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The chemical-physical processes controlling hydrothermal carbonization (HTC) are still not completely understood. This paper focuses on two aspects: the influence on the hydrochar formation of the particle size of the feedstock and the presence of solved compounds in the feedwater. To address these, brewer’s spent grains were crushed to 250 μm proved by HPLC analysis of liquid byproducts, particularly when rPW, containing readily condensable/polymerizable intermediates, is added. This has a positive effect on the yield and carbon content of the hydrochars caused mainly by an increase in its secondary char fraction. The reaction pathways involved are discussed in detail.

This study evaluates the effects of thermal hydrolysis (TH) pretreatment on anaerobic digestion (AD), through results obtained by biochemical methane potential (BMP) tests under mesophilic conditions (35 °C). Thickened sludge from a wastewater treatment plant (WWTP) was thermally treated under two different temperatures (150 and 170 °C) and reaction times (30 and 60 min). Results show a significant increase in soluble COD, compared with the untreated sludge, when sludge was treated at 170 °C for 60 min. Moreover, the following BMP tests point out that TH pretreatment of sludge accelerated the AD rate and increased the biogas yield contributing to an increase in methane production, ranging between 17 and 24% compared with the raw sludge. Furthermore, the hydrolysis constant was estimated and methane production and degree of disintegration of the TH pretreated sludge were correlated, in order to deep the knowledge on the hydrolysis as the AD rate-limiting step. Further, the combined effects of TH pretreatment and AD on sludge show a reduction of total and volatile solids up to 19% and 24%, respectively.

Co-firing of biomass and coal may increase short-term renewable fuel usage. However, the lower heating value and higher reactivity (at lower temperatures) of raw biomass can result in fuel segregation in boilers, causing burnout at lower temperatures, lower steam generation efficiency and fouling. In addition, the relatively high water content of some biomasses requires extensive drying prior to combustion. These issues may be addressed by hydrothermally carbonizing moist biomasses to produce hydrochars that more closely resemble coal’s properties prior to co-firing. In the present work, we probe the co-oxidation behavior of a series of hydrothermally carbonized biomass samples over a range of hydrochar-coal blend ratios to determine the degree of carbonization necessary to reduce fuel segregation. However, due to the presence of an extractable amorphous secondary char, even highly carbonized hydrochars have considerably higher oxidative reactivity than a representative bituminous coal sample. When blended, the hydrochars and coal display distinct derivative thermogravimetric oxidation ranges, in which a low-temperature peak is dominated by the secondary char oxidation, followed by a high-temperature char oxidation peak of the primary solid hydrochar. After extraction of the secondary char, the primary char displays a lower reactivity than the coal. As a co-fired fuel, it appears that blending hydrochars up to 10 wt% with a bituminous coal is possible as a partial fuel substitution. To increase the percentage of hydrochars blended with coal, it may be necessary to extract this secondary char (which contains valuable biofuels and platform chemicals) before blending.

The present study addresses the coupling of hydrothermal carbonization (HTC) with anaerobic digestion (AD) in wastewater treatment plants. The improvement in biomethane production due to the recycling back to the anaerobic digester of HTC liquor and hydrochar generated from digested sludge is investigated and proved. Mixtures of different compositions of HTC liquor and hydrochar, as well as individual substrates, were tested. The biomethane yield reached 102 ± 3 mL CH4 g−1 COD when the HTC liquor was cycled back to the AD and treated together with primary and secondary sludge. Thus, the biomethane production was almost doubled compared to that of the AD of primary and secondary sludge (55 ± 20 mL CH4 g−1 COD). The benefit is even more significant when both the HTC liquor and the hydrochar were fed to the AD of primary and secondary sludge. The biomethane yield increased up to 187 ± 18 mL CH4 g−1 COD when 45% of hydrochar, with respect to the total feedstock, was added. These results highlight the improvement that the HTC process can bring to AD, enhancing biomethane production and promoting a sustainable solution for the treatment of the HTC liquor and possibly the hydrochar itself.

With the increasing needs of clean water supplies, the use of biomass wastes and residues for environmental remediation is essential for environmental sustainability. In this study, the residues from winery and citrus juice industries, namely grape skin and orange peel, respectively, were first converted to hydrochars by hydrothermal carbonization (HTC) and then a cationic dye (methylene blue) adsorption was studied on hydrochars. Hydrochars from both feedstocks were produced at three different temperatures (180, 220, and 250 °C) and a fixed residence time (1 h) to evaluate the hydrochar’s performance on the dye adsorption. The hydrochars were characterized in terms of their pH, pH at point of zero charge (pHPZC), surface functionalities, and surface area. A batch adsorption study of the dye was carried out with variable adsorbate concentration, pH, and temperature. Two adsorption isotherms namely Langmuir and Freundlich models were fitted at 4, 20, and 36 °C. The thermodynamic properties of adsorption (Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)) were evaluated from the isotherms fittings. Results showed that the dye adsorption on both hydrochars was significant and followed Langmuir isotherm. The maximum adsorption capacity on citrus waste hydrochar was higher than the winery waste hydrochar at any corresponding HTC temperature. Although hydrochars showed the lowest surface area (46.16 ± 0.11 and 34.08 ± 1.23 m2/g for citrus and winery wastes, respectively) at 180 °C, their adsorption was the highest, owing to their maximum density of total oxygen functional groups (23.24 ± 0.22 and 32.69 ± 1.39 µmol/m2 for citrus and winery wastes, respectively), which decreased with the increase in HTC temperature. This research shows a sustainable route for the production of highly effective adsorbent materials at lower HTC temperatures from citrus and winery wastes.

Hydrothermal carbonization (HTC) technology is addressed in the framework of sewage digestate management. HTC converts digestate into a stabilized and sterilized solid (the hydrochar) and a liquor (HTCL) rich in organic carbon. This study aims to optimize the HTC operating parameters, namely the treatment time, in terms of hydrochar production, HTC slurry dewaterability, HTCL bio-methane yields in anaerobic digestion (AD), and process energy consumption. Digestate slurry was processed through HTC at different treatment times (0.5, 1, 2 and 3 h) at 190 °C, and the dewaterability of the treated slurries was addressed through capillary suction time and centrifuge lab-testing. In addition, biochemical methane potential (BMP) tests were conducted for HTCL under mesophilic conditions. Results show that by increasing the HTC treatment time the dewaterability was further improved, ammonium concentration in HTCL increased, and methane potential of HTCL decreased. 0.5 h HTCL had the highest bio-methane potential of 142 ± 3 mL CH4/g COD yet the treatment time was not sufficient for improving the slurry's dewaterability. HTC treatment time of 1 h at 190 °C was identified as the optimum trade-off for improved dewaterability and utilisation of HTCL for biogas production. 1 h HTCL bio-methane potential can cover around 25% of the HTC and AD thermal and electrical energy needs without considering the eventual use of the hydrochar as a biofuel.

Hydrothermal carbonization (HTC) of pure cellulose (CE) and birchwood (BW) samples was carried out at temperatures between 160 and 280 °C, 0.5 h residence time and biomass-to-water ratio 1:5, to investigate the reactivity of cellulose in lignocellulosic biomass. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) showed that the CE samples remained unaltered at temperatures up to 220 °C, but were significantly decomposed at 230 °C producing a thermal recalcitrant aromatic and high energy-dense material. FTIR showed that dehydration and aromatization reactions occurred at temperature equal or higher than 230 °C for the CE samples while a similar increase in aromatization for the BW hydrochars was evident only at temperatures equal or higher than 260 °C. Acid hydrolysis, TGA and FTIR suggested that a higher thermal resistance of naturally occurring cellulose in BW (when compared to CE sample) could be related to a ‘protecting shield’ offered by interlinked lignin in the plant matrix.

Globally, as societies urbanize and demand for energy increases, the need to manage mounting quantities of municipal solid waste (MSW), produce renewable energy, and insure clean water supplies becomes more pressing each year. These issues could be addressed by integrating pyrolysis of MSW to recover liquid and gaseous biofuels and a solid biochar, with CO2 activation of the latter to produce activated biochars for water treatment. This potential conversion pathway is experimentally demonstrated by pyrolyzing a model MSW stream at 408 °C, the peak mass loss rate pyrolysis temperature and compared to pyrolysis at 900 °C. As pyrolysis temperature increases, we see conversion of plastic intermediaries into paraffins and polycyclic aromatic compounds, though the desirable gas components (methane, hydrogen, carbon monoxide) of the pyrolysis gas increase substantially. The CO2 activated biochars (activated at 600 °C and 900 °C) show surface areas over 300 m2/g, with the lower pyrolysis temperature and higher activation temperature yielding the highest areas. Adsorption experiments were performed with methylene blue to determine the ability of the activated MSW-biochar to remove organic pollutants from water. Adsorption is well described by the Langmuir isotherm, with equilibrium adsorption capacities upwards of 250 mgdye/g for all activated biochars.

This study reports the implications of using spent coffee hydrochar as substrate for anaerobic digestion (AD) processes. Three different spent coffee hydrochars produced at 180, 220 and 250 °C, 1 h residence time, were investigated for their biomethane potential in AD process inoculated with cow manure. Spent coffee hydrochars were characterized in terms of ultimate, proximate and higher heating value (HHV), and their theoretical bio-methane yield evaluated using Boyle-Buswell equation and compared to the experimental values. The results were then analyzed using the modified Gompertz equation to determine the main AD evolution parameters. Different hydrochar properties were related to AD process performances. AD of spent coffee hydrochars produced at 180 °C showed the highest biomethane production rate (46 mL CH4/gVS.d), a biomethane potential of 491 mL/gVS (AD lasting 25 days), and a biomethane gas daily composition of about 70%.

Opuntia ficus-indica cladodes are a potential source of solid biofuel from marginal, dry land. Experiments assessed the effects of temperature (180-250°C), reaction time (0.5-3h) and biomass to water ratio (B/W; 0.07-0.30) on chars produced via hydrothermal carbonization. Multivariate linear regression demonstrated that the three process parameters are critically important to hydrochar solid yield, while B/W drives energy yield. Heating value increased together with temperature and reaction time and was maximized at intermediate B/W (0.14-0.20). Microscopy shows evidence of secondary char formed at higher temperatures and B/W ratios. X-ray diffraction, thermogravimetric data, microscopy and inductively coupled plasma mass spectrometry suggest that calcium oxalate in the raw biomass remains in the hydrochar; at higher temperatures, the mineral decomposes into CO2 and may catalyze char/tar decomposition.

This study investigates the suitability of a sequencing batch reactor (SBR) for treating the liquor (HTCL) derived from hydrothermal carbonization (HTC) of sewage sludge in addition to the influent municipal wastewater. The SBR was fed for 80 days with an increasing mixing ratio HTCL/municipal wastewater. HTCL was used as external carbon source to enhance the denitrification process in the water line of the wastewater treatment plant (WWTP). The feeding of the HTCL caused an overloading in the COD and TKN concentration of the biological treatment equal to, respectively, 25% and 8% (Period II), 50% and 16% (Period III) and 100% and 32% (Period IV). Results revealed that good efficiencies of COD removal were obtained during the entire experimental test, accounting up to 91% in Period IV. Moreover, the removal of TN was improved increasing from 28% in the reference period (Period I), where no HTCL was fed, to 33%, 47% and 64% respectively in Period II, III and IV. Thus, an improvement in the denitrification process was obtained when HTCL was fed to the biological reactor in addition to the influent wastewater. The implementation of the SBR system was supported by nitrate uptake rate (NUR) tests and respirometric assays to evaluate the nitrate removal after the addition of HTCL and the fraction of readily biodegradable COD (RBCOD) and soluble biodegradable COD (sCODbio) on the total COD of the HTCL.

Hydrothermal carbonisation was used to upgrade fuels from two types of agro-industrial wastes: olive tree trimmings and olive pulp. Hydrochar yield, elemental and proximate analyses, thermal stability, higher heating value (HHV), and energy yield at different reaction temperatures (120, 150, 180, 200, 220, 235 and 250 °C) and solid load (biomass to water ratios − B/W − equal to 7, 10, 15 and 25%) were assessed for a fixed reaction time of 30 min. HHV varied linearly with hydrochar mass yield and reaction temperature in the temperature range 180–250 °C. Solid load proved to be a crucial parameter in determining the energy properties of hydrochars. The higher B/W, the higher were the degree of carbonisation (in terms of fixed and total carbon), the hydrochar HHV, and the hydrochar yield. Elemental analysis showed that during HTC, olive pulp samples underwent a greater degree of carbonisation when compared to the corresponding olive tree trimmings residues. High solid load and high reaction temperature promoted secondary char formation. Secondary char showed a sphere-like structure formed by overlapping layers. EDS microanalysis showed that secondary char is characterised by a significantly higher carbon content than parent primary char, thus confirming its contribution towards enhancing the HHV of hydrochars.

Hydrothermal carbonization (HTC) is a thermochemical process that can reduce the environmental burdens of wet, heterogeneous biomasses such as the organic fraction of municipal solid waste (OFMSW). Whilst the effect of processing parameters on hydrochar properties is well known, post-treatments to valorize hydrochars are infrequently investigated. Moreover, more severely carbonized hydrochars have a reactive species present on their surface that may limit hydrochars’ use as a solid fuel or soil amendment/environmental adsorbent. To address these potential limitations, a low-temperature (180 °C) thermal treatment and a chemical extraction (1:4 methanol: dichloromethane) were performed on OFMSW hydrochars. The thermal extraction removed up to 12% of this reactive volatile matter, comprised of alkanes, furans, ketones, and fatty acids. Chemical extraction removed up to 61% of the hydrochar, and the extract comprised mostly fatty acids, suggesting a potential pathway for recovery of fatty acids and condensation of fuel molecules in the solid hydrochar. The higher heating values of the extracts were much greater than the non-extractable solid hydrochar. The non-extractable primary char showed similar oxidative and pyrolytic behavior to a standard bituminous coal. The results indicate that HTC could valorize OFMSW by converting this wet waste into a dry solid fuel, soil amendment or environmental adsorbent while simultaneously extracting valuable biodiesel and biofuel precursors. Given increasing legislative pressure to divert OFMSW from landfills, this new pathway offers an alternative to traditional anaerobic digestion management strategies that produce only methane as a green energy product.

The solubility of grape (Vitis vinifera L.) seed oil in supercritical CO2 was measured in the temperature range 313–343 K and pressure range 20–50 MPa using the dynamic technique. Several data and global trends were reported. The results show that, at constant temperature, the solubility increases with the increase in pressure, while the effect of the temperature is different for low and high pressure. The experimental data were modeled by eight density-based models and a thermodynamic model based on the Peng-Robinson equation of state. By best fitting procedures, the “free parameters” of the various models were calculated: in general, all the tested models have proved to be able to predict the solubility of grape seed oil in supercritical CO2. Differences in model capabilities have been discussed based on the main characteristics of the various models, evidencing their distinct and common features. The predictive capability of the thermodynamic model was comparable to that of the density-based models.

Hydrothermal carbonization (HTC) was evaluated as a promising treatment to enhance the biomethane potential during anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The OFMSW was carbonized at different conditions and HTC products were tested for biomethane potential into AD. Results proved that the use of HTC liquid and slurry into AD led to an increase in biomethane production up to 37% and 363%, respectively, compared to OFMSW. Methane production increased as the HTC process severity decreased, reaching its maximum at 180 °C, 1 h for both HTC products. Energy assessment demonstrated that the combustion of biogas produced by AD of HTC liquid and slurries covers up to 30% and 104% of the HTC thermal demand, respectively. When the energy from hydrochar and biogas combustion was recovered, the process efficiency reached 60%. Hence, HTC coupled with AD demonstrates to be an efficient way to valorize OFMSW.

This study focuses on the maximization of the phenolic compounds of spent coffee grounds, by coupling hydrothermal delignification with ultrasonic assisted extraction. Temperatures of 200°C, 230 °C and 260 °C were applied for hydrothermal treatment for 1h and 3h. Produced hydrochars contain high values of fuel ratio (0.35 - 0.69) compared to raw feedstock (0.20). The increment of the reaction severity decreases the energy yield from 95.23 % to 82.99 %. After the hydrothermal treatment, the total phenolic content (TPC of the process water), determined relatively to a gallic acid standard (GAE), was found to be in a similar range for all process conditions (9.52 – 8.07 mg GAE / mg of dry sample). Using methanol as a solvent into produced dry hydrochars during ultrasonic assisted extraction reveals the highest values of TPC (20.33 – 11.66 mg GAE/ mg of dry sample).This study focuses on the maximization of the phenolic compounds of spent coffee grounds, by coupling hydrothermal delignification with ultrasonic assisted extraction. Temperatures of 200°C, 230 °C and 260 °C were applied for hydrothermal treatment for 1h and 3h. Produced hydrochars contain high values of fuel ratio (0.35 - 0.69) compared to raw feedstock (0.20). The increment of the reaction severity decreases the energy yield from 95.23 % to 82.99 %. After the hydrothermal treatment, the total phenolic content (TPC of the process water), determined relatively to a gallic acid standard (GAE), was found to be in a similar range for all process conditions (9.52 – 8.07 mg GAE / mg of dry sample). Using methanol as a solvent into produced dry hydrochars during ultrasonic assisted extraction reveals the highest values of TPC (20.33 – 11.66 mg GAE/ mg of dry sample).

Conventional activated sludge systems, still widely used to treat wastewater, produce large amounts of solid waste that is commonly landfilled or incinerated. This study addresses the potential use of Hydrothermal Carbonization (HTC) to valorize sewage sludge residues examining the properties of hydrochars depending on HTC process conditions and sewage sludge withdrawal point. With increasing HTC severity (process residence time and temperature), solid yield, total Chemical Oxygen Demand (COD) and solid pH decrease while ash content increases. Hydrochars produced from primary (thickened) and secondary (digested and dewatered) sludge show peculiar distinct properties. Hydrochars produced from thickened sludge show good fuel properties in terms of Higher Heating Value (HHV) and reduced ash content. However, relatively high volatile matter and O:C and H:C ratios result in thermal reactivity significantly higher than typical coals. Both series of carbonized secondary sludges show neutral pH, low COD, enhanced phosphorous content and low heavy metals concentration: as a whole, they show properties compatible with their use as soil amendments.

Hydrothermal carbonization of the organic fraction of municipal solid waste (OFMSW) could mitigate landfill issues while providing a sustainable solid fuel source. This paper demonstrates the impact of processing conditions on the formation and composition of hydrochars and secondary char of OFMSW. Harsher conditions (higher temperatures, longer residence times) decrease generally the solid yield while increasing the higher heating value (HHV), fixed carbon, and elemental carbon. Energy yields upwards of 80% can be obtained at both intermediate and high temperatures (220 and 260–280 °C), but the thermal stability and reactivity of the intermediate hydrochars suggest the formation of a reactive secondary char that condenses on the surface of the primary hydrochar. This secondary char is extractable with organic solvents and is comprised predominantly of organic acids, furfurals and phenols, which peak at 220 and 240 °C and decrease at higher carbonization conditions. The HHVs of secondary char are significantly higher than those of primary char.

Reliable information on the decomposition of polysaccharides is important to evaluate the evolution and properties of hydrothermally carbonized chars. Hyperspectral imaging offers a quick and robust alternative to expensive and time-consuming laboratory methods to determine the polysaccharide contents of biomass and biomass-derived chars. Here, we show that the decomposition of hemicellulose and cellulose were visible in the acquired hyperspectral images even without image calibration. Image regression based on sample holocellulose, glucan and the sum of xylan, galactan, arabinan and mannan provided good calibration models and enabled visualizing the decomposition of polysaccharides based on carbonization temperature. Hyperspectral imaging thus provides a non-destructive alternative to traditional polysaccharide analyses of hydrochars for laboratory and potential future industrial applications.

Food processing residues are often rich in bioactive compounds which, if properly extracted and recovered, can be re-utilized as food supplements or in nutraceutical formulations, with obvious advantages from the health and economical standpoints. High pressure extraction processes can be utilized for such purpose. They are usually performed or using supercritical fluids, namely supercritical CO 2 suitable for extracting non-polar solutes, or using pressurized liquids, for instance water capable to extract polar and semi-polar compounds. This short review highlights the application of high pressure technologies for the extraction of bioactives from food processing residues with special emphasis on the most recent works and patents.

Supercritical water gasification (SCWG) of biomass was studied by means of a stoichiometric thermodynamic model. Such approach is based on reaction equilibria and it allows calculating the extent of the single reactions involved. A very simple model was proposed, involving only 6 components and 3 independent reactions. The model was validated against literature experimental data for different feedstock and it was used to understand the influence of biomass and operating conditions. The analyses allowed calculating the values of the reaction extent of water-gas shift (WGS) and CO methanation at equilibrium: a graphical approach was proposed in order to interpret the outcomes. Results showed that the influence of pressure is very limited. Moreover, it was observed that the maximum H 2 production is linked to a parameter ψ , function of the H/C and O/C ratios of the feedstock. Finally, considerations about the role of WGS and methanation in the production of H 2 were traced.

Polyphenols were extracted from grape skins and defatted grape seeds (cultivar: Pinot Nero) by using subcritical water in a semi-continuous mode. Extractions were performed at a pressure of 10 MPa, at three different temperatures (80, 100 and 120 °C) and with two water flows. For both skins and defatted seeds, total polyphenol (TP) yield significantly increased with temperature: for skins from 44.3 ± 0.4 to 77 ± 3 mg/g, while for defatted seeds from 44 ± 2 to 124 ± 1 mg/g when the temperature increased from 80 to 120 °C. Importantly, TP yield decreased with flow rate at constant temperature. The extraction kinetics was simulated by a simple model from literature. The model adjustable parameters were calculated by best fitting procedures with experimental data: the model fitted the experimental kinetics curves in a satisfactory way, providing reference values for the adjustable parameters. The present research outlines the potentialities of using subcritical water for extracting valuable polyphenols from food processing by-products, and the effect of the operating conditions. Moreover, it proves that a very simple model from literature allows the interpretation of the extraction curves on the base of mass transfer and partition coefficients.

The effect of the main process variables affecting the supercritical CO 2 extraction of oil from seeds (namely grape seeds) was investigated, both experimentally and through modeling. The dependency of the extraction kinetics on the variables more tested in the literature (pressure, temperature, particle size and solvent flow rate) was confirmed, and original trends were obtained for the less investigated variables, such as the bed porosity ɛ and the extractor diameter to length ratio ( D / L ). The extraction kinetics did not depend on ɛ for 0.23 ≤ ɛ ≤ 0.41, while a further decrease in ɛ lowered the extraction rate, likely due to the occurrence of channeling. The effect of a variable D / L ratio was studied letting constant the ratio of substrate mass to CO 2 mass flow rate: the lower was D / L , the lower the specific CO 2 consumption. Through modeling, the values of internal and external mass transfer parameters were calculated and critically discussed on the basis of well-known literature correlations.

Summary Grape seeds collected from vinification of various grape varieties were extracted by supercritical CO2 for oil recovery. The defatted residues thus obtained were considered as a re-utilisable co-product and assessed for phenolic content, reducing capacity and inhibitory activities against mammalian α-amylase and α-glucosidase enzymes. Supercritical CO2 treatment led to higher recovery of anthocyanins. Reducing capacity of phenolic extracts reached up to ~2200 mmolFe(II) kg−1, much higher than that of various natural phenolic sources. The anthocyanin-rich extracts showed the highest inhibitory effectiveness towards α-glucosidase (I50 value equal to ~40 μg gallic acid equivalents (GAE)/mL ~ half than acarbose). Inhibitory effectiveness towards α-amylase activity was similar among grape varieties, with I50 values comparable to that of acarbose and correlated with proanthocyanidin contents. These results could pave the way for an efficient processing of grapes, including cascade processes, namely: winemaking, oil extraction from recovered grape seeds and phenolic extraction from defatted grape seeds as potential cost-effective nutraceuticals.

Supercritical water gasification (SCWG) is an interesting technology for the production of energy from wet and residual biomass. To date, the complete understanding of the fundamental phenomena involved in SCWG is still an open issue. An interesting aspect to be investigated is represented by the interactions among the single constituents of biomass, such as cellulose and lignin. This can be accomplished by using glucose and phenol as model compounds. In the present study, four glucose/phenol mixtures were utilized. All mixtures presented a constant organics mass fraction of 5%, where the relative fraction of phenol ranged from 0% (pure glucose) to 30%. The mixtures were gasified at 400 °C and 25.0 MPa in a continuous tubular reactor, with a residence time between 10 and 240 s. Results showed that, at the considered reaction conditions, phenol mostly behaves as a sort of inert in terms of total gas production, although it plays an inhibitory action towards H 2 . The analysis of the liquid phase revealed that phenol likely inhibits Cannizzaro and de-carbonylation reactions and it advantages the pathways involving de-hydration reactions.

The objective of this study was to evaluate the feasibility of supercritical oil extraction from Jatropha curcas L (JCL). The influence of the operating conditions on oil yield, free fatty acid content of JCL oil, and oil quality was examined, which included pressure, temperature, particle size, and percentage of hull. The conditions for the fractionation of fatty acid were selected to obtain good-quality oil for biodiesel production. Finally, an experiment was conducted under different conditions in which the greatest amount of free fatty acids (FFA) (26.3 wt.%) was extracted during the first fractions and then the pressure was increased to achieve good oil removal (91 wt.% oil yield) performance with low content of free fatty acids (1 wt.%). This study has a promising role to fill as a more cost-effective processing technology, and it is not necessary to carry out a degumming, esterification and dehydration in the oil of the last fractions. Furthermore, all the phorbol ester was removed from the oil by conducting a supercritical extraction using CO 2 .

Supercritical water gasification (SCWG) is an emerging technology for the valorization of (wet) biomass into a valuable fuel gas composed of hydrogen and/or methane. The harsh temperature and pressure conditions involved in SCWG (T > 375 °C, p > 22 MPa) are definitely a challenge for the manufacturing of the reactors. Metal surfaces are indeed subject to corrosion under hydrothermal conditions, and expensive special alloys are needed to overcome such drawbacks. A ceramic reactor could be a potential solution to this issue. Finding a suitable material is, however, complex because the catalytic effect of the material can influence the gas yield and composition. In this work, a research reactor featuring an internal alumina inlay was utilized to conduct long-time (16 h) batch tests with real biomasses and model compounds. The same experiments were also conducted in batch reactors made of stainless steel and Inconel 625. The results show that the three devices have similar performance patterns in terms of gas production, although in the ceramic reactor higher yields of C2+ hydrocarbons were obtained. The SEM observation of the reacted alumina surface revealed a good resistance of such material to supercritical conditions, even though some intergranular corrosion was observed. View Full-Text

The current study focuses on the recovery of grape seed oil by supercritical CO2 extraction. Grape seeds from six grape cultivars were extracted in two subsequent harvesting years, and the resulting oils were characterized for the relative amount of: (a) lipid classes; (b) lipid acyl chains; and (c) tocopherols and tocotrienols. Comparative extractions were performed by utilizing n-hexane as solvent and by mechanical pressure. A well-established modeling approach was applied to evaluate the mass transfer parameters affecting the kinetics of supercritical CO2 extraction: with these parameters, process scale-up can be addressed. The results reported in this study testify the potentiality of grape seed oil as a source of unsaturated fatty acids and tocols. Moreover, they offer a clear picture of the similarities and differences among oils from different grape cultivars and obtained through different extraction techniques.

Biopharmaceutical, nutraceutical and food sectors are experiencing an increasing market interest in omega-3 concentrates. Fish and fish processing by-products represent the major source of lipids rich in omega-3. The present work focuses on the supercritical CO 2 fractionation of fish oil derivatives for obtaining omega-3 concentrates, which seems a promising process given that it allows utilizing low temperatures (well below 100 °C) and it can be performed also at industrial scale. The process was conceived, modeled, and evaluated in terms of the main parameters affecting its performances: solvent to feed ratio, reflux ratio, temperature, and pressure of both the fractionation column and the column head separator. The process was further optimized minimizing its operating costs. The optimum foresaw operating the column at high temperature (80 °C) and pressure (19.5 MPa), which allowed for a reduced reflux ratio (=0.92) and solvent to feed ratio (=63). At these conditions, the process cost per unit product (omega-3 concentrate) turned out to be of about 2.3 €/kg. Finally, the plant was designed for three different throughputs: 10, 100, and 300 kg/h. This allowed estimating the investment costs, in order to outline a preliminary process feasibility evaluation.

Batch reactors made of stainless steel and Inconel® 625 were used for the hydrothermal gasification of glucose and beech sawdust under both subcritical (350 °C) and supercritical (400 °C) conditions at a pressure of 30 MPa. These tests were executed over residence times ranging from 60 to 300 min. The amounts of solid, liquid and gas produced and the composition of the resulting gas phase were measured. The results showed that a higher H 2 output was achieved in the stainless steel reactors, while the Inconel® 625 reactors were more effective for the synthesis of CH 4 and light hydrocarbons. A visual observation of the metal surfaces was performed using scanning electron microscopy to explain the persistence of catalytic activity even after an aging treatment and many hours of operation.

This study evaluates and compares the composition in bioactives and the antioxidant activity of six different grape seed oils. In addition, the comparison also concerns two different techniques, namely supercritical carbon dioxide (SC-CO2) extraction and conventional solvent extraction (Soxhlet method with n-hexane as solvent). Tocopherols, tocotrienols, chlorophylls, carotenoids and total phenol contents, as well as lipophilic and hydrophilic antioxidant activities were quantified. Significant differences were noticed among grape cultivars for all the studied bioactives, as well as in the antioxidant activities. As a whole, results demonstrate that grape seed oil is a good source of tocols, and in particular of α-tocopherol, α-tocotrienol and γ-tocotrienol. These three forms constitute between 72.4 and 80.4%, and between 78.5 and 85.1% of the total tocol contents of oils extracted by n-hexane and SC-CO2, respectively. Statistical analysis showed that SC-CO2 extraction allowed for higher total tocols (362–567 mg/kg) and carotenoids (2.7–4.8 mg/kg) levels associated with higher lipophilic antioxidant activity (4.9–8.1 μmol trolox/g oil), in comparison with the extraction with n-hexane. Conversely, total phenolic content, chlorophylls content and hydrophilic antioxidant activity were not affected by the extraction method. Finally, correlations between bioactive lipophilic components and the lipophilic antioxidant activity were established and discussed.

The supercritical water gasification (SCWG) of biomass for H2 production is analyzed in terms of process development and energetic self-sustainability. The conceptual design of a plant is proposed and the SCWG process involving several substrates (glycerol, microalgae, sewage sludge, grape marc, phenol) is simulated by means of AspenPlus™. The influence of various parameters – biomass concentration and typology, reaction pressure and temperature – is analyzed. The process accounts for the possibility of exploiting the mechanical energy of compressed syngas (later burned to sustain the SCWG reaction) through expansion in turbines, while purified H2 is fed to fuel cells. Results show that the SCWG reaction can be energetically self-sustained if minimum feed biomass concentrations of 15–25% are adopted. Interestingly, the H2 yields are found to be maximal at similar feed concentrations. Finally, an energy balance is performed showing that the whole process could provide a net power of about 150 kWe/(1000 kgfeed/h).

The aim of this work is to model the supercritical water gasification (SCWG) of methanol by means of a detailed kinetics model based on elementary reactions. The challenge consists in modeling SCWG by using existing models developed for combustion or supercritical water oxidation (SCWO) and adjusting their initial conditions to make them suitable for SCWG. To this purpose, three models (GRI-Mech 3.0, Brock and Savage and Webley and Tester) were selected, implemented in MatLab ® and run. Webley and Tester's model seems to describe quite well methanol conversion as a function of time. On the other hand, some mechanisms, like water–gas shift and methanation, are not correctly predicted. The main reaction pathways are identified and outlined.

Thermo-gravimetric analysis (TGA) was performed on grape seeds, skins, stalks, marc, vine-branches, grape seed oil and grape seeds depleted of their oil. The TGA data was modeled through Gaussian, logistic and Miura–Maki distributed activation energy models (DAEMs) and a simpler two-parameter model. All DAEMs allowed an accurate prediction of the TGA data; however, the Miura–Maki model could not account for the complete range of conversion for some substrates, while the Gaussian and logistic DAEMs suffered from the interrelation between the pre-exponential factor k0 and the mean activation energy E0 – an obstacle that can be overcome by fixing the value of k0 a priori. The results confirmed the capabilities of DAEMs but also highlighted some drawbacks in their application to certain thermodegradation experimental data.

Winemaking by-products present a high environmental impact due to their considerably high biochemical and chemical oxygen demands. This study is focused on the optimization of the traditional solvent extraction technology of phenols from Pinot Noir grape skins (Vitis vinifera). To such a purpose, the combined effects of the extraction time (9, 19 and 29 h) and the solid-liquid ratio (0.10, 0.20 and 0.30 gDW/mL), were investigated by a 32 full factorial design combined with response surface methodology; total polyphenols, flavonoids and trans-resveratrol extraction yields were used as response variables. Results demonstrated that Pinot Noir skins had high levels of both total polyphenols (3.22 mgGAE/gDW) and flavonoids (1.01 mgCE/gDW), being the optimum extraction time 19 h approximately. t-resveratrol was found in a considerable amount (2.24 mg/100 gDW), while the main phenolic compounds analyzed with Reverse Phase-High Performance Liquid Chromatography were gallic acid, catechin and quercetin. A significant linear correlation was found between polyphenols concentration and their antiradical power. PRACTICAL APPLICATIONS Winery by-products (grape marc) are a possible font of antioxidants and their extracts can represent a significant economic and social benefit. The research of the efficient methods for phenolics compound extraction is one of great interest. Collected experimental data could be used in further studies as a comparison with those of other innovative technologies, such as supercritical fluid, ultrasound and/or microwave-assisted extraction.

In the present work, the supercritical water gasification (SCWG) of biomass is analyzed with a view to outlining the possible thermodynamic constraints that must be taken into account to develop this new process. In particular, issues concerning the formation of solid carbon and the process heat duty are discussed. The analysis is conducted by means of a two-phase non-stoichiometric thermodynamic model, based on Gibbs free energy minimization. Results show that char formation at equilibrium only occurs at high biomass concentrations, with a strong dependence on biomass composition. As regards the process heat duty, SCWG is mostly endothermic when biomass concentration is low, although a very small amount of oxidizing agent is able to make the process exothermic, with only a small loss in the heating value of the syngas produced.

This paper analyses the effects on the extraction kinetics of a solvent flow which is non-uniform in the extraction column bed cross-section. When modeling the extraction kinetics of a solute from a solid matter (for instance of oil from seeds), the solvent motion is normally assumed as consisting in plug flow, eventually corrected by the axial dispersion coefficient. Some experimental evidence put into question this simplified description. We have shown to which extent the effects of a non-uniform extraction bed permeability reflect on the extraction kinetics: in particular conditions, these effects could be even more significant than the effects due to the mass transport resistances governing the extraction of the solute out from the matrix.

This research focussed on the exploitation of grape by-products as a source of polyphenolic compounds, which are of interest to the food, pharmaceutical and cosmetic industries. In particular, two substrates were tested: Pinot Noir grape skins and grape seeds. Pinot Noir grape skins were extracted by supercritical CO2 added with ethanol as modifier at constant temperature (45 °C) and at variable pressure (200, 300, 400 or 500 bar). The supercritical extraction kinetics of polyphenolic compounds was obtained. Grape seeds were extracted by combining supercritical (at 40 °C and 500 bar and using CO2 or CO2 added with ethanol as modifier) with liquid ethanol extraction. The supercritical technique seemed not to be really effective in extracting polyphenolic compounds; it can be anyway utilized to selectively extract grape seed oil by avoiding any solvent contamination of the matrix which can be further extracted for the recovery of polyphenolic compounds by means of liquid organic solvent.

This paper presents some experimental results about biomass gasification obtained with a bench-scale gasifier consisting of an indirectly heated batch reactor, inserted in a high temperature furnace. Spruce wood has been used as feedstock in different forms and sizes (as pellets and sawdust). The experimental activity includes the analysis of the thermal response of the system (using an inert bed material) and the characterization of the gasification products. The yield of the gaseous compounds found in the syngas has been measured using an on-line gas-chromatography technique. The experimental results have been compared against calculations obtained by applying a thermochemical equilibrium model, improved to predict both the gas and the solid phase product yields. The experimental (average) yield of reaction products has been found to be in a satisfying agreement with the thermodynamic model.

In this work, an extraction model capable of predicting the supercritical extraction process of seed oil is presented. The model bridges the ‘broken and intact cells’ and the ‘shrinking-core’ models available in the literature: as the former, the proposed model takes into account the seed structure with the presence of oil-bearing cells; as the latter, it assumes that the particles progressively exhaust their oil content from the outside to the inside, with a core shrinking during the process. The internal mass transport coefficient is described with three alternative models: the discrete and the semi-continuous models are superior to the continuous one which undervalues the same coefficient. By means of a supercritical extractioncolumn model and utilizing several experimental data of supercritical grape-seed oil extraction, the value of the internal mass transport coefficient of a single layer of oil-bearing cell has been calculated: its value is roughly the same for all the experimental cases analyzed (average value: 5 × 10 −8 m/s), verifying the reliability of the proposed model.

In this paper, a typical analysis of the effect of model uncertainties on predictions is extended to a supercritical extraction process for an extractor feed by vegetable seeds and utilizing supercritical CO2 as solvent. The sensitivity analysis reveals that two parameters are particularly important for the extraction process modeling: the particle diameter and the internal mass transfer coefficient. Therefore, a deeper analysis of the sensitivity of these two parameters has been performed: the sensitivity depends on the length of the process. In the supercritical extraction process, two successive phases can be considered: the former is controlled by the solubility of the oil in the supercritical solvent, and it is therefore almost completely insensitive; the second phase, on the contrary, is mainly controlled by internal transport phenomena and it is very sensitive to the above mentioned parameters. The effect of changing some operative conditions is also investigated, underlining how the solvent flow rate and the seed milling affect the extraction process. From these results, an extraction procedure is proposed that would reduce the solvent consumption without resorting to the connection in series of several extractors.

This paper presents results of normal hardness, plasticity index and elastic modulus for a selection of organic polymers (a poly(methylmethacrylate), PMMA, a poly(styrene), PS, a poly(carbonate), PC, and an ultra-high molecular weight poly(ethylene), UHMWPE) obtained using the contact compliance method. The paper describes in detail the dependence of the imposed penetration depth, the maximum load and the deformation rate upon the hardness and elastic modulus values for these polymeric surfaces; typical penetration depths range from about 10 nm to m where the imposed loads are less than 300 mN. The results show a considerable strain-rate hardening effect for the present systems and possibly a peculiarly harder response of these materials at the near-to-surface (submicron) layers. The paper includes considerations of a practical nature which are drawn in order to overcome some intrinsic limitations of this technique when it is used for polymeric surfaces, especially for a creeping phenomenon which may be observed at the incipient unloading experimental segments. The appropriateness of using a tip calibration constructed upon hard substrates when indenting polymers is reviewed at the conclusion of the paper.

Lipid profiles of fish oil extracted from trout heads, spines and viscera using supercritical carbon dioxide and Randall extraction with hexane were measured. The amount of unsaturated fatty acids (as a percentage of total fatty acids) was within the range of 72.6–75.3% in all the substrates. A significant presence of the most important omega-3 fatty acids was detected. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content in oil from spines, heads and viscera resulted to be 8.7% and 7.3%, 7.9% and 6.3%, and 6.4% and 6.0%, respectively. A low (≈3%), but worth noting, presence of lipids with omega-1 polyunsaturated fatty chains was observed in all the oils. Finally, significant differences were noticed in the relative amounts of triacylglycerides (TAG), diacylglycerides (DAG) and free fatty acids (FFA). Whereas oil from heads and spines was essentially composed of TAG (≈98%), in viscera oil the molar distribution ratio became TAG:DAG:FFA = 87:8:5.

In the present work an equilibrium model (gas-solid), based on the minimization of the Gibbs energy, has been used in order to estimate the theoretical yield and the equilibrium composition of the reaction products (syngas and char) of biomass thermochemical conversion processes (pyrolysis and gasification). The data obtained from this model have also been used to calculate the heating value of the fuel gas, in order to evaluate the overall energy efficiency of the thermal conversion stage. The proposed model has been applied both to partial oxidation and steam gasification processes with varying air to biomass (ER) and steam to carbon (SC) ratio values and using different feedstocks; the obtained results have been compared with experimental data and with other model predictions obtaining a satisfactory agreement.

In order to point out the interactions of oxygen with a liquid metal and to study the influence of the actual operating conditions, dynamic surface tension measurements of a liquid test metal (tin), were performed under vacuum conditions by using the large drop method. This classical method has been improved by applying a new experimental procedure which allowed to obtain reliable surface tension measurements at high temperature as a function of time and varying the oxygen content. Further, complementary information on molten metal-oxygen interactions can be obtained. In particular, in this work, the trend of the surface tension temperature coefficient has been analysed as a function of different operative parameters, highlighting some crucial points such as the dependence of the temperature coefficient on the accuracy of the surface tension experimental data and the influence of the dissolved oxygen. It was demonstrated that the surface tension and its temperature coefficient do not depend on the quantity of dissolved oxygen when this is inside a certain range of values.

A theoretical model on oxygen transport at the surface of liquid metals has been validated by dynamic surface tension measurements performed on liquid tin as test metal. The oxygen contamination conditions have been obtained at different oxygen partial pressures under low total pressure conditions (Knudsen regime), confirming that an oxide removal regime occurs under an oxygen partial pressure much higher than the equilibrium one (the “Effective Oxidation Pressure”). Experimental results are reported which give a new insight on the relative importance of the various processes due to the oxygen mass transport between the liquid metal and the gas phase. The critical aspects involved in surface tension measurements of liquid metals, related to the problem of liquid metal–oxygen interactions, are also carefully underlined.

This note considers the problem of the interpretation of experiments of capillary phenomena in molten metals. Reference is made to a previous published paper, where a theoretical analysis of the behaviour of molten metals in the presence of oxygen was presented [1] . Such a theoretical analysis allowed relating the gas phase composition at the surface, which is hardly measurable, to the composition in the feed or at the outlet. The application of the theory was effective for the study of the Si–O system. On the other hand, after the publication of the paper, some aspects of the theory remained unclear or misunderstood. So we deemed necessary to present a further in-depth analysis of the theoretical approach, with the goal to definitely clarify its use and consequences for the experimental praxis. Simple and clear rules will be derived, in the most suitable form for the potential users of the theory, mainly experimentalists of capillary phenomena. Moreover, new relevant experimental results are shown, which corroborate the theory.