Maxim M. Trubyanov

An improved back-flush-to-vent gas chromatographic method for determination of trace permanent gases and carbon dioxide in ultra-high purity ammonia

A novel method for rapid, quantitative determination of trace permanent gases and carbon dioxide in ultra-high purity ammonia by dual-channel two-dimensional GC-PDHID is presented. An improved matrix back-flush-to-vent approach combining back-flush column switching technique with auxiliary NaHSO4 ammonia trap is described. The NaHSO4 trap prevents traces of ammonia from entering the analytical column and is shown not to affect the impurity content of the sample. The approach allows shortening the analysis time and increasing the amount of measurements without extensive maintenance of the GC-system. The performance of the configuration has been evaluated utilizing ammonia- and helium-based calibration standards. The method has been applied for the analysis of 99.9999+% ammonia purified by high-pressure distillation at the production site.

Kinetics of germanium tetrachloride reduction with hydrogen in the presence of pyrolytic tungsten

Pyrolytic tungsten coatings have been produced on the surface of ash microspheres under steady-state conditions using tungsten hexacarbonyl as a precursor. The nanostructured composites thus obtained were characterized by X-ray diffraction and scanning electron microscopy. We have studied the kinetics of the catalytic reduction of germanium tetrachloride with hydrogen in the temperature range 423–973 K in the presence of the composites as catalysts and determined the reaction order and activation energy for the catalytic reduction of germanium tetrachloride with hydrogen.

Temperature dependence of the separation factor in the batch distillation of ammonia between the normal boiling point and the critical temperature

The temperature dependence of separation factor has been investigated for fine purification of ammonia in batch packed distillation columns. For a number of binary ammonia-impurity systems, the separation factor as a function of temperature between the normal boiling point and the critical temperature passes through a maximum. The position of this maximum depends on the separation coefficient of the binary mixture.

Separation of ammonia-containing gas mixtures in a one-compressor multistage membrane apparatus

Separation of the gas mixtures 7.7 vol % nitrogen in ammonia and 5.5% carbon monoxide in ammonia in one-compressor multistage membrane devices with one and two separation steps has been compared. The apparent values of selectivity have been determined for these gas mixtures. Expressions relating the degree of separation to the stage cut and the degree of purification to the product loss have been experimentally obtained. The degree of purification has been shown to increase with the number of stages despite of the fact that the degree of separation at individual stages is lower than in a single membrane module.

Catalytic effects of electrode material on the silicon tetrachloride hydrogenation in RF-arc-discharge

A silicon tetrachloride reduction in RF-arc-discharge (40.86 MHz) has been experimentally studied. The electrode material significantly affects the composition of the chlorosilanes in the gas phase at the outlet of the reactor which may be attributed to high and at the same time different catalytic activity of Cu, Ni, Nb, and Zr metals belonging to the transition of d-elements and W f-elements of the periodic table. The corrosion has been observed on the electrodes with the formation of chlorides of Cu, Ni, Nb, Zr, and W metals. In the system formed by two electrodes and plasma there are three main reactive regions in which the recovery of silicon tetrachloride by hydrogen at different flows is conducted independently from each other. The analysis of exhaust gases, chemically active plasma and condensed phase by emission-spectroscopy and GCMS spectrometry made it possible to propose the mechanism of formation of observed intermediate species and final products. On the basis of the obtained results we can conclude that this type of RF-plasma discharge includes two mechanisms of plasma chemical reactions: one with the participation of active particles formed in plasma and one initiated by the catalytically-active surface of the electrode.

Modeling of Fast-Permeant Component Removal from Gas Mixture in a Membrane Module with Pulsed Retentate

The process of unsteady-state membrane gas separation (fast-permeant impurity removal) with a pulsed retentate flow operation was considered. A semiempirical mathematical algorithm was developed to describe this process taking into account its kinetic characteristics (total cycle time, stripping time and withdrawal time, withdrawal velocity) using the MathCad® software package. Based on the developed algorithm, the basic operational parameters that affect the separation efficiency of the unsteady-state process were analyzed. It was shown that the optimal ratio of the stripping time and the withdrawal one determined by the maximum efficiency criterion more corresponds to the minimum retentate concentration than to the maximum productivity. However, the developed algorithm allows to set the productivity minimum limit by introducing additional initial data into the calculation procedure. The mathematical modeling results correlate well with the experimental data.

Total Reflux Operating Mode of Apparatuses of a Membrane Column Type during High Purification of Gases to Remove a Highly Permeable Impurity

Performance of a three-module membrane column in high gas purification processes to remove highly permeable impurities has been experimentally evaluated using the separation of the CH4/CO2 binary gas mixture (CO2 content of 1 vol %) as an example. The time to reach the steady-state regime in a total reflux operating mode has been determined for two configurations, the three-module membrane column (TMC) and the continuous membrane column (CMC) proposed by Hwang with colleagues. The influence of the efficiency of removal of the highly permeable impurity on the degree of purification of the low-permeability target component has been shown. The obtained product purity has appeared to be 99.997 or 99.93% at the recovery rate of 15 or 81%, respectively. It has been demonstrated that the three-module membrane column hold promise for use in high gas purification.

Towards the interaction between calcium carbide and water during gas-chromatographic determination of trace moisture in ultra-high purity ammonia

The current study focuses on the processes involved during the flow conversion of water into acetylene in a calcium carbide reaction cell for the trace moisture analysis of ammonia by reaction gas chromatography. The factors negatively affecting the reproducibility and the accuracy of the measurements are suggested and discussed. The intramolecular reaction of the HOCaCCH intermediate was found to be a side reaction producing background acetylene during the contact of wet ammonia gas with calcium carbide. The presence of the HOCaCCH intermediate among the reaction products is confirmed by an FTIR spectral study of calcium carbide powder exposed to wet gas. The side reaction kinetics is evaluated experimentally and its influence on the results of the gas chromatographic measurements is discussed in relation to the determination of the optimal operating parameters for ammonia analysis. The reaction gas chromatography method for the trace moisture measurements in an ammonia matrix was experimentally compared to an FTIR long-path length gas cell technique to evaluate the accuracy limitations and the resource intensity.