WO2018191466A1

WO2018191466A1 - Method of cleaning a polyamide reactor

Info

Publication number: WO2018191466A1
Application number: PCT/US2018/027250
Authority: WO
Inventors: Glenn B. SWANNER; Frank Dean PRICE; Daniel Paul LAZZARO
Original assignee: Basf Se
Priority date: 2017-04-13
Filing date: 2018-04-12
Publication date: 2018-10-18

Abstract

A polyamide reactor contains a polymer mixture. A method of cleaning the reactor includes providing a cleaning composition including triethylene glycol present in an amount of from 85 to 95 wt % and adipic acid present in an amount of from 5 to 15 wt %. The method also includes introducing the cleaning composition into the polyamide reactor, refluxing the cleaning composition to dissolve at least a portion of the polymer mixture, removing the cleaning composition from the reactor after the step of refluxing, and optionally introducing water into the reactor to rinse the reactor after the step of removing the cleaning composition. The method reduces the amount of the polymer mixture in the reactor by at least 95 weight percent based on the total amount of the polymer mixture in the reactor and measured after the step of removing the cleaning composition from the reactor.

Description

METHOD OF CLEANING A POLYAMIDE REACTOR

FIELD OF THE DISCLOSURE

[0001] The present disclosure generally relates to a method of cleaning a polyamide reactor. More specifically, the disclosure relates to using a specific cleaning composition to clean the reactor.

BACKGROUND

[0002] Formation of polyamides can lead to plugging of reactors over time. This can occur in one or more portions of the reactors such as in mixers, ports, valves, filters, heat exchangers, etc. The cause of the plugging may be the polyamides becoming too thick to properly flow, because of insufficient water to initiate reactions, because of insufficient heat to melt a masterbatch, because of excess cross-linking, or many other events. Upon plugging, the efficiency of the reactors decreases and the reactors typically need to be taken off-line for expensive and time consuming cleaning. Accordingly, there remains an opportunity for improvement.

SUMMARY OF THE DISCLOSURE

[0003] The present disclosure provides a method of cleaning a polyamide reactor that contains a polymer mixture. The method includes providing a cleaning composition including triethylene glycol present in an amount of from 85 to 95 wt % and adipic acid present in an amount of from 5 to 15 wt %. The method also includes introducing the cleaning composition into the polyamide reactor, refluxing the cleaning composition to dissolve at least a portion of the polymer mixture, removing the cleaning composition from the reactor after the step of refluxing, and optionally introducing water into the reactor to rinse the reactor after the step of removing the cleaning composition. The method reduces the amount of the polymer mixture in the reactor by at least 95 weight percent based on the total amount of the polymer mixture in the reactor and measured after the step of removing the cleaning composition from the reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Other advantages of the present disclosure will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0005] Figure 1 is a schematic of a generic VK reactor that may be utilized in a non- limiting embodiment of the instant method.

DETAILED DESCRIPTION OF THE DISCLOSURE [0006] The instant disclosure provides a method of cleaning a polyamide reactor (10). The reactor (10) contains or includes a polymer mixture, e.g. an initial amount of at least one of a polyamide and a monomer used to form a polyamide. The polymer mixture may be a masterbatch as described below. The polymer mixture may be any mixture or combination of any two or more monomers and/or polymers described below. The polymer mixture may include any one or more additives, salts, etc. described below and/or any contaminants commonly known in the art to be present in polyamide production.

[0007] The reactor (10) that is utilized is not particularly limited and may be any known in the art. For example, the reactor (10) may be as generally shown in Figure 1 but is not limited to such a reactor. In one embodiment, the reactor (10) is further defined as a VK (Vereinfacht Kontinuierlich) tube reactor (i.e., a simplified continuous tube reactor). Typically, VK tube reactors include a vertical tube which may be operated either at atmospheric pressure or under pressure, wherein heating and prepolymerization take place in an upper part and the polyamide is formed in a lower part. Alternatively, the reactor (10) may be further defined as an AKU (Algemene Kunstzijde Unie) reactor. It is also contemplated that the reactor (10) may be a batch reactor. The reactor (10) may be of any size and design and type. In various embodiments, the reactor (10) has a capacity of from 25,000 to 50,000, from 50,000 to 100,000, up to 150,000 lbs, or more. In various embodiments, the "reactor" is a laboratory scale having a capacity from 0.5 to 5 liters.

[0008] The design of the reactor (10) is not particularly limited and may include a heat- jacket (12) disposed on its exterior wherein the heat-jacket (12) surrounds or encapsulates some or all of the reactor (10). The reactor (10) may also include one or more agitators, mixers, heat exchangers, or any other components known in the art. In addition, the reactor (10) may be atmospheric or pressurized. If pressurized, it is theorized that cleaning time could be reduced. Moreover, the reactor (10) may include an agitator, e.g. disposed on a top or head of the reactor (10). In addition, the reactor (10) can include one or more inputs such that gas can be introduced into the reactor (10), e.g. N₂, for bubbling. This may be accomplished through use of a nitrogen introduction apparatus (14), e.g. by use of plant nitrogen via a hose connected to one or more reactor inlets or instrumentation wells. It is theorized that increased bubbling leads to increased agitation and may decrease cleaning time. Moreover, the reactor (10) may or may not have an active mixhead. In various embodiments, the cleaning composition is contained entirely within the reactor (10) throughout the method. In such embodiments, the cleaning composition is not moved through any external piping, valves, tanks, etc., after loading into the reactor (10). This increases efficiency and safety. Of course, the instant disclosure is not limited to any particular type of reactor (10).

Polyamide/Monomer:

[0009] Any one or more of the components of the polymer mixture may be as described below. For example, a polyamide and a monomer used to form a polyamide can be any known in the art. The polyamide typically includes, is, consists essentially of, or consists of, a dimer, trimer, tetramer, or polymer formed from polymerization of one or more monomers. The polyamide is typically further defined as a polymer that is linked together through peptide bonds and that is formed from a polymerization reaction of amide monomers.

[0010] The polyamide and/or polymer mixture may be, include, consist essentially of, or consist of, a homopolymer (e.g. nylon 6), a co-polymer (e.g. nylon 6,6), a terpolymer (e.g. nylon 6/66), or any other higher polymer that is formed from more than three or more different monomers. In one embodiment, the polyamide is formed from a condensation reaction of a first monomer having an amino group and a second monomer having a carboxyl group or acid chloride group. Alternatively, the polyamide may be formed from a condensation reaction of two molecules of the first monomer wherein the first monomer has both an amino group and a carboxyl group or acid chloride group. In still another embodiment, the first monomer and the second monomer are both bi-functional wherein one of the two monomers has two amino groups and the other of the two monomers has two carboxyl groups, two acid chloride groups, or one carboxyl group and one acid chloride group.

[0011] Typically, the polyamide may be or include, consist essentially of, or consist of one or more nylons, aramids, proteins, metal poly(aspartates) such as sodium poly(aspartate), and combinations thereof. Nylons are condensation copolymers typically formed by reacting diamines and dicarboxylic acids to form peptide bonds. In one embodiment, the nylon is further defined as having less than 85% of amide-linkages attached directly (-CO-NH-) to two aliphatic groups. Aramids, also known as aromatic polyamides, are typically formed by reacting amines and carboxylic acid halides. In one embodiment, the aramid is further defined as having at least 85% of amide linkages (-CO-NH-) attached directly to two aromatic rings. The aramid may be any known in the art but is typically further defined as an AABB polymer, such as Nomex^®, Kevlar^®, Twaron^® and/or New Star. As is well known in the art, Nomex^® and New Star include predominantly meto-linkages and are typically further defined as poly-metaphenylene isophthalamides. Kevlar^® and Twaron^® are both para- phenylene terephthalamides (PPTA), the simplest form of an AABB pam-polyaramide. PPTA is a product ofp-phenylene diamine (PPD) and terephthaloyl dichloride (TDC or TCI). Alternatively, the aramid may be further defined as the reaction product of PPD, 3,4'- diaminodiphenylether, and terephthaloyl chloride (TCI). Proteins are organic compounds including amino acids arranged in a linear chain and joined together by peptide bonds between carboxyl and amino groups. Metal poly(aspartates), such as sodium poly(aspartate), are known in the art as condensation polymers based on aspartic acid.

[0012] More typically, the polyamide may be or include, consist essentially of, or consist of one or more of polyamide 6, polyamide 6,6, polyamide 6/66, poly(4-aminobutyric acid) (nylon 4), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(l l- aminoundecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), nylon 4,6, poly(hexamethylene sebacamide) (nylon 6, 10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(hexamethylene azelamide) (nylon 6,9), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(tetramethylenediamine-co-oxalic acid) (nylon 4,2), the polyamide of n- dodecanedioic acid and hexamethylenediamine (nylon 6, 12), the polyamide of dodecamethylenediamine and n-dodecanedioic acid (nylon 12, 12), trimethylene adipamide/hexamethylene azelaiamide copolymer (nylon trimethyl 6,2/6,2), hexamethylene adipamide-hexamethylene-azelaiamide caprolactam copolymer (nylon 6,6/6,9/6), poly(tetramethylenediamine-co-isophthalic acid) (nylon 4,1), polyhexamethylene isophthalamide (nylon 6,1), hexamethylene adipamide/hexamethylene-isophthalamide (nylon 6,6/61), hexamethylene adipamide/hexamethyleneterephthalamide (nylon 6,6/6T), poly (2,2,2-trimethylhexamethylene terephthalamide), poly(m-xylylene adipamide) (MXD6), poly(p-xylylene adipamide), poly(hexamethylene terephthalamide), poly(dodecamethylene terephthalamide), polyamide 6T/6I, polyamide 6/MXDT/I, polyamide MXDI, a terpolymer of lauryl lactam, isophthalic acid and bis(4-amino-3-methylcyclohexyl)methane and polynorbomamide, and combinations thereof. Even more typically, the polyamide is chosen from polyamide 6, polyamide 6,6, polyamide 6/66, and combinations thereof. Most typically, the polyamide is further defined as polyamide 6. Polyamide 6 is also known as polycaprolactam and is commercially available from BASF Corporation under the trade name Ultramid^® B. Polyamide 6,6 is a copolymer of hexamethylene diamine and adipic acid and is commercially available from BASF Corporation under the trade name Ultramid^® A. Polyamide 6/66 is a co-polymer of polyamide 6 and polyamide 66 and is commercially available from BASF Corporation under the trade name of Ultramid^® C. As used in the multiple paragraphs above, the terminology "consists essentially of typically describes that the polyamide is free of other polymers (not described above) that, if present, would affect the physical properties of the polyamide, wherein this effect and such properties would be recognized by those of skill in the art. For example, the polyamide may be free of one or more additional polyamides, such as one or more described above. In one embodiment, the polyamide is nylon 6 and is free of all other polyamides or other polymers. The polyamide may have one or more typical additives known in the art, e.g. salts. These can be chosen by one of skill in the art or omitted.

Method of Forming the Polyamide:

[0013] The polyamide may be formed by any method in the art using any appropriate monomers known in the art. The method of forming the polyamide may be completed prior to the utilization of the cleaning composition. The method of forming the polyamide is not required and is optional in this disclosure.

[0014] The method of forming the polyamide may include the steps of (A) introducing a monomer into the reactor (10) and (B) polymerizing the monomer in the reactor (10) to form the polyamide.

[0015] The monomer may be any compound or molecule known in the art capable of undergoing polymerization to form the polyamide. Thus, the monomer may include or be the polymerization product of a single compound or two or more different compounds, so long as the polymerization product itself is capable of undergoing further polymerization to form the polyamide of this disclosure.

[0016] In various embodiments, the monomer is chosen from caprolactam, 4- aminobutyric acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10- aminodecanoic acid, 1 1 -aminoundecanoic acid, 12-aminododecanoic acid, hexamethylene sebacamide, heptamethylene pimelamide, octamethylene suberamide, hexamethylene azelamide, nonamethylene azelamide, decamethylene azelamide, tetramethylenediamine-co- oxalic acid, n-dodecanedioic acid, hexamethylenediamine, dodecamethylenediamine, trimethylene adipamide, tetramethylenediamine-co-isophthalic acid, hexamethylene isophthalamide, hexamethyleneterephthalamide, 2,2,2-trimethylhexamethylene terephthalamide, m-xylylene adipamide, 7-xylylene adipamide, hexamethylene terephthalamide, dodecamethylene terephthalamide, isomers thereof, and combinations thereof. In another embodiment, the monomer is chosen from hexamethylene diamine, adipic acid, caprolactam, and combinations thereof. Typically, the monomer is further defined as caprolactam, i.e., a caprolactam monomer. In other embodiments, the monomer may be caprolactam, cyclic dimers, cyclic trimers, cyclic tetramers, and cyclic pentamers through octamers, and combinations thereof. In further embodiments, the monomer may be any known to form one or more of the aforementioned polyamides.

[0017] The monomer may be introduced into the reactor (10) in a continuous or batch mode. The monomer may be introduced into any portion of the reactor (10), typically the top of the reactor (10). Typically, the monomer is introduced into the reactor (10) in a continuous mode. In addition, the monomer may be introduced into the reactor (10) as a solid, a liquid, a gas, a gel, a gum, a paste, a dispersion, or as a powder. Typically, the monomer is introduced into the reactor (10) as a liquid. In one embodiment, the monomer is introduced into a top of the reactor (10) such that the monomer can move downwards in the reactor (10) and polymerize to form the polyamide of this disclosure. In another embodiment, the monomer is introduced into a side of the reactor (10) also so that the monomer can move downwards and polymerize.

[0018] The monomer may be combined with a carrier and be utilized as a masterbatch. In one embodiment, the terminology "masterbatch" is further defined as a concentrate of the monomer in the carrier but may also be made out of polychip or a pre-polymer. In another embodiment, the terminology "masterbatch" is further defined as a homogeneous mixture of the monomer in the carrier. In still another embodiment, the terminology "masterbatch" is further defined as a mixture including an increased concentration of the monomer in the carrier, wherein the mixture is later diluted with another compound. Typically, an optional step of forming the masterbatch is defined as combining the monomer and the carrier in a desired weight ratio. The step of combining may be further defined as mixing, extruding, or any other type of mixing step known in the art.

[0019] The masterbatch may include any ratio of the monomer to the carrier, such that the monomer and the carrier may be present in the masterbatch in any amount as desired by one of skill in the art. In one embodiment, the monomer is present in an amount of up to about 50 parts by weight per 100 parts by weight of the masterbatch. In other embodiments, the monomer is present in amounts of from 1 to 50, from 25 to 50, from 1 to 25, from 1 to 20, from 1 to 15, from 1 to 10, or from 1 to 5, parts by weight per 100 parts by weight of the masterbatch. In still other embodiments, the monomer is present in amounts of about 1, 2, 3, or 4 parts by weight per 100 parts by weight of the masterbatch. In various embodiments, the masterbatch includes 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 wt% PA-6 with the remaining 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 wt% being sodium sulfo-isophthalic acid. In one embodiment, the polymer mixture is further defined as a masterbatch including 75 wt % polyamide 6 + 5 wt % and 25 wt % sodium sulfo-isophthalic acid ± 5 wt %.

[0020] The masterbatch may include the monomer and the carrier, consist essentially of the monomer and the carrier, or consist of the monomer and the carrier. The terminology "consist essentially of refers to the masterbatch including the monomer and the carrier but not any other compounds that would materially affect the basic and novel characteristics of the masterbatch, such as additional polymers. Moreover, the terminology "about" typically describes that the value may fluctuate by, for example, ± 1, 2, 3, 4, or 5 %.

[0021] The carrier may be any compound or mixture of compounds known in the art and is typically chemically and/or physically compatible with the monomer and the polyamide. Typically, the masterbatch, including the monomer and the carrier, has a similar melt viscosity as the polyamide formed in this disclosure for equivalent relative solution viscosities. This similarity allows the masterbatch to melt with the polyamide being formed which leads to maximized homogenous formation of the polyamide, tends to maximize an extent of polymerization (i.e., amounts and rates of polymerization) that can occur in the polyamide reactors (10), tends to maximize rates of polyamide discharge from the reactors (10), and tends to reduce excessive foaming in the reactors (10) thereby avoiding problems associated with poor agitation and non-uniformity of the polyamide. Use of the masterbatch also tends to reduce issues associated with the hydroscopicity and agglomeration, issues associated with inconsistent and non-homogenous polymerization, and issues associated with clogging of supply pipes. Said differently, use of the masterbatch eases handling and processing issues associated with polymerization.

[0022] The carrier is typically chosen from polyesters, modified polyolefins, polyamides, and combinations thereof. In one embodiment, the carrier is the same as one of the polyamides described above. Alternatively, the carrier may be a polyamide different from one described above. The carrier may include a mixture of polyamides. In one embodiment, the carrier is further defined as a thermoplastic carrier. In another embodiment, the carrier is a plastic. In still another embodiment, the carrier is chosen from nylon 6, nylon 6/6, polyesters, olefins, and combinations thereof. In various other embodiments, the carrier includes one or more of a terpolymer of ethylene or mixtures of ethylene with higher alpha- olefms, an acrylic, methacrylic acid or glycidyl ester, maleic anhydride, and combinations thereof. In one embodiment, the carrier is further defined as a semi-crystalline thennoplastic polyester including, but not limited to, poly(butylene terephthalate), poly(trimethylene terephthalate), poly(ethylene terephthalate-co-isophthalate), and combinations thereof. Typically, the carrier is not a liquid.

[0023] If a masterbatch is utilized, the method may also or alternatively include the step of introducing the masterbatch into the reactor (10). In other words, the step of introducing the monomer may be replaced with the step of introducing the masterbatch, if the masterbatch includes the monomer. The masterbatch may be introduced into the reactor (10) by any mechanism known in the art including in a continuous mode or in a batch mode. In one embodiment, the masterbatch is introduced into the reactor (10) in a continuous mode. The masterbatch may be introduced into the reactor (10) as a solid, a gas, a gel, a gum, a paste, a dispersion, or as a powder. In other embodiments, the masterbatch is introduced into the reactor (10) as a solid or paste and most typically as a solid. It is contemplated that the paste may include water or may be free from water. The paste may be oligomeric.

[0024] Alternatively, the masterbatch and the monomer may be introduced into the reactor (10) simultaneously or sequentially. The masterbatch may be combined with the monomer before introduction into the reactor (10). Alternatively, the masterbatch and the monomer may be introduced into the reactor (10) separately. Like the masterbatch, the monomer may be introduced into the reactor (10) in a continuous or batch mode. Typically, the monomer is introduced into the reactor (10) in a continuous mode. In addition, the monomer may be introduced into the reactor (10) as a solid, a liquid, a gas, a gel, a gum, a paste, a dispersion, or as a powder. Typically, the monomer is introduced into the reactor (10) as a liquid. In one embodiment, the monomer is introduced into a top of the reactor (10) such that the monomer can move downwards in the reactor (10) and polymerize to form the polyamide of this disclosure. For example, the monomer may flow downwards. In another embodiment, the monomer is introduced into a side of the reactor (10) also so that the monomer can move downwards and polymerize. Most typically, the masterbatch and the monomer are simultaneously introduced into a top of the reactor (10) in a continuous mode from different sources. That is, the masterbatch and the monomer are not typically combined prior to introduction into the reactor (10). Alternatively, the masterbatch and the monomer may be premixed and introduced into the reactor (10) simultaneously. In other embodiments, the masterbatch and the monomer are introduced into the reactor (10) sequentially with either the masterbatch or the monomer introduced first.

[0025] The step of polymerizing the monomer in the reactor (10) is also not particularly limited and may include one or more steps known in the art. The step of polymerizing may include reacting caprolactam with water to form 6-aminohexanoic acid as is shown below:

6-aminohexanoic acid

Caprolactam

As such, a polyamide resin may be formed from the following chemical reaction:

Caprolactam 6-Aminohexanoic acid Polycaprolactam (Nylon 6) wherein n is an integer of two or greater.

[0026] The step of polymerizing is typically further defined as heating the monomer to a temperature of from 230 to 300, from 235 to 295, from 240 to 290, from 245 to 285, from 250 to 280, from 255 to 275, from 260 to 270, or from 265 to 270, °C, to cause the monomer to polymerize and form the first intermediate. The step of polymerizing typically occurs in a time of from 4 to 24 hours.

[0027] The method of forming the polyamide may lead to one or more portions of the reactor (10) becoming clogged or fouled. For example, any one or more of the aforementioned reactor (10) components may become clogged. It is theorized that a lack of flow of reactants, an increased heat buildup in various parts of the reactor (10), a formation of hot-spots due to heat distribution, etc. can lead to fouling. For example, when polyamides are forming, their viscosity increases with increased heat. At that point, reactor flow can diminish causing the polyamides to remain in the reactor (10) for extended times, thereby leading to increased cross-linking and plating, even further increased viscosity, and ultimately clogging or fouling of components. The polyamides that clog the components may form rock-like structures that are very difficult to remove with conventional methods. The instant method and cleaning composition are used to improve cleaning, improve efficiency, and improve ease.

Method of Cleaning the Polyamide Reactor:

[0028] The method of cleaning the polyamide reactor (10), which is the focus of this disclosure, may or may not include one or more of the aforementioned method steps of forming the polyamide. The method of cleaning the polyamide reactor (10) includes the step of providing a cleaning composition. The cleaning composition includes triethylene glycol present in an amount of from 85 to 95 wt % based on a total weight of the cleaning composition and adipic acid present in an amount of from 5 to 15 wt % based on a total weight of the cleaning composition. The method also includes the step of introducing the cleaning composition into the polyamide reactor (10) and refluxing the cleaning composition to dissolve at least a portion of the polymer mixture (e.g. the polyamide and/or the monomer). The portion may be any weight percent of the total of the polymer mixture. In various embodiments, the portion may be 90, 95, 96, 97, 98, 99, or even approximately 100 weight percent of the total of the polymer mixture.

[0029] The method further includes the step of removing the cleaning composition from the reactor (10) after the step of refluxing and optionally includes the step of introducing water into the reactor (10) to rinse the reactor (10) after the step of removing the cleaning composition. In other words, the step of introducing the water may or may not be utilized. The method reduces the initial amount of the polyamide and/or the monomer by at least 95 weight percent measured after the step of introducing the water but may reduce this amount by 96, 98, 98, 99, or even approximately 100, percent.

Cleaning Composition:

[0030] The cleaning composition may include, be, consist essentially of, or consist of the triethylene glycol present in the amount of from 85 to 95 wt % based on a total weight of the cleaning composition and the adipic acid present in an amount of from 5 to 15 wt % based on a total weight of the cleaning composition. The terminology "consist essentially of describes various embodiments that are free of one or more monomers, polymers, glycols, acids, etc. that are not triethylene glycol or adipic acid. This terminology may also describe embodiments that are free of one or more solvents, whether aqueous or organic, polar or non- polar. Water may be included or excluded. Any one or more solvents may be included or excluded. Similarly any one or more known cleaning additives, enhancers, etc. may be included or excluded. If any one or more of the aforementioned solvents, additives, monomers, polymers, glycols, acids, etc. are included they may be included in less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.1 , or 0.01, weight percent based on a total weight of the cleaning composition. Moreover, all values and ranges of values including and between those described above are hereby expressly contemplated for use herein.

[0031] The triethylene glycol (C6H14O4; e.g. CAS number 1 12-27-6; also known as 2-

[2-(2-hydroxyethoxy)ethoxy]ethanol) is present in an amount of from 85 to 95 wt % based on a total weight of the cleaning composition, e.g. + 0.1, 0.5, 1, 2, 3, 4, or 5 wt %. In various embodiments, the triethylene glycol is present in 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, or 95, wt % based on a total weight of the cleaning composition. [0032] The adipic acid (C6H10O4; e.g. CAS number 124-04-9; also known an hexane- 1,6-dicarboxylic acid or hexane-l,6-dioic acid) is present in an amount of from 5 to 15 wt % based on a total weight of the cleaning composition, e.g. + 0.1, 0.5, 1, 2, 3, 4, or 5 wt %. In various embodiments, the adipic acid is present in 5, 6, 7, 8, 9, 10, 1 1, 12, 13, 14, or 15, wt % based on a total weight of the cleaning composition. In various non-limiting embodiments, all values and ranges of values including and between those described above are hereby expressly contemplated for use herein.

[0033] The triethylene glycol and the adipic acid react with each other to form a polyester. For example, the cleaning composition may have an initial pH of 1, 2, 3, etc. which may rise to approximately neutral (e.g. 7) after reaction. This suggests that the adipic acid is neutralized. Similarly, it is theorized that the polyester groups formed from the reaction of the triethylene glycol and the adipic acid are similar enough in polarity and structure to the monomers and polyamides formed in the reactor (10) that the polyamides and/or monomers can be brought into solution and kept in solution without significant precipitation. In various embodiments, the saturation limit of polyamides in the cleaning composition is theorized to be approximately 12-15 wt% at approximately 220°C and atmospheric pressure. Above this value, the polyamides and/or monomers will tend to fall out of solution when cooled. Similarly, it is theorized that the adipic acid allows the polyamide to remain in solution and not significantly precipitate even upon subsequent rinsing of the reactor (10) with water, as described in greater detail below. If significant precipitation were to occur at any point in the process, the system and reactor (10) could become re-clogged.

[0034] The method of cleaning the polyamide reactor (10) includes the step of providing the cleaning composition. The method also includes the step of introducing the cleaning composition into the polyamide reactor (10). The cleaning composition may be provided as a whole or in parts. For example, the cleaning composition may be introduced into, or provided to, the reactor (10) by any method in the art, e.g. pumping, conveying, and/or dumping. Each component of the cleaning composition may be provided or introduced separately or together. Moreover, any order of addition can be utilized. The step of introducing the cleaning composition into the polyamide reactor (10) may occur for any length of time, at any temperature, and at any pressure, chosen by one of skill in the art. In various embodiments, the cleaning composition is introduced into the reactor (10) at ambient temperature or slightly higher, e.g. 40-70°C to encourage dissolution of the adipic acid in the triethylene glycol. The amount of cleaning solution to be added to the reactor (10) is determined by one of skill in the art. For example, the reactor (10) may be completely filled or less than completely filled. Typically, an expansion of 2-4 percent by volume is allowed so that the reactor (10) is not overfilled.

[0035] The method further includes the step of refluxing the cleaning composition to dissolve at least a portion of the polyamide and/or the monomer. The step of refluxing may be further defined as heating to the reflux temperature of the cleaning composition, which can be calculated by those of skill in the art. In various embodiments, the reflux temperature is from 210 to 230°C, e.g. 215 to 225°C, 215 to 220°C, 220 to 225°C, 220 to 230°C, etc. The step of refluxing can be carried out for any length of time deemed suitable by one of skill in the art. For example, reflux time may be increased or decreased depending on the composition of the polyamide and/or the monomers present in the reactor (10). In various embodiments, the step of refluxing may occur from 1 to 1 ,000 hours, or any number of hours or range of hours therebetween. In other embodiments, the step of refluxing may occur from 1 to 100, 5 to 95, 10 to 90, 15 to 85, 20 to 80, 25 to 75, 30 to 70, 35 to 65, 40 to 60, 45 to 55, 50 to 55, 45 to 50, 2 to 14, 3 to 13, 4 to 12, 5 to 1 1, 6 to 10, 7 to 9, 7 to 8, 4 to 7, or 4 to 5, days. Similarly, any number of days or range of days therebetween may be utilized. If salts are present, e.g. as additives in the polyamide, a longer reflux time may be required since many salts are not readily soluble in triethylene glycol. Moreover, temperature of reflux may be higher than that described above based on pressure in the reactor. Such temperatures are hereby contemplated and can be calculated by one of skill in the art based on the pressure utilized in the reactor during cleaning. In various non-limiting embodiments, all values and ranges of values including and between those described above are hereby expressly contemplated for use herein.

[0036] During reflux, agitation (e.g. manual or with gas bubbling) may be utilized or may be omitted. Increased agitation may increase cleaning efficiency and/or reduce needed cleaning time. Similarly, increased temperature and pressure may do the same.

[0037] The method further includes the step of removing the cleaning composition from the reactor (10) after the step of refluxing. The step of removing may also be further defined as any known in the art. The step of removing is typically defined as draining the cleaning composition from the reactor (10). The step of draining is not time dependent and may occur as fast or slow as desired by those of skill in the art. In various embodiments, the cleaning composition is cooled before the step of removing. For example, the cleaning composition may be cooled to a temperature of from 50 to 100°C, 55 to 95°C, 60 to 90°C, 65 to 85°C, 70 to 80°C, 75 to 85°C, or 50 to 70°C before the step of removing. All values and ranges of values including and between those set forth above are also expressly contemplated for use in various non-limiting embodiments.

[0038] Typically, when the cleaning composition is cooled, precipitation of the polyamides is minimal to none. As first described above, triethylene glycol alone will allow the polyamide to go into solution. However, upon cooling and/or introduction of rinse water, the polyamides will precipitate and re-clog various components of the reactor (10). The adipic acid is theorized to allow the polyamide to remain in solution with little to no precipitation both on cooling and rinsing.

[0039] The method further includes the step of introducing water into the reactor (10) to rinse the reactor (10) after the step of removing the cleaning composition. The water can be introduced into the reactor (10) by any method known in the art. The water is typically used to wash away organics and residues from the reactor (10). Typically, most everything in the reactor (10) at this point in the method is water soluble or miscible with water. The rinsing step may occur once or be repeated two or three times. In various embodiments, zero TOC is analytically detected after a second or third rinse.

[0040] Typically, the water is pumped into the reactor (10) from the top, side, or bottom. The temperature, flow rate, and pressure of the water may be chosen by a person of skill in the art. The water may be any type including potable or non-potable water, purified or non- purified, etc. Typically, the water is introduced into the reactor (10) at room temperature. However, the water can be at any temperature.

[0041] The water may be circulated within the reactor (10) using any equipment known in the art and for any length of time. The water may be heated or not heated while in the reactor (10) or before being introduced into the reactor (10).

[0042] The method reduces the initial amount of the polyamide and/or the monomer by at least 95 weight percent measured after the step of introducing the water. This is typically measured by determining an approximate amount of the fouling or clogging polyamide or monomers that are present in the reactor (10) before cleaning and after cleaning. For example, a camera can be introduced into the reactor (10) to estimate a volume percent of various reactor parts that are clogged. Upon knowing an approximate density of the clogging material and the approximate volume of the various clogged reactor components, a total weight of the clogging material can be accurately estimated. After cleaning, the camera can again be used for the same calculations. In various embodiments, the reactor components are entirely clean to the naked eye, thereby suggesting that at least 95, 96, 97, 98, or even 99 to approximately 100 weight percent of the polyamides and monomers clogging the reactor (10) were removed. The instant method can be repeated as many times as is necessary to clean the reactor (10).

EXAMPLES

[0043] In a first comparative example, a comparative composition of 60 wt% caprolactam, 30 wt% water, and 10 wt% propionic acid was formed. Approximately 6,000 gallons of this comparative composition was then added to a VK reactor. The composition was added at a temperature of about 100°C. The VK reactor included a maximum estimation of about 500 lbs polyamide 6 and related monomers typically formed during production. Those of skill in the art appreciate which related monomers would typically be formed and present. The comparative composition was stirred in the reactor for about 72 hours at about 100° C. The comparative composition was then removed from the reactor.

[0044] The amount of residual polyamide 6/monomers was calculated using a camera to evaluate the inside of the VK reactor and estimate volume. The approximate density of the residual polyamide 6/monomers is 1.2 g/mL and the approximate volume of the clogged area of the VK reactor is approximately 35 cu. ft. This comparative composition removed approximately 0 weight percent of the residual polyamide 6/monomer clogging the reactor. In other words, upon visual evaluation, it did not appear that any of the residual polyamide 6/monomers was removed.

[0045] In a second comparative example, cleaning of a similar VK reactor included simply heating the reactor to a temperature of about 240°C for about 36 hours in an attempt to ash the residual polyamide 6/monomers clogging the reactor.

[0046] The amount of residual polyamide 6/monomers was calculated using the method described above and a camera to estimate volume. This method removed approximately 0 weight percent of the residual polyamide 6/monomers clogging the reactor. In other words, upon visual evaluation, it did not appear that any of the residual polyamide 6/monomer was removed.

[0047] In an example that is representative of one embodiment of this disclosure, approximately 6,000 gallons of a cleaning composition that was 90 wt% triethylene glycol and 10 wt% adipic acid was introduced into a 48,000 lb capacity VK reactor including approximately 500 lbs of polyamide 6 and the monomers described above. The cleaning composition was refluxed at approximately 220° C for about 52 days and then drained from the reactor. Subsequently, 5,500 gallons of feed water was introduced into the reactor at about 75° C and stirred for about2 hr for rinsing. The rinsing was completed one time.

[0048] The amount of residual polyamide 6/monomers was calculated using the method described above and a camera to estimate volume. This method removed approximately 99 weight percent (or more) of the residual polyamide 6/monomers clogging the reactor. In other words, upon visual evaluation, it did not appear that any of the residual polyamide 6/monomer remained. Based upon visual inspection, all of the residual polyamide 6/monomer was removed.

[0049] In another example that is representative of one embodiment of this disclosure, about 100 g of a cleaning composition that was 89 wt% triethylene glycol and 11 wt% adipic acid was introduced into a 250 mL round bottom flask with 2.56 g of polyamiude 6/monomers. The cleaning composition was refluxed at approximately 220° C for about 4 hours such that all of the polyamide 6/monomers were dissolved. At that time, the solution and setup were cooled. The volume of the solution was doubled with water, where no observable precipitation was seen.

[0050] In an example that is representative of one embodiment of this disclosure, about 800 g of cleaning composition that was 89 wt% triethylene glycol and 11 wt% adipic acid was introduced into a 1 L sealable flask with 93.45 g of polyamide 6/monomers. The cleaning composition was refluxed at approximately 220° C for about 5 days such that all of the polyamide 6/monomers had dissolved. At that time, he solution and setup were cooled. The volume of a sample of the solution was doubled with water, where no observable precipitation was seen.

[0051] The results of this experimentation demonstrate that the cleaning composition of this disclosure clearly outperforms the comparative examples by not only dissolving the polyamide 6/monomers most efficiently, but also by not allowing precipitation after dissolution is complete regardless of treatment. This is particularly important for safety, post cleaning rinsing, and subsequent start up as other equipment will not become plugged or affected.

[0052] All combinations of the aforementioned embodiments throughout the entire disclosure are hereby expressly contemplated in one or more non-limiting embodiments even if such a disclosure is not described verbatim in a single paragraph or section above. In other words, an expressly contemplated embodiment may include any one or more elements described above selected and combined from any portion of the disclosure. In various non- limiting embodiments, all values and ranges of values including and between those described above are hereby expressly contemplated for use herein.

[0053] One or more of the values described above may vary by ± 5%, ± 10%, ± 15%, + 20%, ± 25%, etc. Unexpected results may be obtained from each member of a Markush group independent from all other members. Each member may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims. The subject matter of all combinations of independent and dependent claims, both singly and multiply dependent, is herein expressly contemplated. The disclosure is illustrative including words of description rather than of limitation. Many modifications and variations of the present disclosure are possible in light of the above teachings, and the disclosure may be practiced otherwise than as specifically described herein.

[0054] It is also to be understood that any ranges and subranges relied upon in describing various embodiments of the present disclosure independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. One of skill in the art readily recognizes that the enumerated ranges and subranges sufficiently describe and enable various embodiments of the present disclosure, and such ranges and subranges may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range "of from 0.1 to 0.9" may be further delineated into a lower third, i.e. from 0.1 to 0.3, a middle third, i.e. from 0.4 to 0.6, and an upper third, i.e. from 0.7 to 0.9, which individually and collectively are within the scope of the appended claims, and may be relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as "at least," "greater than," "less than," "no more than," and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of "at least 10" inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange may be relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. Finally, an individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range "of from 1 to 9" includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1, which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1. A method of cleaning a polyamide reactor containing a polymer mixture, said method comprising the steps of:

A. providing a cleaning composition comprising;

(1) triethylene glycol present in an amount of from 85 to 95 wt % based on a total weight of the cleaning composition, and

(2) adipic acid present in an amount of from 5 to 15 wt % based on a total weight of the cleaning composition;

B. introducing the cleaning composition into the polyamide reactor;

C. refluxing the cleaning composition to dissolve at least a portion of the polymer mixture; and

D. removing the cleaning composition from the reactor after said step of refluxing; and

E. optionally introducing water into the reactor to rinse the reactor after said step of removing the cleaning composition;

wherein the method reduces the amount of the polymer mixture in the reactor by at least 95 weight percent based on the total amount of the polymer mixture in the reactor and measured after said step of removing the cleaning composition from the reactor.

2. The method of claim 1 wherein the polyamide reactor is a VK tube reactor.

3. The method of claim 2 wherein the VK tube reactor comprises a heating jacket and a nitrogen bubbler, the step of refluxing the cleaning composition comprises heating the cleaning composition using the heating jacket, and the method further comprises the step of agitating the cleaning composition using the nitrogen bubbler.

4. The method of any one of claims 1-3 wherein the cleaning composition is contained entirely within the polyamide reactor throughout said method.

5. The method of any one of claims 1-4 wherein the triethylene glycol is present in the cleaning composition in an amount of 90 wt % ± 2 wt % and the adipic acid is present in the cleaning composition in an amount of 10 wt% ± 2 wt %.

6. The method of any one of claims 1-4 wherein the triethylene glycol is present in the cleaning composition in an amount of 90 wt % ± 0.5 wt % and the adipic acid is present in the cleaning composition in an amount of 10 wt% ± 0.5 wt %.

7. The method of any one of claims 1-4 wherein the cleaning composition consists essentially of the triethylene glycol and the adipic acid.

8. The method of any one of claims 1 -4 wherein the cleaning composition consists of the triethylene glycol and the adipic acid.

9. The method of any one of claims 1-8 wherein the step of refluxing is further defined as refluxing at a temperature of from 210°C to 230°C.

10. The method of any one of claims 1-9 wherein the cleaning composition is cooled before said step of removing.

1 1. The method of any one of claims 1-9 wherein the cleaning composition is cooled to a temperature of from 50°C to 70°C before said step of removing.

12. The method of any one of claims 1-11 wherein the step of refluxing continues for 4 to 7 days.

13. The method of any one of claims 1 -12 wherein the step of rinsing is repeated.

14. The method of any one of claims 1-13 wherein the triethylene glycol and the adipic acid react to form a polyester.

15. The method of any one of claims 1-14 wherein the step of introducing water into the reactor to rinse the reactor does not produce precipitate of the polyamide.

16. The method of any one of claims 1-15 wherein the polyamide is chosen from polyamide 6, polyamide 6,6, polyamide 6/66, and combinations thereof.

17. The method of any one of claims 1-15 wherein the polyamide is polyamide 6.

18. The method of any one of claims 1-15 wherein the polymer mixture is further defined as a masterbatch including 75 wt % polyamide 6 ± 5 wt % and 25 wt % sodium sulfo-isophthalic acid ± 5 wt %.