Sucrose carbonates, preparation

Fig. 4.17 Plot of log,o(n/(mmol g ) against logfo (p7p) for the adsorption of benzene at 20°C on a series of progressively activated carbons prepared from sucrose. (Courtesy Dubinin.)...

The total surface area of the template carbons prepared by sucrose impregnation is significantly higher than the surface area of the corresponding silica template (Table 2), that confirms the formation of micropores during the carbonization. Just an opposite tendency is observed... 

We will not discuss here models for pores in carbons, as this topic is treated in Chapter 5, and elsewhere in specialist [15] or general reviews [106, 107]. For similar reasons, we will not discuss porosity control [44, 108] in detail. However, porous carbons prepared by the template technique, especially the ordered ones, deserve special attention. Ordered mesoporous carbons have been known to scientists since 1989 when two Korean groups independendy reported their synthesis using mesoporous silicas as templates [109, 110]. Further achievements have been described in more recent reports [111, 112]. One might have expected that the nanotexture of these materials would merely reflect the nature of the precursor used, namely phenol-formaldehyde [109] or sucrose [110] in the two first ordered mesoporous carbon syntheses (as is well known, these two precursors would have yielded randomly oriented, isotropic carbon had they been pyrolyzed/activated under more conventional conditions). However, the mesopore walls in some ordered mesoporous carbons exhibited a graphite-like, polyaromatic character [113, 114], as described in Chapter 18. This information was obtained by nitrogen adsorption at low relative pressures, as in classical... 

Several monolithic enzyme biocatalysts were prepared and characterized with carbon coatings consisting of carbonized sucrose, carbonized polyfurfuryl alcohol, and carbon nanofibers. The coated carbon monoliths were also compared with an integral (composite) carbon monolith. A lipase from Candida antarctica was adsorbed on the monolithic supports. Adsorption on carbon coatings can be very effective, depending on the carbon microstructure. For a high lipase loading. 

Eigure 2.7 shows the FESEM images of porous carbons prepared at 1000°C using different mass ratios of sucrose to zeolite NaY template [77]. As can be seen, proper control of this ratio (R) allowed us to obtain carbon structures with... 

Having access to protected sucroses 10, 11, 12, and 14 we proposed an efficient method of the preparation of various derivatives such as amines (15), uronic acids (16), or higher sucroses i.e. compounds homologated at the desired terminal position by functionalized carbon unit e.g. 17) examples are shown in Fig. 2. The most complex derivative representing higher sucroses was prepared from phosphonate 18 and di-acetonogalactose aldehyde 19 which - under mild phase transfer conditions - provided enone 20 converted further into polyol 21. ... 

Uniformly labeled D-glucose, D-fructose, and sucrose are prepared by photosynthesis using an appropriate plant and isotopic carbon dioxide 248), Similarly, uniformly labeled D-galactose is obtained by photosynthesis with C 02 and the red alga Irideae laminarioides, where it occurs as a 2-glycerol D-galactopyranoside (65). 

Carbons prepared from sucrose have surface areas up to 1500 m g , and pore volumes up to 1 cm g (Table 1). These carbons also have micropore volumes of around 0.210 cm g, which is likely related to the intrinsic microporosity of the carbon precursor. For both samples a capillary condensation occurs in the p/po range between 0.1-0.4 and 0.3-0.6, which clearly indicates that the structural porosity of the silica framework is replicated in the carbon. The pore size distributions for these carbons are very narrow with peak maxima at 1.2 nm and 1 nm, for T30 SUC and T60 SUC, respectively. Additionally, a slight development of complementary mesoporosity (estimated from the amount of nitrogen adsorbed at p/po > 0.7) can be seen, accounting for 6 % and 7 % of the total pore volume. 

Methylfurfural may be prepared by a modification of this method, which is more rapid but gives lower yiddsd A solution of 800 g. of sucrose in i 1. of hot water is allowed to flow slowly into a boiling solution of 500 g. of stannous chloride crystals, 2 kg. of sodium chloride, and 4 1. of 12 per cent sulfuric acid in a 12-I. flask. The aldehyde distils ofl as rapidly as it is formed and is steam-distilled from the original distillate after rendering it alkaline witlr sodium carbonate. The product is isolated by benzene extraction of the second distillate and distillation under reduced pressure. The yield is 27-35 g- (10-13 per cent of the theoretical amount). 

The following process description is taken from U.S. Patent 2,987,449. An appropriate S. aureofaciens strain such as mutant S1308 (ATCC No. 12,748) is grown aerobically in a suitable inoculum medium. A typical medium used to grow the primary inoculum is prepared according to the following formula sucrose, 20.0 g corn steep liquor, 16.5 ml ammonium sulfate, 2.0 g calcium carbonate, 7.0 g and water to 1,000 ml. 

The pores of the silica template can be filled by carbon from a gas or a liquid phase. One may consider an insertion of pyrolytic carbon from the thermal decomposition of propylene or by an aqueous solution of sucrose, which after elimination of water requires a carbonization step at 900°C. The carbon infiltration is followed by the dissolution of silica by HF. The main attribute of template carbons is their well sized pores defined by the wall thickness of the silica matrix. Application of such highly ordered materials allows an exact screening of pores adapted for efficient charging of the electrical double layer. The electrochemical performance of capacitor electrodes prepared from the various template carbons have been determined and are tentatively correlated with their structural and microtextural characteristics. 

---