Aqueous-Phase Processing

The Dumesic group at the University of Wisconsin has developed a method to upgrade the aqueous-phase sugars and alcohols derived from biomass into either H or alkanes [7, 55-61]. For the production of H from biomass, aqueous-phase reforming of the sugar solution over many different catalysts has been studied [56]. Silica-supported Ni (19.1 wt %), Pt (5.85 wt %), Pd (4.78 wt %), Rh (9.37 wt %), Ru 

In addition to the metal catalysts previously mentioned for the formation of H from aqueous-phase biomass-derived compounds, tin-promoted Raney-nickel catalysts also selectively generate H and alkanes similarly to Pt(3 wt catalysts 

The direct conversion of woody biomass [63] or cellulose [64] via aqueous-phase reforming using a Pt/Al Oj catalyst results in the formation of In this process, the biomass is mixed with Pt(0.5 wt and water and is subsequently hydro- 

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Huber, G. W. Chheda, J. N. Barrett, C. J. Dumesic, J. A., Production of liquid alkanes by aqueous-phase processing of biomass-derived carbohydrates. Science 2005, 308(5727), 1446-1450. 

The hydroformylation reaction is highly exothermic, which makes temperature control and the use of the reaction heat potentially productive and profitable (e.g, steam generation). The standard installation of Ruhrchemie/Rhone-Poulenc s aqueous-phase processes is heat recovery by heat exchangers done in a way that the reboiler of the distillation column for work-up of the oxo products is a falling film evaporator... 

Peroxy radicals are intermediates in the atmospheric oxidation of virtually all organic compounds. HO is soluble in aqueous aerosols (21) and can participate in a number of oxidation reactions in the aerosols. The overall importance of the aqueous-phase processes compared to the gas-phase chemistry is uncertain. 

Katuri KP, Mohan SV, Sridhar S et al (2009) Laccase-membrane reactors for decolorization of an acid azo dye in aqueous phase process optimization. Water Res 43 3647-3658... 

Processes for depolymerization of the biopotymer, sqiaration of the various chemical types, and aqueous phase processing all must be established for biomass conversion to chemical products to become widespread. 

Poisoning of catalysts.in aqueous phase processing of biomass-derivedfeedstocks... 

Many commercial aqueous phase processes could be modified to treat such solutions. This chapter discusses precipitation, reductive precipitation, electrolysis, electrokinetic remediation, adsorption, solvent extraction and ion exchange, biological processes, membrane processes, and foam separations. Specifically, it focuses on their advantages, shortcomings, and possible modifications that might broaden their applicability. 

Fig. 3 The inclusion of membrane techniques in aqueous-phase processes.

Combinations of thermoregulating reaction mixtures with the use of membrane processes are discussed in Sections 4.4 and 6.1.4 and [22], Although the membrane process constitutes an additional process step, its use allows regeneration of the catalyst simultaneously and continuously and could thus be acceptable in terms of cost. The integration of membrane techniques in an aqueous-phase process is demonstrated in Figure 3 [22]. 

Atmospheric (gas-phase) compounds undergo chemical transformation by three possible routes (1) photolysis (2) chemical attack by free radical and other species and (3) dissolution in droplets followed by aqueous-phase chemical reaction. In this section we briefly discuss photolysis and then introduce the most important gas-phase species responsible for chemical attack in the troposphere. We will discuss aqueous-phase processes in Section X. 

Sulfur dioxide (S02) reacts under tropospheric conditions via both gas-and aqueous-phase processes (see Section X) and is also removed physically via dry and wet deposition. With respect to chemical removal, reaction with the OH radical is dominant ... 

Various protocols describe aqueous-phase processes with heterogeneous catalysts such as the reforming of oxygenated hydrocarbons over Sn-modified Ni catalysts [22a], the epoxidation of aUcenes over zeolites [22b], etc. [22c-i,l,m]. 

For escample, for reasons discussed in Chapter 2, there is a limited variety of reactants suitable for the aqueous-phase mode - a drawback which hampers the scope of application. The same is true for the organic/organic variant, due to the inadequate number of solvent pairs that act suitably. Although there is much recent information available [9], it is difEcult to find (or develop) suitable solvent/solvent mixtures or solvent pairs. A reliable assessment, however, is not yet possible. The same is true for the sensitivity to poisons, with the exception of the aqueous-phase process, which is extremely insensitive. Because of very limited publicity, the status of the SHOP process is unknown. 

Carbonylation reactions have been extensively studied in ILs, in particular, the hydroformylation of higher alkenes. The intense academic and industrial interest is mainly due to the limitations of the current aqueous phase process to short-chain (<5C) alkenes, due to the very low solubility of heavier olefins in water for an effective and reasonable reaction rate to occur. Note that 1-octene possesses a much higher solubility in [G G3,Im]PF6 ( 2 w/w%) than in water under the same conditions. 

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