Facilitated Mass Transport in Surface-activated Ag Nanoparticles/Polymer Composites

Abstract

The concept of facilitated transport has been applied for separation of olefin/paraffin mixture such as propylene/propane and ethylene/ethane mixture. The facilitated transport occurs because of the carrier-mediated transport in addition to normal Fickian transport. Here the carrier denotes any chemical compound which reacts with a specific solute reversibly. Facilitated transport membranes become a powerful tool to improve both selectivity and permeability, simultaneously. For separation of olefin/paraffin mixtures, the surface-activated Ag nanoparticles (s-Ag NPs) as olefin carrier were dispersed in a polymeric matrix to make nanocomposite membranes. The Ag nanoparticles were chemically activated for reversible olefin complexation upon inducing positive charge on their surface by electron polarizer such as p-benzoquinone (p-BQ), 7,7',8,8'-tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF). Recently, high permeable matrix and chemical stability of the olefin carrier have been a major concern in facilitated olefin transport membranes for practical applications. In this dissertation, 1. Schematic contribution of facilitated transport to the separation performance and 2. Roles of reduced graphene oxide dispersed in the PVP matrix and 3. Chemical stability of facilitated transport membrane, in particular against acetylene, are investigated. In chapter 1, the importance of the separation of olefin/paraffin mixture and the advantages of membrane process were introduced. The solid state facilitated transport membranes utilizing silver polymer electrolytes were investigated and the problems for practical applications were also issued: the importance of high flux membrane and chemical stability of carrier, especially. In chapter 2, the excellent separation performance for propylene/propane mixture was observed using nanocomposite membranes containing surface-activated Ag NPs by TCNQ dispersed in a PVP matrix. To understand the olefin separation performance, the contributions of both the facilitated transport due to the olefin carrier activity and the free volume effects of nanocomposites were investigated by X-ray photoelectron spectroscopy (XPS) and positronium annihilation lifetime spectroscopy (PALS). Upon the introduction of neutral and surface-activated Ag NPs to the PVP matrix, the size of the large free volume increased. Furthermore, the binding energy of surface-activated Ag NPs was enhanced due to the induction of the positive surface charge of the surface of Ag NPs by TCNQ. As a result, the high propylene permeation was attributed to both the free volume effects of the matrix and facilitated transport phenomena on the olefin carrier, but predominantly by the latter. In chapter 3, the reduced graphene oxide (rGO) was introduced to the s-Ag NPs/PVP composite membranes. rGO lead to the increase in the free volume size in the nanocomposites and the enhancement of the carrier activity of s-Ag NPs surface. The enhanced carrier activity was evidenced by the increase in the work function of s-Ag NPs. In the case of s-Ag NPs/PVP/rGO composite membranes, the mixed-gas selectivity decreased slightly while the mixed-gas permeance increased from 3.5 to 12.1 GPU, nearly 4 fold. Furthermore, the s-Ag NPs/PVP/rGO composite membranes have not been any kind of change to the separation performances during 160 hours. Therefore, the s-Ag NPs/PVP/rGO composites have high permeation flux and long-term stability, suitable for practical olefin separation process. In chapter 4, it has been well known that Ag cation can react with acetylene to produce the silver acetylide, a thermally, mechanically and chemically instable compound. Thus, the chemical stability of the facilitated transport membranes was investigated against acetylene. The results indicated that no silver acetylide was formed from the membranes containing s-Ag NPs dispersed in PVP matrix, as confirmed by Raman and thermogravimetric analysis (TGA). In conclusion, the s-Ag NPs have been successfully utilized as an olefin carrier for facilitated transport to separate olefin/paraffin mixture. The free volume effects of the nanocomposites and the surface activation for inducing the olefin carrier activity were confirmed by PALS and XPS/UPS, respectively. The olefin permeation behavior was also additionally enhanced as introduction of rGO into the s-Ag NPs/PVP composites and maintained the long-term stability. Furthermore, no silver acetylide, which is known as an explosive material, was formed from the s-Ag NPs/PVP composite membranes upon contact with acetylene. Therefore, potential applications for separation of olefin/paraffin mixture by facilitated transport membranes containing s-Ag NPs and rGO were suggested.|석유화학 공정에서 올레핀/파라핀 혼합기체를 분리하기 위해 저온 증류공정을 사용하고 있으나 증류공정은 넓은 부지를 필요로 하고 많은 에너지를 필요로 한다는 단점을 가지고 있어서 이를 대체할 수 있는 촉진수송 분리막 공정의 개발이 현재 활발하게 이루어지고 있다. 촉진수송 분리막은 분리막 소재 내부에 올레핀과 특별/상호 작용 할 수 있는 운반체를 함유하고 있어 혼합기체가 분리막을 통과하면서 올레핀만을 선택적으로 분리할 수 있으며, 투과도와 선택도를 동시에 향상시킬 수 있는 장점을 가지고 있다. 올레핀/파라핀 분리를 위해 표면이 활성화 된 은 나노입자 등을 운반체로 주로 사용하고 있으며, 은 나노입자의 표면을 활성화 하기 위하여 p-benzoquinone (p-BQ), 7,7',8,8'-tetracyanoquinodimethane (TCNQ) 그리고 tetrathiafulvalene (TTF) 등 다양한 전자분극제가 개발되었다. 이러한 소재를 석유화학 실공정에 적용하기 위해서 높은 투과성능을 유지하고 분리특성을 오랫동안 안정적으로 유지할 수 있도록 뛰어난 내구성을 갖는 분리막의 개발이 이루어지고 있다. 본 학위 논문에서는 1. 분리막 소재에서의 촉진수송 현상에 대한 분석, 2. 분리막 소재 내에서의 reduced graphene oxide (rGO)의 역할, 3. 촉진수송 분리막 소재의 아세틸렌에 대한 안정성 등의 연구내용을 다루고 있다. 1단원에서는 올레핀/파라핀 혼합물 분리의 중요성과 분리막 공정이 가지고 있는 장점과 특징에 대해 설명하였다. 촉진수송 분리막의 실공정 적용을 위해 고투과성 분리막 소재 개발 및 분리성능의 장기안정성 확보와 화학적 안정성의 필요조건 등을 확인하였다. 2단원에서는 표면이 활성화 된 은 나노입자/고분자 복합소재의 우수한 올레핀 분리특성을 확인하였고, 분리현상에 대한 이해를 돕고자 positronium annihilation lifetime spectroscopy (PALS) 장비를 이용하여 복합소재 내부의 free volume을 분석하였다. 또한 올레핀 운반체로 사용되는 은 나노입자의 표면 활성화도를 확인하기 위하여 X-ray photoelectron spectroscopy (XPS) 장비를 통해 은 나노입자 표면 활성화 정도를 확인하였다. 3단원에서는 표면이 활성화 된 은 나노입자/고분자 복합소재에 reduced graphene oxide (rGO)를 도입하여 복합소재 내부의 free volume의 증가뿐만 아니라, 은 나노입자의 표면 활성화도 극대화를 ultraviolet photoelectron spectroscopy (UPS) 장비를 이용하여 확인하였다. 또한, rGO를 도입함에 따라 투과성능이 400%이상 향상하고 160시간이상의 내구성을 확인하였다. 4단원에서는 석유화학 공정 상에 존재할 수 있는 아세틸렌과 분리막 소재로 개발되었던 은 이온이 반응하여 불안정한 물질인 은 아세틸라이드를 생성할 수 있는 가능성이 제기됨에 따라 다양한 은 물질로 이루어진 촉진수송 분리막 소재와 아세틸렌의 반응성을 확인하였다.; The concept of facilitated transport has been applied for separation of olefin/paraffin mixture such as propylene/propane and ethylene/ethane mixture. The facilitated transport occurs because of the carrier-mediated transport in addition to normal Fickian transport. Here the carrier denotes any chemical compound which reacts with a specific solute reversibly. Facilitated transport membranes become a powerful tool to improve both selectivity and permeability, simultaneously. For separation of olefin/paraffin mixtures, the surface-activated Ag nanoparticles (s-Ag NPs) as olefin carrier were dispersed in a polymeric matrix to make nanocomposite membranes. The Ag nanoparticles were chemically activated for reversible olefin complexation upon inducing positive charge on their surface by electron polarizer such as p-benzoquinone (p-BQ), 7,7',8,8'-tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF). Recently, high permeable matrix and chemical stability of the olefin carrier have been a major concern in facilitated olefin transport membranes for practical applications. In this dissertation, 1. Schematic contribution of facilitated transport to the separation performance and 2. Roles of reduced graphene oxide dispersed in the PVP matrix and 3. Chemical stability of facilitated transport membrane, in particular against acetylene, are investigated. In chapter 1, the importance of the separation of olefin/paraffin mixture and the advantages of membrane process were introduced. The solid state facilitated transport membranes utilizing silver polymer electrolytes were investigated and the problems for practical applications were also issued: the importance of high flux membrane and chemical stability of carrier, especially. In chapter 2, the excellent separation performance for propylene/propane mixture was observed using nanocomposite membranes containing surface-activated Ag NPs by TCNQ dispersed in a PVP matrix. To understand the olefin separation performance, the contributions of both the facilitated transport due to the olefin carrier activity and the free volume effects of nanocomposites were investigated by X-ray photoelectron spectroscopy (XPS) and positronium annihilation lifetime spectroscopy (PALS). Upon the introduction of neutral and surface-activated Ag NPs to the PVP matrix, the size of the large free volume increased. Furthermore, the binding energy of surface-activated Ag NPs was enhanced due to the induction of the positive surface charge of the surface of Ag NPs by TCNQ. As a result, the high propylene permeation was attributed to both the free volume effects of the matrix and facilitated transport phenomena on the olefin carrier, but predominantly by the latter. In chapter 3, the reduced graphene oxide (rGO) was introduced to the s-Ag NPs/PVP composite membranes. rGO lead to the increase in the free volume size in the nanocomposites and the enhancement of the carrier activity of s-Ag NPs surface. The enhanced carrier activity was evidenced by the increase in the work function of s-Ag NPs. In the case of s-Ag NPs/PVP/rGO composite membranes, the mixed-gas selectivity decreased slightly while the mixed-gas permeance increased from 3.5 to 12.1 GPU, nearly 4 fold. Furthermore, the s-Ag NPs/PVP/rGO composite membranes have not been any kind of change to the separation performances during 160 hours. Therefore, the s-Ag NPs/PVP/rGO composites have high permeation flux and long-term stability, suitable for practical olefin separation process. In chapter 4, it has been well known that Ag cation can react with acetylene to produce the silver acetylide, a thermally, mechanically and chemically instable compound. Thus, the chemical stability of the facilitated transport membranes was investigated against acetylene. The results indicated that no silver acetylide was formed from the membranes containing s-Ag NPs dispersed in PVP matrix, as confirmed by Raman and thermogravimetric analysis (TGA). In conclusion, the s-Ag NPs have been successfully utilized as an olefin carrier for facilitated transport to separate olefin/paraffin mixture. The free volume effects of the nanocomposites and the surface activation for inducing the olefin carrier activity were confirmed by PALS and XPS/UPS, respectively. The olefin permeation behavior was also additionally enhanced as introduction of rGO into the s-Ag NPs/PVP composites and maintained the long-term stability. Furthermore, no silver acetylide, which is known as an explosive material, was formed from the s-Ag NPs/PVP composite membranes upon contact with acetylene. Therefore, potential applications for separation of olefin/paraffin mixture by facilitated transport membranes containing s-Ag NPs and rGO were suggested.