Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2002-01-28
2003-12-23
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S355000, C528S359000, C525S415000, C210S321830, C210S336000, C210S494100, C210S500290, C210S600000, C210S634000
Reexamination Certificate
active
06667385
ABSTRACT:
FIELD OF INVENTION
This invention relates to producing dilactic acids or dimers more efficiently by specifically producing aminium lactate salts from lactic acid fermentation broths, e.g. cheese whey. The salts are then thermally dissociated in an inert gas stream at low temperatures in the presence of a cyclization catalyst to form dilactic acids (dimers or diesters). The resulting dilactic acids or diesters may then be used to produce biodegradable polymers such as polylactic acid, and cosmetics and pharmaceuticals.
BACKGROUND OF THE INVENTION
Lactic acid is currently processed into polylactic acid which can be used in many biodegradable polymer applications. Polylactic acid is a multi-functional thermoplastic which can be processed into staple fibers (e.g. carpet fibers), spinning fibers in woven applications to replace (or in blends with) cotton, wool, and polyesters, extruded films for wrappings, injection and thermo-molded products such as polyethylene, propylene and styrene foam products, and thermo-formed plastics such as eating utensils, coatings, etc. Polylactic acid is completely recyclable and is the only major polymer which slowly yet totally biodegrades during composting.
The use of polylactic acid as a mass polymer, until now, has been limited due to the high costs associated with its production, primarily energy costs, making it uncompetitive with similar non-biodegradable petroleum-based polymers and polyesters. There are two major routes to producing polylactic acid directly from the lactic acid monomer. The first route involves removal of water of condensation by using a solvent under high vacuum and temperature. This approach is currently used, for example, by Mitsui Toatsu Chemicals to produce a low to intermediate molecular weight polymer. In a second alternative route, which is considered to be the classical approach to producing polylactic acid, water is removed under milder conditions directly from lactic acid, without solvent, to produce a cyclic (ring closing) intermediate dimer referred to as “dilactic acid.” This dimer is then purified under vacuum distillation and then “ring-opening” polymerization is accomplished using heat, without solvent, to produce polylactic acid. This “ring-opening” method of producing polylactic acid is currently used worldwide and is the subject of many patents and other literature. This process, however, suffers from long reaction times and high temperatures and the formation of a number of side reactions and by-products. It usually results in a low (50%-55%) chemical yield for the polylactic acid polymer.
Recently (1992) a third route of producing polylactic acid has been patented and is now being commercially practiced by Cargill, see U.S. Pat. No. 5,142,023 of Aug. 25, 1992. This process relies on the initial production of an impure polylactic acid polymer as a feedstock in the production of polylactic acid. This impure polymer must then be depolymerized using additional energy steps in order to achieve a more pure polylactic acid polymer. These steps are also energy expensive and therefore result in a high production cost associated with producing polylactic acid.
Yet another process of producing dilactic acids or dimers and subsequently producing polylactic acid avoids such energy intensive steps as described in the Cargill process of U.S. Pat. No. 5,142,023. This particular method uses an aminium lactate salt (crystal) instead of an impure polylactic acid as a starting material in the production of dilactic acids or dimers. It is described in Kamm et al, Formation of Aminium Lactates in Lactic Acid Fermentation, Acta BioTechnol. 17, (1997) 1, 3-18. It describes the use of organic amines (technically called heterocyclic amines, e.g. Piperazine) within the lactic acid fermentation broth to produce aminium lactate (salts). Though aminium lactate salts are referred to specifically, other salts such as ammonium lactate salts may also be produced and used in such a process. Aminium lactate salts have lower melt points of from 80° C.-150° C. and can dissociate in the presence of catalysts (acetonitrile, dioxan, ethylene glycol monoethylether, dimethyl sulphoxid-d6) and low heat to form dilactic acids or dimers. This process completely avoids the need to first produce impure polylactic acid polymers as the feedstock in order to produce such dilactic acids. In this process, however, ultrafiltration and electrocoagulation are used to concentrate and extract the lactic acids and lactate salts. The fallacy of this process, for large scale processing, lies in the use of the organic amines within the fermentation broth and the use of ultrafiltration membranes that require high-energy pressures to remove and separate out the cell mass from the lactic acid/aminium salt. Once the lactic acid is separated from the cell mass, electrocoagulation is then used to bring about the separation or breakdown of the lactic acid from the amine salt in order to concentrate it to a minimum of a 45-85% pure lactic acid. The purer lactic acid is then re-contacted with the organic amine once again, e.g. Piperazine, to form the Piperazine salt once again. In this method the ultrafiltration membranes requires high-energy pressure during operation and often becomes fouled and plugged. It is therefore not suitable for commercial scale processing. In addition, the electrocoagulation step is also not scaleable for commercial use. The Kamm process, as described, requires unnecessary steps of forming the salt from the lactic acid in order to achieve a higher concentration of the lactic acid (45-85%), which then must be re-crystallized to form the salt. This then must be destructured to form the dilactic acid or dimmer. This process results in the production of impure dilactic acids and aminium lactate salts (as an interim step), and the impurities in the lactic acid produced during fermentation within this process has limited the polymer length achievable, mainly due to such lactic acid refining techniques practiced and described in the Kamm process.
It has now been discovered that the aminium lactate salts of the Kamm process can, under certain conditions, become a low cost and low energy step in the production of polylactic acid. The present invention, unlike the Kamm process, does not rely on the concentration of lactic acid to 45-85% purity and thus represents a major energy saving step within the present invention.
Accordingly, as can be seen from the above description, a new and more efficient method is needed for the production of dilactic acids (dimers) that produces interim aminium lactates (salts) more efficiently than that disclosed in the so-called “Kamm process”. Such aminium lactates (crystals) could therefore become a new, low-cost feedstock for the production of dilactic acids or dimers. These salts could then be processed more efficiently and with less energy cost to produce such dilactics (acids) or dimer esters and subsequent polylactic acid polymers more economically. It is a primary object of this invention to fulfill this need.
Besides fulfilling this need for a new route to producing dilactic acids (dimers) and subsequent polylactic acid polymers as described, several additional objects and advantages of the present invention are:
(a) to provide a less capital and energy expensive new route to producing dilactic acids (dimers) and subsequent polylactic acid polymers that relies on producing such dilactic acids (dimers) directly from aminium lactate salt (crystal) rather than impure polylactic acid through ring-closing catalysis. Though aminium lactate salts are specifically discussed within the present invention, the present invention is not limited to the use of such specific salts but may include other earth and alkaline salts which may also be produced and used accordingly. Therefore, where mentioned, aminium lactate salts refers also to such other salts as well;
(b) to provide a less expensive and more efficient method to produce aminium lactate salts using methods that are readily commercially scaleable;
(c) to provide a less ex
Massie Cecil T.
Pierce Sammy Mayfield
Energenetics International, Inc.
Hampton-Hightower P.
McKee Voorhees & Sease, P.L.C.
LandOfFree
Method of producing aminium lactate salt as a feedstock for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing aminium lactate salt as a feedstock for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing aminium lactate salt as a feedstock for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3168187