Normal Butane (C4H10) and Iso-Butane (also C4H10): Component of LP
Gas, Feedstock for Butadiene Used in Synthetic Rubber Manufacture, Aerosol
Propellant, Refrigerant, Lighter Fuel, Component of Alkylate, and Gasoline
Additive
Normal butane (n-butane) and its isomer, iso-butane
(2-methyl propane) have the same chemical formula but different atomic structures.
Their properties are mostly similar but there are some differences. The vapor
pressure of both is less than that of propane (about 3-4 times less) and far
less than ethane. In so-called “refined” iso-butane, or iso-butane with
impurities removed, concentrated flames in special-made torches can heat up to
2700 deg F, which makes these specialized torches applicable for many specific scientific,
medical, construction, soldering, and craft uses. Both butanes are also a common
component in LP gas (liquefied petroleum gas) but propane is typically the main
component. Butane is the lighter fuel of choice as well as being commonly used
for camp stoves. It is also used as an aerosol propellant and increasingly as a
refrigerant that replaces the CFCs (chlorofluorocarbons) and HFCs (hydrofluorocarbons)
implicated in global warming and making a hole in the ozone layer. Butane does
have one limitation as a heating fuel: it can fail to gasify in real cold
weather. This is why butane is not higher in LP gas. Since camp fuel is mostly
used in the summer, the butane canisters are popular.
Butadiene
Butane is a feedstock for 1,3-butadiene (C4H6) which is used
to make synthetic rubber. 1,3-Butadiene can be extracted from normal butane and
petroleum in various ways: steam cracking, catalytic dehydrogenation,
dehydrogenation of butenes, from ethanol, and from acetylene. In Russia it was
commonly extracted from ethanol until the 1970’s. Production from steam
cracking distillation is now the most common method but requires “heavy feeds,”
or an NGL feedstock with significant amounts of normal butane and iso-butane
relative to lower-carbon alkanes like propane and ethane. Like the NGLs butadiene
is a liquid under pressure but a gas at normal pressure. It is also a component
of motor vehicle exhaust, considered to be toxic as such. Thus, it is a volatile
organic compound (VOC) that is found in ambient air in urban areas although it
breaks down quickly in the atmosphere.
Iso-Butane: from Natural Gas Processing or from Isomerization of Normal
Butane
Iso-butane is preferred as a refrigerant and aerosol
propellant. It may come directly from natural gas processing (and more does now
due to the increased production of NGLs from shale gas) or it may be made from
normal butane in isomerization units (butamer units) which change the chemical
structure of normal butane to iso-butane. This is typically done at the
alkylization plant before making alkylate. Iso-butane usually costs more than
normal butane on the market and this price differential can dictate how much
normal butane is isomerized to iso-butane. If the price differential is high
enough more profit can be made from the normal butane by converting it to
iso-butane. Actually, the isomerization units can balance the isobutane
market factors fairly quickly by producing more during a shortage and less
during a glut. This gives it a slight advantage over other NGL markets. Normal butane
is typically more abundant than iso-butane in natural gas streams. The authors
at the RBN Energy blog (see references) note that the EIA does not distinguish
isomerized isobutane from a refinery from natural isobutane supply separated at
gas plants. EIA thus estimated that in 2012 isobutane was 9-10% of NGL volume
but when isomerized isobutane was factored out the amount from gas plants was
about 6-7 of NGL volume. Overall normal butane and isobutane supplies have been
increasing since fracked shale ‘wet’ gas from the Marcellus and Utica has come
to dominate new U.S. natural gas production. Isobutane is also used as a
petrochemical feedstock for propylene oxide, isobutylene, and iso-octane. The
abundance of isobutane from shale gas may effect isomerization unit usage but
could be counteracted by increased production of alkylate utilizing propylene made
from isobutane.
Alkylate: High-Octane, Low Vapor Pressure, Low Sulfur Gasoline Blend
Made from Isobutane and Butylene or Propylene
Gasoline is a complex mixture blended to meet various quality
specifications. Alkylate, which is made in alkylization units, is made from isobutane
and NGL byproducts like butylene or propylene. Typically, alkylate makes up
11-13 % of gasoline. More is added during the summer since it leads to lower
vapor pressure in the warm months. Alkylate is also currently and commonly more
expensive per volume than gasoline. Alkylate increases the octane rating of the
gasoline which allows for greater compression in the engine before ignition of
the air/gas mix and thus avoids any engine damage. However, most vehicles are
designed to run on lower octane (87). Some more powerful high performance
engines are designed to run on octane ratings of 89, 91, or 93. Since ethanol
increases the RVP (Reid vapor pressure) in the ethanol blends and there are
requirements in the summer to keep the RVP down, more alkylate is added in
summer. Alkylate percentage is higher in summer than in winter. Alkylate is
thought to be protective to engines and to increase ‘drivability.’ Alkylate is
used more to lower RVP than to increase octane since the ethanol blended into
gasoline is better than alkylate at increasing octane.
Normal Butane is Also Blended in Gasoline
Normal butane is also blended in gasoline during the winter
months due to its lower cost. This is actually the main use by volume of normal
butane. This increases the RVP (Reid vapor pressure) so more alkylate is also
added to re-balance the RVP by dropping it down. Gasoline is a complex blend (or seasonal blends) of products refined from crude oil and other products made
from processed/extracted NGLs.
Current and Future Supply and Demand of Butanes
The advent of shale gas has assured adequate and likely abundant
supplies of the butanes for the foreseeable future. EIA predicts production to
rise modestly from about 600,000 to 700,000 Bbls per day over the next year or
two. In terms of pricing isobutane averages just a little above normal butane
and both butanes sell for a higher price than propane and ethane – typically the
more carbon atoms in an alkane the higher the price. Net exports of butanes
grew by 30,000 Bbls per day in 2015 and are projected to grow by 60,000 Bbls
per day in 2016 and 20,000 Bbls per day in 2017, according to the EIA. This is
with two new Gulf Coast export terminals opening up in late 2015. One new
terminal in Texas is slated to open in 3Q 2016. Refinery and blender production
of butane is seasonal and is projected to stay flat over the next few years as
is overall domestic consumption. The production growth will be for exports to
meet modest demand increases.
Pipeline Issues and Recent Pipeline Projects
NGLs are typically pipelined as ‘y-grade’ or ‘raw mix’ of
all NGLs or as one NGL-component ‘purity products.’ Sometimes two NGLs are
mixed together and transported. One recent pipeline being built to transport NGLs
in Ohio will also transport natural gasoline. This 45,000 Bbl per day Cornerstone
Pipeline will bring butane, propane, condensate mix, and natural gasoline 42
miles from Utica field gas processing facilities in Eastern Ohio to a refinery
in Canton with some refined products shipped via pipeline to Lima, Ohio. They
will be transported in batches to the Canton refinery. The refinery recently
added a condensate splitter that can process 25,000 Bbls per day of Utica
condensate.
There was a fire from an accidental liquid butane pipeline
rupture in Lively, Texas in 1996 when a pickup truck drove through the butane
vapor cloud igniting it and the two people in the truck (on their way to report
the incident to 911) were killed in the fire. The rupture was subsequently
determined to have been caused by failure to properly detect and mitigate corrosion
in the line by the pipeline company.
LP Gas Export Dynamics and Increased U.S. Export Dock Capacity
Since LP Gas demand is fairly flat in the U.S. about 50% of
what is produced as mostly propane and some butanes is exported. U.S. LP gas
has replaced African and Middle Eastern sources in Latin America and now in
Europe. The African and Middle Eastern sources have been diverted to Asia, the
biggest demand driver for LP gas, particularly China and then India. Basically, sources are adjusting to supply more locally which has the advantage of lower shipping costs. The U.S.
will likely continue to be a major exporter of NGLs with the significant
reserves of wet and rich gas in the Marcellus and Utica and in other shale
plays.
New Alkylate Plant(s?) Being Planned for the Marcellus-Utica Region
The recent merger of Markwest with a pipeline firm owned by
Marathon Petroleum Corporation has allowed the companies to work together toward
a possible alkylate plant in the tri-state area of West Virginia, Pennsylvania,
and Ohio. Markwest markets about 75% of the NGLs in the Marcellus-Utica region
and they have lots of butane to sell. Marathon Petroleum’s refineries would be
one of several companies’ refineries that would buy the alkylate to be added to
gasoline. The new company as MPLX predicts a 20% increase in NGL processing and
a 30% increase in ethane and propane fractionation in 2016.
References:
Butane, entry in Wikipedia.com
Marathon Pipe Line Kicking Off Construction of 42 Miles of 16” in Ohio
What is Butane Commonly Used For?
The Important Role that Butane Plays in the Medical Industry – posted on
the blog at butanesource.com
Why Refined Butane is Better for Jet Torches – posted on the blog at
butanesource.com
1-3,Butadiene, entry in Wikipedia.com
Pipeline Accident Summary Report: Pipeline Rupture, Liquid Butane
Release, and Fire, Lively, Texas, August 24, 1966 – National Transportation
Safety Board
You Can Just Iso My Butane: Isobutane and Isomerization in the Shale
Gas World – by Callie Mitchell at RPN Energy Blog, March 10, 2013
Wasted Away in Butane Blendingville – by Brandon Bello at RBN Energy
Blog, Nov. 28, 2012
Skipping the Alkylate Fandango – The Octane Boost in Gasoline Blending –
by Sandy Fielden at RBN Energy Blog, Feb 14, 2013
The Domino Effect: How the Shale Revolution is Transforming Energy
Markets, Industries, and Economies – by E. Russel Brazel, CWL Publishing, 2016
Marathon Pipe Line Looking to Expand Cornerstone Pipeline for Utica
Shale Liquids – by Bob Downing, in Akron Beacon Journal, April 12, 2016
Short-Term Outlook for Hydrocarbon Gas Liquids – by Energy Information
Administration (EIA), March 2016
Marathon, Markwest Consider Building Plant in the Marcellus Region – by
Anya Litvak, Pittsburgh Post-Gazette, January 27, 2016
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