Title Page

ABSTRACT

Contents

Chapter 1 : Introduction 22

1.1. Background 25

1.2. Research Motivation 29

1.3. Research Objectives 30

1.4. Organization of Dissertation 31

References 33

Chapter 2 : Literature Review 35

2.1. Diethylene Glycol 35

2.1.1. Basic characteristics of diethylene glycol 35

2.1.2. Thermo-Oxidation Degradation of Glycols 42

2.2. Slurry recycling process in solar cell production 44

2.2.1. Wafer Slicing Process 44

2.2.2. The stability of SiC particles in Suspension. 46

2.2.3. Carrier Fluid(Suspension Agent for slurry) 50

2.2.4. Slurry Recycling Process 52

2.3. Pervaporation 56

2.3.1. Overview of Pervaporation 56

2.3.2. Mechanism of Transport for pervaporation 61

References 64

Chapter 3 : Pervaporative dehydration of diethylene glycol (DEG) through a hollow fiber membrane 67

3.1. Abstract 67

3.2. Introduction 68

3.3. Materials and Methods 71

3.3.1. Materials 71

3.3.2. Membrane module preparation 73

3.3.3. Pervaporation 74

3.4. Results and discussion 77

3.4.1. Effect of feed composition 77

3.4.2. Effect of feed temperature 83

3.5. Conclusions 92

References 94

Chapter 4 : Development of High efficiency Coolant (DEG) Recycle System (Pilot scale test) 96

4.1. Abstract 96

4.2. Introduction 97

4.3. Filiteration System 101

4.3.1. Experimental 101

4.3.2. Results and Discussion 110

4.4. Dehydration Membrane System 117

4.4.1. Experimental 117

4.4.2. Results and discussion 120

4.5. Effect of recycled DEG on silicon wafers for solar cells (Wire-Sawing Test of Recycled DEG) 123

4.5.1. Experimental 123

4.5.2. Results and discussion 124

4.6. Conclusions 126

References 127

Chapter 5 : Model Simulation of Hollow Fiber Membrane Pervaporative Dehydration Performance with Diethylene Glycol (DEG) 129

5.1. Abstract 129

5.2. Introduction 130

5.3. Simulation Model 133

5.3.1. Mass and heat balances over differential element volume in the unit membrane module 133

5.3.2. Batch process 137

5.4. Experimental 145

5.4.1. Membranes 145

5.4.2. Membrane module preparation 145

5.4.3. Pervaporation 146

5.5. Results and Discussion 147

5.5.1. Determination of permeation parameters and verification of the simulation model 147

5.5.2. Simulation of the pervaporation process 150

5.6. Conclusions 170

Nomenclature 172

References 173

Chapter 6 : Conclusions 175

국문요약 179

Publications 183

Patents 184

Table 1.1. Slurry consumption during wire sawing (500 MW/year, 78 wires sawing equipments base) 29

Table 2.1. Applications of diethylene glycol 38

Table 2.2. Physical properities of diethylene glycol 39

Table 2.3. Comparison of the physical properties of glycols and water 40

Table 2.4. Specification of fresh DEG 41

Table 2.5. Composition of impurities in fresh DEG 41

Table 2.6. Worldwide commercialization technology of Slurry Recycle System 55

Table 2.7. Industrial suppliers of pervaporation systems 60

Table 3.1. Comparison of the physical properties of DEG and water 87

Table 4.1. Estimated Cost Savings Analysis for "N" company (500 MW/year wafer production base) 100

Table 4.2. Compositions of waste coolant derived from each process 102

Table 4.3. Size distribution of particles in waste coolant (2nd Decanter Oil)(이미지참조) 102

Table 4.4. Experimental procedures of the pilot system 107

Table 4.5. Flux variations before and after backwashing 111

Table 4.6. Operating conditions for the production of recycled coolant 112

Table 4.7. Characteristics of recycled coolant after filtration 113

Table 4.8. Classification of chemicals for removal of foulants 115

Table 4.9. Variation of flux and quality of recycled coolant after cleaning test 115

Table 4.10. Classification according to CIP sequence 115

Table 4.11. Composition of recycled DEG (after final purification) 122

Table 4.12. Specifications of R-DEG for wafering slurry 122

Table 4.13. Estimate of the total forecast time for production 122

Table 4.14. Mixing ratio of slurry in wafer sawing test 124

Table 4.15. Line test results of recycled DEG by a local company 125

Table 5.1. Operation parameters used in both the simulation and experiment 148

Table 5.2. Base Parameters for simulation of the batch pervaporation process 155

Table 5.3. Total pumping rate of feed with connection mode 159

Table 5.4. The result of simulations for pervaporative dehydration at different feed flow rates 162

Table 5.5. The results of simulations for pervaporative dehydration at different maximum temperature drops 166

Figure 1.1. Process steps from chunks to clean silicon wafers 24

Figure 1.2. A schematic drawing of wafer slicing process 24

Figure 1.3. Existing slurry regeneration system for SiC recovery and the scope of this research 32

Figure 1.4. Schematic flow chart of the DEG recycling process (Hybrid membrane system) 32

Figure 2.1. Chemical structure of diethylene glycol (CAS＃111-46-6) 35

Figure 2.2. Comparative hygroscopicities of various glycols at 21℃ 36

Figure 2.3. Viscosities of aqueous diethylene glycol solutions 37

Figure 2.4. Therm-oxidation degradation of ethylene glycol 43

Figure 2.5. Possible reaction scheme for the cyclodehydration of DEG 43

Figure 2.6. Therm-oxidation degradation of Propylene glycol 43

Figure 2.7. Schematic drawing of multi-wire saw and illustration of the cutting process in one sawing channel 44

Figure 2.8. Schematic diagram of SiC surface functional groups 48

Figure 2.9. Zeta potential of SiC particles at various pH values 48

Figure 2.10. Sedimentation behaviour of Slurry A dispersions [fresh DEG (pH＝6.88) 45% + fresh SiC 55%, by sonication], Evolution of transmission profiles with time at 2300xg, 25℃ 49

Figure 2.11. Sedimentation behaviour of Slurry B dispersions [denaturated DEG (pH＝3.13) 45% + fresh SiC 55%, by sonication], Evolution of transmission profiles with time at 2300xg, 25℃ 49

Figure 2.12. Overview of Slurry Recycling Process in "N" company 54

Figure 2.13. Schematic diagram of pervaporation process 57

Figure 2.14. The effect of (a) permeate pressure and (b) feed pressure on the flux of hexane through a rubbery pervaporation membrane 58

Figure 2.15. Mass transport through a solution diffusion membrane in pervaporation 62

Figure 3.1. Structure of the pervaporation hollow fiber membrane 72

Figure 3.2. Braid-reinforced pervaporation hollow fiber membrane 73

Figure 3.3. Schematic representation of the pervaporation apparatus 74

Figure 3.4. Plots of the total permeation rate and separation factor as a function of the water content in the feed at 353 K 81

Figure 3.5. Plots of the permeation rates of individual components as a function of the water content in the feed 81

Figure 3.6. Water flux as a function of the feed composition at different feed temperatures 82

Figure 3.7. Water content in the feed mixture in the feed tank as a function of the permeating time at different feed temperatures 82

Figure 3.8. Plots of the total permeation rate and separation factor as a function of the feed temperature with a water content of 1 wt. % in the feed 84

Figure 3.9. Permeation rates of individual components as a function of the feed temperature with a water content of 1 wt. % in the feed 89

Figure 3.10. Parameters used in the water flux equation as a function of the feed temperature 89

Figure 3.11. Comparison of the calculated and experimentally obtained total fluxes as a function of the water content in the feed at a feed temperature of 353 K 91

Figure 3.12. Comparison of the calculated and experimentally obtained permeation rates as a function of the water content in the feed at different feed temperatures 91

Figure 4.1. Process concept for used DEG recycling. 99

Figure 4.2. Size distribution of particle in waste coolant (2nd Decanter Oil), Beckman Coulter LS 13 320, Laser Diffraction Particle Size Analyzer(이미지참조) 102

Figure 4.3. Individual ceramic membrane fiber (100㎚) 104

Figure 4.4. Cross-section of ceramic fiber with magnified view of asymmetric pore structure 104

Figure 4.5. Ceramic membrane module 105

Figure 4.6. Schematic design of the pilot scale filtration system 106

Figure 4.7. Ceramic membrane pilot scale filtration system 106

Figure 4.8. Schematic design of modified pilot system with CIP tanks 108

Figure 4.9. Modified automation pilot scale filtration system 109

Figure 4.10. Flux variations before and after backwashing with time 112

Figure 4.11. Comparison of feed and permeate samples after filtration 113

Figure 4.12. Change of membrane surface by CIP 116

Figure 4.13. Schematic diagram of pervaporation system 119

Figure 4.14. Pilot-scale pervaporation system 119

Figure 4.15. Water content vs. operation time for pilot scale test [1~4th : The Pilot system is installed by PC2 membrane (effective area : 5.57㎡)] manufactured by SepraTek(이미지참조) 121

Figure 5.1. Mass and heat transfer across the membrane during flow through the differential unit volume of a single hollow fiber in the membrane module 134

Figure 5.2. Module configuration in the batch pervaporation process 139

Figure 5.3. Finite difference grid used in the numerical solution 140

Figure 5.4. Comparison of simulated feed compositions to experimental data with permeation time in the dehydration of DEG at various feed temperatures through hollow fiber membrane module with a membrane area of 0.16 ㎡ 149

Figure 5.5. Simulated feed compositions in the feed tank with permeation time at various feed temperatures in the dehydration of DEG through a hollow fiber membrane module composed of 10 commercial unit modules, each with a... 153

Figure 5.6. Simulation results of pervaporative dehydration of DEG through 10 hollow fiber membrane modules connected in series at various feed temperatures 154

Figure 5.7. Simulation results of pervaporative dehydration of DEG through 10 hollow fiber membrane modules connected in series at various feed flow rates 157

Figure 5.8. Simulation of pervaporative dehydration of DEG through 10 hollow fiber membrane modules connected in parallel at various feed flow rates per unit module and comparison to the series module configuration 160

Figure 5.9. Calculated constituent module numbers in series and parallel module assemblies with feed flow rate per unit module for pervaporative dehydration of DEG 163

Figure 5.10. Simulation of pervaporative dehydration of DEG through the module assemblies determined in Figure 5.9 at different feed flow rates per unit module 167

Figure 5.11. Calculated constituent module numbers in series and parallel module assemblies with max. temperature drop of feed stream in module assembly for pervaporative dehydration of DEG 168

Figure 5.12. Simulation of pervaporative dehydration of DEG through module assemblies determined in Figure 5.10 at different max. temperature drops of feed stream in module assembly 169

 본 연구에서는 태양광 웨이퍼 제조공정에서 투과증발막을 이용한 에너지절약형 쿨란트 재생시스템을 개발하였다. 웨이퍼 생산공정에서 연마재 슬러리는 웨이퍼 품질에 중요한 역할을 하며, 또한 공정에서 많이 사용되고 있기 때문에 생산비용의 절감과 환경 문제해결을 위하여 폐슬러리의 재이용 기술 개발은 중요하다.

본 연구에서는 기존 재생방법의 에너지 과소비 및 재생품의 열변성으로 인한 문제점을 개선하기 위하여 두 가지 유형의 분리막 기술을 이용한 혼성분리막공정으로 개발하였다.

첫번째는 분리막을 이용한 글리콜류의 탈수방법에 관한 것이었다. 글리콜류의 상업화된 탈수기술은 다단 증류법이 최선으로 알려져 있다. 그러나 이 공정으로 고순도의 글리콜을 얻기 위해서는 높은 장비초기비용과 에너지비용이 수반되며, 고온증류로 인하여 글리콜의 열적변성에 의한 부산물이 형성될 수 있다. 본 연구에서는 투과증발막을 이용하여 에너지절약형 탈수기술개발에 대해 연구를 수행하였다. 우선적으로 실험실 규모에서 상업용 중공사막을 통한 디에틸렌글리콜의 투과증발탈수에 적용가능성과 그 고분자막을 이용하여 디에틸렌글리콜의 투과특성을 운전조건별로 고찰하였다. 두번째는 막여과 시스템과 투과증발막으로 구성된 파일렛규모의 절삭유 재생시스템을 구성하였다. 이 혼성분리막 시스템은 실제 웨이퍼절단 공정에서 발생하는 폐절삭유의 재생을 위하여 사용되었다. 첫 단계는 폐절삭유에 잔류한 미분입자성분을 제거하기 위한 막여과시스템의 연구이다. 본 연구에서는 무기성 세라믹 재질의 한외여과막을 도입하여 폐절삭유중에 잔류하고 있는 미분(주로 실리콘, 실리콘카바이드, 철, 구리성분)을 거의 완벽하게 제거하였다. 다음 단계로, 투과증발막을 이용한 파일럿규모 실험에서 디에틸렌글리콜 재생품의 최종 수분 농도 0.5% 이하 수준을 달성하였다. 본 연구를 통하여 상업화 시스템설계와 자동연속운전에 필요한 운전조건 확립 및 분리막 모듈 재질의 문제를 확인하고 개선할 수 있었다. 또한 최종 생산된 재생품의 품질 적합성을 평가하기 위하여, 웨이퍼 절단공정에서 사용되는 슬러리를 재생품으로 제조하여 웨이퍼의 생산성과 품질을 비교 평가한 결과 거의 동등하였으며, 단결정 실리콘웨이퍼 생산시 일부 품질특성은 더 좋은 수준으로 평가를 받았다. 그리고, 마지막으로 투과증발시스템의 모듈과 공정 설계를 위한 현상학적 접근 방법에 의한 시뮬레이션 모델을 확립하였다. 그 결과로 현장적용 조건에서 모듈내에서 투입물의 최대온도저하가 투과증발공정설계시 가장 중요한 인자중 하나임을 확인할 수 있었다.

향후, 본 연구의 막여과기술은 다이아몬드 와이어쇼잉 방식의 웨이퍼제조공정에서 발생하는 쿨런트 재생 기술에 독립적으로 사용될 수 있고, 투과증발막기술은 다른 글리콜류와 바이오 알코올류의 탈수에 응용될 수 있을 것으로 기대된다.