Isobutane Conversion Research Articles

Effect of Si/Al ratio of high-silica HZSM-5 catalysts on the prins condensation of isobutylene and formaldehyde to isoprene

A series of HZSM-5 catalysts with different Si/Al ratio were prepared and characterized with various characteristic methods XRD, BET, NH3-TPD, FT-IR spectra of adsorbed pyridine, etc. The effect of Si/Al ratio of HZSM-5 catalysts on the prins condensation of isobutylene and formaldehyde to isoprene was investigated in detail. It is resulted that the catalytic activities are dependent on the acid strength, decreasing with the ratio of Si/Al increases. The optimized catalyst was HZSM-5 (600) with 8.8% of isobutene conversion and 90.2% of selectivity to isoprene, indicating that the higher Si/Al ratio was termed as appropriate for prins condensation of isobutylene and formaldehyde to isoprene. On the contrary, the low Si/Al ratio may lead to the formation of by-products and coke deposits, which leads the catalysts deactivation.

Dehydrogenation of Isobutane over a Ni–P/SiO2 Catalyst: Effect of P Addition

The addition of P to a Ni/SiO2 catalyst greatly changes the isobutane dehydrogenation performance. The Ni:P ratio is an important influencing factor for a Ni–P/SiO2 catalyst because of the formation of different Ni–P compounds. When the Ni:P ratio equals 1:1, a Ni–P/SiO2 catalyst with Ni2P formed on the surface exhibits an optimum dehydrogenation performance (an isobutane conversion of 22% and an isobutene selectivity of 81.3%). The in situ Fourier transform infrared characterization was performed to determine the adsorption mode of isobutane. Isobutane is adsorbed onto the Ni–P surface with one H atom in a methyl group, and the intermediate tends to form isobutene rather than C–C bond scission. Moreover, the decreased adsorption energy of isobutene on the Ni2P surface inhibits its further reaction. The deactivation of a Ni–P/SiO2 catalyst is mainly caused by the phase transformation from Ni2P to Ni12P5 and coke deposition. Finally, some general rules are summarized to get a deep understanding of the second component added to a Ni/SiO2 catalyst.

High-quality fuel distillates produced from oligomerization of light olefin over supported phosphoric acid on H-Zeolite-Y

Oligomerization of isobutene to produce high-quality fuel distillates in the range of gasoline, jet fuel and diesel free of sulfur, nitrogen and aromatic hydrocarbons has been investigated over a new environmental-friendly, clean and long-lifetime supported phosphoric acid on H-Zeolite-Y catalyst with SiO2/Al2O3 mol ratio of 60. The catalyst was obtained by acid impregnation and ultrasonic vibration technique with successive heating at different temperatures and under atmospheric pressure. The catalysts were characterized by several techniques (BET, SEM, XRD, TDA, TGA and XPS). The oligomerization reactions were carried out in a gas phase using fixed-bed flow reactor at variable temperature ranges between 50 and 100 °C under atmospheric pressure with a space velocity (WHSV) of 176 h−1.The fuel distillates were identified by GC/MS and quantified by gas chromatography. The results showed that the conversion of isobutene into distillates ranges between 97 and 100%. The maximum selectivity to C8= isomers is about 65%, and a flow rate of isobutene 5.0 ml/min. and temperature 50 °C were obtained. Research octane number under the above-mentioned conditions ranges between 85 and 96, and Reid pressure ranges between 27 and 125 Pa.

Dimerization of Isobutene in C4 Mixtures in the Presence of Ethanol Over Acid Ion-Exchange Resin DH-2

Isobutene dimerization of C4 mixtures with the simulated components of industrial fluid catalytic cracking (FCC) gas stream was carried out in a fixed-bed microreactor over the acid ion-exchange resin (DH-2) in the presence of ethanol. The influences of ethanol/isobutene molar ratio and reaction temperature on the isobutene dimerization reaction were studied. For 1-butene, both isomerization and oligomerization simultaneously take place, but the isomerization reaction is more sensitive to reaction temperature than oligomerization. And both reactions were inhibited noticeably in the presence of ethanol. Although the conversion of isobutene was reduced to some extent when ethanol was introduced, it was beneficial for improving the weight fraction of dimers in oligomers as well as trimethylpentenes in dimers. With ethanol addition, the dimerization reaction was less sensitive to the reaction temperature thus the isobutene dimerization reaction can be performed in a wide temperature range.

Synthesis and Catalytic Performance of a Dual-Sites Fe–Zn Catalyst Based on Ordered Mesoporous Al2O3 for Isobutane Dehydrogenation

Ordered mesoporous Zn/OMA-Fe materials were easily prepared via one pot evaporation induced self-assembly (EISA) method in combination with incipient wetness strategy. Dehydrogenation of isobutane to isobutene were carried out on these materials, the isobutane conversion of 50.7% and the yield of 37.8% were obtained over 13Zn/OMA-10Fe catalyst at 580 °C with 300 h−1 GHSV. The synthesized materials with large specific surface areas and uniform pore sizes were characterized by XRD, N2 adsorption–desorption, TEM, XPS, H2-TPR, Mӧssbauer and NH3-TPD. A portion of Fe species were highly dispersed on the support surface and others incorporated into Al2O3 frameworks, Zn species existed in the form of hexagonal ZnO phase. The total acidity of these catalysts was increased by the introduction of Zn, facilitating the conversion of isobutane. Moreover, the conversion of Fe species might play a major role in improving isobutene selectivity.

Facile synthesis of ordered mesoporous zinc alumina catalysts and their dehydrogenation behavior.

Ordered mesoporous Zn/Al2O3 materials with varying Zn content were simply prepared via an evaporation-induced self-assembly (EISA) method. Dehydrogenation of isobutane to isobutene was carried out on these materials; an isobutane conversion of 45.0% and isobutene yield of 39.0% were obtained over the 10%Zn/Al2O3 catalyst at 580 °C with 300 h−1 GHSV. The obtained materials with Zn content up to 10% possess large specific surface area and big pore volume and zinc species can be highly dispersed on the surface or incorporated into the framework. The acidity of these catalysts was changed by the introduction of Zn, the decrease of strong acid sites is conducive to the promotion of isobutene selectivity and the weak and medium acidic sites played an important role in isobutane conversion. In addition, these catalysts exhibited good catalytic stability, due to the effective inhibition of coke formation by the ordered mesoporous structure.

Metal-free silicon boride catalyst for oxidative dehydrogenation of light alkanes to olefins with high selectivity and stability

Due to the free coking and no equilibrium limitation in alkanes conversion, the oxidative dehydrogenation of light alkanes to olefins offers an attractive route, but encounters the difficulty in selectivity control for olefins because of the over-oxidation reactions that produce a substantial amount of CO2. Here we report silicon boride exhibiting good oxidation resistance property at high temperature, as a metal-free catalyst efficiently catalyzed dehydrogenation of light alkanes to olefins with a high selectivity at a given reaction conditions. The stability was evidenced by the operation of a 100-h test with steady conversion and product selectivity. When the conversion of ethane, propane and isobutane reached 18.8%, 19.1% and 6.0%, the selectivity of olefins were up to 98.0%, 94.4% and 96.4%, respectively. This work experimentally supports that the catalytic origin of the boron species from the metal-free catalyst initiate the oxidative dehydrogenation of light alkanes.

Multi-objective Optimisation of MTBE Reactive Distillation Process Parameters based on NSGA-II

Optimisation of reactive distillation (RD) process parameters is very important and complex because of a large number of variables and a strong coupling between them. A hybrid method of orthogonal numerical test and non-dominated sorting genetic algorithm II (NSGA-II) was presented for optimisation of the methyl tert-butyl ether (MTBE) RD process parameters such as the reflux ratio, the number of trays etc. on maximizing the conversion of isobutene and minimizing TAC of MTBE RD process simultaneously. Firstly, Aspen Plus was used to simulate MTBE RD process and the key parameters were selected by univariate sensitivity analysis. Secondly, the orthogonal test method was used to design the experiment scheme, and correlation formulations between the process parameters and objective functions (conversion of isobutene and total annual cost) were determined by second order regressions model according to the results of orthogonal numerical tests. Finally, based on the fitting function equations, NSGA-II was used to optimize the MTBE RD process parameters, and a non-dominated solution set was obtained and presented. The results indicate that the combination of orthogonal numerical test and the NSGA-II can not only reduce the number of experiments effectively, but also get the optimal and effective process parameters set for process design and operation.

Study on coupling separation process of etbe and absolute ethanol

The coupling separation process of ETBE production can be combined with the ethanol dehydration to save energy consumption. A new idea of introducing the dilute ethanol feedstock made from biomass material into the coupling separation process was proposed to enhance the sustainability of ETBE production. The ethanol concentrate is optimized in terms of minimizing the cost of energy consumption and maximizing the gross annual profit (GAP), respectively. The GAP is discussed at different prices of dilute ethanol feedstock and compared with those of conventional ETBE production process and process based on reactive distillation (RD). Meanwhile, the impact of ethanol-to-olefin ratio and conversion of isobutene on the optimal mass fraction is also explored. The result shows that the minimum feasible mass fraction of ethanol concentration is optimal when minimizing the energy consumption cost. The ethanol-to-olefin ratio and conversion of isobutene would affect the optimal mass fraction by affecting the minimum feasible mass fraction. Besides, to make the GAP maximum, the optimal mass fraction of ethanol concentration would take minimum or maximum feasible mass fraction at different prices of dilute ethanol feedstock. And the coupling separation process would have economic advantages compared to conventional ETBE process and RD-based process to some extent when the price of dilute ethanol feedstock is less than 7.372 €/t and the optimal mass fraction of ethanol concentration is 95 wt% in this case.

Isobutene oligomerization on MCM-41-supported tungstophosphoric acid

Oligomerization offers a broad potential for converting light olefins into liquid fuels. Here, tungstophosphoric acid, TPA, was impregnated on a mesoporous silica support, MCM-41, at varying loadings from 1 to 90 wt%. The IR and XRD results indicated the presence of interactions between the TPA clusters and MCM-41, especially at loadings below 50 wt%. These interactions led to variations in acid site density and their corresponding strength as evidenced by the results of temperature programmed desorption of ammonia measurements. Consequences of these changes were investigated on isobutene oligomerization. Results obtained at 393 K and 15 bar indicated that the TPA/MCM-41 catalysts provide more than 75 wt% isobutene conversions at a weight hourly space velocity (WHSV) of 46 h−1. Results further showed that the catalysts were more selective towards distillate range products especially at very low TPA loadings. The relative selectivity of trimers over dimers in the oligomerization product pool was approximately four at a TPA loading of 1 wt% and it decreased to 1.5 with increasing TPA loading. Ruling out the presence of any strong correlations between acid strength and catalytic performance, the data presented a strong dependence of the product selectivity on the availability and vicinity of the acid sites.

Novel Pt\u2013Ni Bimetallic Catalysts Pt(Ni)\u2013LaFeO3/SiO2 via Lattice Atomic-Confined Reduction for Highly Efficient Isobutane Dehydrogenation

In this study, a series of novel Pt–Ni bimetallic catalysts supported on LaFeO3/SiO2 with different amounts of Ni were prepared by the lattice atomic-confined reduction of LaFe1−x(Ni, Pt)xO3/SiO2 perovskite precursors and applied in isobutane dehydrogenation to isobutene reaction. The catalysts were characterized by X-ray diffraction, H2-temperature-programmed reduction, Brunauer–Emmett–Teller analysis, transmission electron microscopy, energy dispersive X-ray, CO chemisorption, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The as-synthesized Pt–Ni bimetallic catalysts possessed smaller most probable particle size with tunable Pt–Ni interaction, depending on the Ni content. The catalyst with Ni content of 3.0 wt% showed excellent activity and stability (the isobutane conversion and isobutene selectivity remained at about 38% and 92%, respectively, after 310 min) for the isobutane dehydrogenation reaction. It also provided approximately six times turnover frequency of the catalyst without Ni. The excellent activity and stability of the 3.0 wt% Ni-containing catalyst can be attributed to its small metal nanoparticles with high dispersion and suitable Pt–Ni interaction. Moreover, the Pt(Ni)–LaFeO3/SiO2 catalyst with Ni content of 3.0 wt% had been run for more than 35 h without obvious loss of activity, indicating its long-term stability, and the decrease in the Pt–Ni interaction that accompanied the formation of the FeNi alloy phase was thought to be responsible for the slight decrease in activity.

Olefin oligomerization via new and efficient Brönsted acidic ionic liquid catalyst systems

Olefin oligomerization reaction catalyzed by new catalyst systems (a Brönsted-acidic ionic liquid as the main catalyst and tricaprylylmethylammonium chloride as the co-catalyst) has been investigated. The synthesized Brönsted acidic ionic liquids were characterized by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV), 1H nuclear magnetic resonance (NMR), and 13C NMR to analyze their structures and acidities. The influence of different ionic liquids, ionic liquid loading, different co-catalysts, catalyst ratios (mole ratio of ionic liquid to co-catalyst), reaction time, pressure, temperature, solvent, source of reactants, and the recycling of catalyst systems was studied. Among the synthesized ionic liquids, 1-(4-sulfonic acid)butyl-3-hexylimidazolium hydrogen sulfate ([HIMBs]HSO4) exhibited the best catalytic activity under the tested reaction conditions. The conversion of isobutene and selectivity of trimers were 83.21% and 35.80%, respectively, at the optimum reaction conditions. Furthermore, the catalyst system can be easily separated and reused; a feasible reaction mechanism is proposed on the basis of the distribution of experimental products.

Effect of Phosphoric Acid on HZSM-5 Catalysts for Prins Condensation to Isoprene from Isobutylene and Formaldehyde

A series of HZSM-5 zeolites modified with different amounts of phosphoric acid(P/HZSM-5) was pre-pared. The physicochemical features of the P/HZSM-5 catalysts were characterized via X-ray diffraction(XRD), N2 adsorption-desorption, NH3-temperature programmed desorption(NH3-TPD) and Fourier tranform infrared(FTIR) spectra of the adsorbed pyridine, and the performances of the catalysts for Prins condensation to isoprene from iso-butylene and formaldehyde were investigated. The maximum isobutene conversion and isoprene selectivity were 10.3% and 94.6% on the HZSM-5 catalyst with a Si/Al molar ratio of 600 using 5%(mass fraction) phosphoric acid. The phosphoric acid modification not only modulated the amount of acidic sites but also regulated the acid type. An appropriate amount of weak Lewis and Bronsted acid sites served as the active sites for the condensation of isobutene with formaldehyde, and the strong acid sites could cause side reactions and coke deposition.

Simple Preparation of Spherical Activated Carbon with Mesoporous Structure from Phenolic Resol and Associated Catalytic Performance in Isobutane Dehydrogenation

This study provides a detailed report on the synthesis of spherical activated carbon with mesoporous structure using a soluble low molecular weight phenolic resol precursor through an ammonium alginate assisted sol–gel method. The effects of calcinating temperature and the addition of CaCO3 as a pore-enlarging agent on texture structure and catalytic performance in isobutane dehydrogenation to isobutene were investigated. Characterization of N2 sorption, mechanical strength tests, and optical photographs confirmed that the obtained carbon materials had high mechanical strength, a good degree of sphericity, and a large surface area. Introducing CaCO3 as a pore-enlarging agent during the preparation process promoted the formation of a mesoporous structure of carbon spheres and evidently increased the surface area and oxygen content, which can improve isobutane conversion and isobutene selectivity of these carbon spheres. The conversion of isobutane reached up to 28% for this spherical activated carbon, and the selectivity of isobutene reached up to 96%. Isobutane conversion increased with an increase in calcination temperature due to an increase in the oxygen content, whereas the selectivity of isobutene decreased due to the slight decrease in the specific surface area.

Enhancing the vanadium dispersion on V-MCM-41 by boron modification for efficient iso-butane dehydrogenation

A series of boron modified V-MCM-41 catalysts were in situ synthesized. The modification effect of boron to the vanadium species and catalytic performances were systematically studied. The catalysts could still maintain mesoporous structure and relatively large specific surface area after boron modification. Boron species were mainly in the form of triangular [BO3]3− units on the surface and the pores of the catalysts. The introduction of boron could effectively enhance the dispersion of vanadium species and increase the amount of surface vanadium sites. The catalysts showed high activity towards iso-butane dehydrogenation. The results of catalytic tests showed that both the iso-butane conversion and iso-butene selectivity improved with the presence of boron species. The best catalytic performance was obtained on the sample with the maximum vanadium sites. The performance of the catalyst still remained stable after several cycles of tests and regenerations, which was promising for industrial application in moving bed or fluidized bed reactor in the future.

Three-phase modeling of dehydrogenation of isobutane to isobutene in a fluidized bed reactor: Effect of operating conditions on the energy consumption

This paper presents a numerical simulation of dehydrogenation of isobutane to isobutene in a bubbling fluidized bed reactor using the three-phase model. The effects of the operating conditions on the isobutane conversion and the rate of energy consumption in the reactor are investigated. For this purpose, a numerical algorithm is developed to solve the coupled system of nonlinear governing equations of the model in an iterative manner. It is found that the energy consumption in the bed shows a reverse trend to the isobutane conversion with increase in the initial pressure of isobutene and the entering superficial velocity of isobutene while both of them show the same trend with increase in the bed temperature. The simulation results also show that the volume flow rate of the feed stream (the entering superficial velocity of isobutane) strongly affects the energy consumption in the bed. From a design viewpoint, quantitative energy analysis presented makes it possible to evaluate the right operating conditions for the fluidized bed reactor.

Silicalite-1 zeolite acidification by zinc modification and its catalytic properties for isobutane conversion.

A series of Zn-modified Silicalite-1 (S-1) zeolites (Znx/S-1) were prepared by the wetness-impregnation method and applied in the catalytic conversion of isobutane. The structure and location of Zn species in Znx/S-1 were investigated using UV-Vis and N2 physical adsorption. The acidity and origin of the acid sites in Znx/S-1 were studied by NH3-temperature programmed desorption and Fourier-transform infrared analysis. The catalytic performance of Znx/S-1 for isobutane conversion was investigated in a fixed-bed microreactor. In the experiments, the acidity of S-1 zeolite was dramatically increased by modification with Zn, with both Lewis and Brønsted sites identified in Znx/S-1. The relationship between Brønsted acid sites and Zn–OH groups on ZnO clusters of Znx/S-1 was also revealed for the first time. Furthermore, Znx/S-1 catalysts exhibited excellent catalytic performances in both isobutane dehydrogenation and butene isomerization reactions. A high selectivity of total butene products ranging from 84.6 to 97.2 was achieved on the catalysts with different Zn loadings. Moreover, the linear correlation between isobutane conversion and the acid amount (determined by NH3-TPD) confirmed that the weak-to-medium acid sites in Znx/S-1 should play a key role in isobutane conversion.

Scaling Relations for Acidity and Reactivity of Zeolites.

Zeolites are widely applied as solid acid catalysts in various technological processes. In this work we have computationally investigated how catalytic reactivity scales with acidity for a range of zeolites with different topologies and chemical compositions. We found that straightforward correlations are limited to zeolites with the same topology. The adsorption energies of bases such as carbon monoxide (CO), acetonitrile (CH3CN), ammonia (NH3), trimethylamine (N(CH3)3), and pyridine (C5H5N) give the same trend of acid strength for FAU zeolites with varying composition. Crystal orbital Hamilton populations (COHP) analysis provides a detailed molecular orbital picture of adsorbed base molecules on the Brønsted acid sites (BAS). Bonding is dominated by strong σ donation from guest molecules to the BAS for the adsorbed CO and CH3CN complexes. An electronic descriptor of acid strength is constructed based on the bond order calculations, which is an intrinsic parameter rather than adsorption energy that contains additional contributions due to secondary effects such as van der Waals interactions with the zeolite walls. The bond order parameter derived for the CH3CN adsorption complex represents a useful descriptor for the intrinsic acid strength of FAU zeolites. For FAU zeolites the activation energy for the conversion of π-adsorbed isobutene into alkoxy species correlates well with the acid strength determined by the NH3 adsorption energies. Other zeolites such as MFI and CHA do not follow the scaling relations obtained for FAU; we ascribe this to the different van der Waals interactions and steric effects induced by zeolite framework topology.

Features of low-temperature oxidation of isobutane in water vapor and carbon dioxide with increased density of reagents

The oxidation of isobutane at high density of reagents in a mixture of i-C4H10/O2/H2O and i-C4H10/O2/CO2 with oxygen deficiency (a molar ratio [O2]0/[i-C4H10]0 = 3.5–5.8) has been studied for the first time. The experiments were carried out in a tubular reactor under uniform heating (1 K/min) to 590 K. Data on the kinetics, auto-ignition temperature, and the products of isobutane conversion have been obtained. The auto-ignition was found to be a two-stage process and begin at a temperature of 510–522 K. The heat capacity of the reaction mixture suppressed the autoacceleration of the oxidation. Mass spectrometric analysis of the reactants revealed a difference in the mechanisms of isobutane conversion in water vapor and carbon dioxide. In water vapor, the oxidation is dominant and is realized with the participation of vibrationally excited O*2 molecules, which appear mainly from resonant exchange with H2O* molecules. In the CO2 medium, the oxidation proceeds against the background of intense isobutane dissociation, initiated by the vibrational pumping of i-C4H10 molecules in their resonant excitation by CO*2 molecules.

Dehydrogenation of Isobutane to Isobutene with Carbon Dioxide over SBA‐15‐Supported Chromia‐Ceria Catalysts

A series of SBA‐15‐supported chromia‐ceria catalysts with 3% Cr and 1%–5% Ce (3Cr‐Ce/SBA) were prepared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N2 adsorption, SEM, TEM‐EDX, Raman spectroscopy, UV–vis spectroscopy, XPS and H2‐TPR, and their catalytic performance for isobutane dehydrogenation with CO2 was tested. The addition of ceria to SBA‐15‐supported chromia improves the dispersion of chromium species. 3Cr‐Ce/SBA catalysts are more active than SBA‐15‐supported chromia (3Cr/SBA), which is due to a higher concentration of Cr6+ species present on the former catalysts. The 3Cr‐3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570 °C after 10 min of the reaction.