Pentane Isomerization Research Articles

Selective skeletal isomerization of alkanes over partially reduced MoO3

The surface area and the pentane isomerization activity of Pt/MoO3 were enlarged by H2 reduction. The enlargements was observed only when the reduction proceeded through the formation of hydrogen molybdenum bronze, HxMoO3. The catalytic activities of H2-reduced MoO3 with different noble metals for pentane isomerization and 2-propanol dehydration depended on the ability of noble metal to produce the HxMoO3 phases. H2-reduced Pt/MoO3 was more active for pentane isomerization than Pt/Hβ, and its activity was comparable to that of Pt/HZSM-5. In heptane isomerization, H2-reduced Pt/MoO3 exhibited a lower activity than Pt/Hβ, although heptane was isomerized very selectively. Strong adsorption of heptane onto H2-reduced Pt/MoO3 is likely to be a reason for its lower heptane isomerization activity.

N-Pentane isomerization over promoted SZ/MCM-41 catalysts

With metal sulfate as the precursor, the catalysts of sulfated zirconia on MCM-41, Al- and Ga-promoted sulfated zirconia on MCM-41 (named as SZ/MCM-41, ASZ/MCM-41 and GSZ/MCM-41, respectively) were prepared by direct dispersion in the as-synthesized MCM-41 materials, followed by thermal decomposition. The catalysts were characterized with various techniques such as XRD, FTIR, N 2 adsorption, NH 3-TPD, DRIFT, and TPR-MS. The ordered porous structure was still maintained in the catalysts. The addition of promoters helps to retard the phase transformation of ZrO 2 from tetragonal phase to monoclinic phase. Isomerization of n-pentane was investigated over the catalysts. In comparison to SZ/MCM-41, both promoted catalysts showed much improved catalytic activity and selectivity for isomerization of n-pentane. Moreover, the catalytical activities of both promoted catalysts for pentane isomerization remained steady over the period of 180 min while the activities of the unpromoted catalyst decreased in <120 min. Characterization of acidity showed no significant difference in strength distributions of the acid sites over the catalysts. The nature of acid sites in SZ/MCM-41 was affected by the presence of aluminum, but not affected by the presence of gallium. On the other hand, TPR study shows sulfur on GSZ/MCM-41 is much easier to reduce than SZ/MCM-41 and ASZ/MCM-41. The presence of gallium improved the redox capability provided by the sulfate ions in GSZ/MCM-41 catalyst. The causes for the promotion effects of Ga and Al are discussed.

Amorphous titanium hydrogenphosphate?an inorganic sorbent and a catalyst

Amorphous titanium hydrogenphosphate, originally prepared to act as an inorganic sorbent superior for K+ and other alkaline metal ions of certain size, proved to be also an active catalyst in alcohol dehydration. Its activity was tested in cyclohexanol, methanol, and pentanol conversions. The reactions were selective and thus cyclohexene was practically the only product of cyclohexanol dehydration, methanol gave dimethyl ether (DME) as the main product and pentanol yielded pentene isomers, the mutual ratios of which depended on temperature and contact times. Characteristically, the studied catalysts acquired their high activity only after a period of work at temperatures higher than 275 °C, the temperature of an endothermic transition observed in DTA. After the catalyst had been activated, it retained its activity even while working at lower temperatures, but lost it upon staying at room temperature for longer times. Most probably, these changes are related to the increase in the interlayer distance and the insertion of water and alcohol, making thus the inner acidic sites available for the reaction.

Anomalous diffusion of linear and branched pentanes within zeolite NaY

Molecular dynamics studies of n-pentane and iso-pentane in zeolite NaY are reported. Radial distribution of the pentane isomers within the supercage, angle distribution of the end-to-end vector with the radial vector, distribution of end-to-end distance in the two isomers, average guest–zeolite interaction energy, properties during intercage migration event, diffusivity, autocorrelation function for the centre of mass and angular velocities are reported. Results suggest that iso-pentane has a higher diffusivity and lower activation energy than n-pentane. This surprising result is attributed to the need for change from trans to gauche during intercage migration in the case of n-pentane. This is suggested by the increase in gauche population in n-pentane near the window while no such increase is observed in iso-pentane. Another reason for the higher diffusivity of iso-pentane appears to be due to the similarity of the cross-sectional diameter of iso-pentane with the diameter of the 12-ring window.

Amorphous titanium hydrogenphosphate—an inorganic sorbent and a catalyst

Amorphous titanium hydrogenphosphate, originally prepared to act as an inorganic sorbent superior for K+ and other alkaline metal ions of certain size, proved to be also an active catalyst in alcohol dehydration. Its activity was tested in cyclohexanol, methanol, and pentanol conversions. The reactions were selective and thus cyclohexene was practically the only product of cyclohexanol dehydration, methanol gave dimethyl ether (DME) as the main product and pentanol yielded pentene isomers, the mutual ratios of which depended on temperature and contact times. Characteristically, the studied catalysts acquired their high activity only after a period of work at temperatures higher than 275°C, the temperature of an endothermic transition observed in DTA. After the catalyst had been activated, it retained its activity even while working at lower temperatures, but lost it upon staying at room temperature for longer times. Most probably, these changes are related to the increase in the interlayer distance and the insertion of water and alcohol, making thus the inner acidic sites available for the reaction.

In situ measurements of butane and pentane isomers over the subtropical North Pacific

Butane and pentane isomers were measured in situ in the remote marine atmosphere at the Bellows Beach, on the east side of the Island of Oahu, Hawaii during July and August 1998. Air masses arriving at Bellows Beach site originated mainly from the eastern North Pacific, and sometime polluted air masses of island origin arrived at the sampling site. The median mixing ratios were 11 pptv (i-butane), 18 pptv (n-butane), 1 pptv (i-pentane), and 3 pptv (n-pentane) in clean marine air, which were 3-12 times lower than those encountered in the polluted island air. The observed mixing ratios of the alkanes in marine air are within the range of those previously reported in the Atlantic and Pacific Ocean. The concentration ratios of pentane isomers suggest that the sources of the observed pentanes in marine air were not only derived from the ocean but also from the unidentified anthropogenic sources. Based on the comparison with values in the literature on sea-to-air fluxes, oceanic emissions of these alkanes were estimated to account for less than 30% of the observed mixing ratios. Continental emissions are not the important anthropogenic source due to the air mass trajectory analysis, suggesting that there are unidentified anthropogenic sources associated with ship activity and oceanic oil pollution.

Influence of calcination temperature on surface acidity of the solid superacid of sulfated alumina

The acidity of sulfated alumina catalysts was studied by analyzing DTG and heat of Ar adsorption together with the isomerization of pentane. The initial acid sites were Bronsted-type, and converted into Lewis-type upon increasing the pretreatment temperature. The heat of Ar adsorption of the most active sulfated alumina was 18.9 kJ mol−1, this value being a little smaller than that of sulfated zirconia (23.6 kJ mol−1).

Effect of H2 reduction on the catalytic properties of MoO3 with noble metals for the conversions of pentane and propan-2-ol

The catalytic properties of H2-reduced MoO3 with noble metals for the conversions of pentane and propan-2-ol were studied. No appreciable difference appeared in the pentane isomerization activity and in the propan-2-ol dehydration activity among Pt, Pd, Rh, and Ir/MoO3 catalysts after reduction at 773 K for 12 h. H2-Reduced Ru/MoO3 exhibited lower isomerization and dehydration activities than the other catalysts. The isomerization and the dehydration activities of H2-reduced Ru/MoO3 was improved by an increase in the amount of Ru loading, while those of H2-reduced Pt/MoO3 changed very little. XRD and TPR studies showed that the reduction process of Ru/MoO3 varied with the amount of Ru. By contrast, reduction of Pt/MoO3 involved the formation of a hydrogen molybdenum bronze, HxMoO3, irrespective of the amount of Pt. We suggest from these results that reduction of HxMoO3 can yield the active phase for pentane isomerization and for propan-2-ol dehydration.

Pentane Isomerization over Molybdenum Oxide Prepared by H2 Reduction of a Hydrogen Molybdenum Bronze.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Long Term Thermal Resistance of Pentane Blown Polyisocyanurate Laminate Boards

The accurate estimation of the thermal performance of insulation products over their expected lifetime has been a recognized challenge for over twenty years. This is because the lifetime of such products is long (10-25 years), thermal aging is caused by the diffusion of a multitude of gases, and the insulation product is not homogeneous. Two classical approaches to accelerating diffusion controlled phenomena, namely aging at higher temperature and aging a thin slice, have limitations when applied to insulation materials like polyisocyanurate (PIR) laminate board. Raising temperature does not change the diffusion coefficients of all the different gases involved in the aging process at the same rate. In the case of pentane blown PIR board, these gases are CO2, air and the different pentane isomers used to blow the foam. Thin slicing of core foam and scaling techniques, such as those in the ASTM C 1303 -00 procedure, do not account for the fact that PIR laminate boards are denser at the surface layer than in the core foam.

Comparative study of n-pentane isomerization over solid acid catalysts, heteropolyacid, sulfated zirconia, and mordenite: dependence on hydrogen and platinum addition

Skeletal isomerization of pentane over solid acid catalysts (NH 4) 2.5H 0.5PW 12O 40, sulfated zirconia, and H-mordenite has been studied. Hybrid bifunctional catalysts obtained by grinding equal weights of Pt/SiO 2 and each of the above solid acids were also used for the reaction. Various mechanistic aspects for n-pentane isomerization over monofunctional and bifunctional catalysts, in the presence or absence of hydrogen in the feed, are discussed. Analysis of product distributions at 423 and 473 K indicated that over monofunctional heteropolyacids and sulfated zirconia catalysts, the main reaction path is the bimolecular one, involving conjunct polymerization and cracking. Under these operating conditions the selectivity to isopentane is low. Monofunctional H-mordenite shows a significant activity only at 498 K. HPA and ZrO 2–SO 4, although showing stronger acidity than H-mordenite, do not activate n-pentane through a monomolecular path as “superacid-type catalysts” are expected to. Bifunctional isomerization of pentane appears at a reaction temperature of 473 K and up since the equilibrium concentration of pentene is significant only when the reaction temperature is 473 K and up. A monomolecular bifunctional mechanism is the preferred route for reaching high isomerization selectivity.

Pentane Isomerization over Molybdenum Oxide Prepared by H2 Reduction of a Hydrogen Molybdenum Bronze

Abstract Physical and catalytic properties of hydrogen molybdenum bronze, H1.55MoO3 varied markedly with H2 reduction. The surface area was enlarged from 10 m2/g to 250 m2/g by H2 reduction at 673–723 K. H1.55MoO3 became an active and selective catalyst for pentane isomerization after reduction. H2-reduced H1.55MoO3 exhibited a comparable isomerization activity to H2-reduced Pt/MoO3.

Analysis of the Evolution of PIR Foams in the Context of the Phase Out of HCFCs

PIR foams are known for their outstanding fire properties and for their good insulation performances. The fire behavior can be attributed to the aromatic structure of the isocyanurate ring and to the nonflammability of the blowing agent that is used nowadays. For environmental reasons, HCFC-141b will have to be phased out as of 01.01.2003 for the production of PIR laminates boards, in Europe and in the United States. This evolution represents a challenge for the producers as they need to find a high performance alternative in a relatively short period of time. As a major requirement, this alternative will have to maintain the properties of the PIR foams, notably the fire behavior and the k-value at a high quality level. Several blowing agent alternatives have been presented, and some of them have already been implemented in production plants. Among them, pentane is seen as a candidate for economical reasons, but because of its high flammability, its use shows some limitations. The nonflammable alternative HFC-365mfc/HFC-227ea has proven to be an interesting alternative to obtain a good insulation value and good fire properties. Besides, the existence of azeotropic blends between HFC-365mfc and the pentane isomers increases the degree of freedom of the system and makes the optimization process easier. When using the right combination of blowing agent, it is possible to reach an interesting compromise between the insulation characteristics, the fire performance and the cost of the system. An analysis of properties of PIR foams produced with the several alternatives will be presented in this paper.

1-Pentene isomerization over FER and BEA

On a fresh BEA zeolite, skeletal isomerization of 1-pentene is accompanied by various side reactions, such as dimerization–cracking, hydrogen transfer and coking. Coking causes a significant increase in skeletal isomerization and a decrease in the other reactions. IR spectroscopy from samples after 95 min time on stream shows a decrease of Brønsted acid sites of 93 and 28% for the silanol groups. This is in agreement with TPD measurements of ammonia and especially pyridine on fresh and used BEA zeolite. It can be seen that the concentration and strength of acid sites decreased. Acid sites close to the pore mouth of BEA are discussed as active sites for isomerization catalysis. In contrary to BEA, on ferrierite (FER) side reactions are negligible and a high selectivity to iso-pentenes is observed. The restricted pore size of FER and the monomolecular pathway of n-pentene isomerization can explain this fact. Deactivation is more pronounced at lower temperatures for both catalysts.

Comparison of the catalytic properties of H 2-reduced Pt/MoO 3 and of Pt/zeolites for the conversions of pentane and heptane

The catalytic properties of H 2-reduced Pt/MoO 3 for the isomerization of pentane and heptane were compared to those of Pt/zeolites. H 2-reduced Pt/MoO 3 was more active for pentane isomerization than Pt/Hβ and Pt/USY. In contrast, the heptane isomerization activity decreased in the following order: Pt/Hβ>H 2-reduced Pt/MoO 3>Pt/USY. All of the catalysts gave negative kinetic orders toward hydrogen in both pentane and heptane isomerization. The reaction order toward pentane was positive in all cases. The reaction order toward heptane on H 2-reduced Pt/MoO 3 was found to be −0.3, whereas those on Pt/Hβ and Pt/USY were zero and positive, respectively. These results indicate that heptane was more strongly adsorbed on H 2-reduced Pt/MoO 3, resulting in the low heptane isomerization activity. Adsorption studies showed that interaction of heptane with the surface of H 2-reduced Pt/MoO 3 was hindered, probably by its porous structure. We suggest from these results that the low catalytic activity of H 2-reduced Pt/MoO 3 for heptane isomerization can be caused by steric effects as well as by the strong adsorption of heptane.

1-Pentene Isomerization over Zeolites Studied by in situ IR Spectroscopy

The skeletal isomerization of 1-pentene at 1.2 bar total pressure and 30 mbar 1-pentene partial pressure was investigated by in situ IR measurements over FER and BEA zeolites. If the reaction was carried out isothermally a small loss of Bronsted acid sites due to coke formation, a constant conversion and a high selectivity to isopentenes was found over FER. A loss of acid sites and a decrease in conversion was found over BEA, but the selectivity to isomerization increased remarkably. The pore size of FER favored the monomolecular reaction of 1-pentene and suppressed bimolecular reactions. In the bigger pores of BEA initially dimerization–cracking and hydrogen transfer reactions leading to a coke layer took place then the skeletal isomerization of 1-pentene prevailed.

Catalytic properties of H 2-reduced MoO 3 and Pt/zeolites for the isomerization of pentane, hexane, and heptane

The catalytic properties of H 2-reduced MoO 3 for the isomerization of C 5–C 7 alkanes were compared to those of Pt/HY and Pt/Hβ zeolites. The pentane isomerization activity decreased in the following order: Pt/Hβ>H 2-reduced MoO 3>Pt/HY. In contrast, H 2-reduced MoO 3 exhibited the lowest activity for heptane isomerization among the catalysts tested. H 2-reduced MoO 3 catalyzed the isomerization of heptane more selectively than other catalysts, although no appreciable difference appeared in the selectivity for pentane isomerization. Kinetic parameters on H 2-reduced MoO 3 were identical with those on Pt/zeolites, suggesting that isomerization reactions on H 2-reduced MoO 3 proceeded via the bifunctional mechanism. We suggested from the results of 2-propanol conversion that the low dehydrogenation–hydrogenation activity of H 2-reduced MoO 3 was a reason for its low isomerization activity. Adsorption of heptane was found to be restricted on H 2-reduced MoO 3, leading to the low activity for heptane isomerization.

Effect of the Flow Rate of H2 in the Reduction Process on the Physical and Catalytic Properties of H2-Reduced Pt/MoO3

Abstract The surface area of H2-reduced Pt/MoO3 decreased with increasing the flow rate of H2 in the reduction process at 773 K, while the opposite tendency was observed at 523 and 623 K. The surface area was found to depend on the extent of reduction, which was raised by an increase in the H2 flow rate. The largest surface area, about 300 m2 g-1, was obtained at a reduction degree of 64%. A study of reduction with a mixture of H2 and H2O showed that the extent of reduction declined in the presence of H2O. We suggest from these results that the reduction of Pt/MoO3 was prohibited by the action of H2O produced by the reduction. The pentane isomerization activity of H2-reduced Pt/MoO3 was also dependent on the extent of reduction. The highest isomerization activity was obtained at a reduction degree of 76%. H2-reduced Pt/MoO3 exhibited a comparable catalytic activity for pentane isomerization to Pt/H-mordenite.

Cationic complexes of iridium: diiodobenzene chelation, electrophilic behavior with olefins, and fluxionality of an Ir(I) ethylene complex.

The synthesis of a series of dicationic Ir(III) complexes is described. Reaction of Ir(CO)(dppe)I (dppe = 1,2-bis(diphenylphosphino)ethane)) with RI (R = CH(3) and CF(3)) results in formation of the Ir(III) precursors IrR(CO)(dppe)(I)(2) (R = CH(3) (1a) and CF(3) (1b)). Subsequent treatment with AgOTf (OTf = triflate) generates the bis(triflate) analogues IrR(CO)(dppe)(OTf)(2) (R = CH(3) (2a) and CF(3) (2b)), which undergo clean metathesis with NaBARF (BARF = B(3,5-(CF(3))(2)C(6)H(3))(4)(-)) in the presence of 1,2-diiodobenzene (DIB) forming the dicationic halocarbon adducts [IrR(CO)(dppe)(DIB)][BARF](2) (R = CH(3) (3a) and CF(3) (3b)). Complexes 3a and 3b demonstrate facile exchange chemistry with acetonitrile and carbon monoxide forming complexes 4 and 5, respectively. NMR investigation of the mechanism reveals that the process proceeds through an eta(1)-diiodobenzene adduct, where labilization at the coordination site trans to the alkyl group occurs first. Complex 3a reacts with ethylene forming the cationic iridium(I) product [Ir(C(2)H(4))(2)(CO)(dppe)][BARF] (6), which demonstrates fluxional behavior. Variable-temperature NMR studies indicate that the five-coordinate complex 6 undergoes three dynamic processes corresponding to ethylene rotation, Berry pseudorotation, and intermolecular ethylene exchange in order of increasing temperature based on NMR line shape analyses used to determine the thermodynamic parameters for the processes. The DIB adducts 3a and 3b were also found to promote olefin isomerization of 1-pentene, and polymerization/oligomerization of styrene, alpha-methylstyrene, norbornene, beta-pinene, and isobutylene via cationic initiation.

The characterization of tungsten-oxide-modified zirconia supports for dual functional catalysis

The results of catalytic titration measurements indicated that WOx/ZrO2 catalysts prepared by coprecipitation have higher acid site density and strength, and are more active for pentane isomerization, than catalysts prepared by impregnation. The coprecipitated WOx/ZrO2 contains ∼0.004 meq-H+/g-catalyst. XPS of chemisorbed 2,6-dimethylpyridine and pyridine revealed the presence of Lewis acid sites as well as strong and weak Bronsted acid sites on the surface of these catalysts. The concentration of strong Bronsted sites was close to the concentration of Lewis sites, suggesting that the high acidity of these materials may originate from a conjugate Bronsted–Lewis site. Pt/WOx/ZrO2 undergoes a reversible loss of hydrogen chemisorption capacity with increasing hydrogen pretreatment temperature, accompanied by a reversible loss of pentane isomerization activity. This loss can be attributed to a strong Pt-reduced tungsten oxo species interaction (SMSI). Room temperature hydrogen spillover is observed in the Pt/WOx/ZrO2 (∼16% W) catalyst, consistent with the presence of bulk WO3 in this material as observed by TPR.