By Martin O’Brien, Rebecca DiStefano and Andrew Harris.
Understanding the different types of activated carbon products, their specific properties and best practices for use is essential to the design of effective environmental treatment processes
Activated carbon is a type of manufactured carbon material used for a range of adsorptive processes, including drinking water treatment, industrial operations, environmental remediation and many other applications. Reports suggest that crude activated carbons have been used in various ways for millennia, for example by ancient Egyptians and Romans as medicine or for water filtration, but the science of more effective modern activated carbons has been continuously developing over many decades. Today’s activated carbon products include cutting-edge manufactured materials that are crucial to society’s water and energy infrastructure, as well as modern industry. Activated carbon provides an environmental solution for ensuring clean air and drinking water and contributes to the efficient production of many industrial products. Understanding the different types of activated carbon products, their specific properties, and best practices for use is important to the design of effective treatment processes.
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Activated carbon is ubiquitous because it is a versatile adsorbent material with the ability to separate and retain components of many liquids and gases (Figure 1). Within an activated carbon particle, the immense specific surface area facilitates the physical adsorption of molecules onto the carbon surface. In contrast to absorption, where fluids enter the internal area of a material, causing it to expand, adsorption is a phenomenon that describes how molecules physically adhere to a surface. Physical adsorption onto activated carbon occurs through weak intermolecular forces called Van der Waals forces in the internal surface area of carbon, often called the pores of the carbon, which give activated carbon its exceptional ability to adsorb and retain organic compounds. Activated carbon adsorption is non-specific and the adsorbate properties contribute to practical capacity for a given contaminant. The adsorption strength of a compound onto activated carbon increases with molecular weight and aromaticity, and can be influenced by functional groups. This adsorptive capability allows activated carbon to be utilized in a wide range of separation processes. Some common factors that affect adsorption are detailed in Table 1.
TABLE 1: COMMON FACTIORS THAT AFFECT ADSORPTION | |||
Property | Effect on Liquid phase adsorption | Property | Effect on vapor phase adsorption |
Solubility | The higher the solubility, the more difficult to adsorb/ Độ hòa tan càng cao thì càng khó hấp phụ | Concentration | Wt.% loading on carbon increases as inlet species concentration increases |
Concentration | Wt.% loading on carbon increases as inlet species concentration increases/ công suất hấp phụ tăng khi nồng độ đầu vào tăng | Saturation pressure | The closer to saturation pressure the more strongly adsorbed/ gần áp suất bão hòa thì hấp phụ mạnh hơn. |
Molecular weight | The higher the molecular weight, the better adsorbed/ KL phân tử lớn thì hấp phụ tốt hơn | Relative humidity | RH above 50% interferes with adsorption efficiency-lower adsorbed capacity/ rất nhạy cảm với độ ẩm cao |
Functional groups | More complex structures adsorb more strongly/ cấu trúc phức tạp thì hấp thụ mạnh hơn | Temperature | Higher temperatures result in lower wt.% loading/ nhiệt độ cao hấp thụ kém hơn |
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