Sorbents are insoluble materials or mixtures of materials used to recover liquids through the mechanism of absorption, or adsorption, or both. Absorbents are materials that pick up and retain liquid distributed throughout its molecular structure causing the solid to swell (50 percent or more). The absorbent must be at least 70 percent insoluble in excess fluid. Adsorbents are insoluble materials that are coated by a liquid on its surface, including pores and capillaries, without the solid swelling more than 50 percent in excess liquid. To be useful in combating oil spills, sorbents need to be both oleophilic (oil-attracting) and hydrophobic (water-repellent). Although they may be used as the sole cleanup method in small spills, sorbents are most often used to remove final traces of oil, or in areas that cannot be reached by skimmers. Sorbent materials used to recover oil must be disposed of in accordance with approved local, state, and federal regulations. Any oil that is removed from sorbent materials must also be properly disposed of or recycled.
Natural organic sorbents include peat moss, straw, hay, sawdust, ground corncobs, feathers, and other readily available carbon-based products. Organic sorbents can adsorb between 3 and 15 times their weight in oil, but there are disadvantages to their use. Some organic sorbents tend to adsorb water as well as oil, causing the sorbents to sink. Many organic sorbents are loose particles such as sawdust, and are difficult to collect after they are spread on the water. These problems can be counterbalanced by adding flotation devices, such as empty drums attached to sorbent bales of hay, to overcome the sinking issue, and wrapping loose particles in mesh to aid in collection.
Natural inorganic sorbents consist of clay, perlite, vermiculite, glass wool, sand, or volcanic ash. They can adsorb from 4 to 20 times their weight in oil. Inorganic sorbents, like organic sorbents, are inexpensive and readily available in large quantities. These types of sorbents are not used on the water's surface.
Synthetic sorbents include man-made materials that are similar to plastics, such as polyurethane, polyethylene, and polypropylene and are designed to adsorb liquids onto their surfaces. Other synthetic sorbents include cross-linked polymers and rubber materials, which absorb liquids into their solid structure, causing the sorbent material to swell. Most synthetic sorbents can absorb up 70 times their own weight in oil.
Any new sorbent materials may need to be listed on the National Contingency Plan, Subpart J, Product Schedule. Please contact the EPA Oil Program at 202-564-1970 for more information.
Biochar is a stable carbon-rich by-product synthesized through pyrolysis/carbonization of plant- and animal-based biomass. An increasing interest in the beneficial application of biochar has opened up multidisciplinary areas for science and engineering. The potential biochar applications include carbon sequestration, soil fertility improvement, pollution remediation, and agricultural by-product/waste recycling. The key parameters controlling its properties include pyrolysis temperature, residence time, heat transfer rate, and feedstock type. The efficacy of biochar in contaminant management depends on its surface area, pore size distribution and ion-exchange capacity. Physical architecture and molecular composition of biochar could be critical for practical application to soil and water. Relatively high pyrolysis temperatures generally produce biochars that are effective in the sorption of organic contaminants by increasing surface area, microporosity, and hydrophobicity; whereas the biochars obtained at low temperatures are more suitable for removing inorganic/polar organic contaminants by oxygen-containing functional groups, electrostatic attraction, and precipitation. However, due to complexity of soil-water system in nature, the effectiveness of biochars on remediation of various organic/inorganic contaminants is still uncertain. In this review, a succinct overview of current biochar use as a sorbent for contaminant management in soil and water is summarized and discussed.
CO2 capture by CaO-based sorbents is based on the reversible chemical reaction (carbonation/calcination): CaO(s) + CO2(g) = CaCO3(s). CO2 separation from flue gas is possible in a multi-cycle process in a dual reactor. This involves reaction of CaO with CO2 from flue gas in a carbonator, and regeneration of sorbent in a calciner . In the ideal case, carbonation/calcination cycles can be carried out indefinitely with the only limitations due to the kinetics of the reactions and thermodynamics of the equilibrium system. The use of the carbonation reaction (exothermic) is limited by the maximum temperature that allows CO2 capture at the desired concentration in cleaned flue gas and the minimum temperature that allows a practical reaction rate. The calcination reaction is limited by the minimum temperature necessary to obtain sufficient CO2 concentration at the calciner outlet.
Despite the simple chemistry of carbonation/calcination looping cycles, undesirable side reactions such as sulphation and processes such as sintering and attrition take place in practice. SO2 from flue gas under CO2 looping cycle conditions irreversibly reacts with CaO, forming CaSO4. A portion of the CaO sorbent is, therefore, lost as CaSO4, and the CaO reaction surface is covered by this product, preventing contact of CaO and CO2 [15,16]. Attrition of sorbent is a significant problem for FBC systems, leading to sorbent elutriation from the reactor . The major and most investigated challenge for CO2 looping cycles is the decrease of reversibility for the carbonation reaction due to sorbent sintering [18,19].
A Perkin Elmer TGA-7, or a Mettler Toledo TGA/SDTA851e/LF/1100 C TGA was usually used for the experiments. The sample was in a ceramic or platinum pan (5 mm diameter). The gas flow rate, controlled by a flowmeter, was 0.04 dm3/min. Calcination/carbonation cycles were carried out under different conditions. The calcination stages were done under milder conditions in an N2 atmosphere [15,23,25,26,31,43], or at higher temperature in pure CO2, simulating real sorbent regeneration conditions [21,44,45].
The Fuel Cell Technologies Office's sorbent storage materials research focuses on increasing the dihydrogen binding energies and improving the hydrogen volumetric capacity by optimizing the material's pore size, pore volume, and surface area, as well as investigating effects of material densification.
Unlike other forms of solid-state storage, one of the advantages of using adsorbents as a storage medium is that dihydrogen retains its molecular form throughout the adsorption/desorption cycle with minimal activation energy. The primary disadvantage of using sorbents is the relatively weak adsorption enthalpies that are typical of gas-solid interactions when compared to that of bond formation with chemical hydrogen, or interstitial atomic hydrogen in metal hydrides. Additionally, the van der Waals dimension of molecular hydrogen is large in comparison to that of atomic hydrogen, putting limits on the overall volumetric density that systems based on dihydrogen can achieve.
Unlike chemical hydrogen or metal hydrides, the quantity that is measured either gravimetrically or volumetrically is the Gibbs surface excess.3 This quantity is a true measurement of increased concentration of gas at the surface of an adsorbent over the concentration that might be expected from the gas law and is the only value that is determined empirically.
The enthalpy range for hydrogen adsorbents can run typically from 5 to 10 kJ/mole. For sorption, the term "enthalpy" is not a single valued quantity, although it is often referenced this way. When reported, a single enthalpy value generally refers to the "differential enthalpy of adsorption at zero coverage," more commonly referred to as the Henry's Law value, where the gas concentration varies linearly with pressure.4 The Henry's Law value is essentially the enthalpy or potential assigned to the initial molecule adsorbed onto a surface. This value will generally be the highest quantity as the initial molecule adsorbs onto the highest potential site and adsorbs free of the influence of neighboring adsorbed gas molecules. Of more general technological interest is the isosteric enthalpy of adsorption, which traces the change in enthalpy over as large a range of coverage as pressure measurements allow. In all known instances for hydrogen sorption, the isosteric enthalpy of adsorption is expected to decay monotonically.
The sorbents that have been investigated recently range from coordination polymers5 to activated carbons. These classes of materials have the initial requirements for high gravimetric density as adsorption relies on having a high number of sites, upon which gas molecules can adsorb. For activated carbons, we can generally expect the absolute quantity of adsorbed gas molecules to vary as a function of surface area and micropore volume.6 As the gravimetric adsorption is highly correlated with surface area, maximizing surface area consistent with retaining a high micropore volume is the geometric combination that will best satisfy the design criteria for successful adsorbents.
SKC offers a complete selection of sorbent tubes designed specifically for solvent extraction specified in many OSHA, NIOSH, ASTM, EPA, and non-agency methods. Quality SKC Sorbent Tubes feature consistent sorbent mesh size, validation, and over 45 years of proven performance.
Uniquely constructed and versatile SKC OVS tubes combine sorbent and filter into one glass tube to trap aerosols and vapors simultaneously and overcome inconveniences of earlier methods. SKC OVS Tubes meet the specifications of several OSHA, NIOSH, and non-agency methods for sampling pesticides, explosives, alcohols, and biocides. Require an OVS Tube Holder 041b061a72