Nitrogen Sweep Gas Research Articles

Investigation of experimental variables on polyether sulfone (PES) membrane in dehydration of natural gas

This study has been carried out to investigate the dehydration of natural gas of Tabnak sweet gas field by using membrane process, with PES membrane as a new, simple and cheap separation process. The effects of various experimental variables, such as pressure, temperature and nano silica particles in dehydration of natural gas by PES were investigated. PES and its silica nanocomposite membranes were prepared by solution blending in N,N-Dimethylformamide (DMF) and casting-evaporation method.The homogeneity and nano scale distribution of prepared PES-silica membranes were characterized using Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscope (SEM). Dehydration tests were done in pressure range of 2 to 10 bar and temperature range of 20 to 50° C, with nitrogen sweep gas. With an increase in the feed pressure, the permeated water was inhanced. On the other hand decreasing temperature, caused to improve the dehydration on process. Using PES-silica membrane increased water permeation.

Comparison of experimental and simulation results on catalytic HI decomposition in a silica-based ceramic membrane reactor

In this study, the catalytic decomposition of hydrogen iodide was theoretically and experimentally investigated in a silica-based ceramic membrane reactor to assess the reactor's suitability for thermochemical hydrogen production. The silica membranes were fabricated by depositing a thin silica layer onto the surface of porous alumina ceramic support tubes via counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. The performance of the silica-based ceramic membrane reactor was evaluated by exploring important operating parameters such as the flow rates of the hydrogen iodide feed and the nitrogen sweep gas. The influence of the flow rates on the hydrogen iodide decomposition conversion was investigated in the lower range of the investigated feed flow rates and in the higher range of the sweep-gas flow rates. The experimental data agreed with the simulation results reasonably well, and both highlighted the possibility of achieving a conversion greater than 0.70 at decomposition temperature of 400 °C. Therefore, the developed silica-based ceramic membrane reactor could enhance the total thermal efficiency of the thermochemical process.

Upgrading bio-oil produced from the catalytic pyrolysis of sugarcane (Saccharum officinarum L) straw using calcined dolomite

In this study, the catalytic pyrolysis of sugarcane straw (SCS) into bio-oil and chemicals using calcined dolomite was applied for upgraded bio-oil production. Experiments were performed in a custom-built SS316 tube reactor, and the effects of the pyrolysis parameters, including the different dolomite calcination conditions, temperature (400-600°C), biomass feed rate (0.3–1.2kgh−1), sweeping gas flow rate (80–200cm3min−1) and average size distribution (250–1000µm), were systematically investigated. The results showed that the SCS catalytic pyrolysis process obtained liquid yields of 36.15wt%, gas yields of 52.09wt% and solid yields of 11.76wt% when using a pyrolysis temperature, biomass feed rate, nitrogen sweep gas, and average biomass size of 450°C, 0.6kgh−1, 80cm3min−1 and 500µm, respectively, with 10wt% calcined dolomite. The calcined dolomite influenced the bio-oil components from the carbonylation and the cracking of volatile vapor and resulted in an upgraded bio-oil with a lower oxygen content, higher gross calorific value and decreased acid corrosion.

Enhancing cation exchange capacity of chars through ozonation

The use of ozone to increase the cation exchange capacity (CEC) of two chars produced from pyrolysis of Douglas fir (Pseudotsuga menziessii) and a control bituminous coal activated carbon (AC) is reported. Chars were produced from the wood fraction of Douglas fir (DFWC) and the bark (DFBC) at 500 °C using an auger driven reactor with a nitrogen sweep gas under mild vacuum. Five ozone treatment times, ranging from 5 min to 60 min, were investigated. The initial properties of each char were found to differ significantly from the other samples in terms of surface area, proximate composition, and elemental composition. DFWC did not show significant mass loss or temperature variation during ozone treatment; however, after 1 h of oxidation both DFBC and AC samples resulted in 20% and 30% mass loss, respectively, and reactor temperatures in excess of 60 °C. Analysis of the pore size distribution of each treatment shows that ozone treatment did not significantly affect small micropores after 30 min of treatment for any material, but did reduce the apparent surface area of mesopores. Increases in carboxylic groups were identified with ozone treatment and found to correlate strongly with changes in measured CEC. The formation of lactone was found to correlate positively with reactor temperature during oxidation. These results indicate that the properties of chars, including surface area, pore structure, and chemical composition, as well as reactor conditions strongly affect the ozone oxidation of chars.

English

Pyrolysis of palm kernel shell in a fixed-bed reactor was studied in this paper. The objectives were to investigate the effect of pyrolysis temperature and particle size on the products yield and to characterize the bio-oil product. In order to get the optimum pyrolysis parameters on bio-oil yield, temperatures of 350, 400, 450, 500 and 550 °C and particle sizes of 212–300 µm, 300–600 µm, 600µm–1.18 mm and 1.18–2.36 mm under a heating rate of 50 °C min -1 were investigated. The maximum bio-oil yield was 38.40% at 450 °C with a heating rate of 50 °C min -1 and a nitrogen sweep gas flow rate of 50 ml min -1 . The bio-oil products were analysed by Fourier transform infra-red spectroscopy (FTIR) and gas chromatography–mass spectroscopy (GCMS). The FTIR analysis showed that the bio-oil was dominated by oxygenated species. The phenol, phenol, 2-methoxy- and furfural that were identified by GCMS analysis are highly suitable for extraction from the bio-oil as value-added chemicals. The highly oxygenated oils need to be upgraded in order to be used in other applications such as transportation fuels.

Benchmarking of Hydrogen Selective Membranes: Experimental and Modelling Approach to Compare Membrane Performance

Precombustion CO2 capture can be feasible with mature palladium-based membranes in modules. Before moving on to demonstration, benchmarking of membranes is a crucial step in their introduction. The strategy presented here, consisting of matching results from experiments and model development, will be a valuable tool in benchmarking membrane performance. Using experiments with pure hydrogen feed and no sweep, the permeation of hydrogen through the metallic palladium layer was accurately fitted with a standard permeation equation (1) with Q and n as regressed parameters. The pressure drop in the membrane support was included but was found to be small (14kPa). Hydrogen-nitrogen separation experiments without sweep gas could be predicted by a 2D laminar flow convection and diffusion model. Thus, convective and diffusive transport of hydrogen and inert in the modules was successfully accounted for by the module model. Experiments with nitrogen sweep gas have shown significant resistances in the membrane support. These were predicted by the dusty gas model to be both a small pressure drop and a rather large mole fraction gradient in the support layer, the latter being far more important than the former. The derived model allows to quantify, as a function of operating conditions, the intrinsic and external mass transfer resistances. In order to make the final step toward full use of the model in benchmarking of membranes the model is currently be extended to incorporate the effect of inhibition of syngas components. The final model will be used to run selected cases and the results will be validated with hydrogen permeation results from experiments in syngas. The model will also be used for predicting membrane performance at commercial scale.

Influence of the support on permeation of palladium composite membranes in presence of sweep gas

The influence of the porous support on hydrogen permeation of a Pd-composite membrane in presence of sweep gas has been evaluated. A 20μm thick palladium membrane has been prepared by electroless plating on a tubular stainless steel support. H2 permeation tests have been performed in a laboratory pilot loop up to 400°C and 800kPa; a nitrogen sweep gas in the 0–100Nl/h flow rate range has been fed to the permeate side. H2 flux through the Pd-membrane has been first measured in absence of sweep gas. Permeation can be described by the Sieverts’ law and the best fitting of the pressure exponent (n-value) at 400°C is 0.67. Support resistance, estimated by using dusty-gas model equation, determines an increase of H2 pressure at the interface between Pd-layer and support from 100 to 140kPa, and a H2 flux reduction of the 9.8%, approximately. While feeding N2 as a sweep gas, a H2 flux much lower than expected by considering Sieverts’ law is measured. The difference between experimental results and expected values, calculated by a simple uni-dimensional model is about the 30%, at the higher flow rates. Moreover the increase of n-value from 0.68 up to 0.9 suggests a strong increase in the mass transfer resistance of the support. The resistance to H2 diffusion due to presence of stagnant N2 in the support pores has been then estimated by using the dusty gas model equation, which combines Knudsen diffusion, viscous flow and binary diffusion. Results indicate that binary diffusion of H2 in stagnant N2 can be responsible of the observed H2 flux reduction. H2 partial pressure calculated at the interface between Pd-layer and support in presence of sweep gas is always significantly higher than H2 partial pressure measured in the permeate. This difference is progressively increasing while increasing sweep gas flow rate and tends to saturate at high flow rates.

Evaluation of the water gas shift reaction in a palladium membrane reactor

The water gas shift (WGS) reaction of a syngas mixture has been carried out in a tubular palladium membrane reactor at a temperature of 410–414 °C. A composite palladium-porous stainless steel membrane, 29 μm thick, obtained by electroless plating, has been first extensively tested with pure gases (H 2, He, CO 2) and syngas mixtures in the 310–455 °C temperature range and up to 800 kPa. Long-term stability of the membrane in H 2 at 400 °C has also been checked over a period of 1200 h. The membrane has been then used for WGS tests in a membrane reactor. The membrane reactor, packed with a pulverized Fe/Cr commercial catalyst, has been operated at a reaction pressure of 100–600 kPa in the counter-current mode, with a nitrogen sweep-gas. The reactor has been fed with a shift gas mixture with a 7.6% CO concentration and H 2O/CO ratio in the 2.7–3.6 range. The membrane reactor was able to achieve up to the 85.0% of CO conversion, while only the 37% as a maximum, was reached with the traditional reactor in the same operating conditions. Up to the 82% of hydrogen has been recovered with a purity exceeding the 97%.

Effect of Thermal Treatment on Acidic Organic Species from Athabasca Bitumen Heavy Vacuum Gas Oil, Analyzed by Negative-Ion Electrospray Fourier Transform Ion Cyclotron Resonance (FT-ICR) Mass Spectrometry

We examine suspected molecular transformations of thermally treated Athabasca bitumen heavy vacuum gas oil (HVGO) by ultrahigh-resolution negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Liquid products from HVGOs treated under an inert N2 atmosphere at temperatures of 300, 325, 350, and 400 °C were each characterized by class (heteroatom content), type (double-bond equivalents = number of rings plus double bonds to carbon), and carbon number distribution. In addition, the inert N2 sweep gas of the autoclave was collected, condensed, and analyzed. The total acid number (TAN) of the HVGO liquid products decreases with an increasing treatment temperature (from 4.13 at 300 °C to 1.46 at 400 °C), indicative of potential carboxylic acid decomposition. The highly abundant O2 class contains species with DBE = 3; however, no compositional changes occur with increased treatment temperature. A bimodal DBE distribution is observed for the S1O2 class, suggesting two possible stable core structures. Only low relative abundance classes show slight changes with thermal treatment. Condensed nitrogen sweep gas obtained at 350 and 400 °C contains highly abundant O2 species with DBE of 3 and but at lower carbon number. Similarly, the condenser product S1O2 classes display the same bimodal DBE distributions as the HVGO liquid products but with lower carbon number (∼18−27 for condenser versus ∼25−35 for the liquid products). The similarity of the O2 speciation in the HVGO liquid products after thermal treatment combined with the detailed analysis of the condenser products suggests that the gross decrease in total acid number (TAN) at higher temperature is due to global (class, DBE, and carbon number indiscriminant) decomposition of the naphthenic acids as well as a small contribution from the loss of the lower boiling, lower carbon number acids by simple distillation.

A new test method for measuring the water vapour permeability of fabrics

The water vapour permeability of textile fabrics is a critical determinant of wearer comfort. Existing test methods are either time consuming or require large amounts of material. A new test apparatus was developed for characterizing the water vapour permeability of fabrics. An aluminium cylinder covered with waterproof and vapour permeable PTFE laminate is used for generating water vapour source on one side of the sample. A dry nitrogen sweep gas stream is used to carry water vapour away. The calculation of the rate of water vapour transmission across the fabric is based on the measurement of the relative humidity of the outgoing nitrogen stream. This new measuring apparatus offers a short test time and calls for a small sample size. The comparison measurements show that the test results correlated well with those obtained from ISO 11092 and ASTM E96. Therefore, this test method provides a new technique to accurately and precisely characterize the water vapour transport properties of fabrics.

Infrared spectroscopic measurement of water permeability in polymer films exposed to liquid water

The details of a method for measuring the water vapor transport rate through polymer films utilizing Fourier transform infrared spectroscopy (FTIR) are given. Water flows across one side of the membrane and a nitrogen sweep gas carries the water vapor into the flow-through cell of the spectrometer for measurement. The method was used to test two polymers that have literature values and four new polymers. The resulting FTIR data was analyzed with a partial least-squares method. Experimentally the method is easy to apply and very accurate.

Modeling of tritium release from ceramic breeder materials by focusing on transport process in breeder grain

The effect of water vapor on the releases of tritium from a lithium silicate was investigated. Out of pile tritium release experiments were conducted using the ceramic breeder irradiated in a research reactor. Tritium was released from the lithium silicate breeder material using a nitrogen sweep gas with 0.1% water vapor. It was found that the addition of water vapor to the sweep gas greatly enhances the release rate of tritium from the ceramic breeder. The results of the tritium release experiment were analyzed using a numerical model of diffusion control. However, the analysis indicates that the assumption of only diffusion control cannot reproduce the experimental results. Thus, the effect of trapping sites was also considered in the model. It was found that the model with the trapping site effect reproduce the experimental tritium release curve.

Carbonisation of bagasse in a fixed bed reactor: influence of process variables on char yield and characteristics

Carbonisation experiments on samples of sugar cane bagasse were conducted in a static fixed bed reactor to determine the effect of process variables such as temperature, heating rate, inert sweep gas flow rate and particle size on the yield and composition of solid product char. Experiments were performed to the final temperatures of 250–700°C with heating rates from 5 to 30°C/min with nitrogen sweep gas flow rate of 350 cc/min. Additional tests were aimed at studying the effect of different flow rates of nitrogen sweep gas from 0 to 700 cc/min during carbonization and different particle size fractions of bagasse. The results showed that as the carbonisation temperature was increased, the yield of char decreased. The reduction in yield was rapid up to a final temperature of 500°C and was slower thereafter. The yield of char was relatively insensitive to the changes in heating rate and particle size. Increasing the sweep gas flow rate to 350 cc/min reduced the yield of char. It appears the presence of inert sweep gas reduced secondary reactions which promoted char formation. The proximate analysis of the char suggests that fixed carbon and ash content increased with temperature. The char obtained at temperatures higher than 500°C have high carbon content and is suitable as renewable fuel and for other applications. The carbonization of bagasse has the potential to produce environmental friendly fuels and can assist in reducing deforestation for the production of charcoal.

Use of polysulfone hollow fibers for bubbleless membrane oxygenation/deoxygenation of water

Abstract The oxygenation of water by a pure oxygen stream and the removal of dissolved oxygen from water by a nitrogen sweep gas were studied in a transverse flow module made with 1058 hydrophilic polysulfone hollow fibers. In the range of water flow rates of 0.3–3 l h −1 the overall mass-transfer coefficient ranges from (0.52 to 1.8)×10 −6 m s −1 , and from (0.77 to 3.7)×10 −6 m s −1 for water flow outside and inside the hollow fibers respectively. For water flow outside the fibers the main resistance to oxygen transfer is in the liquid-phase boundary layer, whereas for water flow inside the fibers the main resistance is in the membrane. The liquid-phase mass-transfer coefficient is proportional to the water flow rate raised to powers ranging from 0.63 to 0.67. The mass transfer coefficient of the membrane phase at 291 K ranges from (3.6 to 4.7)×10 −6 m s −1 , which is three orders of magnitude lower than that for hydrophobic polypropylene hollow fibers. Nevertheless, polysulfone hollow fibers can be successfully used at low water flow rates to reduce the dissolved oxygen level in feed water from 8–9 mg l −1 to less than 0.04 mg l −1 or to achieve almost complete saturation of water with pure oxygen.

Membrane reactor for water gas shift reaction

In this experimental study the water gas shift (WGS) reaction is considered as a particular application of a catalytic membrane reactor (CMR). Experiments on the WGS reaction were carried out using a composite palladium membrane obtained by coating an ultrathin double-layer palladium film on the inner surface of the support of a commercial tubular ceramic membrane by a so-called co-condensation technique. The best operating conditions were determined at various H 2O CO molar ratios, temperature, P Iumen, gas feed flow, and with and without nitrogen sweep gas. For a non-porous stainless steel tube and for the commercial ceramic membrane having the same geometrical dimensions, the conversion results are always lower than the equilibrium value. For the composite palladium membrane, the conversion also depends on the flow of the sweep gas utilized. For example, using a nitrogen sweep gas flow of 28.2 cm 3/min, the maximum conversion value reaches 99.89%. The study of the effect of temperature on conversion of carbon monoxide in the WGS reaction shows that at higher reaction temperature, the thermodynamic equilibrium conversion of CO decreases. In contrast for the CMR considered in this work, there is a maximum conversion value around 600 K. This value is a compromise between the kinetic rate of the reaction (which increases with increasing temperature) and thermodynamic considerations for the WGS reaction. The effect of the time factor ( W F ) on conversion of CO, with and without sweep gas at three different temperatures (595, 615 and 633 K) shows that at greater W F there are correspondingly higher values of the CO conversion for each temperature considered. For each temperature there is a slight effect of the sweep gas, and this is higher at 595 K. The good performance of the composite ceramic-palladium membrane is confirmed by a comparison with experimental results recently presented in the literature for the same reaction. Reaction tests have been carried out for a feed mixture also. In this case, however, the resulting values are always below the equilibrium ones.

Evaluation of steam as a sweep gas in low temperature thermal desorption processes used for contaminated soil clean up

The purpose of this investigation was to compare the effectiveness of steam as a sweep gas in the low temperature thermal desorption (LTTD) process. The intent is to determine if steam may be substituted for nitrogen, which is the sweep gas of choice for many thermal desorption processes. Steam has several advantages over nitrogen. Among those advantages is lower cost and the availability of on-site generation facilities. The study was conducted by placing a stainless steel tube containing a predetermined amount of contaminated soil in an electrical furnace. The tube had openings at each end. One end of the tube was connected to the source of the sweep gas with the other end being connected to a ice bath condenser. The effectiveness of steam and nitrogen were compared as sweep gasses at similar operating conditions. The contaminants of interest in this study were: volatile compounds, p-xylene (Normal Boiling Point (NBP), 138°C), trichloroethylene — TCE (NBP, 86.9°C), and a semi-volatile compound, phenanthrene (NBP, 340°C). Sweep gas flow rate was varied over a range that would be expected in a commercial size LTTD unit. The sweep gas efficiency was evaluated over a series of exposure times and three temperatures of 177, 232, and 288°C. The residual concentration of the contaminant was determined by gas chromatographic analysis. Rates of contaminant desorption were determined as a function of time, sweep gas volume, and specific contaminant. The data generated allowed a general comparison of nitrogen and steam as sweep gases. In most cases tested, the treatments using steam as the sweep gas exhibited characteristics that were comparable to or better than nitrogen sweep gas treatments. The advantage of steam was more pronounced with the higher boiling point semi-volatile compound phenanthrene.