Experimental studies on the effect of inert gases on diffusion distillation of ethanol–water mixtures

BACKGROUND: Diffusion distillation of ethanol–water mixtures in the presence of air as an inert gas has been used to produce fuel grade ethanol, and studies on the effect of vaporization temperature and feed composition on the selectivity and total molar flux have been presented recently. This paper describes the separation of ethanol–water mixtures by diffusion distillation in the presence of light and heavy inert gases such as helium and argon and reports the changes in selectivity and total molar flux in comparison with those in air. RESULTS: Total molar flux in the presence of light inert gases like helium increases rapidly with vaporization temperature but at the cost of reduced selectivity. The use of heavy inert gases like argon results in increased selectivity but total molar flux decreases. Compared with helium and air at a constant temperature, the quantity S_az(N₂/N₁) is found to be higher for argon. CONCLUSIONS: Experimental results demonstrate that a high degree of separation can be achieved by using heavy inert gases. The higher value of the quantity S_az(N₂/N₁) for argon indicates that the heavy inert gas results in enhanced separation. The light inert gas can be used if high transfer rates are required at low vaporization temperature. The quantity S_az(N₂/N₁) can be used not only for vaporization temperature optimization but also for selecting the appropriate inert gas for the process. Copyright © 2011 Society of Chemical Industry     

惰气存在下的热敏物料真空精馏

本文针对热敏物系精馏存在的问题,通过加入惰性气体以降低精馏温度,较全面地考察了惰性气体对精馏塔的影响,说明惰气真空精馏可以有效地解决热敏物质的精馏问题。     

Fuel grade ethanol by diffusion distillation: an experimental study

BACKGROUND: Fuel grade ethanol (anhydrous ethanol) is considered to be an excellent alternative clean burning fuel to gasoline. It is now used as an additive to gasoline to enhance its octane number and combustibility. Owing to its high energy values, ethanol is the most promising future biofuel. Because of azeotrope formation, anhydrous ethanol cannot be achieved by conventional distillation. Diffusion distillation is one of the several processes that can be used to separate azeotropes. Diffusion distillation takes advantage of differences in relative rates of diffusion using inert gas as selective filter. RESULTS: Effect of vaporization temperature and feed composition on diffusion distillation of an ethanol–water mixture using air as the inert gas has been studied. A new quantity S_az(N₂/N₁) has been suggested to find the optimum vaporization temperature. In the present study this was found to be about 46 °C. The pseudo‐azeotrope has been observed at 0.697 mole fraction of ethanol at a vaporization temperature of 50 °C. Separation is effected by diffusion distillation even at the azeotropic ethanol mole fraction of 0.894. The experimental results were compared with a Stefan–Maxwell equations based mathematical model and found to be in good agreement with theoretical results. CONCLUSIONS: Experimental results demonstrate that fuel grade ethanol can be produced by diffusion distillation. The new quantity S_az(N₂/N₁) is a key variable for vaporization temperature optimization. Copyright © 2011 Society of Chemical Industry     

Suppression of Osmotic Distillation in Gas Membrane Processes

Abstract

Suppression of osmotic distillation of water is important for the commercial scale application of gas membranes. We have equalized the water vapor pressure on either side of the membrane by increasing the temperature of the stream with the lower water vapor pressure. The experimentally determined temperature gradient is many times larger than predicted from water vapor pressure–temperature data. The larger temperature gradient may be explained by considering the heat flux across the membrane. The economic viability of adjusting the temperature of the feed and strip streams to suppresses water vapor transport depends on the additional energy costs involved.     

Experimental investigation on a membrane distillation based micro-separator

In this work a novel micro-separator combining the sweep gas membrane distillation principle with micro-fluidic channels was designed and tested for the separation of a mixture of methanol and water with a low to high methanol concentration. The performance of the new separation device was studied with different liquid–vapor/gas membrane contactors with respect to the separation factor and the distillate flux rate by varying the relevant operating parameters of the process like the methanol concentration in the feed (5–70 wt.%), the feed temperature (40–65 °C), the feed flow rate (up to 30 ml/min), and the flow rate of the inert carrier gas nitrogen (up to 600 ml/min at standard conditions). For all performed experiments, the feasibility of the separation has been proved and the possibility to separate mixtures with high methanol concentration by using a membrane distillation based micro-separator has been for the first time reported. The inert gas flow rate was identified as the crucial operating parameter influencing the separation performance of the micro-separator. In addition, the selection of an appropriate membrane liquid–vapor/gas contactor was found to be an important design parameter for the reduction of temperature polarization effects.     

Diffusion distillation - A new separation process for azeotropic mixtures Part 1: Selectivity and transfer efficiency

A new separation process for azeotropic mixtures3̄diffusion distillation—is proposed. A liquid mixture is evaporated below the boiling temperature, diffuses through an inert gas gap and is recondensed. Hence the separation effect is not only based on the relative volatility of the components concerned but also on their diffusivity in the inert gas. In a wetted-wall column consisting of two concentric tubes, a significant separation effect can be achieved. Several experiments were carried out with a binary isopropanol-water mixture and a ternary isopropanol-water-methanol mixture at different evaporation and condensation temperatures, with different inert gases and annular widths in the wetted-wall column. The experimental results were well described by the vapour-liquid equilibrium and the Stefan-Maxwell equations, that is, by steady-state molecular diffusion.     

Electrochemical Separation of Hydrogen Sulfide from Natural Gas

Abstract

An electrochemical process has been developed for the removal of H₂S from contaminated natural gas. Removals as high as 80.7% have been achieved from a simulated process gas (2000 ppm H₂S). H₂S is removed by reduction to the sulfide ion and hydrogen gas at the cathode. The sulfide ion migrates to the anode through a molten electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. No materials are required beyond initial electrolyte membrane installation; the H₂S is converted in one step to elemental sulfur making it an economically attractive process both from the lack of raw materials and the lack of any solvent regeneration.     

Influences of Drying and Storage of Lycopene-Rich Carrots on the Carotenoid Content

ABSTRACT

The stability of β-carotene and lycopene was investigated during convective air and inert gas drying, microwave vacuum drying, and freeze-drying for lycopene containing carrots (Daucus carota L. cv. Nutri Red). After convection drying at temperatures below 70°C, β-carotene and lycopene contents remained unchanged independent of the drying medium. Freeze-drying did not show any advantage to convection-drying regarding carotenoid retention. Microwave vacuum–drying led to dry products with high carotenoid retention within very short drying times of about 2 h. Storage in air and in inert gas (nitrogen) containers was studied for convection-dried products, observing a better retention of carotenoids when using inert gas for a period of up to 6 months. After convection- and microwave vacuum–drying, an even better carotenoid extractability could be observed. No changes in the isomere fractions could be detected in any case.     

分子蒸馏过程模型化研究进展

介绍了分子蒸馏基本原理和常用分子蒸馏设备 ,系统地对分子蒸馏过程模型化的研究进展情况进行了叙述 ,重点介绍了蒸发系数法、液体内部传质传热和蒸馏区惰性气体压力对分子蒸馏的影响等方面的研究结果 ,并对其进行了评述 ,同时对分子蒸馏过程研究的进一步发展提出了一些展望。     

THESES/DISSERTATIONS/1963-1983, POLAND

ABSTRACT

A fluidized bed of inert particles lpar;packing)--> can be used advantageously for the drying of paste-like materials of high moisture content. Wet pasty material is fed into a fluidized bed of chemically inert coarse particles. The wet material coats the surface of the inert particles. Drying takes place mainly in the thin layer formed on the surface of particles. After reaching a certain moisture content, the dried material film breaks off the surface of the packing particles, and leave the fluidized bed as a fine powder in the exit gas stream.

Experiments were performed using different organic and inorganic materials e.g. raw materials from human and veterinary     

A Selective Silicon-Based Membrane Formed by Pyrolysis of Silicon Resin

Abstract

A new, highly selective silicon-based membrane was developed by pyrolyzing a thermosetting silicon resin precursor in two steps. The pyrolysis step was performed under an inert gas in the range of 800 to 950°C. The activation step was conducted at the same temperature as the first step. Oxygen content in the activation gas was located between 0.5 and 1.0%. The crosslinking density and the matrix structure of the polymeric precursor were important factors for the permeable characteristics of the resulting pyrolysis membrane. The average selectivity was 5 to 10 times those of a pyrolysis membrane from silicon rubber. Additives in the precursor had significant effects on toughness and stability of the resulting membrane. By varying the additive content in the precursor, silicon-based pyrolysis membranes with different stabilities in air were obtained.     

FREEZE DRYING OF A FROZEN LIQUID IN A PHIAL

ABSTRACT

A sorption-sublimation mathematical model for a freeze dryer is presented, and is used to investigate the design and operation of a freeze dryer, in which a frozen liquid enclosed in a phial is dried.

With the material chosen, it was found that the best operating condition would correspond to minimum chamber inert gas pressure. The most desirable design of dryer appears to be one in which moderate but consistent resistances to heat transfer are incorporated, so that the heat flux program of the lower heating plate could be optimized by operating at a higher temperature, either under feedback or preprogrammed feedforward controllers.     

Low Temperature Distillation Through Hydrophobic Membranes

Abstract

The use of hydrophobia porous membranes makes it possible to maintain liquid-vapour interfaces localized at a membrane surface. Based on that, thermally driven separation processes were obtained through the membrane and thoroughly analyzed both experimentally and theoretically, Two experimental conditions were used: i) the porous membrane is in direct contact with two liquid aqueous phases on both sides and the vapour phase is trapped inside the pores (capillary distillation); ii) on one side of the porous membrane there is a warm aqueous solution, while an additional gaseous gap is maintained on the opposite side of the porous membrane; the vaporizing component diffuses through the entire gas phase and condenses at a cold surface confining the gaseous gap (cold wall distillation).

The mathematical model, describing both the separation rate and the energy flux is presented and compared with the experimental results. The influence of the gas membrane thickness is also discussed.     

INFLUENCE OF THE PARTICLE SIZE AND SUPERFICIAL GAS VELOCITY ON THE SUBLIMATION OF PURE SUBSTANCES IN FLUIDIZED BEDS OF DIFFERENT SIZES

Abstract

In the present study the sublimation of large solid carbon dioxide particles inside fluidized beds of fine particles is investigated. A model which takes the surface area of the sublimable particles into account is used to describe the sublimation kinetics. Based on this model, the results of different experiments, namely single particle experiments using a precision scale, batch experiments in a laboratory-scale fluidized bed and continuous experiments in a larger circulating fluidized bed are compared. The main focus of the study is to evaluate the influences of the particle size, of the inert bed material, of the bed temperature and of the superficial gas velocity, respectively.     

CARBON COMBUSTION RATES AND TEMPERATURES IN SHALLOW FLUIDIZED BEDS

Abstract

The mechanism of combustion of carbon in shallow fluidized beds at temperatures 750-1000°C is studied by measuring burning rates and temperatures of spherical carbon particles ranging from 2 mm to 12 mm diameter directly in an experimental fluidized bed. Among variables investigated were inert particle size, superficial fluidizing velocity, temperature, the influence of neighbouring active particles and oxygen concentration in the fluidizing gas.

Under the experimental conditions explored, combustion was mainly kinetically controlled, so that with carbon particles larger than about 4 mm, burning rates are significantly higher than those predicted by combustion models which assume combustion to be controlled by the rate at which oxygen diffuses through a stagnant particulate phase surrounding the burning particle. The higher burning rate seems to arise because the greater mobility of particles in the bed causes the restriction to oxygen flow to the carbon surface offered by the particulate phase to be reduced and has important consequences for combustor design.

Measured carbon particle temperatures were influenced considerably by bed operating conditions ranging from 15 to 215°C higher than bed temperature.

Measured burning rates of carbon particles were found to be reduced significantly when other active particles were present in the bed. This sensitivity of burning rate to changes in active particle concentration in the bed was shown to be increasingly important once the concentration of carbon in the bed exceeded about 1%

Increasing the bed inert particle size, superficial fluidizing velocity, oxygen concentration in the fluidizing gas and bed temperature resulted in higher burning rates. The implication of these findings on combustor design are discussed.     

新型蒸馏技术及应用

介绍了萃取精馏、共沸精馏、反应 (催化 )蒸馏、吸附蒸馏、膜蒸馏、惰性气体蒸馏、动态高效规整填料塔精馏和分子蒸馏等新型蒸馏技术的基本原理、特点、研究进展和发展方向。     

Facilitated Transport Membrane Hybrid Systems for Olefin Purification

Abstract

A new membrane system has been developed by BP for refinery and chemical plant olefin purification and recovery. This facilitated transport system, coupled with distillation, offers lower capital and operating costs than conventional distillation alone. Initial results on lab scale hollow fiber devices indicate membrane flux ranging from 8.75×10^?6 to 8×10^?5 m³/m²/sec (2.5 to 23 scfd/ft²) and selectivities from 150 to 300. Pilot plant experiments on propylene/propane and ethylene purge gas recovery over three to six months duration show membrane stability and product purity of 98.5% or greater using refinery grade propylene feed. Hybrid system optimization data for membranes and distillation indicate that using a side draw from the distillation tower provides advantages in terms of membrane area, purity of feed to the membrane, and low per-pass recovery coupled with high overall propylene recovery. Membrane performance data under various conditions will also be presented. In addition to performance data, economic evaluation and energy savings will be discussed.     

Preparation of Highly Purified 1,3-Dimethyl-5-t-butylbenzene by Normal Freezing

Abstract

A combination of fractional distillation and normal freezing was used to purify 1,3-dimethyl-5-t-butylbenzene. Analysis by gas chromatography indicates that the final product was > 99.999% pure. A number of physical constants are given of the pure material.     

Natural gas sweetening using low temperature distillation: simulation and configuration

ABSTRACT

Hypothesis: Separation of CO₂ from a stream of natural gas using low-temperature distillation process is complicated not only because of the existence of ethane (C₂) and CO₂ azeotrope but owing to the freezing of CO₂. A modified process based on an existing Ryan–Holmes process in the form of a low-temperature distillation is presented here for the separation of sour gases. In addition, solvents were employed to prevent CO₂ freezing and to avoid formation of the C₂-CO₂ azeotrope.

Simulation: Simulation calculations were carried out using a natural gas stream containing CO₂ and H₂S. The process was designed and simulated using Aspen HYSYS 9.

Findings: A low-temperature process for the separation of a feed stream containing up to 30 mole% CO₂ and 2.5 mole% H₂S was achieved, which lowered the levels of these gases to within 50 and 4 ppm, respectively. These values conform to liquefied natural gas specifications. The compositions of the product streams, the required solvent circulation flow rates, and the total energy requirements were estimated. The reported process successfully separated H₂S and produced CO₂ at a pressure of 25.0 bar and a temperature of ?13°C, thereby ensuring its suitability for application in enhanced oil recovery. This described process also delivered the desired natural gas product at 35 bar and ?90°C ready for liquefaction and further cooling.     

Membrane Distillation Employed for Separation of Water Isotopic Compounds

Abstract

An attempt to apply membrane distillation (MD) for the enrichment of water isotopic compounds was made. The process was conducted as a direct-contact MD with flat-sheet microporous, hydrophobic polytetrafluoroethylene (PTFE) membranes in the temperature range 323–353K. The distillate condensation was carried out directly into a stream of cooling water. The comparison between calculated Rayleigh distillation curves and the results of permeation experiments demonstrated the MD process to be more efficient than simple distillation for enrichment of the heavy isotopes in water.