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* cited by examiner
1
SLOPED TUBULAR REACTOR WITH
SPACED SEQUENTIAL TRAYS
BACKGROUND OF THE INVENTION
5
1. Field of the Invention
This invention relates to reactors for processing liquidcontaining reaction mediums. In another aspect, the invention concerns polycondensation reactors used for melt-phase production of polyesters. 10
2. Description of the Prior Art
Melt-phase polymerization can be used to produce a variety of polyesters, such as, for example, polyethylene terephthalate (PET). PET is widely used in beverage, food, and other containers, as well as in synthetic fibers and resins. 15 Advances in process technology coupled with increased demand have led to an increasingly competitive market for the production and sale of PET. Therefore, a low-cost, highefficiency process for producing PET is desirable.
Generally, melt-phase polyester production facilities, 20 including those used to make PET, employ an esterification stage and a polycondensation stage. In the esterification stage, polymer raw materials (i.e., reactants) are converted to polyester monomers and/or oligomers. In the polycondensation stage, polyester monomers exiting the esterification stage 25 are converted into a polymer product having the desired final average chain length.
In many conventional melt-phase polyester production facilities, esterification and polycondensation are carried out in one or more mechanically agitated reactors, such as, for 30 example, continuous stirred tank reactors (CSTRs). However, CSTRs and other mechanically agitated reactors have a number of drawbacks that can result in increased capital, operating, and/or maintenance costs for the overall polyester production facility. For example, the mechanical agitators and 35 various control equipment typically associated with CSTRs are complex, expensive, and can require extensive maintenance.
Thus, a need exists for a high efficiency polyester process that minimizes capital, operating, and maintenance costs 40 while maintaining or enhancing product quality.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, there is pro- 45 vided a process comprising subjecting a reaction medium to a chemical reaction in a reactor comprising a downwardly sloped elongated tubular member and a plurality of spaced apart trays disposed in the tubular member. The tubular member is elongated along a central axis of elongation that is 50 oriented at a downward angle in the range of from about 5 to about 75 degrees below horizontal. Each of the trays presents an upwardly facing surface across which at least a portion of the reaction medium flows as the reaction medium flows through the reactor. 55
In another embodiment of the present invention, there is provided a process for making polyethylene terephthalate (PET), the process comprising: (a) introducing a polycondensation feed into a polycondensation reactor, wherein the polycondensation feed forms a predominately liquid reaction 60 medium in the reactor, wherein the polycondensation feed comprises PET having an average chain length in the range of from about 5 to about 100; (b) subjecting the reaction medium to polycondensation in the reactor, wherein the reactor comprises a substantially straight downwardly sloped pipe and at 65 least four spaced apart trays disposed at different elevations in the pipe, wherein the pipe is sloped downwardly at an angle in
2
the range of from about 10 to about 60 degrees below horizontal, wherein the reaction medium flows primarily by gravity through the reactor, wherein each of the trays presents an upwardly facing surface across which at least a portion of the reaction medium flows as the reaction medium flows through the reactor, wherein the upwardly facing surface is sloped less than about 10 degrees from horizontal, wherein each of the trays defines a plurality of apertures through which at least a portion of the reaction medium passes as the reaction medium flows through the reactor; and (c) recovering a predominately liquid polycondensation product from the reactor, wherein the polycondensation product comprises PET having an average chain length that is at least about 10 greater than the average chain length of the PET in the polycondensation feed.
In still another embodiment of the present invention, there is provided a reactor comprising a downwardly sloped tubular member and a plurality of spaced apart trays disposed at different elevations in the tubular member. The tubular member is elongated along a central axis of elongation that is oriented at a downward angle in the range of from about 5 to about 75 degrees below horizontal. Each of the trays presents an upwardly facing surface that is sloped less than about 25 degrees from horizontal.
BRIEF DESCRIPTION OF THE DRAWINGS
Certain embodiments of the present invention are described in detail below with reference to the enclosed figures, wherein:
FIG. 1 is a cut-away top view a sloped tubular reactor configured in accordance with one embodiment of the present invention and suitable for use as a polycondensation reactor in a melt-phase polyester production facility; and
FIG. 2 is a partial sectional side view of the sloped tubular reactor taken along line 2-2 in FIG. 1, particularly illustrating the manner in which a reaction medium passes over and through the series of spaced apart internal trays as it progresses downwardly through the reactor.
DETAILED DESCRIPTION
FIGS. 1 and 2 illustrate an exemplary sloped tubular reactor configured in accordance with one embodiment of the present invention. The configuration and operation of the reactor depicted in FIGS. 1 and 2 are described in detail below. Although certain portions of the following description relate primarily to reactors employed in a melt-phase polyester production process, reactors configured in accordance with embodiments of the present invention may find application in a wide variety of chemical processes. For example, reactors configured in accordance with certain embodiments of the present invention may be advantageously employed in any process where chemical reactions take place in the liquid phase of a reaction medium and a vapor is produced as a result of the chemical reaction. Further, reactors configured in accordance with certain embodiments of the present invention may be advantageously employed in chemical processes that are enhanced by increasing the surface area of the reaction medium.
Referring now to FIGS. 1 and 2, one embodiment of a sloped tubular reactor 10 is illustrated as generally comprising a vessel shell 12 and a series of spaced apart internal trays 14a-e disposed in shell 12. Vessel shell 12 comprises a downwardly sloping tubular member 16, an upper end cap 18 coupled to the top of tubular member 16, and a lower end cap 20 coupled to the bottom of tubular member 16. Vessel shell 12 defines a feed inlet 22 near the top of reactor 10, a liquid
3
product outlet 24 near the bottom of reactor 10, and a vapor outlet 26 near the top of reactor 10.
Tubular member 16 is elongated along a downwardly sloping central axis of elongation. In certain embodiments of the present invention, the central axis of elongation of tubular 5 member 16 is sloped at an angle in the range of from about 5 to about 75 degrees below horizontal, about 10 to about 60 degrees below horizontal, or 12 to 45 degrees below horizontal. In the embodiment illustrated in FIGS. 1 and 2, tubular member 16 is a substantially straight, substantially cylindri- 10 cal, elongated pipe. However, in certain embodiments, tubular member 16 can be an elongated tubular member having a variety of cross-sectional configurations (e.g., rectangular, square, or oval).
Vessel shell 12 and/ortubularmemberl6 canhaveamaxi- 15 mum internal length (L) that is greater than its maximum internal diameter (D). In certain embodiments, shell 12 and/ or tubular member 16 has a length-to-diameter (L:D) ratio in the range of from about 2:1 to about 50:1, about 4:1 to about 30:1, or 8:1 to 20:1. In certain embodiments, L is in the range 20 of from about 10 to about 200 feet, about 20 to about 150 feet, or 30 to 80 feet, and D is in the range of from about 1 to about 20 feet, about 2 to about 10 feet, or 3 to 5 feet.
Internal trays 14a-e present respective upwardly facing surfaces 28a-e across which a liquid can flow, as described in 25 detail below. In the embodiment illustrated in FIGS. 1 and 2, upwardly facing surfaces 28a-e of trays 14a-e are substantially planar and substantially horizontal. Alternatively, upwardly facing surfaces can extend at any angle that is within about 25 degrees of horizontal, within about 10 30 degrees of horizontal, or within 3 degrees of horizontal.
Trays 14a-e each define a plurality of downwardly extending apertures 30a-e through which a liquid can flow. Alternatively, at least one or a majority of trays can define a plurality of downwardly extending apertures through which a liquid 35 can flow. The number, size, and shape of apertures 30a-e can vary greatly depending, for example, on the production capacity of reactor 10 and the viscosity of the medium processed therein. In certain embodiments of the present invention, each tray 14a-e defines in the range of from about 5 to 40 about 200,000 apertures, about 200 to about 50000 apertures, or 1000 to 10000 apertures. In certain embodiments of the present invention, the average number of holes per unit area is in the range from about 0.5 to about 50 holes per square inch, about 1 to about 20 holes per square inch, or 3 to 10 holes per 45 square inch. In certain embodiments of the present invention, the percent open of each tray 14a-e is in the range of from about 5 to about 80 percent, about 10 to about 60 percent, or 15 to 50 percent.
Trays 14a-e each present respective terminal edges 32a-e 50 that are spaced from the inside wall of tubular member 16. Alternatively, at least one or a majority of trays can present terminal edges that are spaced from the inside wall of tubular member 16. Flow passageways 34a-e are defined by the gaps between the inside wall of tubular member 16 and terminal 55 edges 32a-e of trays 14a-e, respectively. One or more of trays 14a-e can, optionally, be equipped with an upwardly extending weir located proximate terminal edges 32a-e. Trays 14a-e also present respective coupling edges 36a-e that are sealingly coupled to the inside wall of tubular member 16 by any 60 suitable method (e.g., welding).
In the embodiment illustrated in FIGS. 1 and 2, each tray 14a-e is a substantially flat, substantially horizontal plate that is sealingly coupled to the inside wall of downwardly sloped tubular member 16 at its respective coupling edge 36a-e. 65 Thus, in the embodiment depicted in FIGS. 1 and 2, the shape of each tray 14a-e can generally be that of a truncated oval,
4
with coupling edges 36a-e defining the curved portion of the oval and terminal edges 32a-e defining the truncated portion of the oval.
Although FIGS. 1 and 2, show trays 14a-e as being supported in tubular member 16 via the rigid attachment of coupling edges 36a-e to the inside wall of tubularmember 16, it should be noted that a variety of mechanisms for supporting trays 14a-e in tubular member 16 can be employed. For example, trays 14a-e can be supported in tubular members 16 using support members that support trays 14a-e from the bottom of tubular member 16 and/or suspend trays 14a-e from the top of tubular member 16. However, if the sides of trays 14a-e are spaced from the inside wall of tubular member, tray sidewalls may be required to keep reaction medium from prematurely flowing around the sides of trays \4a-e.
In the embodiment illustrated in FIGS. 1 and 2, each tray \4a-e has a substantially identical configuration. However, in certain embodiments of the present invention, the orientation and/or configuration of trays \4a-e can be different in order to optimize the configuration of reactor 10 to match the application for with reactor 10 is employed. For example, when reactor 10 is used to process a reaction medium whose viscosity increases as it flows downwardly through reactor 10, it may be desirable for trays \4a-e to have an increasing downward slope to facilitate the flow of the higher viscosity reaction medium across the lower trays. Further, in such an application, it may be desired for the size of apertures 30a-e, number of apertures 30a-e, or percent open of trays \4a-e to increase downwardly to facilitate flow of the higher viscosity reaction medium through the lower trays.
The total number of internal trays 14 employed in reactor 10 can vary greatly depending on a variety of factors such as, for example, the length of tubular member 16, the slope of tubular member 16, and the viscosity of the medium processed in reactor 10. In certain embodiments of the present invention, the number of trays 14 employed in reactor 10 can be at least 4, at least 6, or in the range of from about 2 to about 50, about 4 to about 25, or 6 to 15.
In operation, a predominately liquid feed is introduced into reactor 10 via feed inlet 22. In the upper portion of reactor 10, the feed forms a predominately liquid reaction medium 38 that flows downwardly on the bottom of tubular member 16 until it reaches uppermost internal tray 14a.
Oncereactionmedium38 is on uppermost tray 14a, it flows across the upwardly facing surface 28a. When tray 14a is configured with apertures 30a, a portion of reaction medium 38 passes downwardly through apertures 30a and onto the bottom of tubular member 16 and/ or onto the upwardly facing surface 2%b of the next lower tray \4b. In accordance with one embodiment of the present invention, the portion of reaction medium 38 that passes through apertures 30a forms strands that extend below tray 14a. These strands can greatly increase the surface area of reaction medium 38 when compared to the flow of reaction medium 38 through a non-trayed tubular member or across a tray without apertures. In one embodiment, reaction medium 38 flows primarily by gravity through reactor 10.
The portion of reaction medium 38 that does not pass through apertures 30a flows over terminal edge 32a of tray 14a, passes downwardly through flow passageway 34a, and onto the next lower tray \4b. When tray 14a is equipped with a weir, the portion of the reaction medium flowing over terminal edge 32a must pass over, around, through openings in, and/or under the weir prior to entering flow passageway 34a. Flow of reaction medium 38 over and through the remaining trays \4b-e can occur in generally the same manner as described above for uppermost tray 14a.
5
As reaction medium 38 flows through reactor 10, a chemical reaction takes place within reaction medium 38. A vapor 40 can be formed in reactor 10. Vapor 40 can comprise one or more byproducts of the chemical reaction carried out in reactor 10 and/or one or more volatile compounds present in the 5 feed to reactor 10 that vaporize therein. Vapor 40 is disengaged from and flows generally upwardly and over reaction medium 38 as reaction medium 38 progresses downwardly through reactor 10. In particular, vapor 40 generated in the lower portion of reactor 10 can pass upwardly through flow 10 passageways 34a-e countercurrent to reaction medium 38 passing downwardly through flow passageways 34a-e. Vapor 40 exits reactor 10 via vapor outlet 26, while reaction medium 38 exits reactor 10 as a predominately liquid product via liquid product outlet 24. Alternatively, vapor 40 can flow 15 generally downwardly with reaction medium 38 and exit a vapor outlet (not shown) located near the lower end of reactor 10.
As mentioned above, weirs can be employed on one or more trays 14a-e to help maintain the desired depth of reac- 20 tion medium 38 on trays 14a-e. In one embodiment of the present invention, the maximum depth of reaction medium 38 on each tray 14a-e is less than about 0.8D, less than about 0.4D, or less than 0.25D, where D is the maximum internal diameter of tubular member 16. 25
Sloped tubular reactors configured in accordance with certain embodiments of the present invention require little or no mechanical agitation of the reaction medium processed therein. Although the reaction medium processed in the sloped tubular reactor may be somewhat agitated by virtue of 30 flowing through the reactor and falling from one reactor level to another, this flow agitation and gravitational agitation is not mechanical agitation. In one embodiment of the present invention, less than about 50 percent, less than about 25 percent, less than about 10 percent, less than about 5 percent, 35 or 0 percent of the total agitation of the reaction medium processed in the sloped tubular reactor is provided by mechanical agitation. Thus, reactors configured in accordance with certain embodiments of the present invention can operate without any mechanical mixing devices. This is in 40 direct contrast to conventional continuous stirred tank reactors (CSTRs) which employ mechanical agitation almost exclusively.
As indicated above, sloped tubular reactors configured in accordance with embodiments of the present invention reac- 45 tors can be used in a variety of chemical processes. In one embodiment, a sloped tubular reactor configured in accordance with the present invention is employed in a melt-phase polyester production facility capable of producing any of a variety of polyesters from a variety of starting materials. 50 Examples of melt-phase polyesters that can be produced in accordance with embodiments of the present invention include, but are not limited to, polyethylene terephthalate (PET), which includes homopolymers and copolymers of PET; fully aromatic or liquid crystalline polyesters; biode- 55 gradable polyesters, such as those comprising butanediol, terephthalic acid and adipic acid residues; poly(cyclohexanedimethylene terephthalate) homopolymer and copolymers; and homopolymers and copolymers of 1,4-cyclohexanedimethanol (CHDM) and cyclohexane dicarboxylic acid or 60 dimethyl cyclohexanedicarboxylate. When a PET copolymer is produced, such copolymer can comprise at least 90, at least 91, at least 92, at least 93, at least 94, at least 95, at least 96, at least 97, at least 98 mole percent of ethylene terephthalate repeat units and up to 10, up to 9, up to 8, up to 7, up to 6, up 65 to 5, up to 4, up to 3, or up to 2 mole percent of added comonomer repeat units. Generally, the comonomer repeat
6
units can be derived from one or more comonomers selected from the group consisting of isophthalic acid, 2,6-naphthaline-dicarboxylic acid, CHDM, and diethylene glycol.
In general, a polyester production process according to certain embodiments of the present invention can comprise two main stages—an esterification stage and a polycondensation stage. In the esterification stage, the polyester starting materials, which can comprise at least one alcohol and at least one acid, are subjected to esterification to thereby produce polyester monomers and/or oligomers. In the polycondensation stage, the polyester monomers and/or oligomers from the esterification stage are reacted into the final polyester product. As used herein with respect to PET, monomers have less than 3 chain lengths, oligomers have from about 7 to about 50 chain lengths (components with a chain length of 4 to 6 units can be considered monomer or oligomer), and polymers have greater than about 50 chain lengths. A dimer, for example, EG-TA-EG-TA-EG, has a chain length of 2, and a trimer 3, and so on.
The acid starting material employed in the esterification stage can be a dicarboxylic acid such that the final polyester product comprises at least one dicarboxylic acid residue having in the range of from about 4 to about 15 or from 8 to 12 carbon atoms. Examples of dicarboxylic acids suitable for use in the present invention can include, but are not limited to, terephthalic acid, phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, diphenyl-3,4'-dicarboxylic acid, 2,2-dimethyl-l,3-propandiol, dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and mixtures thereof. In one embodiment, the acid starting material can be a corresponding ester, such as dimethyl terephthalate instead of terephthalic acid.
The alcohol starting material employed in the esterification stage can be a diol such that the final polyester product can comprise at least one diol residue, such as, for example, those originating from cycloaliphatic diols having in the range of from about 3 to about 25 carbon atoms or 6 to 20 carbon atoms. Suitable diols can include, but are not limited to, ethylene glycol (EG), diethylene glycol, triethylene glycol, 1,4-cyclohexane-dimethanol, propane-l,3-diol, butane-1,4diol, pentane-l,5-diol, hexane-l,6-diol, neopentylglycol,
3- methylpentanediol-(2,4), 2-methylpentanediol-(l,4), 2,2,
4- trimethylpentane-diol-(l,3), 2-ethylhexanediol-(l,3), 2,2diethylpropane-diol-(l,3), hexanediol-(l,3), l,4-di-(hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)propane, 2,4-dihydroxy-l,l,3,3-tetramethyl-cyclobutane, 2,2,4,4tetramethyl-cyclobutanediol, 2,2-bis-(3-hydroxyethoxyphenyl)-propane, 2,2-bis-(4-hydroxy-propoxyphenyl)-propane, isosorbide, hydroquinone, BDS-(2,2-(sulfonylbis)4,l-phenyleneoxy))bis(ethanol), and mixtures thereof.
In addition, the starting materials can comprise one or more comonomers. Suitable comonomers can include, for example, comonomers comprising terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl -2,6 -naphthalenedicarboxy late, 2,6 -naphthalene-di carboxylic acid, ethylene glycol, diethylene glycol, 1,4-cyclohexane-dimethanol (CHDM), 1,4-butanediol, polytetramethyleneglycol, trans-DMCD, trimellitic anhydride, dimethyl cyclohexane-l,4dicarboxylate, dimethyl decalin-2,6dicarboxylate, decalin dimethanol, decahydronaphthalene 2,6-dicarboxylate, 2,6-dihydroxymethyl-decahydronaphthalene, hydroquinone, hydroxybenzoic acid, and mixtures thereof.
According to one embodiment of the present invention, the esterification in the esterification stage can be carried out at a
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