Abstract
Humins, waste from biomass hydrolysis, are the main factor limiting the utilization efficiency of biomass carbon. In the present study, waste humins were employed for activated carbon production though KOH activation in a temperature range of 500–900 °C. The structure and properties of the activated carbons were studied, and a honeycomb-like macropore structure was observed. High activation temperature was demonstrated to be capable of promoting the formation of activated carbon with high surface area, high pore volume and high adsorption capacity. The activated carbon obtained by carbonization at 800 °C (KOH800) was selected as sorbent to adsorb methylene blue (MB) and phenol in aqueous solution, and the adsorption process can be explained by pseudo-second-order kinetic model. The adsorption behavior complies with Langmuir isotherm model and exhibits superior adsorption capacity of 1195 and 218 mg/g for MB and phenol, respectively. The impacts of surface area, acidic active sites and pore structures were also investigated, and it was found that the adsorption of approximately 44.0% MB and 39.7% phenol were contributed by the pores with apertures from 1.7 nm to 300 nm.
Highlights
Acid-catalyzed hydrolysis of biomass-derived hexoses to produce platform chemicals, such as 5-hydroxymethylfurfural and levulinic acid, has attracted considerable attention recently [1,2,3,4]
For levulinic acid production through cellulose hydrolysis, 30–50 wt. % of cellulose carbon was converted to humins [13]
High temperature can cause low yields (15%–39.2%), the activated carbons obtained at high temperature usually have high BJH pore volume, high BET surface area (428–1975 m2/g), and better adsorption capacity of N2, phenol and Methylene blue (MB)
Summary
Acid-catalyzed hydrolysis of biomass-derived hexoses to produce platform chemicals, such as 5-hydroxymethylfurfural and levulinic acid, has attracted considerable attention recently [1,2,3,4]. One of the state-of-the-art processes is the Biofine process, which can produce levulinic acid in commercial-scale [5]. The monomer of cellulose, is usually the reactant for levulinic acid and 5-hydroxymethylfurfural production in biomass hydrolysis process. The acid-catalyzed hydrolysis process, inevitably forms low-value-added byproducts, humins [6,7], and the humins yield in pure glucose acid hydrolysis can reach 21–36 wt. For levulinic acid production through cellulose hydrolysis, 30–50 wt. % of cellulose carbon was converted to humins [13]. Developing cost-effective methods for converting humins to high value products is essential
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