George A. Kraus 1

1 Department of Chemistry and Institute for Physical Research and Technology, Iowa State University, Ames, IA, USA. 

# Review
Synthetic Methods for the Preparation of 1,3- Propanediol

The market for 1,3-propanediol (PDO) is currently over 100 million pounds per year and is growing rapidly. PDO is a component of industrial polyesters such as Dupont’s
Soronam and CDP Natureworksm or Shell Chemical’s CorterraTM 

### . Markets for the polyester include thermoplastics, textiles, carpets, and upholstery. This paper reviews themethods for the production of 1,3-propanediol by focusing on four feedstocks: glycerol, ethylene oxide, acrolein, and glucose.

Keywords: Fermentation; Hydroformylation; 1,3-Propanediol; Synthesis ;
Received: April 1, 2008; revised: May 8, 2008; accepted: May 15, 2008

DOI: 10.1002/clen.200800084



## 1 Introduction

PDO is a common abbreviation for 1,3-propanediol. It is a chemical intermediate used in resins, engine coolants [1], dry-set mortars [2],water-based inks [3], but mostly in the manufacture of polytrimethylene terephthalate (PTT) [4]. PTT is marketed under trademarks such as Dupont’s Soronam and CDP Natureworksm or Shell Chemical’s CorterraTM 

### [5]. The structure of PTT is depicted in Fig. 1.

Polymers based on PDO and terephthalic acid exhibit a number ofadvantages over polyesters based on ethylene glycol or 1,4-butanediol and terephthalic acid. The advantage stems in part from the difference in molecular structure, with the polymer derived from PDOand terephthalic acid having a zig-zag or coil-like shape. This coillike shape translates into a polymer having superior stretching andstretch-recovery characteristics. Additionally, the dyeing temperature is lower than for other commercially available polyesters and awider range of colors can be accommodated [4]. The PDO-based polyester is more resistant to stains and has better washfastness. ThePDO-based polyester also resists UV-degradation from sunlight better than other polyesters, making it attractive for sports apparel [4]. The polyester can be injection molded, pressure molded, and blowmolded [6]. Major markets for the Sorona polymers also include textiles, carpets, and upholstery. The huge polymer and terephthalate plastics industry has an estimated sales volume of over six billion dollars.

In recent years technological breakthroughs in the preparation of 1,3-propanediol have resulted in lower market prices, currently in the $0.80 per pound range. This in turn has created an increasingdemand from textile, fabric and carpet manufacturers for PDObased polymers. Increasing PDO demand and expanding product applications have led to an estimated 100 million pound annual U.S. demand for 1,3-propanediol.

During the 1990's, Shell Chemical Company developed new catalyst technology for the conversion of ethylene oxide into PDO,allowing the company to produce PDO at commercially viable pricing levels. This technology led to the Corterra brand of thermoplastic polyesters. Shell produces PDO at an 83,000 ton petroleum-based manufacturing unit in Geismar, Louisiana. DuPont produces 10,000tons per year of Sorona brand polymers, using PDO and terphthalate, at its Kinston, North Carolina facility. Dupont has also partnered with Tate & Lyle to produce PDO using corn-based fermentation at its Louden, Tennessee, facility. The fermentation route toproduce PDO from a glucose feedstock is estimated to be price competitive with the petrochemical methods.

The development of new, cost-competitive processes that utilizerenewable resources or by-products from the emerging biorefineries as feedstocks will aid rural revitalization. These processes also represent important milestones toward the goal of reducing the United States' dependence on foreign oil. Introduction of such processes not only avoids the use of more petroleum, but also has the potential to provide substantial energy savings, and reduce greenhouse gas emissions.



## 2 Feedstocks

2.1 Glycerol

Glycerol is the major by-product of biodiesel production from soybean oil or animal fats. This three-carbon triol arises from the transesterification of triglycerides with methanol. For every gallon of biodiesel that is produced, one pound of glycerol is also produced. Most Correspondence: Dr. G. A. Kraus, Department of Chemistry and Institute for Physical Research and Technology, Iowa State University, Ames, IA 50011, USA. E-mail: gakraus@iastate.edu

Abbreviations: PDO , 1,3-Propanediol; PTT, Polytrimethylene terephthalate



## i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Figure 1. Structure of polytrimethylene terephthalate. 648 Clean 2008, 36 (8), 648 – 651Clean 2008, 36 (8), 648 – 651 Preparation of 1,3-Propanediol 649



### industry experts predict that the U.S. biodiesel industry will generate approximately 1.8 billion pounds of glycerol per year by the end of 2009. This is in addition to approximately 560 million pounds of glycerol produced annually from non-biodiesel sources [7]. While there was enough need for glycerol in past years, the recent increases in biodiesel production make it necessary to create new applications for glycerol. Some reports indicate that at a $0.03 perpound price level for glycerol, it may actually be useful to burn glycerol as a fuel. Inefficient use of this by-product weakens the overallprofitability of biodiesel plants in the biodiesel industry. The utilization of a by-product from the biodiesel industry to produce PDOwould add value, thereby benefiting the emerging biodiesel industry in the United States.

Early studies to produce PDO from glycerol involved the fermentation studies reported by Bock [8], Zeng [9, 10], and Wang [11]. These early studies demonstrated that 1,3-propanediol could be generated from glycerol using microorganisms such as Citrobacter freundii

, Klebsiella pheumoniae, or Clostridium pasteurianum . The reaction is catalyzed by an enzyme that effects dehydration (a coenzyme B12 dependent glycerol dehydratase) followed by an enzyme that effects reduction of the aldehyde (a 1,3-propanediol oxidoreductase).Although concentrations of approximately 70 g/L of 1,3-propanediol have been reported, this concentration may be close to the amount that inhibits growth of the microorganisms. In 2007, Zang reported that 1,3-propanediol could be generated from glycerol using a recombinant form of Escherichia coli that expressed glycerol dehydratase, 1,3-propanediol oxidoreductase and the reactivatingfactor for glycerol dehydratase [12]. In 2008, Papanikolaou and coworkers reported that crude glycerol directly from the biodiesel plant could be used as a substrate with Clostridium butyricum [13]. They showed that 47.1 g/L of propanediol could be produced from batch anaerobic cultures.

Glycerol could also be used to make 1,3-propanediol (PDO) byselective deoxygenation of the secondary alcohol using organometallic catalysts. This deoxygenation might occur via a dehydration/ hydrogenation pathway or by way of the reduction of a cationicintermediate. Several strategies focusing on selective deoxygenation reactions have been reported. Drent and coworkers reported one of the first strategies for the deoxygenation of glycerol usingorganometallic catalysts [14]. They utilized heterogeneous palladium or platinum catalysts. Although they obtained acrolein as the major product of the reaction, they also produced 1,3-propanediol as a minor product.

Bullock has reported an innovative reduction of 1,2-diols to primary alcohols. An example is illustrated below in Fig. 2. While thischemistry works well for the deoxygenation of certain 1,2-diols, preliminary experiments suggest that this technology does not work well with glycerol [15].

The hydrogenation method of Schlaf is illustrated below in Fig. 3for the reduction of 1,2-propanediol. He has reduced glycerol to generate both PDO and 1-propanol [16]. The boiling points of PDO and tetramethylenesulfone, the solvent used in the Schlaf reduction, are within thirty degrees of each other, making purification a challenge on a large scale. In the case of the glycerol reduction, the conversion was modest, but the reaction conditions had not yet been optimized. The authors indicated that the reduction of glycerol can be complicated by the acid-catalyzed formation of acetals derived from 3-hydroxy propionaldehyde.

In 2008 Kurosaka and coworkers reported the reduction of glycerol using a heterogeneous organometallic catalyst composed of platinum, tungsten trioxide on a zirconium dioxide support as shown in Fig. 4 [17]. The reaction was conducted at 170 8 C and elevated pressures of hydrogen to provide a 24% yield of 1,3-propanediol with 12% 1,2-propanediol and 28% 1-propanol. The use of alumina or silica supports gave lower yields of 1.3-propanediol.



### 2.2 Ethylene Oxide

The hydroformylation of ethylene oxide to produce 1,3-propanediol involves a two-stage process. This approach to the synthesis of PDOhas been studied extensively by scientists at Shell Chemical Company. In the first-stage, ethylene oxide reacts with carbon monoxide and an organometallic catalyst to produce a hydroxy aldehyde. Inthe second stage, the hydroxy aldehyde is reduced to a diol by hydrogenation. One of the successful organometallic catalysts is a homogeneous cobalt catalyst that effects ring opening of ethylene oxide followed by insertion of carbon monoxide to form the three-carbon hydroxy aldehyde. Heterogeneous organometallic catalysts can alsobe employed. The aldehyde reduction stage can use a copper chromite catalyst with synthesis gas (hydrogen and carbon monoxide) as the hydrogen source [18].

The two-stage process can be combined in a single reaction asdepicted in Fig. 5. A patent by scientists from Shell Chemical Company describes a homogeneous bimetallic catalyst formed from a cobalt compound and a ruthenium compound in a 1:1 ratio with a 1,2-diphospholanoethane ligand. This catalyst reacts with ethylene oxide in the presence of synthesis gas in methyl tert-butyl ether at elevated temperatures and pressures to generate 1,3-propanediol in approximately 90% yield in a single pot reaction [19].

Although this method employs a catalyst, the need for methyltert-butyl ether as a solvent and the petroleum-based starting material are counter to the principles of green chemistry. Recently, Powell and Weider reported that the hydroformylation of ethylene oxide could be successfully conducted in expanded solvents [20]. Apractical disadvantage is that PDO generated by the hydroformylation route contains almost ten times the level of impurities than PDO derived from fermentation [5].



## i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Figure 2. Selective reduction of 1,2-propanediol. Figure 3. Reduction of 1,2-propanediol.

Figure 4. Reduction of glycerol.650 G. A. Kraus Clean 2008, 36 (8), 648 – 651



### 2.3 Acrolein

Acrolein is a third major feedstock for the production of 1,3-propanediol. The acrolein approach has been rigorously evaluated by researchers at Degussa and DuPont. The two-step process is shown in Fig. 6 and involves the addition of water to acrolein to form 3- hydroxy propionaldehyde followed by catalytic hydrogenation togenerate PDO. The addition of water to acrolein is generally mediated by acid catalysts. The selectivity of the addition is only around 70 to 80% when zeolites or ion exchange resins are used. Recently, Tsunoda and Nomura reported that a silicoaluminophosphatebased molecular sieve afforded a selectivity of 96% when the reaction was conducted in aqueous solution at 60 8 C [21].

Although acrolein is currently generated from the oxidation of propylene, recent studies have demonstrated that glycerol can beefficiently converted into acrolein using catalytic quantities of sulfuric acid in hot compressed water [22, 23]. The acrolein can be produced at 80% selectivity at 90% glycerol conversion [23].

The reduction of 3-hydroxypropionaldehyde has been studiedwith a number of catalysts and supports. One problem is the plugging of the nickel catalysts by impurities in the feedstock. Gallezotand coworkers reported that a ruthenium catalyst on a macroporous titanium dioxide support was not subject to fouling by oligomeric organic impurities. However, the same catalyst on a microporous or mesoporous support was deactivated [24]. Using the ruthenium catalyst on a macroporous support, Gallezot and coworkersachieved yields of 98% in the reduction of 3-hydroxypropionaldehyde to 1,3-propanediol.



### 2.4 Glucose

The pathways based on ethylene oxide or acrolein both have the disadvantage that the starting materials are derived from petroleum. A pathway based on the fermentation of renewable resources isexpected to be more environmentally benign and have fewer greenhouse gas emissions than its petroleum counterpart [25]. Now that the cost of oil routinely exceeds $100 a barrel, it might also be morecost effective, provided that high titers and good separation procedures are available.

DuPont has recently developed a commercial process for the production of 1,3-propanediol from D-glucose using genetically engineered E. coli [26]. The recombinant E. coli expressed a group of genes that encoded dehydratase activity, dehydratase reactivation factor, glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase.The group of genes in their original study also contained a 1,3-propanediol oxidoreductase; however, they found that removal of that enzyme resulted in a higher titer of 1,3-propanediol. This result was unexpected. Apparently E. coli is capable of converting 3-hydroxypropionaldehyde into 1,3-propanediol by an endogenous enzyme. The authors speculated that the higher titer of 1,3-propanediol might be due to increased cell viability during the fermentation [26]. This process has been commercialized. It has been reportedthat PDO produced by the fermentation process has fewer impurities than the PDO produced using petroleum-based feedstocks [5].

Chinese researchers have recently reported the development of a recombinant Saccharomyces cerevisiae strain that can convert D-glucose into 1,3-propanediol in a one-pot reaction [27]. Further researchinto this promising area will be necessary before a commercial process can be envisioned.



## 3 Concluding Remarks

In summary, polyesters derived from 1,3-propanediol have improved properties compared to other polyesters and are now used in thermoplastics, textiles, carpets, and upholstery. The expanding uses have stimulated considerable research into cost effective preparations of 1,3-propanediol. Both fermentation-basedroutes and organometallic catalyst-based routes have been commercialized.



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## i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Figure 5. Hydroformylation of ethylene oxide.

Figure 6. Conversion of acrolein to 1,3-propanediol.Clean 2008, 36 (8), 648 – 651 Preparation of 1,3-Propanediol 651

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## i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com