Gas cleanup - ?ncal Mineral Gübre ve Yem San. Ltd. ?ti.

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Each year enormous amounts of ash and gases like suifur dioxide and carbon monoxide are ejected into the atmosphere especially in the Northern Hemisphere due to industrial development. This results in an important problem for the environment. Also in some cases, emitted components interact with each other in air forming smog and acids. The basis of gas purification is to recover the valuable compounds in ejected gases and also to protect environment .

Various gas purification systems involving adsorption become important at this point since only adsorbents can cause complete trapping of impurities and the purification of certain components. Among many types of adsorbents, most suitable for unsaturated and polar compounds are zeolites. Clinoptilolite based zeolites are widely used to eliminate impurities like 002, HaS, SO?, Nl-la, NxOy and Cts [6].

Today, natural gas is preferred in house - heating and industrial processes as it is a clean energy source. The separation of nitrogen from methane is therefore becoming increasingly important for natural gas recovery and enhanced oil recovery. Natural gases, which contain significant amounts of nitrogen, need to be upgraded in order to meet the pipeline quality for minimum heating value specifications (typically 950 BTU=ft3 or S 4% inert for US pipeline specifications). [7]

Despite the advantages of using adsorption for methane upgrading, this separation has been found particularly difficult because of the lack of a satisfactory sorbent. Such a sorbent needs to have high nitrogen/methane selectivity. For this application clinoptilolites can be chosen.

The experiments done to dinoptilolites (140 mesh) show that clinoptilolites have a potential for nitrogen/methane separation and with some improvements they can replace the commerdat sorbents used today [7].

Other important application area of the zeolites in gas purification is the elimination of sulfur dioxide. Non - ferrous metallurgical plants using low grade coal and liquid fuel are the main sources of environmental pollution with suifur dioxide. Another important point of sulfur dioxide recovery is the usage of this valuable raw material for the production of sulfuric acid, elemental sulfur and ammonium sulfate.

There are two types of solid (ad)sorbents commonly used in controlling S02 emissions: one is non-regenerative. The common examples are CaO andMgO obtained from different sources such as hydroxide, carbonate and acetates. The other is regenerative, such as zeolites, silica gel, and charcoal

The major advantage of using zeolites is their ability for the successive regeneration. The reaction temperature is also relatively lower. In this application, advantages of zeolites are aiso based on their adsorption characteristics rather than their molecular sieving actions. The experimental setup for researching the SOz breakdown on natural zeolites is shown below
Fig.9. Experimental Setup of SOz Purification

According to experimental results published, it was clearly stated that the performance of the zeolite materials in the powdered form was found to be superior, in terms of breakthrough times, to that for relatively larger size pellets, although the breakthrough curves for smaller size particles were observed to be steep [8].
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