Structural characterization of Ti centres in Ti-silicalite and reaction mechanisms in cyclohexanone ammoximation

The main results obtained by means of many physical methods (IR, Raman, UV-Vis and XAFS spectroscopies) concerning the structure of the Ti centre in titanium silicalite and the reaction intermediates in the ammoximation of cyclohexanone are concisely reviewed.

The Ti is in tetrahedral coordination in vacuo and expands its coordination sphere upon interaction with adsorbates. In the presence of H₂O and H₂O/H₂O₂ solutions one of the SiOTi bridges is hydrolyzed with formation of (SiO)₃L₂TiOH (LH₂O) and (SiO)₃L₂TiOOH species, respectively. When NH₃ is dosed on (SiO)₃L₂TiOOH structures (SiO)₃L₂TiOO⁻NH₄⁺ species are formed. These species are thought to play an important role in the ammoximation reaction. The geometries of the peroxidic species (open or bridged) are discussed also on the basis of ab initio calculations.     

A heterostructured titanium silicalite-1 catalytic composite for cyclohexanone ammoximation

Submicron-sized titanium silicalite-1 is difficult to recover in industrial process because of their fineness and rapid decrease in catalytic activity due to particle agglomeration. To solve these problems, we present a heterostructured titanium silicalite-1 (TS-1) catalytic composite using bentonite clay as the catalyst support. The catalytic composite is synthesized by hydrothermal treatment which directly crystallizes TS-1 on the bentonite clay surface. The synthesized composite has been characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TS-1 crystals have been found on and between the layers of the bentonite with strong attachment. Characterizations suggest that crystallization temperature of 175 °C is the optimum hydrothermal temperature to produce TS-1 on the bentonite support with characteristics necessary to promote selective catalytic reactions. It is found that prolonged crystallization duration does not necessarily increase the crystallinity of TS-1 on the bentonite surface. The heterostructured composite is able to maintain high conversion of cyclohexanone (97%) and oxime selectivity (83%) after three reaction cycles which is contrary to the unsupported TS-1 that shows apparent decrease in activity (>10%), especially in the selectivity to oxime. The synthesized composite also has significant improvement in separation efficiency with respect to the unsupported catalytic system. Therefore, we conclude that the heterostructured TS-1 composite is a promising catalytic material for cyclohexanone ammoximation and potentially for other TS-1 related processes where catalyst recovery and reuse are required.     

环己酮肟钛硅分子筛催化剂的研究进展

钛硅分子筛(TS-1)催化环己酮氨肟化合成环己酮肟的新工艺具有工艺流程简单、副产物少及无污染等特点,为己内酰胺的生产开辟了新的工艺路线;经典法合成的TS-1合成成本昂贵,合成条件苛刻,严重制约着其工业化应用;详述了TS-1的合成、改性及其在环己酮氨肟化反应中的应用研究进展,以及TS-1催化环己酮氨肟化的反应机理;在环己酮氨肟化反应中,开发廉价且高效的TS-1合成体系、工业上TS-1的分离和回收技术,以及明确其催化环己酮氨肟化的反应机理等是未来该领域的研究方向。     

Oxidation with no-redox oxides: ammoximation of cyclohexanone on amorphous silicas

The ammoximation in gas phase of cyclohexanone is a reaction with an oxidation step performed on an insulator oxide such as amorphous silica. Conventional mechanisms for such a kind of reaction are not useful. This paper reviews the efforts carried out to understand the catalytic behavior of the silica and highlights the particular catalytic features of the tars, the carbonaceous products formed during the ammoximation, in the oxidation step of the reaction. The catalytic behavior and the role of the acid sites, of the tars and of the activated forms of molecular oxygen were investigated on several commercial amorphous silicas and on pure and doped silicas prepared by sol-gel method. The silica catalyst shows a bifunctional behavior: acid sites are necessary for the formation of imine, the intermediate of the reaction, and oxidizing sites for the formation of oxime. For the first step the presence of silanols of the right acidity results is essential. For the oxidative step the carbonaceous products formed during the reaction seem to play an essential role. It has been suggested that the tars are formed by a polymerization reaction which occurs at the silica surface and involves, in the initiation stage, activated oxygen species generated by the silica surface. The reaction progression with time involves increasing amounts of the carbonaceous products, with a corresponding decline in access to the active sites by pore blockage and, as a consequence, with a corresponding decline in the catalytic activity.     

磷钨酸绿色催化氧化环己酮合成己二酸

以30%H2O2为氧源,NaHSO4.H2O、KHSO4为酸性配体,磷钨酸为催化剂催化氧化环己酮合成了己二酸。考察了催化剂用量、H2O2用量、酸性配体用量、反应时间以及催化剂重复使用性等因素对己二酸收率的影响。结果表明,磷钨酸在反应体系中有良好的催化活性,并且具有操作方便,条件温和等优点。适宜反应条件为n(环己酮)∶n(磷钨酸)=1∶0.002(摩尔比),硫酸氢钠0.1 g,30%H2O245 mL,回流反应6 h,己二酸收率66.7%;以KHSO4为酸性配体时,己二酸的收率可达71.2%。     

催化氧化法合成环己酮技术研究进展

介绍了以环己烷为原料催化氧化合成环己酮的主要方法,分析了环己烷氧化采用的主要催化剂。环己烷硼酸催化氧化法和钴盐催化氧化法存在环己烷转化率低及结渣现象;分子筛催化氧化法、金属氧化物以及金属络合物仿生催化氧化法可提高环己烷转化率及醇酮选择性;金属络合物仿生催化氧化法具有良好的开发应用前景。     

环己酮氨肟化工艺最危险场景确定

环己酮氨肟化工艺是制取化工原料的重要工艺,但该反应具有放热失控风险。为了确定氨肟化反应的最危险场景,筛选了环己酮氨肟化工艺可能存在的6个危险场景,并对每一危险场景设定了实验方案。采用泄放设计装置Ⅱ(VSP2)绝热量热仪对每一场景对应的方案进行了量热实验,实验发现:环己酮氨肟化反应为快速强放热反应,能够使反应体系的温度瞬间提高至200℃左右。反应结束后,继续升高温度,无二次反应失控。双氧水质量分数过高是环己酮氨肟化工艺最危险场景。针对氨肟化反应的泄放设计,必须以此场景作为设计依据。建议对双氧水进料线进行重点监控,以防止反应失控发生。     

钛硅分子筛TS-1合成及催化环己酮氨氧化的研究进展

钛硅分子筛TS- 1催化的环己酮氨氧化反应是一个绿色过程。介绍了TS- 1分子筛的合成、TS- 1分子筛催化的环己酮氨氧化及环己酮氨氧化与过氧化氢生产的集成。指出提高催化剂的性能、降低其生产成本是今后研究的重点 ,绿色氧化剂过氧化氢的生产与氨氧化过程的集成是今后环己酮肟生产的发展方向     

吡啶磷钨酸盐的制备及其催化环己酮氨肟化反应

分别以氯代辛基毗啶、氯代十四烷基吡啶、氯代十六烷基吡啶与磷钨酸为原料制备了3种不同阳离子大小的吡啶磷钨酸盐,采用傅里叶红外光谱仪、TGA/DSC同步热分析仪及元素分析等技术对催化剂进行了表征,3种催化剂都保持了磷钨酸的keggin结构,且为A_3B型组成.考察了不同催化剂在环己酮氨肟化反应中的催化性能,并进行了催化剂的回收和重复使用实验.结果表明,吡啶磷钨酸盐表现出了很好的催化活性,能够回收和重复使用.     

气相色谱法测定环己酮氨肟化反应尾气中的氨气

采用气相色谱法测定了环己酮氨肟化反应尾气中氨气含量,探讨了气相色谱操作条件,并与奥氏气体化学吸收法进行了比较。结果表明:采用Porapark Q,Porapark N混合色谱柱,柱温80℃,汽化温度120℃,检测温度150℃,检测器为热导检测器,桥流100 mA,载气为H2,流量为25 mL/min,以外标法定量,能够准确测定环己酮氨肟化反应尾气中的氨气;该方法的回收率为97.6%～100.5%,相对标准偏差为0.46%～0.92%;该方法较奥氏气体化学吸收法误差小、准确度高。     

TS-1分子筛催化环己酮氨肟化反应的失活动力学

采用间歇反应器,对液相环己酮氨肟化过程中TS-1分子筛的催化活性变化规律进行了考察,在失活原因分析的基础上建立失活动力学模型:rde=1.01×1014exp(-1.17R×T105)C0A.76C0B.82C0C.38a1.64,并对模型参数进行估值。     

WHZSM-5的合成及其对环己酮的催化性能

采用无机法,以水玻璃为硅源,硫酸铝为铝源,钨酸为钨源,在酸性条件下合成了具有ZSM-5结构的微孔分子筛(WZSM-5),经过离子交换合成了WHZSM-5分子筛。通过X射线衍射、红外吸收光谱等手段对催化剂进行了表征。结果表明:所制得的分子筛具有ZSM-5的特征结构,钨原子进入了ZSM-5骨架;以质量分数30%双氧水为氧化剂,环己酮与双氧水体积比为1:5时,催化剂用量为5 g/L,反应温度100℃,反应时间为6 h,催化氧化效果最好,环己酮转化率达93%;催化剂连续使用5次,反应活性基本不变。     

氨肟化装置膜分离系统的应用和优化

分析了环己酮肟生产中氨肟化装置膜分离系统运行不稳定的原因;提出了技术改造和工艺优化措施。结果表明:膜分离系统膜管表面污染导致其运行不稳定,原因是生产中弱碱性条件下破碎的催化剂颗粒附着在膜表面形成沉积层。通过提高错流速率,稳定反冲压力,改变反冲方式和反冲介质等优化措施,可实现膜分离系统的稳定运行。     

Selective conversion of cyclohexane to cyclohexanol and cyclohexanone using a gold catalyst under mild conditions

The oxidation of cyclohexane to cyclohexanol and cyclohexanone are investigated using supported gold catalysts using mild conditions of temperature and pressure. These catalysts are found to show some limited activity at 70 °C. However, the gold catalysts do not exhibit significantly different behaviour from supported Pt or Pd catalysts, and the selectivity observed is solely a function of conversion which in turn is a function of reaction time. It is clear that at very low conversions very high selectivities can be observed, but high selectivity under these mild reaction conditions cannot be maintained at higher conversions.     

磁性钛硅催化剂催化环己酮氨肟化传递-反应研究

磁性钛硅分子筛是具有原子经济特征和磁回收功能新型绿色催化剂。通过研究磁性钛硅分子筛催化环己酮氨肟化制备环己酮肟过程,考察了环己酮、H2O2和NH3·H2O的初始浓度和搅拌雷诺数对氨肟化过程的影响。在消除内扩散和外扩散的条件下,确定了环己酮氨肟化的动力学方程,反应指前因子为5.89×1012(mol-0.87·L0.87)·min-1,反应活化能为101.3kJ·mol-1,环己酮、H2O2和NH3·H2O的反应级数分别为0.65、0.16和1.06,对反应速率计算值和实验值进行了比较,平均相对误差为6.86%。     

微波照射硅钨酸催化合成环己酮乙二醇缩酮

在微波辐射下,以硅钨酸为催化剂、环已烷为带水剂,合成了环已酮乙二醇缩酮。考察了催化剂的用量、反应时间、酮醇物质的量之比、带水剂的用量及微波功率等诸多因素对产品收率的影响。实验表明,在环已酮用量为0.2mol、n（环已酮）：n（乙二醇）=1.0：1.35、催化剂用量为反应物料总质量的2.7％、以15mL环已烷为带水剂、微波功率为500W和反应时间为30min等优化条件下,环已酮乙二醇缩酮的收率可达71．8％。     

Oxidation of cyclohexanone to adipic acid with a cobalt acetate/oxygen/acetic acid system

The liquid phase oxidation of cyclohexanone to adipic acid at 378 K using oxygen as the oxidising agent and cobalt acetate as the catalyst in an acetic acid medium was investigated both at atmospheric pressure and at a pressure of 0.5MN m⁻². The effects of catalyst concentration, solvent concentration and partial pressure of oxygen, were studied at a constant stirrer speed of 535 rev min⁻¹. Increasing the solvent concentration and decreasing the catalyst concentration (up to 0.113×10⁻³ kmol m⁻³) had positive effects on the overall first order reaction rate constant. It was also found to vary linearly with gas flow rate.     

A highly active Au/Al2O3 catalyst for cyclohexane oxidation using molecular oxygen

The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol has been investigated over Au/Al₂O₃ catalysts using molecular oxygen in a solvent-free system. The catalysts were prepared by a modified direct anionic exchange method and characterized by AAS, N₂ adsorption and TEM. The results showed that the catalytic performance of Au/Al₂O₃ is very high in terms of turnover frequency. Moreover, the nano-size effect of gold is also reported in the reaction.     

环己酮氧化制备十二碳二元酸

探讨了环己酮氧化制备十二碳二元酸的机理以及最佳反应条件。以环己酮为原料,甲醇作为溶剂,双氧水为氧化剂,Fe2+为催化剂,低温下经自由基反应生成目标产物。0℃下反应30 m in,十二碳二元酸收率24%;温度升高,自由基发生迁移,生成副产物2-丁基-辛二酸。     

苯乙烯分子氧环氧化多相催化剂研究进展

针对近年来国内外苯乙烯分子氧环氧化多相催化剂的研究进展进行了综述,主要介绍了钴系、金系、铁系及其他催化体系等催化剂。其中,钴系催化剂活性高,工艺条件温和,绿色环保,但价格昂贵;金系催化剂在低温条件下对苯乙烯分子氧环氧化表现出良好的活性;铁系催化剂活性低,但经济性好。指出负载型钴系、金系催化剂在苯乙烯分子氧环氧化研究中有潜在的应用前景。