Feasibility of local cotton stalks for production of activated carbon by H3PO4 on a pilot scale

Good adsorbing carbon was obitained, for the first time in a pilot scale, from cotton stalks in a locally-designed rotary pyrolyzer. Activation was performed in absence of any purging gases by imprgnation with 50% H3P04 followed by heat treatment at 420°C. Mechanically cut short sticks were soaked in diluted H3PO4 for a short duration [Batch 1] and an extended period [Batch 2] prior to thermal treatment. The derived carbons contained both coarse and fine grains with acidic effect. Porosity was characterized by N2 adsorption at 77 [o]K and the isotherms analyzed by the alpha-method to estimate total and microporous surface areas in addition to total and microporous volumes. The produced carbons exhibited well-developed porosity that was essentially microporous in composition. Several key performance parameters were altered considerably as a result of impregnation with H3PO4 and the extended chemical activation period [Batch 2]. Most of the internal porosity of both carbons was accessible to adsorption of iodine, whereas the uptake of methylene blue dye was proportional to the average size of micropores which were larger for the batch with a longer acid soaking time. SEM and FTIR investigations revealed the presence of a developed honeycomb structure and different oxygen functionalities on surfaces of the activated products which are advantageous in liquid-phase applications. Preliminary laboratory-scale experiments with Pb[II] indicate that adsorption capacity of target heavy metals compares favorably with commercially-available activated carbons. The raw material, pre-processing, and activation process prove feasible for the production of activated carbon on a large scale, thereby providing a sustainable strategy for treatment of toxic waste streams

Minimizing water pollution via removal of hazardous organics onto biomass-activated carbons

Liquid-phase adsorption of phenol [P], para-nitrophenol [PNP], 2, 4-dinitrophenol [DNP], 4-aminophenol [PAP] and 2,4-dichlorophenol [DCP] onto a series or activated carbons were measured under equilibrium conditions, at room temperature. Three carbon samples were obtained from maize stalks by impregnation with different concentrations of H3PO4. One activated carbon sample was obtained by the one-step steam pyrolysis at 700°C, the last fifth carbon sample was the non activated carbon and was prepared by carbonizing the raw material at 500°C for 3 hr. The adsorption capacity of mthelyene blue [MB], rhodamine B [RB] and Congo red [CR] dyes onto the investigated adsorbents was determined via one point bottle test as mg/g. The raw material and their carbon adsorbents showed high adsorption capacity towards both categories of pollutants, phenolics and dyes. Linear form or Langmuir and Freundlich equations were employed to analyze the equilibrium adsorption data which show a satisfactory fit in most cases. The results indicate that Langmuir isotherm was more favorable for the removal of these phenolic derivatives in most cases whereas the Freundlich isotherm is better for the high porosity sample of medium acid concentration which adsorbed the biggest amounts of these pollutants. The sequence of phenolic uptake was DCP>DNP> PNP>P> PAP and was found to be related to both nature or the carbon-surface and porosity besides the solubility and molecular dimensions of the solutes. Low affinity towards phenol may be associated with its competition with water molecules which are more favorably attracted to the acidic surface that are charged with oxygen functional groups. The dye uptake onto the studied sorbents follows the order MB>RB>CR which was attributed to the fact that MB are more accessible to a significant fraction of the pore system which is not available for both others bulky molecules of RB and CR. Dye uptake was found to be controlled by surface chemical nature rater than porosity. The adsorption or both phenolic derivatives and dyes from their aqueous solutions were found to be controlled by both the surface chemical nature and porosity besides the solute nature

Removal of phenolic pollutants in single and binary solutes from water onto carbons derived from corncobs

Activated carbons derived from corncobs as well as their metal-loaded chars were investigated to find the suitability of their application for the removal of ortho-, meta- and para-nitrophenols besides phenol in single and bi-solute aqueous systems. Three types of activations namely; thermal activation via one step steam pyrolysis at 700°C and two step steam at 850 C as well as chemical activation using H3PO4 impregnation then pyrolysis at 500 C. The non-activated carbon sample, char, was impregnated with calculated amount of each of iron, nickel, copper or calcium nitrates then pyrolysed at 500 C to obtain four metal-loaded carbons. The adsorption capacity of the investigated carbons was carried out via measuring their phenol and/or nitrophenols numbers in single and bisolute systems at 25°C in their aqueous solutions. The results indicate that in bi-solute systems the presence of two solutes decreases the phenolic number of each component than that in the single system, which ascribed to the competition arising between the two solutes on the same number of adsorption sites on the adsorbent surface. It is clear that there are other factors, beside porosity and surface nature, controlling the adsorption process of phenol and/or nitrophenols. The removal capacity of nitrophcnol was found to be affected with the orientation in the nitro-group site and the obtained uptake was ordered 4NP > 3NP > 2NP. The results indicate that in bi-solute systems the presence of two solutes decreases the phenolic number of each component than in the single system, which ascribed to the competition arising between the two solutes on the same number of adsorption sites on the adsorbent surface. Para-nitrophenol measured the highest uptake compared with its other mono-substituted phenols which may be attributed to its ability to form intermolecular hydrogen bonding structure and the absence of steric hindrance which may control the adsorption of the ortho- and meta-nitrophenols. Among the investigated adsorbent, the highest adsorption capacity was exhibited by the one step steam pyrolysis activated carbon sample which refers to its surface nature of highly basic surface and porosity

Effects of doping with CeO[2] and calcination temperature on physicohcemical properties of NiO/Al[2]O[3] system

The effects of doping with CeO[2] and calcinations temperature on physicochemical properties of NiO/Al[2]O[3] system have been investigated using DTA, XRD, nitrogen adsorption measurements at - 196 [degree sign] C techniques and decomposition of H[2]O[2] at 30-50 [degree sign] C. The pure and variously doped mixed solids were subjected to heat treatment at 300, 400, 700, 900 and 1000 [degree sign] C. The amounts of dopant were 0.75, 1.5 and 3 mol% CeO[2]. The results revealed that the presence of NiO with aluminium oxide much enhanced the degree of crystallinity of the gamma-Al[2]O[3] phase. In contrast, the presence of Al[2]O[3] much retarded the crystallization process of the NiO phase. The specific surface areas were found to increase with increasing calcinations temperature from 300 to 400 [degree sign] C and with doping of the system under investigation with CeO[2]. The pure and variously doped solids, calcined at 300 and 400 [degree sign] C, were constituted of amorphous NiO dispersed in gamma-Al[2]O[3] Heating at 700[degree sign] C resulted in formation of poorly crystalline NiO and gamma-Al[2]O[3] phases beside CeO[2] for the doped solids. Crystalline NiAl[2]O[4] phase was formed starting from 900[degree sign] C as a result of solid-solid interaction between the reacted oxides. The degree of crystallinity of NiAl[2]O[4] increased with increasing the calcinations temperature from 900 to 1000 [degree sign]. An opposite effect was observed upon doping with CeO[2]. NiO/Al[2]O[3] system calcined at 300 and 400 [degree sign] has catalytic activity higher than individual NiO obtained at the same calcinations temperature. The catalytic activity of NiO/Al[2]O[3] system increased, progressively, with increasing the amount of CeO[2] dopant. The doping process did not modify the mechanism of the catalyzed reaction but changed the concentration of active sties without changing their energetic nature

insight into KOH activation mechanism via production of microporous activated carbon for heavy metal removal

Maize stalks raw material was activated by KOH. The concentration of KOH was varied between 33-75 wt%. The KOH-treated raw materials were carbonized at 700 degree C to produce a series of four activated carbons, besides a non-activated sample that was prepared and carbonized at 550 degree C. The pore properties of these carbons were characterized by the Langmuir, BET and DubininRadushkevich liner equations as well as both a, and t- methods based on nitrogen adsorption isotherms. The chemical reactions involved during the impregnation and then carbonization processes have been supposed for these hydroxide/lignocellose mixtures. Deep insight has been obtained concerning the possible reactions mechanism. The results showed that the activated carbons obtained are mainly of the microporous type. The KOH ratio was found to be the basic indicator of the micoporosity development, the increase in the concentration of KOH much increased the S values of the resulting carbons reaching a maximum limit at 66 wt% KOH with S alpha of 1680 m2/g and micropore ratio of 85% displaying an inverse correlation thereafter. The thermal behaviour and the surface microstructure in addition to the surface functional groups of the maize stalks and their prepared carbons were investigated by TG, SEM and FTIR. The investigated carbons uptaked significant amounts of Pb2+ ions from aqueous solutions. The application of Langmuir and Freundlich liquid phase adsorption models showed a satisfactory fit to the adsorption data which ascribed, basically, here to both porosity and surface chemical nature of the adsorbents

Surface and catalytic properties of Mn2O3/MgO system doped with ZnO

The effects of calcination temperature and doping of Mn2O3/MgO system with ZnO on its surface and catalytic properties were investigated. The techniques employed were nitrogen adsorption at -196°C. XRD and H2O2 decomposition at 30-50°C. Pure and variously doped solids were prepared by wet impregnation method using manganese nitrate, magnesium basic carbonate and zinc nitrate. The prepared solids were calcined at 400, 600, 700, 900 and 1000°C. The amount of Mn2O3 was fixed at 20 mol% for all solids. The dopant concentration was changed between 0.75 and 3 mol% ZnO. The results revealed that manganese oxides interacted with magnesium oxide to yield crystallized magnesium manganates at temperature starting from 400°C. Pure and doped solids precalcined at 400°C consisted of MgO and MgMnO3 phases. The degree of crystallinity of the detected phases increased with increasing the calcination temperature to 600°C with detection of poorly crystalline Mn2O3. Furthermore, ZnO-doping of the system investigated followed by calcination at 400°C and 600°C resulted in decreasing the intensity of the diffraction lines with subsequent decrease the detected phases, in their crystallite size and increases their surface areas [SBET] up to a certain extent of dopant added. ZnO doping hinders the formation of MgMnO3 phase at 400 and 600°C. At 700°C, Mn2O3, Mg6MnO8 and Mg2MnO4 phases were detected. At 900 and 1000°C, only, well crystalline Mg6MnO8 and Mg2MnO4 phases were detected for all the solids. The doping process carried out at 400 and 600°C increased effectively the catalytic activity of the system under investigation reaching a maximum limit at 1.5 mol% ZnO. The increase in dopant concentration above this limit decreased the catalytic activity which remained greater than those measured for the pure solids calcined at the same temperatures. The presence of 1.5 mol ZnO brought about an increase of 191% and 144% of the catalytic activity of the solids calcined at 400 and 600°C, respectively. The doping process did not affect the activation energy values of the catalyzed reaction but rather increased the concentration of active sites involved in the catalyzed reaction without changing their energetic nature