乙醇脱水反应的动力学研究

在管式固定床反应器中,采用改性的分子筛催化剂,在温度195～220℃、乙醇浓度30～70 wt%、乙醇液时空速0.08～0.17 mol/g-cat./h的范围内,对乙醇脱水反应的本征动力学进行了研究。动力学研究结果表明,在实验条件范围内,乙醇脱水生成乙烯和乙醚的反应属于平行反应,符合Langmuir-Hinshelwood机理模型,表面反应为速率控制步骤。     

生物质基重整油模型化合物芳构化制BTX轻质芳烃

以戊醇和己醇为生物质基重整油的模型化合物,分别在ZSM-5,Beta和USY催化剂上进行醇芳构化反应制取苯、甲苯和二甲苯(BTX)等芳烃的研究。结果表明:ZSM-5催化剂显示出较好的芳构化性能,液相产物中的BTX可达90%以上;采用急冷淬灭反应的方法对可能的中间物种进行了分析和捕捉,发现取代的烯烃和环烷烃是反应的主要中间物种;模型中间体实验验证了醇类化合物经历了脱水、环化和脱氢等步骤生成BTX芳烃的反应历程。     

Phase selection controlled by sodium ions in the synthesis of FAU/LTA composite zeolite

Abstract

Zeolite faujasite (FAU), Linde type A (LTA) and FAU/LTA composite have been synthesized using tetramethylammonium cation (TMA⁺) as template, by adjusting only the concentration of Na⁺ ions in the initial solution (1.00 Al₂O₃ 4.36 SiO₂ : 2.39 (TMA)₂ O : β Na₂ O : 249.00H₂ O). Na⁺ ions alter the phase composition of the product more than TMA⁺ or OH^? ions. When Na₂ O concentration [Na₂ O] increases from 0.024 to 0.168, the product gradually changes from pure FAU to pure LTA via the formation of FAU/LTA composite with increasing LTA fraction. Interestingly, the induction periods of FAU and LTA in the FAU/LTA composite zeolite ([Na₂ O] is 0.072) are both 13 h, quite different from the induction periods of their individual pure phases—45 h for FAU and 4 h for LTA. During the crystallization, the LTA/(FAU + LTA) fraction in the composite zeolite decreases in a nearly linear fashion. Scanning electron microscopy, thermogravimetry and differential thermal analysis indicate some difference between the properties of the FAU/LTA composite zeolite and of the mechanical mixture.     

H2S removal from biogas for fuelling MCFCs: New adsorbing materials

Cu and Zn modified 13X zeolites prepared by ion exchange or impregnation and activated carbons (ACs) treated with KOH, NaOH or Na₂CO₃ solutions were studied as H₂S sorbents for biogas purification for fuelling molten carbonate fuel cells. H₂S sorption was studied in a new experimental set-up equipped with a high sensitivity potentiometric system for the analysis of H₂S. Breakthrough curves were obtained at 40 °C with a fixed bed of 20 mg of the samples under a stream (6 L h⁻¹) of 8 ppm H₂S/He mixture. The adsorption properties of 13X zeolite improved with addition of Cu or Zn:Cu exchanged zeolite showed the best performances with a breakthrough time of 580 min at 0.5 ppm H₂S, that is 12 times longer than the parent zeolite. In general, unmodified and modified ACs were more effective H₂S sorbents than zeolites. Treating ACs with NaOH, KOH, or Na₂CO₃ solutions improved the H₂S adsorption properties: AC treated with Na₂CO₃ was the most effective sorbent, showing a breakthrough time of 1222 min at 0.5 ppm, that is twice the time of the parent AC.     

Electrooxidation of formaldehyde as a fuel for fuel cells using Fe2+-nano-zeolite modified carbon paste electrode

This study aimed to investigate the application of nano ZSM-5 zeolite for preparation of modified carbone paste electrode for electrocatalytic oxidation of formaldehyde. The electrochemical behavior of modified carbon paste electrodes in the forms of Fe/FeZSM-5CPE and unmodified carbon paste electrode were studied using cyclic voltammetric and chronoamprometric techniques. The obtained results show that the modified carbon paste electrode (Fe/FeZSM-5CPE) is the suitable electrode for electrooxidation of formaldehyde in the acidic solution. The transfer coefficient and current density for formaldehyde were calculated 0.23 and 19.8 mA/cm², respectively. The rate constant for catalytic reaction was calculated as 3.6 × 10³ cm³ s^?1 mol^?1 via Cottrell equation.     

废弃分子筛制备群蓝颜料研究

以工业废弃分子筛为原料,加入单质硫、活性碳、碳酸钠和二氧化硅,通过高温煅烧制备群蓝颜料。研究了煅烧温度和氧气含量对制备样品的影响,用XRD表征样品的物相。结果表明,使用废弃分子筛可以制备出色调亮丽的群蓝颜料。     

偏高岭土微波法合成13X分子筛的生长过程

以鄂尔多斯煤系高岭土经730℃煅烧后得到的偏高岭土为主要原料,采用微波加热法合成了13X分子筛。通过XRD、FTIR、SEM和水静态饱和吸附测定等方法对连续晶化期间不同时间下的固相产物进行了分析,研究了微波条件下偏高岭土合成13X分子筛的生长过程。表征结果显示,在晶化时间为55 min时开始出现13X分子筛晶体,在晶化时间为75 min时13X分子筛晶体生长完全,在晶化时间为150 min时13X分子筛开始向P型分子筛转变。13X分子筛晶体的生长过程包括:偏高岭土溶解并释放出硅、铝物种;硅、铝物种与添加的硅源三者形成硅铝酸钠凝胶;凝胶中出现四、六元环和β笼的基本结构单元;基本结构单元通过有序连接形成13X分子筛晶体。     

控ZSM-5分子筛酸性的方法研究进展(Ⅱ)非金属及金属改性

调控ZSM-5酸性一直是ZSM-5分子筛改性研究的重点。采用非金属、碱土金属及过渡金属等对ZSM-5分子筛进行元素掺杂改性是调控其酸性能的主要手段。可通过筛选改性元素种类、控制改性元素用量、对内外表面酸中心同时或分别改性等方法调控ZSM-5分子筛的酸性能。通常在一定范围内,磷、镁、钙元素掺杂改性后的ZSM-5分子筛强酸位点减少,而弱酸位点增加;硼元素掺杂改性后的ZSM-5分子筛只对弱酸位点发生作用;锌、镓元素掺杂改性后的ZSM-5分子筛会导致其B酸量减少,L酸量增加;铜、银元素掺杂改性后的ZSM-5分子筛由于发生氧化还原作用,其还原态Cu-ZSM-5和Ag-ZSM-5的B酸量较高,蒸汽稳定性较好,且裂解性能较高;钨元素掺杂改性后的ZSM-5分子筛也会使其酸量及酸强度降低。同时探讨了不同反应体系中分子筛酸性能与催化性能间的关系,为提高ZSM-5分子筛在各反应的催化性能提供依据。