Presión de cubrimiento de N2 y CO2 sobre carbones activados. Comparación con propiedades energéticas de la superficie de los sólidos

Se determina la presión de cubrimiento, π, para tres carbones activados obtenidos a partir de cuesco de palma africana por activación física con CO2 a 900 °C para tiempos de activación entre 4 y 10 horas, a partir de isotermas de adsorción de N2 a -196 ºC y CO2 a 0 ºC. Los carbones activados son sólidos microporosos con valores de área superficial entre 795 y 1280 m2g-1 y de volúmenes de microporo entre 0,36 y 0,48 cm3g-1.Los resultados obtenidos para la presión de cubrimientode los adsorbatos sobre los carbones activados seencuentran entre 60 y 139 mN m-1 para el N2 y entre 77 y113 mN m-1 para el CO2. Se determina la entalpía de inmersión de los carbones activados en benceno, con resultados entre 96 y 130 Jg-1, con el propósito de establecer su relación con lapresión de cubrimiento. El carbón activado con los valoresmás altos de área superficial y de entalpía de inmersiónpresenta el menor valor para la presión de cubrimientotanto de nitrógeno como de dióxido de carbono

Estudio de la entalpía de inmersión y de la adsorción de fenoles hidroxilados desde solución acuosa sobre carbón activado

Se determinan las entalpías de inmersión de un carbón activado granular comercial CarbochemTM –PS230, CAG, en función de la cantidad adsorbida de derivados fenólicos hidroxilados, fenol, catecol, resorcinol, hidroquinona y pirogalol en soluciones acuosas, con el fin de caracterizar la interacción sólido-solución acuosa y evaluar la influencia de la posición, del número de hidroxilos en el anillo aromático y la solubilidad de los fenoles en la adsorción sobre el carbón activado. Los resultados muestran una variación en la entalpía de inmersión, que se relaciona conla capacidad de adsorción y que favorece la interacción del resorcinol sobre el carbón activado, con un valor de entalpía de inmersión de 41,00 J·g-1, que permite observar que la intensidad de la interacción cambia en función de la solubilidad y de la contribución del número de sustituyentes hidroxilo en el anillo aromático.

Monolitos de carbón activado a partir de cáscara de coco e impregnación con niquel y cobre

Una serie de diferentes monolitos de carbón activado fueron preparados a partir de cáscara de coco por medio de activación química con ácido fosfórico a diferentes concentraciones sin utilizar aglomerantes ni plastificantes. Al monolito que mayor área desarrolló se le impregnó vía húmeda con soluciones de Ni y Cu a diferentes relaciones molares. Las estructuras fueron caracterizadas por la adsorción de N2 a 77 K, y se exploró su morfología por medio de microscopía electrónica de barrido. Los materiales carbonosos obtenidos, níquel-cobre-monolito, fueron analizados por Reducción Térmica Programada (RTP). Los resultados experimentales indicaron que la activación con ácido fosfórico genera una microporosidad, con volúmenes de microporos entre 0,39  y 0,81 cm3g-1 y áreas superficiales entre 703 y 1450 m2g-1, y buenas propiedades mecánicas. Se muestra que tanto el cobre como el níquel se fijan al monolito y se interpretan los resultados de RTP respecto a cuándo se modifica su relación molar

Study of Activated Carbons by Pyrolysis of Mangifera Indica Seed (Mango) in Presence of Sodium and Potassium Hydroxide

Activated carbons (ACs) were prepared by pyrolysis of seeds mango in presence of sodium and potassium hydroxide (chemical activities). Seeds mango from Colombian Mango cultives were impregnated with aqueous solutions of NaOH and KOH following a variant of the incipient wetness method. Different concentrations were used to produce impregnation ratios of 3:1 (weight terms). Activation was carried out under argon flow by heating to 823 K with 1 h soaking time. The porous texture of the obtained ACs was characterized by physical adsorptions of N2 at 77 K and CO2 at 273 K. The impregnation ration and hydroxide type had a strong influence on the pore structure of these ACs, which could be easily controlled by simply varying the proportion of the hydroxides used in the activation. Thus, the development of porosity for precursors with low structural order (high reactivity) is better with NaOH than KOH, whereas the opposite is observed for the highly ordered ones. Variable adsorption capacities and porosity distributions can be achieved depending on the activating agent selected. In general, KOH produces activated carbons with narrower micropore distributions than those prepared by NaOH

Effect of textural and chemical characteristics of activated carbons on phenol adsorption in aqueous solutions

The effect of textural and chemical properties such as: surface area, pore volume and chemical groups content of the granular activated carbon and monoliths on phenol adsorption in aqueous solutions was studied. Granular activated carbon and monolith samples were produced by chemical activation. They were characterized by using N2  adsorption at 77 K, CO2  adsorption at 273 K, Boehm Titrations and immersion calorimetry in phenol solutions. Microporous materials with different pore size distribution, surface area between 516 and 1685 m2  g−1  and pore volumes between 0.24 and 0.58 cm3  g−1  were obtained. Phenol adsorption capacity of the activated carbon materials increased with increasing BET surface area and pore volume, and is favored by their surface functional groups that act as electron donors. Phenol adsorption capacities are in ranged between 73.5 and 389.4 mg · g−1 

Synthesis of Fatty Alcohols from Oil Palm Using a Catalyst of Ni-Cu Supported onto Zeolite

A series of Ni-Cu supported onto zeolite type ZSM-5 has been synthesized by direct hydrothermal method without template agent and characterized using XRD, FT-IR, NRM mass, SEM, CG and N2 adsorption techniques. The catalytic performance of the obtained materials was evaluated and utilized for the hydrogenation of palm oil at 453 K and 40 atmospheres of pressure. The results show that the samples exhibited typical hexagonal arrangement of mesoporous structure with high surface area and the heteroatoms were probably incorporated into the framework of ZSM-5. Catalytic tests show that the bimetallic incorporated materials were effective as catalysts in the hydrogenation of oil palm producing fatty alcohols typical

Chemical modification of activated carbon monoliths for CO2 adsorption

The development of materials with potential application for CO2 capture is a topic of great scientific interest. Activated carbons (AC) can be conveniently used as CO2 adsorbents thanks to their microporous structure and tunable chemical properties. In this work, two AC honeycomb monoliths were synthesized starting from African palm stones through activation either with H3PO4 or with ZnCl2 solution. Surface functionalization was performed in order to add nitrogen groups, aiming at an enhancement of CO2 adsorption capacity. This chemical modification was performed either with ammonia in gas phase or a with 30 % ammonium hydroxide aqueous solution on both AC monolith samples. The original and modified monoliths were characterized by N-2 adsorption at 77 K, infrared spectroscopy, Boehm titration, and immersion calorimetry in benzene and water. CO2 adsorption on both raw and functionalized AC monoliths was evaluated in volumetric equipment at a temperature of 273 K and until 1 bar, and adsorption capacity ranging between 120 and 220 mg(CO2) g (AC) (-1) was obtained. The experimental results indicated that both methods of chemical modification determined an increase in the content of superficial nitrogen groups and thus an increase in CO2 adsorption capacity, the treatment with ammonium hydroxide being slightly preferable

A study by adsorption calorimetry, effect of resorcinol/catalyst at different ratios using polar and non-polar molecules in the synthesis of carbon aerogels.

The heterogeneity and hydrophilicity of a series of aerogels were studied using adsorption calorimetry with molecules of different polarity. Four samples of carbon aerogel were synthesized with different resorcinol/catalytic (R/C) relations: 100, 200, 800 and 1500. The isotherms of N2 at -196 ◦C were determined and from these were calculated the textural parameters using the Dubinin–Astakhov (DA), Barret–Joyner–Halenda (BJH), Non-Local Density Functional Theory (NLDFT) and Quenched Solid Density Functional Theory (QSDFT) models. The adsorption isotherms of polar and non-polar molecules: benzene, hexane, methane, methanol and methyl-ethyl-ketone (MEK) were determined, as well as the differential adsorption enthalpies of these on the aerogel. The results show that the aerogels samples at low R/C have a fundamental development of micropores and at high R/C values present an additional development of mesoporosity. Adsorption isotherms of polar and non-polar molecules were adjusted to the Langmuir–Sips model and In-homogenous DA equation, respectively. Adsorption calorimetry shows that the carbon aerogels at these relations present heterogeneous surfaces that are essentially hydrophilic