Etanolden asetaldehit üretiminde katalist deaktivasyonu, reaksiyon kinetiği ve optimum çalışma koşullarının incelenmesi
Küçük Resim Yok
Tarih
1991
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Ege Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/closedAccess
Özet
72 8. ÖZET Sanayide organik sentezlerde kullanılan asetaldehit, ticari olarak çeşitli yollarla elde edilebilmekte ise de, etanolden üretimi, tarıma dayalı sanayi acısından, ayrı bir öneme sahiptir. Asetaldehitin ticari üretim yöntemlerinden biri olan, etanol' ün buhar fazındaki dehidrojenasyon reaksiyonu, 1 atm toplam basınç ve 265°C ile 295°C sıcaklıklar arasında, CuO, CraOs esaslı bir katalist dolgulu, pilot ölçekte tasarlanan bir reaktörde gerçekleştirilmiştir. Katalistte, kullanımıyla artan ve katalist rejenerasyonu ve yenilenmesi bakımından önemli olan, aktif lik kaybı, ya sabit sıcaklıkta, azalan dönüşümleri, ya da sabit dönüşümde, artan sıcaklıkları içeren deneysel verilerin analiziyle bulunur. Sabit sıcaklıktaki reaksiyon hız verilerinin, zaman aralıkları içinde kümelendirilerek ele alındığı, bu çalışmada uygulana yöntemle, yukarda söz edilen yöntemlerdeki güçlükler aşılmıştır. Bu yöntemde, bir küme içinde tanımlı bağıl zaman ve aktiflik delerleri kullanılarak, "The time on stream" kuramına göre önerilen deaktivasyon modellerinin, önce, enküçük kareler yöntemiyle analizi yapılmıştır. Her bir model için, bulunan katsayılara uygulanan homojenlik testi ve kikare dağılımlarının incelenmesiyle, aktif lik kaybı hızının, sıcaklık ve zamana bağlı, ikinci dereceden bir denklemle verilebileceği saptanmıştır. Reaksiyon hızı modelinin bulunmasında, hızı belirleyen adımlara ve bu çalışmadaki reaksiyon koşullarına göre, Hougen -Watson türünden hız denklemleri önerilmiştir.Aktifliğin de bir değişken olarak alındılı bu modellerin analizi sonucunda, reaksiyon hızının, homojen modele uyduğu görülmüştür. Aktiflik kaybına uğrayan katalitik reaktördeki süreç denetiminde, sıcaklığın, zamanla arttırılması yöntemi, yalnızca, dönüşümdeki değişimi, dar bir aralıkta tutmayı amaçlar. Daha etkin ve verimli bir denetim şekli ise, sıcaklık ayarlamalarının, aynı çalışma süresinde elde edilecek ürün miktarını maksimum kılacak biçimde yapılmasıdır. Kontrol değişkeni olarak reaktör sıcaklığının alındığı, maksimum ürün amaçlı optimizasyon problemi, Maksimum ilkesi temelinde geliştirilen bir algoritma kullanılarak, çözülmüştür. Burada, belirli bir işletme süresi boyunca, tutulması gereken sıcaklık değerleri, kontrol vektörünün ardışık yaklaştırımı yöntemiyle hesaplanmıştır. Katal istin deaktivasyon davranışı, üç değişik işletme süresi için bulunan sıcaklık, dönüşüm ve aktiflik prof illeriyle açıklanmıştır
74 SUMMARY Acetaldehyde, which is an important intermediate in industrial organic synthesis, can be produced commercially by several methods. However, its production from ethanol has a distinct importance regarding the industry based upon agricultural products. The dehydrogenation reaction of ethanol in vapor phase, which is one of the methods ömployed commercially in the acetaldehyde production, was carried out at 1 atm total pressure and temperatures ranging from 265°C to 295°C, in a pilot scale fixed bed catalytic reactor packed with CuO, CrsOs catalyst. The catalyst decay, which increases as the result of being used and of basic importance for the refreshment or/and the regeneration of catalyst, may be described with the analysis of the experimental data collected in two different ways: either i) decrease in conversion at constant temperature or ii) increase in temperature at constant conversion. There are some difficulties in these analyses such as long experimental time, validity of the activity ratio and complexity of calculation. These difficulties, however may be eliminated by adopting a method in which the rate data at constant temperature are grouped. In this method, deactivation models proposed with respect to "The time on stream theory" are analysed by the least squares procedure. It is shown that the deactivation rate, depending on temperature and time, could be represented with an equation of second order, after the75 s~tat.ist.ical parameters found for each groups had been tested for homogeneity, by means of the chi- squared distribution for each models. In order to establish the reaction rate equations by considering the rate controlling steps and experimental conditions, the Hougen-Watson type of rate equations were proposed. According to the analysis of models including activity, it was found that the homogeneous model could be adequately fitted to the reaction rate data. In control of a reactor undergoing deactivation, the manner of increasing temperature from time to time aims only at keeping the changes of conversion in a narrow band. As a more productive and efficient control policy, temperature settings are scheduled to maximize the production through the same operation time. The optimization problem, in which the control variable was reactor temperature and the objective was to maximize the production, have been solved by an algorithm developed from the Maximum Principle. The temperatures to be followed during the given operating life were calculated by using the control vector iteration procedure. The behaviour of catalyst decay have been explained in terms of temperature, conversion and activity profiles found for three different total on stream times.
74 SUMMARY Acetaldehyde, which is an important intermediate in industrial organic synthesis, can be produced commercially by several methods. However, its production from ethanol has a distinct importance regarding the industry based upon agricultural products. The dehydrogenation reaction of ethanol in vapor phase, which is one of the methods ömployed commercially in the acetaldehyde production, was carried out at 1 atm total pressure and temperatures ranging from 265°C to 295°C, in a pilot scale fixed bed catalytic reactor packed with CuO, CrsOs catalyst. The catalyst decay, which increases as the result of being used and of basic importance for the refreshment or/and the regeneration of catalyst, may be described with the analysis of the experimental data collected in two different ways: either i) decrease in conversion at constant temperature or ii) increase in temperature at constant conversion. There are some difficulties in these analyses such as long experimental time, validity of the activity ratio and complexity of calculation. These difficulties, however may be eliminated by adopting a method in which the rate data at constant temperature are grouped. In this method, deactivation models proposed with respect to "The time on stream theory" are analysed by the least squares procedure. It is shown that the deactivation rate, depending on temperature and time, could be represented with an equation of second order, after the75 s~tat.ist.ical parameters found for each groups had been tested for homogeneity, by means of the chi- squared distribution for each models. In order to establish the reaction rate equations by considering the rate controlling steps and experimental conditions, the Hougen-Watson type of rate equations were proposed. According to the analysis of models including activity, it was found that the homogeneous model could be adequately fitted to the reaction rate data. In control of a reactor undergoing deactivation, the manner of increasing temperature from time to time aims only at keeping the changes of conversion in a narrow band. As a more productive and efficient control policy, temperature settings are scheduled to maximize the production through the same operation time. The optimization problem, in which the control variable was reactor temperature and the objective was to maximize the production, have been solved by an algorithm developed from the Maximum Principle. The temperatures to be followed during the given operating life were calculated by using the control vector iteration procedure. The behaviour of catalyst decay have been explained in terms of temperature, conversion and activity profiles found for three different total on stream times.
Açıklama
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Anahtar Kelimeler
Kimya Mühendisliği, Chemical Engineering, Asetaldehit, Acetaldehyde, Deaktivasyon, Deactivation, Etanol, Ethanol, Reaksiyon kinetiği, Reaction kinetics
