Licheng Ling

Preparation and properties of phenolic resin-based activated carbon spheres with controlled pore size distribution

Abstract Three kinds of phenolic resin-based activated carbon spheres (P-ACS) with different pore size distribution were prepared successfully by adding pore-forming agents to novolac-type phenolic resin. Polyethylene glycol and polyvinyl butyral, serving as pore-forming agents, evaporated during pyrolysis and left a small amount of carbon residue in the matrix of the phenolic resin-based carbon, thus changing the carbonization and activation behavior of the resin. Mesopores between 3 and 5 nm were created in the P-ACS, which possessed excellent adsorption properties for creatinine. Ferrocene has little effect on the carbonization process of the phenolic resin, but has a great impact on the activation process. Mesopores and macropores with a range from 3–5 to 10–90 nm were produced in the P-ACS, which exhibited large adsorption properties for VB 12 , a larger molecule than creatinine. P-ACS without pore-forming agents exhibited a small specific surface area and mainly micropores, which resulted in a very small amount of creatinine and VB 12 adsorbed.

Catalytic removal of SO2 over ammonia-activated carbon fibers

Abstract Nitrogen-containing functional groups were introduced onto the surface of activated carbon fibers (ACF) by activating an ethylene tar pitch-based carbon fiber with ammonia water. The activity of the ACF for the conversion of SO2 to aq. H2SO4 in the presence of H2O and O2 is significantly higher than that of other commercial ACF studied before. Both the SO2 adsorption capacity and oxidation activity of ACF are enhanced very much by the nitrogen-containing functional groups.

Preparation of pitch-based spherical activated carbon with developed mesopore by the aid of ferrocene

Abstract In this paper, ferrocene was added into the starting pitch, producing iron-containing pitch spheres. After activation in steam, pitch-based spherical activated carbon with high mesopore ratio was obtained. The factors, such as activation time, activation temperature and iron content, were studied in order to investigate their effects on the formation of mesopore. Results show that the catalytic activation reaction took place at the vicinity of iron particles, leading to the increase of meso- and macropores. On condition that the burn-off was similar, the higher the temperature was, the higher the pore (10.0–80.0 nm) volume and the mesopore ratio would be. The loading method of iron in this study makes it possible to control the catalytic reaction in a wider range. Mesopore volume and size can be controlled within a certain range by selecting appropriate experimental conditions.

Resistivity of carbon fibers/ABS resin composites

Abstract The resistivity of carbon fiber/acrylonitrile–butadiene–styrene (ABS) resin composites was investigated. Short carbon fibers (unoxidized and oxidized) were blended with ABS resin using chloroform as solvent and samples were made by hot pressing method. The composites display good conductivity when fiber volume content is larger than 2%, then the resistivity of composites gradually decreases with increasing filler fraction and the experimental data is in good agreement with the percolation theory. Raising carbon fiber lengths reduces the resistivity of composites. The oxidation of carbon fibers greatly increases the resistivity of composites.

Influence of CO-evolving groups on the activity of activated carbon fiber for SO2 removal

An investigation was made into the influence of CO-evolving and CO2-evolving groups on the activities of activated carbon fibers (ACFs) for the oxidative conversion of SO2 into aq. H2SO4 in the presence of O2 and H2O. The results indicated that the amount of evolved CO determined the SO2 removal activity of ACFs, whereas, the amount of evolved CO2 did not correlate with the ACFs activity for SO2 removal. A direct proportionality between the amount of evolved CO and the enhanced activity of SO2 removal was confirmed by using different oxidizing agents for changing the types and amount of oxygen functional groups in ACFs.

Effect of hydrogen on the mesopore development of pitch-based spherical activated carbon containing iron during activation by steam

Abstract In the present paper, pitch-based spherical activated carbon (PSAC) was activated by steam under various carrier gases such as nitrogen, mixture of nitrogen and hydrogen (H2/N2: 1/3 mol/mol) and pure hydrogen. The results showed that hydrogen inhibited the uncatalyzed C–H2O reaction while accelerated the iron-catalyzed one. Furthermore, the effects of hydrogen became much more remarkable as the proportion of hydrogen increased. In this case, the ratio of mesopore volume of the resultant PSAC increased, but the micropore volume and micropore surface area decreased remarkably. The ratio of mesopore could reach more than 90%, and the mesopore mainly distributed at 10–50 nm. Thus, the PSAC with higher ratio of mesopore can be prepared by the aid of hydrogen as well as iron.

Effect of moisture on stabilization of polyacrylonitrile fibers

The method of modification through pre-stabilization stretching in the presence of plasticizers, such as succinic acid [1], boracic acid [2], dimethylformamide [3] and zinc chlorid [4] etc., has been adopted to prepare small-diameter carbon fibers, which contain fewer defects per unit volume. But the method is relatively complicated and at risk of introducing new flaws. To overcome the above drawbacks, the authors have introduced a modification into the stabilization process, and have chosen moisture in air as the plasticizer. The process is easy to control by damping the atmospheric air and facilitated to applied to continuous process. Foremost in importance is that the new species has not been used, which guaranteed the required cleanliness in the process. Experiments were performed on a PAN-based 3000filament batch, and the shrinkage of PAN fibers was monitored by the displacement of weight. Stabilization was carried out between the temperatures of 180– 220 ◦C, air flow of 0.3 m3/h. The stabilized fibers were then introduced into the carbonization furnace. The carbonization furnace was heated in high-purity nitrogen from room temperature to 1000 ◦C at a rate of 5 ◦C/min, and heating ceased when the temperature was reached. Finally the fibers were taken out when cooled down to room temperature. Experimental details have been published elsewhere [5] and the experimental setup was shown in Fig. 1. A special barothermohygrograph was utilized to examine the amount of moisture in damp air. The result from Fig. 2 show that the fibers can be more easily elongated with increasing R.H. in air. The total amount of length elongation was about 0.2% at 40% of R.H. as compared with 0.8% at 80%. This means that

Effect of hydrophobic group in polymer matrix on porosity of organic and carbon aerogels from sol–gel polymerization of phenolic resole and methylolated melamine

Abstract Organic and carbon aerogels were prepared by solution–sol–gel polymerization of phenolic resole and methylolated melamine followed by supercritical drying and pyrolysis. The hydrophobic group was incorporated into polymer matrix by adding m -cresol in the solution–sol–gel step and the effect of addition on porosity of organic and carbon aerogels was elucidated by nitrogen adsorption and density measurement. The ratios of m -cresol to phenolic resole (R) were changed from 0/7.5 to 2.5/7.5 while ratios of other components to phenolic resole remained unchanged. It is found that the total pore volumes of organic and carbon aerogels exhibit maxima at 1/7.5 and are determined by the total concentrations of reactants and cumulative volume shrinkages of gels from hydrogels to organic aerogels and from hydrogels to carbon aerogels respectively. The macropores in organic aerogels, developed in supercritical drying process, are determined by gel discrete particles–gel discrete particles interactions, which can be tuned by the incorporated hydrophobic groups. The micropores in carbon aerogels are generated by evolving volatile compounds in the pyrolysis process. The meso- and macropores in carbon aerogels are determined by (1) meso- and macropores in relevant organic aerogels; (2) volume shrinkages that convert macropores to mesopores and mesopores to micropores; (3) mass loss in pyrolyzing organic aerogels that increases sizes and volume of carbon aerogels; and (4) coarsening that converts mesopores to macropores to reduce interfacial energy. The mesopore size distributions of organic and carbon aerogels exhibit maxima at 1/7.5, which is also related to the actions of the hydrophobic groups. The BET surface areas of organic aerogels and external surface areas of carbon aerogels are determined by sizes and volumes of mesopores and the BET surface areas of carbon aerogels are determined by micro- and mesopores.

On Porosity of Carbon Aerogels from Sol-Gel Polymerization of Phenolic Novolak and Furfural

Carbon aerogels were prepared by sol-gel polymerization of phenolic novolak and furfural followed by supercritical drying and pyrolysis. The porosity and morphologies of carbon aerogels were characterized by nitrogen adsorption, apparent density, He- pycnometer method, and transmission electronic microscopy (TEM). Effect of ratios of phenolic novolak to furfural (Ra) and total concentration of reactants (C) in sol-gel step on porosity and morphologies of carbon aerogels was investigated. The carbon aerogels synthesized are rich in meso- and macropores. The Ra determines the cross-linking density of polymers, thereby the compatibility of the polymers, and ultimately the shrinkage of gels in the drying and pyrolysis. The network sizes and the porosity of organic and carbon aerogels are mainly determined by Ra. The C has no effect on volume shrinkage of gels in drying and pyrolysis and has only dilute effect in determining bulk density of organic and carbon aerogels, and ultimately the porosity of carbon aerogels. Conversion of mesopores to micro- and macropores is observed, which is related to combination of C and Ra, and determines the partition of micro-, meso- and macropores.

Small angle X-ray scattering study of microstructure changes of organic hydrogels from supercritical carbon dioxide drying

Hydrogels (HG) were prepared by the sol-gel polymerization of phenolic resole, m-cresol resole and methylolated melamine mixtures with different recipes in basic aqueous solution at 85 degreesC for 5 days. Water in the HG was displaced by acetone to obtain acetone gels (AG). Organic aerogels (OA) were obtained by drying of AG under supercritical carbon dioxide. Small angle X-ray scattering (SAXS) using synchrotron radiation as X-ray source was employed to investigate microstructure of HG, AG and OA. It is found that physical cross-linking is dominant in HG and supercritical drying of the physically dominant cross-linked gels cause the following microstructure changes: (1) random growth of large scatterers that bury the scattering peak; (2) shrinking of gels; (3) deswelling of gel network and (4) evolution of gel structure from tangled or rough interface to smooth or flat interface