Analysis of carbon dioxide gas/liquid mass transfer in aerated stirred vessels using non–Newtonian media

Gas/liquid mass transfer has been investigated in an aerated stirred tank using non‐Newtonian media and carbon dioxide as absorbent and gas phase respectively. The volumetric mass transfer coefficients at different operational variables have been measured. The non‐Newtonian media (liquid phases) used were aqueous solutions of two polymers, carboxymethyl cellulose and alginate sodium salts. The influence upon the mass transfer of the rheological properties, polymer concentration, stirring rate and gas flow rate was studied. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymers employed. Reasonable agreement was found between the predictions of proposed models and the experimental data. The results shown in the present paper allow us to understand carbon dioxide transfer to a non‐Newtonian liquid phase and to evaluate the effect of the liquid phase characteristics. The equations used in this paper allow accurate simulation of the transfer of a pure gas to a rheologically complex solution. Copyright © 2004 Society of Chemical Industry     

Gas Holdup and Solid‐Liquid Mass Transfer in Newtonian and non‐Newtonian Fluids in Bubble Columns

Gas holdup and surface‐liquid mass transfer rate in a bubble column have been experimentally investigated. De‐mineralized water, 0.5 and 1.0% aqueous solutions of carboxy methyl cellulose (CMC), and 60% aqueous propylene glycol have been used as the test liquids. Effects of column diameter, liquid height to column diameter ratio, superficial gas velocity and liquid phase viscosity on gas holdup and mass transfer rate are studied. Generalized correlations for the average gas holdup and wall to liquid heat and mass transfer coefficients are proposed. These are valid for both Newtonian and pseudoplastic non‐Newtonian fluids.     

鼓泡反应器中幂律型流体流动与传质特性

很多废水处理装置涉及非牛顿型流体中的多相流动和传质问题,研究其中的气液传质过程有助于实现装置的优化设计和高效节能运行。以鼓泡反应器内清水和不同质量分数的羧甲基纤维素钠（CMC）水溶液为实验对象,分别研究气相表观气速和液相流变特性对气泡尺寸分布、全局气含率和体积氧传质系数的影响。实验结果表明,液相的流变特性对其传质特性参数均有较大影响。与清水相比,CMC水溶液中气泡平均直径和分布范围更大;清水和CMC水溶液的全局气含率均随表观气速的增加而增大;CMC水溶液的体积氧传质系数随CMC水溶液质量分数的增加而减小。基于实验研究,得出修正的体积氧传质系数公式和适用于幂律型非牛顿流体流动体系氧传递过程的无量纲关联式,可很好地实现非牛顿流体流动的废水处理装置中气液传质参数的计算。     

Gas—liauid mass transfer in three-phase stirred tank reagors: Newtonian and non-newtonian fluids

Gas—liquid mass transfer has been investigated in gas—liquid-solid three-phase stirred tank reactors with Newtonian and non-Newtonian liquids. Volumetric mass transfer coefficients and gas hold-ups were measured in a 0.2 m i.d. stirred tank reactor and the effects of low-density polymeric particles (ρ_s, =1030 and 1200 kg/m³; up to 15 vol%) on gas—liquid mass transfer were examined. The volumetric mass transfer coefficients in water were found to decrease due to the presence of solid particles at constant impeller speed and superficial gas velocity. On the other hand, solids loading led to higher mass transfer rates in non-Newtonian carboxymethyl cellulose aqueous solutions. Our previously proposed model for mass transfer in gas—liquid two-phase systems was extended to gas—liquid—solid three-phase systems. Reasonable agreement was found between the predictions of the proposed model and the experimental data.     

Analysis of Liquid Jet Breakup in One‐ and Two‐Phase Flows

The phenomenon of breakup of a jet into drops has been applied mainly to separation technologies in the chemical, pharmaceutical, and metallurgical industries. The paper deals with the experimental analysis directed at the breakup of polymer solutions flowing through an orifice nozzle. The analysis of the breakup and atomization of a liquid jet by a high‐speed gas jet is presented. Additionally, non‐Newtonian effects on the breakup of the liquid jet into drops were studied using the microphotography method. In the experiments, various aqueous solutions of polyacrylamide were used. The polymer solutions studied were power‐law fluids. Analysis of the photographs of the jet breakup showed that the length of the jets depends on the liquid and gas flow rates and on the concentration of the polymer used. High‐molecular‐weight polymers added to a solvent lead to changes in the rheological properties of the liquid and the breakup length of the jet.     

Gas/liquid mass transfer processes in a carbon dioxide/alkane system

A gas/liquid mass transfer process has been studied using carbon dioxide/alkane systems in a stirred vessel. Four linear alkanes (n‐heptane, n‐octane, n‐decane and n‐dodecane) have been used as the liquid phase in the present paper, and they have been employed to study the influence of the carbon length upon the mass transfer velocity. The mass transfer along the liquid phase has been studied using the mass transfer coefficient of the liquid phase, k_L. Pure carbon dioxide has been employed as the phase in all cases for this reason. The effects of the power supplied to the liquid phase and the gas flow rate upon the absorption process have also been analysed. Finally, the equations that allow calculation of the mass transfer coefficients have been applied for these systems, with acceptable results. Copyright © 2005 Society of Chemical Industry     

Studies in the vaporization of mercury in irrigated packed beds

Mass transfer coefficients have been measured for the vaporization of mercury flowing countercurrent to air in irrigated packed beds of spheres and Raschig rings. The measured coefficients increased with gas and liquid flow rates, and were correlated in terms of gas Reynolds number and liquid rate. The mass transfer data for liquid metal irrigation were lower than published data for wetting aqueous systems, due to the non-wetting nature of liquid metals. The lower mass transfer coefficients are believed to be attributed to a lower interfacial area for the non-wetting flow of liquid metals, although direct experimental proof was not obtained. The present results are in agreement with data for zinc absorption in molten lead in packed bed (Warner, 1959) when correlated in terms of the relative velocity and total liquid holdup. The results suggest that for liquid metal irrigated beds, the total hold-up is effective in gas phase transfer processes.     

Carbon Dioxide Absorption in Triethanolamine Aqueous Solutions: Hydrodynamics and Mass Transfer

The carbon dioxide absorption process by triethanolamine aqueous solutions was analyzed in a bubble‐column reactor taking into account the chemical reaction mechanism, gas‐liquid interfacial area, and mass transfer rate. A speciation study of this gas‐liquid system was developed by ¹H and ¹³C NMR spectroscopy in order to obtain the reaction mechanism and stoichiometry. The gas‐liquid interfacial area was evaluated considering the variations of bubble size distribution and gas holdup during the operation time. The liquid‐phase mass transfer coefficient was calculated from the carbon dioxide absorption rate data by interfacial area evolution and reaction stoichiometry.     

Mass Transfer In Trickle‐Bed Reactors With Structured Packing

An experimental investigation was carried out to examine the fluid dynamic and mass transfer behavior of structured packing, with the liquid and gas phase flowing co‐currently downwards in the column. Liquid to packing mass transfer coefficients for three positions within the pack were measured by an electrochemical method, varying both the liquid and gas loads as well as the physical properties of the liquid phase. Due to the high void fraction of structured packing, much higher liquid flow rates can be used than in traditional particle trickle‐beds. It was found that in the range studied, the gas superficial velocity has no effect on the mass transfer rate and thus, a general mass transfer correlation in terms of liquid Reynolds number only, was developed. Wetted areas and the radial distribution of liquid through the packing element were determined by a colorimetric method. Within the range of liquid flow rates investigated, complete wetting is not achieved, even with the low viscosity solutions. The measured ratios of hydraulic to geometric area, agree reasonably well with values predicted by existing relationships.     

A refined model for ozone mass transfer in a semibatch stirred vessel

The mathematical model proposed by Anselmi et al. (1984) for a semibatch stirred gas‐liquid contactor is refined to describe the mass transfer of ozone absorption and decomposition in aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C_ALb), the hold‐up gas (C_AGi), and the outlet gas in the free volume above the liquid surface (C_AGe), respectively. The effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E_r) defined as the ratio of mass absorbed per unit area in time t with chemical reaction (r) to that without chemical reaction or of the purely physical absorption, is considered in the refined model. Furthermore, the refined model also takes into account the variation of E_r with C_ALb, which changes with time during the course of gas‐liquid contacting. Thus this analysis extends the applicability of the model of Anselmi et al. (1984) and is of special importance for ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant, and in the system with variable liquid phase ozone concentration.     

Gas mass transfer to AOT-based microemulsions

The present paper analyses the gas/liquid mass transfer process employing carbon dioxide as gas phase and ternary water in oil microemulsions as absorbent liquid phases. The liquid phases were obtained by a direct mixing of water, 2,2,4-trimethylpentane and sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT). The characteristics of the microemulsions employed as liquid phase have been analysed to interpret the experimental results observed in the absorption process. More specifically, they have been analysed in relation to the percolation phenomenon and the effects produced by this phenomenon upon the different physical properties. Characteristic results have been observed for the gas/liquid mass transfer using microemulsions, because ternary microemulsions with high viscosity values in relation to pure water show a faster absorption process than the carbon dioxide/water system. This characteristic behaviour has been explained on the basis of the microemulsions internal dynamics.     

膜基气体吸收过程中活化剂的活化性能比较

将AMP(2-甲基-2-氨基-1-丙醇)和PZ(哌嗪)作为活化剂,分别添加于MDEA(N-甲基二乙醇胺)溶液中组成复合溶液,在膜吸收装置上考察了其吸收CO2性能. 通过气液流速、气相组成、液相浓度、负载、膜组件结构和膜结构形态等对总传质系数Kov影响的比较,研究了具有多氨基环状结构的化合物PZ和空间位阻结构的化合物AMP在膜气体吸收过程中对传质的加强作用. 结果表明,多氨基化合物PZ比空间位阻胺AMP活化效应更大,PZ对传质的加强作用高于AMP,流体力学因素对传质的影响有限,活化剂的化学活化作用对传质的影响是关键性因素,动力学因素对传质具有本质上的作用.     

A model for mass transfer in packed towers: mass transfer with controlling resistance in the gas phase

A model for mass transfer in the liquid phase in packed towers, proposed in a previous work[5], is employed in the case of mass transfer with controlling resistance in the gas phase. On taking into account the semistagnant liquid pockets by the liquid residence time distribution function, relationships are established between the volumetric mass transfer coefficients in different operations: evaporation, physical absorption, chemical absorption. The calculated values of the mass transfer coefficients agree well with experimental data.     

Bubble Volume and Aspect Ratio Generated in Non‐Newtonian Fluids

Bubble formation from an orifice submerged in quiescent polyacrylamide aqueous solution was investigated numerically with a sharp‐interface coupled level‐set/volume‐of‐fluid method based on the rheological characteristics of the fluid. In both non‐Newtonian fluids and Newtonian fluids, the numerical approach was able to capture accurately the deformation of the bubble surface, validated by comparison with experimental results. The effects of orifice diameter, solution mass concentration, and gas flow rate on bubble volume and aspect ratio were evaluated. Both the instantaneous and detached volume decrease with the orifice diameter but increase with mass concentration and gas flow rate. The aspect ratio at the departing point tends to rise with the orifice diameter and mass concentration and falls with the gas flow rate.     

Simulation study of biobutanol production in a polymer-loaded two-phase partitioning bioreactor (PL-TPPB): Model development

The conventional two-phase partitioning bioreactor (TPPB) containing an organic solvent as a second phase was found to be hardly efficient for biobutanol production because of the relatively low partitioning coefficient of butanol between the organic solvent and aqueous solution. Polymer bead was alternatively employed as the second phase in the TPPB, and Dowex Optipore L-493, a copolymer of styrene and divinyl benzene, was chosen as the optimum polymer because it shows the highest partitioning coefficients of butanol, acetone, ethanol and butyric acid against the aqueous phase among candidate polymers. The mass transfer coefficients of compounds from the aqueous phase into polymer beads were experimentally determined with respect to agitation speed. The mass transfer coefficient related to the stripping of volatile compounds by nitrogen gas was also determined, and the influence of gas flow rate turned out to be greater than that of the agitation speed, though both influences were remarkable. A mathematical model for the TPPB containing the polymer beads was suggested and as many as 40 parameters were cited from other publications or determined in this study. This mathematical model will be subsequently used for the detailed simulation study.     

三相下喷式环流反应器的传质性能

在三相非牛顿型流体体系中，对下喷式环流反应器传质特性进行了实验研究。讨论了表观气速、能量耗散速率、导流筒直径与反应器直径比、喷嘴直径、导流筒下端距反应器底部的距离、固体装填量、羧甲基纤维素钠（ＣＭＣ）溶液浓度及其流变特性对它的影响。实验结果表明，容积传质系数随表观气速和能量耗散速率的增加有所增加，在实验条件下，发现最优的导流筒直径与反应器直径比在０．４～０．４５这一范围、固体装填量大约为３％（体积百分比）、导流筒下端距反应器底部的距离为０．０８ｍ左右。同时提出了容积传质系数的经验关联式。     

Diluted alcohol solutions in bubble columns and draft tube airlift reactors with a single orifice sparger: experiments and simple correlations

BACKGROUND: Bubble columns (BCs) and airlift reactors (ALRs) have important applications as bioreactors, chemical reactors and as contactors in waste‐water treatment. The liquid phase properties in these reactors significantly influence the main hydrodynamic and mass transfer characteristics. Dilute alcohol solutions can be used to simulate real industrial systems in bioreactors. However, only a few research studies have considered such systems. The aim of this paper is to broaden the existing experimental data related to the influence of alcohol addition on the main characteristics of draft tube airlift reactors (DT‐ALRs), and to propose simple correlations for their prediction. RESULTS: New experiments were conducted in a DT‐ALR with a single orifice sparger, and with dilute aliphatic alcohol solutions from methanol to n‐octanol. Also, simple correlations were developed to predict the gas hold‐up and volumetric mass transfer coefficients in BCs and DT‐ALRs, but also the downcomer liquid velocity and liquid circulation time DT‐ALRs with single orifice sparger and dilute alcohol solutions. The proposed correlations included, in addition to the superficial gas velocity, the surface tension gradient as the only factor to characterize the liquid phase. CONCLUSIONS: General conclusion can be made that the gas holdup increased, but the downcomer liquid velocity decreased in a DT‐ALR, with increase in surface tension gradient of the alcohol solutions. Also, very good agreement was achieved between experimental and calculated data, by applying the developed correlations, with relative average errors less than 5%, except for gas hold‐up, where it was in the range 8–32%. Copyright © 2009 Society of Chemical Industry     

Effect of Tween 80 on Bubble Size and Mass Transfer in a Bubble Contactor

Gas absorption in aqueous solutions with Tween 80 and absorption processes based on hydrodynamics and mass transfer is determined. The impact of surfactant concentration on gas holdup and gas‐liquid interfacial area is analyzed, observing an increase of these parameters with surfactant concentration. The influence of liquid‐phase contamination on the absorption process is investigated on the basis of the liquid‐film mass transfer coefficient, removing the effect caused by the presence of a surfactant and the gas flow rate on the interfacial area and, thereby, on the volumetric mass transfer coefficient. The opposite effect on the mass transfer coefficient can be observed which decreases in the presence of the surfactant.     

淋降塔内非牛顿流体的传质研究

本文研究非牛顿幂律流体传质过程,实验采用淋降塔装置,测定高聚物溶液的传质速率.实验结果表明传质速率随温度和溶液流量增加而增大,还随压力和溶液稠度系数下降而增加.并应用相似论原理分析非牛顿幂律流体传质过程,得到柯尔本因子与雷诺数关系式j_m=BRe~B_1,由实验数据经线性回归得到B=2.2708×10~(-5),B_1=-0.7013相关系数0.99.     

Effect of different PVDF and additives on the properties of hollow fiber membranes contactors for CO2 separation

In the present work, different poly(vinil fluoride) (PVDF) were selected for preparing membranes, based on the fact that they are able to form polymer solutions with different viscosities. This characteristic can affect spinning, as well as, mass transfer between the polymer solution and precipitation bath; therefore, each PVDF solution can differently affect membrane formation. The effect of different additives in the polymer solutions was also investigated. Flat sheet and hollow fiber membranes were characterized by Scanning Electron Microscopy analysis, contact angle, gas permeation, porosity, and membrane gas–liquid contactor tests, aiming carbon dioxide removal. The hollow fibers prepared by the polymer which formed a less viscous solution (named PVDF-I) had a faster light transmittance decay, which started around 150 s before the more viscous solution (PVDF-II). Hollow fibers obtained using PVDF-I and propionic acid, in the polymer solution, presented the best gas–liquid contactor performance. CO₂ removal increased from 21 to 35.1%, for PVDF-II and PVDF-I, respectively, using aqueous diethanolamine solution, as absorbent liquid. In conclusion, even though PVDF-I and PVDF-II membranes were obtained by using the same spinning conditions and experimental methodology, the difference between the polymers properties certainly affected the final membrane morphology and transport properties.