A practical guide to methyl ethyl ketone, why its evaporation rate sits where formulators want it, how to read the specification, and how it is supplied, from a US-based distributor.
MEK (methyl ethyl ketone, C4H8O, CAS 78-93-3) is a colorless, fast-evaporating ketone solvent with strong solvency for nitrocellulose, acrylics, and vinyl resins. It boils at 79.6 °C, which makes it evaporate more slowly than acetone and gives coatings time to flow and level. Stratus Chemical supplies 99.5% technical grade in drums and totes across the United States.
| Property | Value |
|---|---|
| Chemical name | Methyl ethyl ketone (butan-2-one) |
| Synonyms | MEK, 2-butanone, butanone, ethyl methyl ketone |
| CAS number | 78-93-3 |
| Molecular formula | C4H8O |
| Molecular weight | 72.11 g/mol |
| EC / EINECS | 201-159-0 |
| Appearance | Colorless liquid |
| Odor | Acetone-like, pleasant |
| Boiling point | 79.6 °C (175.3 °F) |
| Melting point | −86 °C (−122.8 °F) |
| Critical temperature | 262.5 °C (504.5 °F) |
| Specific gravity | 0.805 (water = 1) |
| Vapor pressure | 10.3 kPa at 20 °C |
| Solubility | Soluble in cold water; miscible with diethyl ether and acetone |
| Grades supplied | Technical, industrial |
| Packaging | Drums, totes |
| Documentation | COA & SDS provided on request |
The figures below are representative of technical grade MEK, with the ASTM method used for each parameter. They are indicative rather than guaranteed: specifications vary by source and by lot, and the certificate of analysis for your material governs.
| Property | Test method | Specified limit |
|---|---|---|
| Purity, wt. % | ASTM D2804 | 99.5 min |
| Color, APHA | ASTM D1209 | 10 max |
| Specific gravity, 20/20 °C | ASTM D4052 | 0.805 – 0.807 |
| Water content, wt. % | ASTM D1364 | 0.1 max |
| Acidity as acetic acid, wt. % | ASTM D1613 | 0.003 max |
| Nonvolatile matter, wt. % | ASTM D1353 | 0.003 max |
A specification that names its test method is worth more than one that does not, because two laboratories measuring the same property by different methods can report different numbers. When comparing quotes, check that the methods match as well as the limits.
MEK is the second-simplest ketone after acetone, produced commercially by the dehydrogenation of secondary butyl alcohol. It is a clear, mobile liquid with a sharp odor much like acetone, and it dissolves a broader range of resins than almost any other solvent in its price class.
Its commercial position rests on a narrow but valuable advantage. Acetone is cheaper and a slightly stronger solvent; the higher ketones are slower and better for flow but weaker and more expensive. MEK sits between them, with nearly acetone's solvency at a meaningfully slower evaporation rate, and for a very large number of coating and ink formulations that combination is exactly right.
The difference between MEK and acetone looks small on paper. Acetone boils at about 56 °C; MEK at 79.6 °C. In a formulation that gap is decisive.
When a coating is applied, the solvent has to leave, but not instantly. The film needs time to flow out and level so brush marks and spray texture disappear before it sets. Acetone frequently evaporates too fast for that, leaving orange peel, dry spray, or a rough surface. It also chills the surface as it flashes off, which in humid conditions condenses moisture into the film and produces blush, a milky haze in what should be a clear coat.
MEK's slower evaporation gives the film the working time it needs while still drying fast enough for production throughput. That is the whole reason formulators specify it and pay more than acetone costs.
Water behaviour is the other difference worth noting. Acetone mixes with water in all proportions. MEK is appreciably soluble in cold water but not miscible in all proportions, and its solubility falls as temperature rises. That affects formulation, and it affects what happens in a waste stream.
The largest use. MEK dissolves nitrocellulose, acrylics, vinyl copolymers, alkyds, and epoxies, and appears in lacquers, wood finishes, automotive refinish, industrial maintenance coatings, and marine paint. It functions both as the active solvent and as a component in blends tuned for a target evaporation profile.
Flexographic and gravure inks depend on solvents that release cleanly and fast enough to run at press speed without blocking on the reel. MEK is a standard choice for the nitrocellulose and polyamide resin systems used in packaging printing.
MEK carries adhesive solids and, in solvent cements for PVC and ABS, actually softens the substrate so the two surfaces fuse rather than merely bond. That is a different mechanism from adhesion and it needs a solvent aggressive enough to attack the polymer.
Used to remove uncured resins, adhesive residue, oils, and coatings that milder solvents leave behind, and to prepare surfaces before bonding or painting. It is far more aggressive than isopropyl alcohol and will attack many plastics and finishes, so compatibility should be checked before use on an assembled part.
MEK is used in the solvent dewaxing of lubricating oils, in magnetic tape and film manufacture, in printed circuit production, and as a chemical intermediate.
| Solvent | Where it wins | Trade-off |
|---|---|---|
| MEK | Broad resin solvency with a moderate evaporation rate that allows flow and levelling | More expensive than acetone; low flash point and aggressive toward many plastics |
| Acetone | Cheapest ketone, strongest and fastest, fully water-miscible | Often evaporates too fast, causing orange peel and blush in coatings |
| MIBK (methyl isobutyl ketone) | Slower still, excellent flow and gloss in high-build coatings | Higher cost, weaker solvency, and long dry times slow production |
| Isopropyl alcohol | Gentle on plastics and coated surfaces, water-miscible, cheaper | Far weaker solvency; will not touch cured resins or heavy adhesive residue |
How to choose: for cleaning, work up from the mildest solvent that does the job, because compatibility failures are discovered after the damage. Start with isopropyl alcohol, move to acetone or MEK only when the residue demands it, and test on an inconspicuous area first. For formulation, the question is the evaporation profile the process needs: acetone if it must flash immediately, MEK for the common middle ground, MIBK where flow and gloss matter more than cycle time. Most production blends use two or three ketones rather than one.
Two points that come up regularly in procurement, both of which should be confirmed against current regulation before you rely on them.
MEK is a List II chemical under the Controlled Substances Act, in the same category as acetone and toluene. In practice this means record-keeping obligations on transactions above threshold quantities and notification requirements on exports. It is routine for solvent distribution rather than exceptional, but it is a reason to expect documentation requests on larger orders.
MEK was removed from the federal list of hazardous air pollutants under the Clean Air Act, which changed its position in air permitting relative to many alternative solvents. It remains a volatile organic compound and is regulated as such. Confirm the current federal and state position for your site, since air rules vary considerably by jurisdiction.
MEK is a Class I flammable liquid with a flash point well below room temperature, lower than isopropyl alcohol and most common alcohols. At ordinary ambient conditions the liquid is already producing an ignitable vapor, and this is the most important handling fact about the product.
Store in closed containers in a cool, well-ventilated area designated for flammable liquids, away from heat, sparks, open flame, and strong oxidizing agents. Vapor is heavier than air and will collect in low points and travel along the floor to a remote ignition source. Bond and ground containers before transferring, since flowing solvent generates a static charge.
For exposure, use adequate ventilation and the respiratory, eye, and glove protection specified in the Safety Data Sheet. Vapor is irritating to eyes and the respiratory tract, and prolonged skin contact defats the skin. Note that many common glove materials offer poor protection against ketones, so check the breakthrough data rather than assuming any glove will do. Confirm all handling requirements against the SDS for the specific grade before use.
MEK is used as a fast-evaporating solvent in coatings, printing inks, and adhesives, where it dissolves nitrocellulose, acrylics, vinyl copolymers, and a wide range of other resins. It is also used for surface cleaning and degreasing, in solvent welding of PVC and ABS, in lubricating oil dewaxing, and as a chemical intermediate. Stratus Chemical supplies technical and industrial grade MEK in drums and totes across the United States.
The CAS number for MEK is 78-93-3. Its molecular formula is C4H8O and its molecular weight is 72.11 g/mol. Its EC number is 201-159-0. It is also known as methyl ethyl ketone, 2-butanone, butanone, and ethyl methyl ketone.
They are closely related ketone solvents with similar solvency, and the practical differences are evaporation rate and water miscibility. MEK boils around 79.6 °C against acetone's 56 °C, so it evaporates noticeably more slowly. In a coating that extra time lets the film flow out and level before it sets, which is why formulators reach for MEK where acetone flashes off too fast and leaves orange peel or blush. Acetone is miscible with water in all proportions; MEK is only partially soluble, and that separation behaviour matters in formulation and in waste handling.
A representative technical grade runs purity at 99.5% minimum by weight, color at 10 APHA maximum, specific gravity of 0.805 to 0.807 at 20/20 °C, water content at 0.1% maximum, acidity as acetic acid at 0.003% maximum, and nonvolatile matter at 0.003% maximum. Each parameter is tested to a defined ASTM method. Specifications vary by source and lot, so confirm against the certificate of analysis for the material you are quoted.
Because both cause defects that are expensive to trace back to the solvent. Nonvolatile matter is residue left behind after the solvent evaporates, which shows up as haze, spots, or contamination in a clear coat or on a cleaned surface, so a limit of 0.003% is a cleanliness guarantee. Acidity matters because acidic solvent corrodes equipment over time and can destabilise acid-sensitive resins and pigments in a formulation. Both are the kind of parameter that only gets noticed when it is out of specification.
MEK is a Class I flammable liquid with a flash point well below room temperature, lower than isopropyl alcohol or most common alcohols, so the liquid produces an ignitable vapor at ordinary ambient conditions. Store in closed containers in a cool, well-ventilated flammable-storage area away from heat, sparks, open flame, and strong oxidizers. Vapor is heavier than air and travels along the floor to remote ignition sources. Bond and ground containers when transferring, since flowing solvent generates static. Use the ventilation and personal protection specified in the Safety Data Sheet.
Stratus Chemical supplies MEK in drums and totes, in technical and industrial grades, with a certificate of analysis and Safety Data Sheet provided on request. Tell us the grade, volume, and delivery point and we will confirm pricing and availability within one business day.
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