Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Reexamination Certificate
1999-04-08
2002-04-09
Naff, David M. (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
C435S170000
Reexamination Certificate
active
06368836
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally in the field of separation processes for polymers, and more specifically to purification of polymers derived from biological sources.
Polyhydroxyalkanoates (PHAs) are thermoplastic polyesters which can be produced from bacteria or plants (Williams & Peoples,
CHEMTECH
26:33-44 (1996)). These polymers can be recovered from the biological systems (the biomass) by organic solvent processes, aqueous processes, or a combination of both organic solvent/aqueous processing. Examples of known organic solvent recovery processes are described in U.S. Pat. No. 4,310,684 and No. 4,705,604 to Vanlautem et al. (extraction of PHB from microbes with chlorinated solvents); U.S. Pat. No. 4,968,611 to Traussnig et al. (use of diols, acetalized triols, di- or tricarboxylic acid esters or butyrolactone to extract poly-3-hydroxybutyrate (PHB) and its copolymers from microbes); U.S. Pat. No. 5,213,976 to Blauhut et al. (process for extracting PHB from microbial cells using methylene chloride followed by precipitation of the PHB in water); PCT WO 97/15681; PCT WO 93/11656 (use of acetone to extract poly-3-hydroxyoctanoate polymer from
Pseudomonas oleovorans
); PCT WO 96/06179 and PCT WO 97/15681 (solvent methods for recovering PHAs from transgenic plant crops); and U.S. Pat. No. 5,821,299 to Noda (the use of solvent/partial non-solvent mixtures for extracting PHAs from biomass). Typically, in each of these prior art processes, some of the biomass components are co-extracted with the PHA, which can cause the PHA product to be discolored and/or to have an unpleasant odor.
In some cases, it is useful to extract the PHAs from biomass using aqueous processing techniques, in which the polymer remains in a microparticulate state and the non-PHA biomass is solubilized through mechanical, chemical, and/or enzymatic treatments. The PHA particles then are separated from the solubilized material using centrifugation, filtration, flotation, or other known methods.
EP 0 145 233, for example, discloses aqueous methods for purifying a microbiological 3-hydroxybutyrate polymer wherein the cells are heat-treated at temperatures above 80° C. and then digested with enzymes, surfactants, and/or hydrogen peroxide. U.S. Pat. No. 5,110,980 to Ramsey et al. describes the use of hypochlorite for dissolving non-PHA biomass. U.S. Pat. No. 5,691,174 to Liddell et al. discloses a method for purifying microbial polyesters using the combination of hydrogen peroxide with a chelating agent. The disadvantage of these methods, however, is that the peroxide treatment must be carried out at high temperatures, e.g., 80-180° C., which requires extensive heating and cooling of the product and, in some cases, requires high pressure equipment. Furthermore, the hydrogen peroxide frequently is found to be unstable in the presence of high levels of cellular biomass, which results in the hydrogen peroxide decomposing nonproductively to water and oxygen and generating voluminous foam. Another drawback is that the prolonged high temperatures and hydrogen peroxide also can cause a decrease in the molecular weight of the polymers, and in some cases can promote crystallization of the polymers, which is undesirable for the production of an amorphous polymer latex.
As discussed above, PHAs derived from biomass can have unpleasant odors. PCT WO 94/02541 describes additives to mask odor arising from the PHAs produced, for example, as described in EP 0 145 233 and U.S. Pat. No. 5,691,174 to Liddell et al. It would be advantageous to eliminate the odor associated with PHAs recovered from biomass, particularly if odor removal could be performed during the recovery process, thereby eliminating the need for odor-masking additives in the PHA resin.
It is therefore an object of the present invention to provide improved methods of purifying polyhydroxyalkanoates derived from biomass.
It is a further object of the present invention to enhance extraction of polyhydroxyalkanoates from biomass containing polyhydroxyalkanoates using organic solvent systems, aqueous solvent systems, or combinations thereof
It is another object of the present invention to provide extraction methods which reduce the exposure of the PHA polymers to conditions which can decrease the molecular weight of the polymers.
It is a further object of the present invention to eliminate odors in the process of recovering polyhydroxyalkanoates from biomass.
SUMMARY OF THE INVENTION
Methods are provided for the recovery and purification of polyhydroxyalkanoates (PHAs) from PHA-containing plant and microbial biomass, wherein the methods include contacting the biomass or partially purified PHA with ozone in at least one step of a purification process. Ozone has the beneficial effects of (a) bleaching, (b) deodorization, and (c) solubilization of impurities, facilitating their removal from aqueous polymer suspensions or latexes. The ozone treatment may be used alone or in combination with other treatment, extraction, and separation processes, and is especially suitable for the treatment of PHA-containing latexes, slurries, suspensions, and organic solvent solutions. The ozone contacting step advantageously can be conducted over a wide range of temperatures, including processing temperatures, for example between about 1 and 40° C., which are lower than processing temperatures used in known methods. Treatment with ozone of PHA-containing biomass, partially purified PHA, or solvent-extracted PHA yields an enhanced level of polymer purity suitable for coating and other applications. The ozone treatment also has the added advantage that the resulting PHA polymer or polymer latex is essentially odor-free.
DETAILED DESCRIPTION OF THE INVENTION
Improved methods for the recovery of polyhydroxyalkanoates (PHAs) from biomass including PHAs have been developed. The methods include treating the biomass or partially purified PHA with ozone, in at least one step of a purification process. Ozone treatment can be beneficially applied to PHAs from any source, including PHAs extracted using organic solvents (e.g., by treating an organic solvent solution of the PHAs), in order to further purify and/or deodorize the PHAs.
Polyhydroxyalkanoates
PHAs can be produced in a number of biological systems including bacteria and genetically engineered plant crops. In bacterial systems, the PHAs are accumulated intracellularly as granular inclusion bodies. PHA also can be produced in genetically engineered plant crops. Methods for constructing such crops are described, for example, in U.S. Pat. Nos. 5,245,023 and 5,250,430 to Peoples and Sinskey; U.S. Pat. No. 5,502,273 to Bright et al.; U.S. Pat. No. 5,534,432 to Peoples and Sinskey; U.S. Pat. No. 5,602,321 to John; U.S. Pat. No. 5,610,041 to Somerville et al.; PCT WO 91/00917; PCT WO 92/19747; PCT WO 93/02187; PCT WO 93/02194; PCT WO 94/12014, Poirier et al.,
Science
256:520-23 (1992); van der Leij & Witholt,
Can. J. Microbiol.
41(supp.):222-38 (1995); Nawrath & Poirier,
The International Symposium on Bacterial Polyhydroxyalkanoates
, (Eiggink et al., eds.) Davos Switzerland (Aug. 18-23, 1996); and Williams & Peoples,
CHEMTECH
26: 38-44 (1996). Methods for recovering PHAs from plant biomass are described, for example in PCT WO 97/15681, PCT WO 97/07239, and PCT WO 97/07229.
The PHA-containing biomass derived from bacteria or plants which is to be used in the methods described herein typically is in the form of a polymer slurry, latex, or solution. The polymer slurry, latex, or solution preferably has a solids content between about 1 and 90% by weight, and more preferably between about 5 and 50% by weight.
The ozone purification methods described herein similarly are useful for purification of other PHAs, regardless of source organism or comonomer composition. Representative PHAs include poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV, marketed as BIOPOL™ by Monsanto), poly-3-hydroxybutyrate-co-4-hydroxybutyratepoly-3-hydroxypropionate, poly-3-hydroxybutyrate-co-3-hydroxypropionate,
Brennan Elaine M.
Horowitz Daniel M.
Holland & Knight LLP
Meller Mike
Metabolix Inc.
Naff David M.
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