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  • University of South Florida

    Investigation of Methods and Processes to Increase Efficiency for Carbon Activation Processes

    Joshua Dang

    ENC 3246

    Dr. Dianne Donnelly

    June 20, 2014

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    Abstract: The demand for activated carbon keeps growing while supply will dwindle. As a result economic feasibility of such an important material will become nonexistent. Alternative sources of carbon rich raw material need to be used, along with innovative methods of activating carbon, which currently is a high energy and high cost endeavor. As a result, possible improvements could be made to increase the overall efficiency of the activation process, increase effectiveness of activated carbon desired characteristics, and decrease the detrimental impacts to the environment. These current improvements when applied together within the process chain will allow for greater stability of raw resources, make activated carbon pound for pound more effective, and preserve the environment.

    INTRODUCTION The material known as activated carbon affects countless lives. The application of this material can be found in products throughout household items, including soft drinks and shampoos to large-scale industries including removal of mercury from natural gas, and carbon dioxide from fermentation processes [8]. The reason to the wide application of activated carbon is due to molecular carbons special structure characteristics, which has a great capacity and affinity for impurities. Activated carbon is not found naturally with these characteristics but needs to be created through an extended process. It is said that any carbon rich raw material can be used as a precursor to activated carbon [1]; however current raw materials are mainly sourced from coal and wood [9], and are activated through physical means, which require a high-energy input. These current sources and methods present several issues both economically and environmentally. Activation of carbon is a high energy and cost endeavor; however as research continues for more sustainable sources such as agricultural byproducts, viable processing methods such as chemical activation, and recycling techniques such as regeneration of used activated carbon, the cost will decrease as well as an increased impact to preserve the environment. An investigation of the activated carbon process will result in measures to increase the overall efficiency of the activation process, increase effectiveness of activated carbon desired characteristics, and decrease detrimental impacts to the environment. BACKGROUND History The earliest use of activated carbon has been lost in history [10]. It is believed that the earliest application dates back to 3750 B.C. where activated carbon was used by ancient Hindus in India as a process for water filtration [11]. The first documented

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    use of activated carbon was found on Egyptian papyrus dating back to 1500 B.C. as a method to absorb unpleasant odors [10]. The desirable characteristic of activated carbon have been known for more than one and a half millennia, however its main application today are still targeted at fundamentally similar organic impurities. As late as the 18th century sources of raw carbon were derived from blood and animals, which were then used to purify liquids [11]. Documented uses of activated carbon, which became noted in medical journals, were a treatment for ingested poisons [10]. Early uses were also for medicinal purposes, and most widely accepted in the 19th century were uses found in the treatment of poultices, sloughing ulcers, and gangrenous sores [10]. Some noticeable improvement pertains to the manufacturing process the produces a different shape and size of activated carbon. These different shapes allow for longevity of the carbon purification performance as well as improved shipping and handling durability. At the beginning of the twentieth century activated carbon was only available in a powder form. During the First World War granular activated carbon was used in gas mask to capture deadly organic gases [11], this granular processing eventually lead to the widespread manufacturing of granular activated for other applications such as water treatment, and gas purification. The wide application and available sources of activated carbon throughout history and until this day is a testament to the imperative usefulness of this material. Through activated carbons intrinsic physical and chemical properties the usefulness has been experienced and applied to a vast array of situations. Very prominent to this day is the application of activated carbon to purify both gaseous and aqueous phases of substances to prevent environmental harm. Current Application Widespread uses of activated carbon can be found in industrial, pharmaceutical, water treatment processes. Great focus is put on the protection of the environment and the health effects from emission of gases and waste products in industrial and manufacturing processes. These emissions include volatile organic compounds (VOCs) and are known to cause cancer in tested animals [12]. Activated carbon is vital in the many processes that involve VOCs to stay within EPA regulation of emissions for health concerns. Impurities in an aqueous phase are also an important consideration in many products. These organic impurities are in the form of chemical solvents used in production processes for products such as paints and household cleaners [12]. Activated carbon due to its ability to conduct electricity can also be found as a catalyst in many vital electronic components including batteries, supercapacitors, and fuel cells [7]. A major use of activated carbon is in the purification of water for human consumption. When using this absorbent in the water purification process it is layer after sand and before chlorination [11]. The use of activated carbon not only decreases bad odors and taste but also removes harmful contaminants found in the water sources, such as synthetic organic

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    compounds (SOC). These current applications are a constant issue, as nations economical and industrial development demands more activated carbon to continually produce quality products. Molecular Characteristics Activated carbon has a desired physical and chemical structure due to the porosity and surface area different to non-activated carbon. The porosity describes the amount of microscopic cavity between carbon molecules and affects the total surface area per unit mass. Another important aspect is the pore size, which is due to the process of activation as well as the raw source for carbon. Impurities can range from one one thousand of a micron to ten thousand microns. To effectively capture these contaminants a correct pore size must be used to allow for proper mechanical fit, which is then preceded my chemical interactions. Surface area is directly related to the capacity to hold impurities. To achieve a high surface area the pore structure must be extensive, in that many channels are present [2]. It is evident that the level of desired molecular characteristics can be altered. This provides a variable in the effort to increase the overall efficiency of the production of activated carbon. PROCCESSING RAW CARBON Current and Alternative Sources Current raw carbon sources as a precursor are from coal and wood. In the recent pass, the selected source must meet several of the following requirements. It must have the potential to produce high quality activated carbon, which is a function of the porosity and resulting surface area. It must have large available supplies; this will in effect lower the cost. And finally it must have the ability to be stored for extended periods of time [3]. Both coal and wood have passed these conditions as leading sources for the production of activated carbon, however an important requirement have been dismissed in past decisions. This important neglected requirement is how does sourcing of this material effect the environment? With 130,000 tons per year of wood and 100,000 tons per year of raw material being harvested, the impact to the environment is one of great magnitude. Wood and coal are currently the leading source for the production of carbon. Coal comes from surface and underground mines, with the majority from surface mines at sixty percent [13]. Coal is considered a non-renewable source due to the time it takes to create it. Estimates have said supplies of coal will last only until 2035 [14]. This estimates does not take into account the coal that is too deep and costly to mine. This presents an issue to the economics of using coal as a source. Alternative sources must be researched and tested to keep supplies of raw carbon stable. Without proper preparation a sudden decrease in supply will trigger

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    staggering price hikes, which will effect how companies operate, prices of products, and could even shut down industrial processes and slow the economy. Alternative sources need to meet all constraints previously set as well as an additional constraint of sustainability. This will be the basis to analyzing the pote