Supercritical water extractions

Agricirltrrral shell samples (walnut, almond, hazelnut cotton cocoon, and sunflower shells) were subjected to supercritical water extraction for producing hydrogen-rich gas mixtrrres (Demirbas, 2004). Table 6.10 shows stractrrral analysis results of the shell samples. In a typical nm of this study, the autoclave was loaded with a 5.0 g... 

Fignre 6.20 shows the plots for yields of hydrogen from snpercritical water extraction of shell samples versns cellulose content at different temperatures. The yields of hydrogen from supercritical water extraction increase with increasing cel-Ixflose contents of the shell samples (Demirbas, 2004). 

Fig. 6.19 Plots for yields of hydrogen from supercritical water extraction of shell samples versus temperature...

Demirbas, A. 2004. Hydrogen-rich gas from fruit shells via supercritical water extraction. Int J Hydrogen Energy 29 1237-1243. 

Demirbas, A. 2005b. Hydrogen production from biomass via supercritical water extraction. Energy Sources 27 1409-1417. 

Conversions between 42-68% were obtained for supercritical water extraction of Victorian brown coals at 380°C and 22MPa, considerably higher than using toluene under the same conditions. The conversions obtained with a bituminous and a sub-bituminous coal were much lower. Pressure had a marked effect on both the conversion and the extract composition, whereas temperature had only a slight effect. Considerably higher conversions were achieved using dilute sodium hydroxide rather than water. The composition of the products is discussed. 

The extraction of coals with supercritical fluids is a promising route for the production of liquid fuels from coal. Generally, hydrocarbon solvents, notably toluene, have been used as the supercritical fluid. Supercritical water extraction has not received the same attention and only recently the first detailed study was reported. In that work, Holder et al. ( l) obtained high conversions for extraction of a German brown coal (70-75%) and a Bruceton bituminous coal (ca. 58%) with supercritical water at ca. 375°C and 23 MPa. These high yields, however, contrast with the much lower conversions briefly reported (.2—5) for other coals and there appears to be considerable variation in the extractive power of supercritical water with different coals, even allowing for the differences in the extraction procedure used. None of the above reports discussed in any detail the chemical nature of the products, nor how the products compare with those obtained from more conventional solvents. 

A new apparatus was developed for continuous extraction of contaminated soil material for high pressure (25 MPa) and high temperature (663 K) operating conditions. The extraction of hydrocarbon contaminants from long weathered and highly contaminated soil material could be realised with supercritical water under parallel flow. Within a residence time of only 28 s suspensions of less than 0.75 wt% soil in water could be cleaned (> 90 %). For a concentration of 1 wt% soil in water 43 s were needed to achieve a clean-up result of 98.3 %. The continuous extraction process can be carried out multistage. Then higher concentrated suspensions (2-4 wt%) can be also cleaned by supercritical water extraction. 

The special features of the uses of supercritical water justify dealing with them in a separate section. No commercially available or laboratory-made extractor can operate in a continuous manner under the conditions required by supercritical water. In fact, most of the few reported applications allegedly involving supercritical water extraction actually used subcritical water conditions with not more than two extractions in the supercritical state this can readily be inferred from the equipment used — stainless steel SF extractors can hardly withstand the drastic conditions needed for work with supercritical water. As a... 

The crude black, viscous pyrolysis oil product requires an upgrading step to make it suitable as a refinery feedstock. This is accomplished by high-pressure hydrogenation in a manner very similar to the upgrading step used for the coking products in tar sands processing. The influence of overall process conditions on the polycyclic aromatic compounds found in the product has been examined [62], and the supercritical water extract of the pyrolytic product has been characterized [63]. 

Akinlu, A, Smith, M.S. (2010), Supercritical water extraction of trace metals from petroleum source rock, Talanta, 81,1346-1349. 

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