Reactivity and surface properties of silica supported molybdenum oxide catalysts for the transesterification of dimethyl oxalate with phenol

A series of MoO₃/SiO₂ catalysts were prepared with Mo loadings ranging from 1 to 16 wt% and applied to the transesterification of dimethyl oxalate (DMO) with phenol. The results showed that the catalyst of MoO₃/SiO₂ with 1 wt% Mo content performed best, giving 54.6% conversion of DMO and 99.6% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The surface properties were investigated by means of X-ray diffraction (XRD), X-ray photoelectron (XPS), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR analysis of adsorbed pyridine. XPS and XRD analyses indicated that Mo(VI) species was highly dispersed at low Mo loading and MoO₃ of the crystal structure appeared at higher loading. NH₃-TPD characterization and FTIR analysis of adsorbed pyridine demonstrated that only Lewis weak acids were present on catalyst surface and the amount of Mo loading has little effect on the strength of the surface acid on MoO₃/SiO₂. The catalytic results exhibited that the synergetic effect of Mo active centers with weak Lewis acid sites catalyzed transesterification of DMO with phenol.     

The catalytic activity of CuNi-containing hydrotalcites in the transesterification of dimethyl oxalate with phenol

Under microwave irradiation, a series of hydrotalcite-like compounds (HTL) were prepared in a short time of 10 min. The thus synthesized samples were applied to the catalytic transesterification of dimethyl oxalate (DMO) with phenol, CuNi-containing hydrotalcites (CuNi-HTLR) were found to exhibit good catalytic properties. When the reaction was performed with phenol/DMO molar ratio of 4:1 and 1.9% CuNi-HTLR based on the total weight of reactants as catalyst, at 180 °C for 10 h, the conversion of DMO and the selectivity of MPO + DPO reached over 66% and 95%, respectively.     

TiO2 -GO催化DMC与苯酚酯交换合成碳酸二苯酯

采用氧化石墨烯(GO)改性制备了TiO_2-GO催化剂,用于催化碳酸二甲酯与苯酚酯交换合成碳酸二苯酯。XRD、TEM、XPS、Py-TPD表征结果显示,GO有效促进了活性组分TiO_2的分散;GO的电子效应改变了催化剂中Ti物种的电子环境,促进了活性物种Ti(Ⅳ)的形成;GO改性的催化剂中,中强酸酸位的比例明显增加。催化剂中有效活性位增加,有利于酯交换反应产物的生成。催化反应结果表明,TiO_2-GO催化剂中GO不仅作为载体,同时起到了电子助剂的作用。当催化剂中GO质量分数为50%时,150～180℃下反应9 h后,苯酚转化率可达41.8%,酯交换总选择性为99.9%。     

V-Cu氧化物催化碳酸二甲酯与苯酚酯交换反应

研究了一系列钒-金属复合氧化物对碳酸二甲酯(DMC)和苯酚酯交换合成碳酸二苯酯(DPC)的催化性能,实验结果表明,钒-铜复合氧化物是较好的酯交换合成DPC的催化剂。考察了V/Cu摩尔比,催化剂用量,DMC用量和反应时间对酯交换反应的影响,得到较佳的反应条件： n(V):n(Cu) = 4:1,苯酚用量0.16 mol,V-Cu复合氧化物催化剂的用量为苯酚用量的3.1%（质量比）, n(DMC) : n(苯酚) = 1.5 :1,反应时间9～15 h。在此条件下反应9 h,苯酚的转化率为41.9%,甲基苯基碳酸酯(MPC)及DPC的总收率为40.3%。催化剂重复使用4次后苯酚转化率从41.9%降到29.1%,多次重复使用后的催化剂在空气氛中焙烧即可再生,再生催化剂的催化性能几乎和新鲜催化剂相当,苯酚转化率达到39.8%。     

Role of sulfonic acids in the Sn-catalyzed transesterification of dimethyl carbonate with phenol

Diphenyl carbonate, the key intermediate of the non-phosgene polycarbonate manufacturing process, can be produced by the transesterification of dimethyl carbonate with phenol in the presence of dibutyltin oxide. The use of an alkyl or aryl sulfonic acid in conjunction with dibutyltin oxide significantly enhances the activity of dibutyltin oxide. ¹⁹F and ¹¹⁹Sn NMR studies suggest the formation of tin complex containing strongly electrophilic sulfonate ligand from the reaction of dibutyltin oxide with alkyl or aryl sulfonic acid. Various factors affecting the transesterification of dimethyl carbonate with phenol were investigated.     

草酸亚锡催化酯交换合成水杨酸异辛酯

以草酸亚锡作为催化剂,水杨酸甲酯和异辛醇为原料,用酯交换的方法合成了防晒剂水杨酸异辛酯,并对产品进行指标检测。考察了影响水杨酸甲酯转化率的5个合成条件,再通过正交试验L9(34)得到较佳合成条件为:催化剂草酸亚锡用量(相对于原料的总投入质量)为0.4%,m(酯)∶m(醇)=1∶1.3,终点反应温度为190℃,总反应时间为7 h。验证实验表明该条件下水杨酸甲酯平均转化率为99.2%且具有重复性。所制备的水杨酸异辛酯产品的质量指标接近美国国际特品公司(ISP)的ESCALOL587。     

Catalytic study on the transesterification of dimethyl carbonate and phenol to diphenyl carbonate

Transesterification of dimethyl carbonate and phenol to diphenyl carbonate and catalysts were investigated. The results showed that the transesterification was the reaction of soft base binding to hard acid, and hard acid catalysts had higher transesterification selectivity than the soft and border acid catalysts. When the hard acid n-Bu₂SnO and bases constituted acid–base complex catalysts, it was found that Cu₂O, as a promoter, could enhance the activity of n-Bu₂SnO outstandingly. The conversion of dimethyl carbonate was up to 50.8% with 99.9% transesterification selectivity. A plausible mechanism was also suggested.     

The transesterification of dimethyl carbonate and phenol catalyzed by 12-molybdophosphoric salts

Various 12-molybdophosphoric salts were used in the transesterification of dimethyl carbonate (DMC) and phenol to diphenyl carbonate (DPC) and methyl phenyl carbonate (MPC) as novel solid catalysts. The zinc salt was found to exhibit the highest activity for the transesterification. Several parameters affecting the transesterification were investigated. When the reaction was performed between 150 °C and 180 °C, with a molar ratio of phenol to DMC of 1, a reaction time 12 h, a catalyst amount 0.004 (molar ratio to phenol), the conversion of phenol reached 31%, and the selectivity of MPC and DPC was 29% and 66.1%, respectively. The TON reached 74.8 mol (MPC + DPC)/mol Zn-salt.     

碳酸二甲酯与苯酚反应动力学及工艺研究进展

碳酸二苯酯是一种重要的化工原料中间体,可用于合成多种有机化合物和聚合材料。文章主要对碳酸二甲酯和苯酚酯交换法合成碳酸二苯酯的反应热力学特征、动力学和工艺进行了综述,文章重点分析了近年来酯交换反应动力学研究的现状及难点,并指出了动力学研究的发展方向;同时对酯交换反应一步法和二步法合成工艺进行了深入探讨,其中酯化-歧化二步法工艺因其高转化率和原料利用率而备受关注。     

碳酸二甲酯与苯酚酯交换合成碳酸二苯酯热力学分析

用分子模拟软件M aterial stud io、工艺过程模拟软件ChemCAD结合Benson基团贡献法,计算了碳酸二甲酯与苯酚酯交换合成碳酸二苯酯的反应焓变、反应熵变、吉布斯自由能变及平衡常数。结果表明,该反应为吸热反应,升高温度有利于DPC的生成。反应的热力学平衡常数很小,为了提高DPC收率,必须及时移走副产物甲醇。     

酯交换法合成碳酸二苯酯热力学和催化剂研究进展

碳酸二甲酯和苯酚酯交换合成碳酸二苯酯是一条绿色的化工合成过程,但该反应的热力学平衡常数小,除采用催化蒸馏反应外,还必须选用合适的高活性和选择性的催化剂。在目前研究的均相有机钛和有机锡比非均相催化剂具有较好的活性和选择性,而且其复合催化剂性能较佳。在此基础上进一步开发研究钛 锡非均相催化剂有可能取得重要进展。     

Synthesis of molybdenum (IV) sulphide: Part II. Reaction of molybdenum (VI) oxide with (a) zinc sulphide and (b) cadmium sulphide in the presence of ammonium chloride

Reactions of molybdenum (VI) oxide with (a) zinc sulphide and (b) cadmium sulphide were studied in the temperature range 723–973 K. Small amounts of mixtures of molybdenum (IV) sulphide and molybdenum (IV) oxide, which are difficult to separate, were produced. When ammonium chloride was added to the reactants, 89.1% pure MoS₂ at 773 K and 96.17% pure MoS₂ at 798 K were produced in the case of zinc sulphide and cadmium sulphide respectively.     

pH Dependent formations of dinuclear molybdenum(V) and incomplete cubane molybdenum(IV) complexes with nitrilotriacetate

Nitrilotriacetato oxomolybdenum(V) dinuclear complex (NH₄)₄[cis-Mo₂O₄(nta)₂] · 7H₂O (1) (H₃nta = nitrilotriacetic acid) and its incomplete cubane-type trinuclear molybdenum(IV) complex [Mo₃O(OH)₃(Hnta)₃] · Cl · 3H₂O (2) are isolated in a weak acidic and an acidic solutions, respectively (pH 4.5 and 1.0). The nitrilotriacetate ligand in the anion 1 or the cation 2 displays tridentate mode through the nitrogen atom and the oxygen atoms of β-carboxy groups. Unusual protonations of bridged oxygen atoms in 2 have not effect on the skeleton of molybdenum(IV) cap Mo₃O unit. There are obvious dissociations of molybdenum(V) complexes based on ¹³C NMR observations in solution.     

Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides

ABSTRACT

The use of tetra-alkylcarbamides as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated in this study. Batch extraction experiments show that tetra-alkylcarbamides strongly extract U(VI) with high distribution ratios. Plutonium(IV) can be co-extracted with U(VI) at high nitric acid concentration, while high U(VI)/Pu(IV) selectivities can be reached at lower acidity. Loading capacity experiments with high uranium concentrations show that alkyl chains longer than butyl are necessary to avoid third phase formation. Nevertheless, the viscosity of uranium-loaded solvents gets too high with alkyl chains longer than pentyl. Overall, this study shows that with TPU extractant (with four pentyl chains), an efficient co-extraction of uranium and plutonium can be reached (D_U,Pu > 1) for a concentration of nitric acid higher than 4 mol?L^?1, while the partition between uranium(VI) and plutonium(IV) could be operated even at 2 mol?L^?1 nitric acid without redox chemistry.     

酯交换合成碳酸二苯酯催化剂的研究进展

对近年来碳酸二甲酯和苯酚酯交换合成碳酸二苯酯的催化剂体系进行了较为系统的概述,包括均相催化剂体系(碱或碱金属化合物、Lewis酸、锡和钛的有机化合物等)和多相催化剂体系(各种负载型、金属氧化物、水滑石等),认为开发有机锡、有机钛配合物催化剂以及将其固载化是碳酸二甲酯与苯酚酯交换反应合成碳酸二苯酯催化剂研究的重要方向.     

Ti（OC4H9）4催化酯交换合成碳酸二苯指的研究

研究了以Ｔｉ（ＯＣ４Ｈ９）４为催化剂,苯酚与碳酸二甲酯（ＤＭＣ）经酯交换法合成碳酸二苯酯（ＤＰＣ）的工艺。在常压下,１６０～１９０℃,当ｎ（Ｔｉ（ＯＣ４Ｈ９）４：ｎ（ＰｈＯＨ）＝０．０１２：１,ｎ（ＰｈＯＨ）：ｎ（ＤＭＣ）＝４：１,反应时间８ｈ,总转化率为２８．３％,ＤＰＣ的产率为２５．３％,碳酸甲苯酯（ＭＰＣ）的产率为３．０％,产物中无苯甲醚,ＤＰＣ的选择性为８９．４％。     

MgO/NaY催化甲醇与碳酸乙烯酯酯交换合成碳酸二甲酯

以硝酸镁为前体,通过等体积浸渍法制备不同负载量的MgO/NaY催化剂,用CO2-TPD和TEM对催化剂进行了表征,考察MgO负载量、反应温度、反应时间等条件对甲醇与碳酸乙烯酯（EC）酯交换反应合成对碳酸二甲酯（DMC）的影响。实验结果表明：MgO的负载量对催化剂表面的碱量和MgO分散程度有着重要影响。高分散的MgO物种越多,其催化剂碱量越高。采用12%MgO/NaY为催化剂、反应温度70 ℃、n(甲醇)∶n(EC)= 8∶1、反应时间3 h时,EC的转化率和DMC的选择性最佳,DMC收率高达89%。     

草酸二甲酯加氢制乙二醇Cu/SiO2催化剂失活研究

采用沉淀沉积法制备了草酸二甲酯制乙二醇Cu／SiO₂催化剂。在反应温度210 ℃、压力2.0 MPa、空速0.01 mol·(g·h)^-1和氢酯物质的量比60的条件下,对催化剂的失活规律进行了研究,采用XRD、BET和TG-DTG等手段对反应前、后的催化剂进行表征,结果表明,铜烧结和高聚物可能是导致催化活性降低的主要原因。     

Electrochemical and spectroscopic studies of molybdenum(VI) complexes with aminopolycarboxylic acids

The complexes of molybdenum(VI) with iminodiacetic acid (IDA), nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) were investigated by means of polarographic and spectroscopic methods. The composition of the complexes was determined by the Job's method as following: 1Mo(VI)/1IDA; 1Mo(VI)/1NTA and 2Mo(VI)/1EDTA. The polarographic wave height was fairly dependent on the nature of the complexes. The overall reaction rate for the reduction of Mo(VI)-IDA complex was limited by diffusion. On the other hand, the polarographic reduction of Mo(VI)-NTA and - EDTA complexes were kinetically controlled by the preceding chemical reaction which was composed of protonation, dimerization and substitution of ligands, however, the rate-determining step was the substitution of ligands. The mechanism for the electroreduction of each complex was discussed.     

A modeling of semibatch reactors for melt transesterification of dimethyl terephthalate with ethylene glycol

A mathematical model of a semi batch reactor was developed to investigate the oligomerization reactions in the melt transesterification of dimethyl terephthalate with ethylene glycol catalyzed by metal acetate catalyst. The detailed kinetic scheme based on the molecular species model is used to estimate the conversion of methyl ester groups and the concentrations of various oligomeric species. The numerical simulation of the model shows that the oligomerization reactions lower the overall conversion of methyl ester end groups. Effects of ethylene glycol/dimethyl terephthalate mole ratios, reaction temperature and, catalyst concentration on the conversion, oligomer concentration, oligomer molecular weight, and molecular weight distribution were also analyzed.