Saliha ÇETİNYOKUŞ KILIÇARSLAN, Emre KIRIC, Meltem DOĞAN

zobütan dehidrojenasyonunun CrOx/AC katalizörler üzerinde incelenmesi

Çalışmada, izobütan dehidrojenasyonu için yüksek aktivite ve seçicilikte krom temelli katalizörlerin hazırlanmasıamaçlanmıştır. Krom temelli katalizörlerde yapıda bulunan monokromat miktarı aktivite ve seçiciliği etkileyen anafaktör olarak belirlenmiştir. Ticari aktif karbon(AC) destek izobütan dehidrojenasyonu yanında propen oluşumreaksiyonu için de aktivite göstermiştir. Deneysel çalışmaların ilk kısmı metal tuz çözeltisi ve desteğin temassüresinin dört farklı değerinde 4, 24, 48, 72 saatlik karıştırma sürelerinde yürütülmüştür. En fazla monokromatmiktarı 24 saatlik karıştırma süresinde hazırlanan katalizör yapısında gözlenmiştir. Katalitik testlerde de en yüksekseçicilik değeri aynı karıştırma süresinde hazırlanan katalizör ile elde edilmiştir. Katalizör yapısında metal miktarı(kütlece) %3’den %6’ya yükseltildiğinde monokromat miktarı artmış ancak %6’dan yüksek konsantrasyonlardamonokromat miktarı düşmüştür. Krom miktarı %22’ye yükseltildiğinde kromun çoğunlukla aktif olmayan Cr2O3kristalleri içinde kaldığı tespit edilmiştir. Yüksek oranda krom içeren katalizörler üzerinde yan reaksiyonlarıngerçekleşmesi ile seçiciliğin düştüğü belirlenmiştir. Bu çalışmada Ca eklenmesinin katalizör yapısı ve aktifliğineetkileri de incelenmiştir. Ca/Cr oranı arttıkça monokromat miktarları azalmıştır. Kalsiyum içeren katalizörler ileyürütülen çalışmalarda çok düşük izobütan dönüşümü ve izobüten seçicilik değerleri gözlenmiştir. Kalsinasyonbasamağı CO2 ortamında ve yüksek sıcaklıkta yapıldığında, oluşan monokromat miktarları artmıştır. Sentezşartlarının monokromat miktarını nasıl etkilediğinin gösterildiği çalışmamızın krom temelli katalizör hazırlamaçalışmaları ile ilgili literatüre önemli katkılar sağlayacağı düşünülmektedir.

Investigation of isobutane dehydrogenation over CrOx/AC catalysts

In the study, it was aimed to prepare chromium-based catalysts with high activity and selectivity for isobutane dehydrogenation. Monochromate amount in the structure of chromium-based catalysts was identified as the main factor affecting the activity and selectivity. The commercial activated carbon (AC) support showed activity for propene formation reaction as well as isobutane dehydrogenation. First part of the experimental studies were carried out at four different contact times of metal salt solution and support namely, 4, 24, 48, 72 hours of mixing times. The highest amount of monochromate was observed in the structure of the catalyst prepared at mixing time of 24 hours. The highest selectivity value in the catalytic tests was also obtained with the catalyst prepared at the same mixing time. When the amount of metal in the catalyst structure was increased from 3% to 6% (by mass), the amount of monochromate increased but, the amount of monochromate decreased at concentrations higher than 6%. It was found that the chromium remained mostly in inactive Cr2O3 crystals, when the amount of chromium was increased to 22%. It was predicted that selectivity reduced because of the occurrence of side reactions on the catalysts containing high amount of chromium. In this study the effect of Ca addition on the structure and activity of catalyst was also investigated. As the Ca/Cr ratio was increased, the amount of monochromate decreased. Very low isobutane conversion and isobutene selectivity values were observed in the studies carried out with calcium containing catalysts. The amount of monochromate formed increased when the calcination was performed in CO2 medium and at high temperatures. Our study, which showed how the synthesis conditions affect the amount of monochromate, is thought to provide important contributions to the literature on chromium-based catalyst preparation studies.

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