三维菱形结构微通道内气液传质与强化

研究了具有三维交错菱形结构的微通道对离子液体1-丁基-3-甲基咪唑四氟硼酸盐([Bmim][BF₄])水溶液吸收CO₂过程的传质增强作用。实验主要聚焦于弹状流和破碎弹状流。考察了弹状流型下气液流量、离子液体浓度对体积传质系数k_La、增强因子E、CO₂吸收率X及压力降ΔP的影响。结果表明,较之于直通道,三维菱形通道可以显著提高体积传质系数和CO₂吸收率,其增强因子可达2.1,压力降仅增加 0.9 kPa。提出了一个新的体积传质系数k_La预测式,预测效果良好。采用VOF法模拟了微通道内气液两相流动过程,获得了连续相的速度矢量场。三维菱形通道能诱导涡流,强化传质过程。     

阵列凸起微通道内气液两相传质特性研究

研究了阵列凸起微通道内N-甲基二乙醇胺（MDEA）吸收CO₂过程的气液两相传质特性。在弹状流型下,考察了气液两相流量、MDEA浓度对体积传质系数、CO₂吸收效率、压力降以及能量损耗的影响。弹状气泡受到阵列凸起的挤压作用发生形变,促进了气液两相间的传质。与平滑通道相比,阵列凸起微通道在实验条件下具有更好CO₂吸收效率。在相同的能量损耗时,阵列凸起微通道具有更大的体积传质系数。     

微通道内醇胺/离子液体复配水溶液吸收CO2的传质特性

研究了微通道内醇胺[单乙醇胺(MEA)和甲基二乙醇胺(MDEA)]与离子液体[1-丁基-3-甲基咪唑四氟硼酸([Bmim][BF₄])和1-羟乙基-3-甲基咪唑甘氨酸([C₂OHmim][GLY])]复配水溶液吸收CO₂的传质特性。考察了醇胺/离子液体浓度比(c_AA∶c_IL)对液相体积传质系数(k_La)的影响,发现k_La随反应速率的增大而增大。为进一步阐释复配水溶液吸收CO₂的传质机理,分析了比表面积、扩散速率、增强因子和液弹循环对传质速率的影响。结果表明,四种复配溶液中,反应速率和循环频率(f_cir)分别在低流率和高流率下对传质速率起主导作用。k_La可表示为f_cir的函数,低气相流率下k_La与f_cir呈线性关系,斜率与反应速率成正相关,高气相流率下,液弹循环因膜弹传递困难而对整体传质速率的影响减弱,k_La与f_cir呈指数关系,幂律指数小于1。     

Gas–liquid mass transfer coefficient in stirred tanks interpreted through models of idealized eddy structure of turbulence in the bubble vicinity

Experimental data on the average mass transfer liquid film coefficient (k_L) in an aerated tank stirred by two Rushton turbines on common shaft are presented. Liquid media used were distilled water and 0.5 M sodium sulphate solution. Volumetric mass transfer coefficient (k_La) was measured by the dynamic pressure method with pure oxygen absorption. Specific interfacial area a was taken from Alves et al. [Chem. Eng. Proc., in press] who measured data on local gas hold-up and local average bubble diameter in the same apparatus and batches. Values of k_L are quantitatively interpreted in terms of correlations based on idealized eddy structures of turbulence in the bubble vicinity, namely by “eddy” model by Lamont and Scott [AIChE J. 16 (1970) 513] in the form of k_L=0.523(eν/ρ)^0.25(D/ν)^1/2, which fits the data with the mean deviation of 4.7%. It is shown that the decisive quantity to correlate k_L in the stirred tank is power dissipated in the liquid phase rather than the bubble diameter and the slip velocity as assumed by Alves et al.     

Using expansion units to improve CO_2 absorption for natural gas purification——A study on the hydrodynamics and mass transfer

The usage of capillary tubes for CO₂ absorption suffers from small residence time, which leads to reduced performance for large throughput. This work presents a method of connecting expansion units to capillary tubes to serve as a residence time delayer. The effect of the expansion unit on gas-liquid hydrodynamics, pressure drop and mass transfer coefficient (k_La) are investigated under various operating pressures up to 4.0 MPa, for both physical and chemical absorption. A novel periodic jetting flow is found in the expansion unit, which can intensify the CO₂ absorption. Experimental results show that the strategy can significantly decrease the pressure drop while maintaining the absorption performance to a large extent. The overall k_La for physical and chemical absorption are correlated to pressure drop, respectively. Besides, CO₂ loading in rich absorbents increases dramatically compared to literature studies with only micromixers or capillary tubes, which is beneficial to regenerate solvent. The study verifies the concept that pre-treatment with water can largely reduce the usage of amines, and can also provide a guide for process design in natural gas purification such as biogas recovery.     

Absorption of carbon dioxide into aqueous colloidal silica solution with diisopropanolamine

Carbon dioxide was absorbed into the aqueous nanometer-sized colloidal silica solution of 0–31 wt% and diisopropanolamine of 0–2 kmol/m³ in a flat-stirred vessel with the impeller of various sizes and speeds at 25 °C and 0.101 MPa to measure the absorption rate of CO₂. The volumetric liquid-side mass transfer coefficient (k_La) of CO₂ was used to obtain the empirical correlation formula containing the rheological behavior of the aqueous colloidal silica solution. Reduction of the measured k_La was explained by the viscoelastic properties of the aqueous colloidal silica solution. The theoretical value of the absorption rate of CO₂ was estimated from the model based on the film theory accompanied by chemical reaction and compared with the measured value.     

高温高压下浆态鼓泡床气液传质系数的测定

采用气体动态吸收法,对高温高压下浆态鼓泡床中气液传质系数进行了测定,考察了系统压力、温度、表观气速及固含量等操作条件对传质系数的影响. 结果表明,在温度298~473 K、气体压力1.0~3.0 MPa、表观气速0.03~0.10 m/s、固含量0%~20%(w)的实验条件下,体积传质系数随着压力、温度及表观气速的增加而增大,随固含量的增加而减小. 同时对不同塔径的传质系数进行了比较,表明在相同的操作条件下,大塔的传质系数略高于小塔.     

Structured multiphase reactors based on fibrous catalysts: nitrite hydrogenation as a case study

A new reactor concept designed as a bubble column staged with fibrous catalytic layers is tested on pilot-scale for the reduction of nitrite to nitrogen by hydrogen. Carbon dioxide is used to neutralize the hydroxide ions produced during hydrogenation of nitrite. The effective reaction rate was found to depend on the superficial gas velocity u_g0. The fibrous catalysts demonstrated a high selectivity towards nitrogen. The influence of the mass transport on the effective kinetics is discussed and the volumetric liquid–solid mass transfer coefficient k_Sa_S is estimated as a function of the superficial gas velocity u_g0. The selectivity was found to be independent of the hydrodynamics.     

MODEL COMPARISONS FOR DYNAMIC kLa MEASUREMENTS WITH INCOMPLETELY MIXED PHASES

Oxygen transfer coefficients for gas-liquid systems can be determined by dynamic response experiments. Calculation of the unknown k_La parameter involves analysing the step response data with a model which suitably describes the gas and liquid phase mixing phenomena as well as the electrode dynamics. Various combinations of plug-flow, disperion-flow and well-mixed models are proposed to describe particular gas-liquid systems. Through Laplace transformation, the first moments are calculated in terms of the model parameters. From experimental step response data, the first moment is obtained as the area above the response curve. Using the tabulated relations, dynamic k_La response data can be analysed for many particular gas-liquid oxygen transfer situations. Comparisons between the moment relationships serve for the calculation of the errors in k_La which would be incurred when using an incorrect two-phase model. In general, approximate models may lead to large errors.     

微孔射流毛细管反应器内液-液两相传质和反应选择性

微反应技术在化工过程强化领域已得到广泛应用,尤其适用于快速复杂竞争反应体系。对于液-液两相快速竞争反应,反应过程受传质限制,显著影响反应转化率和收率。本文开发了一种新型的微孔射流毛细管反应器（MJCM）,采用微孔射流强化进口处液-液两相传质性能,分别采用水-苯甲酸-煤油体系和水-氢氧化钠-甲苯-苯甲酸-氯乙酸乙酯体系研究了不同操作参数（流量、流量比、表面活性剂浓度、温度）和结构参数（孔径、管长）下液-液两相传质特性和反应选择性,并获得了舍伍德数Sh的关联式。结果表明：随着两相流量的增加,传质效率E呈下降趋势,总体积传质系数k_La呈增加趋势,反应选择性指数X_s则先减小后增大;孔径的增大则会减弱液液传质和反应选择性;随着毛细管长的增加,E和X_s逐渐增大,k_La则逐渐减小;水相-有机相流量比的变化对E和k_La会产生不同影响,而温度的适当升高则可以提升反应选择性,表面活性剂的加入降低了传质和反应选择性。与其他液液传质设备对比,MJCM在液-液两相传质、反应选择性方面性能良好,可以用于工业生产进行液液传质与反应过程的强化。     

Experimental studies of air-blast atomization on the CO2 capture with aqueous alkali solutions

In this work, an air-blast atomizing column was used to study the CO₂ capture performance with aqueous MEA (mono-ethanol-amine) and NaOH solutions. The effects of gas flow rate, the liquid to gas ratio (L/G), the CO₂ concentration on the CO₂ removal efficiency (η) and the volumetric overall mass transfer coefficient (K_Ga_v) were investigated. The air-blast atomizing column was also compared with the pressure spray tower on the studies of the CO₂ capture performance. For the aqueous MEA and NaOH solutions, the experimental results show that the η decreases with increasing gas flow rate and CO₂ concentration while it increases with increasing L/G. The effects on K_Ga_v are more complicated than those for η. When the CO₂ concentration is low (3 vol%), K_Ga_v increases with increasing gas flow rate while decreases with increasing L/G. However, when the CO₂ concentration is high (9.5 vol%), as the gas flow rate and L/G increases, K_Ga_v increases first and then decreases. The aqueous MEA solution achieves higher η and K_Ga_v than the aqueous NaOH solution. The air-blast atomizing column shows a good performance on CO₂ capture.     

CONTINUOUS PRODUCTION OF DISSOLVED OXYGEN-FREE WATER USING RAMOND SUPERMIXER®

The process of continuous production of dissolved oxygen free water was investigated by means of desorption of dissolved oxygen into fine nitrogen bubbles generated in a novel motionless mixer named Ramond Supermixer® (RSM). The pressure drop across the mixer (ΔP_SM) and the volumetric mass transfer coefficient (k_La) during the desorption of oxygen from water were measured for various combinations of process variables; liquid and gas velocities and number of mixing units. The k_La during absorption was smaller by less than approximately 6% than that during desorption. Specific gas-liquid interfacial areas (a) were measured by the chemical absorption method for a CO₂-aqueous sodium hydroxide solution system. Such process characteristics as ΔP_SM, k_La, and a were correlated with the process variables and compared with those available in the literature. To further confirm the mass transfer characteristics in RSM, the desorption of oxygen from aqueous electrolyte solutions was also investigated. All the correlations obtained for k_La during the desorption of oxygen from water and aqueous electrolyte solutions were compatible to a great higher extent.     

Gas-liquid-liquid slug flow and mass transfer in hydrophilic and hydrophobic microreactors

Gas-liquid-liquid three-phase slug flow was generated in both hydrophilic and hydrophobic microreactors with double T-junctions. The bubble-droplet relative movement and the local mass transfer within the continuous slug and the dispersed droplet were investigated. It was found that bubbles moved faster than droplets under low capillary number (Ca), while droplets moved faster upon the increase of Ca due to the increased inertia. For the first time, we observed that the increased viscosity of droplets fastened the droplet movement. The mass transfer in the continuous slug was dominated by convection, leading to nearly constant global mass transfer coefficient (k_La); while that in the dispersed droplet was dominated by diffusion, resulting in k_L decreasing along the channel. Such features are analogical to the corresponding gas-liquid or liquid-liquid two-phase slug flow, but the formation of bubble-droplet clusters caused by relative movement lowered the absolute mass transfer coefficient. These results provide insights for the precise manipulation of gas-liquid-liquid slug flow in microreactors towards process optimization.     

Absorption of carbon dioxide into aqueous PAA solution containing diethanolamine

Carbon dioxide was absorbed into aqueous polyacrylamide (PAA) solution containing diethanolamine (DEA) of 0–2 kmol/m³ in a flat-stirred vessel with the impeller of 0.034 m and agitation speed of 50 rpm at 25 °C and 0.101 MPa to measure the absorption rate of CO₂. The volumetric liquid-side mass transfer coefficient (k_La) was obtained from the dimensionless empirical correlation formula presenting the rheological behavior of aqueous PAA solution. PAA with elastic property of non-Newtonian liquid made the rate of chemical absorption of CO₂ accelerate compared with Newtonian liquid based on the same viscosity of the solution. The estimated value of the absorption rate of CO₂ was obtained from the model based on the film theory accompanied by chemical reaction and compared with the measured value.     

NaOH-CO2体系下并流立体旋流筛板塔传质性能

二氧化碳捕集是应对全球气候变暖问题的重要技术之一。本文使用NaOH溶液和CO₂作为实验体系,在并流塔中对立体旋流筛板（TRST）的传质性能进行实验研究,测定并计算出全塔及塔板段的气相总体积传质系数[K_Ga_e,(K_Ga_e)_t],重点考察塔板安装数量和方式、空塔气相动能因子和喷淋密度、CO₂和NaOH浓度等参数的影响规律。研究结果表明,塔板段是传质过程的主要区间,增加塔板数量以及采用塔板逆向安装方式是提升传质性能的有效技术手段;塔板段的气相总体积传质系数随空塔气相动能因子和NaOH浓度的增加呈先增大后减小的趋势,随喷淋密度和CO₂浓度的增加而减小,最高可达12.18kmol/(m³·h·kPa);建立塔板段的气相总体积传质系数的经验模型,模型计算值与实验数据的吻合性较好,相对误差小于20%。     

鼓泡床中电石渣加速碳酸化分析与响应面优化

搭建了鼓泡床碳酸化反应器,研究常温常压下电石渣直接液相碳酸化矿化封存CO₂的能力,揭示了重要操作参数表观气速、液固比和CO₂浓度对电石渣矿化封存CO₂能力和碳酸化效率的影响规律。同时构建响应面模型,分析各参数对电石渣碳酸化效率的影响强度,优化获得最大碳酸化效率及相应操作工况。结果表明,增加气速有利于钙离子溶解和CO₂吸收,但反应器中过高气速易导致气相通道效应,不利于气液充分接触。当液固比降低,溶液中钙离子浓度提高,更有利于碳酸化反应,但液固比过低会影响固液间传质。适当增加CO₂浓度有利于提高碳酸化效率,但CO₂浓度增至到一定值后,对碳酸化效率影响降低。响应面建模分析发现,各因素对碳酸化效率影响顺序为：液固比>CO₂浓度>表观气速。优化结果发现碳酸化效率最高为93.58%,工况为表观气速0.07m/s,液固比为8.26mL/g和CO₂体积分数为20.91%。研究可知,鼓泡床中常温常压下电石渣直接液相加速碳酸化反应,具有较大的CO₂固定量和高的碳酸化效率,实验结果为电石渣加速矿化封存CO₂技术的发展提供了基础数据。     

Identification of mass-transfer parameters in cases of simultaneous gas absorption and chemical reaction

The oxidation of hydrogenated 2-ethyl-anthraquinone in a continuous stirred tank reactor has been studied. This reaction is considered usually as slow or moderately fast and both diffusion and reaction affect the overall rate. The interesting mass-transfer parameters: mass-transfer coefficient k_L and the correlation constants of the volumetric mass-transfer coefficient k_La, were estimated with a steady-state model consisting of a set of implicit non-linear, algebraic equations. Ten screening experiments and five sequentially designed experiments based on the D-optimality criterion were carried out. The agitation speed, superficial gas velocity and the pressure served as the control variables. The response monitored was the concentration of unreacted hydroquinone in the effluent stream. The agreement between model prediction and experimental data was good. As all the model parameters could not be identified satisfactorily as such, some parameter transformations were necessary to achieve more accurate parameters. For satisfactory identification of the parameters, their sensitivities were viewed by plotting R² contours of the fit with pairwise parameter intervals. The reaction-diffusion model was simplified by assuming pseudo first-order kinetics for the reaction taking place in the film. The estimated values of mass-transfer quantities correlate well with results published earlier.     

受限空间内浮升气泡与液体间传质行为实验研究

采用紫外诱导荧光(UIF)实验方法,研究Hele-Shaw狭缝受限尺度对受限空间内浮升气泡流体力学与气液传质行为的影响。实验中以二苯并[b,e]吡啶作为荧光剂实现了受限空间内CO₂溶液浓度分布及其气泡运动速度的定量测量,获得了CO₂在受限空间内运动过程中的传质量和气泡动力学参数,并分别计算气泡受限空间内液膜区和自由接触区的传质速率。分析得到受限空间中不同狭缝宽度内CO₂的传质行为,分析了受限尺度对CO₂-水体系传质过程的影响。     

受限空间内浮升气泡与液体间传质行为实验研究

采用紫外诱导荧光(UIF)实验方法,研究Hele-Shaw狭缝受限尺度对受限空间内浮升气泡流体力学与气液传质行为的影响。实验中以二苯并[b,e]吡啶作为荧光剂实现了受限空间内CO₂溶液浓度分布及其气泡运动速度的定量测量,获得了CO₂在受限空间内运动过程中的传质量和气泡动力学参数,并分别计算气泡受限空间内液膜区和自由接触区的传质速率。分析得到受限空间中不同狭缝宽度内CO₂的传质行为,分析了受限尺度对CO₂-水体系传质过程的影响。     

高温高压浆态鼓泡床反应器中的气-液传质

The gas-liquid mass transfer of H2 and CO in a high temperature and high-pressure three-phase slurry bubble column reactor is studied. The gas-liquid volumetric mass transfer coefficients kLa are obtained by measuring the dissolution rate of H2 and CO. The influences of the main operation conditions, such as temperature, pressure,superficial gas velocity and solid concentration, are studied systematically. Two empirical correlations are proposed to predict kLa values for H2 and CO in liquid paraffln/solid particles slurry bubble column reactors.