Environmental Engineering Reference
In-Depth Information
urated aldehydes, acrolein and crotonaldehyde, were the most potent sen-
sory irritants; the saturated aldehydes, acetaldehyde and propionaldehyde,
were least potent. These data, which do not include glutaraldehyde (a potent
irritant in rats), indicate that only a few aldehydes have the potential to be
significant mucous membrane irritants at the relatively low concentrations
that occur in indoor environments, such as residences and nonresidential,
nonindustrial buildings. Of these HCHO, acrolein, and glutaraldehyde are
the most notable. Though a relatively weak sensory irritant, acetaldehyde is
a common contaminant of both indoor and ambient (outdoor) air.
B.
Formaldehyde
Formaldehyde is molecularly the smallest and simplest aldehyde. It is
unique because the carbonyl is attached directly to two hydrogen atoms
cally and photochemically. It has good thermal stability relative to other
carbonyls and has the ability to undergo a variety of chemical reactions,
which makes it useful in industrial and commercial processes. As a conse-
quence it is among the top 10 organic chemical feedstocks used in the U.S.
Formaldehyde is a colorless, gaseous substance with a strong, pungent
odor. On condensing, it forms a liquid with a high vapor pressure (boiling
at -19°C). Because of its high reactivity, it rapidly polymerizes with itself to
form paraformaldehyde. As a consequence, liquid HCHO must be held at
low temperature or mixed with a stabilizer (such as methanol) to pre-
vent/minimize polymerization.
1.
Uses/sources
Formaldehyde is commercially available as paraformaldehyde, which con-
tains varying lengths of polymerized HCHO molecules. It is a colorless solid
that slowly decomposes and vaporizes as monomeric HCHO at room tem-
perature. It has been used in a variety of deodorizing commercial products,
such as lavatory and carpet preparations.
Formaldehyde is also commercially available as formalin, an aqueous
solution that typically contains 37 to 38% HCHO by weight and 6 to 15%
methanol. Because of HCHO's volatility, formalin also has a strong, pungent
odor. In solution it is present as methylene glycol (CH
); in concen-
trated solutions it is in the form of polyoxymethylene glycol (HO-CH
(OH)
2
2
-H.
As a chemical feedstock, HCHO is used in many different chemical
processes. Of particular significance to indoor environments is its use to
produce urea and phenol-formaldehyde resins (50% of HCHO consumed
annually).
Urea-formaldehyde (UF) copolymeric resins are used as wood adhe-
sives in the manufacture of pressed-wood products such as particle board,
medium-density fiber board (MDF) and hardwood plywood, finish coatings
(acid-cured), textile treatments (permanent-press finishes), and in the pro-
duction of urea-formaldehyde foam insulation (UFFI). Urea-formaldehyde
O)
2
n
