Fundamental Biochemical and Biotechnological Principles of Biomass Growth and Use 25

on the other a typical obstacle of many bio-based chemicals. Ethylene (28.05 g mol−^1 ),

the monomer to be polymerized to PE can easily be made from bio-ethanol

(46.07 g mol−^1 ) by dehydration but the stoichiometric product yield is only 0.609 kg kg−^1.

C 2 H 5 OH→C 2 H 4 +H 2 O

In contrast, the fossil-based process reaches a carbon yield of 98 kg kg−^1 .Obviously,

the bio-based process is not cost-competitive as long as biomass feedstock does not offer

a significant cost advantage.

PLA is based on the monomer lactic acid (C 3 H 4 O 2 ), a natural intermediate of lactic

acid bacteria likeLactobacillus, the very same species used in yogurt fermentation. The

monomer is produced by fermentation based on sugar (Grootet al., 2011) but an alter-

native process using lignocellulosic feedstock is under development (Riesmeier, 2013).

Subsequent to lactic acid fermentation all further steps to the polymer are performed

synthetically. PLA belongs to the polyester plastics and finds applications in packaging,

agriculture, automotive, electronics, and textiles industries. The production capacity is

expected to grow to close to 2 million tons by 2020 (Grand View Research, 2014).

1,3-Propanediol (PDO) is another sugar-based monomer. Developed since the 1990s

by DuPont (USA), it is commercialized in its polymerized form under the trade name

Sorona®and finds application especially in replacing fossil-based polytrimethylene

terephthalate (PTT), for example, in plastic bottles. What makes this monomer worth

to be mentioned here is its biological production system because PDO is a molecule not

known to nature. By combining metabolic reaction chains fromS. saccharomycesand

Klebsiellain anE. colicell, this host cell was taught to produce a man-made molecule

(Demain and Sanchez, 2012). Today, the world capacity exceeds 100,000 tons per year

(de Guzman, 2013), and from a financial perspective the market is expected to grow

from $157 million (2012) to $560 million in 2019 (Rohan, 2014).

Vegetable oils are also used as precursors in oleochemical synthesis. For example,

castor oil is of special industrial value because of the presence of hydroxyl groups on

the especially long fatty acid chains of 18 carbons. Long molecular structures give

high-performance properties to the resulting polymers to be applied, for example, in

sports, aircraft, and medical products. Castor oil is becoming increasingly important

in the production of polyurethane plastic, which is an application generally known as

natural oil polyols.

In 2004, the US National Renewable Energy Laboratory (NREL) published a study

that analyzed bio-based chemicals for their potential in the chemical industry from a

technical point of view. It resulted in 12 candidates: 1,4-dicarboxylic acids (succinic,

fumaric, and malic), 2,5-furandicarboxylic acid (FDCA), 3-hydroxpropionic acid

(3-HPA), aspartic acid, glucaric acid, glutamic acid, itaconic acid, levulinic acid,

3-hydroxybutyrolactone, glycerol, sorbitol, and xylitol/arabinitol. Especially succinic

acid draws industrial attention. DSM (Netherlands) and Roquette (France) formed the

joint venture Reverdia (France) and Succinity (Germany) has been founded by BASF

(Germany) and Corbion Purac (Netherlands).

All these molecules are provided by nature. However, it should be emphasized that

the chemical industry to a large extent works with non-natural compounds. There-

fore, PDO presents a special future-oriented example because it demonstrates that

bio-based processes can provide man-made chemical entities for innovative materials

and applications as well. Synthetic biology, emerging since early 2000s, is the principle