Asymmetric Membranes
Dense Layer Porous support Fiber Support
Pore size
Ceramic membrane pictures (CEM)
Membrane structure
• structure: – symmetric – asymmetric
Solute MW (kDa) Rejection (%)
Linear macromolecule
Selective membrane skin Porous support
Globular Protein
Linear polymer
Pepsin
Cytochrome C
Polydextran
35
13
Fouling reduction/cleaning
• Membrane properties and module design • Optimum process conditions (low TMP) • Cleaning regime
–hydraulic cleaning (backwash, forward flush and airflush© )
Cross-flow filtration
• Advantages:
– turbulent flow – continuous concentrate discharge – control of cake-layer build-up
• Disadvantages:
– more complex process layout – high(er) energy consumption – high(er) investment cost
Take of a membrane
The photo of the produced membrane
Make sheets of it in a module
Make a module of it
More than one membraneSubmຫໍສະໝຸດ rge in a MBR tank
膜结构
RO, NF Skin
▪ Porous asymmetric
UF, MF Support
▪ Porous Symmetric
MF
Porous Symmetric Membranes
Nuclepore Membrane 核径迹成孔
Cellulose Membrane
Symmetric membrane
• 铸膜液制备：聚合物+有机溶剂(NMP, DMF, acetone等易与水互溶).
• 添加其它助剂 (pore-formers or nonsolvents).
• 凝固浴 （主要用水和其它聚合物不良溶剂 构成，通过相分离产生‘the pores’ 和‘the membrane body’)
NMP甲基吡咯烷酮 PES聚醚酚
Permeate
Flow IN
Concentrate Spacer
Membrane
Feed flow Permeate
Feed flow
Collection pipe
Residue flow
Feed spacer Membrane
Permeate flow
Membrane
Feed spacer
015-DWG-MW
Fouling of membranes
• Fouling
– Reversible fouling – Irreversible fouling
• Biofouling • Pore blocking • Scaling
foul
a. 1. 肮脏的,污浊的;2. 恶臭的;(食物) 腐败的;3. 邪恶的,可恶的;4. 下流的, 恶语咒骂的;5. (天气等)恶劣的;(风) 逆的;6. (比赛中)犯规的;7. (水管等) 堵塞的;8. (绳索等)被缠住的
ad. 1. 违反规则地;不正当地
n. 1. (比赛中)犯规[C][(+against/on)]
vt. 1. 弄脏;污染;玷污;2. 使堵塞;3. 缠 住;4. 碰撞
vi. 1. 腐败,腐烂;2. (管道等)堵塞 [(+up)];3. (比赛中)犯规;4. (绳索等) 缠结
Resistance Model
–chemical cleaning – relaxation
必需品 • PES聚合物 • NMP 溶剂 •水 • 玻璃片 • 刮膜器
Poly Sulfon (PS)
PS in NMP solution
glassplates
Cleaning glassplates important
Membrane
Filling the knife
knife (0,2 mm) with PS solution
• shapes:
– flat sheet
– tubular:
• tube
(d > 3 mm)
• capillary (0.5 < d < 3.0 mm)
• hollow fibre (d < 0.5 mm)
Module shapes
• Flat Sheet • Spiral Wound • Tubular • Hollow Fiber • Contained vs Submerged
膜制造及膜组件
membranes
膜过程的驱动力
压力驱动 - RO, NF，UF, MF 其它过程 -渗析（浓度差）电渗析（电位差）
压力驱动的膜过滤
进料
浓缩
membrane
膜
透过
• MF
• UF • NF • RO
孔尺寸减小 泵压力增加
实验室膜制备实例
• 高分子材料 (PAN, PES, CA, PVDF).
Fouling in NF/RO
Fouling behavior differs from UF/MF due to: • Lower fluxes and presence of smaller
molecules higher back-diffusion and in general no thick cake layer formation • Charged membrane surfaces (in general negative) adsorption of colloids and biological matter • Scaling (CaSO4, CaCO3)
Dead end Feed
Cross-flow
Feed
Retentate
Permeate
Permeate
Membrane filtration dead-end
Waste water
feed
Permeate
Membrane
Membrane filtration cross flow
concentrate
Reverse Osmose-installation
+/- various configurations
solid level
(fouling
resistance)
plate & frame
+
compactness energy consumption
-
0
price per m2
0
spiral wound
Cascade single pass system
Feed
Concentrate Retentate
Two-stage recirculation system
Permeate
Permeate
Feed pump Feed
Reciprcuumlaption
Stage 1
Concentrate Stage 2
• Porous vs Non Porous • Hydrophilic vs Hydrophobic • Polymeric vs Inorganic
Hydrophilic亲水 Hydrophobic疏水
Porous …………Non Porous Symmetric…… Asymmetric
▪ Dense (Non porous)
100
90
70
0
Cake layer formation
Flow direction
Driving force ∆p
Colloid/protein
Particle
Cake/ fouling layer
Membrane
Fouling in MF/UF
Decrease in flux due to: • Pore-plugging, adsorption and cake-layer formation • No concentration polarization of salts
You can make your own spiral wound module today!!!
• Two A4 papers • Cotton sheet A4 (if available) • Shears to cut • Glue for paper • Plastic tube with a slid (prefabricated)
-
+
+
++
(Є 25/m2)
tube
++
-
0/-
-
(Є 150/m2)
capillary