Patent Application
20060046217
The present invention relates to methods and apparatus for treating the wastes produced in a polyester-manufacturing plant; and in particular, the present invention relates to methods and apparatus for treating the wastes from a PTA or PET plant in which at least one heat source utilizes fuel as a combustion source.
Polyester is a widely used polymeric resin used in a number of packaging and fiber based applications. Poly(ethylene terephthalate) (“PET”) or a modified PET is the polymer of choice for making beverage and food containers such as plastic bottles and jars used for carbonated beverages, water, juices, foods, detergents, cosmetics, and other products. These containers are manufactured by a process that typically comprises drying the PET resin, injection molding a preform and, finally, stretch blow molding the finished bottle. Despite the stringent matrix of properties required for such uses, particularly for food packaging, PET has become a commodity polymer. PET is also used in a number of film and fiber applications. Commercial production of PET is energy intensive, and therefore even relatively small improvements in energy consumption are of considerable commercial value.
In the typical polyester forming polycondensation reaction, a diol such as ethylene glycol is reacted with a dicarboxylic acid or a dicarboxylic acid ester. In the production of PET, terephthalic acid is usually slurried in ethylene glycol and heated to produce a mixture of oligomers of a low degree of polymerization. The reaction can be accelerated by the addition of a suitable reaction catalyst. Since the product of these condensation reaction tends to be reversible and in order to increase the molecular weight of the polyesters, this reaction is often carried out in a multi-chamber polycondensation reaction system having several reaction chambers operating in series. Typically, the diol and the dicarboxylic acid component are introduced in the first reactor at a relatively high pressure. After polymerizing at an elevated temperature the resulting polymer is then transferred to the second reaction chamber which is operated at a lower pressure than the first chamber. The polymer continues to grow in this second chamber with volatile compounds being removed. This process is repeated successively for each reactor, each of which are operated at lower and lower pressures. The result of this step wise condensation is the formation of polyester with high molecular weight and higher inherent viscosity. During this polycondensation process, various additives such as colorants and UV inhibitors may be also added. Polycondensation occurs at relatively high temperature, generally in the range of 280-300° C., under vacuum with water and ethylene glycol produced by the condensation being removed. The heat for the polycondensation reactions is typically supplied by one or more furnaces, such as heat transfer medium furnace (“HTM furnace”). Moreover, the during the polycondensation process, a number of chemical waste byproducts are formed that need to be appropriately treated in order to meet government regulations. Among the waste products needing treatment in the typical PET process are acetic acid, various acid aldehydes, and unreacted ethylene glycol.
In the typical process for making purified terephthalic acid (“PTA”), crude terephthalic acid is made by catalytic oxidation of para-xylene followed by purification of the crude acid. Crude terephthalic acid suitable for making polyesters is typically produced by the oxidation of para-xylene in the presence of catalyst and acetic acid solvent. Oxygen in the air functions as the oxidant and converts the para-xylene in TPA. The reaction mixture typically includes other components in addition to para-xylene. Such additional components include a solvent, a catalyst system, and a promoter. Suitable solvents include monocarboxylic acids such as acetic acid. Catalyst systems that may be used often include a heavy metal or mixture of heavy metals such as cobalt and manganese in the form of acetate salts. Bromine in the form of bromic acid is a commonly used promoter. For example, U.S. Pat. No. 6,137,001 discloses a liquid-phase process in which a benzene derivative or naphthalene derivative is oxidized with oxygen to form a carboxylic acid. The reaction mixture in this process typically includes a reaction catalyst comprising a heavy metal component and a bromine source. U.S. Pat. No. 5,696,285 discloses a process in which the oxidation of para-xylene is carried out using pure or nearly pure oxygen (great to or equal than 75 vol. % oxygen). This process also improves reaction efficiency by rapid dilution of the hydrocarbon feed stock. In a somewhat similar process, U.S. Pat. No. 5,420,316 discloses a process with very low amounts of aldehyde and ketone by-products in which a carboxylic acid is made by the ozonization of an organic compound having at least one olefinic bond followed by further oxidation with molecular oxygen. After manufacturing of the crude terephthalic acid, purification by hydrogenation or other methods and crystallization can be done in order to obtain suitable material for most PET applications. The main impurity (4-carboxybenzaldehyde) is transformed to water-soluble para-toluic acid during hydrogenation. It will also be appreciated that the production of TPA and PTA both produce a number of byproducts that need consideration for proper treatment and disposal.
Accordingly, there is a need for improved methods and apparatus for treating the waste byproducts formed in the various polyester-manufacturing processes in an energy efficient manner.
The present invention overcomes one or more problems of the prior art by providing in one embodiment a method of treating waste in a polyester-manufacturing plant. The method of the invention comprises combining the fuel with a first waste byproduct stream to form a combined fuel and first waste byproduct stream mixture. Next, the combined fuel and first waste byproduct mixture is introduced into the first heat source and combusted. The present invention also provides certain useful variations of this method in which one or more of the following steps are performed: a second waste byproduct stream is introduced and treated in a regenerative thermal oxidizer, a third waste byproduct stream is introduced and treated in a waste water treatment plant, or a fourth waste byproduct stream is introduced and treated in a fluid bed incinerator.
In another embodiment of the invention, a second method of treating waste in a polyester-manufacturing plant is provided. The method of this embodiment comprises combining the fuel with a first waste byproduct stream to form a combined fuel and first waste byproduct stream mixture. Next, the combined fuel and first waste byproduct mixture is introduced into the first heat source and combusted. The method further comprises introducing a second waste byproduct stream into a regenerative thermal oxidizer and introducing a third waste byproduct stream into a fluid bed incinerator.
In yet another embodiment of the invention, an apparatus for treating waste from a polyester-manufacturing plant that utilizes the methods of the invention is provided. The apparatus of the invention comprises a heat source that is used to both provide heat to the one or more polymerization reactors and to combust the waste and a first conduit that transfers a first waste stream from the one or more polymerization reactors to the heat source. In certain variations of the apparatus of the invention, the apparatus further includes one or more of the following components: a regenerative thermal oxidizer; a waste water treatment plant; and a fluid bed incinerator.
Reference will now be made in detail to presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventor.
In an embodiment of the present invention, a method of treating waste in a polyester-manufacturing plant is provided. With reference to
PET manufacturing component 14 produces waste byproduct streams 28, 30. In PET manufacturing component 14, at least one heat source 32 is used to provide heat for the condensation reactions between the glycol and diacid that occur in at least one condensation reactor 34. Ethylene glycol/water separation unit 36 removal waste from condensation reactor 34. Waste byproduct stream 28 includes the aqueous wastes from separation unit 36. Similarly, waste byproduct stream 30 includes waste from condensation reactor 34. As will be shown below, the method of the present invention advantageously utilizes a heat from heat source 32 to combust at least one waste byproduct stream of waste byproduct streams 16, 18, 20, 22, 28, 30. The typical polyester-manufacturing process produces a number of different waste byproducts that may be present in the first waste byproduct stream. One type of waste byproduct stream comprises an aqueous waste stream which includes one or more combustible organic compounds. The type of organic compounds present will depend on the specific polyester process. For example, the manufacturing of PTA or PET typically produce ethylene glycol, acetic acid, acid aldehydes, and combinations thereof. In addition to the aqueous waste streams, the first waste byproduct stream may also include solid organic components. These solid organic components are also usually sufficiently combustible to be burned in the at least one heat source.
Still referring to
In a first variation of the invention, the first waste byproduct stream will combine one or more of waste byproduct streams 16, 18, 20, 22, 28, 30. Preferably, the first waste byproduct stream combines all of waste byproducts 16, 18, 20, 22, 28, 30.
In a second variation of the present embodiment, the method of the present invention further comprises introducing a second waste byproduct stream into a regenerative thermal oxidizer (“RTO”). RTOs are particularly suitable for removing (oxidizing) byproduct streams that include a significant amount of vapor-phase compounds. Often, such byproduct streams will include an inert gas and one or more volatile organic compounds. Examples of volatile organic compounds that are present in the waste streams of PTA and PET plants are acetic acid, methyl acetate, and combinations thereof. The second waste product stream may also be a liquid waste stream which is vaporized before the second waste byproduct stream is introduced into the regenerative thermal oxidizer. In accordance with this variation, the second waste byproduct stream will include the combination of one or more of waste byproduct streams 16, 18, 22, 28, 30. For example, the first waste byproduct stream that is fed into heat source 32 includes wastes stream 20 while the second waste byproduct stream includes waste streams 16, 18, 22, 28, 30 which are fed to RTO 50 via conduit 52. Alternatively, for example, the first waste byproduct stream comprises waste byproduct streams 18, 22, 20, 28, 30 and the second waste byproduct stream includes waste stream 16.
In a third variation of the present embodiment, the method of the invention further comprises introducing a third waste byproduct stream into a waste water treatment plant 60 via conduit 62. This second variation is performed either separately from or in combination with the second variation set forth above. In accordance with this variation, the third waste byproduct stream will include the combination of one or more of waste streams 18, 22, 28, 30. For example, waste stream 20 is fed to heat source 32, waste stream 16 is fed into RTO 50 via conduit 52, and waste streams 18, 22, 28, 30 are fed to one of heat source 32, RTO 50, or water treatment plant 60.
In a fourth variation of the present embodiment, the method of the invention further comprises introducing a fourth waste byproduct stream that is fed into a fluid bed incinerator 70 via conduit 72. Again, this variation is performed separately from or in combination with the first, second, and third variations. The fourth waste byproduct stream comprises solid organic components, the solid organic components being sufficiently combustible to be burned in the at least one heat source. Moreover, the fourth waste byproduct stream may be the take off gas from a distillation tower from the various purification stages in a PET or PTA process. Furthermore, this fourth waste byproduct stream may contain an aqueous waste stream which includes a combustible organic compound. As set forth above, examples of combustible organic compounds that are present in a PET or PTA plant are ethylene glycol, acetic acid, acid aldehydes, and combinations thereof. In accordance with this variation, the fourth waste byproduct stream will comprise waste stream 20. For example, waste stream 16 is fed into RTO 50, waste stream 20 is feed to fluid bed incinerator 70, and waste streams 18, 22, 28, 30 are fed to heat source 32, RTO 50, or water treatment plant 60.
In another embodiment of the invention, a second method of treating waste in a polyester-manufacturing plant is provided. As set forth above, polyester-manufacturing plants typically produce one or more waste byproduct streams. Moreover, such plants will typically have at least one heat source utilizing fuel as a combustion source. The method of this embodiment comprises combining the fuel with a first waste byproduct stream to form a combined fuel and first waste byproduct stream mixture. Next, the combined fuel and first waste byproduct mixture is introduced into heat source 32 and combusted. The method further comprises introducing a second waste byproduct stream into RTO 50 via conduit 52 and introducing a third waste byproduct stream into a fluid bed incinerator 70 via conduit 72. The selection of the heat source is the same as that set forth above for the first embodiment. Moreover, the selection of the compositions of the first waste byproduct stream, the second waste by byproduct stream, and the third waste byproduct streams are also the same as those set forth above. For example waste stream 16 is fed to RTO 50, waste stream 20 is feed to fluid bed incinerator 70, and waste streams 18, 22, 28, 30 are fed to heat source 32 or RTO 50.
In yet another embodiment of the invention, an apparatus for treating waste from a polyester-manufacturing plant is provided. With reference to
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
This application claims priority to U.S. Provisional Application Ser. No. 60/606,857, filed Sep. 2, 2004, the disclosure of which is incorporated herein by this reference to the extent it does not contradict statements made herein.
| Number | Date | Country | |
|---|---|---|---|
| 60606857 | Sep 2004 | US |
