Microwave heat fractionation

During the past decade, MALDI-TOF MS has proven to be an effective tool for the analysis of oligo- and polymeric mannoglucans (for extensive reviews see [222,223]). SEC/MALDI mass spectrometry was employed in the analysis of hemicelluloses isolated by microwave heat-fractionation from spruce and aspen wood [94]. These methods allowed the separation and characterization of the oligo- and polysaccharide fractions derived from the xylan and mannan components of both woods [224]. 

Fig. 11 Elution profile of the ws-material from microwave-heated spruce chips after SEC [218]. Detection by refractometry index (Rl) dotted line) and UV detection at 280 nm (full line). The arrows mark the elution volume of acetylated GGM fractions...

FIGURE 10.5 Elution profile on OH-B12 treated by microwave heating for 6 min during silica gel 60 column chromatography. Fifty milliliters of the treated OH-B12 solution (5 mmol/1) was evaporated to dryness and dissolved in a small amount of w-butanol/2-pro-panol/water (10 7 10, v/v) as a solvent. The concentrated solution was put on a column (1.4 X 15.0 cm) of silica gel 60 equilibrated with the same solvent and eluted with the same solvent in the dark. The eluate was collected at 4.0 ml with a fraction collector. Fractions I to V were pooled, evaporated to dryness, dissolved with a small amount of distilled water, and analyzed with silica gel TLC. Inset represents the mobile pattern of the OH-B12 degradation products of fractions I to V on the TLC plate. Data are typical, taken from one of five experiments. (Reprinted with permission from Watanabe, F. et al., J. Agric. Food Chem., 46, 5177-5180, 1998. Copyright (1998) American Chemical Society.)... 

Sample treatment was studied by the saturated fractional design considering volumes and concentrations of acids, temperatures, ramp time and hold time for the microwave heating. An optimised programme was set after the central composite study... 

Chapters 10-12 cover important aspects of coke formation in metal tubular reactors during pyrolysis of hydrocarbons. Chapters 13 and 14 are concerned with coal and lignite pyrolysis. Chapters 15 and 16 deal with pitch formation from, respectively, heavy petroleum fraction and tar sand bitumen. Chapters 17 and 18 cover studies on the mechanisms of thermal alkylation and hydropyrolysis. Chapters 19 and 20 on oil shale deal with the properties of oil shale and shale oil as developed by techniques of microwave heating and thermal analysis. 

Unlike the black rubber materials, in the absence of conductive black fillers, the white and colored rubber compounds cannot be heated suitably and vulcanized under microwave irradiation. For this reason, only a small fraction of white and colored rubber compounds are processed by means of microwaves. The novel, specialty microwave heating sensitizers for microwave vulcanization of white and colored rubber compounds, their use, costs and benefits were recently discussed by Parodi [141]. 

The starting material was spruce-chips with a mannan content of 12.9% (2). The heat-fractionation of milled spruce-chips was performed in a closed vessel in a microwave oven (MLS 1200 Microwave workstation. Milestone) with 9.1 g dry weight of wood chips in 100 ml of water solution (1, 2). Prior to the heat-fractionation, the milled spruce chips were impregnated (soaked) in either water or water solutions of sodium hydroxide (0.025-2%), potassium hydroxide (0.05%) or sulfuric acid (0.05%) (2). The heat-fractionation was performed at different temperatures and times, ranging from 170° to 220° C and 2 to 20 minutes, respectively. The solids were discarded by filtration and the filtrates were analyzed further. 

With the aim to find conditions allowing the isolation of intact or fragmented AcGGM free from lignin, spruce chips were first impregnated in water media and then heat-fractionated using microwave irradiation. The solids were removed by filtration and the obtained filtrate was then further processed and analyzed (2, 3) as schematically shown in Figure 2. 

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