Determination of sulfur components in natural gas: A review

More stringent environmental regulations as well as higher demands presently being imposed on the sulfur content of natural gas feed-stocks for chemical processes necessitate the development of new analytical procedures for sulfur determination in natural gas. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. The complexity of the natural gas matrix as well as the extremely low concentration levels at which the sulfur species occur make the development of these analytical methods a true challenge. In this review the three steps common for analytical methods for trace analysis in complex matrices, i.e. pretreatment, chromatographic separation, and detection, are discussed in detail. Possible methods for calibration of the system are discussed in the final section. Various techniques to determine sulfur in natural gas are described. Depending on the application, the most suitable system has to be selected. For example, for on-line application in a hazardous area a simple and rugged system is required, i.e. a simple gas chromatograph with a flame photometric detector, while for laboratory application a more complex instrument including preconcentration, column switching, and more exotic detection systems could be more suitable. Therefore it is crucial to define the requirements of the instrument at an early stage and use the information in this review article to develop/select a dedicated instrument/procedure for the problem at hand.     

Morphology and mechanical properties of a novel amorphous polyamide/nanoclay nanocomposite

A novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X-ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactants with phenyl and hydroxyl groups was delaminated in the polymer matrix resulting in well-exfoliated morphologies even at high montmorillonite content. Differential scanning calorimetry results indicated that clay platelets did not induce the formation of a crystalline phase in this amorphous polymer. Tensile tests demonstrated that the addition of nanoclay caused a dramatic increase in Young's modulus (almost twofold) and yield strength of the nanocomposites compared with the homopolymer. The nanocomposites exhibited ductile behavior up to 5 wt % of nanoclay. The improvement in Young's modulus is comparable with semicrystalline aliphatic nylon 6 nanocomposites. Both the main chain amide groups and the amorphous nature of the polyamide are responsible for enhancing the dispersion of the nanofillers, thereby, leading to improved properties of the nanocomposites. The structure-property relationship for these nanocomposites was also explored. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2605–2617, 2008     

Anionic cross-coupling reaction of alpha-metallated alkenyl sulfoximines and alkenyl sulfoximines with cuprates featuring a 1,2-metal-ate rearrangement of sulfoximine-substituted higher order alkenyl cuprates and an alpha-metallation of alkenyl sulfoximines by cuprates

(E)- and (Z)-configured alpha-lithioalkenyl sulfoximines, which are available through lithiation of the corresponding alkenyl sulfoximines, undergo a anionic cross-coupling reaction (ACCR) with organocuprates with formation of the corresponding alkenyl cuprates and sulfinamide. The alkenyl cuprates can be trapped by electrophiles. The ACCR presumably proceeds via the formation of a higher-order sulfoximine-substituted alkenyl cuprate, which undergoes a 1,2-metal-ate rearrangement whereby the sulfoximine group acts as the nucleofuge. The parent (E)- and (Z)-configured alkenyl sulfoximines suffer upon treatment with an organocuprate a deprotonation at the alpha-position with formation of the corresponding alpha-cuprioalkenyl sulfoximines. These derivatives also enter into a similar ACCR with organocuprates. The ACCR of sulfoximines substituted homoallylic alcohols allows a stereoselective access to enantio- and diastereopure substituted homoallylic alcohols.     

Probing occupied states of the molecular layer in Au-alkanedithiol-GaAs diodes

Internal photoemission (IPE) studies were performed on molecular diodes in which the alkanedithiol [HS(CH(2))(n)SH, n = 8, 10] molecular layer is sandwiched between Au and GaAs electrodes. The results are compared to those from Au-GaAs Schottky diodes. An exponential energy dependence in the IPE yield was observed for the molecular diodes, in contrast to the quadratic energy dependence characteristic of metal-semiconductor Schottky diodes, indicating that Au is not the source of electrons in the IPE process in the molecular diodes. From the GaAs dopant density dependence, we also can rule out GaAs being the source of these electrons. Compared with the results of cluster electronic structure calculations, we suggest that IPE is probing the occupied levels of GaAs-molecular interfacial states.     

Direct measurement of the radiative lifetime of vibrationally excited OH radicals

Neutral molecules, isolated in the gas phase, can be prepared in a long-lived excited state and stored in a trap. The long observation time afforded by the trap can then be exploited to measure the radiative lifetime of this state by monitoring the temporal decay of the population in the trap. This method is demonstrated here and used to benchmark the Einstein A coefficients in the Meinel system of OH. A pulsed beam of vibrationally excited OH radicals is Stark decelerated and loaded into an electrostatic quadrupole trap. The radiative lifetime of the upper Lamda-doublet component of the Chi2Pi3/2, v=1, J=3/2 level is determined as 59.0+/-2.0 ms, in good agreement with the calculated value of 58.0+/-1.0 ms.     

Vertical ordering of islands in Ge-Si multilayers

Growth and ordering of GeSi islands in Ge-Si multilayer systems during deposition by Low-Pressure Chemical Vapour Deposition (LPCVD) at 700°C on Si (001) substrates have been investigated for different layer distances by transmission electron microscopy of cross-section and plane-view specimens. Vertical ordering of GeSi islands with almost perfect correlation is observed for distances between the Ge layers of 100 nm. At larger interlayer distances, a continuous decrease of the correlation is found. Vertical ordering in the multilayer system is modelled in terms of the elastic interaction between island nuclei in a newly forming layer and close islands in a buried layer below. Lateral ordering parallel to < 100 >, as observed previously in larger Ge-Si multilayer systems is not found in our systems, consisting of two Ge layers. This difference indicates that lateral ordering in the upper Ge layers of a large multilayer system is triggered by vertical ordering.     

Ab initio calculation of (2+1) resonance enhanced multiphoton ionization spectra and lifetimes of the (D,3)2Sigma- states of OH and OD

High-level ab initio potential-energy curves and transition dipole moments for the OH X 2Pi, 2 2Pi, 1 2Sigma-, D 2Sigma-, 3 2Sigma-, A 2Sigma+, B 2Sigma+, 1 2Delta, 1 4Sigma-, and 1 4Pi states are computed. The results are used to estimate the (2+1) resonance enhanced multiphoton ionization spectrum for the (D,3)2Sigma-(upsilon')<--2hnuX 2Piupsilon") transitions, which are compared with experiments by Greenslade et al. [see M. E. Greenslade, M. I. Lester, D. C. Radenovic, J. A. van Roij, and D. H. Parker, J. Chem. Phys. 123, 074309 (2005), preceeding paper]. We use the discrete variable representation-absorbing boundary condition method to incorporate the effect of the dissociative intermediate 1 2Sigma- state. We obtain qualitative agreement with experiment for the line strengths. Radiative and predissociative decay rates of the Rydberg (D,3)2Sigma- states of OH and OD were computed, including spin-orbit coupling effects and the effect of spin-electronic and gyroscopic coupling. We show that the lifetime of the Rydberg 2Sigma- states for rotationally cold molecules is limited mainly by predissociation caused by spin-orbit coupling.     

Periodic cosmic evolution in f(Q) gravity formalism

We study the periodic cosmic transit behavior of the accelerated universe in the framework of symmetric teleparallelism. The exact solution of field equations is obtained by employing a well-known deceleration parameter (DP) called periodic varying DP, $q=m\cos {kt}-1$. The viability and physical reliability of the DP are studied by using observational constraints. The dynamics of periodicity and singularity are addressed in detail with respect to time and redshift parameter. Several energy conditions are discussed in this setting.     

Impacts of supplier knowledge sharing competences and production capacities on radical innovative product sourcing

An effective sourcing strategy leads to cost savings and value added collaborations. For radical innovative product sourcing (RIPS), the exact nature and demand of products are highly uncertain. As such, knowledge sharing competences and production capacities of potential suppliers are prerequisite capabilities. The main aim is to investigate the impacts of these considerations on sourcing strategies through the development of two optimization models. Under the assumptions of single product sourcing, single period time window, uncertain demand and stochastic supply, KKT conditions are used to solve a simplified nonlinear optimization model analytically. The model is then expanded and particle swarm optimization is used to solve numerically the number of suppliers, order quantities and the level of relationship investments that maximize the value of sourcing. Through extensive scenario and sensitivity analyses, we provide some key insights.     

A column generation approach for the route planning problem in fourth party logistics

In this paper, we address the route planning problem in fourth party logistics (4PL). The problem calls for the selection of the logistics companies by a 4PL provider to optimize the routes of delivering goods through a transportation network. The concept of 4PL emerged in response to the shortfall in services capabilities of traditional third party logistics and has been proven to be capable of integrating logistics resources in order to fulfill complex transportation demands. A mixed-integer programming model is established for the planning problem with setup cost and edge cost discount policies which are commonly seen in practice. We propose a column generation approach combined with graph search heuristic to efficiently solve the problem. The good performance in terms of the solution quality and computational efficiency of our approach is shown through extensive numerical experiments on various scales of test instances. Impacts of cost policies on routing decision are also investigated and managerial insights are drawn.