MEK is in every can of paint, and its waste costs far more than it seems
Open a can of paint: the sharp sweetish smell you will catch belongs to methyl ethyl ketone, MEK. It dissolves paints and varnishes, thins glues, keeps printing ink on the rollers and gives artificial leather its softness. The world consumes about 2 million t of it a year, growing 2–3% a year, and more than 70% goes to Asia, with China the main consumer. A tonne costs about $1,200. We hardly notice it because it evaporates, but the plants that use it pay more and more for it and bury more and more waste.
MEK and water form an azeotrope, so a column cannot dry the solvent
MEK mixes with water only partly: one tonne of water dissolves about 250 kg of MEK. But the main thing is that MEK and water form an azeotrope, a mixture that boils at 73 °C, cooler than pure MEK (80 °C), and its vapour holds 89% ketone and 11% water. Ordinary distillation cannot climb above this point. No matter how many columns you put up, what comes out is the azeotropic mixture, and the dry solvent has to be dried separately: with a second unit, a third substance, one more column. It is the same story as with spirit: however you distil vodka, it will not get stronger than 96%.
Carbon filters turn solvent recovery into a steam bill
The solvent has to be returned, so at paint, glue and artificial leather factories the air with MEK vapour is passed through carbon filters, then the carbon is blown through with steam, and a mixture of MEK and water results. It is run through a column, and every tonne of solvent has to be boiled again. Take a site with 40,000 t of MEK a year in circulation, a mixture of about 160,000 t a year, or 440 t a day, with a solvent value of about $48 million. Steam costs $4–9 million a year, losses $0.5–2 million, carbon $0.4–1.4 million, and fines, water treatment and upkeep another $1–3 million. In total the site spends $6–15 million a year, and this money is included in the price of every can of paint, every sofa and every printed page.
Every alternative removes one problem and brings another
Membranes swell in ketones and quickly lose separation. Extraction brings a third substance into the process, which then has to be separated. Adsorption suits low concentrations, and these are high. The azeotrope does not go anywhere.
ARBOK-MEK works in a cold vacuum and gets past the azeotrope
The ARBOK-MEK technology works in a deep vacuum of about 1 kPa, where water boils at 6–10 °C and MEK boils even more easily. The mixture is not heated: no boiler, no column, no reflux. The condensation heat returns to the cycle through recuperators, up to 98% of the energy goes round in a circle, and 0.7–1 kWh per tonne of mixture is left for electricity. Above the azeotropic point a second cycle works: cold vacuum on the TEGA material that Arbok produces, which takes the residual water out of the solvent without heating and without a third substance. The output is dry MEK, ready to go back into paint or glue. Resins, pigments and oils stay in the still and leave as a dry separated residue: this is the ZWD technology, Zero Waste Discharge. A flow of 440 t a day is handled by 3 container modules of 200 t a day each, installed in 2–4 weeks without stopping production. MEK is flammable, but in a vacuum there is no air to burn, no heating and no rubbing parts to give a spark.
The site spends about $0.3 million instead of $6–15 million
Electricity for the whole flow costs about $0.03 million a year instead of $4–9 million, losses fall to 0.5%, carbon is not emitted at all and the freed quotas can be sold. In all the site spends about $0.3 million a year instead of $6–15 million. The difference is $6–15 million a year, which is 13% to 32% of the value of the solvent in circulation, or $150–380 for every tonne of MEK, and each of the 3 modules gives on average $2–5 million a year. The cold process does not destroy the molecule, so the same solvent returns to work again and again, and fresh solvent is needed only for losses.
On the off-take model the site gets the savings without investment
If world MEK consumption is converted into such sites, there are about 50 of them. They spend from $0.3 to $0.8 billion a year on steam, losses and fines and emit from 160,000 to 360,000 t of carbon dioxide. This money already includes carbon quotas of about $20–70 million a year, and this is how much profit a year ARBOK-MEK can bring the world industry. Payback is 5–7 years, and under BOOM the site makes no own investment: it pays for the service and gets the solvent and water back.