Pyrolysis In Supercritical Water Research Articles

Experimental Investigation on the Pyrolysis and Conversion Characteristics of Organic-Rich Shale by Supercritical Water.

Organic-rich shale oil reservoirs with low-medium maturity have attracted increasing attention because of their enormous oil and gas potential. In this work, a series of experiments on pyrolysis of the particle and core samples were carried out in a self-made supercritical water pyrolysis apparatus to evaluate the feasibility and benefits of supercritical water in promoting the transformation efficiency and oil yield of the low-medium maturity organic-rich shale. Core samples had a mass loss of 8.4% under supercritical water pyrolysis, and many microcracks were generated, which increased the pyrolysis efficiency substantially. The oil yield of shale pyrolysis could reach 72.40% under supercritical water conditions at 23 MPa and 400 °C, which was 53.02% higher than that under anhydrous conditions. In supercritical water conditions, oxygen-containing compounds are less abundant than in anhydrous conditions, suggesting that supercritical water can inhibit their formation. Also, supercritical water conditions produced higher yields for light fraction, medium fraction, and heavy fraction shale oil than those under anhydrous conditions. These results indicate that supercritical water pyrolysis is feasible and has excellent advantages for low-medium maturity organic-rich shale.

Supercritical water pyrolysis of sewage sludge

Municipal sewage sludge (SS) from wastewater treatment plant containing high water content (>85wt.%), lead to the difficulty of co-combustion with MSW or coal due to the high cost of drying. This study explores an alternative method by supercritical water (SCW) pyrolysis of sewage sludge (SS) in a high pressure reaction vessel. The effects of temperature and moisture content of SS on yield and composition of the products (bio-oil, bio char and non-condensable gas) were studied. A temperature of 385°C and moisture content of 85wt.% were found to be the optimum conditions for the maximum bio-oil production of 37.23wt.%, with a higher heating value of 31.08MJ/kg. In the optimum condition, the yields of aliphatic hydrocarbon and phenols were about 29.23wt.% and 12.51wt.%, respectively. The physical and chemical properties of bio-char were analyzed by using XRF and BET. Results of GC analyses of NCG showed that it has the maximum HHV of 13.39MJ/m3 at 445°C and moisture content of 85wt.%. The reaction path from SS to bio-oil through SCW pyrolysis was given. Moreover, carbon balance was calculated for the optimal condition, and finding out that 64.27wt.% of the carbon content was transferred from SS to bio-oil. Finally, this work demonstrates that the SCW pyrolysis is a promising disposal method for SS.

Synergy in co-liquefaction of oil shale and willow in supercritical water

Co-liquefaction of oil shale kukersite and willow Salix viminalis blends by hydrous pyrolysis in supercritical water was studied under the conditions of 380°C, 4h, 38MPa, and water/blend ratio 3/1g/g. The actual yields of the consecutive products of extraction with various solvents did not agree with the additive values calculated by proportional contributions of the blend components. At any share of the components (xA,xB), the synergy (Δ) in the yields of the pyrolysis products estimated was proportional with the product of the shares of the components in the blend according to the equimolecular synergy model, Δ=δxAxB. The values of the synergy factors, δ, decreased in the row of the products as follows [%(g/g)−2]: the oil soluble in benzene 62, acetone 11, water 9, and diethyl ether 5.6, solid residue −9.6 and the sum of gas and pyrogenetic water −79. The main increase in the yield of benzene solubles was result of the positive synergy in the yield of high polar heterocompounds, revealing the synergy factor 69%(g/g)−2.

Experimental Study on Vacuum Residuum Upgrading through Pyrolysis in Supercritical Water

Vacuum residuum (VR) upgrading through pyrolysis in supercritical water was investigated in a bomb reactor and a batch autoclave. The experiments were carried out in the temperature range of 380−460 °C at 25.0 MPa for 5−120 min with a water/VR ratio of 0.78:1−4:1 by weight. The upgrading leads to a reduction of 30.9% in resins and asphaltenes, a reduction of 22.8% in aromatics, and an increase of 98.6% in saturates. The viscosity of the product was reduced from 116 mPa s of the feedback to 6.2 mPa s, which is approximately 179 times. Besides, the average molecular weight was reduced from 1860 to 646 g mol-1, and S, N, Ni, and V contents were reduced by 32, 15, 83, and 85%, respectively. The upgrading mechanism was proposed as ionic and radical reactions in parallel.

Kinetics and mechanisms of styrene monomer recovery from waste polystyrene by supercritical water partial oxidation

Waste polystyrene is becoming a major environmental concern, due to its large production quantities and non-biodegradable nature. Provided that the high molecular-weight material can be broken down into useful low molecular-weight hydrocarbons, waste polystyrene can be viewed as a highly valuable feedstock. This processing step can be accomplished by using supercritical water partial oxidation (SCWPO) technology. This technology uses the unique properties of supercritical water in an oxygen-deficient environment to partially oxidize the polymer. By using this technique, polystyrene has been successfully depolymerized into monomer, oligomer, and other useful hydrocarbons in a relatively short residence time with high efficiency. The kinetics and feasibility of the supercritical water partial oxidation process were experimentally investigated using four different oxygen-feed conditions. The styrene selectivity of the process, based on the product mass versus the feed mass, was determined to be as high as 71%, and was found to depend very strongly on the polymer/oxygen ratio. While the styrene selectivity was very high, the selectivity for benzene, toluene, and other hydrocarbons was substantially lower. The process was also compared with pyrolysis in supercritical water at the same temperature and pressure.

Partial oxidation of n-hexadecane and polyethylene in supercritical water

In this study, we show the results of partial oxidation experiments of n-hexadecane ( n-C 16) and polyethylene (PE) in supercritical water (SCW). The experiments were carried out at 673 or 693 K of reaction temperature and 5 or 30 min of reaction time using a 6 cm 3 of a batch type reactor. Water density ranged from 0.1 to 0.52 g/cm 3 (water pressure: 20–40 MPa). The loaded amount of oxygen was set to 0.3 of the ratio of oxygen atom to carbon atom. Some experiments were made using CO instead of oxygen for the partial oxidation of n-C 16 and PE to explore the effect of water gas shift reaction. In the results of partial oxidation of n-C 16, the yield of CO and some compounds containing oxygen atoms, such as aldehydes and ketones increased with increasing water density. Moreover, 1-alkene/ n-alkane ratio in the products decreased with increasing water density. The 1-alkene/ n-alkane ratio was lower than that of pyrolysis in SCW. Also for the case of PE experiments, in dense SCW (0.42 g/cm 3), the 1-alkene/ n-alkane ratio in partial oxidation was lower than that in SCW pyrolysis. In the case of CO experiments for n-C 16 and PE, 1-alkene/ n-alkane ratio was a little lower than that of pyrolysis in SCW. These results show that the yield of n-alkane, which is a hydrogenated compound, was higher through water gas shift reaction in SCW and also through partial oxidation in SCW. Therefore, these results suggest the possibility of hydrogenation of hydrocarbon through partial oxidation followed by the water gas shift reaction.

Naphthalene oxidation in supercritical water

Characteristic features of naphthalene oxidation and the kinetics of naphthalene pyrolysis in supercritical water (SCW) were studied using a batch reactor under isobaric conditions at a pressure of 30 MPa, in the temperature range from 660 °C to 750 °C, and for different levels of oxygen supply, varying from 0 to 2.5 moles of O2 per mole of naphthalene. The pyrolysis produces benzene, toluene, methane, hydrogen, soot, and carbon oxides. The rate constant for naphthalene pyrolysis in SCW was found to be k = 1012.3±0.2exp(–E/T) s–1 where E = 35400±500 K. For T > 660 °C, water participates in the chemical reactions of naphthalene conversion, particularly, in the formation of carbon oxides. The conversion of naphthalene in pure SCW is accompanied by heat evolution. Molecular oxygen oxidizes a part of naphthalene completely, i.e., to CO2 and H2O, this reaction being so prompt that in some cases, self-heating of the mixture and thermal explosion in the reactor were observed.

D/H isotope ratios of kerogen, bitumen, oil, and water in hydrous pyrolysis of source rocks containing kerogen types I, II, IIS, and III

Immature source rock chips containing different types of kerogen (I, II, IIS, III) were artificially matured in isotopically distinct waters by hydrous pyrolysis and by pyrolysis in supercritical water. Converging isotopic trends of inorganic (water) and organic (kerogen, bitumen, oil) hydrogen with increasing time and temperature document that water-derived hydrogen is added to or exchanged with organic hydrogen, or both, during chemical reactions that take place during thermal maturation. Isotopic mass-balance calculations show that, depending on temperature (310–381°C), time (12–144 h), and source rock type, between ca. 45 and 79% of carbon-bound hydrogen in kerogen is derived from water. Estimates for bitumen and oil range slightly lower, with oil–hydrogen being least affected by water-derived hydrogen. Comparative hydrous pyrolyses of immature source rocks at 330°C for 72 h show that hydrogen in kerogen, bitumen, and expelled oil/wax ranks from most to least isotopically influenced by water-derived hydrogen in the order IIS > II ≈ III > I. Pyrolysis of source rock containing type II kerogen in supercritical water at 381°C for 12 h yields isotopic results that are similar to those from hydrous pyrolysis at 350°C for 72 h, or 330°C for 144 h. Bulk hydrogen in kerogen contains several percent of isotopically labile hydrogen that exchanges fast and reversibly with hydrogen in water vapor at 115°C. The isotopic equilibration of labile hydrogen in kerogen with isotopic standard water vapors significantly reduces the analytical uncertainty of D/H ratios when compared with simple D/H determination of bulk hydrogen in kerogen. If extrapolation of our results from hydrous pyrolysis is permitted to natural thermal maturation at lower temperatures, we suggest that organic D/H ratios of fossil fuels in contact with formation waters are typically altered during chemical reactions, but that D/H ratios of generated hydrocarbons are subsequently little or not affected by exchange with water hydrogen at typical reservoir conditions over geologic time. It will be difficult to utilize D/H ratios of thermally mature bulk or fractions of organic matter to quantitatively reconstruct isotopic aspects of paleoclimate and paleoenvironment. Hope resides in compound-specific D/H ratios of thermally stable, extractable biomarkers (“molecular fossils”) that are less susceptible to hydrogen exchange with water-derived hydrogen.

Polyethylene conversion in supercritical water

This paper describes pyrolysis of polyethylene (PE) and n-hexadecane ( nC16) in supercritical water (SCW). Batch reactions were conducted at temperatures ranging from 673 to 723 K, at a reaction time of 30 min, and water density between 0 and 0.42 g/cm 3. The pyrolysis rate of nC16 in SCW was almost the same as that in 0.1 MPa argon (Ar) atmosphere. Product distribution was also more or less the same for both cases. PE pyrolysis results were clearly different from pyrolysis results in Ar. In SCW, higher yields of shorter chain hydrocarbons, higher 1-alkene/ n-alkane ratio, and higher conversion were obtained. This difference of PE pyrolysis in SCW and in Ar could be explained by considering the difference in the reaction phase.