NGL volumes continue to climb because of all the surging “wet” shale gas production. These days about 7% of gas plant NGL production is “isobutane”, (also known as IC4, I Grade, methylpropane, R600a, iso and “izo” to our friends in Canada). Over the past two years gas plant production of iso is up about 25%, and that volume is expected to increase another 30% over the next two years. Most isobutane is used by refineries to make high-octane alkylate, but what about the rest? Today we take a closer look at this lesser known natural gas liquid (NGL) and the sometimes exotic uses it is put to.
In previous blogs, (See “You Can Just Iso my Butane” Part I and Part II and “Skipping the Alkylate Fandango”) we reviewed some of the idiosyncrasies of IC4. Of the five NGLs - ethane, propane, normal butane, isobutane and natural gasoline—isobutane stands apart in its sources and applications. IC4 is produced in three primary ways: natural gas processing/fractionation, refinery hydrocracking (IC4 is a byproduct - see Complex Refining 101), and the isomerization of normal butane – a process that only happens when the economics (i.e. the spread between isobutane and normal butane prices) justifies the cost. Also in those previous blogs we discussed the complexity of tracking isobutane production – precisely because there are so many different ways to produce it.
Isobutane Supply Projection
Source: RBN Energy (Click to Enlarge)
Figure 1 represents RBN Energy’s outlook for US natural gas processing plant production of isobutane going out through 2015. Note that these numbers do not include isobutane from isomerization of normal butane since that is an optional process.
What is isobutane?
For you engineers and chemists (or recent converts to chemistry from watching “Breaking Bad”), isobutane is an isomer of normal butane. Isobutane has the same molecular formula as normal butane, but the structural formula is different. The chemical formula for both normal butane and isobutane is C4H10. Normal butane has four carbon atoms linked in a row, or chain (called NC4). If one of those carbon atoms links the other three carbon atoms (Figure 2) it is isobutane (called IC4)
Figure 2 (Click to Enlarge)
Peculiar Uses of Iso Butane
Aside from gasoline blending and/or petrochemicals the remaining 15-20% of isobutane production - about 35Mb/d by 2015, will be used for what some may consider peculiar or ‘exotic uses’. For example, isobutane can be used for calorimetric measurements, calibration of gas mixtures and emissions monitoring and (more interestingly) in many day-to-day household products. For instance isobutane is the clear liquid fuel in most “Bic” type lighters; it’s also the propellant used in most hair spray; cooking spray and shaving cream cans; and since the early 90s, it’s been a replacement for Freon in refrigerators.
A Replacement For CFC Propellants
A propellant is essentially the driving force that “sprays” the product out of aerosol cans. When the valve on the top of the can is pushed, it releases pressure being asserted on the liquefied propellant/product solution in the can. That change in pressure “sprays” the product out of the can. Iso is the main aerosol propellant used today, but that has not always been the case. From the 1930’s up until the 1970’s chloroflouro-carbons (CFC’s) were used as propellants in spray cans. CFCs are a combination of chloride (C), fluorine (F) and carbon (C). CFCs were first used in products like bug repellent during WWII. The concept caught on and launched a flood of aerosol products including the first sticky, hard hold resin-based hairspray (more on that later). During the 1980’s CFC’s were determined to be significant contributors to air pollution and ozone damage, and they were eventually banned. Since then isobutane has been the most popular propellant used in aerosol sprays.
In the 1990s, chemists determined that the more environmentally friendly isobutane was also a good replacement for another CFC, “Freon or CFC -12” used in the refrigeration process in home refrigerators and commercial freezers.
Refrigerators work by compressing a refrigerant gas such as isobutane. Initially the pressure on the refrigerant gas creates heat that is then conducted to coils on the outside of the refrigerator. The coils cool the gas - turning it into a liquid that then moves through valves to low pressure coils inside the refrigerator. When the refrigerant hits the lower pressure, it expands and evaporates. During the process of evaporation the refrigerant absorbs heat – cooling the inside of the refrigerator.
In its relatively new capacity as a refrigerant, isobutane gained another name. In the refrigerator game it is referred to as “R-600a”. Since it’s been such a big hit in refrigeration, there is speculation now that R-600a could also be used for domestic and automobile air conditioners one of these days. By the way, there are over eight million refrigerators sold each year in the U.S. Some guys keep a spare in the garage so that they never run out of cold beer space.