Structure and formation of cellulosic chars

The formation and structure of chars produced on heating of cellulose, lignin, and wood have been investigated by FTIR and CP/MAS ¹³C-NMR, and the results have been discussed in conjunction with parallel permanganate oxidation studies reported before. These data show that when cellulose is heated for 5 min within the temperature range of 325–350°C, the IR bands associated with hydroxyl and glycosidic groups in cellulose disappear, and new bands signal the formation of unsaturation and carbonyl groups by dehydration and rearrangement. The NMR data also show the disappearance of the glycosyl carbons at 60–110 ppm and the appearance of methyl and other paraffinic carbons at 0–60 ppm, aromatic carbons at 110–170 ppm, carboxyl carbons at 170–190 ppm, and carbonyl carbons at 190–220 ppm. On heating at 400°C the IR and NMR signals for the glycosyl groups completely disappear, the signals for carbonyl and carboxyl groups diminish, and those for the aromatic and paraffinic groups expand. At this stage the char contains about 69% aromatic and 27% paraffinic carbons. At the temperature range of 400–500°C the paraffinic carbon content is reduced to 12%, and a highly aromatic (88%) char is produced. This is consistent with the permanganate oxidation studies which show the production of polycyclic aromatic structures resulting from extensive condensation and crosslinking at these temperatures. The chars produced from wood and lignin at 400°C had about the same aromatic carbon content as the corresponding cellulose char; however, the char yields were higher due to the presence of the methoxy phenyl groups that survive the heating process, as indicated by strong NMR signals at 55 and 148 ppm.     

Calcium catalysis in air gasification of cellulosic chars

Cellulosic chars containing calcium have been prepared from carboxymethyl cellulose in the calcium form and from pure cellulose containing sorbed calcium acetate, at several heat treatment temperatures (HTTs) in the range 400–900°C. The chars have been gasified in air at 300°C. The results indicated a general decrease in reactivity with increasing HTT. However, instead of a monotonic decrease in reactivity reported previously for coal chars containing indigenous or added calcium, the reactivity versus HTT curve consisted of three distinct regions which probably reflect the transformations being undergone by the catalyst species on increasing the HTT. Crystalline CaO was detected by XRD only in chars heated to 1000°C, at which temperature the catalyst was no longer effective. The relationships between gasification rate and catalyst concentration and also mode of addition have been determined using chars of HTT 600°C. As found by earlier workers with some coal chars, the rate reached a maximum with increasing calcium content and then declined. Chars containing sorbed calcium showed a relatively early decline of rate. They also showed less reactivity than the chars containing ion-exchanged calcium at all calcium concentrations.     

Jump in the air gasification rate of potassium-doped cellulosic chars

Chars prepared from potassium-exchanged carboxy methyl cellulose at several heat treatment temperatures (HTTs) were gasified in air isothermally at selected gasification temperatures (GTs) in the range 633-893 K to investigate the catalytic effectiveness of potassium species. The chars displayed a noticeable jump in gasification rate at a particular gasification temperature (called jump temperature, T_j). The magnitude of jump was much less than that reported for copper and nickel catalysis, but comparable with that for calcium catalysis. Increase in HTT caused a decrease in the jump temperature of chars in contrast with the increase observed in copper, nickel and calcium catalysis; also the magnitude of jump did not decrease, but remained unaltered, on increasing HTT. The different behavior of potassium catalysis is correlated to a change in the chemical state of potassium at higher HTT. The results reveal the dependence of jump phenomenon on chemical state and dispersion of catalyst in the char.     

Influence of inorganic additives on oxygen chemisorption on cellulosic chars

Chemisorption of oxygen on cellulosic chars is the initial step leading to gasification and is a significant factor in controlling chemical reactivity and heat release in smoldering and glowing combustion of cellulose. Oxygen chemisorption kinetics have been determined for chars (HTT 550°C) prepared from cellulose and cellulose treated with inorganic additives. Elovich kinetic analysis indicates that combustion behavior can be correlated with chemisorption kinetics. Addition of the same inorganic additives by grinding with pure cellulose chars had little or no effect on chemisorption kinetics. These data indicate that the mode of action on inorganic additives in enhancing or inhibiting the solid phase combustion of cellulose chars involves their influence on char functionality developed during pyrolysis. Chemisorption of oxygen on chars results in a decrease in free radical concentration, and heat treatment at 400°C in flowing nitrogen restores the original concentration. However, free radical concentrations do not differ significantly between additive treatments over most of the temperature range studied. Therefore, combustion behavior cannot be explained strictly in terms of changes in free radical concentration and other functional groups must also play a significant role.     

Development of porosity in brown-coal chars on activation with carbon dioxide

Two petrographic types of Tertiary brown coals, xylitic and earthy, were carbonized, and activated with carbon dioxide between 1123 and 1273 K. The development of porosity in the activated chars was studied by adsorption of benzene and carbon dioxide at 298 K and by mercury porosimetry. The type of brown coal exerts a dominant influence on the properties of the activated chars. The xylitic brown-coal, when compared with the earthy brown-coal, yields products with a higher pore volume and better sorptive properties. Activated chars from the xylitic brown-coal reach a surface area of 800 m² g^?1, contained principally in micropores and very narrow mesopores (radius below 3.0 nm). Dimensions of pores in the activated chars from the earthy brown-coal are less uniform, the mesopores are broader (an important part of them has a radius between 5.0 and 100.0 nm), and micropores are present to a smaller extent; the surface area of these products is between 200 and 350 m² g^?1. Activated chars from both types of brown coals have a well developed system of macropores.     

Development of a process for making thin-filament cellulosic fibers

This articles examines the production of thin-filament cellulosic (viscose) filament fibers for making a filter-material that can efficiently remove leukocytes from blood and its components. The main requirements for the fibers were formulated on the basis of preliminary studies. Equipment was chosen, an existing AVK-0.6 unit was rebuilt, and a process was developed for producing the fibers. The process includes the stages of fiber formation, regeneration, and washing. Processes were also developed for forming tows from the filament fibers and cutting the tows into fibers 4–6 mm long. The fibers have been used to create a filter-material for filtering leukocytes from blood and its components.     

Catalytic gasification of chars

The gasification of pure and cobalt-doped chars obtained by carbonization of wood sawdust is compared. The catalytic action of cobalt affects both the kinetics of char gasification and the texture of the resulting porous carbons.     

联合生物加工产纤维素乙醇中真菌的开发与应用

联合生物加工（consolidated bioprocessing,CBP）是在单一或组合微生物作用下,将纤维素酶生产、纤维素水解糖化、戊糖和己糖发酵产醇整合于单一步骤的生物加工过程。本文从真菌在CBP产纤维素乙醇中的开发历程着眼,回顾了纤维素乙醇产业化的发展进程,介绍了CBP产纤维素乙醇的作用机理,系统总结了目前国内外文献中报道的CBP底盘真菌的主要种类及优缺点,并综述了CBP真菌的开发策略,包括工程化策略和共培养策略,着重阐述了工程化策略的技术路线和研究进展。指出综合运用先进生物技术和基于代谢分析数据的计算机模拟系统开发CBP目标微生物,设计新型高效的生物反应器以及将CBP技术与现有生物工业整合,是未来将CBP技术应用于纤维素乙醇产业的关键。     

Gasification reactions of chars and modified chars produced from jack pine bark

Chars produced from locally grown jack pine have been gasified at atmospheric pressure with temperatures up to 650°C in a flow reactor. The gases produced were CO, CO₂, CH₄ and H₂ as well as H₂ O. Above the char preparation temperature, 350°C, the yields of gaseous products increased with temperature until 550?600°C when the production of CH₄, CO and H₂ O decreased. Chars modified by the separate inclusion of 1% w/w sodium borate, sodium phosphate and nickel oxide produced changes in the product distribution; an effect which was also studied during the addition of steam to the gasification cycles. Gross calorific values of the chars and allied materials were determined in an adiabatic bomb calorimeter and residues were analysed for C, H and N contents.     

FTIR studies of Saran chars

FTIR spectroscopy has been applied to a study of oxidized Saran chars. A pregrind technique is applied during KBr pellet preparation which, along with inherent advantages of FTIR, produces much higher quality spectra than could previously be obtained. Bands occurring in the spectra of the oxidized carbons at 1720 and 1585 cm^?1 are assigned to carbonyl vibrations in COOH groups and to aromatic ring stretching modes, enhanced in intensity by oxygen containing functional groups, respectively. The intensity of the 1720 cm^?1 band is found to vary linearly with % burn-off in the carbon sample. It is suggested that the activity of the 1585 cm^?1 band which is found to increase in intensity as a function of % burn-off, is caused mainly by an increase in oxygen containing functional groups at advancing levels of burn-off. A mechanism is postulated for the formation of surface anhydrides based on IR results. This involves early formation of anhydride structures followed by conversion of anhydrides to acidic groups via hydrolysis with atmospheric moisture.     

Mechanical stability of intumescent chars

Intumescent fire-retardant systems have been studied in detail from all points of view. However, all works passed around questions of mechanical stability of foamed chars produced during burning. In the present work, mechanical properties of intumescent chars has been discussed. Technique and method of such investigations have been supposed. It was supposed that mechanical stability of foamed chars correlates with high molecular fraction in char residue. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1827–1830, 1998     

Retention of liptinitic structure in vitrinite chars

Liptinitic macerals in medium and low-volatile bituminous coals (C=87.9 and 90.0 wt% daf) which have undergone a plastic stage during primary carbonization (<600 °C) retain their original botanical structure. The liptinite materials retain their original identity but develop coarser grained mosaics and stronger anisotropy than the vitrinite residues of the same coal. The retention of original botanical structure in liptinitic macerals is probably attributable to their simple polymeric structure, which is different from that of the associated vitrinite and to carbonization at high heating rates (10 and 60 °C min^?1) which facilitates the development of a distinct two-phase optical texture and anisotropy in carbonized residues of bituminous coals.     

Disorder in cellulosic fibers

Ruland's concept of an isotropic disorder function is applied to estimate the disorder parameter and the degree of crystallinity in a few cellulosic fibers: two cottons, native ramie, and a high-tenacity rayon. The results indicate an increase in disorder without any change in crystallinity on mercerization of native celluloses. On hydrolysis, with or without a pretreatment of mercerization, the samples exhibit a higher crystallinity, disorder remaining the same as for native celluloses. A ball-milled sample of “amorphous” cellulose is still found to be fairly crystalline with the lowest disorder. On being wetted in water and oven-dried, a distorted form of cellulose II with higher crystallinity and disorder was obtained. The polynosic fiber, Tufcel, has low values for the degree of crystallinity, disorder parameter, as well as crystallite dimension. A strong dependence of the degree of crystallinity on the crystallite size, particularly the lateral, is observed.     

Bioscouring of cellulosic textiles

A study on bioscouring of cotton yarn with the pectinase enzyme was carried out and the results compared with the usual alkali scoured material. The results indicate that the bioscoured yarn has lower percentage of non‐cellulosic constituents (impurities), higher tenacity, higher absorbency and the same whiteness after hydrogen peroxide bleaching as compared with the Solomatic bleached yarn. A similar study on cotton fabric indicates that a combined desizing and bioscouring is not feasible at least at ambient temperature. More work, however, is required to compare bioscouring followed by bleaching with the Solomatic or two step scouring and bleaching methods. One interesting finding is that the efficiency of washing of the desized fabric improves on adding ethylene diamine tetraacetic acid sequestrating agent in the wash liquor. Additional advantages of bioscouring are lower energy cost and more easily biodegradable effluent in comparison to alkali scouring.     

The kinetics of coal chars hydrogasification

Hydrogasification reaction of chars produced from two rank coals was investigated in temperature up to 1173 K and pressure up to 8 MPa. The reactivity of the lignite Szczerców char has been found to be slightly higher than of the subbituminous coal Janina char produced at the same conditions. A high value of the char reactivity was observed to certain carbon conversion, above which a sharp drop takes place. It has been shown that to achieve proper carbon conversion the hydrogasification reaction must proceed at temperature above 1200 K. Based on the active centres theory the kinetic equations of the hydrogasification process were developed and the kinetic constants at the maximum reaction rate evaluated for the analyzed chars.     

Chemical reactivity of Canadian coal-derived chars

The reactivities of eight Canadian coal-derived chars of four different ranks were measured thermogra-vimetrically at 500°C. It has been found that char reactivity decreases with increase in the carbon content (or rank) of the parent coal. Chars containing more calcium and magnesium oxides have higher reactivities. The experimental results of mass conversion are well represented by the shrinking core model in which the initial stage of the reaction is kinetically controlled by chemical reaction and the later stage by gas diffusion through the ash.     

Activation of brown-coal chars with oxygen

Semicokes and cokes prepared respectively at 773 and 1173 K from brown-coals, xylitic and earthy, from Polish coal seams, were activated with gaseous oxygen (10% oxygen and 90% argon) in a thermogravimetric apparatus to different burn-offs. With increasing temperature of oxygen activation a constant decrease of the sum of micropores and mesopores is observed, but probably as a result of chemisorption of oxygen the micropore volume passes through a maximum at 663 K. There is a strong influence of the temperature of carbonization of the char on the formation of porosity in the products of oxygen activation: activated cokes have better adsorptive properties than activated semicokes. The highest value of surface areas (benzene adsorption) are, for semicokes and cokes respectively, 520 and 700 m² g^?1. These differences can be attributed to the uniform microporosity in the non-activated coke as distinct from the wide range of the micropore diameters in the non-activated semicoke, and also to the lack of ultramicropores in the former sample. The earthy type of brown coal yields products with a less developed porosity than the corresponding products from the xylitic coal. For the xylitic semicoke as well as for the coke, after continuing the process of activation to burn-offs higher than 50%, a lowering of adsorptive properties is observed.