Subsequent Steam Activation Research Articles

A comparative study of the pore characteristics and phenol adsorption performance of activated carbons prepared from oil-palm shell wastes by steam and combined steam-chemical activation

Oil-palm shell wastes were successfully converted into useful activated carbons in a systematic and novel approach by optimizing the pyrolysis conditions and subsequent steam activation conditions to maximize the BET surface area. The optimal activation conditions were a steam flow rate of 1.13 kg/h, hold time of 1.5 h and temperature of 950 °C, yielding BET areas of 1432.94 and 1382.95 m2/g for nitrogen-pyrolyzed and vacuum-pyrolyzed chars, respectively. In steam-chemical activation, one-step activation of oil-palm shell in steam with potassium carbonate (K2CO3), sodium carbonate (Na2CO3) or potassium chloride (KCl) was conducted, resulting in BET area output order of shell/K2CO3 (710.56 m2/g) > shell/KCl (498.55 m2/g) > shell (366.7 m2/g) > shell/Na2CO3 (326.62 m2/g). This study reported the first use of KCl and Na2CO3 as chemical reagents in one-step steam-chemical activation of biomass. KCl-activated carbon exhibited retardation of tar formation property, resulting in better pore development than pure steam activated carbon.Phenol adsorption of activated carbon is not only a function of the BET surface area but also the type of pyrolysis used prior to physical activation. Activated carbon (BET area of 1192.29 m2/g) pyrolyzed under vacuum could adsorb 87% more phenol than that pyrolyzed in nitrogen flow which had a higher BET area of 1432.94 m2/g. Phenol adsorption capacities of activated carbons are: shell pyrolyzed under vacuum (275.5 mg/g) > shell pyrolyzed in N2 flow (147.1 mg/g) > shell/K2CO3 (145.7 mg/g) > shell without pyrolysis (12.1 mg/g). These activated carbons would be highly suitable in industry processes to remove phenolic contaminants.

Tailoring mesoporosity of poly(furfuryl alcohol)-based activated carbons and their ability to adsorb organic compounds from water

In this work it was shown that polymers can be recycled into a promising adsorbent for organic dyes and phenols waste removal. For this, a series of activated carbons (ACs) were produced from mixture of ferrocene or titanium acetylacetonate with poly(furfuryl alcohol) (PFA) by steam activation. The introduction of ferrocene as Fe precursor was found to be an efficient catalyst in mesoporosity development during carbonization and subsequent steam activation at 850 °C, whereas the polymer based only and titanium-doped ACs are typically microporous. The porous structure parameters were determined from nitrogen adsorption isotherms measured at 77 K. Scanning electron microscopy was applied to monitor the metal distribution of metal-loaded char and the surface morphology of activated carbons. The adsorption capacity was found to be dependent mainly on pore size distribution. In the case of phenol adsorption, the adsorption was defined by volume of pore with size 0.8–1.4 nm; whereas, for Congo red best fit was observed for volume of pore with size 2–5 nm.

A novel disposal approach of deactivated resin catalyst for methyl tert-butyl ether synthesis: Preparation of low-cost activated carbons with remarkable performance on dibenzothiophene adsorption

In this research, low-cost activated carbons (ACs) derived from deactivated resin catalyst (DRC) for methyl tert-butyl ether synthesis were successfully prepared through carbonization and subsequent steam activation or KOH activation. Differences in physical and chemical properties of ACs and their performance on dibenzothiophene (DBT) adsorption from model fuel were investigated systematically. AC prepared by KOH activation (KSAC) has abundant micropores, whereas mesopores are the major part of AC prepared by steam activation (HSAC). Both KSAC and HSAC have few acidic groups, in accordance with their oxygen content. DBT adsorption performance is dependent largely on physical properties. The maximum adsorption capacity (16.1mgS/g at 100ppmS) and the longest breakthrough time (16h, 10h−1WHSV) were observed for KSAC.

Production of a mesoporous carbon adsorbent from carbon black and petroleum pitch by high-temperature roasting and steam activation

Mesoporous carbon adsorbent may be produced from carbon black and petroleum pitch by high-temperature roasting (at 1100°C) and subsequent steam activation. The samples obtained are compared with samples roasted at 700°C, with losses of 5–70 wt %. It is found that raising the roasting temperature increases the mesopore surface by a factor of 1.5–2.5 (to 200–300 m2/g) and reduces the micropore volume by a factor of 1.5–3.0. The adsorbent obtained may be effectively used in extracting materials from solution.

Electrospun graphene oxide/carbon composite nanofibers with well-developed mesoporous structure and their adsorption performance for benzene and butanone

Freestanding porous carbon nanofibers have been interesting candidate for the adsorption and removal of volatile organic compounds (VOCs). In this study, novel graphene oxide (GO)/carbon composite nanofibers with well-developed mesoporous structure are prepared easily from polyacrylonitrile and different content of GO by electrospinning and subsequent steam activation, and their adsorption performance for VOC vapors is evaluated for the first time. The resultant nanofibers were characterized by scanning electron microscopy, Raman spectroscopy, nitrogen adsorption and X-ray photoelectron spectroscopy. Dramatically, embedment of GO achieves the increased mesopores and high surface oxygen content of series of continuous composite nanofibers, and further mesopore volume, ratio and oxygen content show positive dependence on the amount of GO addition. Owing to such outstanding features, the novel composite nanofibers exhibit improved benzene and butanone adsorption capacities at high relative pressures and enhanced adsorption tendency for butanone over benzene, compared to pristine activated carbon nanofiber and conventional activated carbon fiber. The highest benzene and butanone adsorption capacities of the prepared composite nanofibers at 20°C and relative pressure of 0.98 reach 83.2 and 130.5cm3g−1, respectively. The introduction of GO simultaneously improves the adsorption capacities and adsorptive tendency of the nanofibers for polar VOCs. These results prove the great potential of composite nanofibers in practical adsorption for VOCs, especially polar ones.

Effect of micropore size distribution on phenol adsorption on steam activated carbons

The adsorption of phenol on microporous activated carbons (ACs) produced in laboratory from polyethyleneterephtalate (PET), furfuryl alcohol (PFA), polyacrylonitrile (PAN) and anthracene oil pitch (ASN) have been studied. The ACs have been obtained by carbonization and subsequent steam activation at 850 °C to 50 % burn off. For comparison, commercial activated carbons from coconut shell, and CWZ 22 carbon have been applied. All studied ACs are predominantly microporous and have neutral or basic surface characteristics. The pseudo second kinetic model and Langmuir equation were found to fit the experimental data very well. A very good correlation between the volume of pores with a width smaller than 1.4 nm (V1.4) and the volume of phenol calculated from Langmuir monolayer capacity (qm) was found. Based on that, it can be concluded that the phenol adsorption is governed mainly by micropore filling through the π–π dispersion interaction in micropores smaller than double molecular diameter of phenol.

Surface oxidation of activated electrospun carbon nanofibers and their adsorption performance for benzene, butanone and ethanol

Carbon nanofibers prepared by electrospinning and subsequent steam activation were oxidized by treatment in HNO3 and HNO3/H2SO4 mixture. Surface morphology and degree of graphitic structure of oxidized nanofibers are affected mildly by acid oxidation according to SEM and Raman measurement. Nitrogen adsorption/desorption isotherms demonstrate decrease in specific surface area and pore volume of carbon nanofibers after oxidation. XPS spectra exhibit that oxidized nanofibers possess higher surface oxygen content than pristine nanofibers. Higher water adsorption capacities on oxidized nanofibers determined by water adsorption isotherms suggest the improvement of surface polarity and hydrophilicity. Furthermore, adsorption isotherms of benzene, butanone and ethanol show that surface oxidation enhances the adsorption tendency for butanone and ethanol on nanofibers due to increased surface polarity, indicating that the adsorption selectivity to polar organic compounds is improved.

Adsorption of benzene and ethanol on activated carbon nanofibers prepared by electrospinning

Activated carbon nanofibers (ACNFs) were prepared by electrospinning polyacrylonitrile solutions, and subsequent steam activation process. The ACNFs were characterized by scanning electron microscope, X-ray photoelectron spectroscopy and nitrogen adsorption at 77 K. The adsorption equilibrium data for benzene and ethanol were obtained by using static vapor adsorption system. As-prepared ACNFs demonstrate higher adsorption capacities for volatile organic compounds (VOCs) than activated carbon fibers (ACFs) by virtue of smaller diameter and more available adsorption sites on the surface. The adsorption performance of ACNFs increases with the burn-off, as a result of the increased microporosity. In addition, it is noteworthy that surface chemistry has an important effect on the adsorption of polar VOCs. The ACNF with higher oxygen content has a stronger adsorption tendency for ethanol.

Activated carbon nanofiber anodes for microbial fuel cells

This investigation considers the use of activated carbon nanofiber nonwoven (ACNFN) as a novel anode for microbial fuel cells (MFCs). ACNFN has an ultra-thin, porous interconnected structure with high bioaccessible surface area. Reduced distances from the free surface to the interior maximize use of the available surface area and this, combined with high macroporosity ensures superior performance by decreasing transport limitations. ACNFN was fabricated by pyrolysis of electrospun polyacrylonitrile and subsequent steam activation. Extensive characterization, including surface morphology, material chemistry, surface area, mechanical strength and biofilm adhesion was performed to validate the use of the material as an MFC anode. Preliminary tests in a single chamber MFC showed current densities of 2715A/m3 which is about 10% greater than the highest maximum obtained so far. Further, this was achieved with a conductivity of only a fifth of that of the corresponding material. The bio-electrochemical performance of ACNFN was also compared to that of commonly-used anodes, carbon cloth and granular activated carbon. Such anode architecture will greatly help mitigate low power density issues which are one of the main factors limiting widespread adoption of MFCs.

Chicken Manure Biochar as Liming and Nutrient Source for Acid Appalachian Soil

Acid weathered soils often require lime and fertilizer application to overcome nutrient deficiencies and metal toxicity to increase soil productivity. Slow-pyrolysis chicken manure biochars, produced at 350 and 700°C with and without subsequent steam activation, were evaluated in an incubation study as soil amendments for a representative acid and highly weathered soil from Appalachia. Biochars were mixed at 5, 10, 20, and 40 g kg into a Gilpin soil (fine-loamy, mixed, active, mesic Typic Hapludult) and incubated in a climate-controlled chamber for 8 wk, along with a nonamended control and soil amended with agronomic dolomitic lime (AgLime). At the end of the incubation, soil pH, nutrient availability (by Mehlich-3 and ammonium bicarbonate diethylene triamine pentaacetic acid [AB-DTPA] extractions), and soil leachate composition were evaluated. Biochar effect on soil pH was process- and rate-dependent. Biochar increased soil pH from 4.8 to 6.6 at the high application rate (40 g kg), but was less effective than AgLime. Biochar produced at 350°C without activation had the least effect on soil pH. Biochar increased soil Mehlich-3 extractable micro- and macronutrients. On the basis of unit element applied, increase in pyrolysis temperature and biochar activation decreased availability of K, P, and S compared to nonactivated biochar produced at 350°C. Activated biochars reduced AB-DTPA extractable Al and Cd more than AgLime. Biochar did not increase NO in leachate, but increased dissolved organic carbon, total N and P, PO, SO, and K at high application rate (40 g kg). Risks of elevated levels of dissolved P may limit chicken manure biochar application rate. Applied at low rates, these biochars provide added nutritional value with low adverse impact on leachate composition.

Nickel/Carbon composite materials based on expanded graphite

Monolithic nickel/carbon (Ni/C) composites were prepared from coal tar pitch-impregnated compressed expanded graphite pre-decorated with NiO particles (EG NiO) by pyrolysis at 550 °C and subsequent steam activation at 800 °C. The microstructural arrangement of the Ni-comprising nanoparticles in the composites was investigated using transmission electron microscopy. The specific surface area and porosity of the composites were analyzed by nitrogen adsorption. The catalytic activity of the composites was compared with the material obtained by the conventional H 2 treatment of EG NiO using hydrocracking of 2,2,3-trimethylpentane as a model reaction.

Synthesis and electrochemical properties of activated carbons and Li4Ti5O12 as electrode materials for supercapacitors

New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li4Ti5O12, prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li4Ti5O12 oxide composite as a positive electrode, and an organic electrolyte (LiPF6–dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000–1,600 m2 g−1) and texture parameters, as well as three types of organic electrolytes: Et4NBF4–propylene carbonate (PC), LiBF4–PC and LiPF6–DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g−1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g−1 for the asymmetric SC cell, with good cycleability for both supercapacitor systems, were obtained.

Development of mesoporosity in activated carbons via coal modification using Ca- and Fe-exchange

The calcium and iron loading of coal by ion exchange was proposed as an efficient pretreatment to produce mesoporous activated carbons by carbonization and subsequent steam activation. Lignite (lignite A) was used as a kind of reference precursor due to natural ion-exchangeable ability. The incorporation of Fe into the Ca-loaded lignite led to the activated carbon (AC) with better-developed mesoporosity than produced from Ca- or Fe-exchanged lignite. For gas coal (hvBb), prior to calcium loading, two different treatments, i.e. oxidation with nitric acid and sulfonation with sulfuric acid, were applied to generate the ion-exchangeable groups on the coal surface. The impact of acid pretreatments on the coal structure and the porous texture of resultant activated carbons was determined. The sulfuric acid treatment resulted in a higher cation-exchangeable capacity compared with the use of nitric acid. As a result, the Ca loading level of sulfonated gas coal was higher than that of the oxidized coal. At a solution pH around 2.5, the loading of both Ca-preexchanged coals with iron gave approximately 1 wt.% of a highly dispersed iron in coal. The ACs from Ca/Fe-loaded lignite and gas coal are characterized by mesopore volumes between 0.405 and 0.496 cm 3 g −1 and very high mesopore fraction, in the range of 77–83%. For the AC from loaded sulfonated gas coal the mesopores are mainly distributed at 2–10 nm, whereas the AC from loaded oxidized coal shows a predominant contribution of pores between 10 and 50 nm. Acid washing of resultant mesoporous activated carbons resulted in an increase of mesopore volume, by 20–25%.

Effect of MoCl5 addition on the carbonization and the subsequent steam activation of pitch and coking coals

The present work is devoted to the study of the role of MoCl 5 and its by-products on reactions involved in pore formation during the preparation of activated carbon for the manufacture of carbon-supported catalysts. The carbonaceous precursors were a coal tar pitch and three bituminous coals of increasing rank. Continuous detection of evolved tar and gas during carbonization was implemented and the data were correlated with the porosity development during carbonization and subsequent steam activation. It was found that MoCl 5 promotes the microporosity growth during carbonization by dehydrogenation reactions leading to cross-linking and condensation reactions. The pores left in the char, as well as the residual molybdenum compounds, favour the development of the porosity during steam activation.

カラマツの高度利用を目的とした活性炭の製造 （Ｉ） 回分式流動床法で調製したカラマツ活性炭の表面積

Carbonization of powderd larch wood and bark, with diameter of 0.18-0.50mm, followed by steam activation was made in a batchwise fluidized bed reactor for the production of activated carbon as their advanced use. It is found that carbonization at 773K was optimum in term of specific surface area for activated carbon. In the subsequent steam activation of chars conducted at 1023, 1073 and 1173K for 0.5-3.0h, higher temperature and longer time gave larger surface area at the cost of the yield. This indicated a close relation between surface area and yield for activated carbons obtained. An activated larch wood char had the surface area of 1, 500m2/g as the maximum, and this value was equal or superior to those of activated carbons from fir wood, quercus wood and coconut shell. Larch bark char after activation also was almost equal to coalderived commercial activated carbons in the surface area. These results showed a promising aspect of conversion of the whole larch into activated carbon as higher value added product compared to the conventional use as packing and palette materials.

Porous structure of polyarylamide-based activated carbon fibres

Activated carbons were prepared from two polyarylamide fibres (Kevlar and Nomex) by carbonization and subsequent steam activation to 25 and 50% burn-off. The porous structure of the carbons has been investigated by physical adsorption of CH 2Cl 2 and N 2O at 293 K and immersion calorimetry into liquids of different molecular dimensions. The activated fibres have good sorptive capacities and relatively narrow micropores. The materials resulting from activation at low degrees of burn-off could therefore be of great interest in gas separation, owing to their molecular-sieve properties. Compared to industrial activated carbons, the fibres are hydrophilic and have small external surface areas.

Influence of heat treatment conditions on the porosity changes of sulfonated styrene/divinylbenzene copolymers

AbstractSulfonic cation exchangers with two ion exchange group concentrations (0.5 and 2.4 mmol/g, samples A and B, respectively) were obtained by sulfonation of a porous styrene (S) and divinylbenzene (DVB) copolymer with chlorosulfonic acid. Strong thermal decomposition of the sulfonated copolymer A, accompanied by significant changes in its porous structure, starts at ca. 400°C. The char has no sulfonic groups. After heat treatment at 400°C in steam, a sorbent was obtained (yield 65%) that shows higher phenol sorption than the untreated sample when related to the bed volume. The chlorosulfonic derivatives of the initial copolymer were less thermally resistant than the sulfonic ones obtained by hydrolysis. Pyrolysis of the cation exchanger B, in its H+ and Ca2+ forms, was carried out at 900°C (yield of both chars close to 30%). By subsequent steam activation at 800°C to a 50% burn‐off of the char, sorbents with well‐developed, but distinctly different, porous structures were obtained. The activated char from the sulfonated copolymer in its hydrogen form was highly microporous and indicated an effective surface area of 1180 m2/g. However, because of a low contribution of mesopores, its ability to adsorb phenol from the liquid phase was not very high. The activated char from the calcium‐doped copolymer, indicating a smaller surface area (580 m2/g) but characterized by a well‐developed mesoporosity, was a better sorbent for phenol. © 1994 John Wiley & Sons, Inc.