Dissertations / Theses on the topic 'Coconut shell activated carbon'

A geraÃÃo de ResÃduos SÃlidos Urbanos (RSU) vem aumentando a cada ano no PaÃs, sendo a fraÃÃo orgÃnica normalmente responsÃvel por mais da metade da quantidade total de RSU gerada. Entre as alternativas existentes para o aproveitamento dos resÃduos sÃlidos orgÃnicos, destaca-se a digestÃo anaerÃbia, uma soluÃÃo atrativa, tendo em vista que hà produÃÃo de biogÃs durante o processo. Entretanto, para que suas possibilidades de aplicaÃÃo sejam mais abrangentes, à necessÃrio que o biogÃs seja purificado e posteriormente submetido a um processo de upgrade, a fim de que adquira caracterÃsticas similares ao do gÃs natural. O presente trabalho teve como objetivo sintetizar Carbonos Ativados (CAs) a partir de endocarpo de coco seco (Cocos nucifera), de coco babaÃu (Orbignya speciosa) e a partir de vagem de flamboyant (Delonix regia) por meio de ativaÃÃo com diÃxido de carbono em Ãnica etapa. As caracterÃsticas texturais das amostras foram determinadas por meio de isotermas de adsorÃÃo de N2 a -196 ÂC. Os maiores valores de Ãrea superficial especÃfica e volume de microporos foram obtidos para o bioadsorvente sintetizado a partir do coco seco, com valores de 1452 m2/g e 0,60 cm3/g, respectivamente. Foram selecionados os CAs de coco seco e de coco babaÃu para a anÃlise de suas eficiÃncias na separaÃÃo de misturas CO2/CH4 para aplicaÃÃo no upgrade de biogÃs. Para tanto, ensaios de equilÃbrio de adsorÃÃo dos componentes puros (CO2 e CH4) e da mistura (30% vol. CO2, 70% vol. CH4) foram realizados a 20 ÂC utilizando uma balanÃa de suspensÃo magnÃtica. A capacidade de adsorÃÃo de CO2 pouco se diferenciou entre as duas amostras, apresentando o CA de coco seco melhores resultados. Essa amostra apresentou valores bem maiores de captura de metano a pressÃes acima de 3,0 bar. Os dados experimentais foram comparados com os obtidos pelo ajuste do modelo de TÃth e da IAST (Teoria da SoluÃÃo Adsorvida Ideal) para os dados mono e multicomponentes, respectivamente. Os ajustes de TÃth foram bastante precisos, enquanto os da IAST se adequaram moderadamente. As seletividades das amostras para o CO2 em relaÃÃo ao CH4 foram determinadas e comparadas com a de outros adsorventes comerciais. O CA do coco seco apresentou resultados melhores que o coco babaÃu a baixas pressÃes, com valor de seletividade de 4,2 a 1,0 bar, indicando ser um material competitivo para a aplicaÃÃo proposta.<br>The generation of Municipal Solid Waste (MSW) is increasing every year in Brazil, being the organic matter responsible for more than half of the total MSW generated. Among the current alternatives to the use of organic solid waste, the anaerobic digestion is the most attractive as biogas production occurs in the process. Nevertheless, to increase its usage possibilities, biogas has to be purified and upgraded, in order to acquire characteristics similar to that of natural gas. The present work aims to prepare activated carbons (ACs) from coconut endocarp (Cocos nucifera), babassu coconut (Orbignya speciosa) and flamboyant pods (Delonix regia) by one step CO2 activation. The textural characteristics were determined by N2 adsorption isotherm at -196 ÂC. The best results of BET surface area and micropore volume were obtained for bioadsorbent synthesized from coconut shell, with values of 1452 m2/g and 0.6 cm3/g, respectively. ACs from coconut shell and babassu coconut were selected to analyze their efficiency in CO2/CH4 separation mixture for biogas upgrading application. Therefore, pure component (CO2 and CH4) and mixture (30% vol. CO2, 70% vol. CH4) adsorption equilibria were performed at 20 ÂC using a magnetic suspension balance. The CO2 adsorption capacity slightly differed between samples, presenting the AC from coconut shell better results. This sample had higher methane uptake above pressures of 3.0 bar. The experimental data were compared with the fit of Toth and IAST (Ideal Adsorbed Solution Theory) models for mono and multicomponent data, respectively. The Toth fitting was fairly accurate, while the IAST fit was moderate. The samples selectivity to CO2 over CH4 were calculated and compared with another commercial adsorbent. The AC from coconut shell presented better results than babassu coconut at low pressures, with a selectivity value of 4.2 at 1.0 bar, indicating to be a competitive material for the proposed application.

Made available in DSpace on 2015-05-08T14:59:48Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2106593 bytes, checksum: ab15bacf25992ba8bafb4cdeb1c81ec6 (MD5) Previous issue date: 2012-09-21<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Activated carbon, AC, is a pure state carbon with large porosity, which adsorbs molecules or ions from a fluid medium. In general, it is obtained from the controlled burning of agricultural or industrial by-products. When produced in conventional furnaces, the operating temperatures may rise up to 900°C, resulting in yields inferior to 20 %. The low yield is a consequence of the precursor's large thermal degradation caused by the heat wave front which moves slowly from the surface to its core. Therefore, there is a significant formation of meso and macropores, which lead to a final value of density, &#961;, below of 0.5 g.cm-3. On the other hand, thermal degradation caused by microwaves is less aggressive. The heating process occurs from the core of the precursor to its exterior. As a consequence the activated carbons are denser, have a more selective microporosity, and are more suitable to gas storage. This paper reports the preparation and the results of the qualitative analysis of physically and chemically activated carbons, from coconut shell, using an adapted microwave oven. This adapted microwave allows the settling down of temperature programs' ramp and heating rates. The BET surface area of activated carbons prepared in the microwave oven surpassed 1200 m2.g-1, the apparent density situated at around 0.5 g.cm-3, and the yields remained above 40 %. Comparisons between the electricity consumption of the electrical conventional kiln and of the micro-wave oven in producing a certain quantity of an activated carbon with a BET surface area over 800 m2/g, showed that the use of the microwave oven had allowed, each time, a reduction of about 3,2 kW.h, which represents an average of electricity saving of 85.5 %.<br>Carvão ativado, CA, é uma forma de carbono puro de grande porosidade, que adsorve moléculas ou íons de um meio fluido. É obtido a partir da queima controlada de precursores, geralmente, subprodutos de baixo custo, oriundos da agricultura, ou da indústria. Quando produzido em fornos convencionais, as temperaturas de trabalho podem ser superiores a 900 °C, reduzindo a menos de 20 % a massa de carvão produzida com relação à do precursor (rendimento). Isto se dá em virtude da grande degradação ocasionada pela frente de calor destes fornos, que lentamente se desloca da superfície ao núcleo da massa do precursor. Em consequência, via de regra, a massa específica final, &#961;, registra valores abaixo de 0,5 g.cm-3. No caso das micro-ondas a degradação térmica da matéria se dá, de forma menos agressiva, do interior do precursor para o exterior, proporcionando carvões ativados mais densos, com microporosidade mais seletiva, e, logo, mais adequada ao armazenamento de gás. O presente trabalho relata a obtenção de carvões ativados, por via física e química, a partir do endocarpo do coco da baía, em um forno micro-ondas adaptado, onde é possível se programar rampas de temperaturas e razões de aquecimento. Avalia-se o consumo de energia elétrica do forno micro-ondas adaptado em relação ao do forno elétrico convencional. A área superficial de BET dos carvões química e fisicamente preparados foi superior a 1200 m2.g-1, a massa específica manteve-se próximo a 0,5 g.cm-3, e os rendimentos ficaram acima de 40 %. Ao se comparar o consumo de energia elétrica para produzir, tanto no forno convencional como no micro-ondas, uma determinada quantidade de carvão ativado, com área de BET superior a 800 m2/g, verificou-se que a redução gerada pelo micro-ondas foi de aproximadamente 3,2 kW.h, representando um percentual de economia de energia de 85,5 %.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology.<br>Activated carbons have been produced from various carbonaceous source materials including nutshells, peat, wood, coir, lignite, coal and petroleum pitch and the produced carbons have been used for adsorption of inorganic and organic compounds from numerous matrices. Activated carbons are characterized by large surface area and high degree of microporosity. The ability of activated carbon to adsorb gold from solutions, which is present in very low concentrations while loading to fairly high concentrations, has made it an attractive material for the concentration of gold from dilute solutions. Consequently, the use of activated carbons for the recovery of gold from cyanide-leached liquors has gained wide acceptance in the mining industry. However, the price of commercially prepared carbons, the time taken for them to arrive, the breakage of the carbon during transportation and the interest in utilization of various local wastes for the generation of adsorbents has led to a search of more cost effective and time friendly source for the activated carbons. The focus of this research was to conduct a study in which a comparison was conducted between untreated coconut shell derived activated carbon (CAC) and Macadamia nutshell derived activated carbon (MAC) for the adsorption of gold. These activated carbons were modified with HNO3 and H3PO4 to increase their surface adsorption properties. This was done in order to explore if these activated carbons prepared from Macadamia shells could be an attractive alternative or a complementary supplement to the coconut shell based carbons that are currently being used in the gold extraction industry. The modification of the commercially prepared Macadamia activated carbons was done with 3 different concentrations for both nitric acid and phosphoric acid. The modified activated carbons were labelled MACP20%, MACP40% and MACP60%, to signify the materials prepared from 20% (v/v) H3PO4, 40% (v/v) H3PO4 and 60% (v/v) H3PO4 , respectively . Same labelling was used for 20% (v/v) HNO3, 40% (v/v) HNO3 and 55% (v/v) HNO3 modifications to correspond to MACN20%, MACN40% and MACN55%, respectively. Also, untreated coconut shell derived activated carbon (CAC) and Macadamia nutshell derived activated carbon (MAC) were investigated for gold adsorption for comparison purposes. All the activated carbons prepared in the iii | P a g e study were characterized with Brunauer-Emmet-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermo gravimetric analysis (TGA), elemental analysis (EL) and X-ray diffraction spectroscopy (XRD). The physical properties of the activated carbons were done by determining attrition, ash content, volatile matter, and moisture content of all the activated carbons. Various parameters that affect selective adsorption such as the effect of initial concentration, time, agitation speed, interfering species, and dose of the adsorbent were investigated. Optimal parameters for gold ion adsorption were as follows: solution pH, 10; contact time, 6 h; agitation speed 150 rpm; sorbent amount 4 g and 5.5 ppm for initial concentration of gold. The observed selectivity order was not the same for all the adsorbents but the adsorption of gold was found to be mostly influenced by the presence of nickel and least influenced by copper. The MACP60% was found to be the most effective from the three concentrations investigated for the phosphoric acid modified activated carbons yet proved to have lower adsorption capabilities compared to CAC. The MACN55% was found to be the most efficient and displayed similar adsorption capabilities to those of CAC.

In this study production and characterization of activated carbon from an agricultural waste, pistachio-nut shells, was investigated. To determine optimum production conditions by chemical activation method, effect of tempreature (300, 500, 700 and 900 oC) and effect of impregnation ratio (1:1, 2:1 and 3:1 as activation agent:sample) were investigated by applying two different methods (raw material activation and char activation) and with two different activation agents (phosphoric acid and potassium hydroxide). To produce activated carbon, all the impregnated samples were heated to the final activation temperature under a continuous nitrogen flow (100 cm3/min) and at a heating rate of 10 oC/min and were held at that temperature for 1 hour. Pore structures of activated carbons were determined by N2 adsorption and micro-mesopore analysis was made by &ldquo<br>Non-local Density Functional Theory&rdquo<br>and &ldquo<br>Monte Carlo Simulation&rdquo<br>method (NLDFT-Monte Carlo Simulation Method). BET surface areas of produced activated carbons were found from N2 adsorption data in the relative pressure range of 0.01 to 0.15. BET surface areas of phosphoric acid activated carbons by raw material activation method were found between 880 and 1640 m2/g. The highest value of the BET surface area was obtained in the case of the activated carbon which was produced with an impregnation ratio of 3/1 (g H3PO4/g raw material), at an activation temperature of 500 oC. The repeatibility was also investigated on phosphoric acid activated carbons which were produced with conventional raw matererial activation method. Results showed that, both the BET surface area values and pore size distributions were consistent among themselves. On the other hand char activation experiments with phosphoric acid produced activated carbons having lower BET surface areas than the ones obtained with raw material activation method by creating mesoporous structure. When the same char activation method was tried with potassium hydroxide, it was concluded that elevated temperatures could help in producing activated carbons with high BET surface areas by creating microporous structure. Results also showed that properties of activated carbon such as ash content, slurry pH value, true density, elemental composition, methylene blue number and surface morphology were strongly affected by both production conditions and production method, as pore structure was affected considerably.