Abstract
The purport of this thesis is to investigate the catalytic chemistry of the hydroisomerization of long chain n-paraffin. It mainly focus on how the parameters, such as the pore size/structure, acidity, Si/Al ratio and adding a 2nd polyvalent metal ion into some Pt loaded acid catalysts, affect the reaction activities and the selectivities.Six chapters are included in this systematic study. Chapter 1 describes the driving forces and the importance, makes a short introduction to zeolite and then lists some of its characteristic pore structure discussed in this thesis. Chapter 2, a review survey, describes the state of the art of paraffin’s hydroisomerization. Model compound, n-hexadecane, was used to investigate the chemistry of hydroisomerization in chapter 3, chapter 4 and chapter 5. Chapter 3 focuses on the effect of some preparation parameters of amorphous silica-alumina catalysts. Chapter 4 and chapter 5 are the major part of this thesis. Chapter 4 investigates the pore effects, the effects of acid strength and acid amounts by various modifications. Chapter 5 focuses on the modification effect on the Pt loaded Ferrierite zeolite. Chapter 6 focuses on real feed testing with three selected catalysts which show high hydroisomerization performance on model compound testing. A cooperate research report, the development of catalysts for SO2 oxidation, conducted by Germany DAAD and Taiwan NSC is included also in appendix.The pore structure/size of zeolite plays an important role on the product distribution of the hydroisomerization of n-hexadecane. The conversion at maximum isomerization yield of 12mR zeolite and amorphous silica-alumina catalysts are around 80 wt% and poly-branched iso-hexadecane and central cracking fragments are preferable in these large pore catalysts. For 10mR zeolite, the conversion at maximum isomerization yield are all above 90 wt%, and single-branched iso-hexadecane and terminal cracking fragments are preferable in 10mR zeolite. The ratio of poly-branched to single-branched iso-hexadecane (PSBR) can be used to differentiate 12mR and 10mR zeolite. The ratio of central-branched to terminal-branched iso-hexadecane (CTBR) is well correlated to the pore size. There seems to exist an optimum Si/Al ratio for each catalyst in the hydroisomerization of n-hexadecane. If the acid amounts of the catalyst is too low, higher temperature is required for the reaction to achieve the same conversion, and it is unfavorable for the thermodynamic equilibrium. Contrarily, if the acid amounts is too high, side reactions may play an important role, and it is also unfavorable to the hydroisomerization reaction. In case of zeolite with 1.0 wt% Pt loaded, the optimum Si/Al ratio for H-BEA is around 150, and that for H-USY maybe a little higher. Although zeolite treated with phosphorous compounds does reduce the acid strength and/or the acid amounts, it is helpless and even harmful to paraffin’s hydroisomerization. It may block the pore, poison the Bronsted acid sites or promote the dealumination reaction. The existence of alkaline metal ion, i.e. Na+ or K+, is harmful to paraffin’s hydroisomerization. It mainly poisons the Bronsted acid sites and reduces the activity. However, the addition of small amounts of alkaline earth metal ion can improve the maximum isomerization yield due to the better Pt dispersion. The cracking products of long-chain n-paraffin over Pt/H-FER are mainly distributed on C1-C6, which are significantly different from that of other zeolites, as a result of the special 2-D pore structure of FER zeolite. Adding a second divalent or trivalent metal ion (Mn+, n=2,3) into FER zeolite by ion exchange can significantly improve the performance of paraffin’s hydroisomerization, including increasing the maximum isomerization yield and changing the pattern of cracking products. The reasons for this improvement are multiple:1. Mn+ reduces the acid strength and/or the acid amounts of FER.2. Mn+ improves the Pt dispersion3. Mn+ prefers to locate at special position, such as the intersection of 6mR and 8mR channel, which reduces the possibility for small molecules to diffuse into 8mR channel, hinders the further cracking reaction and changes the cracking pattern. Solid state ion exchange can introduce Pt2+ ion into small pore of FER. In this case, some of the Pt 2+ ion also prefers to locate at the special position to hinder lots of small molecules diffusion into 8mR channel and thus prevents small molecules from being further cracked. The product pattern of n-paraffin’s hydroisomerization over Pt/H-FER, which is prepared by solid-state ion exchange, is very similar to that of Pt/M,H-FER.The properties of lubricant base oil are highly correlated with the characteristics of the catalyst and the process’s parameters. Three catalysts with best hydroisomerization performance on model compound testing were selected to evaluate their performance in real feed. The order of 3 catalysts’ reactivity in wax hydroisomerization is the same as that in model compound testing. Pt/H-BEA shows the highest activity, and the products contain more than 90wt% of saturates with a very dim color. Pt/H-SAPO11 requires the highest reaction temperature to achieve the same conversion due to its low acidity strength. Its products are dark and contain lots of aromatics. Pt/Ca_FER is just in between. Generally speaking, these 3 catalysts are comparable, they have their advantages and their weaknesses for each one.