R. Byggningsbacka

Synthesis and characterization of H-ZSM-22, Zn-H-ZSM-22 and Ga-H-ZSM-22 zeolite catalysts and their catalytic activity in the aromatization of n-butane

Abstract K-ZSM-22 zeolites with a Si/Al ratio of 53 have been synthesized by means of the hydrothermal synthesis method using 1,6-diaminohexane as the templating agent. The H-ZSM-22, Ga and Zn modified ZSM-22 zeolite catalysts have been prepared and characterised by X-ray powder diffraction (Philips pw 1830), scanning electron microscopy (Leica Cambridge Stereoscan 360), nitrogen adsorption (Carlo Erba Instruments), X-ray fluorescence (Outokumpu-8000) and temperature programmed desorption of ammonia. The synthesised ZSM-22 zeolite was highly crystalline and free of amorphous material. The TPD of ammonia profiles revealed that the H-ZSM-22, Ga and Zn modified ZSM-22 were acidic and consisted of Bronsted and Lewis acid sites. The catalytic activity were investigated for the conversion of n-butane to aromatic hydrocarbons over H-ZSM-22, Ga-H-ZSM-22 and Zn-H-ZSM-22 catalysts. Further, the effect of temperature and the space velocity on the conversion of n-butane and the selectivity to aromatic hydrocarbons were studied. The selectivity to aromatics was higher for Ga and Zn modified ZSM-22 than for H-ZSM-22. The effect of time on stream on n-butane conversion and the selectivity to aromatics was studied at 803 K for 4.5 h.

Synthesis and characterization of Pd-MCM-22 and Pt-SAPO-11 catalysts for transformation of n-butane to aromatic hydrocarbons

Abstract Pd-Na-MCM-22, Pd-H-MCM-22 and Pt-SAPO-11 catalysts were synthesized and characterized using techniques of X-ray powder diffraction, scanning electron microscopy, FTIR, nitrogen adsorption and X-ray fluorescency. The FTIR spectra of Pd and Pt modified MCM-22 and SAPO-11 exhibited lower amounts of Bronsted (B) and Lewis (L) acid sites than the unmodified MCM-22 and SAPO-11. The catalysts were tested in the transformation of n -butane to aromatic hydrocarbons. Aluminosilicate type of zeolite catalysts Pd-Na-MCM-22 and Pd-H-MCM-22 exhibited higher selectivity to aromatics than aluminophosphate Pt-SAPO-11. The pretreatment of the catalysts with oxygen and hydrogen was found to influence the n -butane conversion and selectivity to aromatic hydrocarbons. The hydrogen pretreated Pt-SAPO-11 exhibited higher n -butane conversion than the oxygen pretreated. The catalysts exhibited deactivation with time on stream due to coke formation and pore blocking. The specific surface areas of the Pt-SAPO-11, Pd-Na-MCM-22 and Pd-H-MCM-22 deactivated catalysts were found to be lower than the fresh because of coke deposits inside the pores.

Simultaneous dehydrogenation and isomerization of η‐butane to isobutene over ZSM‐22 and zinc‐modified ZSM‐5 zeolites

Direct formation of isobutene from η‐butane was investigated over a zinc‐impregnated potassium‐ion‐exchanged ZSM‐5 dehydrogenation catalyst and an acidic shape‐selective ZSM‐22 skeletal isomerization catalyst. The experiments were performed in a fixed‐bed microreactor system operating at near‐atmospheric pressure. High selectivity to η‐butene was obtained over the zinc‐impregnated potassium‐ion‐exchanged ZSM‐5 dehydrogenation catalysts. The yield of isobutene increased after adding the acidic ZSM‐22 skeletal isomerization catalyst, although the selectivity to butene isomers slightly decreased because the skeletal isomerization of η‐butene was competing with other acid‐catalyzed reactions such as cracking and aromatization.

Aromatization ofn-butane over Ni-ZSM-5 and Cu-ZSM-5 zeolite catalysts prepared by using Ni and Cu impregnated silica, fiber

The reaction ofn-butane aromatization was carried out over Ni-ZSM-5 and Cu-ZSM-5 zeolite catalysts prepared by using Ni and Cu impregnated silica fiber during the process of ZSM-5 zeolite synthesis. The catalysts prepared were characterized by X-ray powder diffraction, nitrogen adsorption and X-ray fluorescency. The acidic properties of the catalysts were investigated by temperature-programmed desorption of ammonia using a mass spectrometer equipped with a QTMD detector. The effect of catalyst pretreatment, reaction temperature, and time on stream on the reaction ofn-butane to aromatic hydrocarbons were investigated. The modification of ZSM-5 by Ni and Cu increased the selectivity to aromatic hydrocarbons. The state of Ni and Cu and their stabilization in the ZSM-5 structure was highly influenced by the mode of catalyst pretreatments.

Comparison of the catalytic properties of Al‐ZSM‐22 and Fe‐ZSM‐22 in the skeletal isomerization of 1‐butene

The catalytic activities of Al‐ZSM‐22 (Al in the framework) and Fe‐ZSM‐22 (Fe in the framework) were compared in the skeletal isomerization of 1‐butene to isobutene. The catalysts synthesized in the laboratory were characterized by means of XRD, FTIR spectroscopy, SEM and surface area measurements. The activity of the zeolites was investigated using a fixed‐bed microreactor system. Al‐ZSM‐22 demonstrated higher activity in 1‐butene transformation compared to Fe‐ZSM‐22, while the selectivity to isobutene, on the other hand, was higher over Fe‐ZSM‐22. Coke formation was monitored using a microbalance and the results showed that the weight gain of Fe‐ZSM‐22 was slightly higher compared to Al‐ZSM‐22.

Acid catalytic effects in the chlorination of propanoic acid

Selective α-chlorination of propanoic acid to form 2-monochloropropanoic (MCA) and 2,2-dichloropropanoic acid (DCA) was investigated in a laboratory-scale, semibatch reactor at 90–130 °C at atmospheric total pressure and in the presence of chlorosulfonic acid (ClSO3H) and 2,2-dichloroethanoic acid (DCA′) as catalytic agents and oxygen as a radical scavenger. The decomposition of the catalyst was investigated with sulfur analysis and UV-spectrometry. The studies revealed that the majority of sulfur remains in the reaction mixture, but is converted to an inactive form during the chlorination. The reasons may be the decomposition of ClSO3H and its reaction with propanoic acid. The kinetic experiments revealed autocatalytic and parallel formation of MCA and DCA, the selectivity being independent of Cl2 concentration in the liquid phase. The experiments with DCA′ also demonstrated that DCA′ has a catalytic effect on the chlorination The experiments confirmed the validity of a previously proposed reaction scheme for α-chlorination, which comprises the formation of the reaction intermediate (propanoyl chloride) from propanoic acid and ClSO3H, the acid-catalyzed enolization of the acid and a hydroxyl-chlorine exchange reaction. The acid-catalyzed enolization is the rate determining step in the reaction sequence. The kinetic data were fitted to rate equations based on the reaction scheme. © 2000 Society of Chemical Industry