- Joe Wong, ADA Carbon Solutions
Chlorinated solvents and petroleum are often two of the most difficult types of contaminants to achieve closure. A major reason for this difficulty is that many amendments don’t have the persistence required to be effective for contaminants sorbed to soil. This means a single application is never enough to deal with the known contaminants—much less the “dark matter” in the soil matrix. That’s why it’s exciting to see activated carbon gain traction—it’s highly persistent, injectable, and is well suited for addressing the expected contaminant mass and any matrix back diffusion. In this blog post, I’ll cover the basics you need to know about using activated carbon on your remediation projects.
Want to dive a little deeper? Register for next week’s webinar, Colloidal Activated Carbons for Hard-to-Treat Contaminants. Cascade’s Vice President of Technology, Eliot Cooper, and I will go into more depth about the use of activated carbon, and answer your questions during the Q&A.
Activated carbon is a class of adsorbent materials that is used in many industrial applications for control of organic, inorganic and heavy metal contaminants. Unlike crystalline carbons, such as diamond, graphite and fullerenes, activated carbon structures have irregular carbon structural arrangements. This amorphous character creates the activated carbon’s unique pore structure, surface and surface area features. These features add to the material’s capability to selectively adsorb and sequester a variety of molecules in a myriad of gas-phase, liquid-phase, structural and functional applications.
Activated carbon can be produced from a variety of carbonaceous raw materials, including coal (bituminous, sub-bituminous and lignite), lignocellulose (sawdust, nut shells, lignin, pits, etc.), peat, plastics, resins, and petroleum residue. These raw materials are heat treated in the presence of steam and/or other chemical reactants. Heat treatment equipment ranging from rotary kilns, multi-hearth furnaces, fluid bed reactors and batch ovens are used with a variety of temperature, residence time and gas conditions to achieve desired activated carbon properties.
The heat treatment process converts the carbonaceous raw material through the basic steps of dehydration, devolatilization, carbonization and activation itself. Elemental carbon is essentially concentrated in the carbon material during carbonization. This carbonized material is sometimes referred to as “char.” Activation of the char begins above about 800°C and below 1000°C in the presence of air, steam, carbon dioxide or other oxidizing agents. At this time, the pore structure formed during carbonization is further developed through oxidation or “burn-off” of the carbon structure and charred organics.
The activated carbon’s surface chemical functionalities can be manipulated throughout the entire heat treatment process. An oxidative atmosphere during activation can enrich oxygen functionalities on the carbon surface. A “reductive” atmosphere can be used to cap these oxygen functional groups to obtain other desired carbon surface properties.
Activated carbons products can be provided in a variety shapes and forms depending on the end-use application requirements.
Powdered activated carbon (PAC) is activated carbon material that is 177 micron or less in particle effective diameter. PAC is used in a variety of liquid-phase contaminant removal applications, such as in water treatment and food purification. PAC can also be used in gas phase applications where high dispersibility is required for contacting dilute concentration of contaminants and rapid contaminant uptake.
Granular activated carbon (GAC) particles are classified as particles greater than 177 micron. GAC is mainly used in gas and liquid-phase applications where the contaminated stream flows through a packed bed of activated carbon. In such a system, the GAC provides a lower pressure drop, which allows for higher process stream flow rates, simpler equipment design, and lower energy requirements.
Activated carbons can be shaped into pellet or spherical forms using binders and extrusion processes. These specialty forms are used in highly specialized high-flow applications more demanding than required for GAC. Other activated carbon forms include fibers and aerogels, which typically tend to be used for high-value specialized applications. Another form of activated carbon that is emerging particularly for in situ soil and ground water remediation applications is a highly dispersible, very small-sized activated carbon particle that is suspended in a pumpable liquid media. These small-sized activated carbon particles could range from 5 micron diameter to less than 1 micron, resulting in a colloidal carbon product (CCP) form.
Activated carbons have also been impregnated, physically bound, and coated onto cloths and fabric. These cloths find utility in air filters, chemical warfare suits, and applications requiring a conformal shape.
Activated carbons are highly adaptable and can serve multiple purposes in removing organic, inorganic and heavy metal pollutants. Their ability to selectively attract and sequester targeted molecules has made activated carbon a highly sought-after and cost-effective technology option.
But using activated carbon to remove contaminants is a complex process. It can be influenced by chemical reaction kinetics, competing contaminant and activated carbon surface interactions, and carbon adsorption capacity, diffusion kinetics and adsorptive energy distribution.
Tuning three key activated carbon properties makes the complexity manageable:
Activated carbons are a customizable solution for a variety of contaminants in liquid, gas and solid phase media. Advances in understanding and tailoring activated carbon surface, pore and particle features are a huge step toward better addressing the complexities faced in removing contaminants in harsh, variable environments.
If you’d like to learn more, join me next week for a webinar I’ll be hosting with Cascade’s Vice President of Technology, Eliot Cooper. We’ll be taking questions, so don’t be afraid to ask!
Chief Technology Officer at Advanced Emissions Solutions
Joe has over 35 years of industrial leadership experience in research & development, product development and business growth in specialty materials. He has deep knowledge in activated carbon development and application and brings a fundamental scientific yet commercially viable approach to building products and businesses. Prior to joining Advanced Emissions Solutions as Chief Technology Officer in 2019, Joe was the Chief Technology Officer for ADA Carbon Solutions starting in 2011. He led a high-performance technology team in activated carbon product development and technical services activities to drive rapid company growth in environmental solutions for the coal power sector. Before ADA Carbon Solutions, Joe worked three years in private consulting, spanning a variety of Lean Six Sigma continuous improvement and operational contributions. Prior to consulting, Joe spent 21 years with MeadWestvaco Corporation in senior leadership positions for the Specialty Chemicals (now Ingevity) and Research & Development sectors. At MeadWestvaco, he led technology and market teams in the development of specialty activated carbon products for a variety of industrial, consumer and emerging markets with concentration in automotive gasoline emissions control. Joe holds a PhD. in Chemical Engineering from the University of Texas.