Membrane Separation

Qian Jiang

2012.11.23

JOURNAL REPORT

A novel poly(dimethyl siloxane)/poly(oligosilsesquioxanes)

composite membrane for pervaporation desulfurization

Qiu Gen Zhang, Bing Cheng Fan, Qing Lin Liu, Ai Mei Zhu, Feng Feng Shi

Journal of Membrane Science 366 (2011) 335–341

Being a hydrophobic polymer with good chain flexibility, large free volume

and high permeability to permeants, PDMS has been widely used as a

membrane material for separation of organic compounds. POSS has high

hydrophobicity due to their CH3 groups, which can make the composite

membranes increase or retain preferential sorption for thiophene.

Inverse gas chromatography (IGC) can be used to determine the infinite

dilution solubility coefficient and diffusion coefficient to evaluate

pervaporation performance of a membrane.

Introduction

Membrane preparation

PDMS(10g)

POSS(wt%)Stired at room temperature for 2h

TEOS(5g)

Stired for 1h

Casted on a porous cellulose acetate

40℃ for 8h

n-heptane(84g)

dibutyltin dilaurate(1g)

Peeled off

IGC experiments

The composite with 5.0wt% POSS loading has the strongest affinity for thiophene, benzene and toluene.

Characterization of membranes

The composite membranes have a sharp peak around 2θ =10◦ with the incorporation of POSS, and this is in agreement with the XRD curve of POSS.

SEM image of the surface and cross-section of the PDMS/POSS composite membrane

(a) The PDMS membrane has a homogeneous surface.

(b) The particles observed are due to the aggregation of the POSS .

(c) Thickness of the separation layer is about 18μm.

Characterization of membranes

Pervaporation performance

The sorption and diffusion behaviors of components are in agreement with the flux and enrichment factor.

Conclusions and helps

●The solubility coefficients and diffusion coefficients of thiophene, benzene and toluene in the composites at infinite dilution are greater than the other four solvents.

●The addition of POSS enhanced solubility and diffusion coefficients of thiophene, benzene and toluene below 5wt% POSS loading.

Helps:◆通过加入与膜材料性质差异较大的物质可以改变膜的性能。◆反气相色谱（ IGC）可以用来预测某些膜的分离性能。

Tailoring the Separation Behavior of Hybrid Organosilica

Membranes by Adjusting the Structure of the Organic

Bridging Group

Hessel L. Castricum , Goulven G. Paradis , Marjo C. Mittelmeijer-Hazeleger , Robert Kreiter , Jaap F. Vente , and Johan E. ten Elshof

Adv. Funct. Mater. 2011, 21, 2319–2329

Introduction

Traditional membrane materials:Organic polymers: lack mechanical stability, lack stability in organic solvent.Zeolite: difficult to grow defect-free thin films.Metal oxides: lack stability for application in water-containing mixtures.

Introduce a new membrane material:An organosilica-based hybrid membrane composed of both organic and unorganic covalent links.A key advantage of hybrid organosilica materials is that they combine the network stability of inorganic silica and the versatility of organic polymers.

Membrane preparation

倍半硅氧烷前驱体

制备溶胶（控制平均粒径为6nm）

均匀涂覆在 ϒ-Al2O3 支撑层表

面

热固化（ 523K，2h ，N2 环境）

几种不同的前驱体

使用DLS监测

Reactivity

The generalized reactions can be described as follows:Step1: Hydrolysis

Step2: Condensation

Membrane Structure

The thicknesses of the membranes are all in the same range.

Gas Permeation Performance

●H2/N2 在 M 和 E 中透过比率最高，主要是由于膜的筛分作用，使动力学 直径较小的 H2 更容易通过。● CO2/H2 通过比率大于 1 ，主要是由于 CO2 在膜中的溶解扩散性好，有 机桥接基团起到了重要作用。● CO2 动力学直径小于 CH4 ，但 CO2 通量比 CH4 大，这是筛分与溶解扩散共同作用的结果。

Membrane Pervaperation Performance

●M 、 E 和 B 膜的分离因子最高。●O 膜的分离因子低是因为其憎水性强，同时有机桥接基团与正丁醇作用较大，使正丁醇易通过。●BP 膜分离因子低，主要是由于桥接基团的刚性结构使其膜孔径较大，从而使正丁醇通量增加。

Conclusions and helps

●The membranes separation properties in gas permeation and pervaporation was affected both by the length of the organic bridges and the affinity to adsorption.● Materials with the shortest bridges may be suitable for size-based molecular sieving.●CO2 tansports through these materials is dominated by the strong affinity to CO2.●Strong hydrophobic character may result in a high n-butanol flux in pervaporation.

Helps:◆根据所要分离物质的特性，选择长度、柔韧性合适的桥接基团。◆使用动态光衍射（ DLS）观测胶粒大小，从而控制合成一定尺寸的胶粒。