Method for revamping a propylene plant

Abstract

A method of revamping a bulk loop reactor propylene plant by incorporating a gas phase reactor with high capacity.

Description

Technical Field

[0001] This invention relates to a method for retrofitting existing propylene equipment. Background Technology

[0002] Numerous propylene polymerization plants operating worldwide utilize various bulk processes to produce polypropylene. For example, the Spheripol process, a bulk slurry process, can be mentioned. In a typical Spheripol configuration, two series-connected loop reactors are optionally connected to at least one downstream gas-phase reactor, which is relatively small. A typical plant combines two loop reactors with a capacity of x tons / hour with a gas-phase reactor with a capacity of 1 / 10x tons / hour. Such configurations are limited to a total capacity of approximately 11 / 10x tons / hour. For example, if the loop reactors produce a total of 20 tons / hour, the additional gas-phase reactor will produce an additional 2 tons / hour, resulting in a total output of 22 tons / hour. Clearly, the capacity is even lower when using only one loop reactor. Generally, larger plants consume less energy to produce each tonne of polymer. Therefore, larger plants with higher capacities are generally desirable. To increase capacity, the loop reactors can be enlarged. This can be done by enlarging the legs of each loop reactor or by adding additional legs to one or both reactors. After scaling up the reactor, steps such as monomer purging and catalyst deactivation must also be debottlenecked to maintain the same purity of the polymer product.

[0003] For example, conventional modifications to existing bulk propylene polymerization processes may include increasing the catalyst feed capacity, increasing the propylene feed capacity, increasing the size of the loop reactor, particularly increasing the length of the heat transfer area, increasing the volume of the drying vessel, and increasing the capacity of the recovery compressor, pump, and scrubber.

[0004] All of the above items refer to the removal and replacement of devices, piping, and instruments in existing equipment. In any case of a major retrofit project, the downstream finishing section (i.e., the homogenization (extruder) section and the granulation section) should also be debottlenated.

[0005] Regardless, the retrofit must be carried out during a complete shutdown, which will be much longer and more complex than normal maintenance and project turnaround. Understandably, a complete shutdown allows for the replacement of pumps and piping, but it has the disadvantage of requiring excessive downtime. Another issue is catalyst mileage. Conventional polypropylene polymerization equipment typically exhibits a fairly limited catalyst mileage, which should be addressed during the retrofit of existing equipment.

[0006] Therefore, there are some problems with retrofitting such existing propylene polymerization equipment. Summary of the Invention

[0007] This invention provides a method for retrofitting existing propylene polymerization equipment, wherein the existing propylene polymerization equipment includes at least one bulk loop reactor, more preferably two bulk loop reactors connected in series, and an optional gas-phase reactor, thereby giving the existing bulk reactor a total capacity of x tons / hour. The method includes,

[0008] A new gas-phase reactor is provided adjacent to the existing propylene polymerization plant, the new gas-phase reactor having a capacity of at least 0.8x tons / hour, more preferably 0.9x tons to 1.2x tons / hour.

[0009] A new gas-phase reactor with a capacity of at least 0.8x tons / hour, preferably 0.9x tons to 1.2x tons / hour, will be connected to a loop outlet; and

[0010] A deactivation and degassing unit is provided downstream of the new gas phase reactor.

[0011] The provision of a deactivation and degassing unit downstream of the new gas-phase reactor is known in the prior art. Retrofitting refers to any activity that modifies existing equipment.

[0012] Providing a new gas phase reactor typically equates to constructing a new gas phase reactor adjacent to existing equipment. Existing equipment can continue operating during such construction work. Once construction is complete, the existing gas phase reactor, along with any other optional units such as high-pressure flash evaporators, low-pressure flash evaporators, steam generators, and dryers with scrubbers, can be easily switched to the new gas phase reactor using a three-way valve or similar device, at least temporarily halting operation.

[0013] Having "at least 0.8 x tons / hour capacity" means that the capacity of the new gas-phase reactor is at least 0.8 times the total capacity of the existing bulk loop reactors, which is, for example, the total capacity of the existing bulk loop reactors when there is only a single bulk reactor; or the total capacity of the two existing loop reactors when there are two loop reactors (e.g., two loop reactors connected in series). The same applies when there are more than three bulk reactors. The capacity of any potential gas-phase reactors is not considered.

[0014] Preferably, the deactivation and degassing unit downstream of the new gas phase reactor includes a product receiving tank (7), a purge chamber (8), a propylene nitrogen recovery unit (9), a distillation column (11), and a vapor recovery pipeline (38).

[0015] The distillation column (11) is preferably connected to the reflux recovery feed container (12), which is connected to the vapor recovery line (38).

[0016] More preferably, the method includes providing a product discharge container (6) downstream of the new gas-phase reactor (3) and upstream of the product receiving tank (7). Such a product discharge container (6) significantly improves the single-pass conversion rate (single pass) of the polymerization equipment. The solids concentration in such a discharge container increases compared to a setup without such a container. The density shift of the fluidized bed relative to the moving bed results in a significant reduction in the discharged gas. Therefore, the need for compression is reduced.

[0017] On the other hand, the method according to the invention includes providing a product receiving tank (7) connected to the tower (7) via a compressor (10) therebetween.

[0018] On the other hand, the distillation column (11) is preferably connected to a reflux recovery feed container (12), which is connected to a vapor recovery line (38). This configuration allows for the separation of propylene from, for example, oligomers, the recirculation of vaporized propylene through the vapor recovery line (38) to the new gas phase reactor (3), and optionally, the recirculation of a portion of the condensed propylene (45) to the propylene feed tank via a propylene-propane separator. The described configuration is particularly advantageous for the production of atactic polypropylene copolymers.

[0019] A further feature of the method according to the invention is that the downtime for conversion from existing equipment is extremely short: the conversion from existing propylene polymerization equipment to modified propylene polymerization equipment preferably does not involve downtime of more than 24 hours.

[0020] In an additional and preferred aspect, the method according to the invention enables an increase in single-pass conversion and / or an increase in catalyst life and / or an increase in the output of existing propylene polymerization equipment.

[0021] In a particularly preferred aspect, the method according to the invention comprises:

[0022] -A deactivation and degassing unit downstream of the new gas phase reactor, comprising a product receiving tank (7), a purge chamber (8), a propylene nitrogen recovery unit (9), a distillation column (11), and a vapor recovery line (38), and the method further comprising providing:

[0023] -The product discharge container (6) is located downstream of the new gas phase reactor (3) and upstream of the product receiving tank (7), and further wherein,

[0024] - The product receiving tank (7) is connected to the distillation column (11) via a compressor (10) therebetween, and wherein

[0025] - The distillation column (11) is connected to a reflux recovery feed container (12), wherein the reflux recovery feed container (12) is connected to a vapor recovery line (38).

[0026] Therefore, in a preferred aspect, the present invention relates to the use of methods as described herein, and more particularly to methods as described above for increasing single-pass conversion, and / or increasing catalyst life and / or increasing the output of existing propylene polymerization equipment.

[0027] In a preferred aspect, the modified propylene polymerization equipment is suitable for producing atactic polypropylene copolymers and / or polypropylene homopolymers. In another aspect, existing polypropylene equipment is suitable for producing heterogeneous polypropylene copolymers. Attached Figure Description

[0028] The present invention will be discussed in more detail with reference to the illustrations.

[0029] A typical existing polypropylene plant to be modified (as described in Ullmann's Polymers and Plastics: Products and Processes 2016, Wiley-VCH, Weinheim ISBN: 978-3-527-33823-8 (page 951)) comprises two loop reactors and an optional gas-phase reactor. After polymerization in the loop reactors, the polymer is separated from the liquid propylene by flashing propylene under high pressure, allowing the flashed propylene to be condensed in a heat exchanger using cooling water. The polymer is then transferred from the high-pressure flash tank to downstream low-pressure degassing, a steam-based deactivation step, and a drying step.

[0030] Alternatively, the polymer is first guided from the high-pressure flash evaporator to the gas-phase reactor, and then the product from the gas-phase reactor is discharged to a low-pressure degassing step. In such a typical existing polypropylene plant, the gas-phase reactor connected by the flash evaporator is usually of limited capacity, meaning the total capacity of the plant is mainly determined by the total capacity of the loop reactor.

[0031] Figure 1 This is a schematic diagram of the modified propylene equipment according to the present invention.

[0032] Figure label:

[0033] 20: Feed line to the prepolymerization reactor

[0034] 0: Prepolymerization reactor

[0035] 1: First loop reactor

[0036] 21: Propylene feed line to the first loop reactor

[0037] 31: Comonomer feed line to the first loop reactor

[0038] 41: Hydrogen feed line to the first loop reactor

[0039] 24: First feed line

[0040] 25: Loop reactor connection pipeline

[0041] 2: Second loop reactor

[0042] 22: Propylene feed line to the second loop reactor

[0043] 32: Comonomer feed line to the second loop reactor

[0044] 42: Hydrogen feed line to the second loop reactor

[0045] 26: Direct feed line to the gas phase reactor

[0046] 3: Gas phase reactor

[0047] 4: Circulating gas compressor

[0048] 27, 28: Gas circulation pipelines

[0049] 23: Propylene feed line to the gas circulation line

[0050] 33: Comonomer feed line to the gas circulation line

[0051] 43: Hydrogen feed line to the gas circulation line

[0052] 29: Gas phase reactor outlet pipeline

[0053] 5: Circulating gas cooler

[0054] 13: Closed-loop chilled water pump

[0055] 14: Closed-loop chilled water heat exchanger

[0056] 29: Gas phase reactor outlet

[0057] 6: Product discharge container

[0058] 34, 34': Product receiving tank feed pipeline

[0059] 7: Product receiving tank

[0060] 35: Purge bin feed line

[0061] 8: Purge the warehouse

[0062] 36: Product Export

[0063] 9: Propylene Nitrogen Recovery Unit

[0064] 46: Propylene Nitrogen Recovery Unit Feed Pipeline

[0065] 47: Tower supply pipeline

[0066] 48: Nitrogen refeed line

[0067] 49: Exhaust pipe

[0068] 10: Gas recovery compressor

[0069] 11: Tower

[0070] 50: Piping connecting the product receiving tank and the gas recovery compressor

[0071] 45: Oligomer Export

[0072] 12: Recycled feed container

[0073] 38: Steam recovery line to the gas phase reactor

[0074] 39: Other recycling pipelines

[0075] 44: Condensed propylene recovery pipeline to the feed tank Detailed Implementation

[0076] The operation of the equipment shown in Figure 2 is briefly described below. Prepolymerization takes place in prepolymerization reactor 0, where reactants are fed into the prepolymerization reactor via feed line 20. Prepolymerization intermediates are conveyed to the first loop reactor (1) via the first feed line (24). Polymerization takes place in loop reactors (1, 2) via propylene, comonomers, and chain transfer agents (e.g., hydrogen) fed through feed lines 21, 31, 41, 22, 32, 42. Intermediates from the second loop reactor are fed into the gas phase reactor (26) via a direct feed line. A "direct feed line" indicates that there is no flash evaporator or similar unit.

[0077] It should be understood that there is no flash unit downstream of the loop reactor and upstream of the new gas phase reactor.

[0078] The new gas phase reactor (3) operates by upward flow using a circulating gas compressor (4), gas circulation lines (27, 28) and a circulating gas cooler (5). The circulating cooler has a closed cooling water loop, which is connected to the cooling system of the entire equipment site via a closed loop chilled water heat exchanger (14).

[0079] The gas recirculation line (28) or alternatively, the gas recirculation line (27) is connected to the vapor recovery line (38). The vapor recovery line (38) allows non-condensable materials, including propylene, hydrogen, and optionally comonomers, to be recycled back into the gas phase reactor. Surprisingly, this connection has been found to be particularly advantageous for the production of atactic polypropylene copolymers. The main reason is likely the higher propylene content in the gas phase during the production of atactic propylene copolymers.

[0080] The emissions from the gas phase reactor enter the product discharge container (6) through the gas phase reactor outlet (29), and further enter the product receiving tank (7) through the product receiving feed line (34) or directly through the product receiving feed line (34'), and further enter the purge chamber (8) through the purge chamber feed line (35). The product receiving tank (7) is connected to the gas recovery compressor (10) through a line (50). The purge chamber (8) is further connected to the propylene nitrogen recovery unit (9). Nitrogen can be fed from the propylene nitrogen recovery unit (9) to the purge chamber (8) through the nitrogen refeed line (48). The product is sent to further downstream processing, such as granulation, through the product outlet (36).

[0081] The recovery unit also includes a distillation column (11) and a loop connected thereto, including an oligomer outlet (45). The distillation column (11) is connected to a reflux recovery feed container (12), which further facilitates propylene recovery and recycling via a vapor recovery line (38) and a condensable recovery line (44).

[0082] Experimental Section

[0083] Comparative example CE1 is constructed using only two loop reactors connected in series.

[0084] The production rate of the random polypropylene copolymer is 90 kg / h. The polymer is removed from the second loop reactor through a flash tube to a high-pressure flash evaporator, where propylene is flashed under high pressure and fed through a scrubber to a recovery unit, condensed, and recycled to a feed tank. The polymer is then fed to a low-pressure bag filter and gravity-fed to a steam generator and dryer.

[0085] A fluidized bed-type gas-phase reactor with a residence time of approximately two hours and a capacity greater than 90 kg / hour is constructed adjacent to existing equipment (such as that used in CE1).

[0086] The polymerization of the invention is carried out by directly redirecting the reaction stream from the second loop reactor to a newly constructed gas-phase reactor.

[0087] like Figure 1As shown, the product receiving tank (7), purge chamber (8), propylene nitrogen recovery unit (9), distillation column (11), and vapor recovery line (38) are used instead of the product discharge container (6) downstream of the new gas phase reactor (3) and upstream of the product receiving tank (7), from which... Figure 1 The polymer is recovered in the new gas-phase reactor shown.

[0088] The advantages of the method according to the invention are: the total output is doubled to 180.9 kg per hour, and the catalyst life is increased by 60%. Furthermore, the single-pass conversion rate is increased from 55% to 80%.

[0089] Invention Example 2. Polymers are recovered by using an additional product discharge container (6) downstream of the new gas phase reactor (3) and upstream of the product receiving tank (7). Building on the advantages of IE1, the single-pass conversion rate is increased to 90%, which means a significant reduction in the load on the gas recovery compressor.

[0090] Comparative Example 2: Polypropylene homopolymer was produced on a single loop reactor and fed through a flash line to a high-pressure flash evaporator and a downstream low-pressure flash evaporator, followed by feeding into a steam chamber and a drying fluidized bed. The polymer was then fed into a finishing section, where additives were fed during extrusion and the polymer was granulated.

[0091] Example 3: Polypropylene homopolymer is produced on a single loop reactor and the polymer slurry is fed directly into a gas-phase reactor for a residence time of approximately two hours. Propylene polymerization continues in this gas-phase reactor, and as shown in Figure 2, the homopolymer is recovered from the gas-phase reactor, but the product discharge container (6) downstream of the new gas-phase reactor (3) and upstream of the product receiving tank (7) is not used.

[0092] The advantages of Invention Example 3 are: the total output is doubled to 120.6 kg per hour, and the single-pass conversion rate of propylene monomer increases from 61% to 80%.

[0093] Table 1 shows the conditions and one-way conversion rate.

[0094]

[0095] Table 2 Comparison of catalyst efficiencies for different configurations.

[0096]

Claims

1. A method for retrofitting existing propylene polymerization equipment, wherein the retrofitted propylene polymerization equipment is suitable for producing atactic polypropylene copolymers and / or polypropylene homopolymers, and the existing propylene polymerization equipment includes at least one bulk loop reactor. Thus, the at least one bulk loop reactor has a total capacity of x tons / hour; the method includes, A new gas-phase reactor (3) is provided adjacent to the existing propylene polymerization plant, the new gas-phase reactor (3) having a capacity of at least 0.8 x tons / hour. The new gas-phase reactor, having a capacity of at least 0.8 x tons / hour, is directly connected to the loop outlet via a direct feed line (26) to the new gas-phase reactor; and A deactivation and degassing unit is provided downstream of the new gas phase reactor; in, The deactivation and degassing unit downstream of the new gas phase reactor includes a product receiving tank (7), a purge chamber (8), a propylene nitrogen recovery unit (9), a distillation column (11), and a vapor recovery pipeline (38). The product receiving tank (7) is connected to the distillation column (11) via a compressor (10) therebetween. The distillation column (11) is connected to a reflux recovery feed container (12), wherein the reflux recovery feed container (12) is connected to the vapor recovery line (38), which enables non-condensable materials including propylene, hydrogen and comonomers to be recycled back to the gas phase reactor.

2. The method as described in claim 1, wherein, The existing propylene polymerization equipment includes two body loop reactors connected in series, thereby giving the two body loop reactors a total capacity of x tons / hour.

3. The method as described in claim 1, wherein, The method includes providing a product discharge container (6) downstream of the new gas phase reactor (3) and upstream of the product receiving tank (7).

4. The method according to any one of claims 1-3, wherein, The conversion from existing polypropylene equipment to upgraded polypropylene equipment does not involve downtime of more than 24 hours.

5. The method according to any one of claims 1-3, wherein, The method is used to increase single-pass conversion, and / or increase catalyst lifespan, and / or increase the output of existing polypropylene equipment.

6. The method according to any one of claims 1-3, wherein, There is a gas circulation line (28) or an alternative gas circulation line (27) and a vapor recovery line (38), the gas circulation line (28) or the alternative gas circulation line (27) being connected to the vapor recovery line (38).

7. The method according to any one of claims 1-3, wherein, The new gas phase reactor (3) has a capacity of 0.9 x tons to 1.2 x tons / hour.

8. The method according to any one of claims 1-3, wherein, There is no flash stage downstream of the loop reactor and upstream of the new gas phase reactor.

9. The method of any one of claims 1-3 is used to increase the single-pass conversion rate relative to the single-pass conversion rate of existing polypropylene equipment.

10. Use of the method according to any one of claims 1-3 for increasing catalyst lifespan.

11. The method of any one of claims 1-3 is used to increase the output of existing propylene polymerization equipment.

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