Abstract
To recommend the beneficial effect of the pulping process on enhancing agro-wastes as precursors for the production of high-performance activated carbons (ACs), different pulping methods (alkali, sulfite and neutral sulfite) were applied on two available Egyptian agriculture by-products (rice straw and sugar cane bagasse), using the one-step pyrolysis method and H3PO4 activating agent. The adsorption performance of the different prepared ACs was evaluated in terms of Iodine Numbers and their sorption properties for removing the methylene blue (MB) from aqueous solutions. The corresponding sorption processes were also analysed using Lagergren first order, pseudo-second order and intraparticle diffusion models. Data revealed that the applied pulping conditions were effective for removing the non-cellulosic constituents of agro-residues. This was demonstrated by the hydrogen/carbon and oxygen/carbon ratios, thermal stability and IR-measurements of the final pulps. These data were effective on the particular sorption properties of RS and SCB-based ACs. Interestingly, the pulping process is a profound modification of the SCB-based fibres, on which it induced a clear increase of the specific surface areas of the corresponding ACs even though they had an impact on the sorption of MB and iodine. These values are superior to the reported data on agro-based ACs with H3PO4 activators. Pulping processes therefore play a dual role in the sorption properties of ACs. The first important role is the impact on the specific surface areas and the second impact is a profound modification of the surface chemistry of the ACs. Therefore, SCB-based ACs can be seen as an economical breakthrough product, and an alternative to the high-cost commercial ACs for the purification of industrial wastewaters.
Highlights
Activated carbons (AC) are still highly regarded materials for a variety of applications, such as adsorbents for toxic materials and pollutants [1,2,3], as well as in the storage of hydrogen and methane [4,5], electrolysis [6], catalysis [7] and many medical and pharmaceutical uses [8,9]
In continuation of our achievements in improving the surface adsorption of ACs from agro-wastes/ by-products, we examined the performance of ACs synthesized from rice straw (RS) and sugar cane bagasse (SCB) versus pulping pretreatment processes
Our findings revealed that the pulping agent plays a significant role in changing the chemical constituents of RS- and SCB-pulps
Summary
Activated carbons (AC) are still highly regarded materials for a variety of applications, such as adsorbents for toxic materials and pollutants [1,2,3], as well as in the storage of hydrogen and methane [4,5], electrolysis [6], catalysis [7] and many medical and pharmaceutical uses [8,9]. Chemical activation of RS using H3PO4 and a one-stage pyrolysis provided ACs with specific surface area lower than 500 m2 g−1, which is too low to comply with commercial ACs. In our former studies, we succeeded in improving the agro- or lignocellulosic products via physical, alkaline and biological pretreatments. The objective of the present work was to evaluate the possibility of enhancing the most available agro-wastes (SCB & RS) as precursors for the production of ACs, via introducing HSO3 groups together with changing the ratio of cellulose/ hemicellulose/lignin To achieve this objective, three pulping processes were applied using soda (SH), sulfite (SS) and sulfite–carbonate mixture (mix SS-SC) (neutral), followed by activation using the phosphoric acid. The sorption properties of the ACs were assessed by performing iodine and methylene blue (MB) sorption from the liquid phase
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