4.10.9 Water Tolerance
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
4.10.9 Water Tolerance
Highest temperature that causes phase separation of oxygenated fuels.
The limits vary according to location and month. For Alaska - North of 62
latitude, it changes from -41C in Dec-Jan to 9C in July, but remains 10C all
year in Hawaii.
Because phosphorus adversely affects exhaust catalysts, the EPA limits
phosphorus in all gasolines to 0.0013g P/L.
As well as the above, there are various restrictions introduced by the Clean
Air Act and state bodies such as California's Air Resources Board (CARB)
that often have more stringent limits for the above properties, as well as
additional limits. More detailed descriptions of the complex regulations
can be found elsewhere [16,41,42] - I've just included some of the major
changes, as some properties are determined by levels of permitted emissions,
eg the toxics reduction required for fuel that has the maximum permitted
benzene (1.0%), means total aromatics are limited to around 27%. There have
been some changes in early 1996 to the implementation timetable, and the
following timetable has not yet been changed.
The Clean Air Act also specifies some regions that exceed air quality
standards have to use reformulated gasolines (RFGs) all year, starting
January 1995. Other regions are required to use oxygenated gasolines for
four winter months, beginning November 1992. The RFGs also contain
oxygenates. Metropolitan regions with severe ozone air quality problems must
use reformulated gasolines in 1995 that;- contain at least 2.0 wt% oxygen,
reduce 1990 volatile organic carbon compounds by 15%, and reduce specified
toxic emissions by 15% (1995) and 25% (2000). Metropolitan regions that
exceeded carbon monoxide limits were required to use gasolines with 2.7 wt%
oxygen during winter months, starting in 1992.
The 1990 Clean Air Act (CAA) amendments and CARB Phase 2 (1996)
specifications for reformulated gasoline establish the following limits,
compared with typical 1990 gasoline. Because of a lack of data, the EPA
were unable to define the CAA required parameters, so they instituted
a two-stage system. The first stage, the "Simple Model" is an interim
stage that run from 1/Jan/1995 to 31/Dec/1997. The second stage, the
"Complex Model" has two phases, Phase I (1995-1999) and Phase II (2000+),
and there are different limits for EPA Control Region 1 (south) and Control
Region 2 (north). Each refiner must have their RFG recertified to the
Complex model prior to the 1/Jan/1998 implementation date. The following
are some of the criteria for RFG when complying on a per gallon basis, more
details are available elsewhere, including the details of the baseline fuel
compositions to be used for testing [16,41,42,43,43a].
1990 Clean Air Act CARB
Simple Complex Phase 2
I II Limit Average
benzene (max.vol.%) 2 1.00 1.00 1.00 1.00 0.8
oxygen (min.mass %) 0.2 2.0 2.0 2.0 1.8 -
(max.mass %) - 2.7 - - 2.2 -
sulfur (max.mass ppm) 150 no increase - - 40 30
aromatics (max.vol.%) 32 toxics reduction - - 25 22
olefins (max.vol.%) 9.9 no increase - - 6.0 4.0
reid vapour pressure (kPa) 60 55.8 (north) - - 48.3 -
(during VOC Control Period) 49.6 (south)
50% evaporated (max.C) - - - - 98.9 93
90% evaporated (max.C) 170 - - - 148.9 143
VOC Reductions - Region I (min.%) 35.1 27.5 - -
(VOC Control Period only) - Region II (min.%) 15.6 25.9 - -
NOx Reductions - VOC Control Period (min.%) 0 5.5 - -
- Non-VOC Control Period (min.%) 0 0 - -
Toxics Reductions (min.%) 15.0 20.0 - -
These regulations also specify emissions criteria. eg CAA specifies no
increase in nitric oxides (NOx) emissions, reductions in VOC by 15% during
the ozone season, and specified toxins by 15% all year. These criteria
indirectly establish vapour pressure and composition limits that refiners
have to meet. Note that the EPA also can issue CAA Section 211 waivers that
allow refiners to choose which oxygenates they use. In 1981, the EPA also
decided that fuels with up to 2% weight of oxygen ( from alcohols and ethers
(except methanol)) were "substantially similar" to 1974 unleaded gasoline,
and thus were not "new" gasoline additives. That level was increased to
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