Development of an alcohol wastewater process
Recently we were tasked with developing a process to recycle a major waste stream for re-used in the plant. This stream contained high concentrations of copper, sodium chloride, nitrate and other organics but the big challenge was that it was 50% ethanol. The goal to remove these impurities and allow the ethanol to be reused.
Challenges of alcohol streams
The unique properties of ethanol pose significant obstacles. In particular, ethanol contributes to the osmotic pressure and while lower than dissolved salts, the high concentrations will push systems to high operating pressures. For example a 10% ethanol solution will need to operate over 40 bar. This unique behaviour required a creative solution.
Developing the solution
Several technologies were considered for this project, including Ion Exchange and Reverse Osmosis. Each offered distinct advantages but faced limitations with this wastewater stream.
Ion Exchange (IX)
Ion Exchange was initially seen as a promising candidate. Its ability to selectively remove contaminants like copper, sodium chloride, and organics without interfering with ethanol could have provided a pure ethanol-rich stream. However, the high ionic load in this particular waste stream meant frequent resin regeneration, generating excessive acid and caustic waste. This trade-off rendered the IX process uneconomical for this application.
Reverse Osmosis (RO)
Reverse Osmosis, a widely used technology for separating impurities, faced two major limitations in this scenario:
- Osmotic Pressure: The ethanol concentration significantly increased the osmotic pressure, pushing feed pressures to impractical levels.
- Product Loss: RO would have left ethanol concentrated with the impurities, undermining recovery objectives.
This meant RO was not technically viable.
The Winning Solution: Nanofiltration (NF)
After careful analysis, Nanofiltration emerged as the optimal solution. Unlike RO, our NF membranes allowed ethanol to pass through while effectively reducing the concentration of copper, sodium chloride, and the organics. This made NF a standout choice, enabling efficient recovery of ethanol without the challenges of high-pressure operations.
Using our 2540 rig, we conducted extensive testing and validation. The results confirmed that NF could reduce impurity levels while maintaining the ethanol content in the permeate stream. Additionally due to the absence of scaling species, we were able to operate to over 90% recovery without significant detrimental effects  The client further verified that the recycled stream met worked will in reuse, demonstrating the solution’s feasibility.
Why Nanofiltration Worked
Nanofiltration is particularly well-suited for alcohol wastewater due to its balance of selective separation and moderate pressure requirements. Key advantages of NF include:
- Selective Ion Rejection: Effective removal of divalent and multivalent ions, such as copper and nitrates, while allowing ethanol to pass through the membrane.
- Energy Efficiency: Compared to RO, NF operates at lower pressures, reducing energy consumption and equipment wear.
- Cost Effectiveness: NF is a much cheaper system to operate compared to the regeneration cost of using an ion-exchange system or the high energy costs of a high pressure RO system.
Ready to Optimize Your Wastewater Process?
Whether you’re grappling with high ethanol concentrations or complex contaminant profiles, our team specializes in designing advanced treatment systems tailored to your needs. Reach out today to explore how RO, NF, and IX solutions can drive sustainability in your operations.
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