Karbonil sülfitin sulu dietanol amin çözeltisi ile yakalanmasının teorik olarak incelenmesi
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Date
2017
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Karbonil sülfit (COS), istenmeyen bir safsızlık olarak çeşitli proses gazlarıyla birlikte salınır. COS'u yakalamak, sıvı absorbentler ile başarılabilir. COS ve dietanolamin (DEA) reaksiyonu için literatürde iki farklı mekanizma önerilmiş ve her ikisi de tiyokarbamat oluşumuna neden olmaktadır. Birinci mekanizma zvitteriyon (dipolar iyon) ara madde mekanizması olup, iki reaksiyon adımında gerçekleşir. İlk adım zvitteriyonun oluşturulması ve ikincisi oluşan zvitteriyodan proton giderme işlemidir. İkinci mekanizma, bir kompleksin bir tek aşamalı reaksiyonda ara madde olarak oluştuğu termoleküler mekanizmadır. COS, DEA ve su arasındaki dört farklı termolekül reaksiyonu kuantum kimyasal hesaplamaları ile araştırılmış ve yapısal, enerjik ve termokimyasal özellikler ortaya konmuştur. Teorik standard serbest aktivasyon (∆‡G°) ve reaksiyon enerjisi (∆G°rxn), denge sabiti (Keq) ve bu dört termoleküler reaksiyon için reaksiyon hızı sabiti (k) değerleri hesaplanmıştır. Yoğunluk Fonksiyonel Teorisi (DFT), bu çalışmanın teorik araştırmaları sırasında B3LYP hibrid fonksiyoneli ve 6-311G (d) baz seti kullanılarak uygulanmıştır. Sonuç olarak, bu çalışmada elde edilen hesaplanan aktivasyon enerjisi ve reaksiyon hızı sabit değerleri literatürde mevcut olan deneysel verilerle karşılaştırılmış ve bu bulguların rehberliği altında, sulu DEA çözeltisi ile COS yakalama için en olası termoleküler reaksiyon mekanizması ortaya çıkmıştır.
Carbonyl sulfide (COS), an unwanted impurity, released with a variety of processing gases. Capturing of COS can be achieved with liquid absorbents. Two different mechanisms are proposed in the literature for COS and diethanolamine (DEA) reaction, and both drive to a formation of thiocarbamate. The first mechanism is zwitterion intermediate mechanism, which takes two reaction steps. The first step is the forming of the zwitterion, and the second one is the deprotonation of the formed zwitterion. The second mechanism is termolecular mechanism in which a complex forms as intermediate in a single step reaction. Four different termolecular reactions among COS, DEA and water were investigated through the quantum chemical calculations, and structural, energetic and thermochemical properties were revealed. Theoretical standard free energy of activation (∆‡G°) and reaction (∆G°rxn), equilibrium constant (Keq) and reaction rate constant (k) values for these four termolecular reactions were calculated. Density Functional Theory (DFT) was applied during the theoretical investigations of this study utilizing the B3LYP hybrid functional, and 6-311G(d) basis set. In conclusion, calculated activation energy and reaction rate constant values obtained in this study were compared with the experimental data available in the literature, and under the guidance of these findings, the most probable termolecular reaction mechanism for the COS capture by aqueous DEA solution was revealed.
Carbonyl sulfide (COS), an unwanted impurity, released with a variety of processing gases. Capturing of COS can be achieved with liquid absorbents. Two different mechanisms are proposed in the literature for COS and diethanolamine (DEA) reaction, and both drive to a formation of thiocarbamate. The first mechanism is zwitterion intermediate mechanism, which takes two reaction steps. The first step is the forming of the zwitterion, and the second one is the deprotonation of the formed zwitterion. The second mechanism is termolecular mechanism in which a complex forms as intermediate in a single step reaction. Four different termolecular reactions among COS, DEA and water were investigated through the quantum chemical calculations, and structural, energetic and thermochemical properties were revealed. Theoretical standard free energy of activation (∆‡G°) and reaction (∆G°rxn), equilibrium constant (Keq) and reaction rate constant (k) values for these four termolecular reactions were calculated. Density Functional Theory (DFT) was applied during the theoretical investigations of this study utilizing the B3LYP hybrid functional, and 6-311G(d) basis set. In conclusion, calculated activation energy and reaction rate constant values obtained in this study were compared with the experimental data available in the literature, and under the guidance of these findings, the most probable termolecular reaction mechanism for the COS capture by aqueous DEA solution was revealed.
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Kimya Mühendisliği, Chemical Engineering
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