Selective Hydroisomerization Research Articles

Sustainable aviation fuel – Comprehensive study on highly selective isomerization route towards HEFA based bioadditives

This paper presents the results of a biofuel production process conducted using a cutting-edge, highly selective hydroisomerization catalyst. Rapeseed oil was used as a basic raw material for the synthesis of sustainable aviation fuel. The objective was to verify the catalysts hydroisomerization activity by comparison the effectiveness of obtained biofuel using a miniature jet engine and its compliance with current standards. The developed two-stage process by Łukasiewicz - ICSO involves the conversion of rapeseed oil into a C15–C18 hydrocarbon fraction through hydrodeoxygenation and subsequent hydroisomerization using the Pt/(SAPO-11 + Al2O3) catalyst. The overall average final yield of the aviation fuel fraction (C9–C18) after 500 h of testing was (60 ± 3)% based on the initial rapeseed oil used.In comparison to 100% petrochemical JET A-1 fraction, a BIO50 blend (mixture of biocomponent and JET A-1) is characterized by a more preferable crystallization temperature (−64 °C) and a 50% lower content of aromatic compounds fulfilling all the requirements of ASTM D-7566 standard. Additionally, tests conducted on a miniature jet engine have shown, that the BIO50 mixture has a higher calorific value compared to standard petrochemical fuel, what allows to reduce the overall fuel consumption and slightly lower CO2 and NOx emissions.

Reaction pathways control of long-chain alkanes hydroisomerization and hydrocracking via tailoring the metal-acid sites intimacy

Designing a bifunctional catalyst to achieve efficient hydroisomerization of long-chain alkanes is very essential for producing high-performance fuel and lubricant base oils. Herein, a bifunctional catalyst composed of an intimate mixture of ZSM-48 zeolite and alumina binder and with platinum (Pt) metal controllably deposited on zeolite or alumina was fabricated by a strong electrostatic adsorption method. The dependence of reaction pathways of hydroisomerization and hydrocracking of n-hexadecane on the metal-acid sites intimacy was investigated. High Brønsted acid density and suitable metal-acid sites intimacy favored to promote the catalytic activity. The selectivity, hydroisomerization mechanism and hydrocracking mechanism were significantly altered by tailoring the metal-acid sites intimacy. Too large or too small metal-acid sites intimacy was conducive to inhibit the occurrence of pore-mouth mode. A linear decease of the hydroisomerization selectivity with the increase of acid steps (nas) was observed. The catalyst with nanoscale intimacy of metal-acid sites (Pt/A-48) showed the highest catalytic activity and isomer selectivity (87%) and the least acid steps (nas = 1.4). This work provides a promising approach to fabricating highly efficient and shape-selective bifunctional catalysts for selective hydroisomerization of long-chain alkanes. A reaction network was proposed over the catalysts with different metal-acid intimacy.

Tuning the Structure and Acidity of Pt/Hierarchical SSZ-32 Catalysts to Boost the Selective Hydroisomerization of n-Hexadecane

Developing highly selective and efficient bifunctional catalysts is an important issue for the hydroisomerization of long-chain n-alkanes. It is vital to tailor the balance of isomerization and cracking reactions in hydroisomerization. Herein, a bifunctional Pt/hierarchical SSZ-32 catalyst was fabricated with a sequential desilication–dealumination treatment to boost the selective hydroisomerization of n-hexadecane (C16). The pore structure and acid sites of SSZ-32 zeolite were tailored. More mesopore and Brønsted acid sites were generated, and the ratio of weak to strong Brønsted acidity (Bw/Bs) was increased by the sequential desilication–dealumination. The generated hierarchical structure had little effect on the selectivity of the reaction pathways of hydroisomerization versus cracking. The ratio of isomers/cracking products increased almost linearly with the increase in the Bw/Bs ratios. Meanwhile, the synergetic effect of the hierarchical structure and acidity regulation promoted the selectivity of monobranched i-C16 products. Therefore, the resulting Pt/SSZ-0.6AS exhibited the highest activity with a total isomer yield of 71.5% at 255 °C and the enhanced formation mechanism of monobranched isomers occurred via the pore mouth.

Modulating acid site distribution in MTT channels for controllable hydroisomerization of long-chain n-alkanes

Bifunctional catalysts with high isomerization activity and mono-branched isomer selectivity are urgently demanded for dewaxing long-chain n-alkanes. In particular, branching location of mono-branched isomer is difficult to control by current techniques. In this study, SSZ-32 zeolite with tunable distribution depth of acid sites in micropore channels is successfully prepared by ion exchange under partial template protection. Loaded with similar Pt nanoparticles, these SSZ-32 catalysts exhibit tunable activity and selectivity for hydroisomerization of n-hexadecane. Characterization results show that the adsorption model and insertion depth of n-alkane is altered by changing the distribution depth of acid sites in SSZ-32 micropore channels. When acid sites distribute in a moderate depth (∼ 4.5 nm) of the micropore channels, high yield of center-position mono-branched isomers (46.85%) is achieved, cracking reaction is significantly inhibited. The mole ratio of 6−/7−/8-methyl isomers to 2−/3-methyl isomers was increased to at least 1.3 times of the traditional catalyst with acid sites distributed throughout the micropores. The cold flow properties of lube base oils in isomerized dewaxing of Fischer-Tropsch wax are improved significantly by achieving an optimal and effective diffusion depth of reaction intermediates in the MTT micropore channels. Efficient and selective hydroisomerization of long-chain n-alkane is realized on Pt/SSZ-32 prepared by the facile partial-detemplation method.

Superior activity and isomerization selectivity in n-dodecane hydroisomerization over Ni clusters on ZSM-22 zeolite with structural defects

Developing nonnoble catalysts with high performance for the selective hydroisomerization of long-chain n-alkanes to isoalkanes that are comparable to commercial Pt catalysts is important but challenging. We report a low-loading nickel catalyst on structure-defective nanosized ZSM-22 zeolite (Ni/SD-HZSM-22, 1.0 wt%) with superior activity and isomerization selectivity for n-dodecane hydroisomerization than a commercial Pt catalyst (Pt, 0.5 wt%). The developed Ni/SD-HZSM-22 catalyst achieves 86.0–88.6 % n-dodecane conversion and 80.0–81.3 % C12-isomer yield, outperforming the conventional ZSM-22–supported Ni catalyst (Ni/HZSM-22; 50.4 % and 41.1 %, respectively) and the commercial Pt catalyst (56.8 % and 52.4 %, respectively) under the same reaction conditions, with high durability for 120 h. This is because SD-HZSM-22 with abundant surface structural defects increased available 10-membered ring openings, anchoring the small-sized Ni species and enhancing the isomerization activity and selectivity, endowing Ni/SD-HZSM-22 with good synergy between metal and acid functions.

Influences of the metal-acid proximity of Pd-SAPO-31 bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization of n-alkanes over bifunctional catalysts is an effective approach for clean fuel production. However, it is still challenging to achieve metal-acid synergy and enhance the catalytic performance by preparation of bifunctional catalysts with suitable proximity between the metal sites and Brønsted acid sites. In this work, three series of bifunctional catalysts with different metal-acid proximities are prepared simply by mixing of SAPO-31 supported Pd (xPd/S) and γ-Al2O3 powders (xPd/S-A(C)), γ-Al2O3 supported Pd samples (xPd/A) and SAPO-31 powders (xPd/A-S(M)), and the mechanical mixing of shaped xPd/A and SAPO-31 granules (xPd/A-S(F)), respectively. The physico-chemical properties and the catalytic performance for the hydroisomerization of n-hexadecane have been investigated. Compared with the xPd/S-A(C) catalysts with the closest proximity between two active sites, the xPd/A-S(M) catalysts with moderate proximity at the micrometer scale demonstrate enhanced catalytic performance in the n-hexadecane hydroisomerization at temperatures above 340 °C. Inparticular, for the 0.15Pd/A-S(M) catalyst with a loading of 0.15 wt% Pd, the highest iso‐hexadecane yield of 80.4% was obtained at the n-hexadecane conversion of 90.4%. Therefore, this work provides an effective route for the simple preparation of bifunctional catalysts with lower Pd loading and favorable metal-acid balance for highly selective hydroisomerization of long-chain n-alkanes.

Design and synthesis of Pt catalyst supported on ZSM-22 nanocrystals with increased accessible 10-MR pore mouths and acidic sites for long-chain n-alkane hydroisomerization

Abstract Synthesis of ZSM-22 with more accessible 10-membered ring (10-MR) openings is important for the preparation of highly active and selective hydroisomerization catalyst. Herein, we synthesized ZSM-22 nanocrystals (HZSM-22-NA) with more 10-MR openings and a mesoporous structure on a large scale. The prepared Pt/HZSM-22-NA catalyst (4.74 × 10−6 mol·g−1·s−1) exhibited higher intrinsic activity than conventional HZSM-22-supported Pt catalyst (Pt/HZSM-22, 2.65 × 10-6 mol·g−1·s−1) in the hydroisomerization of n-dodecane. Additionally, Pt/HZSM-22-NA had higher C12 isomer selectivity (93.5%) and lower cracking selectivity (6.5%) than Pt/HZSM-22 (79.8% and 20.2%) at the same n-dodecane conversion level (~90%). These features could be due to the change in the porous structure and acidity between HZSM-22-NA and HZSM-22. HZSM-22-NA composed of nanocrystals at c-axis could double the number of accessible 10-MR openings and acidic sites, thus enhancing the isomerization activity of Pt/HZSM-22-NA. Furthermore, the mesoporosity of HZSM-22-NA facilitated mass transfer of the intermediates and products, thus inhibiting cracking reaction.

Selective hydroisomerization of isobutane to n-butane over WO3-ZrO2 supported Ni-Cu alloy

To develop a robust and efficient non-noble metal-based catalyst for selective hydroisomerization of short-chain iso-alkanes is of great importance, yet challenging. In the present studies, a series of WO3-ZrO2 supported Ni, Cu catalysts were prepared by incipient wetness impregnation. The characterization results of Mapping, XRD, H2-TPR, TEM, and XPS confirmed the formation of Ni-Cu alloy in the bimetallic catalysts. The results of NH3-TPD indicated that the formation of Ni-Cu alloy increased the amount of medium acidic sites and total acidic sites. Isobutane hydroisomerization to n-butane was used as probe reaction to evaluate the catalytic activity. With the Cu addition up to 1 wt% over 1 wt% WO3-ZrO2, the hydrocracking reactions were inhibited, leading to both a significant increase in the selectivity to n-butane and an improved stability of the catalysts. Under the optimized condition, the yield of n-butane was 38.86% at 450 ℃, 2.5 MPa with an H2/alkane of 4:1, and a LHSV of 1 h−1 over 1Ni1Cu/WZr. The activity of 1Ni1Cu/WZr remained almost unchanged after 123 h on stream. A possible reaction scheme was also proposed for the isobutane hydroisomerization to n-butane over 1Ni1Cu/WZr.

EMM-17, a New Three-Dimensional Zeolite with Unique 11-Ring Channels and Superior Catalytic Isomerization Performance.

A new catalytically active zeolite, designated EMM-17 (ExxonMobil Material-17), with a three-dimensional (3D) 11 × 10 × 10-ring topology has been discovered from high throughput experiments while evaluating a family of new organic structure directing agents (OSDAs), 1-alkyl-4-(pyrrolidin-1-yl)pyridin-1-ium hydroxide. The framework structure was determined by model building techniques and confirmed by diffraction calculations. The EMM-17 structure is a random intergrowth of two polymorphs which have a 3D arrangement of intersecting 11 × 10 × 10-ring pores. EMM-17 is stable to calcination to remove the OSDA and can be reproducibly synthesized in the presence of fluoride using common, inexpensive reagents over a wide Si/Al range from 15 to infinity, enabling the catalyst acidity to be tailored to almost any petrochemical application. Unlike OSDAs for many new zeolite structures, the OSDAs for EMM-17 are prepared in one simple alkylation step, making EMM-17 an easy to prepare, highly accessible, catalytically active zeolite. Zeolites containing odd numbered channel sizes are rare, and this is the first confirmed example of a 3D 11-ring aluminosilicate zeolite with a pore size in between those of the commercially important 10- and 12-ring zeolites such as ZSM-5 and Zeolite-Y, respectively. Catalysts prepared from EMM-17 exhibit significantly higher activity for catalytic isomerization with no loss in selectivity than current state of the art catalysts. Catalytic isomerization of linear to branched alkanes is a critical component of commercial dewaxing, allowing for the improvement of cold flow properties of hydrocarbon fuels and lubricants through selective hydroisomerization of normal paraffins.

Synthesis and Characterization of Iron-Substituted ZSM-23 Zeolite Catalysts with Highly Selective Hydroisomerization of n-Hexadecane

A series of Fe-substituted ZSM-23 samples with different Fe/(Fe + Al) ratios were synthesized. Combined characterization by Fourier transform infrared spectroscopic, ESR, and X-ray photoelectron sp...

Hydroisomerization of n-hexadecane: remarkable selectivity of mesoporous silica post-synthetically modified with aluminum

Post-synthetic aluminum grafting is employed to synthesize highly selective hydroisomerization catalyst and to demonstrate the effect of acid strength and density, catalyst microstructure, and platinum nanoparticle size on reaction rate and selectivity.

Improvement of selectivity from lipid to jet fuel by rational integration of feedstock properties and catalytic strategy

A high yield jet fuel production process by integration of rational feedstock selection and selective hydro-isomerization was proposed and reported in this paper. A Pt/ZSM-12 catalyst was found to be an effective catalyst for the conversion of n-C15 paraffin into multi-branched isomers and mono-branched isomers which satisfied the jet fuel specification. Based on this finding, by integration of feedstock selection, oxygen removing mechanism control and selective hydro-isomerization, a very high weight yield (60%) of algal lipid to jet fuel can be obtained. The obtained jet fuel satisfied the specification of ASTM 7566 standard. Such high jet fuel yield can obviously improve the economics of jet fuel production technology.

IZM-2: A promising new zeolite for the selective hydroisomerization of long-chain n-alkanes

IZM-2 (IFPEn Zeolitic Material number 2) is an aluminosilicate zeolite with unknown structure. The synthesis is performed using 1,6-bis(methylpiperidinium)hexyl dibromide template. According to SEM and TEM, IZM-2 particles consist of intergrowths of 20–60nm nanocrystals of various orientations. The nitrogen adsorption isotherm is characteristic of a nanosize microporous material. Characterization of the pore architecture using m-xylene isomerization and disproportionation and n-decane isomerization-hydrocracking test reaction suggests the presence of two types of pores of different diameter. The catalytic fingerprints of 10-membered ring pores are observed and concluded to be present next to wider pores, tentatively qualified as 12-membered ring pores. Pt/IZM-2 was evaluated in the hydroisomerization of n-hexadecane. Pt/IZM-2 is an excellent hydroisomerization catalyst especially suited for formation of multi-branched skeletal isomers. IZM-2 is a valuable addition to the family of 10-membered ring zeolites and may find application in hydroisomerization processes for selective hydroisomerization of long-chain n-alkanes.

Selective hydroisomerization of n-dodecane over platinum supported on zeolites

In this study, in order to develop catalysts for the selective isomerization of higher paraffin, the hydroisomerization reaction of n-dodecane was performed as a model reaction. Pt/ZSM-48, Pt/HZSM-5, Pt/HY, and Pt/SAPO-11 were examined for the selective hydroisomerization of n-dodecane. The catalysts were characterized via X-ray powder diffraction, N2 adsorption, and the temperature-programmed desorption of ammonia. Among the catalysts studied, the Pt/HZSM-48 catalyst exhibited the best isomerization selectivity in the hydroisomerization reaction of n-dodecane, which is attributed to the moderate acid sites and medium-sized pores present in the HZSM-48. The highest iso-dodecane yield was obtained at a reaction temperature of 280 °C in the Pt/HZSM-48 catalyst. The optimal selectivity of the n-dodecane hydroisomerization over the Pt/SAPO-11 catalyst was obtained at approximately 300 °C, which was slightly higher than that of the Pt/HZSM-48 catalyst.

Hydroisomerization of benzene-containing gasoline fractions on a Pt/SO 4 2− -ZrO2-Al2O3 catalyst: II. Effect of chemical composition on acidic and hydrogenating and the occurrence of model isomerization reactions

The acidic and hydrogenating of Pt/SO 4 2− -ZrO2-Al2O3 samples containing from 18.8 to 67.8 wt % Al2O3 as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of n-heptane decreased with the concentration of Al2O3; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al2O3. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached on the above catalyst sample. This can be explained by lower concentrations of Lewis and Bronsted acid sites in the Pt/SO 4 2− -ZrO2-Al2O3 system, as compared with those in Pt/SO 4 2− -ZrO2. The experimental results allowed us to make a preliminary conclusion that the Pt/SO 4 2− -ZrO2-Al2O3 catalyst whose support contains 67.8 wt % Al2O3 is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically favorable process temperature range of 250–300°C.

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.

Fischer-Tropsch Waxes UpgradingviaHydrocracking and Selective Hydroisomerization

In recent years, the production of hydrocarbon cuts from various sources via the Fischer-Tropsch process has lived a renewed interest. Paraffinic cuts produced via the Fischer-Tropsch reaction can be upgraded either to liquid fuels (middle distillates) or to lubricant base oil of high quality. The first kind of upgrading involves the use of a hydrocracking catalyst whereas for the second kind of upgrading selective hydroisomerization catalysts can be selected. Both catalysts are bifunctional and contain an hydrogenation/dehydrogenation function and an acidic function; however, it is shown that depending of the kind of upgrading needed, the acidic function has to fulfill various requirements. The first part of this article is a short review dealing with long chain n-paraffin hydrocracking mechanisms and catalysts. Specificities of Fischer-Tropsch feedstocks compared to conventional ones as well as the potential impact of oxygenate compounds on the hydrocracking catalysts are underlined. The second part of this article is devoted to the selective hydroisomerization mechanisms and catalysts. It is shown that the topology of the solid acid porosity is a key factor for governing the selectivity of the catalyst towards hydroisomerization.

Selective hydroisomerization of n-pentane to isopentane over highly dispersed Pd-H4SiW12O40/SiO2

Abstract Pd-H4SiW12O40 supported on SiO2 with different loadings of H4SiW12O40 were systematically characterized by X-ray diffractometry (XRD), infrared (IR) spectroscopy, and NH3-temperature programmed desorption (TPD) and benzonitrile adsorption analyses. X-ray diffraction and infrared spectroscopy revealed that very few H4SiW12O40 crystallites formed at less than 20 wt.% loading and that the Keggin structure was retained for all these catalysts. The density of acid sites on the top surface of catalysts determined by benzonitrile adsorption proved the average number of H4SiW12O40 layers on SiO2 to be 2.2, 2.6 and 4.0 at 10, 20 and 40 wt.% acid loading, respectively. NH3 temperature programmed desorption showed that the acid strength increased markedly with the loading of H4SiW12O40, attributed to suppressed interactions between the protons of H4SiW12O40 and the OH groups on SiO2. The selectivity to isopentane in skeletal isomerization of n-pentane was found to be highly sensitive to the loading of H4SiW12O40, decreasing with increasing load, associated with the change in acid strength by the supporting on SiO2. A catalyst with the composition 1 wt.% Pd-20 wt.% H4SiW12O40 on SiO2 exhibited very high selectivity (99.1%) and high activity.

“Coke” molecules trapped in the micropores of zeolites as active species in hydrocarbon transformations

The formation in the channels or cages of zeolites of heavy side products (generally called “coke”) is often responsible for their deactivation owing to poisoning of active sites and/or to pore blockage. However, these coke molecules trapped in the zeolite micropores being relatively simple, are not generally inert with respect to the reactants or intermediates of the desired reactions and, hence can significantly affect the activity and selectivity. This participation in catalytic reactions of the coke molecules trapped in the zeolite micropores is shown here in several examples carried out in liquid or in gas phase, with large, medium or small pore molecular sieves: (i) isopropylation of naphthalene and alkylation of toluene with long chain n-alkenes over HFAU and HBEA zeolites; (ii) selective skeletal isomerization of n-butenes over HFER; (iii) selective hydroisomerization of long chain n-alkanes over PtHTON; (iv) selective methanol conversion into light alkenes over SAPO 34.

99/01900 Molecular sieve-based catalyst and process for the selective hydroisomerization of long straight chain and/or branched chain paraffins using this catalyst: Marcilly, C. et al. Eur. Pat. Appl. EP 863,198, (Cl. C10G45/64), 9 Sep 1998, FR Appl. 97/2,598, 5 Mar 1997, 9 pp. (In French)

99/01900 Molecular sieve-based catalyst and process for the selective hydroisomerization of long straight chain and/or branched chain paraffins using this catalyst: Marcilly, C. et al. Eur. Pat. Appl. EP 863,198, (Cl. C10G45/64), 9 Sep 1998, FR Appl. 97/2,598, 5 Mar 1997, 9 pp. (In French)