Extraction of bitumen with sub- and supercritical water

The sub- and supercritical water extractions of Athabasca oil sand bitumens were studied using a micro reactor. The experiments were carried out in the temperature range of 360–380 °C, pressure 15–30 MPa and water density 0.07–0.65 g/cm³ for 0–2 hrs. The extraction conversion of bitumens increased with solvent power and temperature. A maximum conversion of 24% was obtained after 90 min extraction at the supercritical condition. Hydrogen and carbon mono-oxide were not detected in sub-critical region but in the supercritical region. The supercritical condition was favorable to the hydrogen formation for bitumen extraction. The extraction products were upgraded relative to the original bitumens due to direct hydrolysis of low-energy linkage and H₂ formed by water gas shift reaction in supercritical condition. 18% of initial sulfur in bitumen can be removed at maximum conversion condition. The asphaltene contents of the residue were significantly higher than that of original bitumen due to preferential extraction of aromatic compounds in supercritical condition.     

Extraction of Avgamasya asphaltite with sub- and supercritical solvents

The yields and the nature of the products from the solvent extraction of Avgamasya asphaltite of SE Turkey with benzene and toluene under Soxhlet, subcritical (up to 292 °C) and supercritical (350–450 °C) conditions are reported. The subcritical yield increases with temperature but also depends on pressure; the extra yield is mainly of asphaltenes. The 350 °C supercritical toluene extract shows little evidence of thermal degradation and is similar in yield and chemical nature to that obtained under subcritical conditions except that it contains more pentane-soluble material. At 450 °C the yield is increased and a number of pyrolytic effects are observed, including reduction in molecular mass, loss of heterocyclic and alkyl groups and the presence of toluene decomposition products.     

采用超临界/亚临界水回收热固性树脂基复合材料

综述了近年来国内外研究者利用超临界/亚临界水分解热固性树脂基(如不饱和聚酯,酚醛树脂,环氧树脂等)复合材料的研究,该方法可将热固性树脂基复合材料分解为单体或低聚物,具有环保、经济、安全的特点,作为一种新兴技术,具有较好的发展前景。     

Electron spin resonance of VO radical-ion in sub- and supercritical water

Electron spin resonance (ESR) spectra of VO²⁺ radical-ions in sub- and supercritical water are observed. Upon increasing the temperature from 20 to 100 °C, the fine structure line widths in the ESR spectra of the vanadyl ion are observed to be reduced that is associated with the effective averaging of the g-factor anisotropy and the hyperfine interaction. With further increasing the temperature, the spectrum components of the hyperfine structure are broadened significantly resulting in the unresolved low-intensity line in supercritical water with ΔH_pp ∼ 300 G. The data obtained allow behavior peculiarities of the paramagnetic VO²⁺ ions in sub- and supercritical water including rotational dynamics and spin exchange between the radicals to be elucidated. The registration of the unresolved low-intensity line in supercritical conditions points to an increase in the local ion concentration in the system that can be an initial stage for the formation of vanadium-based particles in supercritical conditions. The study demonstrates that ESR is the powerful tool to investigate properties of sub- and supercritical water in situ.     

Extraction of victorian brown coals with supercritical water

Extraction of five Victorian brown coals with supercritical water in a semi-continuous reactor was investigated. At 380°C and 22 MPa conversions of 42–54% and extract yields of 20–26% were obtained, significantly higher than with toluene under the same conditions. The extracts were separated into oils, asphaltenes and pre-asphaltenes and these were studied by NMR spectroscopy combined with elemental, OH and molecular weight analyses. The extacts have a high asphaltene and pre-asphaltene content, together with a high oxygen content, especially in the asphaltene and pre-asphaltene fractions. Long alkyl chains were present in the oils and asphaltenes. Temperature had little effect on the extraction, whereas pressure has a marked effect on both the conversion and the composition of the extract. The major difference between the toluene and water extracts is the higher oxygen content of the latter. There was a considerable improvement in the conversion using 0.5 M NaOH rather than water. Analyses of some of the chars were also carried out.     

Oxidation reaction of high molecular weight dicarboxylic acids in sub- and supercritical water

Sebacic and azelaic acids, which are representative of high molecular weight dicarboxylic acids, were oxidized in a batch reactor with H₂O₂ oxidant in water from 300 °C to 400 °C at sub- and supercritical conditions. Intermediate products were identified based on GC–MS, HPLC, and ¹H NMR. The main oxidation products were dicarboxylic acids and the minor products were monocarboxylic acids. (ω − 1)-Keto acids, aldehyde-acids, and γ-lactones with carboxylic groups also were identified.On the basis of the products identified, the oxidation pathways of high molecular weight dicarboxylic acids were formulated. The oxidation of high molecular weight dicarboxylic acids proceed with the consecutive oxidation of higher to lower molecular weight dicarboxylic acids mainly through the oxidation at α-, β-, and γ-carbons to a –COOH group. The oxidation of dicarboxylic acids was also accompanied by oxidative decarboxylation, leading to the formation of monocarboxylic acids.     

Liquefaction of rice straw in sub- and supercritical 1,4-dioxane–water mixture

The critical liquefaction of rice straw in sub- and supercritical 1,4-dioxane–water mixture was investigated in a 500 mL autoclave at temperature of 260–340 °C, resistance time of 0–20 min, and volume ratios 0–100 vol.% (1,4-dioxane:mixture). The yields of oil and PA + A (preasphaltene and asphaltene) were in the range of 29.64–57.30 wt.% and 6.42–22.68 wt.%, depending on the temperature, resistance time and volume ratio. The synergistic capability of 1,4-dioxane–water mixture could allow the great decomposition of the tubular structure of lignocelluloses. It was shown by the results that the “oxygen-transfer” reaction, deoxygenation and decarboxylation may occur in the liquefaction of rice straw with 1,4-dioxane–water mixture, while deoxygenation and decarboxylation may be the main reaction. The oil and PA + A fractions obtained at different volume ratios were analyzed by FTIR and GC–MS to investigate the effect of the ratios on the type of the compounds in the liquid products. It is shown that the nucleophilic and hydrolytic functions of water might be weaken at the higher ratio of 1,4-dioxane runs, resulting the lower amount of phenolic, acidic, hydrocarbon and ester derivatives in the oil and PA + A fractions.     

Catalytic hydrothermal treatment of pharmaceutical wastewater using sub- and supercritical water reactions

Application of subcritical and supercritical water technology for destruction of pharmaceutical compounds (carbamazepine, metoprolol and sulfamethaxazole) was investigated. The experiments were conducted inside batch reactor at a temperature ranging from 473 to 773 K and with different residence times of 5 to 50 min. The results show that carbamazepine, metoprolol and sulfamethaxazole are destructed by 90.27%, 99.99% and 98.84% after a 20 min exposure to 623 K, 673 K and 573 K, respectively. In comparison with the conventional methods of pharmaceutical waste treatment, the current technology provides a higher destruction efficiency (approximately 90–100%) which is achievable in shorter durations. NaOH and CuSO₄·5H₂O were also applied as catalysts in the temperature range of 473 K to 723 K. Comparing these catalysts, CuSO₄·5H₂O demonstrates a higher destruction efficiency, especially at lower temperatures. Based on the proposed pathway, the products of destructioncan be classified as environmentally-friendly compounds. The results show that this technology can be used as a green alternative for efficient removal of pharmaceutical compounds from wastewater streams.     

Extraction of coal using supercritical water

An experimental apparatus was developed to inject coal into an autoclave containing preheated supercritical water. The supercritical water appears to act as both solvent and reactant in the conversion of coal to gases and liquids. Experiments were carried out with German brown coal, lignite and bituminous coal and with glucose at both subcritical and supercritical water densities. A significantly larger quantity of char was obtained when operating at subcritical densities and when the coal was mixed with water before heating to supercritical conditions. Smaller amounts of char were obtained as density increased and as reaction time increased.     

Thermal decomposition of hydrazine in sub- and supercritical water at 25 MPa

Supercritical water flow-through test facility (SCW-TF) for the study of hydrothermal fluids is described. The hydrodynamic behavior of the flow-through reactor is examined from ambient to supercritical water conditions by performing residence time distribution measurements. The results indicate that at 25 MPa, the employed reactor configuration exhibits plug flow behavior with a small extent of dispersion over the temperature range from 298 to 773 K. The experimentally determined effective volume of the reactor was used for the calculation of mean residence times of the fluid in the “hot zone” of the flow-through system. The thermal stability of hydrazine in aqueous solution was examined along the 25 MPa isobar from 473 to 725 K. The obtained first-order rate constant for the thermal decomposition of hydrazine increases from 3.73 × 10⁻⁴ s⁻¹ at 473 K to about 0.31 s⁻¹ at 725 K.     

Kinetics of solid acid catalyzed 1-octene reactions with TiO2 in sub- and supercritical water

Acid catalyzed reactions of 1-octene on TiO₂ in sub- and supercritical water were investigated (T = 250-450 °C, P = 11-33 MPa). The main products were 2-octene and 2-octanol. Additionally, other liner C₈ alkenes and liner secondary C₈ alcohols were produced as by-products. Through kinetic analysis, acid catalyzed reactions can divide into the reaction catalyzed by Lewis acidic sites on TiO₂ and the reaction catalyzed by protons produced by the dissociation of water molecules. Each type of the reaction is affected by water density or ionic product of water, respectively, therefore, reaction mechanism changes with temperature and pressure. From the contribution of each reaction type, the temperature dependence of cis/trans ratio of produced 2-octene could also be explained.     

Reaction kinetics of d-xylose in sub- and supercritical water

Reactions of d-xylose were investigated with a flow apparatus in water at high temperatures (350 and 400 °C) and high pressures (40-100 MPa) to elucidate the reaction pathway and reaction kinetics. The products obtained from the reaction of d-xylose were furfural, d-xylulose, glyceraldehyde, glycolaldehyde, dihydroxyacetone, pyruvaldehyde, lactic acid and formaldehyde. Experimental results showed evidence of a dehydration reaction pathway, a retro-aldol reaction pathway and a Lobry de Bruyn-Alberta van Ekenstein (LBET) pathway from d-xylulose. The proposed reaction pathway and kinetic model were in accord with the experimental results. The kinetic constants showed dependence with water density (pressure). At 400 °C and water density of 0.52 g/cm³ at 40 MPa, the reaction from d-xylose to d-xylulose occurred by the LBET pathway with the reverse reaction being negligible. At 400 °C, increasing the water density from 0.52 to 0.69 g/cm³ decreased the kinetic rate constant of the forward LBET pathway and increased that of the reverse LBET pathway. The kinetic rate constant of the dehydration of d-xylulose to furfural increased with increasing water density at constant temperature. The kinetic rate constant of the retro-aldol reaction of d-xylose increased, and the retro-aldol reaction of d-xylulose decreased with increasing water density at 400 °C.     

Palm oil transesterification in sub- and supercritical methanol with heterogeneous base catalyst

An environmentally benign process for the production of methyl ester using γ-alumina supported heterogeneous base catalyst in sub- and supercritical methanol has been developed. The production of methyl ester in refluxed methanol conventionally utilized double promoted γ-alumina heterogeneous base catalyst (CaO/KI/γ-alumina); however, this process requires a large amount of catalyst and a long reaction time to produce a high yield of methyl ester. This study carries out methyl ester production in sub- and supercritical methanol with the introduction of an optimized catalyst used in the previous work for the purpose of improving the process and enhancing efficiency. CaO/KI/γ-Al₂O₃ catalyst was prepared by precipitation and impregnation methods. The effects of catalyst amount, reaction temperature, reaction time, and the ratio of oil to methanol on the yield of biodiesel ester were studied. The reaction was carried out in a batch reactor (8.8 ml capacity, stainless steel, AKICO, Japan). Results show that the use of CaO/KI/γ-Al₂O₃ catalyst effectively reduces both reaction time and required catalyst amount. The optimum process conditions were at a temperature of 290 °C, ratio of oil to methanol of 1:24, and a catalyst amount of 3% over 60 min of reaction time. The highest yield of biodiesel obtained under these optimum conditions was almost 95%.     

Influence of process parameters on the hydrothermal decomposition and oxidation of glucose in sub- and supercritical water

Supercritical water oxidation (SCWO) of wet waste biomass for energy recovery could be an advantageous alternative to conventional combustion with preceding drying. Therefore the reactions of glucose as a model substance for cellulosic biomass were investigated in sub- and supercritical water. The results of hydrothermal and oxidative experiments carried out in a continuous high-pressure plant with a feed solution of 0.2-1.2% (g g⁻¹) glucose at 24-34 MPa, 250-480 °C and residence times of 2-35 s are presented. In the presence of a stoichiometric oxygen concentration (for total oxidation to carbon dioxide and water) glucose decomposes already at subcritical temperatures readily to carbon monoxide and low molecular liquid substances, chiefly organic acids like e.g. acetic acid and glycolic acid. In turn these are in general more stable and react only slowly with oxygen. The effect of temperature, residence time, pressure, reactant concentration and addition of zinc sulfate on the conversion and the yields of reaction products was demonstrated. Already at 350 °C (24 MPa and 30 s) 99% of the glucose are converted. With increasing temperature the production of CO₂ increases. However, even at 480 °C (34 MPa and 4 s) significant amounts of CO are formed and the reaction of glucose to CO₂ and H₂O is not complete. Higher temperatures or greatly longer residence times are needed for a total combustion of the glucose.     

Mesoporous silica synthesis in sub- and supercritical carbon dioxide

Mesoporous silicas were synthesized from sodium silicate (Na₂Si₃O₇) and tetraethylorthosilicate (TEOS) with Pluronic F127 (polyethylene oxide-polypropylene oxide-polyethylene oxide, EO₁₀₆PO₇₀EO₁₀₆) triblock copolymer using sub- and supercritical carbon dioxide (SubCO₂ and SCO₂) respectively, as solvents. Templates were removed using liquid carbon dioxide (LCO₂) and SCO₂. The most efficient template removal was achieved by LCO₂ ? 92.7% (w/w), followed by LCO₂ with ethanol entrainer ? 85.6% (w/w), and by methanol ? 78.8% (w/w). The best efficiency of template removal by SCO₂ was 50.7%. Values of specific surface areas, A_BET, were increased by 10% with the increase of an ageing time from 6 to 24 hours for Na₂Si₃O₇-based silicas at aqueous synthesis conditions, whereas the use of SCO₂ reduced this value by 19.4%. For TEOS-based silicas synthesized using SCO₂, A _BET values increased by 3.8 times. Application of SCO₂ for synthesis of TEOS-based silicas resulted in higher mesopore volumes of 0.719 and 1.241 mL/g with an average mesopore width varying from 3.4 to 3.9 nm. Although Na₂Si₃O₇-based silicas have almost similar mesopore width range, their mesopore volumes were 7 times less than those for TEOS-based silicas. Formation of mesopores in Na₂Si₃O₇- and TEOS-based silicas was at the expense of micropores when synthesized in SCO₂.     

胜利褐煤超临界醇解反应行为研究

对胜利褐煤在甲醇、碱体系中的超临界反应行为进行了研究,考察了反应温度、反应时间和碱的种类分别对胜利褐煤转化率、产物收率和分布规律的影响.结果表明,反应温度显著影响褐煤的转化率和产物收率,产物主要为四氢呋喃可溶组分(占67%～85%)和甲苯可溶组分(占8%～22%);300℃时,胜利褐煤在甲醇-NaOH体系中转化率和收率最高(99%左右);反应时间显著影响褐煤的转化率和产物收率,80 min后褐煤的转化率和产物收率分别为99%和100%;反应过程中四氢呋喃可溶组分可转化为甲苯可溶组分、正己烷可溶组分和水溶性组分;碱的种类对褐煤超临界醇解转化率和产物收率有显著影响.     

Thermochemical liquefaction characteristics of microalgae in sub- and supercritical ethanol

Thermochemical liquefaction characteristics of Spirulina, a kind of high-protein microalgae, were investigated with the sub- and supercritical ethanol as solvent in a 1000 mL autoclave. The influences of various liquefaction parameters on the yields of products (bio-oil and residue) from the liquefaction of Spirulina were studied, such as the reaction temperature (T), the S/L ratio (R₁, solid: Spirulina, liquid: ethanol), the solvent filling ratio (R₂) and the type and dosage of catalyst. Without catalyst, the bio-oil yields were in the range of 35.4 wt.% and 45.3 wt.% depending on the changes of T, R₁ and R₂. And the bio-oil yields increased generally with increasing T and R₂, while the bio-oil yields reduced with increasing R₁. The FeS catalyst was certified to be an ideal catalyst for the liquefaction of Spirulina microalgae for its advantages on promoting bio-oil production and suppressing the formation of residue. The optimal dosage of catalyst (FeS) was ranging from 5-7 wt.%. The elemental analyses and FT-IR and GC-MS measurements for the bio-oils revealed that the liquid products have much higher heating values than the crude Spirulina sample and fatty acid ethyl ester compounds were dominant in the bio-oils, irrespective of whether catalyst was used.