New diol processes: 1,3-propanediol and 1,4-butanediol
Introduction
PPT fibers are characterised by much better resilience and stress/recovery properties than PET and PBT. These properties are due to the crystal structure of PPT. PPT chains are much more angular structured than PET and PBT chains. Therefore these chains can be streched up to 15% with a reversible recovery [1].
In the 1990s three technical processes for the production of 1,3-propanediol were developed. All three processes use different feedstocks. The first process uses acrolein (Ac), the second ethylene oxide (EO), the third glucose as raw materials. The first two processes are classical oleochemical processes, the third is a biotechnological process. The Ac process technology was developed by Degussa-Huels. In 1997 this technology was sold to DuPont. Shell developed the EO process technology. In parallel to the Ac process technology aquisition, DuPont is developing the newest PDO technology, the fermentation of glucose or sucrose to PDO. Production plants were built in recent years, using the Ac and the EO process in Germany and the US.
1,4-Butanediol (BDO) is the most widely used of all the four carbon-based diols in industry today [27]. BDO is used predominately as a polymer feedstock. For example, it is used in the production of both polyurethanes and polybutylene terephthalate (PBT) [27], [28]. PBT is growing in use in the automobile industry for the manufacture of engine and body components. BDO may also be converted to gamma-butyrolactone and tetrahydrofuran, which can be employed an intermediate for materials such as pyrrolidones and as a solvent, respectively. Additionally, tetrahydrofuran is also used as a feedstock for the manufacture of polytetramethylene ether glycol (PTMEG) a component of both urethane elastomers and spandex fibers [28].
In this present paper an overview of current technolgies for the production of 1,3-propandiol and 1,4-butandiol developed in recent years will be presented.
Section snippets
PDO process based on acrolein
Acrolein is easily accessible via selective air oxidation of propene. This technology is commercialized and mainly used to produce methionine and acrylic acid.
The Ac-based PDO process involves two reaction steps. At first acrolein is hydrated in an aqueous solution to from 3-hydroxypropanal (HPA). HPA is consecutively hydrogenated to PDO. The overall yield is 85–90%. The process is designed in a fully continuous mode. Both reaction steps run in adiabatic fixed bed reactors. The only solvent is
PDO process based on ethyleneoxide
The hydroformylation of epoxides provides an easy pathway to ß-hydroxyaldehydes which may be hydrogenated to 1,3-diols (Fig. 1). Because 1,3-propanediol has attracted considerable industrial interest as an intermediate in the production of polyester fibers and films, most work was concentrated on ethylene oxide (EO) as starting material for the hydroformylation of epoxides.
In the early 1960s numerous attempts had been made to subject oxiranes to the hydroformylation reaction. On account of the
BDO process based on formaldehyde and acetylene
BDO has been manufactured industrially for the latter half of the 20th century via the hydrogenation of butynediol. This hydrogenation is typically accomplished through the use of either a nickel or palladium catalyst [27], [29], [30]. Butynediol is synthesized using a formaldehyde ethynylation process commonly called the Reppe process [27], [31]. This process utilizes aqueous formaldehyde solutions into which gaseous acetylene is introduced. The reaction, as practiced industrially, is first
BDO-process based on acetoxylation of butadiene
The first alternative route to appear commercially was the oxidative acetoxylation of 1,3-butadiene developed by Mitsubishi Chemicals [35], [36], [37]. This process, practiced by the Mitsubishi-Kasei Corporation of Japan, combines acetic acid with 1,3-butadiene over a palladium/tellurium catalyst at 3 bar and 80 °C to yield 1,4-diacetoxy-2-butene. This molecule is subsequently hydrogenated and finally hydrolyzed to BDO, while the acetic acid is recycled back to the front of the process.
BDO-process based on butane
The production of BDO via the selective oxidation of butane to maleic anhydride (MAN) is also an area that has received renewed interest in recent years [38], [39]. The reasons for this renewed interest are related to the increased abundance of butane as a feedstock that resulted from its decreased use in gasoline, and the much improved selectivities that are achieved with the newer generations of MAN catalysts [35], [38]. These factors combine to provide a low cost, safe and environmentally
BDO process base on allyl alcohol
Another alternative route to BDO is via the hydroformylation of allyl alcohol. This has been commercialized by Lyondell, formerly ARCO, and is based on their existing propylene oxide technology [36]. The propylene oxide is first isomerized over a lithium phosphate, Li3PO4, catalyst to allyl alcohol. The latter is then hydroformylated to BDO using a rhodium catalyst having a large excess of triphenylphosphine and an equimolar amount of 1,4-diphenylphosphinobutane to rhodium [43]. The
BDO process based on epoxidation of butadiene
The last commercial route to BDO under exploration is based on the epoxidation of butadiene chemistry developed by Eastman Chemical Company [44]. The epoxidation is carried out over a silver catalyst to produce a 3,4-epoxy-1-butene. This molecule is then hydrated using mixtures of hydriodic acid and organic soluble iodine salts as catalysts. It is further hydrogenated using a precious metal catalyst to BDO [45].
Dow Chemical has recently added to this area of research some work that reports on
Outlook
Although polyester polymers are very old, the world polyester market is still growing. More and more new applications are under development. This is caused by many reasons. In contrast to many other polymers recycling is easy. Polyesters contain only C, H and O. For that reasons it is likely that BDO and especially PDO will grow with high rates in the next decades.
Concerning PDO, the Ac to PDO process as well as the EO to PDO process are technically proven. The advantage of the Ac-based process
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