DMAC Odor Removal in Acrylic Fiber Production: Amine-Based Odor Control with Ozone

Introduction

DMAC (dimethylacetamide) is a polar organic compound widely used as a solvent in the wet spinning process for acrylic and modacrylic fiber production, where it dissolves polyacrylonitrile. Although colourless and clear, it has a sharp odor resembling ammonia or fish; its odor threshold is around 46.8 ppmv — a remarkably low level, meaning even very small concentrations can trigger environmental complaints.

This post looks at where DMAC odor originates in a facility, why conventional methods often fail to control it fully, and how ozone-based systems effectively eliminate this odor.

What Is DMAC and Why Does It Create an Odor Problem?

DMAC is produced by reacting dimethylamine with acetic acid or acetic anhydride, resulting in a solvent with a high boiling point and good thermal and chemical stability. These properties make it a preferred solvent not only for acrylic fiber but also for elastane (spandex) fiber production and certain pharmaceutical processes.

Compounds containing nitrogen (amine groups) in their structure are typically detectable by the human nose at very low thresholds. DMAC falls into this category: even at concentrations well below established occupational exposure limits for worker health, it can cause odor complaints in surrounding residential areas. In other words, DMAC odor usually becomes a “good neighbour” and regulatory compliance issue well before it becomes a safety issue.

Where the Odor Originates

In acrylic fiber facilities, DMAC vapour typically enters the exhaust stream at three main points: the air extraction above the spinning bath, the exhaust of fiber washing and drying ovens, and the vent lines of distillation and evaporation columns in the solvent recovery unit. Drying ovens, due to their high temperature, accelerate DMAC evaporation and tend to be the most concentrated odor source.

No matter how high the solvent recovery rate, it is not practically possible to build a system with zero process leakage — so the residual DMAC in the exhaust gas must pass through a treatment or removal step.

Limitations of Conventional Methods

Activated carbon adsorption is commonly used for DMAC removal, but because DMAC is fully water-soluble and highly polar, the carbon's adsorption capacity saturates faster than expected — meaning frequent carbon replacement and high operating costs. Thermal oxidation (incineration) is effective but is not suitable for every facility due to high energy consumption and NOx emission risk.

Simple water-curtain scrubbers provide good primary removal thanks to DMAC's full water solubility (this is DMAC's biggest advantage when it comes to scrubbing) — but the dissolved DMAC in the scrubber outlet water and residual gas-phase traces may not be enough on their own to bring odor below the detection threshold.

How Does Ozone Remove DMAC-Based Odor?

Ozone reacts strongly with organic compounds containing amine and amide groups, oxidising them into odorless, nitrogen-based end products (CO₂, water vapour, and harmless nitrogen compounds). DMAC's full water solubility gives a key advantage for ozone application: ozonated water (dissolved ozone in scrubber liquid) can react effectively with the DMAC molecule in the liquid phase, providing higher contact efficiency than gas-phase ozone application alone.

In practice, the most efficient approach is a system where the scrubber and ozone work together: the scrubber transfers the bulk of the DMAC into water (thanks to high solubility), while ozone oxidises both the dissolved DMAC in the scrubber water and the residual gas-phase traces, bringing the odor below the detection threshold.

System Design and Application Points

A typical system architecture for DMAC odor removal works as follows:

[Drying Oven / Spinning Bath Exhaust]
        ↓
[Water-Curtain Scrubber — Transfers most DMAC into water]
        ↓
[Ozone Injection — Into scrubber water or outlet gas]
        ↓
[Oxidation of Dissolved and Gas-Phase DMAC]
        ↓
[Residual Ozone Monitoring and Clean Gas Discharge]

Before the system is built, exhaust gas flow rate, temperature, humidity, and DMAC concentration (in ppm) must be measured. Without this data, neither the correct scrubber size, circulation rate, nor ozone dose can be determined. Whether the facility's different DMAC sources (drying, spinning, recovery) should be treated separately or combined into a common header is also a design decision to evaluate at the project stage.

Material and Safety Notes

Since DMAC reaches facility equipment at elevated temperatures, the scrubber and ozone injection line materials must be chemically resistant to both DMAC and ozone; stainless steel (316L) is a reliable choice that meets both requirements. Positioning a residual ozone sensor at the system outlet is also a mandatory step for both worker safety and OHS compliance.

The OCS Ozone Approach

At OCS Ozone, we offer acrylic and modacrylic fiber producers end-to-end solutions, from exhaust gas analysis to scrubber design and ozone integration. We design each system specifically for the facility's DMAC concentration and gas conditions, and document the result with an accredited odor measurement after commissioning.

If your facility is dealing with DMAC or a similar amine/amide-based solvent odor problem, get in touch for a free technical assessment.