Chemistry Reference
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O
O
HO
R
O
CH
3
OH
R
3 RCO
2
CH
3
+
HO
HO
Glycerol
O
O
Biodiesel
O
R
Vegetable oil
R = Long chain hydrocarbon
5.5 BTX
BTX is a mixture of benzene, toluene, and xylene. It comes from petroleum
refining. Depending on the source, the composition will vary. For example,
BTX from the cracking of naphtha is typically richer in benzene than BTX
from a gasoline reforming process. The boiling points are sufficiently differ-
ent that they can be separated. In approximate order of importance, benzene
is used to make ethyl benzene, cumene, cyclohexane, and nitrobenzene as
well as many other chemicals. Toluene is used as a solvent and to make
toluene diisocyanate, a monomer used to make polyurethane. Toluene can
also be disproportionated to xylene and benzene.
Of the xylenes, p-xylene has the largest volume use. It is oxidized
to terephthalic acid, which is used as a monomer to make polyesters.
Ortho xylene is oxidized to phthalic anhydride. Phthalic anhydride can be
reacted with long-chain alcohols to make plasticizers to impart flexibility to
PVC resin. Phthalic anhydride is also used to make unsaturated polyester
resins.
CH
3
CO
2
H
CH
3
CO
2
H
p-xylene
Terephthalic acid
O
CH
3
O
CH
3
O
Phthalic anhydride
o-xylene
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