论文总字数：19243字

摘 要

渗透汽化（PV）是一种高效节能的膜分离技术，由于不受气液平衡限制，特别适合共沸物或近沸混合物的分离。与有机膜相比，分子筛膜的通量和分离选择性更高，且耐高温抗溶胀，是应用潜力巨大的渗透汽化膜材料。NaA分子筛膜已经实现工业化，成功应用于甲醇、乙醇、异丙醇等溶剂的脱水分离。然而对于强极性溶剂如二甲基乙酰胺（DMAC），NaA分子筛膜的通量会持续下降，分离稳定性面临很大挑战。本文选择用中空纤维NaA分子筛膜对二甲基乙酰胺/水体系进行渗透汽化脱水。通过对NaA分子筛膜表面进行TiO₂修饰改性，削弱DMAC极性分子与膜表面的静电作用力，提高膜的分离稳定性，并考察不同酸浓度的TiO₂溶胶对修饰后膜的分离稳定性影响。

首先对二氧化钛溶胶粒径进行分析，结果表明随着酸含量增加，TiO₂粒径逐渐减小，从396 nm降低到122 nm。对修饰后的NaA分子筛膜进行XRD表征，发现随着溶胶中酸含量的增加，分子筛膜峰强度逐渐减弱。从电镜图中可以看到随着表面修饰溶胶乙酸含量的增加，外层修饰层厚度增加，TiO₂溶胶完全覆盖表面。考察料液温度对改性后NaA分子筛膜分离性能的影响，发现NaA分子筛膜的渗透通量会随原料液温度的增加而增加，但分离因子却有所下降。根据吸附-扩散机理，这是因为温度升高水的扩散速率加快，同时水的吸附量逐渐减少。最后考察了不同酸浓度修饰后的四种分子筛膜在DMAC/水体系中渗透汽化稳定性，修饰后的NaA分子筛膜在 90 ºC，90 wt％的DMAC/水溶液中持续脱水24小时。结果表明当修饰的溶胶乙酸含量为0.75和1 ml时，分子筛膜渗透通量和分离因子急剧下降，渗透通量分别下降了4.96 kg m^-2 h^-1与4.97 kg m^-2 h^-1，分离因子分别降至103与55。当修饰溶胶乙酸含量为0.25 ml时，分子筛膜脱水12 h后渗透通量开始下降，分离因子变化不大。当溶胶酸含量为0.5 ml时，渗透通量和分离因子变化范围较小，分别稳定在3.33 kg m^-2 h^-1和2323左右，说明此时修饰性能稳定性最好。

关键词：渗透汽化 NaA分子筛膜 修饰 DMA

ABSTRACT

Pervaporation (PV) is a high-efficiency and energy-saving membrane separation technique that is not limited by vapor-liquid equilibrium and suitable for separations of azeotropic and close-boiling mixtures. Compared to polymeric membranes, zeolite membranes provide superior flux and separation selectivity. They also have good stability to withstand high temperature and swelling. NaA zeolite membranes have been industrialization and successfully used in dehydrations of many organic solvents such as methanol, ethanol and isopropanol. However, when the membrane was used in PV dehydration of strongly polar solvents, e.g. dimethylacetamide (DMAC), the flux of membrane decreases continuously, resulting in poor separation stability. Herein, NaA zeolite membranes grown on hollow fibers were modified with TiO₂ to weaken the electrostatic interaction between DMAC and zeolite membrane so as to improve the stability of membrane. Effect of acid content in TiO₂ precursor on the stability of modified membrane was investigated.

Firstly, the particle size of TiO₂ was analyzed, and the results showed that the particle size of TiO₂ gradually decreased from 396 nm to 122 nm as the acid content increased. The modified NaA zeolite membranes were characterized by XRD. It was found that the peak intensity of membranes decreased gradually with the acid content. It can be seen from SEM images that the thickness of TiO2 layer on membrane surface increased with the acid content. The influence of temperature on the separation performance of modified NaA zeolite membrane was investigated. It was found that the total flux of membrane increased with the temperature whereas the separation factor. According to the adsorption-diffusion mechanism, it can be explained by that high temperature accelerated the diffusion of water molecules and reduced their adsorption loading simultaneously. Finally, the PV stability of membranes modified with different precursors for dehydration of DMAC was investigated. The modified NaA zeolite membranes were continuously operated for 24 h in 90 ºC and 90 wt% DMAC/water mixture. The results showed that when the acid content was 0.75 and 1 ml, the permeable flux and separation factor of the molecular sieve membrane decreased sharply, and the loss in permeable flux were 4.96 m^-2 h^-1 and 4.97 kg m^-2 h^-1 respectively, and the separation factor decreased to 103 and 55 respectively. When the acid content was 0.25 ml, the permeable flux began to decrease after 12 h while the separation factor did not change a lot. When the content of sol-acid was 0.5 ml, the permeability flux and separation factor varied a little and they maintained at at about 3.33 kg m^-2 h^-1and 2323 respectively, indicating the good stability of membrane.

Key Words：Pervaporation;Hollow fiber NaA zeolite membrane;Temperature;Modification

目 录

摘 要 I

ABSTRACT i

第一章 文献综述 1

1.1 引言 1

1.2 渗透汽化 1

1.2.1 概述 1

1.3 NaA 分子筛 2

1.3.1 NaA分子筛的概述 2

1.3.2 NaA分子筛膜的应用 3

1.4 分子筛膜的改性 4

1.4.1化学液相沉积 5

1.4.2化学气相沉积 5

1.4.3 原子层沉积法 5

1.4.4 离子交换法 6

1.4.5 表面覆涂法 6

第二章 TiO₂改性分子筛膜DMAC渗透汽化脱水 9

2.1 引言 9

2.2实验部分 10

2.2.1 实验原料及仪器 10

2.2.2 TiO₂溶胶的制备 10

2.2.3 中空纤维NaA分子筛膜表面改性 11

2.2.4 NaA分子筛膜表征 11

2.3 结果与讨论 12

2.3.1 TiO₂纳米颗粒表征 12

2.3.3 料液温度对渗透汽化脱水的影响 16

第三章 结论 19

参考文献 21

致 谢 23

第一章 文献综述

1.1 引言

N,N-二甲基乙酰胺（DMAC）溶解力极强，能与水、酮、芳香族以任意比例混合。含DMAC的废水具有极强的稳定性。工业上，DMAC常用的提纯方法有精馏和萃取两种方式^[1]。这两种方式能耗高，流程复杂且易造成二次污染。在DMAC脱水方面，利用分子筛膜对其进行渗透汽化脱水,能进一步提高脱水的效率。

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