Phenolic Beads Research Articles

Effect of Formaldehyde to Phenol Ratio in Phenolic Beads on Pore Structure, Adsorption and Mechanical Properties of Activated Carbon Spheres


 
 
 Phenolic beads (PBs) prepared from different formaldehyde to phenol (F/P) molar ratios were used as polymeric precursor for activated carbon. Activated carbon spheres (ACSs) have been produced from PBs via the physical activation process using carbon dioxide (CO2) as activating agent at 950 °C for different burn-off. The prepared ACSs were investigated for nitrogen adsorption, surface morphology and compressive strength by means of BET surface area analyser, scanning electron microscopy (SEM) and carbon and sphere tester techniques. The results indicated that the effects of F/P ratio observed, especially variation in the adsorption and mechanical properties. It was found that ACSs obtained from F/P ratio one showed the superior adsorption properties, possessed a high BET surface area in a range of 836 m2 g-1 to 3694 m2 g-1 with high pore volume (0.47 cm3 g-1 - 2.47 cm3 g-1) and 73-97 per cent microporosity. The BET surface area and pore volume increased, while the microporosity gradually decreased, with increasing the extent of burn-off. Compressive strength decreased with increasing F/P ratio as well as the extent of burn-off. ACSs upheld improved compressive strength (from 160 N mm-2 to 9 N mm-2) than those obtained from F/P ratio 2 and 3 in PBs. SEM studies of ACSs demonstrated well developed pore structure.
 
 

Carbon Bead‐Supported Ethylene Diamine‐Functionalized Carbon Nanofibers: An Efficient Adsorbent for Salicylic Acid

The present study describes the removal of salicylic acid (SA) from water by adsorption using ethylene diamine (EDA)‐functionalized carbon nanofibers (CNFs)‐containing porous carbon beads (∼0.5 mm). Briefly, the phenolic beads, separately synthesized using suspension polymerization, were carbonized and activated. The CNFs were grown on the carbon beads, using chemical vapor deposition, and the prepared fibrous beads functionalized with EDA were used as an adsorbent for SA. The prepared materials were characterized by their physico‐chemical properties, including specific surface area, surface morphology, and surface functional groups. The adsorption tests performed over the initial SA concentration range of 100–1500 mg/L revealed the adsorption capacity of the materials to be ∼682 mg/g, which was considerably larger than that of the adsorbents discussed in the literature for SA. The zeta‐potential analysis attributed enhanced adsorption to the electrostatic interaction and hydrogen bonding between the solute molecules and the EDA‐functionalized surface of the CNFs. The material and method developed in this study for the remediation of the SA‐laden wastewater may be extended to other acidic pollutants present in pharmaceutical effluents.

Carbon bead-supported nitrogen-enriched and Cu-doped carbon nanofibers for the abatement of NO emissions by reduction

Carbon nanofibers (CNFs) were grown over highly porous (∼1750m2/g-surface area) carbon beads (∼0.8mm), using catalytic chemical vapor deposition (CVD). The carbon beads were produced by the pre-oxidation, carbonization and activation of the phenolic beads that were synthesized using the suspension polymerization. The beads were doped in situ with copper (Cu) during the polymerization reaction. The carbon beads decorated with the CNFs were treated with pyridine to increase the nitrogen (N) contents of the material. The N-enriched CNFs and Cu nanoparticles (NPs)-doped carbon beads (N–Cu–CNF/CBs) were used for the removal of nitric oxide (NO) by reduction. In its dual role, Cu catalyzed the growth of the CNFs during CVD, and also, the reduction reaction. Approximately 86% of NO conversion was achieved for 400ppm-NO concentration over 1g of the prepared catalyst at 500°C. The high catalytic activity was attributed to the combined roles of the Cu NPs, reactive CNFs and N-containing surface functional groups in the material. The prepared carbon bead-supported CNFs in this study are for the first time effectively used as the catalyst for the NO reduction without requiring ammonia or urea.

Carbon nanofibers containing metal-doped porous carbon beads for environmental remediation applications

Carbon nanofibers (CNFs) were grown in porous carbon beads (∼0.5mm) by chemical vapor deposition (CVD). The beads were prepared by the carbonization and activation of Ni- or Fe-doped phenolic beads produced by suspension polymerization, with the metals incorporated in situ during a polymerization step. The carbon beads decorated with Ni- or Fe-CNFs were tested as adsorbents for the removal of different pollutants in the aqueous phase. The prepared material showed superior performance relative to the parent metal-doped porous carbon beads without CNFs. The loadings of vitamin B12 (vit B12) on Ni-CNF beads and that of arsenic (As) on Fe-CNF beads were determined to be 180mg/g and 18mg/g, corresponding to an aqueous phase vitamin B12 concentration of 250ppm and an As concentration of 50ppm, respectively. These loadings were significantly larger than those obtained for the parent materials. The nanofibrous carbon beads developed here with enhanced adsorption capacity is novel, effective and simple to synthesize.

현탁중합을 이용한 레졸형 구형 페놀입자의 합성

암모니아수 또는 트리에틸아민(TEA)을 촉매로 사용하여 페놀과 포름알데히드로부터 구형 페놀수지를 페놀:포름알데히드=1:1~1:4의 몰 비로 <TEX>$98^{\circ}C$</TEX>에서 현탁중합을 통해 합성하였고, 이를 <TEX>$700^{\circ}C$</TEX>의 질소 환경에서 탄화시켜 구형 탄소입자를 형성하였다. 현탁중합으로 형성된 구형 페놀수지의 열적 특성으로부터 후경화가 필요함을 확인하였다. 현탁중합의 최적조건을 결정하기 위하여 페놀/포름알데히드(P/F)의 몰 비, 촉매의 pH, 안정제의 분자량이 구형 페놀입자의 크기와 수율에 미치는 영향을 나머지 변수를 고정시킨 상태에서 조사하였다. P/F 몰 비에 따라 형성되는 입자 크기는 증가하는 반면 수득율은 감소하는 것을 확인하였고, 촉매의 pH가 클수록 큰 입자가 형성되며, 또한 안정제의 분자량은 입도분포보다는 수득율에 더 큰 영향을 미치는 것을 확인하였다. 또한 후경화를 거쳐 얻어진 구형 페놀수지의 열안정성을 TGA를 통하여 조사하였으며, P/F 몰 비가 높은 경우는 dibenzyl ether의 존재로 인하여 후경화 이후에도 <TEX>$220^{\circ}C$</TEX>의 중량감소가 여전히 존재하며, 반면에 P/F 몰 비가 낮은 경우는 <TEX>$220^{\circ}C$</TEX> 이후 <TEX>$400^{\circ}C$</TEX>에 걸쳐 꾸준한 중량감소가 일어나는 것으로부터 P/F 몰 비가 1:2인 경우가 열안정성이 가장 우수함을 확인하였다. The phenolic beads in macrosize range were obtained by suspension polymerization at <TEX>$98^{\circ}C$</TEX> from phenol and formaldehyde in the presence of basic catalyst with a phenol to formaldehyde (P/F) range of 1:1~1:4, and they were carbonized to spherical carbon beads under nitrogen at <TEX>$700^{\circ}C$</TEX>. Thermal analysis on spherical phenolic beads obtained by suspension polymerization showed that the postcuring process is essential. In order to optimize the suspension polymerization, the effects of the P/F molar ratio, the pH of catalyst, and the molecular weight of stabilizer on the size distribution and yield of spherical phenol beads were examined separatively. The particle size was increased whereas the yield was decreased with P/F molar ratio. The increasing basicity of catalyst made the particle size to increase, while the molecular weight of stabilizer had more effect on the yield rather than on the particle size distribution. The thermal stability of the spherical phenolic beads obtained through postcure was also examined by TGA. The phenol beads of high P/F ratio still showed the weight loss at <TEX>$220^{\circ}C$</TEX> even after postcure due to the high possibility of dibenzyl ether, while those of low P/F ratio showed the steady decrease in weight during <TEX>$220^{\circ}C$</TEX> to <TEX>$400^{\circ}C$</TEX>, which showed that the optimal P/F ratio was 1:2.

Development of novel in situ nickel-doped, phenolic resin-based micro–nano-activated carbon adsorbents for the removal of vitamin B-12

Activated carbon spheres (ACSs) and carbon micro–nanoparticles derived from nickel (Ni)-doped phenolic beads (∼0.8mm) were synthesized as efficient adsorbents for vitamin B-12 (VB12). Ni was incorporated in an intermediate step during a suspension polymerization. ACSs were synthesized by the carbonization and activation of Ni-doped polymeric beads. Carbon micro–nanoparticles (average size ∼200nm) were synthesized by milling polymeric beads followed by carbonization and activation. Adsorption tests were carried out under both batch and dynamic (flow) conditions. The latter tests were carried out in a specially designed and fabricated micro-column packed with carbon micro–nanoparticles. The adsorption loading of VB12 on the adsorbents was determined to be ∼300mg/g, corresponding to an aqueous phase concentration of 500ppm, which is comparable to or larger than the literature data. The method of in situ synthesis of metal incorporated carbon micro–nanoadsorbents and their use in a micro-column under the flow conditions has much potential for bio- and pharmaceutical separation and purification applications.

Synthesis and characterization of phenolic‐type beads by dispersion polymerization of 2‐phenoxyethanol with formaldehyde using gum acacia powder as stabilizer

AbstractIn this study, we report the preparation of phenolic beads (PB) via a novel dispersion polymerization of 2‐phenoxyethanol (PE) and formaldehyde, in which gum acacia powder (GAP), formic acid, and sulfuric acid are employed as the steric stabilizer, the reaction medium and the catalyst, respectively. The effects of a variety of reaction parameters, including the stabilizer concentration, the agitation rate, the polymerization temperature, the molar ratio of formaldehyde to 2‐phenoxyethanol (F/P) and the amount of sulfuric acid, on the particle size and size distribution (PDI) as well as particle morphology have been investigated. Particularly, phenolic beads of a size 565 µm as well as a narrow particle size distribution (PDI = 1.153) have been prepared under the following conditions: the stabilizer concentration 2.5%, the agitation rate 700 rpm, the polymerization temperature 60°C, the molar F/P ratio 3:1, and the amount of catalyst 8 ml. In addition, a mechanism for the particle formation in dispersion polymerization of PE and formaldehyde has also been proposed. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Influence of Heating Rate and Temperature on Carbon Structure and Porosity of Activated Carbon Spheres from Resole-type Phenolic Beads

Activated carbon spheres (ACS) were prepared at different heating rates by carbonization of the resole-type phenolic beads (PB) at in atmosphere followed by activation of the resultant char at different temperatures for 5 h in atmosphere. Influence of heating rate on porosity and temperature on carbon structure and porosity of ACS were investigated. Effect of heating rate and temperature on porosity of ACS was also studied from adsorption isotherms of nitrogen at 77 K using BET method. The results revealed that ACS have exhibited a BET surface area and pore volume greater than and respectively. The structural characteristics variation of ACS with different temperature was studied using Raman spectroscopy. The results exhibited that amount of disorganized carbon affects both the pore structure and adsorption properties of ACS. ACS were also evaluated for structural information using Fourier Transform Infrared (FTIR) Spectroscopy. ACS were evaluated for chemical composition using CHNS analysis. The ACS prepared different temperatures became more carbonaceous material compared to carbonized material. ACS have possessed well-developed pores structure which were verified by Scanning Electron Microscopy (SEM). SEM micrographs also exhibited that ACS have possessed well-developed micro- and meso-pores structure and the pore size of ACS increased with increasing activation temperature.

Synthesis of resole‐type phenolic beads from phenol and formaldehyde by suspension polymerization technique

AbstractThe phenolic beads (PB) in macrosize range were obtained by mixing phenol and formaldehyde in the presence of basic catalyst by suspension polymerization. In this reaction, the triethylamine (TEA), poly(vinyl alcohol), and hexamethylenetetramine (HMTA) were used as initiator, stabilizer, and crosslinking agent, respectively. The resulting PB within size range 0.1–2.0 mm was obtained in this polymerization reaction, carried out at temperature 96°C ± 1°C with agitation rate 475 rpm for 4 h. The effects of different variables such as, formaldehyde to phenol ratio (F/P) by mole, initiator concentration, concentration of crosslinking agent, and temperature on the particle sizes of PB and its formation were investigated. The particle size and its distribution were shown to be dependent on the F/P ratio, initiator concentration, and temperature. The average particle size of PB increased with increasing F/P ratio by mole in the reaction mixture. The average particle size of PB decreased with increasing TEA concentration. The particle size distribution of PB became narrow in size range 0.9–1.3 mm with 86% of yield of 1.0% by weight. As far as the crosslinking is concerned, the uncured phenolic resin was formed in the reaction solution when the reaction was performed in the absence of HMTA at 96°C ± 1°C for 4 h. The amount cured PB formed increased with increase in the concentration of HMTA. The surface morphology, shape and size of PB were studied using scanning electron microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Microporous activated carbon spheres prepared from resole‐type crosslinked phenolic beads by physical activation

AbstractMicroporous activated carbon spheres (ACSs) with a high specific Brunauer–Emmet–Teller (BET) surface area were prepared from resole‐type spherical crosslinked phenolic beads (PBs) by physical activation. The PBs used as precursors were synthesized in our laboratory through the mixing of phenol and formaldehyde in the presence of an alkaline medium by suspension polymerization. The effects of the gasification time, temperature, and flow rate of the gasifying agent on the surface properties of ACSs were investigated. ACSs with a controllable pore structure derived from carbonized PBs were prepared by CO2 gasification. Surface properties of ACSs, such as the BET surface area, pore volume, pore size distribution, and pore diameters, were characterized with BET and Dubinin–Reduchkevich equations based on N2 adsorption isotherms at 77 K. The results showed that ACSs with a 32–88% extent of burn‐off with CO2 gasification exhibited a BET surface area ranging from 574 to 3101 m2/g, with the pore volume significantly increased from 0.29 to 2.08 cm3/g. The pore size and its distribution could be tailored by the selection of suitable conditions, including the gasification time, temperature, and flow rate of the gasifying agents. The experimental results of this analysis revealed that ACSs obtained under different conditions were mainly microporous. The development of the surface morphology of ACSs was also studied with scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis of copolymer beads with various phenolic derivatives attached via different linkages and their antioxidation activity

Macroporous copolymer beads with various phenolic derivatives introduced via three types of linkages—amide, methylene, and ether—were prepared from chloromethyl styrene/tetra(ethylene glycol) dimethacrylate copolymer beads. The antioxidation activity of these phenolic copolymer beads was investigated by the measurement of the inhibition activity against the hydroperoxidation of 1,4-dioxane. The phenolic copolymer beads with the dihydroxybenzene moiety exhibited the highest antioxidation activity, and the antioxidation activity of methylene- or ether-linked phenolic copolymer beads was higher than that of amide-linked copolymer beads. Thus, the antioxidation activity of the phenolic copolymer beads was affected by not only the kinds of phenolic moieties attached but also the type of linkage group. In addition, the swelling of the copolymer beads in an organic solvent was greatly affected by the linkage type of the phenolic copolymer beads. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of reaction parameters on the particle sizes of crosslinked spherical phenolic beads by suspension polymerization of phenol and formaldehyde

AbstractThe crosslinked spherical phenolic beads (PB) were prepared with phenol and formaldehyde in alkaline medium by suspension polymerization technique. Poly(vinyl alcohol) (PVA) hexamethylenetetramine (HMTA), and triethylamine (TEA) were used as stabilizer, crosslinking agent, and basic catalyst respectively. The resulting PB with higher yield (82.5%) and relatively uniform particle size range (0.2–1.8 mm) were formed at 95–97°C, 550 rpm for 4 h, by using varied amounts of PVA as a stabilizer. The particle size and its distribution could be adjusted by selecting a suitable polymerization medium, consisting of monomer added to water, and by varying their relative amounts, mechanical agitation and stabilizer concentration. The yield % of PB was also varied with the concentration of stabilizer, agitation rate, and monomer‐to‐water ratio. The effects of concentration of the stabilizer, agitation rates, and monomer‐to‐water ratio on PB formation and morphology are described. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2323–2330, 2006