Isobutane Conversion Research Articles

Elucidation of active species and reaction mechanism of sulfide V-K/Al2O3 catalyst for isobutane dehydrogenation

Supported sulfide vanadium-based catalyst in dehydrogenation of light alkanes is becoming a promise to replace the commercial used Pt- and Cr-based catalysts, due to the lower cost and toxicity. Nonetheless, the nature of active sites and reaction mechanism for dehydrogenation of isobutane over sulfide vanadium-based catalysts are still ambiguous. In this study, a series of sulfide V-K/γ-Al2O3 catalysts were prepared, presenting diverse distribution of isolated, oligomeric and polymeric vanadium species on catalyst surface. The oligomeric species were demonstrated to be the active dehydrogenation sites, and the TOFoligo showed a closely correlation with the isobutane conversion. Besides, the dehydrogenation reaction mechanism was studied by in-situ DRIFTS. The results showed that isobutane would first dissociative adsorbed on catalyst surface, and the stable intermediates of vanadium-isobutenyl were detected. Furthermore, the deposited coke rather than sulfur loss was found to play the crucial role in deactivation. The vast majority of deposited coke existed as polyaromatic species and the other slight ones presented as aliphatic form. This study enriches the fundamental explorations in active sites and reaction mechanism of sulfide V-K/γ-Al2O3 catalysts during isobutane dehydrogenation, and provides an in-depth strategy to improve the activity and stability of vanadium-based dehydrogenation catalysts.

Molybdenum-based catalysts supported on alumina for direct dehydrogenation of isobutane

A series of Al 2 O 3 supported Mo-based Mo/Al-X ( X = 1, 2, 3, 4) catalysts were prepared by incipient-wetness impregnation method. The Mo/Al-X catalysts were evaluated in the isobutane direct dehydrogenation reaction at 600 °C, and the physicochemical properties of Mo/Al-X catalysts were investigated by using XRD, BET, SEM, H 2 -TPR, NH 3 -TPD, TEM, XPS and TG-DTG techniques. The results indicated that the MoO x species were highly dispersed, and Mo 4+ ions were the main active species for the reaction of isobutane direct dehydrogenation to isobutene. The Mo/Al-1 catalyst displayed the hollow microspheric structure with mesoporous shell and big pore window. And Mo/Al-1 catalyst with the lowest S BET value of 167 m 2 •g −1 exhibited optimal catalytic performance, achieving superior and stable isobutane conversion of 30.5% and isobutene selectivity of 84.6%, respectively. Excellent catalytic performance, anti-sintering and carbon-resistance ability of Mo/Al-1 catalyst are attributed to the low specific surface area, small particle size, high Mo 4+ /Mo 6+ molar ratio, strong Mo species and support interaction, and high concentration and strength of weak and medium-strong acid sites.

Enhanced aromatic selectivity using the core–shell synergistic effects of HZSM-5/SAPO-5 zeolites in isobutane conversion

HZSM-5 molecular sieves are efficient catalysts in the aromatization of light hydrocarbons and the fabrication of HZSM-5-based core–shell composites has become an important strategy to improve their catalytic performance due to the simultaneous modification of the acidity and pore structures in the catalyst. In this paper, HZSM-5/SAPO-5 (CSZP and CSZC) were synthesized via a two-stage crystallization process using PDDA and CTAB as modifiers of HZSM-5, respectively. The structure, acidity, and the weight of carbon deposition of the resulting molecular sieves catalysts were characterized using various methods and their catalytic behavior in isobutane aromatization investigated. The results show that CSZP exhibits a perfect core–shell structure with a uniform and thin shell composed of nano-SAPO-5, while CSZC has an irregular coat configuration with HZSM-5 covered by a rough and thick shell consisting of flaky micro-SAPO-5 crystals. The introduction of SAPO-5 via an in-situ synthesis decreases the Brønsted acidity of the catalysts to different extents and provides a large number of intergranular mesopores due to the stacking of SAPO-5 on the surface of HZSM-5, which is favorable toward improving the BTEX selectivity (benzene, toluene, ethylbenzene, and xylene) and catalytic stability over CSZP and CSZC. Meanwhile, CSZP has more competitive advantages than CSZC in promoting the mass transfer efficiency due to its significantly thinner shell than CSZC, which combined with its moderate acidity and appropriate mesopore structure result in its excellent selectivity and stability during the aromatization of isobutane.

Synthesis, characterization, and application of metal-free acidic ionic liquids as catalysts for oligomerization of isobutene

Butene oligomerization followed by hydrogenation is regarded as a promising way to produce alkylate oil, and the challenge of this process is the oriented conversion of butene to octene, which closely relates to the alkylate quality. Ionic liquids (ILs) are a kind of promising catalyst for olefin oligomerization. In this study, a series of functional metal-free acidic ILs (11 in total) were synthesized, characterized, and used for the oligomerization of isobutene. It was found that among the tested neat ILs, sulfobutyltriethylammonium triflate ([TENBs][CF3SO3]) exhibited the best performance. This IL catalyst could be reused for 25 times, without obvious loss in catalytic activity. To improve catalytic activity of the neat IL, composite ILs formed by mixing [TENBs][CF3SO3] with a second functional IL were developed. In the best composite system with tunable acidity, isobutene conversion could increase by ~88% compared with the neat IL, and meantime the dimer selectivity could increase to 79%. The conversion could increase from 25% to over 80% in the best composite system with enhanced mass transfer capability. Spectroscopic characterization and Gaussian simulation revealed the different catalytic behaviors of these ILs, which demonstrated that ILs with lower bond dissociation enthalpy (< 521 KJ·mol−1) and proper binding energy with isobutene (−27 to −20 KJ·mol−1) could efficiently catalyze isobutene oligomerization, the acidic active sites were from the sulfonic acid group in the cation and the acidic anion, and that deactivation of the IL catalyst after being used for 29 times could be attributed to the loss of the acid sites in both the cation and anion.

Synergistic effects of phases in the selective oxidation of isobutane over supported (NH4)3HPMo11VO40 catalysts

The supported 40 wt% (NH4)3HPMo11VO40 (APMV) catalysts over two different types of supports, supports-I (Cs3PMo12O40, Cs2.5H0.5PMo12O40, Cs4PMo11VO40 and Cs3HPMo11VO40) and supports-II (CeO2, WO3/ZrO2 and S-1 molecular sieve), were synthesized by deposition–precipitation method and further evaluated in the partial oxidation of isobutane to methacrylic acid (MAA) at 340 °C under atmospheric pressure. The fresh and used catalysts were characterized by N2 adsorption/desorption, TG/DTG, XRD, FT-IR, Raman spectroscopy, pyridine- adsorption FT-IR and NH3-TPD to investigate their structure, stability and surface acidity. The better results were obtained by impregnating 40 wt% active APMV phase onto the supports-I phase with same/similar Keggin structure, and it is believed that the formation of coherent interfaces between two structural well-matched phases with the same/similar Keggin anions greatly promotes interfacial transfer abilities of electrons and lattice oxygen, which is responsible for the efficient oxygen insertion to maximize MAA selectivity and conversion of isobutane. The current work provides a concept of phase synergy to design a promising catalyst for selective oxidation of isobutane.

Spectroscopic analysis of acetamide-AlCl3-based ionic liquid analog and their catalytic performance in isobutene oligomerization

The spectral structures of acetamide-AlCl3-based ionic liquid (IL) analogs were determined in detail through IR, NMR, and Raman spectroscopy. IR spectroscopy showed that 0.65AA-1.0AlCl3 was the coordination structure of Al and O atoms because of the resonance structure of acetamide. The mutual verification of the results of 27Al NMR and 1H NMR indicated that acetamide coexisted mainly in the form of cationic Al species and molecular Al species in xAA-1.0AlCl3, and AA/AlCl3 molar ratio affected the transformation of cationic Al species to molecular Al species. xAA-1.0AlCl3 was used as a green acidic catalyst for isobutene oligomerization, and the effects of AA/AlCl3 molar ratio, reaction temperature, reaction time, and volumetric ratio between IL analog and isobutene on product distribution were investigated. Optimal reaction conditions were AA/AlCl3 molar ratio of 0.75, reaction temperature of 60 °C, reaction time of 30 min, and catalyst/i-C4= volumetric ratio of 1.4 v/v. Under optimal conditions, isobutene conversion, (C8= + C12=) selectivity, (C16= + C20=) selectivity, and by-product selectivity were 85.26, 80.20, 6.80, and 13.00 wt%, respectively.

Current status and perspectives in oxidative, non-oxidative and CO2-mediated dehydrogenation of propane and isobutane over metal oxide catalysts.

Conversion of propane or butanes from natural/shale gas into propene or butenes, which are indispensable for the synthesis of commodity chemicals, is an important environmentally friendly alternative to oil-based cracking processes. Herein, we critically analyse recent developments in the non-oxidative, oxidative, and CO2-mediated dehydrogenation of propane and isobutane to the corresponding olefins over metal oxide catalysts. Particular attention is paid to (i) comparing the developed catalysts in terms of their application potential, (ii) structure-activity-selectivity relationships for tailored catalyst design, and (iii) reaction-engineering aspects for improving product selectivity and overall process efficiency. On this basis, possible directions for further research aimed at the development of inexpensive and environmentally friendly catalysts with industrially relevant performance were identified. In addition, we provide general information regarding catalyst preparation and characterization as well as some recommendations for carrying out non-oxidative and CO2-mediated dehydrogenation reactions to ensure unambiguous comparison of catalysts developed in different studies.

Promoted mesoporous Fe-alumina catalysts for the non-oxidative dehydrogenation of isobutane

Production of isobutene is commercially consequential and highly demanding from the end-use industries being a key platform molecule as well as an intermediate for a variety of value-added chemicals. Traditionally, isobutene is prepared via steam cracking and fluid catalytic cracking methods. However, the catalysts used in these conventional methods have disadvantages like coke formation, sintering, etc. In this study, the catalytic non-oxidative dehydrogenation of isobutane over acidic, alkaline, and noble metal promoted mesoporous iron-doped catalysts was investigated. Iron doping has a significant function in controlling isobutene selectivity. The synthesis method is crucial to achieve successful metal doping in the mesoporous alumina matrix. Promoted catalysts exhibited a notable difference in isobutane conversion with a marginal change in dehydrogenation selectivity. Silver promoted catalyst showed slightly higher isobutene yield due to the optimal catalytic properties. Thiscatalyst was stable for a considerable duration, and coke deposition, as well as particle agglomeration, were observed to faintly inhibit the catalytic activity.

Dehydrogenation of isobutane to isobutene over a Pt-Cu bimetallic catalyst in the presence of LaAlO3 perovskite

In this study, isobutane dehydrogenation to isobutene reaction was carried out in a series of Pt-Cu bimetallic catalysts prepared by co-impregnation method. The catalysts were characterized by means of several techniques, including XRD, N 2 adsorption–desorption, TEM, XPS, H 2 -TPR and TG. The results show that the existence of LaAlO 3 perovskite can enhance the dispersion and sintering resistance of metal nanoparticles and facilitate the transfer of carbon deposits from active sites to the support. Interestingly, the perovskite nanoparticles can also inhibit the reduction of CuO x and the formation of PtCu alloys, resulting in the suitable interaction between Pt and Cu. The Pt-Cu/LaAlO 3 /SiO 2 catalyst exhibits the optimal dehydrogenation performance with an isobutane conversion of 47% and isobutene selectivity of 92% after 310 min reaction, which was ascribed to the unique role of LaAlO 3 perovskite as well as the appropriate Pt-Cu interaction.

Conversion of isobutane to n-butane over bifunctional PtAu-solid superacids catalyst

A platinum-substituted alumina-promoted sulfated zirconia (PtAu/SZA) was prepared and used for the conversion of isobutane to n-butane, aiming to optimize the ethylene feedstock in the steam thermal cracking process and increase the ethylene yield. PtAu bimetallic catalysts showed higher catalytic activity than Pt-alone catalyst, and the enhancement is attributed to PtAu alloying. By diluting and separating Pt with PtAu alloy agglomerates, continuous Pt agglomerates disappear and hydrogen dissociation on Pt is enhanced. In addition, the reduction temperature of Pt is decreased with the increase in Au content, while the reduction temperature of sulfate was increased which will delay the loss of sulfate according to the results of H2-TPR and NH3-TPD. However, the acidity of the catalyst decreases with the increase in Au, which is due to that PtAu alloy covers the acid sites on the surface. Overall, we found that the Pt0.5Au0.3/SZA showed the highest yield to n-butane (34.69%).

Investigation of Isobutane Dehydrogenation on CrOx/MCM-41 Catalyst

The syntheses of MCM-41 (Mobil Composition of Matter No. 41) supported chromium oxide cat-alysts at different chromium concentrations (4–10 % by mass) were carried out hydrothermally. The aim of this study was to determine the effect of chromium concentration in the catalyst structure on the chro-mate types and chromium oxidation states, as well as the activity of the catalyst in the isobutane dehydro-genation reaction. Inactive α-Cr2O3 crystals for isobutane dehydrogenation were shown to increase in the catalyst structure as the chromium loading increased. The highest amount of Cr6+ on the catalyst surface was detected in the catalyst (H4-MCM-41) with 4 % chromium by mass. Catalytic tests (T = 600 °C, P = atmospheric pressure, WHSV = 26 h–1) were performed under fixed bed reactor conditions. The high-est isobutane conversion (~60 %) and selectivity (~80 %) were observed on the H4-MCM-41 catalyst, which had the highest amount of Cr6+ and monochromate structures. Catalyst deactivation was not due to coke deposition but, rather, was caused by the formation of inactive α-Cr2O3 crystal structures.

Isobutane Dehydrogenation Assisted by CO2 over Silicalite‐1‐Supported ZnO Catalysts: Influence of Support Crystallite Size

Summary of main observation and conclusionThe ZnO catalysts supported on Silicalite‐1 zeolites with different crystallite sizes (0.08, 0.35, 1 and 1.7 μm, respectively) and 5% Zn were synthesized via an incipient wetness method. The catalysts were characterized by XRD, N2 adsorption, SEM, TEM‐EDX, DRIFT spectra and NH3‐TPD, and their catalytic performance in isobutane dehydrogenation assisted by CO2 was investigated. The catalytic activity is strongly dependent on the crystallite size of Silicalite‐1 support. The ZnO/S‐1‐0.35 catalyst with ca. 0.35 μm crystallite size displays the highest activity, affording an initial isobutane conversion of 51.0% and 74.5% isobutene selectivity. This can be attributed to a higher amount of acid sites present on this catalyst as well as the largest amount of nest silanols possessed by the S‐1‐0.35 support.

Techno-economic and life cycle assessment of triisobutane production and its suitability as biojet fuel

This study assesses the potential of triisobutane as a sustainable biojet fuel blending component to reduce the environmental impacts caused by the continually growing aviation sector. Cellulosic isobutanol, used as feedstock, was sequentially upgraded through dehydration, oligomerization, and hydrogenation processes to produce triisobutane (2,2,4,6,6-Pentamethylheptane). The dehydration process yield is 99.1% of isobutene, and the achieved conversion of isobutene to triisobutene in the oligomerization stage is 90%. The optimal operation conditions to produce the maximum amount of triisobutene during the isobutene oligomerization are 100 °C, 0.20 MPa, and a space–time τ’ of 5.5 g h/L. Triisobutene is converted quantitatively to triisobutane through a final hydrogenation stage. The production model was simulated using Aspen Plus® v.10 software. The production costs were calculated based on a biorefinery that uses 16,264 kg/h of isobutanol to obtain 10,723 kg/h of triisobutane. The predicted minimum triisobutane selling price is 1.34 €/kg or 1.04 €/L. The environmental assessment carried out in Simapro® v.9.0 software, estimated emissions of the isobutanol upgrade to triisobutane of 7 gCO2eq/MJ. A combined footprint of 65 gCO2eq/MJ is obtained considering the 58 gCO2eq/MJ emitted in isobutanol production, which represents a 28% reduction of greenhouse gas emissions compared with the conventional Jet A1 production. Physico-chemical properties of triisobutane were estimated using group contribution methods, and the results comply with the ASTM D7566 standards. The Payload vs. Range analysis confirmed the capabilities of triisobutane as a biojet fuel blend component for a given range flight.

Chromium Oxide Supported on Silicalite-1 Zeolite as a Novel Efficient Catalyst for Dehydrogenation of Isobutane Assisted by CO2

The chromium oxide catalysts supported on silicalite-1 zeolite (Cr/S-1) with a Cr content between 0.5% and 7% were synthesized via an incipient wetness method. The catalysts were characterized by XRD, N2 adsorption, TEM-EDX, UV-vis, DRIFTS, 29Si MAS NMR, XPS, H2-TPR, and NH3-TPD. The optimum 3%Cr/S-1 catalyst with 3%Cr is more active and stable than SBA-15-supported one with the same Cr content, which is a consequence of a higher content of Cr6+ in the fresh 3%Cr/S-1 catalyst and a higher content of Cr6+ retained on the former catalyst during the reaction. The 3%Cr/S-1 catalyst affords an isobutane conversion of 36.5% with 71.2% isobutene selectivity. The catalytic activity is well correlated with the content of Cr6+ in the fresh catalysts. Carbon dioxide displays a promoting effect on the dehydrogenation reaction.

Ca-Doped CrOX/γ-Al2O3 Catalysts with Improved Dehydrogenation Performance for the Conversion of Isobutane to Isobutene

The dehydrogenation of low-carbon alkane to obtain olefins is an effective way to meet the steadily increasing demand of these building blocks in chemical industry. In this study, Ca-doped CrOx/γ-Al2O3 catalysts were fabricated via a one-pot method by employing Cr(OH)3 as the precursor, and their catalytic performances were tested in the dehydrogenation of isobutane to isobutene (DITI) process. The prepared catalysts were intensively characterized by XRD, SEM, NH3-TPD, H2-TPR, low-temperature N2 adsorption–desorption, etc. These characterization results indicated that the doping of Ca into the CrOx/γ-Al2O3 catalysts could tune the acidity properties of the prepared catalysts and enhance the interaction between the active species and support. The Ca-doped CrOx/γ-Al2O3 catalysts, especially the Ca2-Cr/γ-Al2O3 catalyst with a Ca doping of 2 wt%, exhibited a superior catalytic performance in the DITI process in comparison with the undoped catalyst.

Parameters Optimization of MTBE Reactive Distillation Process with Response Surface Methodology

Because of many variables and strong coupling effects between the reaction and distillation processes, the parameters optimization of reactive distillation (RD) process is usually a challenge work. In this study, response surface methodology (RSM) was used to design the numerical experiments and analyze process parameters of the methyl tertiary butyl ether (MTBE) reactive distillation column. Firstly, Packett-Burman design was employed to screen the significant process parameters affecting the conversion of isobutene from 10 variables. Then, a Steepest Ascent method and Box-Behnken design were applied to determine the optimum key process parameters, with maximizing the conversion of isobutene as an objective. The optimum and actual conversion of isobutene were 100 % and 97.54 % which is higher than a conversion of 91.95 % in the literature, under optimum conditions in MTBE reactive distillation process.

Fe-containing N-doped porous carbon for isobutane dehydrogenation

Abstract Fe–N–C catalysts were synthesized via high temperature calcining Fe-ZIF-8 (Zeolitic Imidazolate Framework) for catalytic dehydrogenation of isobutane. The ultimate catalysts are investigated in detail by a series of characterization in order to explore the relationship between the catalyst structure and catalytic performance. XRD, N2 physisorption, TEM and Raman illustrate that Fe doping significantly changes the surface and bulk properties of the catalyst. Increased Fe content causes the decrease of specific surface area and the deposition of Fe2O3 nanoparticles on the catalysts. XPS, ICP-OES and EA show that the surface states and content of N and Fe are also affected with different amounts of Fe. Isobutane and isobutene TPD demonstrate that Fe–N–C catalysts possess reduced adsorption capacity and weaker interaction, thus exhibit lower isobutane conversion and higher isobutene selectivity compared with N–C catalyst. Moreover, combining other characterizations, such as IR and H2-TPR, both carbonyl group (C O) and Fe2O3 species of the Fe–N–C catalysts contribute to the dehydrogenation activity.

Zeolite membrane reactor for high-temperature isobutane dehydrogenation reaction: Experimental and modeling studies

Isobutylene has been produced by packed bed reactors (PBRs), but there is thermodynamic limitations and a critical need for efficient isobutylene production. Catalytic dehydrogenation of isobutane using a membrane reactor is a feasible solution because it helps in overcoming thermodynamic limitations as well as separates isobutylene by allowing H2 to selectively permeate through the membrane. In this study, isobutane dehydrogenation (IBDH) in a packed-bed membrane reactors (PBMRs) in combination with a Pt/Al2O3 catalyst was investigated. MFI zeolite membranes were found to have good H2/i-C4H10 selectivity which enhanced isobutane conversion at high operation temperature. The effect of the PBMR operating conditions such as weight hourly space velocity (0.8-2.7 h−1), temperature (500–650 °C), and sweep gas flow rate (0-40 cm3/min) on isobutane conversion, isobutylene selectivity and isobutylene yield was studied. The highest isobutane conversion, isobutylene selectivity and isobutylene yield was 27%, 97% and 26%, respectively, from experiments. We developed a 1D plug flow reactor model for the IBDH system and isobutane conversion was evaluated at a wider range of operating conditions. Isobutane conversion of >90% was from calculation obtained at practically meaningful operating conditions.

Photoluminescence of surface chromium centers in the Cr/Al2O3 system that is active in isobutane dehydrogenation

A comprehensive study of optical and catalytic properties of highly dispersed single-phase η-, γ- and γ*-Al2O3 ([Cr3+] ∼ 10–4 wt.%) powders and the related model chromia-alumina catalysts with different chromium content ([Cr3+] = 0.25, 0.5 and 1 wt%) was carried out. The catalytic characteristics (product yield, conversion and selectivity) in isobutane dehydrogenation to isobutylene were measured for all the samples under consideration. The surface Cr3+S luminescence centers were detected by photoluminescence spectroscopy in all the samples. The content of Cr3+S centers in the samples was estimated before and after isobutane dehydrogenation. It was shown that the amount of surface Cr3+S centers correlates with isobutylene yields of the reaction. Among the studied samples, the maximum amount of Cr3+S luminescence centers was found for the model 1% Cr/γ-Al2O3 catalyst. This sample has the highest values of isobutane conversion and isobutylene yield. The comprehensive study of the Cr/Al2O3 systems made it possible to propose a method for predicting the catalytic activity of nanostructured materials using the photoluminescence detection of surface luminescence centers and their quantitative evaluation.

Microreactor studies for efficient organic oxidation processes

Abstract Industrially important partial oxidations of hydrocarbons are frequently characterized by low conversions and yields, which are mostly related to mass and heat transfer problems. Due to the reaction conditions, such processes include also important safety risks and are still not sufficiently understood. To study the influence of the process parameters on the product selectivity, a lab facility including a silicon-coated micro reactor of stainless steel has been developed and constructed. Due to its modular construction (e.g. replaceable capillary), it permits for the first time to perform catalysed and non-catalysed oxidations of hydrocarbons with oxygen as a two-phase process in a capillary reactor in wide ranges of residence times (some minutes to 24 h), temperatures and pressures. As an example, the oxidation of isobutane to tertiary butyl hydroperoxide (TBHP) has been studied. The reaction has been investigated for the first time as a Taylor-Flow process in a micro reactor at different reaction conditions as a prerequisite to enhance the space-time yield of the process. The advantages of micro reactors are the high surface-to-volume ratio ensuring efficient heat transfer and the improved, nearly inherent, safety. These permit investigating yet unexplored process windows, for instance within the explosive region of a reaction mixture. The reaction has been studied for varying flow rates, temperature, pressure and the molar ratio of the starting products using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments, the selectivity of the reaction products and the conversion of the reaction have been studied by sampling and analysing the reaction by GC/ MS. The use of TBHP as initiator increased the selectivity of the reaction for the target product TBHP. TBHP as initiator yields a better selectivity since at high temperatures, which are common for DTBP, the formation of propanone already becomes important and favours the decomposition of TBHP. The replacement of the initiator diluent water by decane resulted in a faster reaction and the highest autocatalytic isobutane conversion (˜18%) obtained ever for this reaction in a micro reactor.