Pumping Acetic Acid
Acetic acid aka Ethanoic Acid is a clear, colourless fluid with a distinctive, pungent smell.
Approximately 6.5 million tonnes per year are produced for use in industry and consumption.
Acetic acid is toxic with low concentrations in the air (10ppm) causing irritation to the skin, eyes, respiratory tract and teeth. Higher background concentrations can cause severe medical conditions to employees. Above 90% concentration, particularly at higher room temperatures, acetic acid is flammable.
- Acetic acid is found in Vinegar solutions, usually between 3-9% in concentration for use as a condiment, ingredient or as a preservative.
- In the production of various synthetic materials, acetic acid is a precursor and solvent for various glues and plastics such as polyvinyl acetate, cellulose acetate, nylon and dimethyl terephthalate.
- For the production of organic compounds which are constituent parts of food ingredients, pigments and pesticides, acetic is a widely used agent.
- In waste water treatment, acetic acid may be dosed to correct highly alkaline pH from where caustic soda has been dosed to the fluid stream.
The chief consideration for handling acetic acid is the containment from the surrounding workforce and equipment.
The two aspects defining the risk of a breach in containment is the sealing system and chemical resistance of the wet-side materials.
It is recommended to use a sealing system without a mechanical working part in contact with any aspect of it such as those found on shaft-sealed pump. This is because as the abrasive wear of the shaft rotating on the seal incurs, the seal is gradually worn and will eventually fail, causing a leak.
A mag drive centrifugal pump uses an o-ring sealing system, featuring an o-ring between each fastened pump component. This seal prevents any leakage and is not subject to any wear.
Acetic acid, although classified as a weak acid, is corrosive to many metals and non-metallic materials.
Recommended materials include PTFE, ETFE, PP and titanium. For weaker concentrations stainless steel 304 and 316L are acceptable those these may suffer corrosion over time, causing a problem with tolerances.
Where acetic acid is being dosed, a peristaltic or metering pump provides an excellent solution for the accurate delivery of the fluid. This is commonly found in waste water treatment where the delivery of the chemical is determined by an analytical probe which controls the speed of the inverter rpm or stroke rate and length. A suggested hose material for acetic acid is EPDM which is highly resistant to chemicals, particularly acids.
A flexible and cost-effective solution for barrel or container emptying applications may be to use an AODD diaphragm pump.
Where higher concentrations of acetic acid are used, an AODD made from 100% pure virgin PTFE material can be employed. Known as a ‘solid-block’ pump, this pump is almost entirely inert to chemicals. As diaphragms are a wearable part it is suggested to fit the AODD pump with some type of barrier protection for a rupture and even leak-detection. A spill-pot accessory can be purchased to handle any fluid escaping from the exhaust.