Environmental Engineering Reference
In-Depth Information
Moving forward, the versatility of vegetable oil feedstocks combined with rela-
tively new polymerizations methods, such as acyclic metathesis polymerizations
(ADMET), ring-opening metathesis polymerization (ROMP), ATRP, and RAFT,
provides opportunities to meet the need for specialized and novel thermosets and
thermoplastics [33, 59-62]. Lastly, as research in genetically modified organisms
continues to develop, there is potential for an upstream increase in purity of fatty
acid contents, for an increase in functionalities of fatty acids, and for an increase
in production of vegetable oils [3, 63].
5.3 Furan Chemistry
This section introduces the established but still growing area of polymers devel-
oped from furans. Two furan derivatives are of particular interest: furfural and
5-hydroxymethylfurfural (HMF). Furans and furan derivatives are a promising
field in renewable chemistry as they are platform chemicals that can be used to
produce fine chemicals, pharmaceuticals, and agrochemicals, as well as polymers
[64]. Several excellent in-depth reviews on furan chemistry for biorenewable
polymers are available [64-68].
Furan is a heterocyclic diene. The first-generation derivatives - furfural and
5-HMF, shown in Figure 5.2 - can be produced from mono, oligo, and polysaccha-
ride sources using several methods [67]. Straightforward modifications of furfural
and HMF lead to the production of several monomers suitable for polymerization
[68]. Figure 5.2 depicts some of these, including 2,5-furancarboxydialdehyde
(FCDA), 2,5-furandicarboxylic acid (FDCA), 2,5-furandicarboxylic acid dichloride
(FDCC), and isopropylidene
bis
-(2,5-furandiylmethylene)diisocyanate. Furan
derivatives show promise for the production of polymers, generally following
condensation routes to polyesters, polyamides, polyurethanes, and others [67].
Limited success has been reported with regard to free radical, cationic, and anionic
polymerizations because of difficulties mostly contributed to the central furan
molecule, suggesting limited room for growth [67].
5.3.1
Production of Furfural and HMF
Furfural and 5-HMF are commonly produced by acid-catalyzed dehydration of
pentose and hexose sugars, respectively [67]. Carbohydrate feedstocks for the
production of these chemicals include many by-products, such as corn cobs, rice
hulls, and sugarcane bagasse. Furfural has been a commodity product since the
early twentieth century; production typically consists of a pretreatment, hydroly-
sis, and refining [69]. During the pretreatment, the feedstock (corn cobs, oat hulls,
etc.) are crushed and mixed with sulfuric acid [69]. The hydrolysis is carried out
at high temperatures, and the escaping steam from the reaction mixture carries out
water and furfural; subsequently the steam is filtered and condensed [69]. The
