Difference between revisions of "Membrane filtration"

==Process and technologies==

==Process and technologies==

[[File:Filtration at bbepp.png|thumb|Filtration at BBEPP, Belgium]]

[[File:Filtration at bbepp.png|thumb|Filtration at BBEPP, Belgium]]

Membrane separation processes differ based on driving force and size of the separated particles. Pressure driven processes include microfiltration, ultrafiltration, nanofiltration and reverse osmosis.  Other driving forces such as electrical potential, concentration gradient or vapor/pressure gradient include electrolysis, dialysis, electrodialysis, gas separation, vapor permeation, pervaporation, membrane distillation, and membrane contactors. All processes except for pervaporation involve no phase change. Microfiltration and ultrafiltration is widely used in food and beverage processing, biotechnological applications and pharmaceutical industry, water purification and wastewater treatment, the microelectronics industry, and others. Nanofiltration and reverse osmosis membranes are mainly used for water purification purposes.  

Membrane separation processes differ based on driving force and size of the separated particles. Pressure driven processes include microfiltration, ultrafiltration, nanofiltration and reverse osmosis.  Other driving forces such as electrical potential, concentration gradient or vapor/pressure gradient include electrolysis, dialysis, electrodialysis, gas separation, vapor permeation, pervaporation, membrane distillation, and membrane contactors. All processes except for pervaporation involve no phase change. Microfiltration and ultrafiltration is widely used in food and beverage processing, biotechnological applications and pharmaceutical industry, water purification and wastewater treatment, the microelectronics industry, and others. Nanofiltration and reverse osmosis membranes are mainly used for water purification purposes.  

Membrane filtration can be carried out by means of two operating modes: dead-end filtration and cross-flow filtration. In dead-end filtration, the feed stream flows perpendicular to the membrane and is forced through the membrane. In consequence, the retained components accumulate on the membrane surface forming a cake layer, resulting in a decrease of the filtration rate due to the additional resistance to filtration of this cake layer. Dead-end operation mode is mostly employed in MF and is commonly used for separation of solid biomass from different feedstocks withing pre-treatment process. In cross-flow filtration (CFF), the feed flows parallel to the membrane surface. The tangential flow allows drag of the accumulated rejected solutes on the surface of the membrane, limiting the thickness of the cake layer and helping to maintain the permeate flow. CFF is widely used for concentration, purification or fractionation of target compounds from liquid streams.

Membrane filtration can be carried out by means of two operating modes: dead-end filtration and cross-flow filtration. In dead-end filtration, the feed stream flows perpendicular to the membrane and is forced through the membrane. In consequence, the retained components accumulate on the membrane surface forming a cake layer, resulting in a decrease of the filtration rate due to the additional resistance to filtration of this cake layer. Dead-end operation mode is mostly employed in MF and is commonly used for separation of solid biomass from different feedstocks withing pre-treatment process. In cross-flow filtration (CFF), the feed flows parallel to the membrane surface. The tangential flow allows drag of the accumulated rejected solutes on the surface of the membrane, limiting the thickness of the cake layer and helping to maintain the permeate flow. CFF is widely used for concentration, purification or fractionation of target compounds from liquid streams.

The membrane module is also a key parameter in the performance of a membrane separation process. The modules are designed with the objective of increasing turbulence on the surface of the membrane to reduce the mass transfer resistance and the concentration effects. The most used modules are plate and frame, spiral, tubular and hollow fibres.  

The membrane module is also a key parameter in the performance of a membrane separation process. The modules are designed with the objective of increasing turbulence on the surface of the membrane to reduce the mass transfer resistance and the concentration effects. The most used modules are plate and frame, spiral, tubular and hollow fibres.