Modifiye edilmiş zeolit-Y varlığında selülozun katalitik dönüşümü
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Tarih
2024
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Yayıncı
Bursa Teknik Üniversitesi, Lisansüstü Eğitim Enstitüsü
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Dünya enerji arzının büyük bir çoğunluğunu karşılamakta olan fosil rezervlerin gün geçtikçe tükenmesi, kullanımlarının küresel ısınmaya neden olması ve artan dünya nüfusuyla birlikte insanlık yakın bir gelecekte ihtiyaç duyduğu enerjiyi karşılayamama problemiyle karşılaşacaktır. Bu problemin çözümü ise fosil rezervlere alternatif olabilecek, çevre dostu enerji kaynaklarının kullanımından geçmektedir. Doğada en bol bulunan, yenilenebilir kaynaklar arasında umut verici bir yere sahip olan lignoselülozik biyokütlenin yapısındaki en büyük yüzdeye sahip olan selülozdan, çeşitli platform kimyasallarıının eldesi mümkündür. Bu tez çalışmasında, yeşil kimya ilkeleri çerçevesinde, değerli platform kimyasallarının selülozdan eldesi, Y zeolitinin post-sentez modifikasyonu ile çevre dostu su ortamında araştırılmıştır. Yüksek verimde selüloz eldesi için optimum reaksiyon koşullarının belirlenmesi ve Y zeolitinin kendine özgü özellikleri (yüksek yüzey alanı, şekil seçiciliği ve asitlik) korunurken önemli ölçüde mezogözenekliliğin kazandırılması amaçlanmıştır. Bireysel post-sentez işlemlerin Y zeolitine mezogözenek kazandırmada yetersiz kaldığı göz önünde bulundurularak bu çalışmada sıralı olarak yukarıdan aşağı post-sentez işlemler uygulandı. Bu amaçla Y zeoliti önce alkali çözelti ile desilikasyona (NaOH) ve ardından da alüminasyona (NaAlO₂) maruz bırakıldı. Selüloz dönüşümü; hidrotermal reaktörde, 220˚C sıcaklıkta, 6 saatlik reaksiyon süresince mikrokristal selülozun Y zeolitine oranı 1:1 (ağırlık/ağırlık) olacak şekilde su ortamında gerçekleştirildi. Numuneler ICP-OES, XRF, BET ve XRD yöntemleriyle karakterize edildi. Katalizör modifikasyonu için dört farklı sıcaklık ve üç farklı derişimde gerçekleştirilen çift tekrarlı 12 deneyin sonuçları, herhangi bir işlem görmemiş ham zeolit Y ile karşılaştırılmıştır. Post-sentez işlemler sonucu elde edilen numenelerin kimyasal bileşimleri HPLC ile yapılmıştır. Yapılan deneysel çalışmalar sonucunda, selüloz dönüşümünden ağırlıklı olarak " laktik asit, asetik asit ve formik asit" eldesi gözlenmiştir. Selüloz dönüşümü için optimum sıcaklık 70 °C, optimum derişim 1M olarak belirlenmiştir. Post-sentetik işlemler sonucunda, kristal yapının korunduğu, ancak desilikasyon adımında NaOH ile muamele sonucu mevcut gözeneklerin zarar gördüğü, bu nedenle de yüzey alanı azalırken, gözenek hacminin büyüdüğü sonucuna varılmıştır. Numunelerin % SiO2/Al2O3 oranları incelendiğinde genel anlamda ham zeolit Y'ye göre oranların düşmesi alüminasyon sonucu yapıya Al girdiğini göstermektedir.
With the depletion of fossil reserves, which meet the majority of the world's energy supply, their use causing global warming, and the increasing world population, humanity will face the problem of not being able to meet the energy it needs in the near future. The solution to this problem is the use of environmentally friendly energy sources that can be an alternative to fossil reserves. It is possible to obtain various platform chemicals from cellulose, which has the largest percentage in the structure of lignocellulosic biomass, which is the most abundant in nature and has a promising place among renewable resources. In this thesis, within the framework of green chemistry principles, the production of valuable platform chemicals from cellulose was investigated in an environmentally friendly aquatic environment by post-synthesis modification of Y zeolite. It was aimed to determine the optimum reaction conditions to obtain cellulose in high yield and to provide significant mesoporosity while preserving the unique properties of Y zeolite (high surface area, shape selectivity and acidity). Considering that individual post-synthesis processes were insufficient to impart mesoporosity to Y zeolite, post-synthesis processes were applied sequentially from top to bottom in this study. For this purpose, Y zeolite was first subjected to desilication (NaOH) with alkaline solution and then to alumination (NaAlO₂). Cellulose transformation; It was carried out in a hydrothermal reactor, at 220˚C, in water environment, with the ratio of microcrystalline cellulose to Y zeolite being 1:1 (w/w) during the 6-hour reaction. The samples were characterized by ICP-OES, XRF, BET and XRD methods. The results of 12 replicate experiments performed at four different temperatures and three different concentrations for catalyst modification were compared with raw zeolite Y without any treatment. The chemical compositions of the samples obtained as a result of post-synthesis processes were determined by HPLC. As a result of the experimental studies, it was observed that mainly "lactic acid, acetic acid and formic acid" were obtained from cellulose conversion. The optimum temperature for cellulose transformation was determined as 70 °C and the optimum concentration was 1M. As a result of post-synthetic processes, it was concluded that the crystal structure was preserved, but the existing pores were damaged as a result of treatment with NaOH in the desilication step, therefore the surface area decreased and the pore volume increased. When the SiO2 /Al2O3% ratios of the samples are examined, the general decrease in the ratios compared to the parent zeolite Y shows that Al entered the structure as a result of alumination.
With the depletion of fossil reserves, which meet the majority of the world's energy supply, their use causing global warming, and the increasing world population, humanity will face the problem of not being able to meet the energy it needs in the near future. The solution to this problem is the use of environmentally friendly energy sources that can be an alternative to fossil reserves. It is possible to obtain various platform chemicals from cellulose, which has the largest percentage in the structure of lignocellulosic biomass, which is the most abundant in nature and has a promising place among renewable resources. In this thesis, within the framework of green chemistry principles, the production of valuable platform chemicals from cellulose was investigated in an environmentally friendly aquatic environment by post-synthesis modification of Y zeolite. It was aimed to determine the optimum reaction conditions to obtain cellulose in high yield and to provide significant mesoporosity while preserving the unique properties of Y zeolite (high surface area, shape selectivity and acidity). Considering that individual post-synthesis processes were insufficient to impart mesoporosity to Y zeolite, post-synthesis processes were applied sequentially from top to bottom in this study. For this purpose, Y zeolite was first subjected to desilication (NaOH) with alkaline solution and then to alumination (NaAlO₂). Cellulose transformation; It was carried out in a hydrothermal reactor, at 220˚C, in water environment, with the ratio of microcrystalline cellulose to Y zeolite being 1:1 (w/w) during the 6-hour reaction. The samples were characterized by ICP-OES, XRF, BET and XRD methods. The results of 12 replicate experiments performed at four different temperatures and three different concentrations for catalyst modification were compared with raw zeolite Y without any treatment. The chemical compositions of the samples obtained as a result of post-synthesis processes were determined by HPLC. As a result of the experimental studies, it was observed that mainly "lactic acid, acetic acid and formic acid" were obtained from cellulose conversion. The optimum temperature for cellulose transformation was determined as 70 °C and the optimum concentration was 1M. As a result of post-synthetic processes, it was concluded that the crystal structure was preserved, but the existing pores were damaged as a result of treatment with NaOH in the desilication step, therefore the surface area decreased and the pore volume increased. When the SiO2 /Al2O3% ratios of the samples are examined, the general decrease in the ratios compared to the parent zeolite Y shows that Al entered the structure as a result of alumination.
Açıklama
Anahtar Kelimeler
Kimya Mühendisliği, Chemical Engineering
