Production and characterization of activated carbons made from sunflower stems

Activated carbons (ACs) are artificial materials, prepared from natural or synthetic precursors that are worldwide extensively used. The ACs main characteristics are the noticeable adsorption capabilities provided by the highly developed porous structure and the rich surface chemistry. Because of their versatility and properties the final material can be tailored to have specific properties suitable for a wide range of applications such as medical uses, gas storage, removal of pollutants and odours, gas separation and purification as well as in catalysis. With the increase of activated carbon demand, one of the main challenges lies in the attempt to find new precursors, which are cheap and accessible with good valorisation potential, like industrial and agricultural residues. In the present work we report the production of ACs from sunflower stems, an agricultural by-product, through a physical activation process by CO2 and H2O, using a single step carbonisation at 400ºC, which as far as it came to our knowledge was never made for this precursor

Preparation and Modification of Activated Carbon Fibres by Microwave Heating

Thermal treatment of activated carbon fibres (ACF) has been carried out using a microwave device, instead of a conventional furnace. The results show that microwave treatment affects the porosity of the ACFs, causing a reduction in micropore volume and micropore size. More importantly, the results also show that microwave treatment is a very effective method for modifying the surface chemistry of the ACFs with the production of pyrone groups, detected by FTIR. As a result very basic carbons, with points of zero charge approximately equal to 11, are readily obtained

Fibras de carbono activadas produzidas a partir de precursores acrílicos

Neste artigo é efectuada uma revisão sobre as fibras de carbono activadas (ACF) produzidas a partir de precursores acrílicos abordando vários aspectos relativos à sua produção e características físicas e químicas. As ACF são uma forma relativamente recente de materiais de carbono que apresentam um conjunto variado de vantagens em relação a outros materiais de carbono que lhe conferem um enorme potencial de utilização

Reference data for the adsorption of methanol on carbon

The adsorption of methanol at 298 K on carbon blacks and microporous carbons, including Carbosieve, Takeda molecular sieves, Maxsorb superactivated carbons and an activated charcoal cloth, has been studied. Analysis of the results indicates that the mechanism of adsorption of methanol on carbon blacks shows some similarities to that of water vapour. However, it is still possible to define reference data which can be used to obtain estimates of the surface area of carbon blacks, provided that the surface is reasonably polar, and of external surface area and micropore volume of microporous carbon adsorbents, provided that the pore size is not very large

Mercury Removal from Aqueous Solution and Flue Gas by Adsorption on Activated Carbon Fibres

The use of two activated carbon fibres, one laboratorial sample prepared from a commercial acrylic textile fibre and one commercial sample of Kynol1, as prepared/received and modified by reaction with powdered sulfur and H2S gas in order to increase the sulfur content were studied for the removal of mercury from aqueous solution and from flue gases from a fluidized bed combustor. The sulfur introduced ranged from 1 to 6 wt.% depending on the method used. The most important parameter for the mercury uptake is the type of sulfur introduced rather than the total amount and it was found that the H2S treatment of ACF leads to samples with the highest mercury uptake, despite the lower sulfur amount introduced. The modified samples by both methods can remove HgCl2 from aqueous solutions at pH 6 within the range 290–710 mg/g (ACF) which can be favourably compared with other studies already published. The use of a filter made with an activated carbon fibre modified by powdered sulfur totally removed the mercury species present in the flue gases produced by combustion of fossil fuel

Influence of surface ionization on the adsorption of aqueous mercury chlorocomplexes by activated carbons

The adsorption of aqueous mercury species from chloride solutions on a number of activated carbons has been studied. It was found that whereas the adsorption of neutral HgCl, or positive Hg’+ was very low, significant quantities of the tetrachloromercury(I1) complex, HgCI$-, were adsorbed. Adsorption isotherms of this complex were measured at different pH values, and the results analysed by the Langmuir equation and by a simple surface ionization and specific adsorption model in order to obtain estimates of the adsorption stoichiometry and the mean free energy of adsorption

Scanning electron microscopy of activated carbons prepared from commercial acrylic textile fibres

Scanning electron microscopy has been used to study the variation in surface texture and dimension during carbonisation and activation of three acrylic textile fibres. The results show that both ordered and disorganised forms of carbon exert a direct influence on the macroscopic structure of the carbon materials. In addition, the results also show that the presence of small amounts of an inorganic additive, namely titanium dioxide, can disrupt the graphene structure and lead to modification of the surface texture and reactivity of the carbon material

On the Lo/σ Range of the TVFM .

Adsorption isotherms of nitrogen, carbon dioxide, methanol, dichloromethane, benzene and neopentane were determined on a range of molecular sieve and super-activated carbons with the objective of establishing the range of validity of the Theory of Volume Filling of Micropores (TVFM) in terms of the ratio of pore width to molecular diameter, Lo/σ. It is shown that, in the absence of molecular-sieving effects, both the characteristic curve concept and the DR equation are valid over the whole of the micropore range, corresponding to values of Lo/σ less than or equal to 5 and to at least a slight enhancement in the characteristic energy, E0, of the adsorbent when compared with the corresponding value obtained with non-porous carbon blacks. On the other hand, estimation of the mean micropore width was only possible for values of Lo/σ up to ca. 2.3, corresponding to at least a two-fold enhancement in E0. Results obtained using N2 at 77 K showed some significant differences to those obtained with organic adsorptives at higher temperature

Carbons molecular sieves from PET for separations involving CH4, CO2, O2 and N2

Carbon molecular sieves (CMS) have been made for the first time from PET textile fibres by carbonisation and pore mouth narrowing using CVD of benzene. The diffusion of O2, N2, CO2 and CH4 in these materials, and also in the commercial CMS Takeda 3A, was studied. It was found that the best PET based CMS was obtained after 10 min CVD time and had adsorption capacities and rates of diffusion similar to those of the Takeda 3A

“From commercial textile fibres to activated carbon fibres: chemical transformations

The production of activated carbon fibres from commercial acrylic textile fibres was analysed in order to study the chemical transformations suffered by the precursor during the process. The thermal degradation of the precursor polymeric chain starts with the cyclisation of the structure with acetate ion from vinyl acetate acting as a catalyst. The chemical transformations continue with both cyclisation and dehydrogenation reactions which result in the formation of several functional groups. The groups identified for the carbonised fibre by FTIR were amines, amides, imides, lactones and –OH, whereas for the activated carbon fibre the groups that can be identified were pyrones, lactones, amines, amides and OH