Self-generated Atmosphere Research Articles

Preparation of High Surface Area Mesoporous Activated Carbon: Kinetics and Equilibrium Isotherm

Activated carbon prepared from palm shell by phosphoric acid impregnation, at significantly favorable experimental conditions is characterized for the porous nature and adsorption of methylene blue dye molecules. The activation is carried out using a 2-stage activation process with the activation in a self-generated atmosphere. An activation temperature of 500°C, with an activation time of 75 minutes using a phosphoric acid impregnation ratio of 3 has yielded an activated carbon having unique characteristics. An activated carbon with a yield of 48%, total pore volume of 1.9 cm3/g, surface area of 1956 m2/g, an average pore diameter of 3.8 nm, with the ratio of the mesopore to the total surface area in excess of 75% has been prepared. The activated carbon exhibits a high methylene blue equilibrium adsorption capacity of 438 mg/g with the adsorption isotherm increasing with an increase in the adsorption temperature. Among the various adsorption isotherm models, the Langmuir model is able to explain the adsorption process well, evidenced by the proximity of the model with the experimental data. Among the different kinetic models tested with the experimental kinetic data, a pseudo-second-order model is found to fit the experimental data with close proximity.

Preparation of granular activated carbon from hydrothermally treated and pelletized deciduous wood

Dense mechanically strong granular activated carbon (GAC) was prepared from hydrothermally modified and pelletized grey alder ( Alnus incana (L.) Moench) (GA) wood by direct carbonization and physical activation with superheated steam under a self-generated atmosphere. Hemicellulose autohydrolysis products, formed during hydrothermal treatment, provide a bounding and bulking effect during the modified wood pelletization process. After carbonization and activation, a mechanically strong activated carbon structure containing up to 45% micropores was developed. The influence of the moisture content of the modified wood (MW) before pelletization in a range of 4–12 wt% as well as the carbonization temperature of the obtained pellets 300–700 °C on the thermochemical and mechanical properties, and the developed porous structure of the GAC was studied. It has been found that MW pellets, derived from GA wood treated at 180 °C for 2 h, are thermally more stable than the raw GA wood. Samples with a higher content of cellulose and lignin reached higher char yields. The mechanical and surface properties of GAC depend on the combined effect of the employed conditions. If mechanically strong high-density granular adsorbents are necessary, pelletization of MW with the moisture content 6–12 wt% is preferable, and the optimal carbonization temperature is 600 °C.

Preparation of nanostructured materials through thermolysis of metal chelate complexes

We demonstrate that nanocomposites (metals and metal carbides and sulfides) can be produced by thermolysis (370 and 600°C) in a self-generated atmosphere using Cu(II), Co(II), and Ni(II) 2-hydroxy- and 2-N-tosylaminobenzaldehyde azomethine bis-chelates as precursors.

On the preparation and characterization of activated carbon from mangosteen shell

Activated carbon derived from mangosteen shells has been prepared by K 2CO 3 activation utilizing two stage carbonization process in a self-generated atmosphere. Experiments were carried out at different K 2CO 3/char (K/C) ratios, carbonization temperatures and retention time, which had significant effect on the performances of activated carbons (expressed in terms of iodine and methylene blue numbers and yield). Specific surface area of activated carbon was maximum as 1123 m 2 g −1 at 900 °C with activation duration of 2 h and at a K 2CO 3/char mass ratio of 1.0. The porous properties, surface microstructure in addition to the surface functional groups of the prepared carbons were characterized by N 2 adsorption/desorption isotherm, FE-SEM and FTIR, respectively.

Activation of palm shells by phosphoric acid impregnation for high yielding activated carbon

A compilation of the yield of activated carbons corresponding to good textural characteristics (BET surface area > 1000 m 2/g) derived from palm shells, irrespective of the activation process has revealed a yield lower than 30%. Having known the ability of chemical activation methods to produce high yielding activated carbons, the present study utilizes a two stage activation process in a self-generated atmosphere to prepare activated carbon. A low activation temperature (425 °C) and activation time (30 min) has been utilized, while varying the impregnation ratio of phosphoric acid from 0.5 to 3. The yield of activated carbon is not found to vary with the impregnation ratio and is found to be around 50%. The textural characteristics are found to improve with increase in the impregnation ratio, up to an optimal value of 2, while found to decrease beyond. The BET surface area of activated carbon corresponding to an impregnation ratio of 3, with an iodine number of 1035 mg/g is found to be 1109 m 2/g with a pore volume of 0.903 cm 3/g and an average pore diameter of 3.2 nm. The textural characteristics of activated carbon reveal that the pore size is widely distributed with the contribution of micropores around 50%.

Thermal Decomposition of Magnesium Sulfate heptahydrate under Self-generated Atmosphere

Thermal Decomposition of Magnesium Sulfate heptahydrate under Self-generated Atmosphere

Morphology and Sorption Kinetic Studies of L-Type Activated Carbons Prepared from Oil Palm Shells by ZnCl2 and H3PO4 Activation

The aim of this investigation was to study the morphology and sorption kinetic studies of an L-type activated carbon prepared from Oil Palm Shells (OPS) by way of the two stage activation method in self-generated atmosphere using a muffle furnace. Both L-type dehydrating agents, zinc chloride and phosphoric acid were used as the chemical activation agent. For the ZnCl2 samples, the optimum adsorption capacity was obtained when the samples were subjected to semi-carbonization of 400°C, 5 M ZnCl2 impregnating solution, followed by pyrolysis at 400°C. Whereas for the H3PO4 samples, semi-carbonization of 400°C followed by 4.5 M H3PO4 impregnating solution and pyrolysis at 400°C has shown to produced the optimum adsorption capacity. All activated carbons were fitted well in the Langmuir adsorption isotherm and the pseudo-second-order kinetics. These results demonstrated that this agricultural waste has the potential to be converted into high-capacity adsorbent for the remediation of waste waters. © 2009 Asian Network for Scientific Information.

Sorption Kinetic Studies of Medical Grade Activated Carbon Prepared from Papaya Seeds

The aim of this investigation was to determine the adsorption behavior and kinetics of methylene blue in aqueous solution on activated carbons prepared from papaya seeds by way of the two stage activation method in self-generated atmosphere using a muffle furnace. The optimised activated carbon, AK7, had a sorption kinetic that complied with the pseudo-second order kinetics and was fitted well to Langmuir isotherm model. The highest adsorption capacity of 97.09 mg g-1was obtained when the samples (AK7) were subjected to activation temperature of 500oC for 60 minutes with the percentage of methylene blue removal efficiency of 99.5%.

Composites of lignin and polyacrylonitrile as carbon precursors

Films of polyacrylonitrile and lignin cast from dimethylformamide were studied by dynamic thermal analysis in a self-generated atmosphere and in a vacuum. The occurrence of a thermochemical reaction of the components on heating was demonstrated. The optimal conditions of the reaction between polyacrylonitrile and lignin were determined.

In situ modification of activated carbons developed from a native invasive wood on removal of trace toxic metals from wastewater

Activated carbons were developed by phosphoric acid activation of sawdust from Prosopis ruscifolia wood, an indigenous invasive species of degraded lands, at moderate conditions (acid/precursor ratio = 2, 450 °C, 0.5 h). For in situ modification of their characteristics, either a self-generated atmosphere or flowing air was used. The activated carbons developed in the self-generated atmosphere showed higher BET surface area (2281 m 2/g) and total pore volume (1.7 cm 3/g) than those obtained under flowing air (1638 m 2/g and 1.3 cm 3/g). Conversely, the latter possessed a higher total amount of surface acidic/polar oxygen groups (2.2 meq/g) than the former (1.5 meq/g). To evaluate their metal sorption capability, adsorption isotherms of Cu(II) ion from model solutions were determined and properly described by the Langmuir model. Maximum sorption capacity ( X m) for the air-derived carbons ( X m = 0.44 mmol/g) almost duplicated the value for those obtained in the self-generated atmosphere ( X m = 0.24 mmol/g), pointing to a predominant effect of the surface functionalities on metal sequestering behaviour. The air-derived carbons also demonstrated a superior effectiveness in removing Cd(II) ions as determined from additional assays in equilibrium conditions. Accordingly, effective phosphoric acid-activated carbons from Prosopis wood for toxic metals removal from wastewater may be developed by in situ modification of their characteristics operating under flowing air.

The use of thermogravimetric analysis technique for the characterization of construction materials

The thermogravimetric analysis (TG) technique is widely used in the characterization of diverse types of construction materials related to binders, such as plasters, limes and cements. For calcium sulphate dihydrate (gypsum) two serial dehydration steps are very near in temperature decomposition and overlapping in the thermogravimetric events is observed. The goal of this research is to develop new thermogravimetric analysis procedures that allow obtaining more precise information in the characterization of plasters. The resolution of both dehydration events has been increased using two different strategies: on one hand, the production in the experience of a water vapour self-generated atmosphere by the use of sealed aluminium pan with a pinholed lid. On the other hand, the use of high resolution thermogravimetric analysis (HRTG), based on the variation of the heating rate as a function of the rate of mass loss observed at once. The results obtained for both strategies of improvement of the TG curves, showed that they are two procedures that let to obtain a total resolution of the two dehydration steps for gypsum.

Analysis of Various Experimental Methods and Preparation of Mesoporous Activated Carbon Powders from Sawdust Using Phosphoric Acid

A critical analysis of various reported experimental methods utilized for preparation of activated carbon using phosphoric acid was attempted to identify the right choice of experimental method. The various experimental methods were grouped into three major categories; of these, a two-stage activation process with the precursor exposed to preset furnace temperature in a self-generated atmosphere was identified to be a suitable method. Accordingly, activated carbon powders were prepared utilizing a two-stage activation process, covering the effect of activation time at 500°C with an impregnation ratio of 1.5. The samples were subjected to adsorption using methylene blue dye, and the adsorption capacity was found to increase with increase in activation time. An adsorption capacity greater than 400 mg/g of activated carbon shows highly developed pores, with pore size higher than 1.5 nm signifying its economical application to commercial liquid-phase adsorption processes. The adsorption isotherms were found to match well with the Langmuir isotherm model with correlation coefficient (r 2) greater than 0.95 as compared to the Freundlich isotherm model with r 2 less than 0.8.

Differential thermal analysis under quasi-isothermal, quasi-isobaric conditions (Q-DTA): Part II. Water evaporation and the decomposition mechanism of compounds with structural and crystal water

It is already a generally accepted opinion today that the course of DTA, DSC and TG curves is deteriorated by the non-isothermal heating control and by other experimental conditions to such an extent that it is more characteristic for the experimental conditions, than for the transformation itself.This problem can be eliminated completely by the simultaneous use of “transformation-governed heating control” (TGHC) and “self-generated atmosphere” (SGA) ensuring quasi-isothermal, quasi-isobaric conditions for the DTA measuring technique (Q-DTA).This experience is proven on the examples of the evaporation of water under boiling, the dehydration of Ca(OH)2, CuSO4·5H2O, CaBr2·6H2O, Mg(OH)2 and CaSO4·2H2O by providing both, the results obtained by the DTA, TG and the Q-DTA measuring techniques.

Production of activated carbon from rubber wood sawdust

The present work comprehensively addresses various experimental methods reported in the literature and substantiates the use of two-stage activation process with semi-carbonization stage up to 200°C as first stage followed by an activation stage at a desired temperature, for production of activated carbon from carbonaceous precursors using phosphoric acid. Efforts are made towards developing a high surface area activated carbon from rubber wood sawdust by a two-stage activation process with phosphoric acid as the activating agent. Experiments are conducted in a lab scale muffle furnace under static conditions in a self-generated atmosphere covering process parameters such as impregnation ratio, carbonization time and temperature. The precursor material with impregnation agent is exposed straightaway to semi-carbonization and activation temperature unlike following the specific temperature progression as reported in the literature. The process parameters are optimized based on product yield and iodine number. Semi-carbonization at 200°C for 15min followed by activation at 500°C for 45min with impregnation ratio of 1.5 yielded a product with iodine number 1096 which corresponds to a BET surface area of 1496m2/g with the product yield of 35% and activation agent recovery of 90%.

Kinetics of thermal dehydration and decomposition of hydrated chlorides of some 3d transition metals (Mn-Co series). Part-III. Dehydration and decomposition of CoCl2 hydrates

The kinetics of dehydration of NiCl 2 .2H 2 O have been studied by isothermal method in air and by non-isothermal method in air as well as in flowing nitrogen atmosphere. While in air (or self-generated atmosphere) the dehydration apparently takes place in single step, in nitrogen atmosphere two steps, corresponding to the losses of about 1.46 and 0.48 moles of H 2 O, can be identified in the TG curves. Whereas in static air three-dimensional diffusion (D3 or D4 model) appears to be the best fit mechanistic model, in nitrogen atmosphere the three-dimensional progress of the reaction phase boundary (R3) followed by the first order decay of partially dehydrated porous particles (Fl ) appear to be the best fit models for the two steps of dehydration. When the hydrated salt is calcined at temperature above 450, rapid dehydration renders the material porous and therefore, subsequent dechlorination also follows first order decay law (Fl). Generally, there is a broad agreement in mechanistic model as well as in Arrhenius parameters between isothermal and non-isothermal methods of dehydration.

Kinetics of thermal dehydration and decomposition of hydrated chlorides of some 3d transition metals (Mn-Cu series). Part-I. Dehydration of MnCl2.4H2O

The thermal dehydration of MnCl 2 hydrate has been studied by using simultaneous TG/DTA under the static air (or self-generated atmosphere) and also under the flowing nitrogen condition at different heating rates. In either of the above condition the salt dehydrates in three steps, with the losses of about 1.0, 1.2 and 1.1 moles of water in static air and 0.9, 2.1 and 1.1 moles of water in flowing nitrogen atmosphere. The heats of the three steps of dehydration in air have been estimate2d from area under the corresponding DTA peaks at the heating rate of 10°/min. The first step of dehydration is accompanied with the melting of the salt and therefore does not follow any kinetic model of solid state decomposition. For the other two steps of dehydration changes in the mechanism are observed and attempts have been made to identify these changes. All these have been possible by converting non-isothermal time into isothermal time which is more appropriate in the kinetic analysis. It is observed that either nucleation and growth or progress of the reactant/product interface is generally the most suitable kinetic model for the dehydration of manganese chloride hydrate.

Differential thermal analysis under quasi-isothermal, quasi-isobaric conditions (Q-DTA): Examinations using “transformation-governed heating control” and “self-generated atmosphere” (TGHC-SGA)

The course of conventional DTA or DSC curves is rather characteristic of the experimental conditions then of the transformation itself. The course of Q-TA T curves taken by the Q-DTA measuring technique is not deteriorated by these factors when using the “transformation-governed heating control” (TGHC). In this technique, namely, the temperature of the sample is governed by the transformation itself based on the feed-back principle so that the relay-switch system of the Q-DTA apparatus sensing the change of the Q-DTA t signal governs the heating control unit in a way, in which the transformation proceeds with a predetermined, very small and strictly constant rate by providing the suitable difference between the temperatures of the sample and the furnace. In order to normalise the experimental conditions, for decomposition reactions a particular, so-called “labyrinth crucible” should also be used, which provides a “self-generated atmosphere” already at the beginning of the reaction, and keeps the partial pressure of gaseous decomposition products constant at their maximum value of 100 kPa till the end of the transformation. This way, the unique normal characteristic temperature of reactions and transformations, together with reaction heat belonging to them can be measured, and the course of transformations free of every foreign influence can also be recorded.

Thermochemical Reactions of H Complexes

Thermal reactions of H complexes formed by methyl and ethyl diesters of aromatic tetracarboxylic acids with diamines were studied by thermal analysis. Some kinetic parameters of formation and degradation of polyimides during thermolysis in the self-generated atmosphere were determined.

Detection of four different OH-groups in ground kaolinite with controlled-rate thermal analysis

The thermal behaviour of mechanochemically treated kaolinite has been investigated under dynamic and controlled rate thermal analysis (CRTA) conditions. Ten hours of grinding of kaolinite results in the loss of the d(001) spacing and the replacement of some 60% of the kaolinite hydroxyls with water. Kaolinite normally dehydroxylates in a single mass loss stage between 400 and 600°C. CRTA technology enables the dehydroxylation of the ground mineral to be observed in four overlapping stages at 385, 404, 420 and 433°C under quasi-isobaric condition in a self-generated atmosphere. It is proposed that mechanochemical treatment of the kaolinite causes the localization of the protons when the long range ordering is lost.

Arundo donax cane as a precursor for activated carbons preparation by phosphoric acid activation

Canes from Arundo donax, a herbaceous rapid-growing plant, were used as precursor for activated carbon preparation by phosphoric acid activation under a self-generated atmosphere. The influence of the carbonization temperature in the range 400–550 °C and of the weight ratio phosphoric acid to precursor ( R=1.5–2.5) on the developed porous structure of the resulting carbons was studied for 1 h of carbonization time. Surface properties of the activated carbons were dependent on a combined effect of the conditions employed. Carbons developed either with R=1.5 over the range 400–500 °C, or with R=2 at 500 °C exhibited surface areas of around 1100 m 2/ g , the latter conditions promoting a larger pore volume and enhanced mesoporous character. For both ratios, temperature above 500 °C led to reduction in porosity development. A similar effect was found for the highest ratio ( R=2.5) and 500 °C. The influence of carrying out the carbonization either for times shorter than 1 h or under flowing N 2 was also examined at selected conditions ( R=2, 500 °C). Shorter times induced increase in the surface area ( ∼1300 m 2/ g ), yielding carbons with smaller mean pore radius. Activated carbons obtained under flowing N 2 possessed predominant microporous structures and larger ash contents than the samples derived in the self-generated atmosphere.