Conversion of Poly(Ethylene Terephthalate) Waste into Activated Carbon: Chemical Activation and Characterization

Due to its high carbon content, low impurities, low cost and easy availability, poly(ethylene terephthalate) (PET) waste is considered as a suitable precursor for the production of activated carbon. The chemical activation of PET wastes using different chemical agents such as H₃PO₄, H₂SO₄, ZnCl₂, and KOH was investigated. KOH‐ and ZnCl₂‐activated PET were found to be the best choices for the adsorption of small and large molecules. The capacities of the adsorbents towards I₂, methylene blue, N₂, CH₄, and CO₂ followed the order KOH‐PET >H₃PO₄‐PET > ZnCl₂‐PET > H₂SO₄‐PET; however, in the molasses uptake and selective adsorption of CO₂ compared to CH₄, ZnCl₂‐PET performed better than the other adsorbents.     

Spherical carbons: Synthesis,characterization and activation processes

Spherical carbons have been prepared through hydrothermal treatment of three carbohydrates (glucose, saccharose and cellulose). Preparation variables such as treatment time, treatment temperature and concentration of carbohydrate have been analyzed to obtain spherical carbons. These spherical carbons can be prepared with particle sizes larger than 10 μm, especially from saccharose, and have subsequently been activated using different activation processes (H₃PO₄, NaOH, KOH or physical activation with CO₂) to develop their textural properties. All these spherical carbons maintained their spherical morphology after the activation process, except when KOH/carbon ratios higher than 4/1 were used, which caused partial destruction of the spheres. The spherical activated carbons develop interesting textural properties with the four activating agents employed, reaching surface areas up to 3100 m²/g. Comparison of spherical activated carbons obtained with the different activating agents, taking into account the yields obtained after the activation process, shows that phosphoric acid activation produces spherical activated carbons with higher developed surface areas. Also, the spherical activated carbons present different oxygen groups’ content depending on the activating agent employed (higher surface oxygen groups content for chemical activation than for physical activation).     

Effect of different catalysts on urea–formaldehyde resin synthesis

Four catalysts (H₂SO₄, HCl, H₃PO₄, and NaOH/NH₄OH) were studied in the preparation of melamine modified urea–formaldehyde (UFM) resins. ¹³C‐nuclear magnetic resonance spectroscopic analysis of the UFM resins at different synthesis stages revealed the polymer structure and detailed reaction mechanism. Three acidic catalysts (H₂SO₄, HCl, and H₃PO₄) enhanced the resin polymerization through the formation of various contents of methylene, ether linkages, and urons. H₃PO₄ yielded the most terminal ether linkages at the first stage and enhanced polycondensation by depleting all free urea and glycols to form the most linear methylene linkages NHCH₂NH in the end. However, at the initial synthesis stage, NaOH/NH₄OH catalyzed the formation of UFM prepolymer to a limited extent with a large amount of free urea left, and therefore produced the final polymer with relatively more substituted methylolureas and linear ether linkages. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40644.     

Feasibility of recycling KOH in chemical activation of oil‐sands petroleum coke

Although potassium hydroxide (KOH) is known to be effective in generating highly porous activated carbons, the mechanism of KOH activation has not been well elucidated. To develop porosity in carbon, a high KOH/carbon mass ratio must be maintained. Consequently, KOH, as the activating agent, represents a major part of the cost of the activation process. Focusing on the mechanism, particularly the activation products, the present work attempted to establish the technical feasibility of recycling KOH. Experiments revealed that the major products of KOH activation at 600–900°C are metallic K, K₂CO₃, CO and H₂, which is supported by thermodynamic analysis. The overall reaction may be written as 6KOH + 4C = K₂CO₃ + 4K + 3H₂ + 3CO. At temperatures over 900°C, K₂CO₃ becomes unstable and participates in activation reactions with carbon; a more suitable overall reaction would be KOH + C = CO + K + 0.5H₂. As potassium ion is reduced to metallic K which is readily converted into KOH and hydrogen gas upon reacting with water, KOH recycling is feasible. The reuse of KOH in chemical activation could substantially reduce the cost of activation process. © 2011 Canadian Society for Chemical Engineering     

Characterization and performance of melamine enhanced urea formaldehyde resin for bonding southern pine particleboard

Urea‐formaldehyde resins modified by melamine were synthesized by four catalysts (H₂SO₄, HCl, H₃PO₄, and NaOH/NH₄OH) with a F/U/M molar ratio of 1.38/1/0.074. Resin structure and thermal behavior were studied by ¹³C‐NMR and DSC techniques. For H₂SO₄, HCl, and H₃PO₄ catalysts, resins were prepared by two stage pH adjustment: the first pH stage was set at 1.25 (H₃PO₄ pH 1.60) and second pH stage was set at 5.0. For the NaOH/NH₄OH catalyst, the resin was set at pH 5.0 from the start. Of the four catalysts, HCl catalyzed resins, with the highest free urea and lowest free formaldehyde, consistently yielded the lowest formaldehyde emission; NaOH/NH₄OH catalyst resulted in the best IB strength tested at dry conditions and also after 24 h cold water soak and the lowest water absorption and thickness swell. The resins catalyzed with H₃PO₄ had the highest free formaldehyde and no free urea yielding the highest formaldehyde emission. Each DSC thermogram was proceeded by a weak exothermic peak and followed by an obvious endothermic peak. The exothermic peak temperatures were 125.0, 131.1, 111.4, and 125.2°C, and endothermic peak temperatures were 135.8, 147.6, 118.9, and 138.4°C, respectively, for H₂SO₄, HCl, H₃PO₄, and NaOH/NH₄OH catalysts. The close proximity of the peak temperatures of the exothermic and endothermic reactions strongly suggests that there is potential interference of heat flow between the exothermic and endothermic reactions which may impact resin curing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

CO2 Adsorption by Modified Palm Shell Activated Carbon (PSAC) Via Chemical and Physical Activation and Metal Impregnation

The aim of this study was to verify the ability of nickel-impregnated palm shell activated carbon (PSAC) for CO₂ adsorption and compare its performance with the chemically and physically activated PSAC. Sodium hydroxide and CO₂ were used as activating agents for chemical and physical activation, respectively. Nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) was used as a precursor for metal impregnation. The effect of different chemical loadings (NaOH: 20–50 wt%), metal impregnation (Ni(NO₃)₂·6H₂O: 16–28 wt%), and heat treatment time (1–4 h) was studied as parameters. Adsorption capacity was calculated using breakthrough graphs. The effect of humidity on CO₂ adsorption and desorption of CO₂ was also investigated in this study. The results revealed that chemically modified PSAC yields the highest adsorption capacity (48.2 mg/g) compared to other methods of activation. Interestingly, it was found that the adsorption capacity of nickel-impregnated PSAC was similar to other types of metal-impregnated activated carbon. Humidity gave a negative effect on CO₂ adsorption. In summary, results showed that chemical activation is an efficient technique to modify PSAC for CO₂ adsorption.     

Activated Carbon Preparation from Lignin by H3PO4 Activation and Its Application to Gas Separation

Activated carbons were produced from corn straw lignin using H₃PO₄ as activating agent. The optimal activation temperature for producing the largest BET specific surface area and pore volume of carbon was 500 °C. The maximum BET specific surface area and pore volume of the resulting carbon were 820 m²g^–1 and 0.8 cm³g^–1, respectively. The adsorption isotherm model based on the Toth equation together with the Peng‐Robinson equation of state for the determination of gas phase fugacity provide a satisfactory representation of high pressure CO₂, CH₄ and N₂ adsorption. The kinetic adsorption results show that the breakthrough difference between CO₂ and CH₄ is not obvious, indicating that its kinetic separation performance is limited.     

Understanding chemical reactions between carbons and NaOH and KOH: An insight into the chemical activation mechanism

Direct mixing of an anthracite with hydroxides (KOH or NaOH) and heat treatment up to 730 °C has shown to be a very good activation procedure to obtain activated carbons with very high surface areas and high micropore volumes. The reactions involved during the heat treatment of these hydroxide/anthracite mixtures have been analysed to deep into the fundamental of the knowledge of this chemical activation process, that has not been studied before. For this purpose, the present paper analyses the drying process, the atmosphere during the carbonisation, the chemical state of the activating agents (NaOH, KOH and Na₂CO₃) and the chemical reactions occurring during the heat treatment which have been followed by FTIR and TPD. The analysis of our results allows us to conclude that steam is a good atmosphere for the carbonisation process, alone or joined with nitrogen, but not as good as pure nitrogen. On the other hand, during the activation process, the presence of CO₂ should be avoided because it does not develop porosity. The reactions, and chemical changes, involved during this chemical process are discussed both from a thermodynamical point of view as well as identifying the reaction products (H₂ by TPD and Na₂CO₃ by FTIR). As a result, this paper helps to cover the present lack of understanding of the fundamentals of the reactions of an anthracite with hydroxides which are necessary to understand the activation of the material.     

Removal of Gas Pollutants of a Thermal Oxidizer with a Dynamic Scrubber

The absorption of gas pollutants including CO₂, CO, NO, NO₂, SO₂, and H₂S from the exhaust of a paint recuperative oxidizer into NaOH solution has been studied using an industrial scale dynamic scrubber. Experimental results show the influence of the absorbent concentration on the pollutant removal efficiency. The best removal efficiencies of CO₂, CO, NO, NO₂, SO₂, and H₂S were 79, 80, 80, 100, 75 and 88 %, respectively, with 2 % NaOH as the absorbent. A comparison of these results with previous studies shows that the liquid‐to‐gas flow rate ratio (F_L/F_G) in this dynamic scrubber is much smaller than for traditional NaOH scrubbers and spray dryers.     

Comparative study of the textural characteristics of oil palm shell activated carbon produced by chemical and physical activation for methane adsorption

The objective of this study is to relate textural and surface characteristics of microporous activated carbon to their methane adsorption capacity. Oil palm shell was used as a raw material for the preparation of pore size controlled activated carbon adsorbents. The chemical treatment was followed by further physical activation with CO₂. Samples were treated with CO₂ flow at 850 °C by varying activation time to achieve different burn-off activated carbon. H₃PO₄ chemically activated samples under CO₂ blanket showed higher activation rates, surface area and micropore volume compared to other activation methods, though this sample did not present high methane adsorption. Moreover, it was shown that using small proportion of ZnCl₂ and H₃PO₄ creates an initial narrow microporosity. Further physical activation grantees better development of pore structure. In terms of pore size distribution the combined preparation method resulted in a better and more homogenous pore size distribution than the conventional physical activation method. Controlling the pore size of activated carbon by this combined activation technique can be utilized for tuning the pore size distribution. It was concluded that the high surface area and micropore volume of activated carbons do not unequivocally determine methane capacities.     

Effect of electrolyte environment and Pt crystallite size on hydrogen adsorption—V

The role of Pt crystallite surface morphology on hydrogen adsorption isotherms in H₂SO₄ and alkaline electrolytes was examined by a potentiodynamic sweep technique. By varying the crystallite size (40–280Å) of highly dispersed Pt electrocatalysts, the relative concentrations of edges, vertices and crystallite faces which contribute to the surface morphology are changed. The potentiodynamic i-V profiles for adsorbed hydrogen oxidation on highly dispersed Pt electrocatalysts in 0.05 and 1 M H₂SO₄ showed similar changes with Pt crystallite size. Only two states of adsorbed hydrogen on highly dispersed Pt were observed in 0.05 M H₂SO₄, compared to four states reported by Angerstein-Kozlowska et al on smooth polycrystalline Pt electrodes.In 1 M NaOH and 35 wt % KOH, less than a monolayer of adsorbed hydrogen was present on highly dispersed Pt electrocatalysts at the reversible hydrogen potential. Two states of chemisorbed hydrogen were observed at 23–91°, while at low temperature (?47°) in 35 wt % KOH, an additional adsorbed hydrogen species was evident in the potentiodynamic i-V curves. A Pt crystallite size effect on the adsorption of hydrogen on highly dispersed Pt in alkaline electrolytes was not deduced.     

Activation of coal tar pitch carbon fibres: Physical activation vs. chemical activation

Activated carbon fibres (ACF) are obtained mainly by physical activation with steam or carbon dioxide. Additionally, there are many papers dealing with chemical activation of carbon fibres, or a polymeric raw material, with several chemical agents like for example, phosphoric acid, zinc chloride, aluminium chloride,… Nevertheless, although it is well known that hydroxides are good activating agents, there are few papers about the activation of carbon fibres with KOH or NaOH. In the present work, ACF with high surface area are obtained by chemical activation with KOH and NaOH. Both chemical agents present different behaviour; thus, NaOH developed the highest value of porosity and KOH developed samples with narrower micropore size distribution. In order to compare the results with those obtained by physical activation, some ACF have been prepared using CO₂ activation. The main conclusion of this work is that by using chemical activation it is possible to obtain similar, or even higher, porosity (∼1 ml/g, ∼3000 m²/g) than by physical activation. However, chemical activation presents two important advantages: (1) a much higher yield (27-47% for chemical activation and 6% physical activation for ∼2500 m²/g activated carbon fibres) and (2) the surface of the fibres prepared by chemical activation is less damaged than by physical activation.     

Porous carbon materials produced by the chemical activation of birch wood

It was established that the main factors responsible for the yield and specific surface area of porous carbon materials obtained by the chemical activation of the wood of birch are the nature of a modifying agent and the temperature of pyrolysis. The additional opening of the porous structure of the product of the chemical activation of wood occurs at the stage of its water treatment as a result of the removal of water-soluble compounds. The conditions of the carbonization of birch wood modified with H₃PO₄, KOH, and ZnCl₂ were chosen in order to provide the significant development of the porous structure of carbon materials. The porous carbon material with the highest specific surface area (more than 2560 m²/g) was obtained by the water washing of the product of the carbonization of birch wood modified H₃PO₄ at 400°C.     

Removal of methylene blue (aq) using untreated and acid‐treated eucalyptus leaves and GA‐ANN modelling

In the present batch study, eucalyptus leaves (EUL), H₂SO₄‐treated eucalyptus leaves (SEUL), and H₃PO₄‐treated eucalyptus leaves (PEUL) are used as bio‐adsorbents for the removal of methylene blue (MB). The bio‐adsorption is executed to inspect the results of the variation between different experimental variables such as pH (2–10), adsorbent dose (1–10 g/L), contact time (5–360 min), and temperature (298–318 K) on the bio‐adsorption of MB. The Langmuir isotherm (R² = 0.99) fitted adequately to the bio‐adsorption data for the initial MB concentrations of 10–300 mg/L. It is also necessary to mention that the MB bio‐adsorption occurred in the order of a monolayer on the EUL, SEUL, and PEUL. The bio‐adsorption kinetics have been fitted by the pseudo‐second‐order model (R² ≥ 0.99) for various MB concentrations. The maximum bio‐adsorption capacity was 194.34 mg/g and was achieved for the H₃PO₄‐treated eucalyptus leaves (PEUL). These results showed that EUL, SEUL, and PEUL may be utilized as a favourable low‐cost bio‐adsorbent to eliminate MB from aqueous solutions. With safe disposal methods in mind, this investigation has revealed the eco‐friendliness of the bio‐adsorbents. A prediction of the removal percentage of methylene blue using a genetic algorithm (GA) from the data collected from the experiment has also been tested. The results related to the prediction using the GA‐ANN are accurate.     

Preparation of ordered porous carbon from tea by chemical activation and its use in Cr(VI) adsorption

Ordered porous carbon was prepared from a new carbon precursor??the tea leaves, the most widely used beverage worldwide by a chemical activation process. We obtained well developed spherical interlinked meso and micro pores with uniform pore morphology and high surface area from green, black and waste tea by NaOH as well as H₃PO₄ activation process. The carbon obtained from green tea by H₃PO₄ activation had the highest BET surface area of 1,285?m²g^?1 with total pore volume of 0.6243?mL?g^?1. The as prepared porous carbon showed high adsorption efficiency of Cr(VI) adsorption from aqueous solution.     

Chemical activations of herringbone-type nanofibers

Among new carbonaceous materials, herringbone carbon nanofibers (HCNFs) are one of the most promising precursors for the production of original adsorbents. Nevertheless, little information is available in the open literature on this subject and is mainly restricted to KOH activation. In the present study, the effects of the main activating agents currently used in chemical activation of conventional precursors, namely KOH, NaOH, ZnCl₂ and H₃PO₄, are compared for the same HCNFs. The adsorptive properties of the obtained activated fibers are described through the corresponding nitrogen isotherms and conventional textural parameters. All chemical activations led to a common microporous texture but different efficiencies in terms of developed porosity per activating agent weight. At low activation yield (first activation regime), a microporosity is initiated resulting in a sharp decrease of the apparent mean pore size (from 20 to 15 Å) and Lc₀₀₂ and simultaneously to a small increase in d₀₀₂. At higher activation yield (second activation regime), the mean pore size is found to be almost constant while the specific microporous volume is greatly increased (from 0.1 to 0.32 cm³ × g⁻¹) and the d₀₀₂ and Lc₀₀₂ parameters remain nearly constant. It was observed that the KOH activation is much more efficient than the other ones.     

Simultaneous Adsorption of SO2, NO,and CO2 by K2CO3‐Modified γ‐Alumina

The simultaneous adsorption of SO₂, NO, and CO₂ on K₂CO₃‐modified γ‐alumina under different operating conditions was studied in a fixed‐bed reactor. The experimental results showed that the influence of a temperature increase on the simultaneous adsorption of the three gases was complex and different from the effects seen when both chemical adsorption and competitive adsorption existed. An increase in O₂ concentration and small amounts of water could enhance the adsorption of SO₂ and NO while the adsorption of CO₂ was not influenced. The breakthrough curves of the simultaneous adsorption experiments suggested that the investigated adsorbent may be a good candidate for the simultaneous adsorption of SO₂, NO, and part of the CO₂ while the adsorption capacity for CO₂ still needs to be enhanced.     

Textural Characterization of Activated Carbons Prepared from Oil-palm Stones Pre-treated with Various Impregnating Agents

Activated carbons with relatively high densities and well-developed porosities were prepared from oil-palm stones which were pre-treated with different types of impregnating agents (ZnCl₂, H₃PO₄ or KOH). The benefits derived from impregnation in terms of higher BET surface areas were generally in the following order: 20% ZnCl₂ > 40% H₃PO₄ > 10% KOH. The textural properties such as density and total porosity, overall yield, BET and micropore surface areas and pore size distributions of the activated carbon were related to the concentration of the impregnating solution and the activation conditions (activation temperature and hold time). For the highest BET surface area obtained in this study, the optimum conditions for CO₂ activation were found to be at an activation temperature of 750°C for 1 hour from oil-palm stones pre-treated with 20% ZnCl₂ for 24 hours. Pore size distribution suggests the application of oil-palm-stone activated carbons as gas-phase adsorbents for air pollution control.     

Chemical Production of Activated Carbon from Nutshells and Date Stones

The effect of chemical reagent (H₃PO₄, KOH, and NaOH), temperature (400 °C, 475 °C, 550 °C), and impregnation ratio (100 %, 150 %, 200 %) was investigated on the specific surface area and iodine uptake of the carbons produced from almond, walnut, and pistachio‐nut shells and date stones. The effect of mesh size and holding time was also studied in the case of almond shell. While the alkali activation of the precursors resulted in such fine powders that purifying them of contaminants was almost impossible, the acid activation of the raw materials produced carbons with high iodine numbers (about 1000 mg I₂/g carbon). To further characterize their porosity, the almond‐based carbons underwent BET measurements, with the results showing comparatively high surface areas (about 1400 m²/g). The carbons were rather mesoporous, and thus more suitable for liquid applications, which was confirmed by using the carbons in chromium (VI) uptake in another study [1].     

Spectroscopic,transport, and morphological studies of polyaniline doped with inorganic acids

A conducting polymer, polyaniline, was synthesized by chemical polymerization using different inorganic acids, such as HCl, H₂SO₄, HClO₄, HNO₃, and H₃PO₄, as protonic acid media. The synthesized polymers were characterized using UV‐visible and FT‐IR spectroscopy. A granular type of morphology was observed under SEM for HCl, HNO₃, and H₃PO₄ doped polyanilines. However, HClO₄ doped polyaniline shows the folded lamellar structure derived from the fibers. The thermal stability of these polymers was investigated with the help of thermogravimetric (TG/SDTA) analysis. The formation of a greater fraction of the conducting emeraldine salt phase is observed in HClO₄ as a protonic acid media. The thermal stability of H₃PO₄ doped material is found to be better as compared with other acids. An increase in conductivity with an increase in temperature was observed in all the samples except for HClO₄ doped polyaniline. Polym. Eng. Sci. 44:1676–1681, 2004. © 2004 Society of Plastics Engineers.