Synthesis of multi-walled carbon nanotubes with controlled inner and outer diameters by ethylene decomposition over Ni/MgO and Co/MgO catalysts

In this work, multi-walled carbon nanotubes (MWCNTs) with significantly different mean diameters were produced by catalytic CVD over Ni and Co-based supported catalysts. Our results indicate that Ni nanoparticles in the Ni/MgO catalyst are responsible for controlling the inner diameters of the carbon nanotubes. Contrary, Co nanoparticles in the Co/MgO catalyst control the outer diameters of MWCNTs. The “base-growth” mechanism and smaller diameters of the MWCNTs grown on the Ni/MgO catalyst are associated with a strong metal-support interaction (SMSI) resulting from NixMg1−xO mixed oxide formation. The concept of the weak metal-support interaction (WMSI) between Co nanoparticles and MgO for the Co/MgO catalyst confirms the “tip-growth” mechanism of the MWCNTs.

Redesign of LDPE Secondary Compressor Valves to Better Tolerate Polyethylene Wax Fouling

This paper discusses the redesign of valves in high-pressure reciprocating compressors used in the manufacture of Low Density Polyethylene (LDPE) resin. The compressors have Multi-poppet (MPV) style valves which are affected by LDPE wax fouling. This fouling causes the poppets to stick open leading to gas recirculation (valve leakage) and associated process fluid heating. This heating can cause the compressors to shut down on high discharge temperatures requiring operations personnel to push process gas through the valves to try to clear the waxes, or to have maintenance personnel replace the valves. Poppets sticking due to wax fouling can also result in compressor gas discharge temperatures increasing high enough to cause Ethylene decomposition (Decomp) which can cause the production line to vent to atmosphere. This paper describes analysis and testing to change the valve design from MPV, to Single-poppet (SPV) style valves to reduce the effects of wax fouling.

Surface carbon species formation from ethylene decomposition on Pd(100): a first-principles-based kinetic Monte Carlo study

Based on the activation barriers and reaction energies from periodic density functional calculations, we conducted kinetic Monte Carlo (kMC) simulations of surface carbon species formation from ethylene decomposition on a Pd(100) surface.