Hydrothermal Carbonization Temperature Research Articles

Insights into the evolution of chemical structure and pyrolysis reactivity of PVC-derived hydrochar during hydrothermal carbonization.

Hydrothermal carbonization (HTC) is emerging as an effective technology to convert PVC into highly valuable materials via the removal of chlorine. This means that an in-depth understanding of HTC requires the hydrochar structure, thermal degradation behavior, and relationship between structure and thermal reactivity to be understood. In this work, two typical PVC waste materials were selected for HTC experiments at different temperatures. The structure of the hydrochar was characterized in detail by compositional analysis, FTIR spectroscopy, and 13C NMR analysis. Furthermore, the thermal degradation behavior of the hydrochar was analyzed. The changes after thermal degradation were used to establish a correlation with pyrolysis reactivity. The results showed that the C content and chemical structure of the hydrochar approached that of bituminous coal with increasing HTC temperature. Compared with the untreated PVC feedstock, the hydrochar exhibited higher levels of oxygen-containing functional groups on its surface, and its carbon skeleton structure changed from polymeric straight chains to short-chain paraffins, cycloalkanes, and aromatics. A negative correlation was observed between the CPI value of the hydrochar derived from SPVC and the HTC temperature. The structural evolution path of the hydrochar was altered by additives, which improved its thermal reactivity. These findings are expected to play a significant role in bridging the gap from the creation of a theoretical potential energy source to the development of a sustainable alternative renewable fuel.

Effect of hydrothermal carbonization temperature on fuel properties and combustion behavior of high-ash corn and rice straw hydrochar

Hydrothermal carbonization has been proven to improve the fuel properties of low-ash straw biomass. To explore the effect of hydrothermal carbonization on high-ash straw biomass, the fuel properties and combustion behavior of hydrochar prepared by high-ash rice straw and corn straw at different temperature were studied. The results showed that increased reaction temperature could improve the C content, fixed carbon, heating value, and fuel ratios (FC/VM) in high-ash straw hydrochars, which is similar to the change trend of low-ash biomass. The hydrochar prepared at 260?C has similar H/C and O/C atomic ratios and FC/VM to lignite. In addition, the highest energetic recovery efficiency is obtained at 200?C. While at 180?C, the comprehensive combustion characteristic index of the hydrochar is the best, which is 5.04 ? 10?11 [min?2K?3] and 6.42 ? 10?11 [min?2K?3]. In addition, the C content in the hydrochars at 180?C was lower than the raw material, and the ash content increases with the reaction temperature, which is quite different from the low-ash biomass. In conclusion, the hydrothermal carbonization could improve the fuel quality of high-ash straw, while its ash content remains at a high level.

Insights into the structure evolution of sewage sludge during hydrothermal carbonization under different temperatures

In this paper, hydrothermal carbonization (HTC) of sewage sludge (SS) under different temperatures was investigated, and the effect of the HTC temperature on the structure evolution and properties of the hydrochar was studied. Here, BET, XPS, Raman and the peak separation and fitting of FTIR were used to analyze the chemical structures of hydrochar during HTC comprehensively. The results indicated that the specific surface area of the hydrochar increased and then decreased with the temperature increasing, and the highest specific surface area was got for hydrochar obtained at 200 ℃, which was 18.30 m2/g. Furthermore, the results showed that raising the temperature could decrease the O/C and H/C ratio of the hydrochars, and the decrease of O/C was mainly attributed to the reduction of CO and COOR rather than C-O during the HTC process. Interestingly, the results also showed that the short chain aliphatic or aromatic substituents ring in SS began to breakage at 160 ℃ and the longer aliphatic chain broke when the temperature was higher than 200 ℃. Increasing the temperature could promote the transformation of the relatively small aromatic ring system to the larger aromatic ring system in hydrochar. The results also showed that the aliphatic carbon content decreased and the degree of aromatization increased with temperature increasing. This work may provide comprehensive structural information of SS during the HTC process, and provide a theoretical basis for the application of SS and its hydrochars.

Impact of temperature severity on hydrothermal carbonization: Fuel properties, kinetic and thermodynamic parameters

The current study intended to explore the impact of hydrothermal carbonization temperature (180, 230, and 280 °C) on the fuel properties, kinetics, thermodynamics, and reaction mechanism of sunflower stalks (SS). Hydrochars obtained at different temperatures were pyrolyzed in a TGA (Thermogravimetric analyzer) at three distinct heating rates. The impact on functional groups, surface morphology, and crystallinity were examined based on the characterization methods such as FTIR, FE-SEM, and XRD. The kinetic parameters were estimated based on the isoconversional methods of Kissinger Akahira Sunose (KAS), Ozawa Flynn Wall (OFW), and Vyazovkin (VZK), whereas the reaction mechanism was deduced employing Z(α) master plot method. The mean value of activation energy obtained for the raw-SS, SS-180, SS-230, and SS-280 was (188.71, 189.06, and 176.4 kJ/mol), (165.6, 167.33, and 155.54 kJ/mol), (219.77, 218.78, and 206.83 kJ/mol), and (299.37, 296.6, and 281.02 kJ/mol) based on KAS, OFW, and VZK method, respectively. The findings of the current study can be used to develop and design pyrolysis reactors for clean biofuel generation from SS.

Microwave-assisted synthesis of biodiesel by a green carbon-based heterogeneous catalyst derived from areca nut husk by one-pot hydrothermal carbonization

In this study, we have synthesized a solid acid catalyst by areca nut husk using low temperature hydrothermal carbonization method. The fabricated catalyst has enhanced sulfonic actives sites (3.12%) and high acid density (1.88 mmol g−1) due to –SO3H, which are used significantly for effective biodiesel synthesis at low temperatures. The chemical composition and morphology of the catalyst is determined by various techniques, such as Fourier transform infrared (FTIR), powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Scanning electron microscope (SEM), Energy disruptive spectroscopy (EDS), Mapping, Thermogravimetric analysis (TGA), CHNS analyzer, Transmission electron microscopy (TEM), particle size analyzer, and X-ray photoelectron spectroscopy (XPS). Acid–base back titration method was used to determine the acid density of the synthesized material. In the presence of the as-fabricated catalyst, the conversion of oleic acid (OA) to methyl oleate reached 96.4% in 60 min under optimized conditions (1:25 Oleic acid: methanol ratio, 80 °C, 60 min, 9 wt% catalyst dosage) and observed low activation energy of 45.377 kJ mol−1. The presence of the porous structure and sulfonic groups of the catalyst contributes to the high activity of the catalyst. The biodiesel synthesis was confirmed by gas-chromatography mass spectrometer (GC–MS) and Nuclear magnetic resonance (NMR). The reusability of the catalyst was examined up to four consecutive cycles, yielding a high 85% transformation of OA to methyl oleate on the fourth catalytic cycle.

Effect of temperature during the hydrothermal carbonization of sewage sludge on the aerobic treatment of the produced process waters

The treatment of the highly contaminated process water produced during the hydrothermal carbonization (HTC) of waste activated sludge is of major concern for the full-scale implementation of the HTC process. So far, no satisfying treatment strategies have been elaborated and the biodegradability under aerobic conditions has hardly been studied. To fill these gaps, aerobic tests were first carried out in batches with HTC process waters produced at 190 °C, 218 °C and 249 °C, and two parallel sequencing batch reactors (SBR) were operated to treat process waters produced at 190 °C and 217 °C. Both experiments show that the HTC temperature has only a little effect on the elimination of dissolved organic carbon (DOC). In the aerobic batch tests, DOC removal were 80.5–81.9 %. In the SBR, 28 % of the initial DOC was found to be recalcitrant, and 25–28 % of the initial nitrogen. In the SBR experiments, the nitrification was also monitored, and nitrification inhibition test were conducted on both process waters obtained at 190 °C and 217 °C. Nitrification the initial SBR reactors was only possible after dilution of the process waters, which indicates the presence of inhibiting substances. The inhibition tests validated those observations, and showed that process waters derived at 217 °C had a higher inhibition potential. This study demonstrates that aerobically treated HTC process waters are still too polluted to be discharged in a wastewater treatment plant: model calculations showed an increase in effluent DOC of 8.3 mg C/L.

Valorization of cannabis waste via hydrothermal carbonization: solid fuel production and characterization.

Hydrothermal carbonization (HTC) was employed to convert cannabis waste into valuable solid fuel (hydrochar) under different operating conditions, including reaction temperature (170-230°C), biomass-water ratio (1:10-1:20), and residence time of 60min. The produced hydrochar was examined for their fuel properties including calorific value (HHV), proximate and ultimate analysis, thermal stability and combustion behavior, etc. The results revealed higher HTC temperature led to a higher degree of carbonization, which is beneficial for increasing carbon content and HHV of the hydrochar. The HHV of the hydrochar improved significantly up to 24.65MJ/kg after the HTC compared to 17.50MJ/kg for cannabis waste. The energy yield of hydrochar from the HTC process was in a range of 70.41-82.23%. The optimal HTC condition was observed at 230°C and a biomass-water ratio of 1:10, producing high-quality hydrochar with 24.24MJ/kg HHV and 72.28% energy yield. The hydrochar had similar fuel characteristics to lignite coal with significantly lower ash content. Additionally, recirculation of liquid effluent showed a positive influence on the HHV of hydrochar besides minimizing the release of wastewater from the HTC process. The study revealed that HTC is a promising technique for valorization of cannabis waste into high-value solid fuel, which can be potentially an alternative to coal.

Fuel properties and combustion performance of hydrochars prepared by hydrothermal carbonization of different recycling paper mill wastes

AbstractThe incineration of high‐moisture solid residues generated at the recycling paper mills represents an energetically unfavourable method of resource utilization. Alternatively, hydrothermal pre‐treatment is considered. In this study, low‐value paper sludges from three different recycling streams were hydrothermally carbonized at 205, 225, and 245°C for 3 h. The raw feedstocks and derived hydrochars were analyzed for energy properties, chemical characteristics, surface morphology, functional groups, and combustion performance employing energy densification and mass yield quantification, scanning electron microscopy, elemental analyzer, Fourier‐transform infrared spectroscopy, and thermogravimetry. The increase in reaction temperature was reported to cause a decrease in mass yield and an increase in energy densification and calorific values corresponding to 5.98%–49.35% and 10.10%–58.51% for raw fibre rejects and final sludge‐derived hydrochar, respectively. Hydrothermal carbonization (HTC) had a non‐significant influence on the energy densification of primary clarifier sludge‐derived hydrochar. Higher reaction temperatures favoured the rate of dehydration and decarboxylation, leading to hydrochars with lower H/C and O/C ratios, thereby enhancing the overall fuel properties. The low‐nitrogen and low‐sulphur fuels obtained validated the effectiveness of HTC treatment to produce high‐quality cleaner solid fuel. The burnout temperature was mostly reduced with an increase in HTC temperature. At HTC‐205 and 225°C, the ignition temperature and the combustion performance increased as a result of the HTC reaction mechanisms. HTC effectively recovered hydrochar with increased carbon content, improved energy densification, and good combustion adequacy. Hydrochar derived from recycling mills may play a role in the energy sector as a substitute for coal or in co‐combustion at coal‐fired power plants.

Multifunctional Loblolly Pine-Derived Superactivated Hydrochar: Effect of Hydrothermal Carbonization on Hydrogen and Electron Storage with Carbon Dioxide and Dye Removal.

Pore modulation via hydrothermal carbonization (HTC) needs investigation due to its crucial effect on surface that influences its multirole utilization of such ultraporous sorbents in applications of energy storage- hydrogen and capacitive- as well as for pollutant abatement- carbon capture and dye removal. Hence, loblolly pine was hydrothermally carbonized followed by KOH activation to synthesize superactivated hydrochars (SAH). The resulting SAHs had specific surface area (SSA) 1462–1703 m2/g, total pore (TPV) and micropore volume (MPV) of 0.62–0.78 cm3/g and 0.33–0.49 cm3/g, respectively. The SAHs exhibit excellent multifunctional performance with remarkably high atmospheric CO2 capture of 145.2 mg/g and high pressure cryogenic H2 storage of 54.9 mg/g. The fabricated supercapacitor displayed substantial specific capacitance value of maximum 47.2 Fg−1 at 1 A g−1 in 6 M KOH and highest MB dye removal of 719.4 mg/g. Higher HTC temperature resulted in increased surface porosity as higher SSA, TPV benefitted H2 storage and MB dye removal while superior MPV favored CO2 capture. Moderate HTC temperature ensured higher mesopore-to-macropore volume ratio favoring electrochemical performance. Isotherm modelling of the adsorbates was compared using models: Langmuir, Freundlich, Langmuir- Freundlich and Temkin.

Effects of product recovery methods on the yields and properties of hydrochars from hydrothermal carbonization of algal biomass

This contribution reports the effects of product recovery methods on the yields and properties of hydrochars produced from hydrothermal carbonization (HTC) of algal biomass. A slurry of Chlorella vulgaris with 10 wt% of solid loading was hydrothermally carbonized at 180 – 220 °C with holding time of 15 and 60 min. The resulting hydrochars were recovered by two prevailing methods, namely direct filtration and dichloromethane (DCM)-aided filtration. The results indicate that, under identical HTC conditions, compared with DCM-aided filtration, direct filtration always results in higher hydrochar yield because of the biocrude retained on its surface. The presence of residue biocrude in the hydrochars from direct filtration further leads to considerable differences in their properties, as compared with their counterparts from DCM-aided filtration. Specifically, under identical HTC temperature and holding time, DCM-aided filtration yields hydrochars of lower volatile matter contents but higher fixed carbon and ash contents, as compared with the hydrochars from direct filtration. Direct filtration generally recovers hydrochars of greater higher heating values and energy-based yields as compared to DCM-aided filtration. The product recovery methods show considerable impacts on the concentrations of Na, K, Mg, and Ca and their retentions in the hydrochars at 220 °C for 60 min, with higher concentrations and retentions of these elements being observed in the hydrochars from DCM-aided filtration. The hydrochars at 220 °C for 15 and 60 min from DCM-aided filtration show higher specific reactivity of 0.040 – 0.058 min−1 and 0.066 – 0.096 min−1 at hydrochar conversions of ≤ 82 % and ≤ 78 %, respectively, as compared with their direct-filtration counterparts, due to their higher concentrations of catalytic alkali and alkaline earth metals. These findings highlight the importance of considering product recovery methods when comparing the yields and properties of hydrochars from HTC of algae reported in the literature.

Evaluating combustion characteristics and combustion kinetics of corn stover-derived hydrochars by cone calorimeter

This study investigated the combustion properties of corn stover-derived hydrochars using cone calorimeter. Hydrochars were prepared by hydrothermal carbonization (HTC) at 200, 230, and 260 °C for 30 min. Six different heat fluxes (5–50 kW/m2) were applied to hydrochars to determine critical heat flux (CHF), ignition temperature, thermal response, peak heat release rate (pHRR), thermal hazard risk, and combustion efficiency. Results show that increasing the HTC temperature decreased the CHF and ignition temperature but increased the thermal resistivity. Increasing the heat flux decreased the thermal resistivity and ignition time of all the hydrochars. Thermal hazard analysis indicated that the hydrochars posed lower thermal risk than raw corn stover. Finally, combustion kinetics were proposed using two parallel first order reactions for volatile matters and fixed carbon. The reaction rate of volatile matter was significantly higher than the reaction rate of fixed carbon. HTC increased the fixed carbon activation energies to as high as 24.0 MJ/mol. Overall, HTC forms hydrochars which are less flammable, more stable, and a lower thermally risk material for piloted ignition than raw corn stover.

The stability of carbon from a maize-derived hydrochar as a function of fractionation and hydrothermal carbonization temperature in a Podzol

Hydrochar (HC) produced by the hydrothermal carbonization (HTC) of typically wet biomass is generally considered to be less effective for carbon (C) sequestration in soils compared to biochar (BC) by pyrolysis, due to a higher content of more easily decomposable C. Although the recalcitrance of HC is suggested to improve with increasing HTC production temperature, the way it interacts and becomes associated with soil organic matter (SOM) fractions of different stabilities against decomposition, may also influence its effectiveness for C sequestration in soils. In that respect, this study aimed to verify the potential of HCs from maize silage produced at different HTC temperatures (190, 210 and 230 °C) for C sequestration in a HC-amended sandy loam Podzol. To do this, we conducted a pot trial experiment and traced the fate of HC-derived C (HC-C) within different SOM fractions, namely the free- and occluded particulate organic matter (POMF and POMO, respectively) fractions and that comprising organic matter (OM) bound to clays (OMCl). Approx. 1 year after applying 5% of the different HTC temperature HCs to the soil, the SOM fractions were isolated by density fractionation for each HC treatment (HC190, HC210 and HC230) and the control (absent of HC). All fractions and the HCs were analyzed for organic C (OC) content and isotopic signatures (δ 13C). From the δ 13C signatures, the amount of HC-C and native soil organic carbon (SOC) within each fraction was calculated. Increased C contents and decreased H/C and O/C ratios were observed with increasing HTC production temperatures, which suggests a lower stability for the low temperature HC. After ca. 1 year, a loss of ~ 20–23% of the bulk soil TOC was found in the HC-amended soils. The POMF fraction of the HC-amended soils showed losses of 68–81% HC-C and 52–72% native SOC, which may be due to a positive priming effect caused by HC addition. The POMO and OMCl fractions of the HC-amended soils contained more OC than the control, indicating the integration of HC-C together with SOM within these more stable fractions, while the effect of HTC production temperature on the level of decomposition of the resultant HCs was negligible. In all HC treatments, the OMCl fraction comprised the least amount of HC-C, thus showing the weakest response to C amendment. In conclusion, long(er)-term research on the C net balance that accounts for the observed priming-induced TOC losses and the HC-C enrichment in more stable fractions is required to verify the potential of the different HCs for the purpose of C sequestration in soils.Graphical

Effect of hydrothermal carbonization on woody biomass: From structure to reactivity

Hydrothermal carbonization (HTC) pretreatment is an effective method to upgrade the low quality biomass properties. In this work, the pinewood (PIW) and poplar wood (POW) were selected to study the effect of HTC (180–240 °C) on woody biomass structure and reactivity. The results showed that the slight and moderate HTC can make the cellulose structure more ordered, while the severe HTC leaded to the decomposition of cellulose structure. The mesoporous specific surface area and pore volume increased with the HTC temperature, and the pore structure of PIW was more developed than that of POW. The slight HTC had little effect on cellulose structure and the diffusion effect played the dominant role. The severe HTC increased the relative content of lignin and the pyrolysis followed the high order reaction model. The model-free method was used to determine the relationship between T-β-X, and the specific temperature THTC/Traw was calculated. The THTC/Traw value of PIW and POW located in the range of 0.938–1.340 and 0.924–1.422, indicating the HTC pretreatment had great effect on POW pyrolysis reactivity.

Study on the Effect of Hydrothermal Carbonization Parameters on Fuel Properties of Chicken Manure Hydrochar.

Economic development and population growth lead to the increased production of chicken manure, which is a problematic organic waste in terms of its amount, environmental threats, and moisture content. In this study, hydrothermal carbonization, an emerging way of waste disposal, was performed on chicken manure to produce an energy-rich material called hydrochar. The effects of hydrothermal carbonization temperature (180, 240, 300 °C) and process time (30, 90, 180 min) were summarized. Proximate and ultimate analysis, as well as low and high heating values were applied both on raw material and derived hydrochars. Additionally, the performance of the process was examined. The obtained results show that hydrothermal carbonization is a feasible method for chicken manure disposal and valorization. Although the process time did not influence the fuel properties of chicken manure considerably, a higher temperature led to a significantly higher heating value, reaching 23,880.67 ± 34.56 J × g−1 at 300 °C and 180 min with an improvement of ~8329 J × g−1 compared with raw chicken manure (15,551.67 J × g−1). Considering the energy gain value, the hydrochar derived at 240 °C in 30 min had the best result. Moreover, the energy consumption for this process was relatively low (124.34 ± 8.29 kJ × g−1). With its still feasible fuel properties and high heating value of 20,267.00 ± 617.83 kJ × g−1, it was concluded that these parameters of chicken manure hydrochar are the most beneficial and present a potential alternative for conventional fuel.

Hydrothermal carbonization of kitchen waste: An analysis of solid and aqueous products and the application of hydrochar to paddy soil

Hydrothermal carbonization (HTC) technology can potentially be used to safely and sustainably utilize kitchen waste (KW). However, the characteristics of HTC solid products (hydrochar) and aqueous products (HAP) based on different types of KW have not yet been clarified. Here, four types of KW, cellulose-based (CL), skeleton-based (SK), protein-based (PT), and starch-based (ST) KW, were used for HTC at 180 °C, 220 °C, and 260 °C. The basic physicochemical properties and structures of hydrochars and HAP were analyzed, and the effects of different hydrochars on rice growth were characterized. HTC decreased the H/C and O/C of KW. All hydrochars were acidic (3.12 to 6.78) and the pH values increased with the HTC temperature, while high HTC temperature reduced the porosity of hydrochars. HTC promoted the enrichment of total carbon (up to 78.1 %), total nitrogen (up to 62.6 %), and total phosphorus (up to 171.6 %) in KW. More carbon (60.7–88.0 %) and nitrogen (up to 87.4 %) were present in the hydrochars than in the HAP. The relative content of C1s increased and O1s decreased in CL and ST hydrochars as the HTC temperature increased, while the opposite pattern was observed for SK and PT hydrochars. The dissolved organic matter (DOM) of different hydrochars and HAP were mainly humus-like substances. The biodegradability of the DOM in HAP was often higher than the corresponding hydrochar, and their DOM biodegradability increased with the HTC temperature. The content of heavy metals from different hydrochars did not exceed the relevant thresholds of fertilizer standards. Rice grain yield increased by 3.7–11.1 % in the hydrochar treatments without phosphate fertilizer addition compared with the control treatment. The results of this study provide new theoretical and empirical insights into the potential for HTC technology to be used for the recycling of KW and its products in the agricultural environment.

Synthesis of nitrogen-enriched hydrochar via co-hydrothermal reaction of liquid digestate and corn stalk.

Synthesis of carbon material from low-cost and sustainable precursors has been intensively explored in recent years. In this study, a nitrogen (N)-enriched hydrochar was developed via a facile one-step hydrothermal carbonization (HTC) of corn stalk (CS) with liquid digestate (LD) of food waste. The LD substituted water and functioned as the N precursor during HTC. The physicochemical properties of hydrochar derived at different HTC temperatures (180-300 °C) were examined and the reaction mechanism was investigated. Intermolecular dehydration and condensation were the primary reactions in the HTC process of CS without LD. The CS-chars maintained the original structure and morphology of the raw corn stalk. The ammonia and inorganic salts in LD promoted the lignin removal, and accelerated the cleavage of the glycosidic linkages of the polysaccharide and hydrogen bonds of cellulose. Benefited from the ammonia and metals in the LD, the recalcitrance structure of the corn stalk was disrupted during the co-HTC even at a low temperature of 220 °C. Moreover, carbon spheres were observed in the LDCS-chars, indicating the LDCS-chars were resulted from sequential hydrolysis, dehydration and condensation during co-HTC reactions. Reactions between N compounds in the LD and derivatives from CS contributed to N doping. The N content of LDCS-chars achieved 4.95% at 260 °C and 83.94% of the N was presented as pyridinic-N. Co-hydrothermal treatment of CS and LD not only enhanced the characteristics of hydrochar, but also recovered two-thirds of ammoniacal N from the digestate to reduce greenhouse gas emission.

Phosphorus release from hydrothermally carbonized digested sewage sludge using organic acids

Hydrothermal carbonization (HTC) is a treatment technique with great potential for sanitizing digested sewage sludge (SS) and converting it into valuable products. In particular, phosphorus (P) recovery from hydrothermally carbonized SS has attracted special attention in recent years. This work aims to examine the leaching efficiency of P and the consequent release of metals and heavy metals from SS hydrochars (at 180, 215 and 250 °C) using organic acids (oxalate and citrate) over a range of pH values (0–4) and extraction times (5 min-24 h). Both organic acids triggered P extraction efficiencies exceeding 75 % at the lowest pH, but only oxalate reached a nearly complete P release from hydrochars at pH > 0 and for all carbonization temperatures. Low HTC temperature (180 °C) and short extraction time (5 min) were the optimal conditions treatment for P recovery when reacted in oxalate solutions of maximal pH buffering capacity (pH = 1.4). However, oxalate leaching also transferred metals/heavy metals into the P-leachate, with the exception of Ca being retained in the solid residue from HTC as Ca-oxalate precipitate. Different characterization methods confirmed the presence of this precipitate, and provided information about the surface and morphological changes of the SS hydrochars following acid treatment. The results suggest that HTC not only a promising technique to sanitize and reduce the volume of SS, but also an efficient means for P recovery using oxalic acid, thus contributing to the circular economy of P.

Hydrothermal carbonization (HTC) of dairy waste: effect of temperature and initial acidity on the composition and quality of solid and liquid products.

Background: Hydrothermal carbonization (HTC) of dairy processing waste was performed to investigate the effect of temperature and initial pH on the yield and composition of the solid (hydrochar) and liquor produced. All hydrochars met the EU requirements of organo-mineral solid fertilizers defined in the Fertilizing Products Regulation in terms of phosphorus (P) and mineral content. Methods: Laboratory scale HTC was performed using pressurized reactors, and the products (solid and liquid) were collected, stored and analyzed for elemental composition and nutrient content using Inductively coupled plasma optical emission spectroscopy (ICP-OES), ultraviolet-visible spectrophotometry (UV-Vis) and other analytic techniques. Results: Maximum hydrochar yield (60.67%) was observed at T=180℃ and pH=2.25, whereas the maximum P-recovery was 80.38% at T=220℃ and pH=4.6. The heavy metal content of the hydrochars was mostly compliant with EU limitations, except for Ni at T=220℃ and pH=8.32. Meanwhile, further study of Chromium (Cr) species is essential to assess the fertilizer quality of the hydrochars. For the liquid product, the increase in temperature beyond 200℃, coupled with an increase in initial acidity (pH=2.25) drove P into the liquor. Simultaneously, increasing HTC temperature and acidity increased the concentration of NO 3 - and NH 4 + in the liquid products to a maximum of 278 and 148 mg/L, respectively, at T=180℃ and pH=4.6. Furthermore, no direct relation between final pH of liquor and NH 4 + concentration was observed. Conclusions: HTC allows for the production of hydrochar as a potential fertilizer material that requires further processing. Adjusting HTC conditions enhanced P-recovery in the hydrochar, while retrieving higher nitrate concentrations in the liquid product. Optimizing HTC for the production of qualified hydrochars requires further treatment of Cr content, studying the availability of P in the products and enhancing the hydrochar yield for economic feasibility.

Hydrothermal carbonization of petrochemical sludge: The fate of hydrochar and oil components

In this study, the physical and chemical properties, combustion behaviors, kinetics, and the distribution of C, O, N, and S during different hydrothermal carbonization (HTC) temperatures of petrochemical sludge (PS) were investigated. The increase in HTC temperature is favorable to obtain higher organic-dissolved oil (ODO) content and less water-soluble oil (WSO) content. The solid conversion rate of hydrochar reached a maximum of 83.90% and comprehensive combustion performance is the best at 270 °C. The higher heating values (HHVs) value of hydrochar is stable at 21.00 MJ/kg. While the HHVs value range of ODO and WSO are 32.03–38.65 MJ/kg and 13.90–19.83 MJ/kg, respectively. Except for hard to occur WSO combustion stageⅢ, the Coats-Redfern integral method is well suited for kinetic simulations of all stages of hydrochar, WSO, and ODO. The long-chain alkanes, aromatic hydrocarbons, and cycloalkanes attach to the surface of the solid particles to form ODO and further convert to hydrochar via carbonization process. Nitrogen heterocycles, amines, and ketones remain in the feedwater to form WSO. Therefore, Carbon was maximally preserved in hydrochar and ODO, while N and S were removed by migration into WSO.

Enhancing cleaner biomass-coal co-combustion by pretreatment of wheat straw via washing versus hydrothermal carbonization

Slagging, fouling and fuel segregation issues with co-combustion of wheat straw and coal could be mitigated by clean pretreatments on wheat straw such as washing or hydrothermal carbonization (HTC). Water washing (WW) could remove upwards of 90% of potassium and phosphorus, thus reducing the risk of slagging and fouling. The dehydration and demethylation reactions during HTC increased the heating value of wheat straw to 5.4%–35.7%, simultaneously more organically-bonded calcium and magnesium were removed. Conversely, the potassium retention of hydrochars was improved owing to the relatively higher specific surface area (3.153–4.693 m2g-1) than WS (1.181 m2g-1) and WW (1.375 m2g-1). Moreover, the retention of alkali metals and porous structure showed a dual effect on the co-oxidation property, varying with HTC temperatures. Hydrochars produced at 200 °C had similar ignition temperatures to a representative bituminous coal. Hydrochars produced at 220 °C showed enhanced reactivity, whereas 240 °C hydrochars had decreased reactivity and potentially problematic ash content. The activation energy of the HTC200 blends (40.71 kJ/mol for 20% ratio and 39.24 kJ/mol for 40% ratio) are lower than the WW blends. Overall, blends of 20 wt% hydrochars produced at 200 and 220 °C showed the optimum performance in terms of minimizing fuel segregation and inhibition, lowering the oxidation activation energy barrier, and reducing slagging and fouling.