TWI343835B - Process for the purification of inert gases - Google Patents

Description

1343835 IX. Description of the Invention: The present invention relates to a method for purifying an inert gas containing an impurity formed of an organic compound. The invention further relates to a process for purifying an inert gas recycled from a polymerization reactor and in particular to a solid polycondensation (SSp) reactor for producing an aromatic polymer resin. [Prior Art] The polymer resin is molded into various useful products. One such polymeric resin is t-p-ethylene dicarboxylate (PET) resin. We are well aware of aromatic polyester resins' especially PET (ie copolymers of terephthalic acid with a lower ratio of stearic acid) and polybutylene terephthalate for the production of beverage containers, films, optical fibers. , packaging and tire cords. US 4,064,112 B1 discloses a solid state polycondensation or polymerization (SSP) process for the production of PET resins. For fibers and films, the inherent viscosity of the resin must generally be between 66 dl/g and 0.75 dl/g. For molding materials such as containers and tire cords, a more southerly value is required. Higher intrinsic viscosities such as greater than 0.75 dl/g can only be obtained with difficulty by direct polycondensation of PET (generally referred to as the melt phase method). The SSP method pushes the polymerization to a higher degree by heating and removing the reaction product, thereby increasing the molecular weight of the polymer. Polymers having a higher molecular weight have greater mechanical strength and other properties useful for producing, for example, containers, fibers, and films. The SSP method begins with polymer fragments in amorphous form. 4, 〇 64, 112 B1 teaches that the chips are crystallized and heated in a crystallization vessel under agitation to a density of 〇4〇3 g/em3 to 1415 g/cm3 and 93537.doc 1343835 before agitation into the SSP reactor. Temperature between 230 ° C and 245 ° C (446 ° F and 473 T). Otherwise the viscous fragments tend to stick together. < The SSP reactor may consist of a cylindrical reaction section containing a vertically moving bed (the polymer chips are introduced from the upper portion) and a frustoconical dispersion section at the bottom for distributing product fragments. Usually at 210. The polycondensation reactor was operated at a temperature between 220 ° C (410 F and 428 ° F). Various reactions occur during PET polycondensation. The main reaction to increase the weight of the pet molecule is to eliminate the ethylene glycol group:

PET-COO-CH2-CH2-OH+HO-CH2-CH2-OOC-PET—► PET-COO-CH2-CH2-OOC-PET+HO-CH2-CH2-OH allows an inert gas such as nitrogen to pass through the polymerization The reactor removes impurities from the formed polymer. The impurities present in the inert gas stream used to produce polyethylene terephthalate in the SSP process typically include water and organic materials such as aldehydes and glycols, typically acetaldehyde and ethylene glycol and glycol oligomers. . At the same time, volatile impurities include low molecular weight ruthenium oligomers such as cyclic trimers of ruthenium. Water is removed from the inert gas stream before it is recycled to the SSP because the water accelerates the reverse reaction of the polymerization step. The organic impurities are removed to force the polymer product and ensure that the impurities do not contaminate the target product for compatibility with its use. It is especially important to prevent organic impurities from being filtered out of the resin container to the contents of the beverage. These impurities are removed from the polymeric fragments and allowed to accumulate in the inert gas. The impurities such as the side are present in the inert gas stream to be purified in an amount of from 2 cm to 1.6 mm as defined by the methane equivalent. 5,708,124 B1 discloses that the ratio of the inert gas mass flow rate to the PET polymer solid mass flow rate in the SSP reactor is less than 〇.6. 93537.doc 1343835 We are also familiar with polyamine resin and especially PA 6 , pa 6 6 PA 11 , PA12 and their copolymers in the optical fiber and flexible packaging industry and in the production by blow molding and technology It is widely used in both artifacts. Although the relative viscosity of the resin used for the optical fiber is as low as 2, 4 to 3, 0, a relatively high viscosity of 3.2 to 5.0 is required for articles produced by the blow molding and extrusion techniques. Depending on the type of polyamine used, the relative viscosity is increased to above 3. by the SSP method operating at a temperature between 14 (TC and 23 〇. (: 284 卞 and 446 °F). Still 4,460,762 B1 describes the SSP method for polyamines and different methods for accelerating this reaction. The SSP method for polyamido resins is also described in the article "Nyl〇n 6

Polymerization in the Solid State", RJ Gaymans et al.,joumal of Applied Polymer Science, Vol. 27, 2515-2526 (1982), which states the use of nitrogen as a heating and rinsing aid. 145 〇C (293 °F) It is also known to increase the molecular weight of polycarbonate by the SSP method. The formation of polyamines and polycarbonates also releases organic impurities which must be removed by inert gas flow. The enzymatic gas stream must then be purified. EP 0 222 714 B1 discloses a process for producing polyethylene terephthalate and polyethylene stearate to produce little acetaldehyde to reduce the amount of inert gas required for purification. For purification from SSP process recycling A conventional method of inert gas flow includes an oxidation step of converting organic impurities into CO 2 and a drying step of eliminating water formed in the polymerization process and the oxidation step. Oxygen or an oxygen-containing gas such as air (by using no more than The oxidation step is carried out with respect to the stoichiometric oxygen concentration of the organic impurities. The oxidation step is controlled according to US 5,612,011 B1 93537.doc 1343835 The oxidation step is such that the outlet is inert The gas stream contains an oxygen concentration of no more than 250 ppm, and the oxidation step is preferably controlled according to US 5,547,652 B1 such that the inert gas stream at the outlet contains an oxygen concentration of no more than 1 〇 ppm. These patents teach the oxidation step and the drying step. There is no need for a deoxygenation step that previously required hydrogen to reduce oxygen. Conventionally, the inert gas stream is circulated at 25 (TC and 6 Torr (TC (482 °) by a catalyst bed formed on a catalyst coated with platinum or platinum and palladium. The oxidation reaction is carried out at a temperature between F and 1112. The low oxygen content present in the inert gas stream exiting the oxidation zone allows the same inert gas stream to be recycled to the SSP process after the drying step. The higher oxygen concentration in the circulating inert gas stream, for example, creates a risk of degrading the polymer product by yellowing the product. 公开 Publication No. 20885/71 discloses a reconstitution application to solid state polycondensation. Or a method of polymerizing an inert gas in a linear polyester comprising contacting the gas with a metal oxide at 15 〇 β (: to 〇 C (302 F to 572 F). The organic reaction product contained is oxidized to water and carbon dioxide. However, since the metal oxide loses its activity, it must be heated in the presence of air in a knife batch process. Therefore, the present disclosure is independent of the continuous catalytic gas purification method. The final inert gas purification step is a drying step performed by circulating the gas on a bed of silicone, molecular sieve or other dry material. In this step, the water removed from the polymer fragments by the inert gas stream is simultaneously eliminated. Oxidation step towel produced water 4 After this step, the dragon gas is recycled to the SSP process. The small amount of oxygen present in the recycled inert gas stream does not cause oxygen and/or polymer degradation. Even when the amount of oxygen in the oxidation reactor is stoichiometric or higher, it is possible to reduce the organic impurities to an acceptable level, such as less than 10 ppm as defined by the methanol equivalent. , · E.V. Kuznetsova and others wrote the name "Purification of Industrial ’

The Vapor-Gas Discharges and Wastewaters by Vapor-Phase Catalytic Oxidation " article discloses the use of platinum and other metal catalysts to oxidize organic materials from water vapor from wastewater streams. The article states that when the temperature drops below 250 ° C (482 ° F), the conversion of hydrocarbon species is not as complete as for the aluminum-copper oxide catalyst. ·

Platinum or platinum and palladium catalysts previously used to purify inert gases from the polymerization process must be carried out at 250 ° C to 600 ° C (482 ° F to 1112 T) to ensure adequate oxidation from the use of substantially stoichiometric oxygen. The nitrogen stream is a hydrocarbon impurity. The higher temperatures used in the reaction zone require relatively more expensive equipment and operations to preheat the impure inert gas stream fed into the oxidation zone. In addition, there is a need for greater equipment and operating costs to recover heat from the oxidation step. It is therefore an object of the present invention to provide a substantially stoichiometric amount of oxygen at a low temperature to purge the stream from the inert polymerization reactor. A catalyst for all organic impurities. SUMMARY OF THE INVENTION It has been surprisingly found to contain 0.1 weight. /. Catalyst to 2.0% by weight of platinum (wherein the platinum is in a reduced state) at a temperature much lower than the previously practiced temperature (ie at 250 ° C (482 ° F)) with substantially stoichiometric amount of oxygen almost completely oxidized from the polymerization Organic impurities in the reactor. 93537.doc • 10-1334335 The additional objects, a embodiment and details of the present invention are obtained from the following detailed description of the invention. [Embodiment]

A detailed description of the preferred method of performing this method is presented in the context of a solid state polycondensation or polymerization (SSP) process. However, other types of poly-human methods (such as for polyamines and polycarbonates) can be used in the present invention. The inert gas is used to remove impurities and the impurities can be oxidized, especially to carbon dioxide and water. Polyester resins which can be used in the SSP process are aromatic dicarboxylic acids (especially for stearic acid or esters thereof) and diols having 1 to 12 carbon atoms (such as ethylene glycol, 1,4-dimethylol). A polycondensation product of cyclohexane and hydrazine, 4-butanediol. Poly(p-phenylene terephthalate) (PET) and polybutylene terephthalate are preferred resins. The polyester resin which can be used in the SSP method may also include: an elastic polystyrene resin (including a segment derived from polyethylene glycol) and an aromatic dicarboxylic acid derived from terephthalic acid containing up to 2% by weight. A copolyester of a unit such as a stearic acid. The resin to be subjected to SSP may contain a resin-upgrading additive to accelerate the SSP reaction. Preferably, the lifting compound is a dianhydride of a tetracarboxylic aromatic acid' and especially pyromellitic dianhydride. The lifter is usually used in an amount of from 05% to 2% by weight. Conventional additives such as stabilizers, dyes, flame retardants, and nucleating agents may also be present in the resin. The polyester resin which can be used in the SSP process can also be a material which has been washed, chopped and dried from a recirculating container. The re-ringed material is typically re-melted and pelletized prior to being sent to the SSP process. The polyamidamide resin usable in the method of the present invention comprises: polyamine 6 derived from its own amine, polyamine 93537.doc 1343835 6,6 obtained from hexamethylenediamine and adipic acid. Polyamido η from aminoundecanoic acid, and ι 2 polylaurilacetone copolymerized decylamine 6/1 〇 and 1 〇 / 2 and dimethyl succinimide polyamine. Polycarboxylates can also be used in the process of the invention. Referring to Fig. 1, a polyester SSP process to which the present invention is applicable comprises feeding amorphous, pure polyester chips having an intrinsic viscosity, typically in the range of 0.57 dl/g to 0.65 dl/g, via feed line 10 to feed hopper 12. The inherent viscosity or molecular weight of the starting material is not relevant to the practice of the invention. In general, the SSP method can be successfully performed with a wide range of values of feed. For example, us 5,540,868 B1, US 5,633,018 B1 and US 5'744,074 B1 disclose techniques for using starting materials having a degree of polymerization as low as 2-40, which are ultimately expected to be subjected to the SSP process to increase the molecular weight sufficient to produce useful resins. Moreover, the condition of the post-consumer recycled material may result in an initial intrinsic viscosity of more than 〇 65 d丨& Feed hopper 12 feeds the chips into fluidized bed pre-crystallizer 18 via line 14 and control valve 16. At 17 〇t (338 卞) and 1 〇 3 kpa gauge (1 5 I operating pre-crystallizer 8) to achieve the crystallinity of the polyester chips 35 〇 / 。. Then the polyester chips from the pre-crystallization The device 18 feeds the first crystallizer 24 via line 2 and control valve 22. If a larger capacity is desired, the first crystallizer 24 can be used to hunt the second crystallizer 28 fed by the route 26. In the crystallizer 24, 28 In the case of the mechanical (4) ribs, the shards are bonded to each other, and then preheated or cooled to the ssp reaction temperature. The fragments leaving the knot exhibit 45% crystallinity. Pre-crystallization of the pET particles prevents the particles from sticking during the SSP reaction. The fragments that will leave the *Hour (equal) crystallizer are fed via the route 30 and the control valve 32 93537.doc 1343835 for PET suitable at 15 (rC to Moving packed bed polymerization reactor 34 operated at a temperature of 24 (rc and preferably at 210 ° C to 220 ° C (4 HTF to 428 ° F). The fragments are moved by gravity through the moving bed to 3 6 hours To produce crystalline, opaque pellets, depending on the application of the polyester pellets, 〇.75dl/g Larger intrinsic viscosity. The fragments are recovered from reactor 34 via line 36. An oxygen-free inert gas (usually nitrogen) removes the polymerization reactor, the crystallizer and the pre-crystallizer to remove the fragments. Impurity. The inert gas is passed via line 38 and dispersed by disperser 4 to polymerization reactor 34. Right PET is the product 'the ratio of the mass flow rate of the inert gas to the mass flow rate of the polymer in reactor 34 Preferably, G6 should not be exceeded. Gas route 42 removes the inert gas with impurities from polymerization reactor 34 and splits into recycle route 44 and crystallizer route 46. Crystallizer route. The inert gas is passed to second crystallizer 28 And the route 48 transfers the inert gas from the second crystallizer 28 to the first crystallizer 24. The route 5 传送 delivers the inert gas with impurities to the pre-crystallizer circuit 52 to transport the (four) gas-sandwich recirculation route 44 with impurities. The temperature of the recycled inert gas in the combined recycle route 53 is preferably between 200 C and 22 (TC (392 °: P and 428 〇 F). The combined recycle route 53 is such that (4) Inert gas The flow passes through the filter 54. After the transition of the recycled inert gas stream, the air is injected into the exit path of the transition unit 54 by route 57. If it is desired to achieve the desired oxidation reaction temperature, then via a heater via route 59. (not shown) carrying the air/inert gas mixture to an oxidation reactor 58 wherein the organic impurities are burned by burning the gas stream on a bed comprising a catalyst containing a reducing agent according to the present invention. The substantially stoichiometric amount of oxygen is injected by route 57 to ensure complete combustion of the organic impurities in the oxidation reactor 58 and the maximum allowable oxygen allowance at the outlet of the reactor -58 is not more than 25 〇 ppm, suitably small. · at 100 ppm and preferably not more than 1 〇 ppm. Can be below 35 〇. Oxidation reactor 58 is operated at such temperatures as 匚 (at 662). However, since the low temperature operation is more economical, it is preferred to operate the oxidation reactor below 25 (rc (482 Torr).) This temperature is the unheated temperature of the feed stream in Route 59. Thus heating in Route 59 is avoided. Route 6〇 recovers the effluent from the oxidation reactor brother, which contains only nitrogen, carbon dioxide, water, and traces of oxygen. The carbon dioxide content is stabilized at a particular level due to loss through the SSP equipment, and due to Its chemical nature is like an inert gas-like action. The exit gas stream in the circulation route can be circulated through a heat exchanger (not shown) for heat.

And or substantially all of the catalysts of platinum 93537.doc • 14· 1343835, the catalyst content being up to 5% by weight, based on the total weight of the product catalyst (in which the platinum is in a substantially reduced state), suitably 〇ι The weight is from % to 2.0% by weight and preferably from 0.2% by weight to 8% by weight. It has been found that by providing a catalyst having platinum in a reduced state, the oxidation of such organic impurities is allowed to occur at a temperature much lower than previously performed, i.e., at a temperature below 25 (TC (482 V). By the term "substantially reduced", we mean that at least 7% by weight of the platinum in the catalyst is platinum metal rather than platinum oxide. Suitably at least 9% by weight of the platinum in the catalyst is platinum metal, and Preferably, all of the platinum in the catalyst is reduced. Although not wishing to be bound by any theory, it is believed that the reduction of platinum from a tetravalent or divalent oxidation state to a metal having a zero valence state provides the catalyst at a lower temperature. Significantly greater oxidative activity. In addition, the platinum dispersion has a greater activity on the outermost surface of the support comprising an eggshell surrounding the carrier. Therefore, more than 90% by weight of platinum on the catalyst is present in the catalyst. Since the surface of the catalyst is less than 100 μπΐ2 in depth, this is very important for the diffusion-limited oxidation reaction. The carrier of the catalyst can be US 4,1〇8,971 B1 or us 4,301,033. Any of B1 teaches the alumina produced, which is incorporated herein by reference in its entirety. It is preferred to use a higher than 0.7 coffee, such as 〇3 and above, and still according to the teachings of 4,301,033 81 An apparently bulky catalyst support because we believe that the amount of platinum supported is proportional to the apparent bulk density of the support. It is expected that the cocatalyst and additives will increase the effectiveness of the catalyst. Further, if the catalyst contains more reduction With platinum, the reaction temperature can be reduced even more by 93537.doc • 15 - 1343835. It is also advantageous in the context of the present invention to operate other platinum group metals in the second and third columns of Group VIII of the Periodic Table of the Periodic Table of the Reduction. Finally, it is contemplated that the catalyst of the present invention can be regenerated in situ by removing carbon by known methods. The following examples are given to illustrate and not to limit the invention.

Example I The catalyst of the present invention was prepared in the following manner. 1 ml of a 4.5 wt% hydrogen platinum acid solution was mixed in a flask and stirred for 1 hour. The hydrogen platinum acid solution contained 20% by weight of platinum and 0.69% by weight of thio-fric acid in deionized water. The solution was aged at room temperature for 48 hours and then adjusted to a volume of 600 ml with deionized water. 500 ml of active oxidized pellets were poured into a flask of the aged hydrogen-based acid solution having an apparent bulk density of 0.40 g/ec, a compressive strength of 8.0 kg (17 lbs), and a thickness of 32 mm. The average diameter and the BET surface area of 165 m2/g. The flask was attached to a rotary hair dryer and immersed in a boiling water bath to evaporate the solution under a slight vacuum for 1 hour under rotation. It was then placed in an air flow oven at i5. The impregnated balls were dried for 2 hours under 匸 (3〇2卞) and oxidized for a few hours at 5 〇〇 (932 °F) in the same oven. The oxidized spheres were then charged to a reduction reactor at 2 Torr under a stream of nitrogen. Heat under 卞 (392 卞) for 1 hour. The gas stream was converted from nitrogen to hydrogen and was at 5 Torr. Heat under 卞 (932 卞) for 1 hour. The reactor was then cooled to below. c (392 ΐ) and the gas stream is converted from gas to nitrogen. The catalyst prepared to be charged into the oxidation reactor had a platinum content of 0.45% by weight and all of the platinum was in a reduced state.

Example II Figure 2 shows the performance of this new catalyst having a reduction of 93537.doc -16 - 1343835 compared to the performance of a conventional platinum catalyst which has not been reduced. Figure 2 plots the percentage of hydrocarbon conversion versus temperature. Each of the catalysts was tested in a fully integrated ssp demonstration in which the initial intrinsic viscosity of the 907 kg (l mock) alkaline pET resin from 〇58 d per day was increased to 〇.8〇(1)仏 to 〇81 The ultimate intrinsic viscosity of dl/g. The ssp process comprises a reaction zone through which a 43 kg/hr to 45 kg/hri basic granular resin is lifted at 25 kg/hr nitrogen at 21 Torr (4HTF). The nitrogen used is then heated by electric power and sent to either of the two test reactors containing a conventional catalyst and a catalyst of the present invention. The gas velocity corresponds to a gas hourly space velocity (GHSV) of 5 hr-1 in the catalytic reactors. The gas leaving the reactor was cooled by heat exchange to 60 ° C (140 ° F) 'de-water' and sent to a dehydration dryer containing molecular sieves and dried to a gas dew point below -60 C (-76 F). In all cases, the reaction was controlled to a stoichiometric level of less than 10 ppm oxygen by controlling the oxygen analyzer to add clean, dry air to the reaction vessel. An online hydrocarbon analyzer is used to monitor the conversion process. The alkaline PET resin is a copolymer of pet and isophthalate suitable for the container. These properties are as follows: Intrinsic viscosity of the intrinsic resin, ASTM D-4603 (dl/g) 0.58 to stearic acid and ethylene glycol (% by weight) 96.8 diethylene glycol (% by weight) 1.4 dibasic dicarboxylic acid (% by weight) 1.8 Record (ppm) 245 峨 (ppm) 14 Particle size (mg / particle) 14 93537.doc -17- 1343835 The catalyst of the present invention achieves better smoke conversion at lower temperatures than conventional catalysts without reducing platinum rate. The curve shows that the catalyst of the present invention achieves a complete hydrocarbon conversion rate other than 丨〇ppm when it exceeds only 21 0 C (4 1 Torr), and reaches 1 ppm except just over 240° (: (464 卞)). Complete hydrocarbon conversion rate. The temperature of the conventional catalyst to obtain the same hydrocarbon conversion rate is just 290 (: (554 ?) and 3 10 (: (590 卞) respectively. The catalyst of the present invention is at 270\: (518F) achieves full conversion without residual hydrocarbons. Therefore, when higher rotation is required

The catalyst can be operated at temperatures above 25 Torr (482 times) when the rate of activity or activity is reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a polymerization flow chart in which the present invention can be used. Figure 2 is a graph comparing the performance of a conventional catalyst with the catalyst of the present invention. [Main component symbol description]

12 Feed hopper 16, 22, 32 Control valve 18 Flow bed pre-crystallizer 24 First crystallizer 28 First crystallizer 34 Polymerization reactor 40 Disperser 44 Recirculation route 46 Crystallizer route 53 Combined recirculation route 54 Filter 93537.doc -18- 1343835 58 Oxidation reactor 60 Circulation route 62 Dryer 66 Heater 93537.doc

Claims (1)

Patent Application No. 09ρ14929 Shenwen Qingyuan Patent Range Replacement (April 100) A+, Patent Application Range: 1. A method for removing organic impurities from the polymerization reactor after removing the polymerization reactor, including Purification to add oxygen or an oxygen-containing gas to the gas stream; in the oxidation reactor, the catalyst is flowed with the inclusion metal at a temperature below the 盥? In contact with, the (iv) agent comprises 0" 0% by weight of the pin' of at least 70% by weight in a reduced state, and the amount of oxygen added is substantially stoichiometric with respect to the organic impurities: The gaseous effluent of the reactor contains no more than 250 ppm oxygen; and the gaseous effluent is recycled to the polymerization reactor. &A method of claim 1, characterized in that the polymerization reactor is a solid state polycondensation or polymerization reactor for an aromatic polyester resin. The method of claim 1 or 2 is characterized in that it is impregnated on the catalyst by a method of claim 1 or 2, characterized in that at least 9% by weight of the metal is in a reduced state. The method of claim 1 or 2, characterized in that the reaction temperature is not higher than. The method of claim 1 or 2 is characterized in that the inert gas is nitrogen or includes nitrogen. A method of month length 1 or 2, characterized in that the carrier is activated alumina. 8. For example. The method of claim 1 or 2, characterized in that the catalyst comprises from 1% by weight to 2.0% by weight of the face. 9. The method of claimant or 2, wherein the platinum is dispersed on the surface of the catalyst 93537-10004i4.d〇c 1343835. The method of claim 1 or 2, wherein the effluent from the reactor contains no more than 100 ppm oxygen. 93537-1000414.doc -2- S