MD · Technology
Membrane Distillation
Membrane distillation (MD) is a thermally driven process: a porous, hydrophobic membrane lets water vapor through and holds back liquid water and dissolved solids. The configurations differ in how the vapor is collected on the permeate side: direct contact (DCMD), air gap (AGMD), sweeping gas (SGMD), and vacuum (VMD). Petro Sep's membrane distillation technology is VMD, delivered as AQUA-SEP®; this page covers the wider MD family for comparison.
What it solves
Performance you can size against.
What the process delivers. Every number is testable on your own feed.
- Runs below the boiling point
- MD separates feeds well below their boiling point and at atmospheric pressure, so it can reuse residual and low-grade heat.
- Not capped by osmotic pressure
- Unlike reverse osmosis, MD recovery is not limited by the osmotic pressure of the feed, so water recovery can keep rising as salinity climbs.
- Non-volatile solutes retained
- Dissolved salts are almost completely retained, which is why desalting seawater and brackish water are the most common MD applications.
- Petro Sep's MD platform
- VMD
- Petro Sep runs membrane distillation as vacuum membrane distillation, delivered as AQUA-SEP®.
How it works
The working principle.
Hot feed flows on one side of a hydrophobic membrane. Cool distillate flows on the other side. The temperature differential creates a vapor pressure gradient that drives water vapor through the membrane pores. The membrane stays liquid-tight; only vapor crosses. Distillate condenses on the cool side and is collected.
Performance envelope
Specs and operating range.
For preliminary sizing only. Production sizing is always validated against your specific feed.
- Driving force
- Vapor pressure difference across the membrane
- Membrane
- Porous, hydrophobic
- Configurations
- DCMD, AGMD, SGMD, VMD
- Petro Sep platform
- VMD, delivered as AQUA-SEP®
How we compare
MD vs the alternatives.
Where Membrane Distillation wins, where it does not, and where the alternatives are honestly the better fit.
| Trait | MD | VMD | Multi-Effect Evaporation |
|---|---|---|---|
| Driving force | Temperature gradient across the membrane | Vacuum-induced vapor pressure gradient | Direct boiling, multi-stage |
| Operating temperature | Below the feed's boiling point (typical supply 30 to 60°C) | 60 to 80°C | 100 to 120°C across stages |
| Energy source | Thermal (waste heat ideal) | Thermal heat (about 33 kWh/m³ of feed, 95 at start-up), electrical (26 kW/m³), and cooling water (about 35 kWh/m³); latent heat is recovered in the system | Steam, electrical for compression |
| Specific energy | Depends on configuration and heat recovery | 26 kWh/m³ electricity plus 129 kWh/m³ utilities (AQUA-SEP® data sheet, 100 GPM unit) | High; the same data sheet puts an MVC evaporator plus crystallizer at 43 kWh/m³ electricity plus 300 kWh/m³ utilities |
| Best fit | Sites with abundant low-grade waste heat | High-salinity feeds and high recovery targets | Centralized, very-high-volume facilities |
Driving force
MD
Temperature gradient across the membrane
VMD
Vacuum-induced vapor pressure gradient
Multi-Effect Evaporation
Direct boiling, multi-stage
Operating temperature
MD
Below the feed's boiling point (typical supply 30 to 60°C)
VMD
60 to 80°C
Multi-Effect Evaporation
100 to 120°C across stages
Energy source
MD
Thermal (waste heat ideal)
VMD
Thermal heat (about 33 kWh/m³ of feed, 95 at start-up), electrical (26 kW/m³), and cooling water (about 35 kWh/m³); latent heat is recovered in the system
Multi-Effect Evaporation
Steam, electrical for compression
Specific energy
MD
Depends on configuration and heat recovery
VMD
26 kWh/m³ electricity plus 129 kWh/m³ utilities (AQUA-SEP® data sheet, 100 GPM unit)
Multi-Effect Evaporation
High; the same data sheet puts an MVC evaporator plus crystallizer at 43 kWh/m³ electricity plus 300 kWh/m³ utilities
Best fit
MD
Sites with abundant low-grade waste heat
VMD
High-salinity feeds and high recovery targets
Multi-Effect Evaporation
Centralized, very-high-volume facilities
Where this technology applies
Industries that use this process.
Membrane Distillation fits some sectors better than others.
Engineering FAQ
Questions engineers ask.
The questions we hear weekly. If you have a different one, send it with your consultation request and we will answer it directly.
Does Petro Sep supply non-vacuum MD?
Which configuration suits high-salinity feeds?
Can MD handle scaling-prone feeds?
Have a feed that MD
might fit?
We will pilot before we promise. Send us a sample and a target outcome. If the technology fits, we will tell you what to expect; if it does not, we will tell you that too.