Hydrothermal conversion

The Plato (Proving Lasting Advanced Timber Option) process is derived from a technology that was originally developed by Royal Dutch Shell, and was a spin-off from research into the hydrothermal conversion of biomass into liquid fuels. The Plato thermal modification process involves four stages (Figure 8.3) ... 

High-pressure FeOOH is another rare, laboratory compound that has been prepared by hydrothermal conversion of hematite in NaOH at 400 °C and pressures of 8 Gpa (Fernet et al. 1973). 

Hydrothermal conversion of either ferrihydrite or goethite at 250-300 °C in alkaline media for some hours, followed by a further stage of growth at higher pH (Os-tertag, 1994). Micaceous plates of hematite result. 

The initial process to achieve success was developed by Miyata of Kyowa in the mid 1970s [101].This process is based on the hydrothermal conversion in an autoclave of the fine agglomerated particles formed by addition of ammonia or lime to a magnesium salt solution. This hydrothermal conversion results in the formation of particles of about 1 micron in size and with a fairly low aspect ratio. This original process appears to be expensive to operate because of the low value of the ammonium or calcium chloride co-product which has to be disposed of and because the reported reaction conditions give a low yield and a relatively slow reaction. 

Xu. Ye. Wang, Dazhi, and Yang Lan (2001). Hydrothermal conversion of coral into hydroxyapatite. Material Characteristics, 47 83-87. 

In their original synthesis of MCM-41, Beck et al. (1992) achieved the hydrothermal conversion of aluminosilicate gels in the presence of quaternary ammonium surfactants (e.g. hexadecyltrimethylammonium ions). The washed and air-dried products were calcined at 450°C to remove residual organic material. 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

Paraffins have low dielectric constants and therefore are essentially inert in inorganic synthesis. Because of the relatively low solubility of water, the activity of water in these solvents easily approaches unity, and when inorganic particles are present in the medium, water is easily adsorbed on the particles, where water may facilitate hydrothermal conversion of the inorganic particles (see Section lll.A.l in this chapter). 

A high pressure synthetic form ofFeOOH can be prepared by hydrothermal conversion of a-Fe203 in NaOH at 500 °C at a pressure of 80-90 kb for one hour (Chenavas et al., 1973). The crystal structure is that of In-OOH. It consists of single chains of octahedra rumiing parallel to the c axis and linked by hydrogen bonds. 

Asbestos, the first inorganic fiber material used, is currently still exclusively produced from natural mineral deposits. It is formed by the hydrothermal conversion of basic and ultrabasic volcanic rock (olivine and pyroxene) to serpentine upon which the actual asbestos formation takes place leading to two asbestos sorts with different structures serpentine asbestos and amphibole asbestos. Asbestos can be produced synthetically by several hours heating of a polysilicic acid/metal oxide mixture (e.g. Mg, Fe, Co, Ni) in water at 300 to 350°C and 90 to 160 bar. The properties of four important asbestos types are summarized in Table 5.2-2. 

Figure 15.6 Three dimensional plot of powder diffraction profiles as a function of time during the hydrothermal conversion of zeolite Li/Na LTA to zeolite Li A(BW). The temperature was ramped to 200 °C in 5 min and kept at that temperature. ...

G.C.A. Luijkx, Hydrothermal Conversion of Carbohydrates and Related Compounds, Ph.D. thesis Delft University ofTechnology, 1994. 

Zeolites are the product of a hydrothermal conversion process [28]. As such they can be found in sedimentary deposits especially in areas that show signs of former volcanic activity. There are about 40 naturally occurring zeolite types. Types such as chabazite, clinoptilolite, mordenite and phillipsite occur with up to 80% phase purity in quite large... 

Jin F, Yun J, Li G, Kishita A, Tohji K, Enomoto H (2008) Hydrothermal conversion of carbohydrate biomass into formic acid at mild temperatures. Green Chem 10(6) 612-615... 

Chambon F, Rataboul F, Pinel C, Cabiac A, Guillon E, Essayem N (2011) Cellulose hydrothermal conversion promoted by heterogeneous Brqnsted and Lewis acids r aikable efficiency of solid Lewis acids to produce lactic acid. Appl Catal B 105(1-2) 171-181... 

Kang SM, Li XL, Fan J, Chang J (2013) Hydrothermal conversion of lignin a review. Renew Sustain Energ Rev 27 546... 

Most industrial zeolite-based catalysts originate from the hydrothermal conversion in supersaturated conditions of Si and A1 components in the presence of aqueous alkali, with occasionally added alkali-metal salts and organic molecules [96]. The whole process of zeolitization is schematically presented in Figure 12.6. 

The hydrothermal conversion of modified clay mineral, for example, metakaolin, is another manufacturing route to zeolites. Although the raw material costs may be as much as 15% lower than that of the hydrogel route, the major shortcoming of the process is that iron impurities in the raw material may cause an undesirable coloring of the zeolite product [15,18,99-101,104,108,116,122,123,125,126]. 

Stilbite, stellerite, and barrerite zeohtes were synthesized in the temperature range 200... 250 °C by hydrothermal conversion of water-free precursor glasses at 1 kbar H2O pressure [98G1, 99G1]. The zeolite formation with STI framework was dependent only on the chemical composition of the starting materials, while Na and/or Ca content of the precursor glass was responsible for the formation of the respective phase. 

Calcium phosphates are also prepared from natural marine structures such as corals (Roy and Linnehan, 1974 Vago et al., 2002 Papacharalambous and Anastasoff, 1993), mussel (Macha et al., 2013), sea shells (Bahar et al., 2003), sea urchin (Vecchio et al, 2007 Samur et al., 2013), land snail shells (Kel et al., 2012), cuttlefish bone (Rocha et al., 2006), and pearl (Shen et al., 2006) to name just a few. HAp powders have commonly been prepared using a variety of techniques such as wet chemical synthesis, hydrothermal conversion, solid-state reaction, and calcination of bone. 

Hydrothermal Conversion of Waste Polarizing Film to Acetic Acid... 

Feng-Wen Wang, Zhi-Bao Huo, Yuan-Qing Wang, et al. Hydrothermal conversion of cellulose into lactic acid with nickel catalyst. Research on Chemical Intermediates, 37(2-5) 487-492, 2011. 

The different process routes, in particular with reference to pressure applications, will now be described in more detail. Hydrothermal conversion of highly water-containing biomasses will be described in a different section, due to the special features of these processes. 

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