Dimerization Of Isobutene Research Articles

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Synthesis of 2,5-dimethylhexene by isobutene dimerization with H2S co-feeding.

This study investigates the effect of hydrogen sulfide (H2S) co-feeding on the synthesis of 2,5-dimethyl-1-hexene, 2,5-dimethyl-2-hexene, and 2,5-dimethylhexane (2,5-DMHs), useful compounds, using the dimerization of isobutene under mild pressure conditions. The dimerization of isobutene did not proceed in the absence of H2S, whereas the desired products of 2,5-DMHs were produced under H2S co-feeding conditions. The effect of reactor size on the dimerization reaction was then examined, and the optimal reactor was discussed. To enhance the yield of 2,5-DMHs, we changed the reaction conditions of the temperature, molar ratio of isobutene to H2S (iso-C4[double bond, length as m-dash]/H2S) in the feed gas, and the total feed pressure. The optimum reaction condition was at 375 °C and 2/1 of iso-C4[double bond, length as m-dash]/H2S. The product of 2,5-DMHs monotonously increased by an increment of total pressure from 1.0 to 3.0 atm with a fixed iso-C4[double bond, length as m-dash]/H2S ratio at 2/1.

Supported Metal Sulfate Catalysts FexZny/SiO2 for Selective Dimerization of Isobutene in Mixed C4 to Isooctenes

AbstractIsobutene dimerization is an important route to properly utilize mixed C4 and further produce isooctane with a high‐octane number to replace MTBE in gasoline. A highly selective catalyst, which is effective for isobutene dimerization but ineffective for other olefins in the C4 mixture, is necessary for industrial implementation. In this work, a series of supported metal sulfate catalysts FexZny/SiO2 were prepared and characterized by XRD, SEM, N2 physical adsorption‐desorption, NH3‐TPD, Py‐FTIR, and XPS. Fe0.2Zn1.8/SiO2 can achieve isobutene conversion up to 89 % with 0 % conversion of n‐butene, and the selectivity of isooctenes (C8=) product is 57 % (10 h on stream). Furthermore, isobutene conversion can sustain above 80 % after 50 h. It is found that these supported catalysts contain Zn2+, Zn+, Fe3+, and Fe2+ species, and there is a synergetic effect between Zn2+ and Fe2+. Zn2+ is beneficial to improve the conversion of isobutene, and Fe2+ facilitates the formation of C8=, resulting in a high C8= yield.

Dual-site eutectic ionic liquids based microemulsion for boosting selective dimerization of isobutene

Oligomerization is one of the efficient routes for making use of C4 olefins to produce high value-added chemicals. However, high reagent conversion is usually accompanied by low dimer product selectivity, and vice versa. Ionic liquids (ILs) with intense interaction between Lewis and Brønsted acidic sites were demonstrated to be excellent catalysts for butene oligomerization. Furthermore, it was found that eutectic IL could be formed by strong hydrogen bond when alcohol was added to the IL, which exhibited enhanced butene solubility and thus improved catalytic performance. Moreover, microemulsion could be constructed by adding an IL emulsifier into the IL catalyst, and the improved interfacial area further enhanced efficient contact between butene and catalyst. Combining the strategies of employing dual-site eutectic IL as the catalyst and microemulsion formation, butene conversion could reach 98%, while dimer selectivity was 91%, resolving the contradiction that high conversion and target product selectivity cannot be achieved simultaneously.

Enhance glycerol conversion through co-etherification with isobutene and tert-butanol

tert-Butyl glycerol ethers obtained from etherification of glycerol with isobutene or tert-butanol are desirable fuel additives. While glycerol etherification with isobutene has high glycerol conversion and yield to the desired ethers, it undergoes intricate interphase mass-transfer and the rate is restricted by the low reactant concentration resulting from phase separation. On the contrary, although glycerol etherification with tert-butanol avoids phase separation, the conversion and yield are relatively low due to equilibrium limitation and/or the inhibition from the produced water. We proposed to etherify glycerol with isobutene and tert-butanol simultaneously (co-etherification) to enhance glycerol conversion. Multiphase chemical equilibrium was calculated to explore the phase states of reaction mixtures as well as the equilibrium conversions and yields under a wide range of conditions. The co-etherification was then demonstrated on NKC-9 catalyst, which validated that the solvation function of tert-butanol to the glycerol-isobutene mixture improved the glycerol conversion rate (up to twice). Isobutene addition raised glycerol conversion and yield to the poly-substituted ethers comparing with the etherification with tert-butanol. Co-etherification (G:IB:TBA = 1:3:1) yielded 0.573 poly-substituted ethers at 353 K, while the yield was only 0.069 in the G-TBA etherification (G:TBA = 1:4). Moreover, the presence of tert-butanol effectively hindered the undesired isobutene dimerization.

Promoting di-isobutene selectivity over ZnO/ZrO2-SO4 in isobutene oligomerization

Isooctane attracts great interest in recent years because of its promising potential as friendly-environmental gasoline, which is obtained by dimerization of isobutene with a hydrogenation step. Herein, a solid acid catalyst sulfated zirconia modified by ZnO was prepared. The oligomerization of isobutene had been investigated over ZrO 2 -SO 4 and ZnO( X )/ZrO 2 -SO 4 catalyst in order to find efficient catalysts for the production of isobutene oligomers. The presence of ZnO obviously enhanced the dimerization of isobutene and ZnO( X )/ZrO 2 -SO 4 exhibited the highest di-isobutene yield of 60%. Kinetic studies showed the higher trimerization-to-dimerization activation energy ratios of ZnO( X )/ZrO 2 -SO 4 than those of ZrO 2 -SO 4 from 353 to 393 K. In addition, reaction rate of dimerization was higher than trimerization over ZnO( X )/ZrO 2 -SO 4 . The high L/B ratio manifested the capability to enhance the selectivity of C 8 in isobutene dimerization. Furthermore, ZnO( X )/ZrO 2 -SO 4 exhibited stable conversion for the dimerization of isobutene.

Selective addition of isobutene over ZrSiO4/SiO2-SO3H: Hydroacetoxylation versus dimerization

The acid-catalyzed Markovnikov addition of isobutene is affected by the concomitant isobutene oligomerization. Herein, a solid acid catalyst consisting of the sulfonated silica modified with crystalline ZrSiO4 was prepared, and the ZrSiO4/SiO2-SO3H catalyst went beyond conventional acid catalysts in the hydroacetoxylation of isobutene. The structure of the catalyst was well-characterized, and the role of ZrSiO4 in suppressing the dimerization of isobutene was discussed in terms of both kinetic study and in-situ DRIFT analysis. Moreover, this catalyst also showed general applicability for a broad substrate scope, further highlighting the necessity of ZrSiO4 in the solid acid catalyst.

Comparative Study of Different Acidic Surface Structures in Solid Catalysts Applied for the Isobutene Dimerization Reaction.

Dimerization of isobutene (IBE) to C8s olefins was evaluated over a range of solid acid catalysts of diverse nature, in a fixed bed reactor working in a continuous mode. All catalytic materials were studied in the title reaction performed between 50–250 °C, being the reaction feed a mixture of IBE/helium (4:1 molar ratio). In all materials, both conversion and selectivity increased with increasing reaction temperature and at 180 °C the best performance was recorded. Herein, we used thermogravimetry analysis (TGA) and temperature programmed desorption of adsorbed ammonia (NH3-TPD) for catalysts characterization. We place emphasis on the nature of acid sites that affect the catalytic performance. High selectivity to C8s was achieved with all catalysts. Nicely, the catalyst with higher loading of Brønsted sites displayed brilliant catalytic performance in the course of the reaction (high IBE conversion). However, optimum selectivity towards C8 compounds led to low catalyst stability, this being attributed to the combined effect between the nature of acidic sites and structural characteristics of the catalytic materials used. Therefore, this study would foment more research in the optimization of the activity and the selectivity for IBE dimerization reactions.

Brøsted acidic pyridinium-based ILs catalyzed the selective dimerization of isobutene: Performance and in-situ NMR study

Brøsted acidic pyridinium-based ILs of [NS][CF3SO3] and [NS][HSO4] have been synthesized for oligomerization of isobutene with the excellent conversion of 92.8% and the good selective dimerization at the temperature of below 100 °C. Hydroxyl-containing materials, especially ethanol, could facilitate catalytic activities to excellent conversions of isobutene and 84.2% selectivity of diisobutene. [NS][CF3SO3] could be recovered by a simple liquid-to-liquid separation and reused more than ten times without obvious loss of catalytic activities. The formation process of oligomers has been examined by in-situ NMR spectroscopy, and a step-by-step generation process of carbonium ions varying from C4+, C8+ to C12+ was proposed. The work behaves the significance of constructing a better catalysis system for highly selective dimerization of isobutene, and potential being scaled-up for industrialization.

Direct sulfation of a Zr-based metal-organic framework to attain strong acid catalysts

Abstract The application of Metal-Organic Frameworks (MOFs) in gas phase heterogeneous catalysis is still not widely spread because of their limited stability under reaction conditions. Obtaining stable acidic MOFs to be used in reactions that demand strong acid sites remains a challenge up to the present time. In this work, it is shown that nanocrystals of Zirconium MOF UiO-66 can be conveniently and easily functionalized through a simple one-pot synthetic approach, i.e. the direct treatment of UiO-66 with ammonium sulfate followed by an adequate thermal treatment, giving rise to a highly acidic and thermally stable material (named as S-UiO-66). This material can act as catalyst in the gas phase isobutene dimerization demonstrating high catalytic activity at moderate temperatures while maintaining the structural integrity of the MOF after several catalytic evaluations and/or after reuse cycles. The S-UiO-66 material represents a novel alternative in the search of robust MOF-based catalysts to be applied in gas phase heterogeneous catalytic reactions that demand strong acid sites.

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.

Assessment of acid strength in sodium-exchanged resin catalysts: Consequences on glycerol etherification with isobutene in batch and flow reactors

Consequences of a decrease in the number of acid sites by the cation exchange on the acid strength of the resin catalysts were assessed using ammonia as a probe molecule. IR spectra illustrated that ν(NH) bands on NH3-saturated Amberlyst 15™ shift linearly to higher frequencies with an increase in the degree of sodium exchange associated with an increase in the Brønsted acid strength. These results were further confirmed by density functional theory calculations illustrating that the deprotonation energy of a sulfonated styrene group decreases upon Na+-exchange on its neighboring counterparts. Consequences of these changes in acid strength were investigated on glycerol etherification with isobutene. Batch reactor measurements at high conversions illustrated that selectivity to desired glycerol ethers increases as that of isobutene dimerization is suppressed with an increase in acid strength. The effects of acid strength on the complex reaction network were further investigated using a once-through flow reactor specifically focusing on low conversions. These measurements showed that mono-tert-butyl glycerol ether and di-isobutene were the primary products on pristine Amberlyst 15™, while di- and tri-tert-butyl glycerol ethers also become a primary product on sodium-exchanged counterpart catalysts.

Identification of the strong Brønsted acid site in a metal-organic framework solid acid catalyst.

It remains difficult to understand the surface of solid acid catalysts at the molecular level, despite their importance for industrial catalytic applications. A sulfated zirconium-based metal-organic framework, MOF-808-SO4, was previously shown to be a strong solid Brønsted acid material. In this report, we probe the origin of its acidity through an array of spectroscopic, crystallographic and computational characterization techniques. The strongest Brønsted acid site is shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters. When a water molecule adsorbs to one zirconium atom, it participates in a hydrogen bond with a sulfate moiety that is chelated to a neighbouring zirconium atom; this motif, in turn, results in the presence of a strongly acidic proton. On dehydration, the material loses its acidity. The hydrated sulfated MOF exhibits a good catalytic performance for the dimerization of isobutene (2-methyl-1-propene), and achieves a 100% selectivity for C8 products with a good conversion efficiency.

Dimerization of iso-butene on sodium exchanged Amberlyst-15 resins

This work reports a new technical approach for the production of aviation gasoline through the catalytic dimerization of iso-butene on sodium exchanged Amberlyst-15 resins (20–40 mesh) in the absence of selectivity-enhancing components at T = 50 °C, P = 2 MPa and LHSV of 2 h−1. The dimers selectivity could be significantly improved by effectively controlling the acid capacity of resins via Na+ exchange. When the acid capacity of the catalyst was controlled to <2.45 mmol/g, the 2,4,4-trimethylpentenecontent in C8 olefins reached ~100%. It was also confirmed that the sodium exchanged resins have longer lifetime than Amberlyst-15 resins.

Catalytic diversity conferred by confinement of protons within porous aluminosilicates in Prins condensation reactions

The effects of confinement of transition states and bound intermediates are described here based on kinetic and theoretical studies for Prins condensation and oligomerization reactions of isobutanal-isobutene reactant mixtures catalyzed by Brønsted acid sites of similar strength but confined within diverse microporous (TON, BEA, MFI, FAU) and mesoporous (Al-MCM-41) aluminosilicate structures. Kinetic data and density functional theory (DFT) show that smaller voids lead to more stable bound monomers derived from isobutene and isobutanal and to protons nearly saturated with H-bonded isobutanal. Prins condensation forms 2,5-dimethyl-hexadiene regioisomers (2,5-DMH) with rate constants that reflect the different stability of the kinetically-relevant CC bond formation transition states and their H-bonded isobutanal precursors. Their differences in size lead to reactivities that depend sensitively on the size and shape of the confining voids in each aluminosilicate and even on the location of the Al-atoms (and the protons) within a given framework. Specifically, FAU leads to the highest turnover rates, because larger voids in Al-MCM-41 form less effective van der Waals contacts with the transition state, while the smaller voids within TON and BEA lead to enthalpic and entropic penalties brought forth by host-guest distortions. MFI cage-like intersections provide more effective stabilization than BEA cylindrical channels of similar size and lead to higher turnover rates and smaller DFT-derived activation free energies; these subtle effects of void shape on reactivity are neglected in descriptions of the confining frameworks based on spherical constructs. Reactivity descriptors require instead theoretical treatments that rigorously account for van der Waals interactions and for the entropy losses and host-guest distortions required for confinement, as reported here from confinement free energies ensemble-averaged over all crystallographic locations in each aluminosilicate structure. The ratios of rate constants for these parallel isobutene dimerization and Prins condensation reactions depend only weakly on the nature of the aluminosilicate framework, because of the similar size and shape of their respective transition states and bound precursors. Transition states for secondary skeletal isomerization and cyclization of 2,5-DMH condensation products, however, are stabilized more effectively (relative to condensation transition states) within voids of intermediate size (BEA, MFI), leading to higher selectivity to secondary products. MFI cage-like structures specifically catalyze the conversion of 2,5-DMH to cyclic 1,4-dimethyl-cyclohexene isomers, direct precursors to p-xylene, with unique specificity.

Process Control of Isobutene Dimerization Plant

The development and evaluation of the dynamic flowsheet for isobutene dimerization process is presented. The steps for developing the dynamic model, the control scheme and the controllers tuning are shown and the response of the system to different disturbances is evaluated. The results are presented in graphical form. Methods for changing the plant throughput and for controlling the product specification when the feed composition varies are presented.

Bifunctional Catalysts Based on Tungsten Hydrides Supported on Silicated Alumina for the Direct Production of 2,3‐Dimethylbutenes and Neohexene from Isobutene

AbstractWell‐defined bifunctional supported catalysts that comprise tungsten hydride moieties and Brønsted acid sites were prepared successfully. The catalysts showed outstanding activities and selectivities toward the formation of high‐value‐added products, 2,3‐dimethylbutenes and 3,3‐dimethylbutene, through a combination of the metathesis and dimerization of isobutene. The relationship between the physicochemical properties of the catalysts and their activities and selectivities indicated that isobutene conversion increased from 4 to 95 % as a function of the silica content of the silicated alumina (obtained from Sasol). Nevertheless, the selectivity toward branched hexenes showed a volcano‐shaped curve that presented a maximum for the catalyst with 5 wt % silica. Therefore, the control of the support acidity by the silica loading on alumina resulted in an increase of the selectivity toward neohexene.

Selective and efficient dimerization of isobutene over H3PO4/activated carbon catalysts

Dimerization of isobutene to branched C8 olefins (precursors of high octane gasoline additives) was performed over eco-friendly activated carbon catalysts impregnated with phosphoric acid, under continuous gas phase operating conditions. A series of catalysts differing in phosphoric acid loading were prepared by incipient wetness impregnation and tested in the reaction carried out at various temperatures (100–260°C), with the use of an isobutene/isobutane mixture at a molar ratio of 4:1 as a feedstock. The conversion and selectivity patterns obtained for a selected sample evolved visibly with the reaction temperature and the best results were obtained at 180°C. The effect of phosphoric acid loading on the catalytic activity of the samples at this temperature was investigated and discussed. For the sake of comparison also other acidic activated carbons and the commercially available catalyst Amberlyst 15 were tested. The high H3PO4-loaded materials exhibited excellent catalytic performance in the process (high isobutene conversion, good selectivity to C8 products and high catalyst stability) which was assigned to a combination of acidic and textural properties of the materials obtained.

Al2O3-Phosphated Green Catalysts with High Selectivity to Ecological Gasoline C8= by Dimerization of Isobutene.

In this paper, phosphated-alumina prepared from boehmite and phosphoric acid (1, 4, and 6 mmol of PO4(3-)) is proposed as a good alternative catalyst to obtain ecological gasoline by the reaction of dimerization of butenes in gas phase using a flow reactor and mild conditions (60 degrees C and a C4/C4= molar ratio = 1). XRD spectra of the samples showed the formation of the gamma-alumina phase in the solids. BET specific surface area values of the bare alumina were not notably modified when these materials were phosphate, from 180-m2/g to 170 m2/g. All the solids are mesoporous structured materials. FTIR pyridine-adsorption spectra showed the formation of strong Lewis acid sites, which remains stable even at desorption temperatures above 300 degrees C. Brönsted acid sites were not observed on the materials. The phosphated-alumina catalysts were active for the dimerization of isobutene in mild conditions and 100% selectivitiy to C8= olefins was reached without the presence of olefinic compounds with higher molecular weight (trimers, tetramers).

Production of Isooctane from Isobutene: Energy Integration and Carbon Dioxide Abatement via Catalytic Distillation

Isooctane is a valuable octane enhancer for gasoline and the primary component of aviation gasoline, also known as Avgas, because of its high antiknock quality. Conventional industrial processes for isooctane production involve the steps of dimerization of isobutene, dimer separation, and hydrogenation. The efficacy of catalytic distillation (CD) and its merits, in terms of energy savings and reduction of greenhouse gas emissions, for the production of isooctane are quantitatively presented. The feed considered for the isooctane production is composed of isobutene (C4) and inerts (isopentane) produced in refineries as byproducts of steam cracking of naphtha and light gas oil. Process flow sheets for the two routes for the production of isooctane, with and without CD, are modeled. The conventional industrial flow sheet composed of a dimerization reactor, distillation column, and a hydrogenation reactor (configuration A), is simulated using Aspen Plus. The intensified process flow sheet comprising a CD column for the dimerization, hydrogenation, and separation (configuration B) is modeled using gPROMS. A validated, nonequilibrium, three-phase model is developed in a gPROMS environment and is used to quantify the energy savings and reduction of carbon dioxide emissions achieved using a CD column for the intensified process. Results demonstrate CD to be a promising candidate to replicate the conversions and product purity obtained in the conventional process while resulting in significant energy savings, more efficient utilization of isobutene feed, and reduced carbon dioxide emissions.