica was examined. Sensitivity analyses of the operating conditions; temperature (100–1000 °C), pressure (1–10 atm) and steam to fuel ratio (1–10) were determined. The results showed an increase in biohydrogen yield with increasing temperature although the effect of pressure was negligible. Furthermore, increase in steam to fuel ratio favoured biohydrogen production. Maximum yield of 60 ± 10% at 500–810 °C temperature range and steam to fuel ratio 5–9 was obtained for formic acid, propanoic acid and octanol. The heavier components hexadecanoic and oleic acid maximum hydrogen yield are 40% (740 °C and S/F = 9) and 43% (810 °C and S/F = 8) respectively. However, the effect of pressure on biohydrogen yield at the selected reforming temperatures was negligible. Overall, the results of the study demonstrate that the non-stoichiometry and thermodynamic model can successfully predict biohydrogen yield as well as the composition of gas mixtures from the gasification and steam reforming of bio-oil from biomass resources. This will serve as a useful guide for further experimental works and process development.     

Macromolecule sulfonated Poly(ether ether ketone) crosslinked poly(4,4′-diphenylether-5,5′-bibenzimidazole) proton exchange membranes: Broaden the temperature application range and enhanced mechanical properties

Proton exchange membranes with a wide application temperature range were fabricated to start high-temperature fuel cells under room temperature. The volume swelling stability, oxidative stability as well as mechanical properties of crosslinked membranes have been improved for covalently crosslinking poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) with fluorine-terminated sulfonated poly(ether ether ketone) (F-SPEEK) via N-substitution reactions. High proton conductivity was simultaneously realized at both high (80–160 °C) and low (40–80 °C) temperatures by crosslinking and jointly constructing hydrophilic-hydrophobic channels. The crosslinked membranes exhibited the highest proton conductivity of 191 mS cm⁻¹ at 80 °C under 98% relative humidity (RH) and 38 mS cm⁻¹ at 160 °C under anhydrous, respectively. Compared with OPBI membrane, the fuel cell performance of the crosslinked membranes showed higher peak power density at full temperature range (40–160 °C).     

Characterization and fuel cell performance of divinylbenzene crosslinked phosphoric acid doped membranes based on 4-vinylpyridine grafting onto poly(ethylene-co-tetrafluoroethylene) films

The effect of divinylbenzene (DVB) as crosslinker on the graft polymerization of 4-vinylpyridine (4VP) from poly(ethylene-co-tetrafluoroethylene) (ETFE) films was studied. The resulted films were doped with phosphoric acid (PA) and characterized for mechanical, surface, thermal properties, and fuel cell performance. The crosslinked membrane obtained from grafting a mixture of 4VP with 1% DVB improved the polymerization kinetics and resulted in about 50% graft level depending on graft conditions. The crosslinked membranes were also found to have better mechanical properties compared to its noncrosslinked counterpart. The resulted membrane exhibited proton conductivity as high as 75 mS/cm under 50% relative humidity (RH) at 120 °C, besides almost doubling the power output of fuel cell compared to a noncrosslinked membrane. To the best of our knowledge, DVB crosslinked 4VP based ETFE membranes were, for the first time, tested in practical fuel cell test station correlating their performance to operating temperature. Furthermore, surface properties of produced membranes were additionally correlated to the degree of crosslinking. Humidity dependence is less pronounced in the produced membranes resulting in strong potential for testing at intermediate temperature (80–120 °C) polymer electrolyte membrane fuel cells.     

Sustainable hydrogen production options from food wastes

In this study, two thermochemical processes, namely steam gasification and supercritical water gasification (SCWG), were comparatively studied to produce hydrogen from food wastes containing about 90% water. The SCWG experiments were performed at 400 and 450 °C in presence of catalyst (Trona, K₂CO₃ and seaweed ash). The maximum hydrogen yield was obtained at 450 °C in presence of K₂CO₃ catalyst. In second process, hydrothermal carbonization was used to convert food wastes into a high-quality solid fuel (hydrochar) that was further gasified in a dual-bed reactor in presence of steam. The steam gasification of hydrochar was carried out with and without catalysts (iron?ceria catalyst and dolomite). The maximum hydrogen yield obtained from steam gasification process was 28.08 mmol/g dry waste, about 7.7 times of that from SCWG. This study proposed a new concept for hydrogen production from wet biomass, combination of hydrothermal carbonization following steam gasification.     

Organic-inorganic backbone with high contents of proton conducting groups: A newly designed high performance proton conductor

To prepare new high temperature organic-inorganic proton conductor for applications in proton exchange membrane fuel cells (PEMFC), 2,4,6-triphosphono-1,3,5-triazine (TPT) was synthesized and reacted with three different types of metal ions (Ce, Zr and Fe) in varied molar ratios. In each TPT molecule, three phosphonic acid groups were introduced into the triazine ring to obtain an organic compound with high content of proton conducting groups, which was then reacted with metal ions to ensure the insolubility in water aiming to avoid leaking during PEMFC operation. CeTPT(1:2) exhibited good thermal stability up to 200 °C and showed crystalline phase. MTPT exhibited high ion exchange capacity (IEC, 1.53–2.12 meq. g⁻¹). CeTPT(1:2) exhibited highest proton conductivity among all samples, which reached 0.116, 0.070 and 0.034 S cm⁻¹ at 100% relative humidity (RH), 50% RH and anhydrous conditions at 180 °C, respectively. The corresponding activation energy for proton conduction was 14.5, 16.0 and 21.5 kJ mol⁻¹ at 100% RH, 50% RH and anhydrous conditions, respectively. The mechanism for proton conduction was proposed according to the activation energy. The proton conductor can find promising applications in fuel cells, corrosion inhibition and water desalination due to its good thermal stability and high IEC.     

Crosslinked poly (isatin biphenyl spirofluorene) membranes for proton conduction over a wide temperature range from −40 to 160 °C

It is desired to develop proton exchange membranes (PEMs) working in a wide temperature range considering the practical working condition of devices using the PEMs as the electrolyte. Herein, a novel polymer of poly (isatin biphenyl spirofluorene) (PIBS) is first synthesized and it is afterwards crosslinked by 1,3-bis(4-piperidyl) propane (P) to fabricate membranes. The membranes can work in a temperature range of −40 to 160 °C after doping with phosphoric acid (PA). The proton conductivity of the PA doped membrane reaches 4.4 × 10⁻³ S cm⁻¹ at −40 °C under 80% relative humidity (RH) and 0.16 S cm⁻¹ at 160 °C without humidifying. We demonstrate the uses of the prepared PA doped PIBS-P membranes as membrane electrolytes in single fuel cells within 100–160 °C under anhydrous condition, and in water electrolytic cells within −20 to 60 °C, respectively.     

Effect of anode thickness and Cu content on consolidation and performance of planar copper-based anode-supported SOFC

Planar, Cu-containing Gadolinia-doped ceria anode-supported solid oxide fuel cells to be used at intermediate temperature (500–750 °C) were produced in the present work. The Intermediate temperature solid oxide fuel cells were fabricated using Li₂O as sintering aid for Gadolinia-doped ceria, varying the anode-to-electrolyte thickness ratio (r) from 2 to 10 and the CuO content in the anode from 45 vol% to 55 vol%. Co-sintering of the thermo-pressed green cells was carried out at 900 °C for 3 h. The electrolyte densification was favoured by increasing the r value, this being accounted for the enhanced compressive stresses induced by the supporting anode on the electrolyte upon sintering. Larger CuO content positively influences the overall cell performance, due to the improved electronic conductivity of the anode. Nevertheless, CuO concentration cannot exceed 50 vol% because of the tensile stresses (and corresponding flaws) generated in the electrolyte for larger amount. IT-SOFC containing 50 vol% CuO was characterized by an Open Circuit Voltage ≈0.82 V and a maximum power density of 200 mW cm^?2 at 700 °C.     

Crystallite formation effect on the physicochemical properties of SPEEK membranes for fuel cell application

Crystallite formation in membranes cast from sulfonated poly(etheretherketone) (SPEEK) dispersions in dimethylacetamide has been investigated by differential scanning calorimetry. The crystallites melt at 220 °C and the melting enthalpy (ΔH_m) is strongly influenced by environmental conditions of solvent evaporation. When solvent is evaporated in air, ΔH_m decreases with increasing the evaporation temperature so that no crystallites are formed above 45 °C. The study of crystallite formation at 30 °C, under controlled relative humidity (RH) and solvent evaporation rate, has shown that ΔH_m decreases i) with decreasing RH from 75% to 5%, at constant evaporation rate, and ii) with increasing evaporation rate, especially at low RH. The exchange of protons with sodium ions results in an increase of the crystallite melting temperature thus indicating the presence of sulfonic groups in the crystallites. In comparison with crystallite-free SPEEK membranes, the presence of crystallites turns out in enhanced membrane mechanical properties, reduced hydration in liquid water above 75 °C, strongly anisotropic swelling (occurring mainly in the through-plane direction) and better performance in H₂/air fuel cell at 70 °C.     

7-ethylindole: A new efficient liquid organic hydrogen carrier with fast kinetics

We report a discovery of a new member of the liquid organic hydrogen carrier (LOHC) family, 7-ethylindole (7-EID), with a low melting point of ?14 °C and a decent hydrogen content of 5.23 wt%. Hydrogenation of the compound was carried out over a commercial 5 wt% Ru/Al₂O₃ catalyst in the H₂ pressure range of 5–8 MPa and a temperature range of 120–160 °C, respectively. It was found that the hydrogenation rate positively correlates with the reaction temperature. However, the rate was barely effected by the H₂ pressure if the pressure exceeds 6 MPa. The estimated apparent activation energy of 7-EID hydrogenation is 51.5 kJ/mol. The fully hydrogenated product, octahydro-7-ethylindole (8H-7-EID), was used as the reactant for the dehydrogenation reaction at 170–200 °C over a 5 wt% Pd/Al₂O₃ catalyst. Full dehydrogenation of 8H-7-EID to 7-EID can be achieved within 270 min at 190 °C. The apparent activation energy of 8H-7-EID dehydrogenation was calculated to be 101.9 kJ/mol at 170–200 °C. The liberated H₂ was found to be of high purity, which meets the requirement of proton exchange membrane fuel cells.     

Investigation of hydrothermal carbonization and chemical activation process conditions on hydrogen storage in loblolly pine-derived superactivated hydrochars

While the challenge of storing hydrogen in inexpensive and renewable adsorbents is relentlessly pursued by researchers all over the world, application of hydrochar derived from biomass is also gaining attention as it can be subsequently chemically activated using activating agents like KOH in order to tailor the development of favorable porosity. However, the synergistic effect of hydrothermal carbonization (HTC) process conditions as well as KOH activating conditions on the development of surface morphology is required to be assessed with the application of such porous superactivated hydrochars in hydrogen storage application. In this study, highly porous superactivated hydrochars were fabricated from inexpensive and abundant loblolly pine. Loblolly pine was hydrothermally carbonized at 180 °C, 220 °C and 260 °C and the hydrochars were then activated at different experimental conditions of 700 °C, 800 °C and 900 °C using solid KOH to loblolly pine hydrochar ratio of 2:1, 3:1 and 4:1 to produce superactivated hydrochars. Superactivated hydrochars as well as loblolly pine and its corresponding hydrochars underwent physicochemical analysis as well as surface morphology analysis by SEM and nitrogen adsorption isotherms at 77 K in order to investigate the effect on BET, pore volume, and pore size distribution due to various process conditions. The superactivated hydrochars were then analyzed to quantify total hydrogen storage capacity of these materials at 77 K and up to pressure of 55 bar. Porosity of superactivated hydrochars were as high as 3666 m²/g of BET specific surface area (SSA), total pore volume of 1.56 cm³/g and micropore volume of 1.32 cm³/g with the hydrogen storage capacity of 10.2 wt% at 77 K and 55 bar. It was conclusive from principal component analysis that higher HTC temperature with moderate activation condition demonstrated favorability in developing porous superactivated hydrochars for hydrogen storage applications.