The influence of dopants on the catalytic activity of hematite in the ethylbenzene dehydrogenation

The effect of neodymium, lanthanum, aluminum and zirconium on the textural and catalytic properties of hematite was studied in this work, which aimed to develop catalysts to ethylbenzene dehydrogenation, in the presence of steam, the main commercial route to obtain styrene. Hematite and magnetite were found in fresh and spent catalysts, respectively. All dopants increased the specific surface area of the fresh and spent catalysts and made them more resistant against reduction, but only aluminum avoided sintering during reaction. The dopants increased the catalytic activity per area of hematite, except aluminum which acted only as a textural promoter. The selectivity was decreased due to zirconium and lanthanum while the other dopants did not change this parameter. The neodymium-containing catalyst showed high levels of activity and selectivity and was able to work up to 530 °C, without deactivation, being the most promising with regard to styrene production.     

苯乙烯高温热引发本体聚合的分子量及其分布

对加少量乙苯的苯乙烯高温热引发本体聚合体系进行了研究。测定了不同聚合条件下,不同聚合阶段的分子量及其分布。不同的温度,不同的乙苯加入量以及不同的聚合阶段,聚合产品的分子量及其分布都将发生不同程度上的变化,本文即对其变化规律进行研究,并建立了相应的经验模型,计算表明,模型与实验值吻合得较好。     

苯乙烯热引发本体聚合动力学

研究了加少量乙苯的苯乙烯热引发本体聚合于120～170℃聚合速率在0～95%转化率内的变化规律,建立了如下聚合动力学模型:(dx)/(dt)=A[M]_0~(382)(1-x)~(5/2)/(1+∈x)~(3/2)其中 A=[]A_0+A_1x+A_2x~2+A_3x~3,x 表示转化率A_i(i=0,1,2,3)是温度和乙苯含量的函数。实验测定了不同聚合阶段的转化率,并进行了参数回归。     

气相色谱在乙苯脱氢实验中的应用

阐明了气相色谱在乙苯脱氢制备苯乙烯实验中的应用,叙述了气相色谱的工作原理、工作程序、数据处理、结果分析。     

Dehydrogenation of ethylbenzene in the presence of CO2 using a catalyst synthesized by polymeric precursor method

Catalysts of iron oxide dispersed on Al or Si oxides were prepared via a polymeric precursor derived from the Pechini method and tested in the dehydrogenation of ethylbenzene in the presence of CO₂, in order to contribute with the studies of this reaction. The catalysts were characterized by thermogravimetric analysis (TG), temperature-programmed reduction (TPR), X-ray diffraction (DRX) and temperature-programmed desorption of CO₂ (TPD-CO₂). Analysis of the spent catalysts by TG and Fourier transformed infrared spectroscopy (FT-IR) pointed to the contribution of CO₂ to the coke deposition. The catalytic results suggest that the high initial ethylbenzene conversion is due to the contribution of basic sites, and the CO₂ adsorption in the basic site (lattice oxygen) may compete with the oxidative dehydrogenation of ethylbenzene. Although CO₂ provides the appropriate conditions to lower the consumption of the basic site, it is not able to promote the Fe²⁺ oxidation or to regenerate the basic site (lattice oxygen) in the iron oxide dispersed on Al or Si oxide catalysts.     

乙苯-苯乙烯分离节能新工艺

顺序分离恒沸热回收技术是一项乙苯-苯乙烯分离节能新工艺。与相同规模不同分离工艺进行了比较,结果表明,采用该新工艺技术,可以显著降低装置综合能耗,而设备投资略有增加,综合经济效益显著,可用于苯乙烯装置设计与建设。     

Dehydrogenation of ethylbenzene over iron oxide-based catalyst in the presence of carbon dioxide

The energy required for a new process using CO₂ for the dehydrogenation of ethylbenzene to produce styrene was estimated to be much lower than that of the present commercial process using steam. A Fe/Ca/Al oxides catalyst was found to exhibit high performance in the dehydrogenation of ethylbenzene in the presence of CO₂. And the deactivation of the Fe/Ca/Al oxides catalyst was restrained by the action of CO₂.     

实验室条件下乙苯脱氢制苯乙烯反应条件研究

苯乙烯是重要的有机化工原料。随着需求量的逐渐增加,苯乙烯的生产规模在逐渐的增大,生产方法也在不断的改进。乙苯脱氢法仍是其中的主要生产方法。在实验室的条件下,采用等温式乙苯催化脱氢小型装置,考察反应温度以及水和乙苯的进料比对实验结果的影响,并根据实验结果找出实验室条件下最佳的反应温度范围以及合适的进料比范围。     

茂名石化乙苯/苯乙烯精馏塔的改造

茂名石化采用新型高效脉冲规整填料成功对原板波纹填料乙苯/苯乙烯精馏塔进行了改造,取得了很好的效果,塔顶苯乙烯质量分数由原来的5%降至1%以下,苯乙烯质量分数达到99.9%以上,乙苯质量分数小于500×10-6。     

Conceptual process design of extractive distillation processes for ethylbenzene/styrene separation

In the current styrene production process the distillation of the close-boiling ethylbenzene/styrene mixture to obtain an ethylbenzene impurity level of 100 ppm in styrene accounts for 75–80% of the energy requirements. The future target is to reach a level of 1–10 ppm, which will increase the energy requirements for the distillation even further. Extractive distillation is a well-known technology to separate close-boiling mixtures up to high purities. The objective of this study was to investigate whether extractive distillation using ionic liquids (ILs) is a promising alternative to obtain high purity styrene. Three ILs were studied: [3-mebupy][B(CN)₄], [4-mebupy][BF₄], and [EMIM][SCN]. Extractive distillation with sulfolane and the current conventional distillation process were used as benchmark processes. The IL [4-mebupy][BF₄] is expected to outperform the other two ILs with up to 11.5% lower energy requirements. The operational expenditures of the [4-mebupy][BF₄] process are found to be 43.2% lower than the current distillation process and 5% lower than extractive distillation with sulfolane extractive distillations. However, the capital expenditures for the sulfolane process will be about 23% lower than those for the [4-mebupy][BF₄] process. Finally, the conclusion can be drawn from the total annual costs that all studied extractive distillation processes outperform the current distillation process to obtain high purity styrene, but that the ILs evaluated will not perform better than sulfolane.     

CO2 utilization as an oxidant in the dehydrogenation of ethylbenzene to styrene over MnO2-ZrO2 catalysts

MnO₂-ZrO₂ binary oxide catalytic system was applied for the effective utilization of CO₂ as an oxidant in the ethylbenzene dehydrogenation (EBD) to styrene monomer (SM). MnO₂-ZrO₂ oxides were prepared by co-precipitation method and characterized as solid solution mixture having surface area more than 100² g⁻¹. 10% MnO₂-ZrO₂ mixed oxide catalyst exhibited conversion of 73% with the selectivity of 98% at 650 °C. The MnO₂-ZrO₂ binary oxides were X-ray amorphous whereas the individual oxides (MnO₂ and ZrO₂) having much lower surface areas were crystalline in nature. As a result, MnO₂-ZrO₂ binary oxides exhibited greatly elevated catalytic activity for the conversion of ethylbenzene (EB) than those of individual oxides in the presence of CO₂. However, in the absence of CO₂ poor catalytic activity and stabilities were observed. Gradual enhancement of activities were demonstrated in the higher CO₂ to EB ratios. Hence, CO₂ had a profound role as a soft oxidant by improving both activity and stability in the EBD over MnO₂-ZrO₂ mixed oxide catalysts.     

A SIMPLIFIED KINETIC MODEL FOR OXIDATIVE DEHYDROGENATION OF ETHYLBENZENE OVER Pd-NaBr/Al2O3 CATALYST

The oxidative dehydrogenation of ethylbenzene is gaining considerable importance in recent years as a promising alternative for styrene production. This vapour phase reaction has been studied over Pd-NaBr/Al₂O₃ catalyst in the temperature range 623-793 K in a fixed bed reactor. Kinetic analysis of this reaction has been done using a recursion procedure developed in this work from first principles. The advantage of this method is the absence of any restriction on the conversion level as it uses an integrated rate equation. The rate of styrene formation was found to follow a linear relationship with concentration of ethylbenzene and shows a Langmuir type dependence on the concentration of oxygen.     

Screening of amorphous metal–phosphate catalysts for the oxidative dehydrogenation of ethylbenzene to styrene

The gas-phase oxidative dehydrogenation of ethylbenzene to styrene was carried out by using as catalyst a series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe = Al/Ca = 1) mixed systems: FeAl(PO₄)₂ and Ca₃Al₃(PO₄)₅, that were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. These results were compared to those obtained with 24 commercial inorganic solids (several metal oxides, sulfates and phosphates). Reactions were also carried out without oxygen, under non-oxidative conditions, where the catalytic activity was always appreciably lower than under oxidative conditions. Experimental results indicated that the oxidative gas-phase dehydrogenation of ethylbenzene to styrene could be related to the total number of acid and basic sites of catalysts, so that this reaction probably needs selected acid–basic pairs for coke formation, where the oxidative dehydrogenation process is developed.

The main practical conclusion of the catalyst screening was that the best results were obtained with the synthesized amorphous AlPO₄, where 43% ethylbenzene conversion and 99.7% styrene selectivity were achieved. A very reduced number of commercial inorganic solids like Al₂(SO₄)₃, Cr₂(SO₄)₃, Fe₂(SO₄)₃, NiSO₄, Al₂O₃ and Fe₂O₃ were also able to obtain an acceptable catalytic behavior, with conversions ranging between 18 and 23% and selectivity in the 95–100% range. Among the other synthesized solids, Ni₃(PO₄)₂-A-450 was the only metal phosphate exhibiting results in such a range. All the other catalysts studied were rather inactive and/or selective. Additional experiments carried out at longer times on stream (3.5 h) and longer contact times (W/F 0.254 and 0.654) confirmed the superior catalytic behavior of amorphous AlPO₄. Consequently, this solid could be a good candidate for application as a catalyst in the industrial oxydehydrogenation of ethylbenzene to styrene.     

Iron oxide-based honeycomb catalysts for the dehydrogenation of ethylbenzene to styrene

Corning has recently developed a novel extrusion method to make bulk transition metal oxide honeycomb catalysts. One area of effort has been iron oxide-based catalysts for the dehydrogenation of ethylbenzene to styrene, a major chemical process that yields worldwide 20 MM tons/yr. In industry, the monomer is synthesized mostly in radial-flow fixed-bed reactors. Because of the high cross-sectional area for flow and shallow depth of the catalyst bed in these reactors, low reactor pressure gradients are maintained that favors the yield and selectivity for styrene formation. However, the radial-flow design has inherent detractions, including inefficient use of reactor volume and large temperature gradients that decrease catalyst service life. The overall economics of the process can be improved with parallel-channel honeycomb catalysts and axial flow reactors. The simple axial flow design of honeycomb catalysts provides low-pressure drop, while making more efficient use of reactor volume, with better heat and mass transfer characteristics compared to a conventional radial packed bed. An important part of this concept is the ability to fabricate a wide family of dehydrogenation catalyst compositions into honeycombs with the requisite chemical, physical, mechanical, and catalytic properties for industrial use. The ethylbenzene dehydrogenation (EBD) honeycomb catalysts developed by Corning have compositions similar to those commonly used in industry and are prepared with the same catalyst and promoter precursors and with similar treatments.

However, to enable extrusion of catalyst precursors into honeycomb shapes, especially at cell densities above 100 cell/in.², Corning’s process compensates for the high salt concentrations and the high pH of the batch material that would otherwise prevent or impede honeycomb extrusion. The improved rheological characteristics provide the necessary plasticity, lubricity, and resiliency for honeycomb extrusion with sufficient binder strength needed before calcination to the final product. Iron oxide-based honeycombs after calcination are strong and possess macroporosity and high surface area. In bench-scale testing, particular honeycomb catalyst compositions exhibited 60–76% ethylbenzene conversion with styrene selectivity of 95–91%, respectively, under conventional reaction conditions without apparent deactivation or loss of mechanical integrity.     

Effect of carbon dioxide as oxidant in dehydrogenation of ethylbenzene over alumina-supported vanadium–antimony oxide catalyst

The dehydrogenation of ethylbenzene over alumina-supported vanadium–antimony oxide catalyst has been studied under different atmospheres such as inert nitrogen, steam, oxygen and carbon dioxide as diluent or oxidant. Among them, the addition of CO₂ gave the highest styrene yield (up to 82%) and styrene selectivity (up to 97%) along with stable catalytic performance. Carbon dioxide plays a beneficial role as a selective oxidant in improving the catalytic behavior through the oxidative pathway.     

Dehydrogenation of ethylbenzene with carbon dioxide over MgO-modified Al2O3-supported V–Sb oxide catalysts

Alumina-supported V_0.43Sb_0.57 oxide (VSb/Al) and MgO-modified alumina-supported V_0.43Sb_0.57 oxide catalysts (VSb/Mg_nAl with Mg/Al atomic ratio, n = 0.1, 0.3 or 0.5) have been tested for the dehydrogenation of ethylbenzene with carbon dioxide as an oxidant. Their catalytic behaviors were interpreted by results of several catalyst characterization methods. The decrease in the surface acidity of the VSb/Mg_nAl catalysts due to modification of alumina with MgO favors the prolonged time-on-stream activities. However, the addition of relatively large amounts of MgO (n = 0.3 or 0.5) causes substantial decrease in their surface areas, reducibility of active vanadium oxide component and, consequently, ethylbenzene conversion. These negative factors did not become apparent for the most efficient VSb/Mg_0.1Al system demonstrating high and stable catalytic activity.     

Catalytic dehydrogenation of ethylbenzene with carbon dioxide: promotional effect of antimony in supported vanadium–antimony oxide catalyst

Alumina-supported vanadium oxide, VO_x/Al₂O₃, and binary vanadium–antimony oxides, VSbO_x/Al₂O₃, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by S_BET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO₂ pulse methods. VSbO_x/Al₂O₃ exhibited enhanced catalytic activity and especially on-stream stability compared to VO_x/Al₂O₃ catalyst. Incorporation of antimony into VO_x/Al₂O₃ increased dispersion of active VO_x species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V_0.43Sb_0.57O_x/Al₂O₃ system.     

Electrochemical kinetics and X-ray absorption spectroscopy investigations of select chalcogenide electrocatalysts for oxygen reduction reaction applications

Transition metal-based chalcogenide electrocatalysts exhibit a promising level of performance for oxygen reduction reaction applications while offering significant economic benefits over the state of the art Pt/C systems. The most active materials are based on Ru_xSe_y clusters, but the toxicity of selenium will most likely limit their embrace by the marketplace. Sulfur-based analogues do not suffer from toxicity issues, but suffer from substantially less activity and stability than their selenium brethren. The structure/property relationships that result in these properties are not understood due to ambiguities regarding the specific morphologies of Ru_xS_y-based chalcogenides. To clarify these properties, an electrochemical kinetics study was interpreted in light of extensive X-ray diffraction, scanning electron microscopy, and in situ X-ray absorption spectroscopy evaluations. The performance characteristics of ternary M_xRu_yS_z/C (M = Mo, Rh, or Re) chalcogenide electrocatalysts synthesized by the now-standard low-temperature nonaqueous (NA) route are compared to commercially available (De Nora) Rh- and Ru-based systems. Interpretation of performance differences is made in regards to bulk and surface properties of these systems. In particular, the overall trends of the measured activation energies in respect to increasing overpotential and the gross energy values can be explained in regards to these differences.     

Solid base catalysts for side-chain alkylation of toluene with methanol

A wide variety of solid bases, including alkali-exchanged zeolites X, Y, L and β, and alkali-impregnated carbon and magnesia, were tested as catalysts for the side-chain alkylation of toluene with methanol to form styrene and ethylbenzene. In addition, the effects of adding Group IIIA elements (B, Al, Ga, In) to the catalysts were examined. At 680 K and atmospheric pressure, the major reaction products were styrene, ethylbenzene, and carbon monoxide. Cesium-exchanged zeolite X was the most effective alkali-containing catalyst for the alkylation reaction. Of the Group IIIA additives that were tested, only boron promoted the alkylation reaction. The primary effect of adding boron was to reduce the decomposition of methanol to carbon monoxide. Apparently, boron selectively modifies the sites associated with methanol decomposition without inhibiting the sites active for alkylation. A borated Cs—carbon sample also catalyzed the alkylation reaction, demonstrating that a zeolite framework is not necessary to form the active site. Microporosity seems to play an important role in these catalysts since both the alkali-modified carbons and the zeolites are microporous.     

Oxidative dehydrogenation of ethylbenzene to styrene with CO2 over SnO2–ZrO2 mixed oxide nanocomposite catalysts

SnO₂–ZrO₂ nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO₂ were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO₂–ZrO₂ nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH₃ and CO₂. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO₂ or ZrO₂). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO₂ was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity.