Trade inefficient trial-and-error testing for a systematic approach to solvent
substitution and blends.
Associate Professor of
Sam Houston State
The cleaning chemist’s lament:
First, they took my CFCs;
Then, controlled my VOCs.
Now, they want my 225.
Will my company survive?
This article outlines a systemic evaluation process for making solvent substitution decisions. Environmental, safety, and health information is extracted from the MSDS and is considered along with effectiveness criteria.
The heart of the process is the effectiveness evaluation that is
based upon the Hansen solubility parameters. The theory and
use of HSPs are illustrated in an example of solvent selection
and solvent blending to remove a silicone-based high-vacuum
Although there are many technical subject matter experts
(SMEs), line managers, and industry personnel who are tasked
with solvent selection responsibilities, there are also other
industrial sectors1 that are dealing with solvent substitution
requirements (e.g. refrigeration, air conditioning, foam blowing agents, fire suppression, explosion protection, aerosols,
sterilants, tobacco expansion, adhesives, coatings, and inks).
Industrial chemists and engineers have an impressive track
record of “rising to the occasion” with respect to the increasing
restrictions on acceptable process solvents. They have responded with continual improvement to remove ozone-depleting
(OD) solvents, to reduce hazardous air pollutants (HAPs), to
reduce volatile organic carbon (VOC), to avoid solvents with
a high global warming potential (GWP), to reduce flammability when feasible, and to enhance worker health and safety.
Consequently, the process of solvent selection has become
Some good resources
The U.S. EPA has a website for their Significant New Alternatives
Policy (SNAP) program that reports on the evaluation and
regulation of non-ozone-depleting alternative solvents. The
purpose of this program is “to allow a safe, smooth transition
away from ozone-depleting compounds by identifying sub-
stitutes that offer lower overall risks to human health and the
The SNAP program is primarily focused on non-ozone-
depleting replacements, but there exists an excellent resource—
the Toxics Use Reduction Institute (TURI) 2—that addresses the
reduction of overall toxicity. Their broad evaluations of regulated
chemicals and suitable replacements are a valuable resource for the
cleaning sector as well as other solvent-heavy sectors of industry.
But first, be practical. If a well-established business sector
has a particular work-horse solvent (e.g. perchloroethylene, n-
Propyl bromide, etc.), the first source of information should be
the solvent manufacturer. A good relationship with the technical
representatives is valuable. If a solvent is slated to be phased out,
the supplier will be devoting a large amount of effort to main-
tain their market share by researching alternatives.
It may be the case, though, that a different manufacturer
will have a better replacement and navigating this situation
can be confusing. If one has a critical performance need or a
problem soil-substrate combination, then the various manufacturers are often willing to test their alternative solvent(s)
against the critical need.
However, many SMEs, chemists, and engineers are curious
by nature, and they want to know what is going on behind the
scenes in these solvent evaluations. Some will even want to do
the evaluations themselves to satisfy this curiosity and to instill
confidence in the independence of the evaluation.
This article addresses this “need to know” by briefly describing:
Figure 1: A Hansen solubility parameter plot for several popular
solvents and a particular soil— a high-vacuum grease (HVG). The
solvents and soil are plotted at coordinates ( 2 δD,δP ,δH) so that the
interaction region is spherical5. The data points are colored according
to the relative magnitudes of δD (blue), δP (red), and δH (green) such
that similar colors interact strongly—like dissolves like.