Bioseparation of 1,3-propanediol
Encyclopedia
Bioseparation of 1,3-propanediol is a biochemical process for production of 1,3-propanediol. 1,3-Propanediol
(hence referred to here as "PDO") is an organic chemical that can be used for various ends. In particular, PDO is polymerized with terephthalic acid
to make poly(trimethylene teraphthalate) (hence referred to here as "PTT") , a polyester
that has end-uses such as clothing, fibers, automobile lining, and carpeting .
or ethylene oxide
. In recent years, however, companies such as DuPont
are investing in the biological production of PDO using renewable feedstocks such as corn
,.
and Tate & Lyle
announced that they would start up a joint venture
to build a facility that produces polymers from renewable feedstock instead of petrochemicals . In particular, their goal was to design a fermentation
system that converts corn sugar into PDO (propanediol manufactured in this way is referred to in the media as "BioPDO"). They argue that using such a bioprocess is more energy efficient than conventional petrochemical
processes (conversion of propylene
into propanediol) because the bioprocess has four advantages over the conventional process: smaller environmental footprint, lower operating costs, smaller capital
investment
, and greater sustainability
due to use of renewable corn
feedstock .
in yeast
. However, DuPont has managed to engineer this glycerol functionality into a strain of Escherichia coli
bacterium (hence referred to here as "E. coli"), thereby allowing industrial-scale fermentation of glycerol in a bioreactor
. After the E. coli bacteria produce sufficient BioPDO product, a method to separate the BioPDO from the cellular broth that comes out of the bioreactor is needed. The separation scheme proposed by DuPont follows the following steps: microfiltration
and ultrafiltration
, ion exchange
, flash evaporation
, and distillation
.
and higher. The feed pressure to the microfiltration membrane is typically 65 psia with a transmembrane pressure drop of 40 psia . The feed pressure to each ultrafiltration membrane is 60 psia . Using these feed pressures and temperatures, typical transmembrane liquid fluxes are 108 LMH (liters per hour per square meter) for the microfiltration membrane, and 26 LMH for the ultrafiltration membrane.
cations in solution with hydrogen ions. The first anionic exchanger replaces the anions in solution with hydroxide ions
. The second cationic and anionic exchangers further reduce ion levels in solution. Note that hydrogen ions spontaneously react with hydroxide ions to form water.
, 1,3-propanediol
, and glycerol
articles for boiling point information), so it is removed as distillate in the first column. The bottoms of the first column is then sent to a second column, where BioPDO is removed as distillate because of its lower boiling point. Both columns operate under low pressure (55 mm Hg in the first column; 20 mm Hg in the second column) to lower the boiling points of the distillate and bottoms streams, thereby using a lower pressure steam than that for atmospheric columns. At this point, the BioPDO stream has 99% purity. If the BioPDO is to be used for polymer production, however, then greater purity is required. To achieve greater purity, the BioPDO distillate of the second column is sent to a hydrogenation
reactor to convert the remaining polymer-coloring impurities into non-coloring chemicals. The effluent of the reactor is then sent to a second set of two distillation columns that operate the same way as the first set of columns. The BioPDO distillate of the fourth distillation column has a purity of 99.97%, which is able to meet polymer- and fiber-grade standards .
awarded the BioPDO research teams the "2007 Heroes of Chemistry" award .
1,3-Propanediol
1,3-Propanediol is the organic compound with the formula CH22. This three-carbon diol is a colorless viscous liquid that is miscible with water.-Products:...
(hence referred to here as "PDO") is an organic chemical that can be used for various ends. In particular, PDO is polymerized with terephthalic acid
Terephthalic acid
Terephthalic acid is the organic compound with formula C6H42. This colourless solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several billion kilograms are produced annually...
to make poly(trimethylene teraphthalate) (hence referred to here as "PTT") , a polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
that has end-uses such as clothing, fibers, automobile lining, and carpeting .
Comparison of Production Methods
Conventionally, PDO is produced from crude oil products such as propylenePropylene
Propene, also known as propylene or methylethylene, is an unsaturated organic compound having the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons, and it is also second in natural abundance.-Properties:At room temperature and...
or ethylene oxide
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...
. In recent years, however, companies such as DuPont
DuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
are investing in the biological production of PDO using renewable feedstocks such as corn
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
,.
History of Bioproduction of 1,3-Propanediol
On May 2004, DuPontDuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
and Tate & Lyle
Tate & Lyle
Tate & Lyle plc is a British-based multinational agribusiness. It is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index as of 20 June 2011...
announced that they would start up a joint venture
Venture
Venture may refer to:* VENTURE NOTC, the Canadian Naval Officer Training Centre based in CFB Esquimalt, British ColumbiaIn automobiles:* Chevrolet Venture, a General Motors Corporation minivan.* VentureOne, a concept car by Venture Vehicles...
to build a facility that produces polymers from renewable feedstock instead of petrochemicals . In particular, their goal was to design a fermentation
Fermentation (biochemistry)
Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...
system that converts corn sugar into PDO (propanediol manufactured in this way is referred to in the media as "BioPDO"). They argue that using such a bioprocess is more energy efficient than conventional petrochemical
Petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....
processes (conversion of propylene
Propylene
Propene, also known as propylene or methylethylene, is an unsaturated organic compound having the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons, and it is also second in natural abundance.-Properties:At room temperature and...
into propanediol) because the bioprocess has four advantages over the conventional process: smaller environmental footprint, lower operating costs, smaller capital
Financial capital
Financial capital can refer to money used by entrepreneurs and businesses to buy what they need to make their products or provide their services or to that sector of the economy based on its operation, i.e. retail, corporate, investment banking, etc....
investment
Investment
Investment has different meanings in finance and economics. Finance investment is putting money into something with the expectation of gain, that upon thorough analysis, has a high degree of security for the principal amount, as well as security of return, within an expected period of time...
, and greater sustainability
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...
due to use of renewable corn
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
feedstock .
Bioseparation Process
In nature, BioPDO is made from the fermentation of glycerolGlycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
in yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
. However, DuPont has managed to engineer this glycerol functionality into a strain of Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
bacterium (hence referred to here as "E. coli"), thereby allowing industrial-scale fermentation of glycerol in a bioreactor
Bioreactor
A bioreactor may refer to any manufactured or engineered device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. This...
. After the E. coli bacteria produce sufficient BioPDO product, a method to separate the BioPDO from the cellular broth that comes out of the bioreactor is needed. The separation scheme proposed by DuPont follows the following steps: microfiltration
Microfiltration
Microfiltration is a membrane technical filtration process which removes contaminants from a fluid by passage through a microporous membrane. A typical microfiltration membrane pore size range is 0.1 to 10 micrometres...
and ultrafiltration
Ultrafiltration
Ultrafiltration is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane...
, ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
, flash evaporation
Flash evaporation
Flash evaporation is the partial vapor that occurs when a saturated liquid stream undergoes a reduction in pressure by passing through a throttling valve or other throttling device. This process is one of the simplest unit operations...
, and distillation
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
.
Filtration
The first of the two filtration steps, microfiltration, is used to remove the cells from the reactor broth. Ceramic filters are used because, although expensive, they can last for five to ten years . High temperatures have been found to increase the flux of liquid across the microfiltration membrane, so a minimum temperature of 165 degrees Fahrenheit is specified . A series of three ultrafiltration membranes are used to filter out proteins with a molecular weight of 5,000 DaltonsDaltons
Daltons Weekly is a newspaper published in England. It is published every Thursday.Established during the late 1860s by Herbert Dalton, Daltons Weekly was initially a single broadsheet listing 'Accommodation for Gentleman' in the then fashionable middle class suburbs around Vauxhall in South London...
and higher. The feed pressure to the microfiltration membrane is typically 65 psia with a transmembrane pressure drop of 40 psia . The feed pressure to each ultrafiltration membrane is 60 psia . Using these feed pressures and temperatures, typical transmembrane liquid fluxes are 108 LMH (liters per hour per square meter) for the microfiltration membrane, and 26 LMH for the ultrafiltration membrane.
Ion Exchange
The next step of the scheme, ion exchange, removes impurities that cause the downstream polymer product to turn yellow . Four ion exchange columns in series are used to remove these impurities, and they are arranged in the following order : 1. Strong acid cationic exchanger, 2. Strong base anionic exchanger, 3. Strong acid cationic exchanger, and 4. Strong base anionic exchanger. The first cationic exchanger replaces the divalentDivalent
In chemistry, a divalent ion or molecule has a valence of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent....
cations in solution with hydrogen ions. The first anionic exchanger replaces the anions in solution with hydroxide ions
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
. The second cationic and anionic exchangers further reduce ion levels in solution. Note that hydrogen ions spontaneously react with hydroxide ions to form water.
Flash Evaporation
After the ion exchange step, excess water is produced from the hydrogen and hydroxide ions, and that can dilute the product to less than 10% concentration by weight. By sending the dilute solution to an evaporation system under vacuum, water will flash out of the solution into low-pressure steam, leaving a propanediol solution with up to 80% propanediol by weight. The low-pressure steam is then compressed to a higher pressure and temperature, and afterward directed to the outer casing of the flash evaporation unit to heat the system.Distillation
The final step of the scheme, distillation, comprises two distillation columns, and optionally four distillation columns. The three main types of chemicals in the fluid at this stage of the separation are water, BioPDO, and impurities such as glycerol, sugars, and proteins. Of the three chemicals water has the lowest boiling point (see the waterWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, 1,3-propanediol
1,3-Propanediol
1,3-Propanediol is the organic compound with the formula CH22. This three-carbon diol is a colorless viscous liquid that is miscible with water.-Products:...
, and glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
articles for boiling point information), so it is removed as distillate in the first column. The bottoms of the first column is then sent to a second column, where BioPDO is removed as distillate because of its lower boiling point. Both columns operate under low pressure (55 mm Hg in the first column; 20 mm Hg in the second column) to lower the boiling points of the distillate and bottoms streams, thereby using a lower pressure steam than that for atmospheric columns. At this point, the BioPDO stream has 99% purity. If the BioPDO is to be used for polymer production, however, then greater purity is required. To achieve greater purity, the BioPDO distillate of the second column is sent to a hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
reactor to convert the remaining polymer-coloring impurities into non-coloring chemicals. The effluent of the reactor is then sent to a second set of two distillation columns that operate the same way as the first set of columns. The BioPDO distillate of the fourth distillation column has a purity of 99.97%, which is able to meet polymer- and fiber-grade standards .
Energy Efficiency Comparison
According to DuPont, the BioPDO process uses 40% less energy than conventional processes ,. DuPont also claims that the bioprocess reduces greenhouse gas emissions by 20% ,, and that the production of one hundred million pounds of BioPDO annually "saves the energy equivalent of fifteen million gallons of gasoline per year" . Because of DuPont and Tate & Lyle's success in developing a renewable BioPDO process, the American Chemical SocietyAmerican Chemical Society
The American Chemical Society is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 at New York University, the ACS currently has more than 161,000 members at all degree-levels and in all fields of chemistry, chemical...
awarded the BioPDO research teams the "2007 Heroes of Chemistry" award .