Controlled Modification And Mechanism Study Of HBEA Molecular Sieves For 1-methylnaphthalene Directed Transformation

The C10 aromatics production has reached more than 300,000 tons per year in China, of which alkyl naphthalene accounts for -40%. Owing to the various application of each component among alkyl naphthalene, the conversion of 1-methylnaphthalene (1-MN) was investigated in the dissertation. The products of 1-MN conversion are important intermediates for the synthesis of vitamin K, poly ethylene naphthalene (PEN), liquid crystal polymer, etc. HBEA, a kind of zeolite with three-dimensional 12 rings structure, has been demonstrated as an effective catalyst for the conversion of 1-MN in comparison with other zeolites. In order to further enhance its catalytic performance, the HBEA zeolite was modified by four treatment methods. The structure and acidity of HBEA before and after treatment were investigated and corrected with 1-MN conversion performances, As a result, the reaction and deactivation mechanism of 1-MN isomerization, disproportionation,cracking and coking were proposed.Owing to the controllable acidity strength of SO42-/TiO2 (ST),new composites of SO42-/TiO2-HBEA (ST-HB) catalysts were synthesized via one-step method.Calcination temperature, template agent (TEAOH) and ST amount were corrected with the structure, acidity and catalytic properties of composites, and the formation mechanism of ST-HB in the presence of template were proposed. It was indicated that the strong acid were responsible for the side reactions (dealkylation, cracking, coking,etc.). High SBET and amount of acid sites were advantageous for 1-MN conversion,while the micropore and low proportion of strong acid were accountable for the high selectivity of alkylnaphthalene. The composited catalyst with 15% ST content showed uniform ST loading, high surface area, and improved proportion of moderately-strong acid sites. At 380 ?, the catalytic selectvity of isomerization and disproportionation over 15%- ST-HB was enhanced to 97.36%.In order to further discuss the impact of acidity properties on 1 -MN isomerization, the SiO2-HBEA catalyst was firstly synthesized by method of liquid deposition. The amorphous SiO2 generated on the external surface of HBEA could passivate the non-selective external suface sites, resulting in slight enhancement of 2-methylnaphthalene (2-MN) selectivity from 81.73% to 84.98% at 300 ?. However,the external SiO2 depositing near the zeolite pore entrances slightly narrow the pore mouth of SiO2-HBEA. This was distangeous for the coke diffusing out the pore canal,and the zeolite pore entrance is easily blocked, leading to the deactivation of catalyst.In addition, the prior passivation of external strong Bronsted acid sites and easy blocking of zeolite pore entranc decreased the accessibility of active sites, leading to the lower stability of SiO2-HBEA than HBEA catalyst.Dealumination by various acids were performed to adjust the whole acidity of HBEA. It was found that mixture of hydrocloric and oxalic acids was superior in improving the selectivity of isomerization. Upon mixed-acid treatment, the surface area and pore volume of catalyst were increased, and the amount of strong Bronsted acid sites remained. These were responsible for the high yield of 2-MN. Due to the selective removal of the extra-framework A1 species, a decrease in the number of Lewis acidic sites were advantageous to suppress the hydride transfer and subsequent side reactions that form coke, leading to the increase in 2-MN selectivity from 81.73%to 96.30%. In addition, the decreased coke rate and remained strong Bronsted acidic sites increased the active sites amount per number of coke, resulting in the higher catalytic stability of Mix-HBEA than HBEA. Consequently, the possible reaction and deactivation mechanism of 1-MN isomerization were proposed.The micropore of HBEA is disadvantageous for the diffusion of macromolecule byproduct, despite its benefit for the isomerization activity and selectivity. Therefore,hierarchical HBEA catalysts were prepared through different alkaline treatments. In comparison with pure NaOH, the TPAOH contained in the alkali dissolution process acts as a suitable pore-directing agent absorbed on the HBEA surface and preserves the zeolite microporous framework, leading to regular inter-crystalline mesopores and proportionable increase of Bronsted and Lewis acid sites for hierarchical HBEA.These were responsible for the remained 2-MN selectivity and coke rate over hierarchical HBEA. In addition to the formation of homogeneous mesoporosity, the maintained coke rate and improved strong Bronsted sites increased the active sites amount per number of coke, leading to its 41.7% lower deactivation rate than HBEA.Based on the study of 1-MN isomerization, a suitable process including isomerization, side-stream distillation and extractive distillation was proposed to produce 2-MN from alkyl naphthalene of C10 aromatics. In the process, isomerization of alkyl naphthalene (FB) over mixed-acid treated HBEA catalyst was used to selectively improve 2-MN purity. After that,various parameters of side-stream distillation (SD) and extractive distillation (ED) were optimized by ASPEN PLUS.Based on the optimal simulation results, SD and ED experiments were carried out. As a result, the 2-MN purity reached above 98.09%, and the total yield of 2-MN was 83.84% in the refining process. The residual alkyl naphthalene returned to the mixture of raw material of FB, and the solvent returned to the ED column. Overall, the 2-MN product was more than 2.3 times of initial content in raw material.