Muhammad Atiqullah

Synthesis of Functional Polyolefins using Metallocenes: A Comprehensive Review

The copolymerization mainly of ethylene and propylene with various polar functional comonomers, using various metallocenes and the methylaluminoxane (MAO) cocatalyst, has been primarily reviewed from the perspective of the following two subjects. One is the influence of the various functional groups on the copolymerization reactions, and the properties of the resulting products; the other is the areas of future research. The functional groups have been classified into oxygen-, nitrogen-, and halogen-containing moieties; borane-containing α-olefins; silanes; dienes; cyclic olefins; as well as styrene and its various derivatives. The following areas—synthesis of easily soluble functional cooligomer/copolymer; products with uniform distribution of the comonomer; establishment of relation among the catalyst structure and the various steps of copolymerization (initiation, propagation, and chain termination); the degradation and stabilization study of the functional copolymers and the correlation of the same with the catalyst structure; the application of supported metallocenes to synthesize the resulting polymer; the minimization of multi-step synthesis; and the development MAO cocatalyst formulation (to improve the activity and comonomer incorporation)—have been identified to be the subjects of future research, which will be of special importance to the researchers working in functional polyolefins.

Group 4 Metallocenes: Supported and Unsupported

Abstract The global thermoplastics industry is made up of 74% commodity resins, one-third of which is accounted for by polyethylene alone [1]. It was only in 1933 that polyethylene was discovered by Fawcett and Gibson [2] and it was not until 1953 that Karl Ziegler [3–5], Guilio Natta [6–8], and Paul Hogen [9] discovered the revolutionary first-generation Ziegler-Natta transition metal catalyst system. The second-generation MgCI, and/or donorsupported Ziegler-Natta transition metal catalyst system, which was at least 100 times more active, led to the development of the low-pressure polymerization process for polyolefins and synthetic elastomers [10]. This revolutionary catalyst system resulted in the development of simplified gas-phase low-pressure polymerization plant operation without the need for the removal of residual trace catalyst from the polymer.

XPS investigation of the electronic environment in selected heterogenized zirconocene catalysts

Ethylbisindenyl zirconium dichloride (Et(Ind)2ZrCl2) and the MAO methylalumoxane (MAO) co-catalyst were heterogenized on Davision silica 955 partially dehydroxylated at 275 °C, following the concept of equilibrium adsorption. The influence of MAO on the electronic environment resulting from the heterogenization was investigated using XPS. Heterogenization of Et(Ind)2ZrCl2 and MAO on the above silica generated two types of zirconocenium cations (Cation 1 and Cation 2), independent of the heterogenization methods. Based on the postulated surface chemistry, Cation 1 is presumed to be in the form of an ion-pair [SiO]−[Et(Ind)2ZrCl]+, whereas Cation 2 is presumed to be a trapped multi-coordinated crown complex of MAO. In the absence of MAO, only Cation 1 is formed. The present study provides some support for the postulated surface chemistry regarding heterogenization of Et(Ind)2ZrCl2 and MAO on silica. Copyright

Cyclooctane Metathesis Catalyzed by Silica‐Supported Tungsten Pentamethyl [(SiO)W(Me)5]: Distribution of Macrocyclic Alkanes

Metathesis of cyclic alkanes catalyzed by the new surface complex [(≡SiO)W(Me)5] affords a wide distribution of cyclic and macrocyclic alkanes. The major products with the formula C(n)H(2n) are the result of either a ring contraction or ring expansion of cyclooctane leading to lower unsubstituted cyclic alkanes (5≤n≤7) and to an unprecedented distribution of unsubstituted macrocyclic alkanes (12≤n≤40), respectively, identified by GC/MS and by NMR spectroscopies.

Measurement of shape and size distributions of PVC resin particles by scanning electron microscopy and image analysis

Abstract Characterizing poly(vinyl chloride) (PVC) resin particles in terms of particulate morphology, shape and size distributions is important for various technical reasons. We describe a method that shows how these properties can be simultaneously measured using scanning electron microscopy and image analysis. A computer algorithm, which calculates the distributions, has been developed based on the present mathematical formulation, and the data generated by scanning electron microscope and image analyser. The alogorithm considers the variation in shape and size of each particle. The number of mutually exclusive particles required for these measurements, to have an acceptable level of precision, has been statistically determined to be around 430. The number- and weight-average particle diameters, of the experimental PVC resin, were estimated to be 80.4 and 114.8 μm, respectively. The particle size uniformity index was found 1.43.

Role of Blending Technology in Polyethylene Recycling

Abstract World production of plastics has increased from 1 × lo6 tons to 1000 × lo6 tons over the last half-century. The current concern regarding the disposal of industrial and postconsumer waste in diminishing landfill sites and the general impact of waste on the environment have drawn attention to the need to develop effective reclamation and recycling policies. The high visibility of waste products arising from plastics packaging, which accounts for about 30% of total plastics consumption, has contributed to the percep-tion of plastics as a major environmental problem [1].

Modeling of Axial and Recycle Backmixing Effects in a Biological Packed Bed Loop Reactor

Abstract A theoretical model for a packed bed biological loop reactor is presented by considering both external and internal resistances for the general case of Monod kinetics. Numerical solutions have been obtained by the method of orthogonal collocation for a wide range of saturation parameters to cover the two limiting cases of zero-order and first-order kinetics. The numerical solutions for the limiting cases were found to show good agreement with the analytical solutions. The effects of recycle ratio and axial dispersion on the performance of the reactor were studied parametrically. The results show that for low recycle ratios the conversion increases with decrease in Peclet number for first-order and Monod type kinetics; for zero-order kinetics, however, the conversion is independent of both Peclet number and recycle ratio. The effectiveness factor profiles along the length of the reactor were compared for Monod kinetics. It was found that an increase in recycle ratio tends to flatten the profile. The effect of axial dispersion on the concentration profiles at higher recycle ratio was found to be negligible. The dynamics of how steady state conditions are achieved in the reactor is also presented.

Imperfect/incomplete micromixing effects on copolymerization in a premixed-feed stirred tank reactor

Abstract The effects of varying degrees of micromixing on overall conversion, average copolymer composition and copolymer composition distributions in a premixed feed-stirred tank reactor have been theoretically analyzed. The analysis is based on kinematical considerations from continuum mechanics and the Atiqullah-Nauman micromixing model. The calculated, macroscopic composition distributions widen with the increase in segregation number Nseg. However, the overall conversion and average copolymer composition remain relatively unaffected. The study also shows how the micromixing parameter, that is, the striation thickness s0, can be calculated from the measured- and model-predicted composition distributions, and Nseg.

Analysis of non-isothermal tubular reactor packed with immobilized enzyme systems

Abstract The dynamic and steady state performance of a non-isothermal tubular reactor packed with spherical encapsulated enzyme particles has been modeled in terms of different dimensionless transport and kinetic parameters. The dynamic concentration profile for an initially substrate-free reactor reaches a maximum before achieving steady state. The steady state dimensionless bulk substrate concentration, unlike the temperature, progressively decreases along the reactor bed. On increase in the external mass transfer coefficient K L and Biot number Bi m for mass transfer, the concentration profile decreases more steeply. The simulation study shows that the biocatalyst particles may be considered isothermal. The exit substrate concentration decreases with increase in Peclet number Pe m for mass transfer, i.e. backmixing effects, indicating that a plug flow reactor will have a higher overall conversion than a perfect mixer. The dynamic bulk temperature rises more rapidly near the reactor inlet with increase in the Peclet number Pe h for heat transfer, i.e. thermal backmixing effects. The external resistance to mass and heat transfer becomes negligible above a critical value of K L and external heat transfer coefficient h . The bulk substrate concentration, unlike the temperature, decreases with increase in the dimensionless heat α of reaction. For typical Michaelis-Menten kinetics, the exit conversion and temperature will be limited between those for zero- and first-order kinetics.

Effects of enzyme microcapsule shape on the performance of a nonisothermal packed-bed tubular reactor

The effects of enzyme microcapsule shape (spherical, cylindrical and flat plate) on the performance of a nonisothermal, packed-bed reactor have been modeled as a function of Biot number and Peclet number for mass and heat transfer (Bi m , Bi h , Pe m and Pe h ), and dimensionless heat of reaction α. Under the given simulation conditions, only higher values of Bi m and Bi h (>2.5) confirm the influence of microcapsule shape on the reactor performance such that the axial and overall conversion and bulk temperature decrease as follows : spherical > cylindrical > flat plate. In terms of the shape-independent modified Biot number, Bi* = Bi/{(n + 1)/3), this order is retained for 2 < Bi* < 8. The influence of increasing Pe m , Pe h , and α on conversion and bulk temperature also follows the above order. For the flat plate, the exit conversion and temperature are not influenced by Pe m and Pe h , that is, mass transfer and thermal backmixing effects, respectively. On the other hand, for the spherical and cylindrical microcapsules, overall backmixing effects are negligible only beyond a critical value of Pe m (∼7) and Pe h (∼1.75). The conversion and bulk temperature increase with the increase in α, independent of the microcapsule shape. The spherical and cylindrical microcapsules, unlike the flat plate, cannot be considered isothermal.