Process for the preparation of a polyester for bottles and the reaction apparatus thereof

Abstract

This invention discloses a method for preparing bottle-grade polyester and its reaction equipment. The method uses terephthalic acid and ethylene glycol as main raw materials, and adds isophthalic acid, 1,4-cyclohexanediol, and 2-methyl-1,3-propanediol as polyester modifying monomers. Through continuous esterification and melt polymerization reactions, a polyester melt with an intrinsic viscosity higher than 0.65 dL / g is obtained. Then, after granulation, residual heat crystallization, and temperature equilibration, low-temperature formaldehyde removal is performed, reducing particle acetaldehyde to below 1.0 μg / g and the intrinsic viscosity to above 0.80 dL / g. This invention features superior color, narrow molecular weight distribution, fewer small molecules in the finished product, low crystallinity (polyester crystallinity below 50%), melting enthalpy less than 55 J / g, particle internal and external viscosity difference less than 0.01 dL / g, dust content less than 10 μg / g, initial melt plasticizing temperature less than 205℃, narrow molecular weight distribution, and non-acetaldehyde small molecule content in the finished product less than 0.5 μg / g.

Description

Technical Field

[0001] This invention relates to a method for preparing polyester and its reaction equipment, and more particularly to a method for preparing bottle-grade polyester and its reaction equipment. Background Technology

[0002] Currently, the resin used for transparent outer packaging materials on the market is generally bottle-grade polyester. Bottle-grade polyester is made by mixing ethylene glycol (EG) and terephthalic acid (PTA) in a certain molar ratio to form a slurry. The slurry undergoes an esterification reaction under specific temperature and pressure, and then undergoes pre-condensation and final condensation to produce isophthalic acid-modified polyethylene terephthalate (PET). The intrinsic viscosity of basic bottle-grade PET is generally 0.62 dL / g, and then the intrinsic viscosity of PET is increased to above 0.80 dL / g through solid-phase thickening (SSP). Currently, the mature process for producing bottle-grade polyester is solid-phase viscosity enhancement technology. Representative companies include Bühler (Switzerland), Sinco (Italy), Contex (USA), and Yizheng Chemical Fiber (China). This technology uses hot nitrogen / air to remove small molecules from PET solid particles, thereby increasing the intrinsic viscosity of PET. However, this technology has problems such as high energy and material consumption, uneven molecular weight distribution of PET products, and a lot of dust. In particular, when using 1,4-cyclohexanediethanol (CHDM) for modification, the high-temperature dealdehydeization environment can easily cause CHDM thermal degradation, resulting in yellowing of the color.

[0003] Patent CN 101842208A discloses a method and equipment for preparing low-hydrolysis polyester particles from high-viscosity polyester melt. It uses a high-viscosity polyester melt with a degree of polymerization of 132-165, and prepares low-hydrolysis polyester through underwater granulation, drying, pre-drying, and small molecule removal. The residence time in the pre-drying equipment is at most 8 minutes, and the reaction temperature and residence time in the small molecule removal equipment are 150-180℃ for 6-12 hours. However, in actual verification, the process cannot meet the technical requirement of small molecules being below 1.0 μg / g. Furthermore, this technology uses air atmosphere removal, but polyester particles undergo thermo-oxidative degradation under air atmosphere conditions above 150℃. This degradation leads to yellowing of the polyester particles and breakage of macromolecular chains, resulting in a decline in various properties of the polyester.

[0004] Patent CN 103140337 A discloses a method for increasing the molecular weight of polyester granules using the residual heat. This invention relates to increasing molecular weight by combining latent heat granulation with polyester heat treatment. This newly developed method allows for direct integration of solid post-condensation (SSP) with underwater granulation. The method differs from conventional solid post-condensation in that it increases molecular weight solely using the residual heat and heat of crystallization obtained during the process, without additional heat input. A key feature is improved water separation and dehumidification during granulation. This is the only way to ensure increased viscosity in the presence of small granules with an average particle weight of no more than 20 mg. However, the patent describes directly conveying the granulated particles to an acetaldehyde removal device after passing them through a vibrating screen, without addressing how to solve the problem of sticky crystallization of the granulated particles. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for preparing bottle polyester with excellent color, narrow molecular weight distribution, fewer small molecules in the finished product, and low crystallinity; another purpose of this invention is to provide a reaction equipment for preparing bottle polyester that reduces energy consumption in bottle polyester production, improves the quality of bottle polyester products, enhances processing performance, and achieves green and low-energy consumption.

[0006] Technical solution: The preparation method of bottle-grade polyester of the present invention includes the following steps:

[0007] (1) A polyester melt is prepared by esterification, prepolymerization and final polymerization of raw materials composed of phthalic acid, ethylene glycol and polyester-modified monomers.

[0008] (2) The polyester melt is subjected to underwater granulation, residual heat crystallization and temperature equilibration to obtain polyester particles with small molecules removed from the particles.

[0009] (3) Polyester particles are dealdehyded by high-efficiency boiling flow to obtain the product.

[0010] Furthermore, step (4) involves removing dust and cooling the polyester particles after formaldehyde removal to remove foreign matter from the polyester particles.

[0011] Further, in step (1), the polyester-modifying monomer accounts for 0.2-9.0% of the polyester melt by mass, and the polyester-modifying monomer is a mixture of isophthalic acid, 1,4-cyclohexanediol and 2-methyl-1,3-propanediol in a mass ratio of 0.2-2.0:0-5:0-2.0.

[0012] The main raw materials are terephthalic acid (PTA) and ethylene glycol (EG), with terephthalic acid accounting for (69.3-67.5)% and ethylene glycol accounting for (23.5-30.5)%. Isophthalic acid (IPA), 1,4-cyclohexanediol (CHDM), and 2-methyl-1,3-propanediol (MPO) accounting for (0.2-2.0)% of the melt mass are selected as modifying monomers. This process disrupts the regularity of the PET macromolecular chain, slows down the crystallization rate of bottle polyester during processing, and achieves the purpose of high transparency and high brightness.

[0013] Furthermore, in step (1), the intrinsic viscosity of the obtained polyester melt is 0.70 to 0.78 dL / g, the degree of polymerization is 110 to 135, and the acetaldehyde content in the melt is less than 60 μg / g.

[0014] Furthermore, in step (2), underwater granulation controls the residence time of particles in the transport water to be less than 0.5s, the surface temperature of the particles after leaving the water to be greater than 125℃, and the crystallinity to be greater than 15%.

[0015] Furthermore, in step (2), the residual heat crystallization time is 10 to 60 minutes, and the particle temperature after residual heat crystallization is greater than 160°C, the crystallinity is greater than 30%, and the temperature equilibrium temperature is 170 to 200°C.

[0016] Further, in step (3), the formaldehyde removal tower adopts a high-efficiency particle boiling flow. The particles flow evenly into the boiling bed from the upper part of the distribution. Small holes are opened on the surface of the boiling bed to facilitate the bottom nitrogen to flow out from the bottom up. The nitrogen temperature is equal to or higher than the particle temperature. The particles rely on the nitrogen to boil and flow, and flow into the lower boiling bed from the bed overflow plate. Each boiling bed has a separate hot nitrogen inlet and outlet. After each layer of particles passes through the boiling bed, the acetaldehyde content is reduced compared to the inlet particles. After passing through a certain number of boiling beds, the acetaldehyde content is lower than 1 μg / g. The nitrogen temperature of the formaldehyde removal tower is controlled above 178℃ (below 178℃, the residual EG and its oxides in the particles cannot be effectively removed). The formaldehyde removal temperature of the particles in the formaldehyde removal tower is controlled at 178~200℃, and the residence time is controlled at 20~40h to ensure that the acetaldehyde content in bottled PET products is lower than 1 μg / g.

[0017] To alleviate issues such as the modified monomer's poor heat resistance, susceptibility to thermo-oxidative degradation, and the high amount of small-molecule impurities in the final product, the process after melt polymerization was redesigned. Underwater granulation, residual heat crystallization, temperature balancing, and low-temperature formaldehyde removal were employed to achieve acetaldehyde removal, viscosity increase, and small-molecule removal in bottle-grade PET. The key to mitigating thermo-oxidative degradation, viscosity increase, and small-molecule removal lies in controlling the nitrogen temperature at the bottom of the formaldehyde removal tower above 178℃. Below 178℃, residual EG and its oxides within the particles cannot be effectively removed; above 200℃, the modified monomer continues to generate small molecules through thermo-oxidative degradation. The formaldehyde removal temperature within the tower is controlled between 178 and 200℃, and the residence time is controlled between 20 and 40 hours to ensure that the viscosity and acetaldehyde content of the bottle-grade PET product meet national standards.

[0018] On the other hand, the reaction equipment used in the preparation method of bottle polyester of the present invention includes a final shrinkage reactor, a granulator, a dryer, a waste heat crystallizer, a temperature balancer, and a formaldehyde removal tower connected in sequence. The waste heat crystallizer is connected in sequence to a nitrogen purification and drying system and a nitrogen heating system. The nitrogen heating system is connected to the formaldehyde removal tower, and the formaldehyde removal tower is connected to the waste heat crystallizer. The formaldehyde removal tower adopts a vertical tower structure and has an acetaldehyde removal fluidized bed inside.

[0019] Furthermore, a filter and a melt pump are sequentially connected between the final shrinkage reactor and the granulator.

[0020] Furthermore, it also includes a dust collector connected to the formaldehyde removal tower, and a vibrating screen connected to the dust collector for removing irregularly shaped slices.

[0021] This invention uses terephthalic acid (PTA) and ethylene glycol (EG) as main raw materials, and adds isophthalic acid (IPA), 1,4-cyclohexanediol (CHDM), and 2-methyl-1,3-propanediol (MPO) as polyester modifying monomers. Through continuous esterification and melt polymerization reactions, a polyester melt with an intrinsic viscosity higher than 0.65 dL / g is obtained. Then, after granulation, residual heat crystallization, and temperature equilibration, low-temperature dealdehydeing is carried out. During the dealdehydeing process, the particulate acetaldehyde is reduced to below 1.0 μg / g and the intrinsic viscosity is above 0.80 dL / g.

[0022] The formaldehyde removal tower of this invention adopts a vertical tower structure with an internal high-efficiency acetaldehyde removal fluidized bed. Particles flow evenly into the fluidized bed from the top, and small holes on the surface of the fluidized bed facilitate the upward flow of nitrogen gas from the bottom. The nitrogen temperature is equal to or higher than the particle temperature, causing the particles to boil and flow into the next fluidized bed from the overflow plate. Each fluidized bed has a separate hot nitrogen inlet and outlet. After passing through each fluidized bed, the acetaldehyde content is reduced compared to the inlet particles, and after passing through a certain number of fluidized beds, the acetaldehyde content is below 1 μg / g. If a solid-phase viscosity enhancement process (SSP reactor) is used, the bottle polyester produced using the above formula is prone to sticking due to the decreased melting and crystallization temperature, especially agglomeration under the gravity bed accumulation in the SSP reactor. Experiments have shown that having ≥6 fluidized beds in the formaldehyde removal tower effectively ensures uniform dispersion and prevents agglomeration of the modified bottle polyester particles, while simultaneously improving nitrogen contact efficiency, effectively reducing acetaldehyde content and small molecule content, and increasing the viscosity increase rate.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) It has excellent color, narrow molecular weight distribution, fewer small molecules in the finished product, low crystallinity, polyester crystallinity less than 50%, melting enthalpy less than 55J / g, viscosity difference between the inside and outside of the particles less than 0.01dL / g, dust content less than 10μg / g, initial melting and plasticizing temperature less than 205℃, narrow molecular weight distribution, and non-acetaldehyde small molecules in the finished product less than 0.5μg / g;

[0024] (2) Low energy consumption. Modified monomers are added during the melt polymerization stage to produce melt with intrinsic viscosity higher than 0.65dL / g. Bottle polyester products are produced by underwater granulation, residual heat crystallization and low-temperature dealdehyde thickening. The rheological properties of the particles at the screw processing injection temperature are significantly improved compared with SSP products, and the screw injection temperature can be reduced by more than 10℃.

[0025] (3) The acetaldehyde content of the injection-molded product is reduced by 15% compared with the SSP product, the viscosity of the product is reduced by 24%, and the haze of the product is reduced by 50%, achieving a breakthrough in green, low-energy consumption, and bottle-grade polyester production technology.

[0026] (4) The acetaldehyde content is lower than the national standard of 1.0 μg / g. At the same time, compared with the SSP process, the formaldehyde removal temperature is reduced by 20-50℃, avoiding the thermo-oxidative degradation of modified monomers such as IPA, CHDM, and MPO in a high-temperature nitrogen environment. This effectively reduces the increase in the b-value of bottled polyester products and reduces the generation of impurities other than acetaldehyde in the final product. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention;

[0028] Figure 2 The heating curves of Example 7 and Comparative Example 1 before eliminating thermal history are shown.

[0029] Figure 3 Rheological curves of BG80 and BG80L at low shear rates in Example 7 and Comparative Example 1;

[0030] Figure 4 The rheological curves of BG80 and BG80L at medium shear rates in Example 7 and Comparative Example 1 are shown.

[0031] Figure 5 The relationship between preform viscosity drop and injection temperature in Example 7 and Comparative Example 1;

[0032] Figure 6 The relationship between acetaldehyde content in the preform and injection temperature in Example 7 and Comparative Example 1;

[0033] Figure 7 The spectrum of the bottle-grade polyester produced in Example 5;

[0034] Figure 8 The spectrum of the bottle-grade polyester produced in Example 6;

[0035] Figure 9 The spectrum of the bottle-grade polyester produced in Comparative Example 1;

[0036] Figure 10 The graph is for the direct production of high-viscosity polyester using liquid-phase thickening in Comparative Example 3.

[0037] Figure 11 The spectrum of the bottle-grade polyester produced in Comparative Example 4; Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0039] Colorants are generally added to bottle-grade polyester during the production process, and the amount of colorant added is consistent in the embodiments and comparative examples of this invention.

[0040] Example 1

[0041] like Figure 1 As shown, the reaction equipment used in the preparation of bottle polyester according to the present invention includes a final shrinkage reactor 1, a filter 2, a melt pump 3, a granulator 4, a dryer 5, a waste heat crystallizer 6, a temperature balancer 7, and a formaldehyde removal tower 8 connected in sequence. The waste heat crystallizer 6 is connected in sequence to a nitrogen purification and drying system 9 and a nitrogen heating system 10. The nitrogen heating system 10 is connected to the formaldehyde removal tower 8, and the formaldehyde removal tower 8 is connected to the waste heat crystallizer 6. The formaldehyde removal tower 8 adopts a vertical tower structure and is equipped with an acetaldehyde removal fluidized bed inside. The formaldehyde removal tower 8 is connected to a dust collector 11, which is connected to a vibrating screen 12.

[0042] The method for preparing bottle-grade polyester using the above-described reaction equipment includes the following steps:

[0043] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 67.7% of the melt mass, ethylene glycol accounts for 30.5% of the melt mass and IPA accounts for 1.8% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.65 dL / g.

[0044] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.7g per 100 particles, control the residence time of the particles in the transport water to 0.5s, the surface temperature of the particles after leaving the water is 145℃, and the crystallinity is 26%.

[0045] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 60 minutes, the particles reach 170°C and the crystallinity is 35%.

[0046] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 10 minutes. After a short heating period, the particle temperature is 180°C.

[0047] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 5. The nitrogen temperature in the acetaldehyde removal tower is 178℃, the fluidized particle temperature is 180℃, the residence time is controlled at 35h, and the acetaldehyde content of the outlet particles is 0.9μg / g.

[0048] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.80 dL / g, a product b-value of -2.5, a non-acetaldehyde small molecule content of 0.1 μg / g, a crystallinity of 48%, a melting enthalpy of 55 J / g, a viscosity difference between the inside and outside of the particles of 0.008 dL / g, a dust content of 10 μg / g per ton of product, an initial melt plasticizing temperature of 205℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 10℃ reduction in screw injection molding temperature.

[0049] The acetaldehyde content of the injection-molded product is 4.5 μg / g, the viscosity is 0.77 dL / g, and the haze of the 0.5 mm thick sheet is 2.3%.

[0050] Example 2

[0051] The present invention provides a method for preparing bottle-grade polyester, comprising the following steps:

[0052] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 68.5% of the melt mass, ethylene glycol accounts for 29.0% of the melt mass, IPA accounts for 1.0% of the melt mass, CHDM accounts for 1.0% of the melt mass and MPO accounts for 0.5% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.68 dL / g.

[0053] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.6g per 100 particles, control the residence time of the particles in the transport water to 0.4s, the surface temperature of the particles after leaving the water is 138℃, and the crystallinity is 24%.

[0054] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 60 minutes, the particles reach 168°C and the crystallinity is 33%.

[0055] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 15 minutes. After a short heating period, the particle temperature is 182℃.

[0056] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 6. The nitrogen temperature in the acetaldehyde removal tower is 180℃, the fluidized particle temperature is 182℃, the residence time is controlled at 30h, and the acetaldehyde content of the outlet particles is 0.8μg / g.

[0057] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.82 dL / g, a product b-value of -3.0, a non-acetaldehyde small molecule content of 0.2 μg / g, a crystallinity of 50%, a melting enthalpy of 54 J / g, a viscosity difference between the inside and outside of the particles of 0.009 dL / g, a dust content of 9 μg / g per ton of product, an initial melt plasticizing temperature of 203℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 15℃ reduction in screw injection molding temperature.

[0058] The acetaldehyde content of the injection-molded product is 4.8 μg / g, the viscosity is 0.79 dL / g, and the haze of the 0.5 mm thick sheet is 2.4%.

[0059] Example 3

[0060] The present invention provides a method for preparing bottle-grade polyester, comprising the following steps:

[0061] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 68.0% of the melt mass, ethylene glycol accounts for 27.5% of the melt mass, IPA accounts for 1.5% of the melt mass, CHDM accounts for 2.0% of the melt mass and MPO accounts for 1.0% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.70 dL / g.

[0062] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.5g per 100 particles, control the residence time of the particles in the transport water to 0.3s, the surface temperature of the particles after leaving the water to 125℃, and the crystallinity to 15%.

[0063] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 50 minutes, the particles reach 165°C and the crystallinity is 30%.

[0064] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 20 minutes. After a short heating period, the particle temperature is 185℃.

[0065] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 7. The nitrogen temperature in the acetaldehyde removal tower is 190℃, the fluidized particle temperature is 185℃, the residence time is controlled at 20h, and the acetaldehyde content of the outlet particles is 0.95μg / g.

[0066] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.85 dL / g, a product b-value of -3.2, a non-acetaldehyde small molecule content of 0.1 μg / g, a crystallinity of 46%, a melting enthalpy of 52 J / g, a viscosity difference between the inside and outside of the particles of 0.01 dL / g, a dust content of 5 μg / g per ton of product, an initial melt plasticizing temperature of 201℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 10℃ reduction in screw injection molding temperature.

[0067] The acetaldehyde content of the injection-molded product is 4.6 μg / g, the viscosity is 0.81 dL / g, and the haze of the 0.5 mm thick sheet is 2.1%.

[0068] Example 4

[0069] The present invention provides a method for preparing bottle-grade polyester, comprising the following steps:

[0070] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 67.7% of the melt mass, ethylene glycol accounts for 26.0% of the melt mass, IPA accounts for 1.8% of the melt mass, CHDM accounts for 3.0% of the melt mass and MPO accounts for 1.5% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.72 dL / g.

[0071] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.8g per 100 particles, control the residence time of the particles in the transport water to 0.2s, the surface temperature of the particles after leaving the water to 145℃, and the crystallinity to 30%.

[0072] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 10 minutes, the particles reach 170°C and the crystallinity is 35%.

[0073] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 20 minutes. After a short heating period, the particle temperature is 200℃.

[0074] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 8. The nitrogen temperature in the acetaldehyde removal tower is 205℃, the fluidized particle temperature is 200℃, the residence time is controlled at 22h, and the acetaldehyde content of the outlet particles is 0.60μg / g.

[0075] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.87 dL / g, a product b-value of -3.1, a non-acetaldehyde small molecule content of 0.05 μg / g, a crystallinity of 45%, a melting enthalpy of 50 J / g, a viscosity difference between the inside and outside of the particles of 0.01 dL / g, a dust content of 6 μg / g per ton of product, an initial melt plasticizing temperature of 204℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 12℃ reduction in screw injection molding temperature.

[0076] The acetaldehyde content of the injection-molded product is 4.1 μg / g, the viscosity is 0.82 dL / g, and the haze of the 0.5 mm thick sheet is 2.0%.

[0077] Example 5

[0078] The present invention provides a method for preparing bottle-grade polyester, comprising the following steps:

[0079] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 69.0% of the melt mass, ethylene glycol accounts for 24.5% of the melt mass, IPA accounts for 0.5% of the melt mass, CHDM accounts for 4.0% of the melt mass and MPO accounts for 2.0% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.75 dL / g.

[0080] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.5g per 100 particles, control the residence time of the particles in the transport water to 0.1s, the surface temperature of the particles after leaving the water to 140℃, and the crystallinity to 28%.

[0081] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 30 minutes, the particles reach 167°C and the crystallinity is 32%.

[0082] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 30 minutes. After a short heating period, the particle temperature is 195℃.

[0083] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 5. The nitrogen temperature in the acetaldehyde removal tower is 200℃, the fluidized particle temperature is 195℃, the residence time is controlled at 24h, and the acetaldehyde content of the outlet particles is 0.70μg / g.

[0084] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.87 dL / g, a product b-value of -3.0, a non-acetaldehyde small molecule content of 0.1 μg / g, a crystallinity of 48%, a melting enthalpy of 49 J / g, a viscosity difference between the inside and outside of the particles of 0.009 dL / g, a dust content of 6 μg / g per ton of product, an initial melt plasticizing temperature of 202℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 14℃ reduction in screw injection molding temperature.

[0085] The acetaldehyde content of the injection-molded product is 4.3 μg / g, the viscosity is 0.81 dL / g, and the haze of the 0.5 mm thick sheet is 1.9%.

[0086] Example 6

[0087] The present invention provides a method for preparing bottle-grade polyester, comprising the following steps:

[0088] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 68.7% of the melt mass, ethylene glycol accounts for 24.0% of the melt mass, IPA accounts for 0.8% of the melt mass, CHDM accounts for 5.0% of the melt mass and MPO accounts for 1.5% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.70 dL / g.

[0089] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.7g per 100 particles. Control the residence time of the particles in the transport water to 0.2s. The surface temperature of the particles after leaving the water is 144℃ and the crystallinity is 29%.

[0090] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 10 minutes, the particles reach 160°C and the crystallinity is 30%.

[0091] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 40 minutes. After a short heating period, the particle temperature is 190°C.

[0092] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 5. The nitrogen temperature in the acetaldehyde removal tower is 195℃, the fluidized particle temperature is 190℃, the residence time is controlled at 20h, and the acetaldehyde content of the outlet particles is 0.60μg / g.

[0093] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.81 dL / g, a product b-value of -2.9, a non-acetaldehyde small molecule content of 0.06 μg / g, a crystallinity of 49%, a melting enthalpy of 48 J / g, a viscosity difference between the inside and outside of the particles of 0.007 dL / g, a dust content of 7 μg / g per ton of product, an initial melt plasticizing temperature of 199℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 10℃ reduction in screw injection molding temperature.

[0094] The acetaldehyde content of the injection-molded product is 4.0 μg / g, the viscosity is 0.78 dL / g, and the haze of the 0.5 mm thick sheet is 2.2%.

[0095] Example 7

[0096] The present invention provides a method for preparing bottle-grade polyester, comprising the following steps:

[0097] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 69.4% of the melt mass, ethylene glycol accounts for 25.5% of the melt mass, IPA accounts for 0.1% of the melt mass, CHDM accounts for 3.0% of the melt mass and MPO accounts for 2.0% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.73 dL / g.

[0098] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.6g per 100 particles, control the residence time of the particles in the transport water to 0.05s, the surface temperature of the particles after leaving the water to 150℃, and the crystallinity to 32%.

[0099] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 20 minutes, the particles reach 175°C and the crystallinity is 36%.

[0100] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 30 minutes. After a short heating period, the particle temperature is 180°C.

[0101] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 6. The nitrogen temperature in the acetaldehyde removal tower is 185℃, the fluidized particle temperature is 180℃, the residence time is controlled at 40h, and the acetaldehyde content of the outlet particles is 0.50μg / g.

[0102] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.80 dL / g, a product b-value of -3.3, a non-acetaldehyde small molecule content of 0.08 μg / g, a crystallinity of 48%, a melting enthalpy of 51 J / g, a viscosity difference between the inside and outside of the particles of 0.006 dL / g, a dust content of 6 μg / g per ton of product, an initial melt plasticizing temperature of 195℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a reduction of the screw injection molding temperature by 18℃.

[0103] The acetaldehyde content of the injection-molded product is 4.2 μg / g, the viscosity is 0.78 dL / g, and the haze of the 0.5 mm thick sheet is 2.1%.

[0104] Comparative Example 1

[0105] PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol, and phosphoric acid. PTA accounts for 67.7% of the melt mass, ethylene glycol accounts for 30.5% of the melt mass, and IPA accounts for 1.8% of the melt mass. After pulping, esterification, pre-condensation, and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.60 dL / g.

[0106] Columnar basic particles with a weight of 1.7g per 100 particles were produced using a strip granulation equipment. After being cooled to 50°C, the particles passed through a pre-crystallizer, crystallizer, and preheater in the solid-phase thickening process to reach 215°C before being conveyed to the solid-phase thickening reactor. The particles accumulated in a bed inside the reactor, with nitrogen gas introduced at the bottom and escaping from the top. The nitrogen gas temperature at the bottom was 60°C, and the particle temperature inside the reactor was 220°C. The reaction residence time was 18 hours, and the acetaldehyde content of the outlet particles was 0.80μg / g.

[0107] The final produced bottle-grade polyester has an intrinsic viscosity of 0.80 dL / g, a b-value of -1.5, a non-acetaldehyde small molecule content of 0.8 μg / g, a crystallinity of 55%, a melt enthalpy of 60 J / g, an internal-external viscosity difference of 0.015 dL / g, a dust content of 20 μg / g per ton of product, an initial melt plasticizing temperature of 225℃, an acetaldehyde content of 6.5 μg / g in the injection-molded product, a product viscosity of 0.74 dL / g, and a haze of 5.4% for 0.5 mm thick sheets.

[0108] Comparative Example 2

[0109] PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol, and phosphoric acid. PTA accounts for 69.0% of the melt mass, ethylene glycol accounts for 27.2% of the melt mass, IPA accounts for 0.5% of the melt mass, CHDM accounts for 2.5% of the melt mass, and MPO accounts for 0.8% of the melt mass. After pulping, esterification, pre-condensation, and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.60 dL / g.

[0110] Columnar basic particles with a weight of 1.7g per 100 particles were produced using a strip granulation equipment. After being cooled to 50°C, the particles passed through a pre-crystallizer, crystallizer, and preheater in the solid-phase thickening process to reach 215°C before being conveyed to the solid-phase thickening reactor. The particles accumulated in a bed inside the reactor, with nitrogen gas introduced at the bottom and escaping from the top. The nitrogen gas temperature at the bottom was 60°C, and the particle temperature inside the reactor was 220°C. The reaction residence time was 18 hours, and the acetaldehyde content of the outlet particles was 0.80μg / g.

[0111] The final product has the following intrinsic viscosity for bottle use: 0.80 dL / g, b-value: 0.9, non-acetaldehyde small molecule content: 1.2 μg / g, crystallinity: 55%, melting enthalpy: 60 J / g, particle viscosity difference: 0.014 dL / g, dust content per ton of product: 20 μg / g, initial melt plasticizing temperature: 218℃, acetaldehyde content of the injection-molded product: 6.5 μg / g, product viscosity: 0.75 dL / g, and haze of 6.0% for 0.5 mm thick sheets.

[0112] Comparative Example 3

[0113] PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol, and phosphoric acid. PTA accounts for 69.0% of the melt mass, ethylene glycol accounts for 27.2% of the melt mass, IPA accounts for 0.5% of the melt mass, CHDM accounts for 2.5% of the melt mass, and MPO accounts for 0.8% of the melt mass. After pulping, esterification, pre-condensation, and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.8 dL / g.

[0114] Columnar basic particles with a weight of 1.7g per 100 particles were produced using a strip granulation equipment. The particles were directly conveyed to a solid-phase reactor at 185℃ without cooling. The particles accumulated into a bed inside the reactor. Nitrogen gas was introduced from the bottom and escaped from the top. The temperature of the nitrogen gas at the bottom was 60℃. The temperature of the particles inside the reactor was 185℃. The reaction residence time was 12h. The acetaldehyde content of the particles at the outlet was 0.70μg / g.

[0115] The final product has the following intrinsic viscosity for bottle-grade polyester: 0.81 dL / g, b-value: 0.9, non-acetaldehyde small molecule content: 1.2 μg / g, crystallinity: 50%, melting enthalpy: 52 J / g, particle internal and external viscosity difference: 0.009 dL / g, dust content per ton of product: 8 μg / g, initial melt plasticizing temperature: 199℃, acetaldehyde content of the injection-molded product: 4.9 μg / g, product viscosity: 0.76 dL / g, and haze of 2.7% for 0.5 mm thick sheets.

[0116] Comparative Example 4

[0117] (1) PET bottle-grade polyester is made from terephthalic acid, isophthalic acid, ethylene glycol and phosphoric acid. PTA accounts for 67.7% of the melt mass, ethylene glycol accounts for 30.5% of the melt mass and IPA accounts for 1.8% of the melt mass. After pulping, esterification, pre-condensation and final condensation, the intrinsic viscosity of the final condensation melt is controlled at 0.70 dL / g.

[0118] (2) Use underwater granulation equipment to produce spherical basic particles with a weight of 1.7g per 100 particles, control the residence time of the particles in the transport water to 0.5s, the surface temperature of the particles after leaving the water is 145℃, and the crystallinity is 26%.

[0119] The granulated particles are directly transported to the waste heat crystallization chamber. Under the exothermic effect of the particle core layer and the exothermic effect of crystallization, the particle temperature is increased. After staying in the waste heat crystallizer for 60 minutes, the particles reach 170°C and the crystallinity is 35%.

[0120] The particles exiting the waste heat crystallization chamber are transported to the temperature balancer by the hot nitrogen system. The temperature balancer is a screw-driven type, with a residence time of 10 minutes. After a short heating period, the particle temperature is 175°C.

[0121] (3) The particles are fed into the acetaldehyde removal tower by the temperature balancer. The number of fluidized bed layers in the acetaldehyde removal tower is 5. The nitrogen temperature in the acetaldehyde removal tower is 175℃, the temperature of the fluidized particles is 175℃, the residence time is controlled at 50h, and the acetaldehyde content of the outlet particles is 0.95μg / g.

[0122] The particles leaving the formaldehyde removal tower are cooled by cold air and subjected to a vibrating screen to remove residual dust and irregularly shaped pieces. The final product, bottle-grade polyester, has an intrinsic viscosity of 0.80 dL / g, a product b-value of -2.3, a non-acetaldehyde small molecule content of 5.6 μg / g, a crystallinity of 47%, a melting enthalpy of 54 J / g, a viscosity difference between the inside and outside of the particles of 0.006 dL / g, a dust content of 10 μg / g per ton of product, an initial melt plasticizing temperature of 202℃, a narrow molecular weight distribution, and a low weight-average molecular weight. The rheological properties of the particles at the screw injection molding temperature are significantly improved compared to SSP products, allowing for a 10℃ reduction in screw injection molding temperature.

[0123] The acetaldehyde content of the injection-molded product is 4.6 μg / g, the viscosity is 0.77 dL / g, and the haze of the 0.5 mm thick sheet is 2.5%.

[0124] Table 1. Impact of process parameter variations on product performance and finished product performance.

[0125]

[0126]

[0127] Regarding the effectiveness of the invention, the following is a quality verification study of the related products:

[0128] The performance of BG80 (Comparative Example 1), a water bottle polyester produced using solid-phase viscosity enhancement technology, and BG80L (Example 7), a product produced using the technology of this invention, were compared.

[0129] Table 2 Thermal properties of BG80 and BG80L before eliminating thermal history.

[0130]

[0131] Table 3 Thermal properties of BG80 and BG80L after eliminating thermal history.

[0132]

[0133] like Figure 2 Table 2 shows that both BG80 and BG80L are isophthalic acid (IPA) modified PET copolyesters. With the formulation unchanged, BG80L produced using liquid-phase thickening technology exhibits a lower melt plasticizing initiation temperature Tm0 and melt enthalpy ΔHm, indirectly indicating that the plasticizing temperature can be reduced and the screw torque relatively decreased compared to BG80 during screw processing. Furthermore, two endothermic melting peaks appeared on the DSC spectrum before eliminating the thermal history: the melting point Tm1 formed under the corresponding treatment conditions, and the melting point Tm2 formed under the measured conditions. This is due to the gradual improvement of imperfect crystals as the temperature increases and the time extends. Looking at the differences between Tm1 and Tm2, ​​BG80 uses a solid-phase thickening technology with a reaction temperature greater than 210℃. Under a nitrogen atmosphere, the surface layer of polyester particles thickens at a higher rate than the core layer, resulting in a difference in viscosity between the inside and outside. At the same time, the crystallinity of the surface layer is higher than that of the core layer. In the DSC test, Tm1 is narrow and sharp with a complex peak shape. On the other hand, BG80L uses a new bottle-grade polyester production process. The reaction process is relatively mild, and the difference in crystallinity and viscosity between the inside and outside of the particles is small. Tm1 shows a short and wide distribution.

[0134] As shown in Table 3 after eliminating thermal history, the parameters of BG80L are basically the same, except that its cold crystallization temperature (Tc) is 23°C higher than that of BG80. The reason for this is likely that BG80L achieves a high degree of polymerization during the melt polymerization stage, resulting in a more uniform distribution of molecular chains during liquid polycondensation. In contrast, BG80 uses SSP technology, where EG initially escapes from the outer layer of the particles during solid-state polycondensation. As the residence time increases, EG gradually diffuses from the inside out, resulting in higher viscosity on the particle surface and slightly lower viscosity in the core layer. While the average degree of polymerization is similar, the distribution is wider, leading to a lower cold crystallization peak temperature.

[0135] 3. Molecular weight distribution

[0136] Table 4. Molecular weight distribution of polyester for water bottles produced using two technologies.

[0137]

[0138] As shown in Table 4, BG80L has a lower weight-average molecular weight (Mw), fewer macromolecules in the polymer, more uniform degree of polymerization of molecular chains, and a lower distribution index (PDI). In contrast, BG80, due to the inherent limitations of its solid-phase thickening process, has a higher weight-average molecular weight (Mw), a wider PDI, and poorer melt flowability. This is because increasing the number-average molecular weight of a polymer can be achieved through either high-temperature, short-time methods or low-temperature, long-time methods. Compared to the patented technology, solid-phase thickening involves high temperature and short residence time, resulting in a viscosity increase of over 0.20 dL / g for bottle-grade polyester. The activation energy for the condensation reaction during this process is much greater than the activation energy for small molecule diffusion. The generated small molecules and other byproducts do not have enough time to diffuse, and the difference in reaction rate caused by the concentration of small molecules from the inside to the outside of the chip particles amplifies, leading to a higher weight-average molecular weight and PDI. In contrast, the patented technology uses a gentler reaction temperature, with the weight-average molecular weight primarily increasing in the liquid phase. Therefore, BG80L has lower Mw and PDI even with a relatively consistent number-average molecular weight (Mn).

[0139] 4. Rheological properties

[0140] like Figure 3 As shown in the rheological curves of BG80 and BG80L at low shear rates, BG80L exhibits a higher shear viscosity than BG80 at low shear rates, but its number-average, weight-average molecular weight, and intrinsic viscosity are all lower than those of BG80. This indicates that the BG80L produced by the new process benefits from a narrower molecular weight distribution and more uniform molecular chains. Under the same plasticizing conditions, the melt viscosity decreases less, resulting in a higher apparent shear viscosity. This indirectly demonstrates that appropriately reducing the intrinsic viscosity of BG80L particles can still meet the quality requirements of BG80 produced by the conventional SSP process.

[0141] like Figure 4 As shown in the rheological curves of BG80 and BG80L at medium shear rates, under the condition of screw shear rate, the apparent shear viscosity of BG80 at 290℃ is comparable to that of BG80L at 280℃, demonstrating the processing performance advantages of BG80L due to its low melt plasticizing initiation temperature and low crystallinity. Injection molding manufacturers can appropriately reduce the screw processing temperature to reduce operating energy consumption or increase the screw speed to increase output while keeping the load constant.

[0142] 5. Post-processing performance

[0143] BG80 and BG80L exhibit viscosity reduction and acetaldehyde content reduction in injection molded products at 265–280℃. Figure 5 and Figure 6 As shown.

[0144] BG80L exhibits a 24% decrease in average injection molding viscosity and a 15% decrease in acetaldehyde content in products at 265–280°C compared to BG80, demonstrating superior performance in post-processing applications.

[0145] 6. Changes in small molecules within the finished product particles

[0146] Using headspace gas chromatography, the changes in small molecules within the finished product particles of Examples 5-6, Comparative Examples 1, 3, and 4 were tested at 150°C and a retention time of 30 min. The study found that using low-temperature dealdehyde removal combined with a proprietary dealdehyde removal tower can effectively reduce the thermal degradation of modified monomers and the content of small molecules within the product particles.

[0147] like Figure 7-11 As shown, regardless of whether it's the SSP process or the liquid-phase viscosity enhancement process, the final product will show thermal oxide peaks other than acetaldehyde, indicating that the product has undergone thermo-oxidative degradation and small molecules cannot be removed. Using the process of this invention, at a formaldehyde removal temperature of 178–200°C and a nitrogen atmosphere, the final product only has an acetaldehyde peak, and the modified monomer has not undergone thermo-oxidative degradation.

[0148] Table 5 Test data for the product (packaging box)

[0149]

[0150] As shown in Table 5, compared with the solid-phase thickening process, the process using this patent has lower crystallinity, lower melting enthalpy, less difference in viscosity between the inside and outside, fewer small molecules inside, and better product color. Compared with the direct high-viscosity process of liquid-phase thickening, the product contains no impurities such as modified monomers or polyester thermal oxides. Therefore, the haze of the product prepared by this invention is significantly improved after it is made into an finished product.

Claims

1. A method for preparing bottle-grade polyester, characterized in that, Includes the following steps: (1) The raw materials consisting of phthalic acid, ethylene glycol and polyester-modifying monomers are esterified, pre-condensed and finally condensed to obtain polyester melt; the polyester-modifying monomer accounts for 0.2-9.0% of the polyester melt by mass, and the polyester-modifying monomer is a mixture of isophthalic acid, 1,4-cyclohexanediol and 2-methyl-1,3-propanediol in a mass ratio of 0.2-2.0:0-5:0-2.0; the intrinsic viscosity of the obtained polyester melt is 0.70-0.78 dL / g and the degree of polymerization is 110-135; (2) The polyester melt is subjected to underwater granulation, residual heat crystallization and temperature equilibration to obtain polyester particles with small molecules removed from the particles; (3) Polyester particles are dealdehyded using a high-efficiency boiling flow process. The dealdehydeing temperature is 178~200℃ and the dealdehydeing time is 20~40h, thus obtaining bottle-grade polyester.

2. The method for preparing bottle-grade polyester according to claim 1, characterized in that, It also includes step (4) where the polyester particles after formaldehyde removal are subjected to dust removal and cooling vibration to remove foreign matter from the polyester particles.

3. The method for preparing bottle-grade polyester according to claim 1, characterized in that, In step (1), the acetaldehyde content in the obtained polyester melt is less than 60 μg / g.

4. The method for preparing bottle-grade polyester according to claim 1, characterized in that, In step (2), underwater granulation controls the residence time of particles in the transport water to be less than 0.5s, the surface temperature of the particles after leaving the water to be greater than 125℃, and the crystallinity to be greater than 15%.

5. The method for preparing bottle-grade polyester according to claim 1, characterized in that, In step (2), the residual heat crystallization time is 10~60 min, and the temperature of the particles after residual heat crystallization is greater than 160℃, and the temperature equilibrium temperature is 170~200℃.

Images