What Is Carbon Monoxide Used For?

Carbon monoxide (CO) reduces iron ore into steel, refines nickel, makes bulk chemicals like methanol and acetic acid, holds the red color in packaged meat, and measures lung function.

Blast furnaces consume it by the ton, while a sealed package of ground beef holds a 0.4% trace.

WestAir supplies carbon monoxide across California and Arizona.

What Makes Carbon Monoxide Useful to Industry?

Carbon monoxide is useful to industry because of two properties: it pulls oxygen away from metal oxides, and it inserts a single carbon atom into organic molecules.

The first property makes it a reducing agent. At high temperature, CO takes the oxygen from a metal oxide and leaves the metal behind, becoming carbon dioxide in the process.

The second makes it a chemical feedstock. Carbonylation reactions bolt CO onto an existing molecule, adding exactly one carbon and turning simple starting materials into acids, aldehydes, and alcohols.

For chemical use, the CO typically comes from synthesis gas, the hydrogen-and-CO mixture produced by steam reforming natural gas or gasifying coal; in metal reduction it is often generated in place from coke. Plants either feed that stream straight into a reactor or separate the CO out first, depending on what the process needs.

How Is Carbon Monoxide Used to Make Chemicals?

Chemical synthesis is the largest use of carbon monoxide by volume, and four product families account for most of it: methanol, acetic acid, oxo aldehydes and alcohols, and phosgene.

Methanol is made by hydrogenating carbon monoxide. Synthesis gas passes over a copper-zinc oxide catalyst on an alumina support, where CO picks up hydrogen and becomes methanol. The carbon dioxide in that same stream does the same thing, so both carbon oxides in the feed end up as product.

Acetic acid is then made by carbonylating that methanol. The Monsanto process uses a rhodium catalyst at 150 to 200°C (302 to 392°F). BP’s Cativa process uses a promoted iridium catalyst and now accounts for a large share of global capacity and is often retrofitted into existing rhodium-based plants. It first ran commercially at Texas City in November 1995, the same site where the Monsanto route started up in 1970.

Hydroformylation, also called the oxo process, adds CO and hydrogen across a carbon-carbon double bond to produce aldehydes with one more carbon than the starting alkene. World output of oxo chemicals is around 10 to 11 million metric tons a year, feeding plasticizers, detergents, and solvents.

Phosgene is produced by passing CO and chlorine over a bed of activated carbon. In the U.S., roughly 80% of phosgene production goes into isocyanates for polyurethane, and about 10% into polycarbonate, which shows up in electrical housings and break-resistant glazing.

How Does Carbon Monoxide Turn Iron Ore Into Steel?

Carbon monoxide strips the oxygen out of iron ore inside a blast furnace, turning it into molten iron that a second furnace then refines into steel. Three molecules of CO take the oxygen from one molecule of iron oxide, producing two iron atoms and three molecules of carbon dioxide.

The coke charged into a blast furnace exists largely to generate that CO. Coke is coal baked in a sealed oven until the volatile compounds cook off, leaving a hard, porous mass of almost pure carbon.

Hot air blown through nozzles at the base burns the coke at temperatures reaching about 2,000°C (3,632°F). That partial combustion produces CO, which rises through the descending charge and does its reducing work in the 400 to 800°C (752 to 1,472°F) zone as the gas cools.

Solid coke and solid ore barely react on contact, which is why the reaction has to run through the gas phase. Ores are sintered or pelletized to stay porous so CO can penetrate the particle and reach the oxide throughout, not just at the surface.

Direct reduced iron plants apply the same chemistry below the melting point of iron. Ore pellets are reduced in a shaft furnace by a hydrogen-and-CO gas made from natural gas and steam, producing solid metallic iron that feeds an electric arc furnace.

How Is Carbon Monoxide Used to Refine Metals?

Nickel refining uses carbon monoxide to pull nickel away from its impurities through a reaction that runs in both directions. The method is called the Mond process.

Impure nickel is exposed to CO at 50 to 60°C (122 to 140°F). The nickel reacts to form nickel tetracarbonyl, a gas that carries the nickel off and leaves impurities behind as solids.

Heating that gas to 220 to 250°C (428 to 482°F) reverses the reaction. The carbonyl decomposes back into nickel metal and CO, delivering nickel above 99% purity and releasing the carbon monoxide to run the cycle again.

That same decomposition step gets used deliberately for coating. Nickel carbonyl breaks down onto a heated substrate and lays down a nickel layer.

Nickel tetracarbonyl is a volatile, highly toxic liquid, and it’s much more dangerous than the carbon monoxide that forms it. The gas must stay sealed inside the system from the moment it forms until it decomposes back to metal.

Why Do Meat Packagers Use Carbon Monoxide?

Meat packagers use a trace of carbon monoxide to hold the red color shoppers associate with freshness. CO binds to myoglobin, the pigment in muscle tissue, forming carboxymyoglobin, which is slower to oxidize into the brown metmyoglobin that makes a package look old.

The Food and Drug Administration (FDA) accepted industry determinations that CO in modified atmosphere packaging is generally recognized as safe at a maximum concentration of 0.4%, covering bulk master bags in 2002 and retail packages in 2004. A typical package pairs that 0.4% CO with carbon dioxide and a nitrogen balance.

The European Union prohibits the practice outright. Critics in the U.S. have petitioned the FDA to withdraw its approval, arguing that stable color can outlast the meat and hide spoilage a shopper would otherwise visually notice.

Where Is Carbon Monoxide Used as a Fuel Gas?

Carbon monoxide gets burned as a fuel wherever an industrial process already produces it as a byproduct. Steel mills are the main setting, along with plants that fire producer gas or syngas for process heat.

Blast furnace gas comes off the top of the furnace still carrying roughly 20 to 25% CO, alongside about half nitrogen, a fifth carbon dioxide, and a few percent hydrogen.

That mixture has a heating value near 90 to 100 BTU per cubic foot, against roughly 1,000 for natural gas. Mills strip the particulate out and burn it in hot blast stoves and boilers, frequently blending it with coke oven gas or natural gas to sustain a stable flame.

A blast furnace produces 2.5 to 3.5 tons of this gas per ton of steel. Mills burn it on site so they have to buy less natural gas, and flare off whatever their boiler capacity can’t absorb.

Because carbon monoxide is itself flammable, with a lower explosive limit of 12.5% in air, these streams need the same ignition controls any other fuel gas gets.

Why Do Lung Tests Use Carbon Monoxide?

Doctors have patients breathe in a small amount of carbon monoxide because the property that makes it dangerous is what makes it useful for measuring.

CO binds to hemoglobin, the oxygen carrier in blood, 200 to 250 times more strongly than oxygen does. The instant it crosses from the air sacs into the bloodstream, hemoglobin binds it, so almost none stays loose in the blood. With the blood side staying nearly empty, CO keeps crossing at a steady rate. How fast it moves depends mainly on the lung tissue it passes through rather than on blood flow, though capillary blood volume and hemoglobin level also affect the result.

The test is called DLCO, short for diffusing capacity of the lung for carbon monoxide. The patient breathes in a mixture of about 0.3% CO along with a marker gas such as helium or methane, holds it for about 10 seconds, then breathes out into an analyzer. The CO passes into the blood and the marker gas does not, so comparing what comes back out shows how much made the crossing.

A slower version covers situations where holding a breath isn’t practical, such as measurement during exercise. Patients breathe about 0.1% CO, or 1,000 parts per million, for roughly seven minutes.

What Does Safely Working With Carbon Monoxide Require?

Continuous monitoring, because carbon monoxide cannot be sensed without an instrument. It is colorless, odorless, and tasteless at every concentration, including lethal ones.

CO has a relative density of 0.967 against air—close enough that it mixes through a space instead of pooling at the floor or collecting at the ceiling. Detectors therefore belong at breathing height, where workers are positioned.

A detector is only trustworthy if it has been checked against a known concentration. Bump tests and full sensor calibrations run on calibration cylinders holding 50-200 ppm CO in a nitrogen or air balance.

The Occupational Safety and Health Administration (OSHA) sets the enforceable U.S. exposure limit, and the National Institute for Occupational Safety and Health (NIOSH) publishes stricter recommendations:

• OSHA permissible exposure limit: 50 ppm as an 8-hour time-weighted average (Cal/OSHA sets a stricter 25 ppm limit in California)
• NIOSH recommended exposure limit: 35 ppm as a time-weighted average over up to a 10-hour workday, with a 200 ppm ceiling
• NIOSH immediately dangerous to life or health value: 1,200 ppm

Forklifts, generators, and gasoline-powered tools like pressure washers and concrete saws all produce CO through incomplete combustion, and NIOSH has issued alerts about workers poisoned by them indoors. Preventing these cases means keeping the equipment outdoors, since NIOSH investigations have found that ventilating an enclosed space does not reliably keep CO to safe levels.

If you’re working out monitoring for a space where carbon monoxide could build up, our team can help you get it right.

Tyler O'Brien

Tyler is a results-driven marketing professional specializing in the industrial gases and equipment industry, bringing his 10 years of technical expertise and digital marketing acumen to the complex industrial gas B2B environment.