Membrane filtration

Technology
Technology details
Name:	Membrane filtration
Category:	Separation process
Feedstock:	all materials
Product:	separated products

Membrane filtration as a separation technology covers all engineering approaches for the transport of substances between two fractions with the help of permeable membranes.

Feedstock

Origin and composition

Cross Flow Membrane Filtration

In membrane separation processes, the membrane acts as a selective barrier between two phases with the ability to facilitate or limit the transport of one or more components from one phase to another by the action of a driving force. This driving force can be pressure, concentration, electrical potential, or temperature gradient. The stream passing through the membrane is the permeate, whereas the stream containing the rejected components is the retentate. The most common applications in biotechnology are the separation of solid biomass from feedstocks, separation of production cells within a pre-treatment or a downstream process and separation of target dissolved substances from liquid streams.

Pre-treatment

For membrane filtration, no specific pre-treatment is needed since it is used to separate different fractions within a process chain. Sometimes, it is combined with other separation technologies, such as centrifugation.

Process and technologies

Filtration at BBEPP, Belgium

Membrane separation processes differ based on driving force and size of the separated particles.

Different driving forces

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.

Operation modes

Nanofiltration solute transport

Nanofiltration exclusion mechanisms

Membrane filtration can be carried out by means of two operating modes: dead-end filtration and cross-flow filtration.

Dead-end 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 within pre-treatment processes.

Cross-flow filtration

In cross-flow filtration (CFF), the feed flows parallel to the membrane surface. The tangential flow allows the accumulated rejected solutes on the surface of the membrane to be entrained, 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.

Products

The products of a membrane filtration are the compounds retained by the membrane and the permeate stream that can be further processed.

Post-treatment

The post-treatment of the filtrate is depending on the next steps within the production chain.

Technology providers

Company name

Membrane filtration provider

General information
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Technology and process details
Technology name:		Technology category:	Pre-processing (Separation technologies), Post-processing (Separation technologies)
TRL:		Capacity:	kg·h-1
Filter material:		Hydrophobicity:
Molecular cut-off:	kDa	pH:
Pore size:	µm	Pressure:	bar
Processable volume:	L	Surface area:	m2
Temperature:	°C	Other:
Feedstock and product details
Feedstock:		Product:

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Open access pilot and demo facility providers

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Patents

Currently no patents have been identified.

References and further readings

• Membrane filtration in Wikipedia