Abstract
The choice of activating agent for the thermochemical production of high-grade activated carbon (AC) from agricultural residues and wastes, such as feedstock, requires innovative methods. Overcoming energy losses, and using the best techniques to minimise secondary contamination and improve adsorptivity, are critical. Here, we review the importance and influence of activating agents on agricultural waste: how they react and compare conventional and microwave processes. In particular, adsorbent pore characteristics, surface chemistry interactions and production modes were compared with traditional methods. It was concluded that there are no best activating agents; rather, each agent reacts uniquely with a precursor, and the optimum choice depends on the target adsorbent. Natural chemicals can also be as effective as inorganic activating agents, and offer the advantages that they are usually safe, and readily available. The use of a microwave, as an innovative pyrolysis approach, can enhance the activation process within a duration of 1–4 h and temperature of 500–1200 °C, after which the yield and efficiency decline rapidly due to molecular breakdown. This study also examines the biomass milling process requirements; the influence of the dielectric properties, along with the effect of washing; and experimental setup challenges. The microwave setup system, biomass feed rate, product delivery, inert gas flow rate, reactor design and recovery lines are all important factors in the microwave activation process, and contribute to the overall efficiency of AC preparation. However, a major issue is a lack of large-scale industrial demonstration units for microwave technology.
Highlights
Activated carbon (AC), is a carbonaceous solid derived from coal or biomass via thermal or thermochemical processes
The chemical activation process can be achieved in several ways, as outlined below: The chemical activation method is accomplished by the infusion, mixing and permeation of a solution, usually a dehydrating chemical with the ability to induce and accelerate material decomposition by pyrolysis, while inhibiting the creation of semi-solid volatile substances before activation
Activating agents play major roles in the activation process, and the various compounds used react differently depending on the biomass type and the temperatures employed
Summary
Activated carbon (AC), is a carbonaceous solid derived from coal or biomass via thermal or thermochemical processes. The abundance of agricultural waste generated globally remains a significant environmental issue [13] and AC production offers the prospect of using it as a renewable carbon source to produce highly porous AC. This study reviews agricultural waste as an AC precursor regarding its activation conditions and chemical activating agents, with a substantial emphasis on the characteristic properties of AC [22] and adsorption application targets [23]. This study considers the effectiveness of some of the chemical activating agents used for AC production under various production conditions and looks at the effects on the product characteristics, of surface functional groups and of overall adsorption efficiency for several applications. This review concentrates on the behaviour and chemical properties of precursors relative to several treatments, production conditions, comparative analyses of modes of production and their challenges
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