Hydrothermal Carbonization Treatment Research Articles

Microstructures and ablation properties of Cf/C-SiC-MoSi2 composites: Influence of the SiC:MoSi2 mass ratio

In order to find out the influence of relevant content of SiC and MoSi2 on the properties of Cf/C-SiC-MoSi2 composites, SiC and MoSi2 were introduced into C/C composites by vacuum filtration infiltration (VFI) process, and the composites were densified through hydrothermal carbonization treatment using glucose as the carbon source. The composition, pore size distribution, microstructure and ablation resistance of the composites were investigated. Results showed that with the increase of SiC content, the interface bonding between carbon fibers and ceramic matrix was improved, companied with much smaller pore size in C/C-SiC-MoSi2 composites. As the SiC:MoSi2 mass ratio was 15:51, the composites exhibited compact microstructure, which was beneficial to good ablation resistance. After being exposed to an oxyacetylene torch flame at 2000°C for 60s, the mass and linear ablation rates were respectively decreased by 84% and 66% compared to those of composites without SiC. The good anti-ablation performance was attributed to the generation of SiO2 layer, which was regarded as an effective barrier between corrosive gases and inner materials.

Chitosan-derived carbonaceous material for highly efficient adsorption of chromium (VI) from aqueous solution

A carbonaceous adsorbent for effectively removing Cr(VI) was synthesized by facile hydrothermal carbonization of chitosan (HTC-chitosan). The prepared HTC-chitosan exhibited good stability in acid solution while the amine groups were retained completely after simple and green hydrothermal carbonization treatment. Structure characteristics of the HTC-chitosan as well as its adsorption behaviors for Cr(VI) in aqueous solution were investigated. Under optimal conditions, the adsorption capacity of the HTC-chitosan for Cr(VI) reached as high as 388.60mgg⿿1, which was much higher than that of other materials reported previously. The prepared HTC-chitosan adsorbent could be reused at least five times with adsorption efficiency more than 92%. These results indicate that HTC-chitosan exhibited great superiority for Cr(VI) adsoption from aqueous solution both in terms of the preparation process and adsorption performance.

Comparison of liquid and vapor hydrothermal carbonization of corn husk for the use as a solid fuel

The effect of the phase during the hydrothermal carbonization (HTC) of corn husks was studied to determine whether liquid water or water vapor was the more suitable reaction medium, as well as if the HTC process could produce a solid fuel (hydrochar) from green corn husks that was comparable to coal. Using liquid water for the HTC process produced a hydrochar with an increased heating value (27.66MJkg−1) compared to using water vapor (25.46MJkg−1). HTC using liquid water removed 90% of the potassium contained in raw corn husk, whereas the water vapor HTC treatment removed 58%. The liquid water treated hydrochar contained a 29% decrease in ash content compared to the water vapor hydrochar. Using a TGA-FTIR analysis the liquid treated hydrochar demonstrated a more coal-like combustion in terms of mass loss and heat production, compared to the vapor treated hydrochar.

Graphene Oxide Assisted Hydrothermal Carbonization of Carbon Hydrates

Hydrothermal carbonization (HTC) of biomass such as glucose and cellulose typically produces micrometer-sized carbon spheres that are insulating. Adding a very small amount of Graphene oxide (GO) to glucose (e.g., 1:800 weight ratio) can significantly alter the morphology of its HTC product, resulting in more conductive carbon materials with higher degree of carbonization. At low mass loading level of GO, HTC treatment results in dispersed carbon platelets of tens of nanometers in thickness, while at high mass loading levels, free-standing carbon monoliths are obtained. Control experiments with other carbon materials such as graphite, carbon nanotubes, carbon black, and reduced GO show that only GO has significant effect in promoting HTC conversion, likely due to its good water processability, amphiphilicity, and two-dimensional structure that may help to template the initially carbonized materials. GO offers an additional advantage in that its graphene product can act as an in situ heating element to enable further carbonization of the HTC products very rapidly upon microwave irradiation. Similar effect of GO is also observed for the HTC treatment of cellulose.

Process Development Unit (PDU) for Hydrothermal Carbonization (HTC) of Lignocellulosic Biomass

Hydrothermal carbonization (HTC) is an effective means of upgrading raw lignocellulosic biomass to a more uniform solid hydrochar, having increased energy density. The HTC process is conducted in hot (200–300 °C) pressurized liquid water. Most experimental investigations of HTC have been conducted at small scale, using bench-top batch reactor vessels. In this work, we report the design, fabrication, and demonstration of a larger-scale process development unit (PDU) that enables semi-continuous HTC treatment of approximately 3 kg of biomass. This auger-equipped tubular reactor system conveys raw biomass through a zone of hot pressurized water, and deposits the solid hydrochar product in an accumulator vessel that is maintained at a lower temperature. Gaseous and liquid samples can be collected both while the PDU is at operating temperature, and after it has cooled. Characterization of gaseous, aqueous, and solid samples from a set of PDU experiments indicated good agreement with results from previous HTC experiments conducted in a much smaller (2-L) batch reactor. This suggests that the PDU provides a reliable scale-up of the HTC process.

Chars produced by slow pyrolysis and hydrothermal carbonization vary in carbon sequestration potential and greenhouse gases emissions

Bio-char, biomass that has been deliberately charred to slow its rate of decomposition, has been proposed as an amendment with the potential to sequester carbon and improve certain soil properties. Slow pyrolysis (temperature ≤500 °C) and hydrothermal carbonization (low temperature, high pressure) are two efficient methods to produce bio-char with high yield and are applicable to a broad range of feedstocks. Chars made using slow pyrolysis (PC) and hydrothermal carbonization (HTC) of the same feedstock material (corn, C4) differed in physical appearance, chemical properties and decomposition behavior. We added these HTC and PC chars as amendments to three soils with C3-derived organic matter that differed in clay content, pH, and land use (managed spruce forest, unmanaged deciduous forest and agriculture), and compared their impacts on carbon sequestration and net greenhouse gas (CO2, 13CO2, N2O and CH4) emissions. HTC addition (1% w/w) significantly increased CO2 emissions in all three soils (p < 0.001), with much of the extra C derived from HTC decomposition. In contrast, PC addition (1% w/w) had almost no impact on deciduous forest soil and actually decreased CO2 emission from the agricultural soil. HTC treatment resulted in increased CH4 emission from all soils but reduced N2O fluxes in the agricultural and spruce forest soils. PC amendment had no significant effect on CH4 emission, and resulted in intermediate levels of N2O emission (between control and HTC treatments). Although both HTC and PC chars were produced from the same feedstock, PC had markedly higher potential for carbon sequestration than HTC.

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.