N-butane Isomerization Research Articles

Effect of hydrothermal treatment on the structure and acid properties of the surface of molded gamma-aluminum oxide

Mechanism of the hydrothermal modification of gamma-aluminum oxide was studied. A set of physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks are dispersed, which leads, at a certain treatment duration, to an increase in the specific surface area. In this case, the content of acid centers also increases according to the results of a temperature-programmed desorption of ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes.

Deactivation of industrial alumina catalyst for the skeletal isomerization of n-butenes

The reasons for deactivation of alumina catalyst during the skeletal isomerization of n-butenes, reducing conversion from 31 to 26%, are investigated. It is shown that contamination with metal Fe and Mg microimpurities lowers n-butene conversion in total by approximately 2.5%. The catalyst’s activity can be restored by washing out metal microimpurities. Water vapor and feedstock pipelines turn out to be the source of metal impurities. The δ-modification of alumina accumulates during catalyst operation, reducing n-butene conversion by ∼3 abs % and creating an irreversible type of deactivation. The drop in the temperature of phase transition in the presence of Fe and Mg microimpurities is one possible reason for the partial phase transition at a temperature lower than 600°C. It is shown that the accumulation of microimpurities and the alumina δ-phase reduces the number of acid sites and thus the efficiency of alumina catalytic conversion. To prolong the catalyst’s operational life, it is recommended that metal impurities be captured from the vapor-feedstock flow by installing a protective layer of a macroporous material with a developed surface inert to the butane fraction upstream of the catalyst.

Sulfated Zirconia-catalyzed Alkylation of Phenol with Camphene and Isomerization of n-butane

Sulfated zirconia modified with polyvalent cations is capable of catalyzing alkylation of phenol with camphene and isomerization of utane into isobutane.

Effect of different acidity modifications on the activity and selectivity on H-ZSM5 zeolites in n-butene isomerization

H-ZSM-5 was modified by silylation [tetraethylorthosilicate (TEOS) and triaminopropyltriethoxysilane], alkali (NaOH), acid (HCl) and ammoniumhexafluorosilicate (AHFS) treatments. The parent and modified zeolite forms were tested in n-butene isomerization. Modifications affected total acidities, the strength of the acid sites, pore sizes and surface areas of the H-ZSM-5 differently. The modifications decreased the conversion obtained by the parent catalyst. TEOS and alkali modifications did not promote formation of isobutene. Pre-alkali treatment before acid treatment increased selectivity to isobutene from 56.0 to 66.7 %, while conversion changed a little, it dropped from 52 to 50 %. AHFS modification provided the highest enhancement in selectivity to isobutene (87.5 %) for which n-butene conversion was dropped by about 10 % compared to H-ZSM-5. This was attributed to a slight modification of the pore size and to the reduction in strong and weak acid sites and generation of new Lewis acid sites.

Effect of crystal size on the skeletal isomerization of n-butene over H-FER zeolite

Three H-FER zeolites with different crystal sizes were successfully obtained via the conventional static hydrothermal method by introducing an aging step to the synthesis procedure. The samples were characterized by XRD, SEM, TEM, NH3-TPD, XRF, and BET analyses. While the number of acid sites decreased with decreasing crystal sizes, the H-FER zeolite with submicron-scale crystal sizes exhibited not only high activity but also good stability during the skeletal isomerization of n-butene. These results are attributed to the large external surface area and abundance of mesopores in the sample. The resulting isobutylene yield reached approximately 45 wt%. The concept of pore mouth catalysis over H-FER zeolites for the reaction was also supported by catalytic performance varied with crystal size.

The Preparation of Modified ZSM - 35 and its Catalysis Effect Analysis on N-Butene Isomerization

In order to study the effect that the modified ZSM - 35 as a catalyst brings to n-butene isomerization catalysis. In this paper, by considering the performance analysis brought by different silica alumina ratio, reaction temperature, concentration of nitrogen and macro porous silica gel embellish acting on butene isomerization reaction of modified ZSM - 35 molecular sieve catalyst , Al2O3 samples being "15" shows better performance; Adding appropriate amount of silicon carbide catalyst or modified silicone can further improve the selectivity of butene; Nitrogen dilution has certain help in improving butene isomerization reaction performance.

Isomerization of n-butane over Pd–SO4/ZrO2 catalyst: Prospects for commercial application

Increase in productivity of the refineries and improvement the fuel quality demands to engage isobutane as a key feedstock for producing both alkylates and oxygenated additives. Substantial growth of isobutane output via isomerization of n-butane poses a real technological challenge. The goal of this study is to investigate performance of Pd promoted sulfated zirconia catalysts (Pd–SZ) in n-butane isomerization. The physical–chemical characteristics of various anion-modified zirconia catalysts (XRD and IR spectra, BET surface) are presented. It was observed that Lewis acid sites of medium and strong strength and two types of Brönsted acid sites exist. Approximately 90–97% of zirconia is in tetragonal phase.The influence of parameters on conversion of n-butane and selectivity towards isobutane was investigated by varying the temperature (90–290°C), pressure (15–26bar), WHSV (0.5–5h−1), and molar ratio H2/C4 (0.08–3). Mainly, temperature and H2/C4 ratio are responsible for increasing the effectiveness of the process. At H2/С4=0.08–0.3 the apparent activity of Pd–SZ catalyst was high enough to reach the equilibrium conversion of n-butane to isobutane at 140°С value, that is, ∼65%. The best results were obtained on Pd–SZ granules in the form of 2mm trilobe. Water impact and the catalyst lifetime were studied in the pilot setup. Endurance testing of Pd–SZ catalyst in course of 90h showed its sustained operation at H2O concentration up to 20ppm without loss of activity.The estimated process specifications on Pd–SZ catalyst were compared to a conventional process; potential benefits of making use Pd–SZ catalyst are emphasized and discussed.

N-Butane Isomerization over Silica-Supported Heteropolyacids: Study of Some Parameters

Isomerization of n-butane was studied on silica-supported heteropolyacids. The activity depends strongly on the solvent used for the preparation and on the polyoxometalate loading. This behavior was explained by different proportions of isolated and bulk heteropolyacids. Silicotungstic acid is inherently more selective than phosphotungstic acid. In presence of platinum and hydrogen the catalysts are stable and highly selective (more than 97%) to isobutane. A study as a function of temperature shows that there is an optimal temperature for performing the reaction.

An aluminum promoted cesium salt of 12-tungstophosphoric acid: a catalyst for butane isomerization

Aluminum doped cesium salts of tungstophosphoric acid, AlxCs2.5–3xH0.5PW12O40 (x = 0.05, 0.1 and 0.15), were prepared via a solid state synthesis method and their catalytic activity in n-butane isomerization reaction was tested using the 13C MAS NMR technique and 1-13C-n-butane as the reactant. All AlxCs2.5–3xH0.5PW12O40 catalysts show higher catalytic activity than Cs2.5H0.5PW12O40. Among them, Al0.1Cs2.2H0.5PW12O40 exhibits the best performance. The MAS NMR technique was further employed to characterize the acidity of the catalysts using trimethylphosphine and 2-13C-acetone as the basic probe molecules. Al0.1Cs2.2H0.5PW12O40 possesses higher Bronsted acid strength than Cs2.5H0.5PW12O40, which parallels the activity of the catalysts. For a catalyst used in n-butane isomerization reaction, to enhance its Bronsted acid strength rather than to increase its acid density is more important for improving the activity of the catalyst.

Carbon Aerogel-Supported Pt Catalysts for the Hydrogenolysis and Isomerization of n-Butane: Influence of the Carbonization Temperature of the Support and Pt Particle Size

Carbon aerogels prepared at different carbonization temperatures and with varying mesopore volumes were used as supports for Pt catalysts to study the n-C4H10/H2 reaction. Mean Pt particle size depended on the mesopore volume of the support, showing a linear decrease when the mesopore volume increased. The turnover frequency (TOF) for hydrogenolysis was much higher than for isomerization in catalysts supported on carbon aerogels obtained at 900–950 °C. However, both TOF values were similar in catalysts supported on the carbon aerogel obtained at 500 °C. TOF for hydrogenolysis and isomerization were related to the mean Pt particle size in catalysts supported on carbon aerogels obtained at 900–950 °C. In addition, both reactions showed a compensation effect between the activation energy and pre-exponential factor, indicating that they have the same intermediate, i.e., the chemisorbed dehydrogenated alkane.

Introducing sustainability assessment and selection (SAS) into chemical engineering education

Assessment of a sustainable process design centres on the three pillars of sustainability. However, satisfying all criteria is sometimes difficult. Nevertheless, it is important to have an effective and systematic tool for a concrete and justifiable decision. Introduction of such tool into chemical engineering education would be beneficial as students will encounter situations in making decision which may imply deciding on the best process design, suppliers, supply chain, etc. In light of this matter, we introduce a concept called sustainability assessment and selection (SAS) into Computer Aided Plant Design (CAPD) course at Technical University of Berlin. The idea of the methodology is to assess process designs and select one which is most sustainable. Within the framework of this course, a 1-day lecture has been conducted that touch on the methods to assess sustainable process design. It is also aimed to introduce systematic multi-criteria decision making methodology called analytic hierarchy process (AHP). A practical example in choosing n-butane isomerization process designs is illustrated. From the class evaluation we found that the response towards the idea was very promising. We believed the method would add an extra edge to the students especially in performing sustainability assessment and systematically solving multi optional problems that they may encounter in their career.

WO3 monolayer loaded on ZrO2: Property–activity relationship in n-butane isomerization evidenced by hydrogen adsorption and IR studies

The property–activity relationship of WO3 supported on ZrO2 (WZ) was evaluated in n-butane isomerization for a series of catalysts with WO3 loading ranging from 5 to 20wt% on ZrO2. The catalysts were prepared by incipient-wetness impregnation of Zr(OH)4 with an aqueous solution of (NH4)6[H2W12O40·nH2O], followed by drying and calcination at 1093K. The introduction of WO3 continuously increased the tetragonal phase of ZrO2, WO3 surface density and coverage. The specific surface area and total pore volume passed through a maximum of WO3 loading at 13wt%; this loading corresponds to 5.9WO3/nm2 and is near the theoretical monolayer-dispersed limit of WO3 on ZrO2. The IR results indicate that the presence of WO3 eroded the absorbance bands at 3738 and 3650cm−1 corresponding to bibridged and tribridged hydroxyl groups up to near the monolayer-dispersed limit of WO3. A new broad and weak band appeared, centered at 2930cm−1, indicating the presence of bulk crystalline WO3 for WO3 coverage exceeding the theoretical monolayer-dispersion limit. In addition to the band at 2930cm−1, two WO stretching bands were observed at about 1021 and 1014cm−1 for all WZ catalysts, confirming the existence of WO connected to coordinative unsaturated (cus) Zr4+ through O and to the other W through O, respectively. Pyridine adsorbed IR and NH3-TPD revealed that the presence of WO3 modified the nature and concentration of acidic sites. The highest acidity was observed with 13wt% loading WO3. The decrease in the intensity of peaks due to increasing WO3 loading was much higher on Lewis acid sites than on Brønsted acid sites. Hydrogen adsorption isotherms and the IR results for hydrogen adsorption on preadsorbed pyridine were used to evaluate the formation of active protonic acid sites from molecular hydrogen. The catalyst with 13wt% WO3 loading showed the maximum hydrogen uptake capacity and formation of protonic acid sites. These results show a direct correlation with the activity of WZ in n-butane isomerization at 573K in which 13wt% WO3 loading on ZrO2 yielded the highest amount of isobutane. It is suggested that the presence of strong Lewis acid sites on monolayer-dispersed WO3 facilitates the formation of protonic acid sites from hydrogen in the gas phase which act as active sites in n-butane isomerization. The presence of permanent Brønsted acid sites could not be directly associated with activity. In fact, no isomerization activity was observed in the absence of hydrogen.

Influence of hydrothermal treatment conditions on the structure and catalytic activity of alumina during the skeletal isomerization of n-butenes

In order to obtain an efficient alumina catalyst for skeleton isomerization of n-butenes with a high catalytic activity, we study the influence of hydrothermal treatment (HTT) of alumina systems at 150–200°C on the parameters of the crystalline and pore structure, and acid-base properties of industrial γ-Al2O3. It is shown that the HTT of aluminum hydroxide increases the sizes of microcrystallites and reduces the alumina’s specific surface area and the number of acid-base centers. This reduces the activity in the reaction of skeletal isomerization of n-butenes. HTT of the two-phase alumina-aluminum hydroxide system produces smaller crystallites of γ-Al2O3 and raises the acidity of the alumina obtained after calcination at 550°C; as a result, the catalytic activity increases. This method can be used to enhance the activity of industrial samples of alumina in the reaction of skeletal isomerization of n-butenes.

Changes in Surface Acidity of Silica-Supported Dodecatungstosilicic Acid in Relation to the Loading Amount

Changes in surface acidity of H4SiW12O40/SiO2 in relation to the loading amount were investigated by using temperature-programmed desorption (TPD) of benzonitrile (BN), BN infrared (BN-IR) spectroscopy, and test reactions, including skeletal isomerization of n-butane and double-bond shift of 1-butene. From BN-TPD profiles and BN-IR spectra, H4SiW12O40/SiO2 had medium strength Brønsted (Mid-B site) and strong Brønsted acid sites (Strong-B site) on its outermost surface, whereas there was no evidence for Lewis acid sites regardless of the loading amount. The number of Strong-B sites correlated with the catalytic activity for the skeletal isomerization of n-butane and was a maximum when the loading amount was 50 wt %. On the other hand, the number of Mid-B sites was a maximum for 30 wt % H4SiW12O40/SiO2, which had the highest activity for the double-bond shift reaction of 1-butene. Mid-B sites of H4SiW12O40/SiO2 were present in the starting H4SiW12O40, whereas the Strong-B sites formed when H4SiW12O40 was supported on SiO2. There were no Strong-B sites on H4SiW12O40/SiO2 with low loadings, including 5 and 10 wt %. Thus, it was concluded that the direct interaction of H4SiW12O40 with the surface of SiO2 caused the Strong-B sites to form in the second-layer of H4SiW12O40 exposed on the surface.

Surface characterization and catalytic activity of sulfated-hafnia promoted zirconia catalysts for n-butane isomerization

Sulfated-hafnia promoted zirconia containing various compositions of hafnia (1–10wt.%) were prepared by precipitation method in an attempt to ultimately carry n-butane isomerization reaction. The catalyst samples were calcined under dry air flow at 600°C. The structural and crystal changes were monitored by FTIR and XRD whereas the textural changes were estimated by low temperature N2 adsorption. FTIR spectroscopy has been used to characterize the hydroxyl groups and to determine the concentration of Brönsted and Lewis acid sites from pyridine adsorption. The catalytic activity, stability and selectivity of the catalyst samples were tested for n-butane isomerization at 250°C. The results reveal that the existence of a small content of hafnia increases the surface sulfate density, stabilizes the tetragonal phase of zirconia, increases the amount and strength of Brönsted acid sites and enhances the initial catalytic activity of the samples. Increasing hafnia content to 5 and 10wt.% is accompanied with the formation of hafnia monoclinic phase which causes a drastic decrease in the amount of Brönsted acid sites and the initial activity of the catalyst. The isomerization of n-butane occurred through bimolecular pathway with the formation of iso-butane, propane and pentanes as primary products. In spite of the high activity of the samples, the catalyst deactivates rapidly during the first hour of the reaction due to coke formation, retreating the catalyst at 450°C in the presence of dry air before the catalytic reaction lead to regeneration of the initial catalytic activity of the catalyst which implies that the coke formation is the main source for catalyst deactivation.

Sorption of alkanes on sulfated zirconias—Modeling of TAP response curves

The transient TAP method was applied to investigate sorption phenomena of alkanes on differently prepared sulfated zirconias to provide further explanation of different catalytic performances in the n-butane isomerization. A modified “three-zone” model was developed to describe the experimental results of a single-pulse response experiment. It allowed the extraction of the ratios of adsorption and desorption rate constants. The introduction of a second sorption center in the model is proposed to reproduce the sorption behavior for larger alkanes quantitatively better, especially in the low-temperature region. Moreover, the new model is able to reflect the heterogeneous distribution of active centers, e.g., different acidic sites in combination with surface sulfate species. Temperature dependent measurements have been performed to calculate heats of adsorption for various alkanes. The impact of these values on the catalytic properties is discussed.

Solid Synthesis of GaxCs2.5-3xH0.5PW12O40 Salts and Their Catalytic Activity in the Isomerization of n-Butane

Ga x Cs 2.5-3 x H 0.5 PW 12 O 40 ( x = 0.05, 0.10, and 0.15) salts were prepared using a solid synthesis method and they showed higher catalytic activity than that of Cs 2.5 H 0.5 PW 12 O 40 for n -butane isomerization, which possibly comes from their enhanced acid strength as a result of Ga doping. 利用室温固相法制备了一系列掺镓的钨磷酸铯盐催化剂 Ga x Cs 2.5-3 x H 0.5 PW 12 O 40 ( x = 0.05, 0.1, 0.15). 与钨磷酸铯盐相比, 掺镓的钨磷酸铯盐催化剂的结构未产生变化, 但其酸强度提高, 在正丁烷异构化反应中催化活性增强, 其中以 Ga 0.1 Cs 2.2 - H 0.5 PW 12 O 40 和 Ga 0.15 Cs 2.05 H 0.5 PW 12 O 40 最为显著. A solid synthesis method was used to prepare a series of Ga doped Cs 2.5 H 0.5 PW 12 O 40 salts and the products show enhanced acid strength leading to higher n -butane isomerization activity compared with Cs 2.5 H 0.5 PW 12 O 40 .

HZSM-5 and H-Ferrierite Acidity Modification by Silylation and Their Activities in n-Butene Isomerisation

H-ZSM5 and H-Ferrierite acidities were modified by chemical liquid deposition using tetraethylorthosilicate (TEOS), silicontetratchloride (SiCl4) and triaminopropyltriethoxysilane (3-APTES). All depositions were carried out at room temperature for deposition times of 0.5 and 1 h. Reaction tests were performed in a tubular quartz fixed bed reactor at 375°C for weight hour space velocities of 22 h-1. Surface area and pore volume of the catalysts were decreased upon modifications. The least modification of acidity was achieved by TEOS. However, SiCl4 and 3-APTES deposition modification strongly decreased the number of Bronsted and Lewis acid sites. As the effect of the modification increased, total acidity of the SiCl4 modified catalyst decreased. The catalysts were tested in isomerization of n-butene. Modification decreased the activity of the catalysts, but improvement in selectivity was observed with TEOS deposition. TEOS deposition increased the selectivity of the catalysts; for synthesized H-ZSM5 from 57.95 to 63.74 percent, for commercial H-ZSM5-C from 26.78 to 32.52 percent, and for H-FER from 63.06 to 81.23 percent. However, modification with SiCl4 and 3-APTES decreased both conversion and selectivity of the parent catalysts.

1-butene and 2-butenes production using the positional isomerization of butenes catalyzed by sulfonic acid cation exchangers

Pure 1-butene and 2-butenes can be efficiently obtained from butane-butene fractions by combining the positional isomerization of n-butenes on sulfonic acid cation exchanger catalysts with sharp distillation. At 50–60°C, an equilibrium 2-butenes: 1-butene ratio of ∼25: 1 is attained. The 2-butenes, which are comparatively high-boiling compounds, can be sufficiently completely separated from detrimental impurities (1,3-butadiene and isobutene), 1-butene, and isobutane by distillation. The back isomerization of the purified 2-butenes into 1-butene with continuous removal of the latter as distillate affords pure 1-butene at a relatively low cost.

ChemInform Abstract: Skeletal Isomerization of n-Butenes Catalyzed by Medium-Pore Zeolites and Aluminophosphates

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