Oxidation alkaline glycerol

Alkaline glycerol electrochemical oxidation on Pt-Pd alloys is dependant on the surface composition of the alloys. Compared with the pure metals, enhanced activity is found when the alloy contains about 33% Pd, leading to a synergetic effect [63]. 

The classical Pd-on-carbon catalyst has been used occasionally in this context, specifically for the aerobic oxidation of glycerol into glyceric acid under alkaline conditions (328). This procedure in an aqueous medium is evidently limited to water-soluble reactants such as carbohydrates (329). Alternatively, a water-soluble (sulfonated) bathophenantroline Pd(II) complex enables alcohol oxidation in a biphasic water-alcohol system (330). 

Simoes M, Baranton S, Coutanceau C (2010) Electro-oxidation of glycerol at Pd based nanocatalysts for an application in alkaline fuel cells for chemicals and energy cogeneration. Appl Catal B Environ 93 354—362... 

Simoes, M., Baranton, S. and Coutanceau, C. (2010). Electro-oxidation of Glycerol at Pd Based Nano-catalysts for an Application in Alkaline Fuel Cells for Chemicals and Energy Cogeneration, Catal. B Environ., 93, pp. 354-362. 

The structure of these products is uncertain and probably depends on pH and concentrations in solution. The hydroxyl or carboxyl or both are bonded to the titanium. It is likely that most, if not all, of these products are oligomeric in nature, containing Ti—O—Ti titanoxane bonds (81). Thek aqueous solutions are stable at acidic or neutral pH. However, at pH ranges above 9.0, the solutions readily hydroly2e to form insoluble hydrated oxides of titanium. The alkaline stabiUty of these complexes can be improved by the addition of a polyol such as glycerol or sorbitol (83). These solutions are useful in the textile, leather (qv), and cosmetics (qv) industries (see Textiles). 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

Fuels cells are of interest both from energetic and environmental considerations. When methanol is fed directly to an anode, as in Direct Methanol Fuel Cells , electric power is generated, making the devices suitable for small and lightweight uses [53], Alternative fuels such as polyhydric alcohols like ethylene glycol and glycerol are much less volatile and toxic, on the one hand, and electrochemically oxidizable on the other [54]. Therefore, the electrochemical oxidation of various polyhydric alcohols has been investigated in acidic as well as in alkaline conditions. 

The electrochemical oxidation of polyhydric alcohols, viz. ethylene glycol, glycerol, meso-erythritol, xilitol, on a platinum electrode show high reactivity in alkaline solutions of KOH and K2C03 [53]. This electro-oxidation shows structural effects, Pt(lll) being the most active orientation. This results from different adsorption interactions of glycerol with the crystal planes [59]. 

In the case of ethanol, Pd-based electrocatalysts seem to be slightly superior to Pt-based catalysts for electro-oxidation in alkaline medium [87], whereas methanol oxidation is less activated. Shen and Xu studied the activity of Pd/C promoted with nanocrystalline oxide electrocatalysts (Ce02, C03O4, Mn304 and nickel oxides) in the electro-oxidation of methanol, ethanol, glycerol and EG in alkaline media [88]. They found that such electrocatalysts were superior to Pt-based electrocatalysts in terms of activity and poison tolerance, particularly a Pd-NiO/C electrocatalyst, which led to a negative shift of the onset potential ofthe oxidation of ethanol by ca 300 mV compared... 

PAN can be hydrolyzed quantitatively to N02 in alkaline solution. Thus, at least partial retention of PAN on alkali-coated denuders is likely. Ferm and Sjodin (42) reported up to 10% retention of PAN on an open-tube denuder coated with Na2C03. Facile conversion of N02 to N03 on carbonate-impregnated filters by oxidation with 03 has been reported (21), so similar conversion on alkali-coated denuders is likely. The use of glycerol in the alkaline denuder coating has been shown to decrease substantially the extent of nitrite oxidation (55). Slow oxidation of N02 to N03" in extracts of the denuder coating is also probable, a factor that can probably be minimized by low-temperature storage and by minimizing delays before analysis. 

Traditionally metal soaps have been manufactured by reactiOTi of alkali- or alkaline earth oxides or carbonates with natural fats or oils. Both compraients are mixed and at higher temperatures the triglyceride is decomposed yielding metal soap and glycerol. Under such conditions the soap is dispersed in an excess of oil or molten fat, and lubricating greases are yielded that way. 

---