P.V. Aravind

The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability

50 years ago, Karl Ziegler and Giulio Natta were awarded the Nobel Prize for their discovery of the catalytic polymerization of ethylene and propylene using titanium compounds and aluminum-alkyls as co-catalysts. Polyolefins have grown to become one of the biggest of all produced polymers. New metallocene/methylaluminoxane (MAO) catalysts open the possibility to synthesize polymers with highly defined microstructure, tacticity, and steroregularity, as well as long-chain branched, or blocky copolymers with excellent properties. This improvement in polymerization is possible due to the single active sites available on the metallocene catalysts in contrast to their traditional counterparts. Moreover, these catalysts, half titanocenes/MAO, zirconocenes, and other single site catalysts can control various important parameters, such as co-monomer distribution, molecular weight, molecular weight distribution, molecular architecture, stereo-specificity, degree of linearity, and branching of the polymer. However, in most cases research in this area has reduced academia as olefin polymerization has seen significant advancements in the industries. Therefore, this paper aims to further motivate interest in polyolefin research in academia by highlighting promising and open areas for the future.

Biosyngas Utilization in Solid Oxide Fuel Cells With Ni∕GDC Anodes

The combination of biomass gasification systems with fuel cells promises adequate systems for sustainable, decentralized energy conversion. Especially high temperature fuel cells are suited for this task because of their higher tolerance to impurities, their internal steam reforming potential, and favorable thermal integration possibilities. This paper presents the results of biosyngas utilization in solid oxide fuel cells with Ni/GDC anodes at 850 and 920°C. The relation between the fuel composition and the electrochemical performance is discussed, as well as the impact of sulfur up to a concentration of 9 ppm H 2 S. The investigations have made clear that Ni/GDC anodes can be operated within a wide range of biosyngas compositions. Sulfur has appeared to deactivate the anode for methane reforming. The oxidation of hydrogen and carbon monoxide are insensitive to sulfur, suggesting that both nickel and GDC are active electrocatalysts.

Diffusion Impedance on Nickel/Gadolinia-Doped Ceria Anodes for Solid Oxide Fuel Cells

Electrochemical impedance measurements were carried out on symmetrical nickel/gadolinia-doped ceria test cells. For H2, N2, and H2O mixtures, the diffusion length obtained based on the impedance measurements is on the order of centimeters. This high value of the diffusion length is attributed to the flow field in the reactor. It is suggested that a detailed analysis of the gas flow field inside the test reactor is essential before interpreting the impedance measurements with various solid oxide fuel cell test configurations.

Microwave-Driven Plasma Gasification for Biomass Waste Treatment at Miniature Scale

Gasification technology may combine waste treatment with energy generation. Conventional gasification processes are bulky and inflexible. By using an external energy source, in the form of microwave-generated plasma, equipment size may be reduced and flexibility as regards to the feed composition may be increased. This type of gasification may be combined with fuel cell technology to generate electricity for on-site microwave generation. In this paper, we present short gasification experiments with cellulose, as model biomass compound, in air plasma. In order to optimize reaction rates, gasification and plasma generation are combined in the same volume in order to expose the solids to plasma of maximum intensity. The heating value of the fuel gas yield exceeds, up to 84%, the net microwave energy transmitted into the reactor over a range of operating conditions. As the system has not been optimized, in particular regarding residence time, the results give confidence that this concept can eventually be developed into a viable small-scale decentralized gasification technology.

Flow Distribution in the External Manifold of SOFC Stack

In this paper fluid dynamic behaviors of cathode gas flow in an external gas manifold of a planar solid oxide fuel cell (SOFC) stack are simulated to investigate the overall pressure variation and flow distribution. External manifold models are built in three dimensions for a 60-cell planar SOFC stack. Cell units of the stack are treated as porous media with appropriate resistances, which were determined by the previous results of cell modeling. In order to simplify this model, electrochemical reactions, heat and mass transport phenomena are ignored inside cells. The flows of cathode gas in the external manifolds of stack are modeled by means of computational fluid dynamics (CFD) methods. A commercial CFD package “Fluent” was used for geometry creation, grids generation of flow volume interiors, solving mass, momentum equations, plotting computational results. The detailed results of pressure variation and flow distribution of gases in the stack were achieved. The effects of different designs and parameters such as a gas distributor inside the external manifold, the permeability of porous media in cells and cathode gas feeding rate on gas distribution and pressure variation are studied. Comparison of different cases is carried out by the modeling results. Modeling results show for the proposed stack design in this paper the additional gas distributor located in the center of the inlet manifold and a rise of resistance in cells can respectively enhance the uniformity of flow distribution over 60 cells.Copyright

Solid oxide fuel cell integrated with biomass gasification for power generation for rural areas in China

Fuel cells coupled with biomass gasifiers can offer the potential of highly efficient and renewable power generation in an environmentally friendly and CO2-neutral manner. Three key aspects, i.e. the fuel resources and fuel cell types as well as gas cleaning for this combined system were discussed to present the feasibility of applying biomass gasification (BG) based solid oxide fuel cell (SOFC) system for distributed power generation in developing countries. The performance of BG-SOFC based combined heat and power (CHP) system and future work was also presented.

Three-dimensional Modeling of Anode-supported Planar SOFC with Direct Internal Reforming

This paper presents a three-dimensional model of an anode-supported planar SOFC with corrugated bipolar plates serving as gas channels and current collector above the active area of the cell, based on the direct internal reforming reaction of methane and the electrochemical reaction of hydrogen. A co-flow system with gas mixture of methane, water vapor and a small amount of hydrogen as anode gas and air as cathode gas fed at an inlet temperature of 973K was modeled at a single cell unit level. A simple equation for the cell resistance with measured values for the quasi ohmic resistance is used for the calculation of the current density. The modeling results show the current density distribution and temperature profiles in the cell and gas concentrations profiles along the length of the cell channel. Furthermore, the temperature gradient inside the cell was investigated.