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Khayitov Ruslan Rustamjonovich, Institute of General and Inorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan, doctoral student, the Laboratory of Chemistry of Oil
E-mail: [email protected] Narmetova Gulnara Rozukulovna, Institute of General and Inorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan, Chief scientific officer, the Laboratory of Chemistry of Oil Shermatov Bobomirza Eshbaevich, Uzbek Scientific Research Chemical-Pharmaceutical Institute
named after A. Sultanov UzKFITI, Tashkent, Uzbekistan, head of the laboratory, E-mail: [email protected]
Regeneration of activated carbon used in adsorption purification of alkanolamines
Abstract: Studied the methods of regeneration of spent activated carbon. Regeneration of spent activated carbon was carried out in laboratory conditions by high temperature treatment of spent activated carbons in an environment of water vapor and nitrogen at 750±20 °C; 800±20 °C; 850±20 °C temperature regimes.
Keywords: activated carbon, regeneration, adsorption, desorption, reactivation, heat treatment, the specific area, adsorption activity.
Introduction. The adsorption process has wide application in environmental engineering for treating and cleaning gas industrial emissions and sewage. It allows you to quickly and effectively remove from any environmental toxicants. As adsorbents can be used various materials with a certain chemical composition, crystal structure, the mechanism of their action must conform to the following principles [1]:
- have a high adsorption activity directed action;
- do not change the natural balance of substances in all parts of the ecosystem;
- have the ability to regenerate;
- to be able to recycling.
On oil and gas companies to capture hydrocarbons of oil and oil products from waste water is used as a highly effective adsorbent activated carbon, which meets all the
Section 6. Chemistry
requirements. It has a high specific surface area, adsorption ability (activity) and selectivity to polar components, which is one of the major harmful environmental contaminants specific to the oil and gas industry. In addition, activated carbons can be used not only in water but also dry and wet gas flows, thereby extending the range of their application.
However, the practical use of activated carbon for trapping hydrocarbons of oil and petroleum products is constrained because ofproblems ofregeneration, which is necessary since during the operation ofthe specific surface and sorption activity of their gradually declining.
Earlier, in our studies the adsorption process was used to regenerate the spent alkanolamine used for purification of natural gas from acidic components by using activated carbon from local raw materials.
The aim of this work was to study the effect of temperature regimes regeneration of spent activated carbon, passivated during regeneration of spent alkanolamine used for purification of natural gas from acidic components, the degree of recovery of their specific surface and sorption activity.
Objects and methods of research. Because adsorption is in principle a reversible process, the contaminants can be removed from activated carbon by desorption (separation of adsorbed substances). The strength of Van-der-Waltz, which is the main driving force for adsorption is weakened, so that the contaminant could be removed from the surface of the coal, there are three technical method [2]:
- the method of temperature fluctuations: the effect of forces ofVan-der-Waltz decreases with increasing temperature. The temperature increases due to hot nitrogen stream or by increasing the steam pressure at a temperature of110-160°C;
- the method of pressure fluctuations: with decreasing partial pressure, the effect of the forces of Van-der-Waltz is reduced;
- extraction — desorption in the liquid phase. The adsorbed substances are removed by chemical means.
All these methods have disadvantages. Some amount of the pollutant may remain in the pores of activated carbon. With the use of steam regeneration 1/3 of all adsorbed species, is still in the activated carbon.
The chemical regeneration understand the processing of the sorbent liquid or gaseous organic or inorganic reagents at a temperature of usually not higher than 100 °C. Chemically regenerate like carbon, and not carbon sorbents. As a result of this processing, the sorbate is desorbed either unchanged or desorb the products
of its interaction with the regenerating agent. Chemical regeneration often occurs directly in the adsorption apparatus. Most methods of chemical regeneration is narrowly specialized for the solutes of a certain type.
Low-temperature thermal regeneration is in the processing of the sorbent with steam or gas at 100-400 °C. this Procedure is quite simple and in many cases it leads directly to the adsorbers. Water vapor due to the high enthalpy are often used for low-temperature thermal regeneration. It is safe and available in production.
Chemical recovery and low-temperature thermal regeneration does not ensure full recovery of the adsorption of coals. Thermal regeneration process is very complex, multistage, affecting not only the sorbate and the sorbent. Thermal regeneration close to the technology of obtaining active coals [3]. The carbonisation of the solutes ofvarious type of coal most of the impurities decomposes at 200-350 °C and at 400 °C is typically destroyed about half of the total adsorbate. CO, CO2, CH4 are the main products of decomposition of organic sorbate is released when heated to 350-600 °C. In theory, the cost of such regeneration is 50% of the cost of a new activated carbon. This suggests the need to continue the search and development of new highly effective methods of regeneration of sorbents.
Reactivation — regeneration of activated carbon by steam at a temperature of 600 °C. the Contaminant is burned at this temperature, without burning the coal. This is possible due to the low concentration of oxygen and the presence of large quantities of steam. Water vapor selectively reacts with adsorbed organic matter, having high reactivity in water at these high temperatures, thus there is complete combustion. However, you cannot avoid the minimum combustion of coal. This loss must be offset by new coal. When you reactivate often the case that activated carbon shows a large internal surface and higher reactivity than conventional coal. These facts are due to the formation of additional pores and coking contaminants in the activated carbon. The pore structure also changes — they are increasing.
Reactivation is performed in an oven for reactivation. There are three types of kilns: rotary and shaft furnaces with variable gas flow. Oven with variable gas flow has the advantages of low losses in combustion and friction. Activated carbon loaded in a stream of air and combustion gases can be blown up through the grate. Activated carbon becomes partially fluid due to the intense gas stream. Gases also transporterowych the products of combustion during reactivation of activated carbon in the afterburner chamber. Air is added to the second com-
bustor, so the gases that have not been fully inflamed, can now be burned. The temperature increases to about 1200 °C. After the combustion gas flows to the gas washing apparatus in which the gas is cooled to temperatures between 50-100 °C by the cooling water and air. In this cell, the hydrochloric acid which is formed adsorbed chlorinated hydrocarbons greatly from purified activated carbon, neutralized with sodium hydroxide. Due to the high temperature and rapid cooling is no formation of toxic gases (dioxins and furans).
The most common regeneration technique used in industrial processes is thermal regeneration. The thermal regeneration process consists of three steps [4]:
- the adsorbent is dried at about 105 °C;
- the high temperature desorption and decomposition (500-900 °C) in inert atmosphere without oxygen;
- residual organic gasification by an oxidizing gas (steam or carbon dioxide) occurs at elevated temperatures (800 °C).
The heat treatment stage utilizes the exothermic nature of adsorption and results in desorption, partial destruction and polymerization of the adsorbed organics. The final step aims to remove charred organic residue formed in the porous structure at the previous stage and re-build the porous carbon structure, restoring its original surface features. After this procedure, the adsorption column may again be used. In the process of heat of adsorption the regeneration cycle of 5-15% of the mass of the carbon layer is burned, resulting in a loss of adsorption capacity. Thermal regeneration is energy intensive process due to the necessary high temperatures, making it commercially expensive process. Plants that rely on thermal regeneration of activated carbon, must have a certain power before it is economically feasible to have local funds for regeneration.
References:
Results and their discussion. The process of regeneration, we conducted in laboratory conditions by high temperature treatment of spent activated carbons in an environment of water vapor and nitrogen at the following temperature regimes:
750±20°C; 800±20°C; 850±20°C.
As follows from the obtained data, the temperature of the regeneration process has a significant influence on the sorption properties and porous structure of activated carbons.
Thus, the regeneration temperature of 750±20°C the degree of recovery of specific surface area of the sorbent was 72±3% and its sorption activity is 75±3% when the regeneration temperature of 800±20 °C the degree of recovery of specific surface area was 80±3% and its sorption activity — 83±3% when the regeneration temperature of850±20 °C the degree of recovery of specific surface area was 87±3% and its sorption activity of 90±3%.
Thus, the results of experimental work show that the regeneration of waste activated carbon using high temperature treatment in the range of 750-850 °C leads to effective recovery of the main chromatographic parameters: the specific surface and sorption activity. The degree of recovery of the sorption properties of activated carbon depend on the temperature of the regeneration mode: the higher the temperature, the higher the degree of regeneration of sorption properties. When the regeneration temperature 850 °C maximum recovery of the surface, pore structure and activity of the sorbent.
The obtained data for the development of modes of regeneration of activated carbon used in manufacture, as sorbent, in the engineering protection of air and water basins from contamination sorption method.
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