Halim Hamid

Effects of climate change and UV-B on materials

The outdoor service life of common plastic materials is limited by their susceptibility to solar ultraviolet radiation. Of the solar wavelengths the UV-B component is particularly efficient in bringing about photodamage in synthetic and naturally occurring materials. This is particularly true of plastics, rubber and wood used in the building and agricultural industries. Any depletion in the stratospheric ozone layer and resulting increase in the UV-B component of terrestrial sunlight will therefore tend to decrease the service life of these materials. The extent to which the service life is reduced is, however, difficult to estimate as it depends on several factors. These include the chemical nature of the material, the additives it contains, the type and the amount of light-stabilizers (or protective coatings) used, and the amount of solar exposure it receives. Concomitant climate change is likely to increase the ambient temperature and humidity in some of the same regions likely to receive increased UV-B radiation. These factors, particularly higher temperatures, are also well known to accelerate the rate of photodegradation of materials, and may therefore further limit the service life of materials in these regions. To reliably assess the damage to materials as a consequence of ozone layer depletion, the wavelength sensitivity of the degradation process, dose-response relationships for the material and the effectiveness of available stabilizers need to be quantified. The data needed for the purpose are not readily available at this time for most of the commonly used plastics or wood materials. Wavelength sensitivity of a number of common plastic materials and natural biopolymers are available and generally show the damage (per photon) to decrease exponentially with the wavelength. Despite the relatively higher fraction of UV-A in sunlight, the UV-B content is responsible for a significant part of light-induced damage of materials. The primary approach to mitigation relies on the effectiveness of the existing light stabilizers (such as hindered amine light stabilizers, HALS) used in plastics exposed to harsh solar UV conditions coupled with climate change factors. In developing advanced light-stabilizer technologies, more light-resistant grades of common plastics, or surface protection technologies for wood, the harsh weathering environment created by the simultaneous action of increased UV-B levels due to ozone depletion as well as the relevant climate change factors need to be taken into consideration. Recent literature includes several studies on synergism of HALS-based stabilizers, stabilizer effectiveness in the new m-polyolefins and elucidation of the mechanism of stabilization afforded by titania pigment in vinyl plastics.

A comparison between β- and USY-zeolite-based hydrocracking catalysts

Abstract Two series of zeolite-based hydrocracking catalysts were prepared to study the effects of the support type, preparation method and metal loading on catalyst properties and hydrocracking activity for hydrotreated vacuum gas oil (HT-VGO). The support used was γ-Al2O3 and β-zeolite in the first series and γ-Al2O3 and USY-zeolite in the second series. Nickel and tungsten were loaded as active metals on these supports. The prepared catalysts were characterized as to their surface area, pore volume, thermal stability, reducibility and acidity characteristics. The characterization results revealed that catalysts displayed significant differences in properties dependent on the preparation method and the type of support used. Catalysts from both series showed promising results for HT-VGO hydrocracking in the batch reactor. A correlation exists between the reducibility of oxidic form and the hydrogenation activity of the sulfided form of the catalysts. The higher the reducibility, the higher the hydrogenation activity. Catalysts prepared on mixed supports gave higher amounts of saturates.

Characterization of high surface area smectite supported cobalt oxides catalysts for hydrodesulfurization by means of TPR, TPS and ESR

Abstract Catalysts of cobalt oxide loaded on smectic clays having high surface areas were prepared. Smectic clays used were montmorillonite, saponite, porous saponite, hectorite and stevensite. The catalysts were tested for hydrodesulfurization (HDS) activity with thiophene in a pulse flow reactor at different temperatures. Co–porous saponite catalyst prepared by an ion-exchange method in the series including CoMo–Al 2 O 3 shows the highest thiophene HDS activity so far studied. The catalytic properties of the selected catalysts were characterized by temperature-programed-reduction (TPR) and -sulfiding (TPS) together with electron spin resonance (ESR). The HDS performance with thiophene is closely dependent upon the reduction temperature of cobalt oxide obtained by TPR for Co–smectite catalysts. The TPS measurements indicate that small particles of cobalt oxide are highly dispersed in the smectic layer by means of ion-exchange method. It is suggested that the properties such as sensitivity toward H 2 S and catalyst color of cobalt oxide on Co–porous saponite by ion-exchange method are different from those of Co–porous saponite by impregnation method. Reactivity of loaded cobalt oxide with H 2 S is strongly dependent upon the sulfiding paths.

Hydrogen spillover phenomenon in noble metal modified clay-based hydrocracking catalysts

Homemade clay-based catalysts and a commercial hydrocracking catalyst were evaluated for hydrocracking activity using vacuum gas oil (VGO) from Saudi Arabian light crude oil. The clay-based catalysts were prepared in our laboratories by cobalt loading and one of them was impregnated with a noble metal belonging to group VIII of the periodic table. The reactions were conducted in both flow and batch reaction system. The amount of saturates were found to increase while aromatics and polars were decreasing with the increase in conversion of feed to lighter products. The cracking activities of both clay-based catalysts were found better than the catalyst C (commercial). In the flow reactor, at 360 °C reaction temperature, the activity of catalyst A (having noble metal) was 2 times more than that of the catalyst B (without noble metal), while 2.5 times more than that of the commercial catalyst. Similarly, at 380 and 400 °C temperatures, the activity of catalyst A was 2 times more than that of the catalyst C and substantially higher than that of catalyst B. In the batch reactor, higher cracking and HDS activity were observed for catalyst A and more saturates were found in the reaction product as well. The amount of carbon deposited was found to be lower on the spent clay catalyst A. This study clearly shows that even in hydrocracking of VGO which contains complex hydrocarbons and substantial amounts of sulfur, nitrogen and metals, hydrogen spillover phenomena do occur.

Temperature-programmed desorption and reduction of sulfided alumina-pillared montmorillonite

Abstract As a part of our fundamental studies on the acid function of catalysts for hydrocracking, alumina-pillared montmorillonite catalysts were prepared and characterized by means of temperature-programmed desorption with NH 3 from sulfided catalysts (TPD-S) and temperature-programmed reduction of sulfided catalysts (TPR-S). The TPD-S and TPR-S characteristics of catalysts thus obtained have been compared with the activities of cumene cracking in a pulse-type micro reactor. Commercial hydrocracking catalysts were also characterized with similar methods and the performance of cumene cracking was tested. TPD, TPR profiles and cumene cracking activity changed after sulfiding of alumina-pillared montmorillonite. Both the chemical property changes by the heat treatment and the sulfur species adsorbed on the surface allow us to alter its acid property and cumene cracking activity as well.

A novel catalyst for heavy oil hydrocracking

Abstract This paper reports the development of novel hydrocracking catalysts supported on high-surface area saponite clay and pillared with either cobalt or nickel oxide. The catalysts were prepared by aging the Co or Ni nitrate solution, followed by addition of saponite, washing, drying and calcination. The catalysts were evaluated for HDS, HDN and hydrocracking activities in a batch autoclave reactor using vacuum gas oil as feedstock. The results show that the HDS, HDN and cracking activities of the novel catalysts are comparable to that of a conventional NiW/SiO2-Al2O3 catalyst. The Co catalyst gave better HDS activity while the Ni catalyst showed higher HDN and cracking activity. Calcination before metal loading does not seem to effect the overall performance of the Co catalysts. It should be noted these activities are achieved despite the use only one metal as the active ingredient. The results of this study clearly indicate that the saponite clay based catalysts are a potential alternative to the conventional hydrocracking catalysts.

Nonisothermal, uncontrolled homo- and copolymerization of ethylene using selected zirconocenes

Nonisothermal, uncontrolled polymerization, conducted in varying mixing regimes, offered a facile methodology to evaluate the influence of several important process development factors such as mixing, reaction exotherm, and thermal perturbations on the catalytic activity and kinetic stability, polymerization performance, and properties of the resulting polymers. Ethylene was homo- and copolymerized with hexene-1 under varying impeller speeds (hence, thermal perturbations), using Ind2ZrCl2 and Et(Ind)2ZrCl2 and the MAO cocatalyst. With respect to the effects of the above process development factors, the following was observed: The reaction exotherm profiles, tracing the polymerization history, qualitatively represented the kinetic profile and the catalytic stability. The unbridged Ind2ZrCl2 was shown to be more stable than the bridged Et(Ind)2ZrCl2. With change in the level of stirring from a diffusion-controlled regime to a nondiffusion-controlled, external gas–liquid mass-transfer resistance-free one, the reaction exotherm and the run time-average catalytic activity increased. So far as the influence of the chiral versus the achiral zirconocene structure is concerned, the copolymer composition distribution and soluble fraction generated by chiral Et(Ind)2ZrCl2 were more sensitive to the mixing conditions and thermal perturbations than were those produced by achiral Ind2ZrCl2. Et(Ind)2ZrCl2 produced higher molecular weight backbones, incorporated more hexene-1 and chain branching, and introduced less crystallinity in the copolymers than did Ind2ZrCl2. The influence of Ind2ZrCl2 on higher-weight homopolymer backbones was opposite to that of Et(Ind)2ZrCl2. Incorporation of hexene-1 significantly decreased the average molecular weights and density and increased the run-time-dependent average catalyst activity. A positive comonomer effect took place. The bulk polymer properties did not critically depend on the mixing state. Thermal perturbations broadened the polydispersity index.

61 Preparation, characterization, and catalytic evaluation of first stage hydrocracking catalyst

Abstract A series of amorphous silica-alumina and zeolite based first stage hydrocracking catalyst was prepared. Nickel and molybdenum were impregnated as active metals on 0.8 mm extrudates of silica-alumina supports prepared with an alumina binder. For the better performance of hydrocracking catalyst a balance between the acid function and hydrogenation/dehydrogenation function of the catalyst is required. Determination of acidity is straight forward but the measurement of the metal function of bi-functional hydroprocessing catalyst is a complicated procedure. An attempt has been made to measure the metal function by cyclohexane dehydrogenation reaction. The catalysts were characterized for acidity measurement by temperature programmed desorption of ammonia (TPD), pulse reaction test (PRT) method for hydrogenation/dehydrogenation activity and evaluated for vaccum gas oil (VGO) conversion. The characterization results are discussed in relation to the catalytic activities in hydrocracking reactions.