Arthur Garforth

The conversion of butanes in HZSM-5

The distribution of products from the conversion of iso- and normal butane on HZSM-5 has been determined from 300 to 550°C over a wide range of conversions. The results clearly indicate that the nature of the products changes significantly in altering both the temperature and conversion conditions. High temperatures and low conversions favor low molecular weight products expected from a protolytic or radical attack on the butane. Reverse conditions favor C3 and higher hydrocarbons. These products are indicative of a classical carbenium ion mechanism. As conditions were changed the transition in mechanism was indicated by the amount of methane produced. For the first time H2 was detected as a primary product in the conversion of normal butane indicating that a tertiary C-H bond is not required for its production.

Catalytic degradation of high density polyethylene: An evaluation of mesoporous and microporous catalysts using thermal analysis☆

Abstract Catalytic degradation of waste polymers offers the potential for the selective recovery of useful chemical fractions by influencing the product distributions. Thermogravimetric analysis has been used to investigate the activity of various aluminosilicate catalysts in the degradation of high density polyethylene (HDPE). Amorphous silica-alumina significantly reduced the apparent activation energy as compared with uncatalysed thermal processes. Zeolites Y and ZSM-5 further reduced the activation energy resulting in more rapid degradation. Aluminium containing MCM-41 was found to be active in the degradation of HDPE at a rate similar to that of HZSM-5, confirming the potential of this family of materials in the cracking of heavier hydrocarbons.

Deactivation of US-Y zeolite by coke formation during the catalytic pyrolysis of high density polyethylene

Abstract Catalytic pyrolysis of waste polymers over zeolitic catalysts has the potential to recover valuable hydrocarbons. Thermogravimetric analysis has been used as a tool to characterise the activity, regenerability and deactivation behaviour of zeolite US-Y in the degradation of high density polyethylene (HDPE). Deactivation of the catalyst occurs due to the deposition of coke. Analysis of the TGA results allowed a relationship between catalyst activity and coke content to be derived. The catalyst activity was found to fall exponentially with coke content.

A solvent extraction method to study the location and concentration of coke formed on zeolite catalysts

Abstract The location and composition of the coke formed over H-ZSM-5 zeolites during the cracking of hexadecane at 350°C and at 20 atmospheres was studied. A solvent extraction technique using two different solvents located the coke either on the external surface or within the pores of the zeolite and GC-MS analysis characterised the soluble coke. Coke was also examined using 13C MAS NMR and high resolution TEM. Substituted benzenes were identified as the major precursors to coke formation, and the external coke had a graphitic structure. The contact time was shown to affect only the rate of formation but not the composition of the coke.

Brönsted acidity in US-Y zeolites

FTIR analysis of the hydroxyl region in a series of US-Y zeolites was used for semiquantification of the enhanced acidity, involving Bronsted hydroxyls in both super and β cages, which correlates with the catalytic activity in n-hexane cracking.

The Synthesis and Characterisation of Iron Silicate Molecular Sieves Sieves

Ferrisilicates, containing iron in both framework and extraframework positions were synthesised. Characterisation using MASNMR, ESR, TPDA, ESCA and SIMS gave results which were consistent with framework substitution. Alumino-silicates crystallised more rapidly than corresponding ferrisilicates and a secondary nucleation of silicalite was observed in the iron system at prolonged crystallisation times. Acid sites in ferrisilicates were weaker than those in aluminosilicates. Product distributions, in the methanol conversion, were intermediate between those for H-ZSM-5 and silicalite. Relatively more coke and C 10 aromatics were observed with ferrisilicates and with iron impregnated silicalite. In the Fischer-Tropsch synthesis ferrisilicates were less active than iron impregnated silicalite but activity was improved by hydrothermal treatment which dislodged framework iron.

A comparison of direct synthesis and vapour phase alumination of MCM-41

Mesoporous AlMCM-41 materials were prepared by both direct synthesis and the reaction of siliceous MCM-41 with aluminium chloride vapour. The products were characterised using XRD, N2 sorption, EDAX and both MAS NMR and FTIR spectroscopy, and acid catalytic activity was evaluated using the conversion of 1,3,5-triisopropylbenzene (1,3,5-TIPB) as a test reaction. Acid site concentrations (Bronsted and Lewis) were estimated from sorption of pyridine, using FTIR. The concentrations of acid sites were correlated with the fraction of aluminium in the solids and comparisons were made with results published previously for similar mesoporous materials. Both the compositions of the gels used in the synthesis of Al-mesoporous materials and the procedures used to introduce aluminium into mesoporous silica strongly influenced the above correlation. In all cases, the ratio of total acid site concentration to aluminium concentration was less than unity. Consideration of the present catalytic results for conversion of 1,3,5-TIPB along with results published previously for conversion of cumene, demonstrates that acid catalytic activity is better correlated with Bronsted rather than with Lewis site concentration.

TGA-DTA study on calcination of zeolitic catalysts

Abstract Template decomposition upon calcination of EMO and EMT zeolites has been studied using thermal analysis techniques. For both samples, desorption of water occurs below 200°C and template decomposition at 250–450°C. It is concluded that the template decomposition in EMO and EMT zeolites is relatively slow and is not structure-sensitive; it is accompanied by rapid desorption of the products, XRD studies on the calcined samples show no decrease in their crystallinity. However, both NMR-and IR-spectroscopy indicate partial distortion of the framework and formation of Lewis acid sites. A non-destructive activation of zeolites prepared with organic templates is proposed.

Hydrocarbon Transformations over Analogues and Derivatives of Zeolite Y

Abstract Zeolites of type Y are prepared by either primary or secondary synthesis. Structures include zeolite Y in both the cubic and hexagonal forms, SAPO-37 and faujasitic frameworks containing Ga or Zn. These materials are characterised using solid state NMR, X-ray powder diffraction, infrared spectroscopy, surface analysis and sorption. Catalysts are then evaluated for the conversion of n-hexane, cyclohexane and gas-oil. Results are interpreted in terms of the effectiveness of catalytic sites in alkane activation and in the effect of both density and distribution of active sites.

Pyrolysis GC-MS study of external coke composition on H-ZSM-5 zeolite catalysts

Abstract The composition of coke formed on the external surface of H-ZSM-5 during the cracking of hexadecane, at 350°C and 20 atm pressure of hydrogen, was analysed using a combination of pyrolysis mass-spectrometry and transmission electron microscopy. It was shown that the external coke consisted of regions of graphite and areas of polyaromatic hydrocarbons. Pyrolysis at a range of temperatures showed cracking products with up to five aromatic rings. Using standard compounds, it was shown that cracking only occurred at exo-cyclic bonds, and therefore we can say that the regions of amorphous coke consist of large polyaromatic molecules linked by saturated hydrocarbon chains. It would appear that these amorphous regions act as precursors to graphitic coke.