Ethylene production by pulsed compression

The study investigates methane to ethylene conversion using non-oxidative thermal coupling with pulsed compression technology. A pulsed compression reactor (PCR) is used that utilizes a free piston concept, compressing gases up to 600 bar in around 8 ms and raising temperatures to 4000 K. The PCR operates at lower temperatures (< 588 K), making it promising for ethylene production from abundant natural gas. This research explores methane and ethane conversion, revealing high selectivity to ethylene and other valuable products. Chapter 2 analyzes the single shot reactor (SSR) and develops a simplified model for gas compression behavior. Chapter 3 demonstrates methane conversion without oxygen, using nitrogen as a diluent, with high selectivity to ethylene. Chapter 4 maps operational conditions to maximize product concentrations, achieving 28% methane conversion and 99% selectivity for desired products. Chapter 5 examines the impact of different bathing gases on reaction rates, highlighting a dependency on gas type. Chapter 6 presents a kinetic model for methane and ethane pyrolysis, improving predictive capabilities over existing models. Chapter 7 introduces a continuous free piston reactor design for endothermic reactions, showing promise for continuous operation despite operational challenges. Finally, Chapter 8 concludes that converting ethane diluted in methane is the best way forward for ethylene production, shifting the ethane dehydrogenation process towards net conversion of methane, thus enhancing ethylene production

Investigation of the effects of inlet shapes on fan noise radiation

The effect of inlet shape on forward radiated fan tone noise directivities was investigated under experimentally simplified zero flow conditions. Simulated fan tone noise was radiated to the far field through various shaped zero flow inlets. Baseline data were collected for the simplest baffled and unbaffled straight pipe inlets. These data compared well with prediction. The more general inlet shapes tested were the conical, circular, and exponential surfaces of revolution and an asymmetric inlet achieved by cutting a straight pipe inlet at an acute angle. Approximate theories were developed for these general shapes and some comparisons with data are presented. The conical and exponential shapes produced directivities that differed considerably from the baseline data while the circular shape produced directivities similar to the baseline data. The asymmetric inlet produced asymmetric directivities with significant reductions over the straight pipe data for some angles

Substrate Capture by ABC Transporters

Most ABC importers known to date employ a soluble substrate-binding protein to capture the ligand and donate the molecule to the translocator. The SBP can be a soluble periplasmic protein or tethered to the membrane via a lipid moiety or protein anchor or fused to the translocator. In the hybrid ABC transporters, multiple SBDs can be fused in tandem and provide several extracytoplasmic substrate-binding sites. A subset of ABC transporters employs a membrane-embedded S-component to capture the substrate. The S-component together with the ECF module also forms the translocation path for the substrate. Multiple S-components can associate consecutively with one and the same ECF module. An overview of the mechanism of substrate capture by different types of ABC transporters is presented, together with a scheme illustrating the alternating access mechanism for the overall transport process

The effect of inert gases (Xe, Ar, Ne, He) on decomposition reactions of N₂O, CH₄ and CO₂ at high pressures

In a pulsed compression reactor (PCR) experiments were done with N2O (4%mol), CH4 (1%mol) and CO2 (2%mol) diluted in the inert gases Xe, Ar, Ne and He. The mixtures were compressed up to 250 bar, reaching temperatures of up to 4000 K. At equal temperature, pressure and volume, significant differences (up to 20%) were measured in the conversion of the three species in different noble gases. The measurements with N2O decomposition showed that the reaction is the fastest in the most heavy noble gas tested. The conversion decreased as the molar mass of the noble gas decreased. Likewise, methane pyrolysis was measured to be the fastest in xenon and slowed down in accordance with the mass of the inert molecule. A reverse trend was measured for the decomposition of CO2 to CO and O⋅, which is explained by the dominant role of the reverse reaction. As a result, the CO2 data is also explained by conversion rates that are higher in heavier gases. This paper provides a first attempt to understand the observed influence of the molar mass of the inert bathing gas on the reaction rate in the high pressure domain. A theory is proposed based on a Newtonian description of reactant activation by the inert bathing gas.</p

Diversity of membrane transport proteins for vitamins in bacteria and archaea

BACKGROUND: All organisms use cofactors to extend the catalytic capacities of proteins. Many bacteria and archaea can synthesize cofactors from primary metabolites, but there are also prokaryotes that do not have the complete biosynthetic pathways for all essential cofactors. These organisms are dependent on the uptake of cofactors, or at least their precursors that cannot be synthesized, from the environment. Even in those organisms that contain complete biosynthetic pathways membrane transporters are usually present, because the synthesis of cofactors is more costly than uptake.SCOPE OF REVIEW: Here we give an overview of bacterial and archaeal transport systems for B-type vitamins, which are either cofactors or precursors thereof.MAJOR CONCLUSIONS: Prokaryotic vitamin transporters are extremely diverse, and found in many families of transporters. A few of these transport systems have been characterized in detail, but for most of them mechanistic insight is lacking.GENERAL SIGNIFICANCE: The lack of structural and functional understanding of bacterial vitamin transporters is unfortunate because they may be targets for new antibiotics. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins. Guest Editor: Bjorn Pedersen.</p