Isopentane Yield Research Articles

A novel synthesis of highly active and highly stable non-noble-nickel-modified persulfated Al2O3@ZrO2 core-shell catalysts for n-pentane isomerization

The non-noble metal modified sulfated zirconia was found easy to deactivate. Herein, highly active and highly stable non-noble core-shell Ni-S2O82−/Al2O3@ZrO2 catalysts (Ni-SA@Z-x, x = Al content in wt%) have been successfully prepared and investigated for n-pentane isomerization. The results showed that the core-shell Ni-SA@Z-30 provided a sustained high isopentane yield (63.1%) with little or no deactivation within 5000 min at a mild reaction pressure of 2.0 MPa, which can be attributed to the following factors: (i) carbon deposition was greatly suppressed by the large pore size and huge pore volume; (ii) the loss of sulfur entities was suppressed because the small and highly dispersed tetragonal ZrO2 particles can bond with the S species strongly; (iii) strong Brønsted acidity can be maintained well after the isomerization. The pore structures and acid nature of the core-shell Ni-SA@Z-x are entirely different from those of the normal structure Ni-S2O82−/ZrO2-Al2O3, even though the Al content and the compositions of the individual components are the same. The Al2O3 cores endow the catalysts with high internal surface area and high mechanical strength. Meanwhile, the ZrO2 shell, which consists of more and smaller tetragonal ZrO2 particles because of the large surface area of the Al2O3 core, promotes the formation of more stable sulfur species and stronger binding sites.

A novel method for the synthesis of highly stable nickel-modified sulfated zirconia catalysts for n-pentane isomerization

A highly stable Ni modified sulfated zirconia catalyst was prepared by two different methods and used for n-pentane isomerization. The results showed that compared with the catalyst prepared by the sol-gel method, the catalyst prepared by the hydrothermal method showed higher surface area, larger pore size, smaller crystallite size of tetragonal ZrO2, more stable S-containing adsorbed species and a high isopentane yield. In particular, the Ni−/S2O82−-ZrO2–Al2O3, which was prepared by the hydrothermal method (Ni/SZA-R), provided a sustainable high isopentane yield (ca. 68%) with a slight deactivation (15%) only within 50h of continuous reaction. This result was ascribed to the catalyst's larger mean pore size and the increased concentration of more stable S-containing species formed compared to the catalyst prepared by the sol-gel method. The stability behavior of this Ni/SZA-R catalyst in terms of isopentane yield vs time appears by far larger (increase by a factor of ~ 2–15) compared to other non noble metal modified sulfated zirconia-based catalysts reported in the open literature.

Effect of Preparation Conditions on the n-Pentane Isomerisation Performance of Pt-S2O82–/ZrO2–Al2O3 Catalysts Prepared by the Microemulsion Method

Pt-promoted S2O82–/ZrO2–Al2O3 (SZA) catalysts were successfully prepared by the microemulsion (Pt-SZA-M) and impregnation (Pt-SZA-I) methods. The effects of the preparation parameters (surfactant-to-oil ratio, surfactant-to-cosurfactant ratio, types of cosurfactant and oil phase, etc.) on the catalytic activity of Pt-SZA-M catalysts in the isomerisation of n-pentane were investigated. The results showed that the optimal catalyst preparation conditions were: a cetyltrimethylammonium bromide (CTAB)/ n-butanol mass ratio of 4:6, a (CTAB + n-butanol)/cyclohexane mass ratio of 3:7, a content of H2PtCl6 solution in microemulsion of 3.6 wt% and a N2H5OH/H2PtCl6 molar ratio of 25:1. A comparison of the isopentane yield for Pt-SZA-M with that for Pt-SZA-I was also performed. The results showed that the microemulsion method led to smaller and more uniform Pt particles (4.5 nm) on the SZA. In comparison with Pt-SZA-I, the isopentane yield for Pt-SZA-M was increased by 13.5% at 180 °C, showing the catalytic performance of Pt-SZA-M at lower temperature was improved significantly. At a reaction temperature of 230 °C, a pressure of 2.0 MPa, a hydrogen/ n-pentane molar ratio of 4:1 and a weight hourly space velocity of 1.0 h−1, the yield of isopentane for Pt-SZA-M reached 60.8%.

The Effect of Zinc Content on n-Pentane Isomerisation Over Zn–S2O82–/ZrO2–Al2O3 Catalyst

A number of Zn–S2O82–/ZrO2–Al2O3 (Zn( x)–SZA) catalysts with different Zn mass fractions were synthesised and characterised by using X-ray diffraction, the Brunauer–Emmett–Teller method, and H2 temperature-programmed reduction. The structure and isomerisation performance of Zn( x)–SZA catalysts were studied using n-pentane as a probe reaction. The results showed that a pure tetragonal ZrO2 phase was formed on Zn( x)–SZA, and the ZrO2 crystallite sizes of the tetragonal phase increased in the order: Zn(0.5)–SZA < Zn(1.0)–SZA < Zn(1.5)–SZA < Zn(2.0)–SZA < SZA. Zn can strengthen the interaction between persulfate ions and the support, promote the formation of stronger acidity, lead to a better dispersion of sulfate ions on the surface, and improve the redox performance of the catalysts. The Zn(1.0)–SZA catalyst exhibited the best catalytic activity for n-pentane isomerisation. At a temperature of 170 °C, a reaction pressure of 2.0 MPa, a molar H2/ n-pentane ratio of 4:1, and a weight hourly space velocity of 1.0 h−1, the isopentane yield reached 58.0%.

Comparison of Ni-S2O82–/ZrO2–Al2O3 Catalysts prepared by Microemulsion and Impregnation Methods and their Performance for Isomerisation

Bifunctional Ni-S2O82–/ZrO2–Al2O3 (Ni-SSZA) solid superacid catalysts were prepared by microemulsion (Ni-SSZA-M) and impregnation (Ni-SSZA-I) methods and their performance for n-pentane isomerisation was studied. The catalysts were characterised by BET, XPS, XRD, FTIR, Py–FTIR, TPR, TEM and CO uptake. The results show that, compared with the Ni-SSZA-I catalyst, the Ni-SSZA-M catalyst shows smaller and more uniform Ni particles, higher surface area, smaller crystallite size of tetragonal ZrO2, more metal active sites and stronger acidity. The activity test indicated that loading Ni by the microemulsion method can significantly improve the isomerisation activity of the catalyst at lower reaction temperatures. In comparison with the Ni-SSZA-I catalyst, the isopentane yield for Ni-SSZA-M was improved by 11.6% and the optimum temperature was decreased by 60 °C.

Effect of calcination temperature of La- and Ni-promoted S2O82–/ZrO2–Al2O3 catalysts on the isomerisation of n-pentane

A series of bimetal La- and Ni-promoted S2O82–/ZrO2–Al2O3 (SZA) catalysts were prepared at different calcination temperatures. The effect of calcination temperature on the characteristics and performance of La-Ni-S2O82–/ZrO2–Al2O3 (La-Ni-SZA) catalysts towards the n-pentane isomerisation reaction was determined. In order to relate the catalytic activity to their physical, chemical and textural features, the catalysts were characterised by various techniques including X-ray powder diffraction, thermogravimetric-differential thermal analysis, Fourier transform infrared spectroscopy (FTIR), FTIR spectra of adsorbed pyridine and BET specific surface area and H2 temperature-programmed reduction analyses. The results showed that tetragonal ZrO2 was the dominant phase in the calcination temperature range of 600–700 °C. The change of textural features of the catalysts results from transformation of the ZrO2 crystal phase and the collapse of the partial pore structure occurs at the high calcination temperature of 700 °C. The sulfur could be lost at calcination temperatures > 660 °C. The total acidity of the catalysts at a desorption temperature of 350 °C decreases in the order: La-Ni-SZA-650 > La-Ni-SZA-600 > La-Ni-SZA-700 > La-Ni-SZA-550. The La-Ni-SZA catalyst calcined at 650 °C had more tetragonal phase ZrO2, higher acidity, higher sulfur content, a larger BET surface area and exhibited the best catalytic performance, with the isopentane yield reaching a maximum 66.5% at a lower reaction temperature of 150 °C, with a selectivity to isopentane of 98.5%.

Isomerization of n-pentane over La-Ni-S2O82−/ZrO2-Al2O3 solid superacid catalysts: Deactivation and regeneration

A La-Ni-S2O82−/ZrO2-Al2O3 (La-Ni-SZA) catalyst was prepared and studied in the isomerization of n-pentane. The mechanisms of deactivation and methods for regeneration of the La-Ni-SZA catalyst were explored. The results revealed that the yield of isopentane using fresh La-Ni-SZA was maintained above 65% in the first 1000min. However, the yield fell sharply from 65% to 25% during the subsequent 2000min. The decline in pentane isomerization activity was slow initially, but increased significantly after 1000min. The deactivation of the La-Ni-SZA catalyst may be due to a combination of carbon deposition, loss of Brønsted acidity, removal of sulfur entities. Based on this analysis, two regeneration methods were proposed. It was found that catalytic activity of the spent catalyst could be partially recovered (58%) by calcination. Resulfating the calcined catalyst with 0.5molL−1 (NH4)2S2O8 increased the acidity significantly, especially Brønsted acidity, compared with fresh catalyst. The isopentane yield using the resulfated La-Ni-SZA was maintained at about 58%, with isopentane selectivity above 90%, during the tested 3000min. Compared with fresh catalyst, the resulfated catalyst showed sustained excellent stability, although the initial activity was slightly lower. The improved stability of the resulfated catalyst can be explained by: (1) suppression of carbon deposition to some extent; (2) formation of improved acidic nature by resulfation, favoring isomerization on acidic sites; (3) restructuring of the acid and metal sites via the calcination-resulfation procedure.

Rare earth metals modified Ni–S2O82 −/ZrO2–Al2O3 catalysts for n-pentane isomerization

The effects of adding rare earth (RE) metals, such as Ce, Yb and Pr to Ni–S2O82−/ZrO2–Al2O3 (Ni–SZA) on the structure of catalysts as well as their isomerization performance were studied. The prepared catalysts were characterized by XRD, BET, FT-IR, Py-IR, and H2-TPR. The results showed that the addition of RE metals can increase the strength and amounts of the acid sites, improve the redox properties of catalysts. The Yb–Ni-SZA catalyst showed the best redox properties, which could provide enough metallic sites. In addition, it provided the largest amounts of weak and moderately strong acid sites. Among RE metals modified Ni-SZA catalyst, Yb-Ni-SZA exhibited the highest isopentane yield of 61.7% at 160°C. The optimum isomerization catalytic performance of the catalysts decreased in the order of Yb-Ni-SZA>Pr-Ni-SZA>Ni-SZA>Ce-Ni-SZA.

Acid strength of Ni–S2O 8 2− /ZrO2 catalyst and its catalytic activity for n-pentane isomerization

A series of bifunctional Ni–S2O82−/ZrO2 (Nix-SSZ-T) catalysts with different Ni mass fraction (x, %) and calcintion temperature (T, °C) were prepared by impregnation method. The catalysts were characterized by XRD, FTIR, and py-FTIR. The effects of Ni content and calcination temperature on the acidic property and isomerization performance of catalyst were investigated using n-pentane isomerization as a probe reaction. The results show that the acidity of Nix-SSZ-T catalysts mainly derives from L acid. The addition of a suitable amount of Ni can induce the formation of more acid sites and in turn enhance the isomerization performance of Nix-SSZ-T catalyst. With increasing the calcination temperature from 550 to 700°C, B acid strength of catalyst weakens gradually, while the L acid strength increases first and then decreases. The Nix-SSZ-T catalyst with Ni content of 1 wt % and calcination temperature of 650°C exhibits the best isomerization performance. At reaction temperature of 230°C, pressure of 2. 0 MPa hydrogen /hydrocarbon molar ratio of 4: 1, and weight hourly space velocity (WHSV) of 1.0 h−1 the isopentane yield reaches 57.0%.

The effect of Zn–Fe modified S2O8 2−/ZrO2–Al2O3 catalyst for n-pentane hydroisomerization

Fe–Zn-doped S2O82−/ZrO2–Al2O3 (SZA) catalysts were synthesized and characterized by using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, Fourier transform infrared (FT–IR) measurements, hydrogen temperature-programmed reduction (H2–TPR), and pyridine infrared (Py–IR) measurements. The effects of Fe and Zn on the structure and isomerization performance of SZA were studied using n-pentane as a probe reaction. Results showed that all of the samples show the pure peaks of tetragonal ZrO2. The addition of Zn can improve the redox performance of the catalysts, while Fe can lead to a better dispersion of sulfate ions on the surface of the catalysts. As a result, an improvement in the redox performance of the Zn–Fe–SZA catalyst was observed. The Zn or Fe can increase mainly Lewis acidity of the SZA, and the total acidity of samples decrease in the following order: Zn–Fe–SZA > Zn–SZA > Fe–SZA > SZA. The Fe–Zn–SZA catalyst exhibits the best catalytic activity for n-pentane isomerization. The isopentane yield of the Zn–Fe–SZA catalyst reaches 67.2 % at 443 K, which is an increase of 44.2 % when compared with that found for SZA at its optimum temperature of 573 K.

Effect of Pd content on the isomerization performance over Pd-S2O8 2−/ZrO2-Al2O3 catalyst

The effect of Pd content on the performance of the Pd-S2O8 2−/ZrO2-Al2O3 solid superacid catalyst was studied using n-pentane isomerization as a probe reaction, and the catalysts were characterized by FTIR, BET, TG-DTA, H2-TPR, NH3-TPD and XPS. The results showed that an appropriate amount of Pd could promote the formation of acid sites, enhance the acidity of catalyst, improve the redox properties of the catalyst, and delay the decomposition of S2O8 2− effectively. The Pd-S2O8 2−/ZrO2-Al2O3 catalyst with 0.05 wt % Pd exhibited the best catalytic activity for n-pentane isomerization. At the reaction temperature of 200 °C, reaction pressure of 2.0 MPa, weight hourly space velocity of 1.0 h−1, H2/n-pentane molar ration of 4.0, the n-pentane conversion, iso-pentane selectivity and yield reached 61.1, 96.7, and 59.1 %, respectively, the isopentane yield with the Pd-S2O8 2−/ZrO2-Al2O3 increased by 39.1 % compared to S2O8 2−/ZrO2-Al2O3, and no obvious catalyst deactivation was observed within 100 h.

Effect of Al Content on the Isomerization Performance of Solid Superacid Pd–S2O82−/ZrO2 –Al2O3

The effect of Al content on the performance of the Pd–S2O82−/ZrO2–Al2O3 solid superacid catalyst was studied using n-pentane isomerization as a probe reaction. The catalysts were also characterized by X-ray diffraction (XRD), Fourier transform Infrared (FTIR), specific surface area measurements (BET), thermogravimetry–differential thermal analysis (TG–DTA), H2-temperature programmed reduction (TPR) and NH3 temperature-programmed desorption (NH3-TPD). The Pd–S2O82−/ZrO2–Al2O3 catalyst made from Al2O3 mass fraction of 2.5% exhibited the best performance and its catalytic activity increased by 44.0% compared with Pd–S2O82−/ZrO2. The isopentane yield reached 64.3% at a temperature of 238°C, a reaction pressure of 2.0MPa, a space velocity of 1.0h−1 and a H2/n-pentane molar ratio of 4.0. No obvious catalyst deactivation was observed within 100h.

La–Ni modified S2O82−/ZrO2-Al2O3 catalyst in n-pentane hydroisomerization

The La–Ni–S2O82−/ZrO2–Al2O3 (La–Ni–SZA) was prepared and the effect of La and Ni on the structure and isomerization performance of catalyst was investigated. The addition of La could lead to a higher dispersion of metal and more acid sites. The addition of Ni can promote redox performance of catalyst and formation of Lewis acid sites. The highest isopentane yield of 66.5% at a lower reaction temperature of La–Ni–SZA can be attributed to the synergistic interaction between La and Ni.

Ir/Pt-HZSM5 for n-pentane isomerization: Effect of Si/Al ratio and reaction optimization by response surface methodology

The effects of Si/Al ratio on the properties of Ir/Pt-HZSM5 and n-pentane isomerization were studied. XRD results indicated that the increasing Si/Al ratio increased the percentage crystallinity of the catalysts, whereas, FTIR results showed that the increasing Si/Al ratio decreased the number of strong Brönsted and Lewis acid sites which led to decrease the catalytic activity towards n-pentane isomerization. Ir/Pt-HZSM5 with Si/Al ratio of 23 showed highest activity towards n-pentane isomerization, and the operating condition was further optimized by using response surface methodology (RSM). The RSM experiments were designed by using face-centered central composite design (FCCCD) by applying 24 factorial points, 8 axial points and 2 replicates, with three response variables (n-pentane conversion, isopentane selectivity and isopentane yield). The Pareto chart indicated that the reaction temperature have largest effect for all responses. The optimum condition of n-pentane isomerization over Ir/Pt-HZSM5 was at treatment temperature of 723K, treatment time of 6h, reaction temperature of 548K and F/W of 500mlg−1min−1 in which the predicted value for the n-pentane conversion, isopentane selectivity and isopentane yield was 63.0%, 98.2% and 61.9%, respectively.

Catalytic activity of Pt and Pd catalysts supported on HWP/HMS in the selective hydroisomerization of n-pentane. Effect of reaction temperature

Non order structure type HMS was synthesized through a S°I° mechanism. These solids were modified by incorporation of acid (30wt.% of tungstophosphoric acid) and metallic sites (1% of metal: Pt or Pd), and tested in the hydroisomerization reaction of n-pentane. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption and desorption, chemisorption of H2, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). For the catalyst containing Pt, the effect of reaction temperature was investigated in the range of 200–400°C, the optimal catalytic activity was reached at 350°C. The Pt catalyst showed higher conversion, iso-pentane yield and catalytic stability than its Pd counterpart.

HYDROISOMERIZATION OF 1-PENTENE TO ISO-PENTANE IN A SINGLE REACTOR

It has been shown that hydroisomerization of an olefinic feed to an iso-paraffinic product can be performed in a single reactor using a platinum on mordenite (Pt-MOR) zeolite catalyst. This conversion finds application in a Fischer-Tropsch refinery where the syncrude is rich in olefins and conventional hydroisomerization would require hydrogenation of the feed as a feed pretreatment step. In order to demonstrate that the proposed process configuration is viable from a catalysis point of view, the hydroisomerization of 1-pentene over Pt-MOR has been investigated experimentally in the range 200°–270°C, 2 MPa, WHSV 1–3 h−1, and H2:1-pentene molar ratio of 3:1–5:1. The catalyst was stable during one week of continuous operation. The highest iso-pentane yield (69%) was obtained at 250°C. Side reactions (dimerization and cracking) increased with increasing temperature, decreasing H2:1-pentene ratio, and increasing space velocity.

Molecular Spectroscopy of Oxide Catalyst Surfaces

The La –Ni–S2O82−/ZrO2 –Al2O3 (La–Ni–SZA) was prepared and the effect of La and Ni on the structure and isomerization performance of catalyst was investigated. The addition of La could lead to a higher dispersion of metal and more acid sites. The addition of Ni can promote redox performance of catalyst and formation of Lewis acid sites. The highest isopentane yield of 66.5% at a lower reaction temperature of La–Ni–SZA can be attributed to the synergistic interaction between La and Ni.