CN1688609B - Polymerization reactor with large length-diameter ratio - Google Patents

Abstract

A loop polymerization reactor comprising a loop reaction zone, a continuous take off, and a fluid slurry in the reaction zone. The generally cylindrical wall defines the loop reaction zone. The length of the loop reaction zone and the nominal outside diameter of a generally cylindrical wall define a length to diameter ratio of greater than 250. The reactor may be charged with a fluid slurry comprising olefin monomer reactants, solid polymer particles and a liquid diluent. The concentration of solid polymer particles in the slurry may be greater than 40% by weight based on the weight of said polymer particles and said liquid diluent. Also disclosed is a polymerization process for forming the above fluid slurry by polymerizing at least one olefin monomer in a liquid diluent in the loop reaction zone of the above reactor.

Description

Polymerization reactor with large aspect ratio

related application

This application claims priority to US Provisional Application 60/411,208, filed September 16, 2002, and US Non-Provisional Application 10/251,662, filed September 20, 2002.

federally funded research or development

not available

Microfiche/Copyright Reference

not available

Background of the invention

This invention relates to the polymerization of olefin monomers in liquid diluents.

Addition polymerization is usually carried out in a liquid which is a solvent for the polymer formation. This method was used when high density (linear) ethylene polymers were first produced commercially in the 1950s. It was quickly discovered that a more efficient method of producing such polymers was to conduct the polymerization under slurry conditions. More specifically, the polymerisation technique of choice becomes continuous slurry polymerisation in a loop reactor, the polymerised product being withdrawn for recovery through settling legs operating on the batch principle. This technology is a worldwide success, producing billions of pounds of ethylene polymer each year. This success has resulted in the need to build a smaller number of large reactors than a greater number of small reactors for a given plant capacity.

However, there are two problems with the settling branch. First, they impose "batch" techniques on essentially continuous processes. Each time the settling leg reaches a stage where it "pumps" the accumulated polymer slurry, interfering with the flow of slurry upstream of the loop reactor and downstream of the recovery system. In addition, since it is difficult to maintain the seal of the large-diameter valves that close the settling branch, the valve equipment that is mainly used to periodically close the settling branch and the upstream of the loop reactor and the downstream of the recovery system requires frequent maintenance.

Second, there are many logistical problems with the settling legs as the reactor becomes larger. If the diameter of the tube is doubled, the volume of the reactor is increased by a factor of 4. However, due to the valves involved, the size of the settling legs cannot be easily increased further. As a result, the number of branch pipes required begins to exceed the physical space available.

Despite these limitations, settling legs are still used where the olefin polymer is formed as a slurry in a liquid diluent. This is because olefin polymer slurries in diluent are typically limited to no more than 37-40% unlike bulk slurry polymerizations (i.e., monomers are diluent), where solids concentrations greater than 60% are often obtained (weight) solid. Therefore, it is believed that the settling leg must yield greater than 37-40% of the final slurry product at the settling leg outlet. This is because, as the name implies, settling occurs within the laterals, thereby increasing the solids concentration of the slurry that is eventually recovered as product slurry.

Another factor affecting the maximum solids concentration in a practical reactor is the circulation rate, since a limiting factor in operation is reactor fouling due to polymer build-up in the reactor, the higher the rate for a given reactor diameter Allows for higher solids concentrations.

Two related patents dealing with slurry polymerization loop reactors are US 6,239,235 and 6,204,344, each of which is hereby incorporated by reference in its entirety for a description of the loop reactor and its diameter, length, equipment and operation.

Summary of the invention

One aspect of the invention is a charged loop polymerization reactor comprising a loop reaction zone, a continuous outlet and a fluid slurry disposed in the reaction zone. The ordinary cylindrical pipe wall defines the reaction section of the loop pipe. The length of the reaction section of the loop pipe and the nominal outer diameter of the ordinary cylindrical pipe wall determine an aspect ratio greater than 250. The fluid slurry comprises at least one olefin monomer reactant, solid olefin polymer particles and a liquid diluent. The concentration of solid olefin polymer particles in the slurry is greater than 40% by weight, based on the weight of polymer particles and liquid diluent. The continuous outlet is used to continuously take out the fluid slurry from the reaction section of the loop pipe.

Another aspect of the present invention is a loop polymerization reactor comprising a loop reaction section and a continuous outlet. The ordinary cylindrical pipe wall defines the reaction section of the loop pipe. The length of the loop reaction section and the diameter of the ordinary cylindrical tube wall determine an aspect ratio greater than 1000. The continuous outlet is used to continuously take out the fluid slurry from the reaction section of the loop pipe.

Another aspect of the invention is a process for producing a fluid comprising liquid diluent and solid olefin polymer particles by polymerizing at least one olefin monomer in a liquid diluent in the loop reaction section of a reactor as defined above Slurry Polymerization Process. In the described process, the concentration of solid olefin polymer particles in the slurry is maintained at greater than 40% by weight, based on the weight of polymer particles and liquid diluent. Solid olefin polymer product is withdrawn from the reaction zone by continuously withdrawing a slurry from the reaction zone.

Brief introduction to the drawings

In the accompanying drawings which form a part hereof,

Fig. 1 is the perspective view of loop reactor and polymer recovery system;

Fig. 2 is a sectional view along the line 2-2 of Fig. 1 representing the continuous outlet attachment;

Fig. 3 is a sectional view along line 3-3 of Fig. 2 showing the plunger valve device in the continuous outlet assembly;

Fig. 4 is a sectional view of the tangent position of the continuous outlet assembly;

Figure 5 is a side view of the elbow of the loop reactor showing the settling leg and continuous outlet assembly;

Figure 6 is a cross-sectional view along line 6-6 of Figure 5 showing the orientation of two successive spout assemblies;

Figure 7 is a side view showing another orientation of the continuous spout assembly;

Figure 8 is a sectional view of the impeller mechanism;

Figure 9 is a diagram showing another configuration of the collar, wherein the upper section 14a is a 180 degree semicircle, and the vertical section is at least twice as long as the horizontal section; and

Fig. 10 is a diagram showing a major axis of a horizontal arrangement.

Detailed description of the invention

Surprisingly, it has been found that a continuous outlet for product slurry in an olefin polymerization reaction carried out in a loop reactor in the presence of an inert diluent allows the reactor to be operated at much higher solids concentrations. Commercial production of predominantly ethylene polymers in isobutane diluent typically limits the maximum solids concentration in the reactor to 37-40% by weight. However, it has been found that continuous outlets allow for greatly increased solids concentrations. In addition, the continuous discharge itself also gives an additional increase in solids content compared to the in-reactor concentration of the product withdrawn from the reactor due to the replacement of the continuous discharge attachment, which starts at a more concentrated solids content The slurry is selectively removed from the material layer. Concentrations of greater than 40% by weight are thus possible according to the invention.

Throughout the application, the weight of the catalyst is not much considered because the productivity is extremely high, especially with chromia/silica catalysts.

Also surprisingly, it was found that a more aggressive circulation (with higher solids concentration) could be used. Indeed, solids concentrations greater than 50% by weight can be withdrawn from the reactor through a continuous discharge port by using a more active circulation in combination with a continuous discharge port for the slurry. For example, continuous discharge ports can easily allow operation at 5-6 percent higher; that is, adjustable reactors can easily increase the solids concentration by 10 percent; percent, so that the solids concentration of the reactor exceeds 50%. However, because the continuous outlet is located to withdraw the slurry from a laminar flow in a stream with a higher than average solids concentration, the actual recovered product is about 3 percent higher than the average reactor slurry concentration. Thus, operation can achieve an effective slurry concentration of 55% by weight or higher, ie, 52% on average in the reactor, while actually withdrawing 55% of the components (ie, 3 percentage points higher).

It must be emphasized that in commercial operations, increases in solids concentrations as small as 1 percent are important. So it is important to reach even 41% solids concentration at an average of 37-40% in the reactor; thus reaching above 50% is indeed significant.

The present invention is applicable to any olefin polymerization in a loop reactor using a diluent to produce a product slurry of polymer and diluent. Suitable olefinic monomers are 1-alkenes having up to 8 carbon atoms per molecule and having no branches closer to the double bond than position 4. The invention is particularly suitable for the homopolymerization of ethylene and the copolymerization of ethylene with higher 1-olefins such as butene, 1-pentene, 1-hexene, 1-octene or 1-decene. Particularly preferred are ethylene and 0.01-10 wt%, preferably 0.01-5 wt%, most preferably 0.1-4 wt% higher olefins based on the total weight of ethylene and comonomer. Alternatively, sufficient comonomer may be used to obtain the aforementioned amounts of comonomer added to the polymer.

Suitable diluents (other than solvents or monomers) are well known and include hydrocarbons which are inert liquids under the reaction conditions. Suitable hydrocarbons include isobutane, propane, n-pentane, isopentane, neopentane and n-hexane, with isobutane being particularly preferred.

Suitable catalysts are well known. Particularly suitable are chromia/supports such as silica catalysts such as are broadly disclosed in US 2285721 (March 1958) by Hogan and Banks, incorporated herein by reference.

Referring now to the drawings, Figure 1 shows a loop reactor 10 with reactor piping having a vertical section 12, an upper horizontal section 14, and a lower horizontal section 16, some or all of which typically have cylindrical walls, sections of some length Connected end to end by joints such as elbows to form a complete loop or loop, sometimes called a loop reaction section. These upper and lower horizontal sections define the upper and lower sections of horizontal flow. In this embodiment, each elbow or elbow 20 is smooth, providing a continuous flow path substantially free of internal obstructions.

The reactor tubing may have any suitable inner diameter and any suitable outer diameter to provide a wall thickness sufficient to withstand the pressure of the reactor and support the reactor, and to provide a wall thickness sufficient to allow effective heat transfer. For example, having a nominal outside diameter of 20 inches (0.51 m), 22 inches (0.56 m), 24 inches (0.61 m), 26 inches (0.66 m), 28 inches (0.71 m) or greater or any value in between Diameters of tubing are contemplated. Such tubing may have the inner and outer diameters listed in Table 1, where the outer diameter is nominal and the inner diameter is calculated to withstand the pressure expected in one embodiment of the invention.

The reactor is cooled with a double tube heat exchanger formed by tube 12 and jacket 18 . More heat exchangers can be used in the horizontal section of the reactor if desired or applicable.

The reaction slurry is circulated by an impeller 22 (shown in FIG. 8 ) driven by a motor 24 . As shown in Figure 8, the diameter of the impeller 22 and the impeller enclosed by the casing or reactor wall may be larger than the typical diameter of the piping forming the reactor. This feature is particularly desirable where the loop reactor has a high length/outside diameter ratio, which creates greater resistance to flow around the loop than in lower ratio loops.

Since the volume flow of material through each cross-section of the reactor is substantially the same, the use of larger diameter impellers 22 and larger impeller motors 24 than the typical pipe size used in the loop increases the flow rate through the nominal diameter piping. A high velocity is desirable in order to transport the components of the slurry around the loop in a high length/outer diameter ratio reactor without adding time.

The flow rate of the slurry is also kept high enough to avoid bouncing or settling of solids from the slurry. The beating velocity of the slurry is specified as the minimum flow rate required to avoid beating, which varies with process conditions. For example, the larger the diameter of the reactor, the greater the beating velocity. Furthermore, the greater the proportion of solids in the slurry, the greater the beating velocity. Because high solids content is desirable, one way to maintain flow rates above the beating velocity at high solids content is to use relatively small diameter reactors.

It should also be understood that the reactor loop may have more than one impeller or more than one impeller/motor set in series surrounding the loop. The impellers in tandem may be close together, distributed in an annulus, or arranged in any suitable manner. Existing pump technology is expected to support a reactor of approximately 44,000 or 45,000 gallons (166 or 170 m ³ ), depending on the diameter and configuration of the reactor. This assumes a loop velocity of 32 ft/s (9.75 m/s) is maintained.

Referring to the Figure, the reactive monomers, comonomers (if any) and make-up diluent are fed through lines 26 and 28, respectively, which may enter the reactor directly at one or more locations, or may be combined with the shown The condensed diluent in the recycle line 30 is combined. Catalyst is fed through catalyst feed port 32 which provides a stage (location) for catalyst feed. The elongated hollow attachment for continuous withdrawal of the intermediate product slurry is broadly designated by parameter 34. The continuous outlet mechanism 34 is located at or near the downstream end of one of the lower horizontal loop reactor sections 16 , or near or on the connecting elbow 20 . While continuous discharges are generally preferred, either in general or in part, reactors with settling legs or instantaneous discharges may also be used without departing from certain aspects of the invention.

The continuous outlet attachment is shown at the downstream end of the lower horizontal section of the loop reactor, which section is the preferred location. The location may be in the area near the end in the loop where the flow changes upwards before the catalyst feed point so that fresh catalyst remains in the reactor for the longest possible time before passing through the discharge point. However, continuous spout attachments can also be located on any segment or elbow.

In addition, the reactor section attached to the continuous outlet can have a larger diameter in order to slow down the flow rate, thus further laminar flow, so that the withdrawn product can have an even greater solids concentration.

The continuously withdrawn intermediate product slurry is sent to a high-pressure flash chamber 38 through a conduit 36 . Conduit 36 includes an outer conduit 40 to which heated fluid is supplied that indirectly heats the slurry in flash conduit 36 . Vaporized diluent exits flash chamber 38 via conduit 42 for further processing, the latter comprising condensation by simple heat exchange using recycle condenser 50, and then returned to the loop reactor via recycle diluent line 30 without compression.

Circulating condenser 50 may utilize any suitable heat exchange fluid known in the art under any conditions known in the art. It is preferred, however, to use fluids at economically available temperatures. For this fluid, the desired temperature range is 40-130°F (4-54°C). Polymer particles are removed from high pressure flash chamber 38 via line 44 for further processing by techniques known in the art. Preferably, the polymer particles are sent to a low pressure flash chamber 46 after which they are recovered via line 48 as polymer product. The separated diluent is sent to line 42 by compressor 47 . This high pressure flash design is extensively disclosed in US 4424341 (January 3, 1984) by Hanson and Sherk, hereby incorporated by reference.

Surprisingly, it has been found that the continuous discharge port not only allows for a higher solids concentration upstream of the reactor, but also allows for better operation of the high-pressure flash, whereby most of the diluent withdrawn is flashed off and stored without compression. down cycle. In fact, 70-90% of the diluent can usually be recovered in this way. It should be recognized that this result is due to several reasons. First, flash line heaters work better because the flow is continuous rather than intermittent. In addition, the proportional automatic control valve that regulates the flow rate of the continuous stream out of the reactor has a smaller pressure drop, which means that when the slurry is flashed, it causes a lower temperature drop, allowing for more efficient use of the flash line heater .

Figure 2 shows the elbow 20 with the continuous spout mechanism 34 in more detail. The continuous discharge port mechanism includes a discharge cylinder 52 , a slurry withdrawal line 54 , an emergency shutoff valve 55 , a proportional automatic control valve 58 to regulate flow, and a flush line 60 . The reactor was run under full "liquid". Because of the presence of dissolved monomer, the liquid is slightly compressible so that the pressure of a completely liquid system can be controlled by a valve. The feed rate of diluent is usually kept constant, and the proportional automatic control valve 58 is used to control the speed of the continuous feed port to maintain the total pressure of the reactor within the design set point.

Figure 3, taken along line 3-3 of Figure 2, shows the continuous spout mechanism 34 in more detail. The elbow 20 is an elbow with accessories. As shown, the mechanism described comprises a discharge cylindrical tube 52 connected in this case at right angles to the outer surface of the elbow. A slurry discharge line 54 exits the discharge cylindrical tube 52 . Mounted within the discharge cylindrical tube 52 is a plunger valve 62 which serves two purposes. First, it provides an easy and reliable mechanism for clearing the discharge cylinder should it ever become soiled with polymer. Second, it acts as a simple and reliable shut-off valve for the entire continuous spout assembly.

Figure 4 shows a preferred connection orientation for the discharge cylindrical tube 52 which extends along a tangent to the curved surface of the elbow 20 at a point just before the flow of the slurry becomes upward. This opening in the inner surface is elliptical. To improve the removal of solids, the holes can be enlarged.

Figure 5 shows four situations. First, it represents the angular orientation of the discharge cylindrical tube 52 . The removal of the cylindrical tube is shown at an angle α to a plane (1) perpendicular to the centerline of the horizontal section 16 and (2) at the downstream end of the horizontal section 16 . The angle to this plane is chosen in the downstream direction of the plane. The apex of the angle is the center point of the elbow radius shown in FIG. 5 . Said plane may be referred to as the cross-section of the horizontal section. Here, the angle shown is about 24 degrees. Second, it represents a plurality of successive spout attachments 34 and 34a. Third, it shows one appendage 34 oriented in the vertical centerline plane of the lower section 16, and the other appendage 34a situated at an angle to such plane, as more fully illustrated in FIG. Finally, it represents the combination of a continuous discharge attachment 34 and a conventional settling leg 64 for intermittent discharge (if required).

In another embodiment of the present invention, such a polymerization process is provided. The method comprises: 1) polymerizing at least one olefin monomer in a liquid diluent in a loop reaction section to generate a fluid slurry, wherein the fluid slurry contains liquid diluent and solid olefin polymer particles; 2) The fluid slurry is withdrawn by alternately performing the following steps: a) allowing the fluid slurry to settle into at least one settling section, subsequently withdrawing such settled slurry in batches from the settling section as an intermediate product of the process, and thereafter cutting off the settling and b) thereafter continuously withdrawing a fluid slurry containing withdrawn liquid diluent and withdrawn solid polymer particles as an intermediate product of the process. In step b), during start-up, the reactor conditions may be adjusted to increase the reactor solids content by at least 10%.

As can be seen from the relative dimensions, the continuous outlet cylindrical tube is much smaller than the conventional settling branch. Three 2" (5 cm) ID continuous outlet attachments can take as much product slurry as fourteen 8" (20 cm) ID settling legs. This is important because existing large commercial loop reactors with a production capacity of 15,000-18,000 gallons (57-68 ^m3 ) require six 8-inch (20 cm) settling legs. Increasing the size of the settling leg is undesirable due to the difficulty of making large diameter reliable valves. As previously pointed out, doubling the pipe diameter quadruples the volume and there is not enough room to easily install 4 times as many settling legs. Thus, the present invention enables the operation of larger and more efficient reactors. Reactors of 30,000 gallons (114 ^m3 ) or larger are possible using this method. Typically, the continuous outlet cylindrical tube has a nominal inside diameter of 1 to less than 8 inches (2.5-20 cm). Preferably, they are about 2 to 3 inches (5-7.5 cm).

Fig. 6 is taken along the line 6-6 of Fig. 5, showing the outlet cylindrical pipe 34a connected to the plane forming an angle β to the vertical plane containing the center line of the reactor. This plane may be referred to as the vertical center plane of the reactor. This angle can be chosen from one side of the plane or from both sides, if it is not zero. The apex of the corner is on the centerline of the reactor. As shown in Figure 6, the corners are contained in a plane perpendicular to the centerline of the reactor.

There are three orientation concepts regarding the relationship of the outlet cylindrical tube 34a to the reactor piping. The first is the connection orientation, ie the tangential orientation in Figure 4 and the vertical orientation in Figures 2 or 7 or any angle between these two extremes of 0 and 90 degrees. The second is how far it is oriented relative to the bend connecting the elbow, as indicated by the angle α (Fig. 5). The angle alpha may be 0-60 degrees, but preferably 0-40 degrees, more preferably 0-20 degrees. The third is the angle β from the center plane of the longitudinal section (Fig. 6). This angle may be 0-60 degrees, preferably 0-45 degrees, more preferably 0-20 degrees.

Figure 7 shows an embodiment in which the continuous spout cylinder 52 has a vertical, 0-degree alpha orientation (characteristic because it is still at the end of a straight line segment) and a 0-degree beta orientation, that is, it Perpendicular to the vertical centerline plane of the lower horizontal section 16 .

Figure 8 shows in detail the impeller 22 for moving the slurry along its flow path. As can be seen in this embodiment, the impeller 22 is within a slightly larger housing (relative to the rest of the reactor wall) which acts as the impelling section for the circulating reactants. Preferably, said system has a pressure differential of at least 18 psig (12 N/cm 2 ), preferably at least 20 psig (14 N/cm ² ) between the upstream and downstream ends of the push section in a reactor with a nominal diameter of 2 feet (0.61 m). cm ² ), more preferably at least 22 psig (15 N/cm ² ), with a total flow path length of about 950 feet (290 meters), using isobutane to make primarily ethylene polymer. Up to 50 psig (34 N/ ^cm2 ) or greater is possible. This can be done by controlling the speed of the impeller, reducing the clearance between the impeller and the inner wall of the pump casing, or by using a more active impeller design, as is known in the art. This higher differential pressure can also be generated by using at least one external pump.

Typically, the system is operated so as to produce a pressure drop of at least 0.07, typically 0.07 to 0.15 feet, of slurry height per foot of reactor length for a nominal 24 inch (0.61 meter) diameter reactor (i.e., 0.07 per meter of reactor length). -0.15 m slurry height pressure drop). For a 24-inch (0.61 meter) diameter reactor, it is preferred that this pressure drop be 0.09-0.11 units per unit length. For larger diameters, higher slurry velocities and higher pressure drops are required per unit length of the reactor. This assumes that the density of the slurry is typically about 0.5-0.6 g/ml.

Referring now to Figure 9, the upper section is shown as a 180 degree semicircle, which is the preferred configuration. The vertical segment is at least twice as long as the horizontal segment, typically about 7-8 times as long. For example, the vertical run length may be 190-225 feet (60-69 meters) and the horizontal run length may be 25-30 feet (7.6-9.1 meters). Any number of collars other than four shown here and eight shown in Figure 1 may be used, but typically four or six are used. A reference to a nominal diameter of 2 feet (0.61 meters) implies an internal diameter of about 21.9 inches (0.556 meters). Reactor flow path lengths are generally greater than 500 feet (152 meters), usually greater than 900 feet (274 meters), with about 940-1350 feet (286-411 meters) being quite satisfactory.

Commercial pumps used eg to circulate reactants in closed loop reactors are routinely tested by their manufacturers, and the pressure required to avoid cavitation is readily determined routinely.

Example 1

One embodiment of the invention is a method of using low density metallocene resins with heat transfer limitations. The temperature of the reactor was 175°F (79°C) and the minimum temperature of the coolant at the reactor inlet was 115°F (46°C). Catalyst production is sufficient to maintain the desired high production rate and low ash content, and other conditions are controlled such that the rate of heat transfer is the limiting factor in the production rate. The dimensions of the individual reactors of different nominal diameters are as described above.

In this process, as listed in Table 2, the surface area per unit reactor volume and the production rate (% of non-thermally limited production) decrease with decreasing reactor diameter compared to the production rate for non-thermally limited resin. Increase.

Table 3 lists the effect of the percent solids in the reactor on the runout velocity for a given reactor diameter, which provides the minimum circulation rate to avoid runout increasing with reactor diameter.

Example 2

A 4 vertical branch polymerization reactor using a 26 inch (0.66 meter) Lawrence Pumps Inc. pump impeller D51795/81-281 in a M51879/FAB enclosure was used for ethylene and hexene-1 polymerization. This pump is compared to a 24 inch (0.61 meter) pump that produces a smaller active circulation (0.66 ft/ft or m/m pressure drop vs. 0.98 ft/ft or m/m). This is then compared to the same more aggressively circulating and continuous spout assembly of the type indicated by parameter 34 of FIG. 5 . The results are listed in Table 4.

Example 3

Representative loop reactor length/reactor outer diameter ratios are calculated in Table 5 for the various loop reactors disclosed in US 6239235 and 6204344. In Table 5, the "Row" column is provided for easy reference to a specific data column. The "Reference" column indicates the reactor described in said patent publication (US6239235 and 6204344 patents) and the disclosure is found in that column and row of the patent. (For example, the first item represents the description in column 7, lines 12-14 of US6239235 patent). "OD" denotes the nominal or outside diameter of the reactor tube (this should not be mistaken for the diameter of the loop, which should be much larger), while "ID" denotes the inside diameter of the reactor tube. "Length" is the length of the reactor (ie one circle of the loop reactor). "Vol." is the volume of the reactor. "L/OD ratio" is the ratio of the reactor length to the tube diameter, expressed in the same units, so the stated ratio is unitless.

In each of the US6239235 patent entries (columns 1-6 and 8-10), the OD of the tubes and in some cases the reactor length is given in column 7, lines 12-14 of the US6239235 patent. For some other cases, the reactor length of the US6239235 patent is calculated by the reactor volume, especially refers to a volume greater than 20000 gallons (76 meters ³ ) (see column 8, claim 9) or greater than 30000 gallons (114 meters ³ ) (see Column 2, line 9 or column 8, the reactor of claim 10). In these cases, 24 inch (0.61 meter) OD reactor tubing with a 21.9 inch (0.5562 meter) ID was used to calculate the tube length required for the reactor volume in gallons stated.

In each of the US 6204344 patents (columns 7 and 11), said patent discloses the length (833 feet, 254 meters) and volume (11500 gallons, 44 ^m3 ) can be used to calculate the reactor ID (18.4 inches, 0.47 m). The reactor ID was then used to calculate the length of the 20,000 gallon (76 ^m3 ) reactor cited in the US 6204344 patent.

Calculations in Table 5 show that the disclosed length/outer diameter ratio is at 250 (actually it is disclosed as greater than 250 as it is given in the above reference for greater than 500 ft (152 m) and an OD of 2 ft (0.61 m) reactor length) and 869 (based on a 20,000 gallon (76 ^m3 ) reactor ID of 20 inches (0.51 m)).

The present invention contemplates length/outer diameter ratios equal to or greater than about or exactly 250, 300, 350, 383, 400, 450, 460, 470, 475, 500, 511, 600, 675, 700, 767, 800, 869, 900 , 1000, 1100, 1200, 1300, 1370, 1400, 1500 reactors, wherein "about" represents a change of plus or minus one to the last significant figure stated in the number. For example, "about" 700 means 600-800, and "about 767" means 766-768. The inventors further contemplate an aspect ratio having either the smallest of the above values and the largest of the above values. A few non-limiting examples of such limited ranges are 250-1500, 511-1370 and 1000-1100.

More generally, the inventors contemplate that the length/outer diameter ratio of the loop reactor should be increased to a larger value than that of existing reactors in order to provide a more favorable ratio of reactor volume to transmission for more efficient cooling. thermal area ratio. If the ratio is increased by using relatively small diameter tubing for the loop, two heat transfer benefits are obtained. First, the area of the piping increases relative to the volume of the piping. Second, the wall thickness of the piping can be reduced because the smaller diameter piping has higher strength per unit surface area and the beating velocity of the slurry is reduced, so the pressure head can be reduced. These two factors increase the heat transfer through the tube wall.

Increasing the length/outer diameter (L/OD) ratio of the reactor is that it increases the versatility of the reactor. For example, in relatively low L/OD ratio equipment, the productivity of low density resins may be limited by the relatively low heat transfer rate in this equipment, an example of which is low density polyethylene. All other things being equal, this problem may be solved by increasing the length of the reactor. In the same equipment, the productivity of high-density resins may be limited by the need to remove the polymer in the reactor after a relatively short residence time in order to avoid ash formation, which involves the length of the loop, the overall length and the monomer reactant The length between the point of entry and the point at which polymer product is withdrawn. All other things being equal, this problem may be solved by increasing the length of the reactor. Because a single conventional reactor can only be of one length, if a reactor is optimized for one type of resin, it will be less efficient when used to produce other resins.

Using the present invention, resins where heat transfer is the limiting factor can be efficiently processed by increasing the reactor surface area per unit volume, thereby increasing heat transfer without reducing overall throughput. Resins for which residence time is the limiting factor can be processed more efficiently in the same equipment by pumping the slurry at the same volume rate. Thus, both types of resins can be efficiently produced in the same equipment, or at least a wider range of resins can be efficiently produced in the same equipment.

"CTO" means Continuous Outlet

"CTO" means Continuous Outlet

Claims (8)

1. the loop polymerization reactor of a charging, the loop polymerization reactor of described charging comprises: the loop reaction zone that the common cylinder tube wall is determined, the nominal outside diameter of the length of wherein said loop reaction zone and described common cylinder tube wall is determined the length-to-diameter ratio greater than 800, and wherein nominal outside diameter is at least 0.56 meter; A continuous discharge port mechanism that takes out fluid slurry from described loop reaction zone continuously; With a fluid slurry that is located in the described loop reaction zone, described fluid slurry comprises at least a olefinic monomer reactant, solid olefin polymer particles and liquid diluent, wherein by the weight of described polymer beads and described liquid diluent, the concentration of described solid olefin polymer particles in described slurry is greater than 40 weight %; Be located in the loop reaction zone and configuration is used under the speed of the speed of beating greater than fluid slurry impeller by loop reaction zone circulating fluid slurry.

2. according to the loop polymerization reactor of the charging of claim 1, wherein said length-to-diameter ratio at least 1000.

3. according to the loop polymerization reactor of the charging of claim 1, wherein said length-to-diameter ratio at least 1300.

4. according to the loop polymerization reactor of the charging of claim 1, wherein said external diameter is 61 centimetres.

5. according to the loop polymerization reactor of the charging of claim 1, wherein said external diameter is 66 centimetres.

6. according to the loop polymerization reactor of the charging of claim 1, the volume of wherein said loop reaction zone is greater than 114 meters ³

7. annular-pipe reactor, described annular-pipe reactor comprises:

The loop reaction zone that the common cylinder tube wall is determined, the nominal outside diameter of the length of wherein said loop reaction zone and described common cylinder tube wall is determined the length-to-diameter ratio greater than 1000, wherein nominal outside diameter is at least 0.56 meter; Be located in the loop reaction zone and dispose and be used under the speed of the speed of beating greater than fluid slurry, promoting the round-robin impeller of fluid slurry by loop reaction zone; And continuous discharge port mechanism that takes out fluid slurry from described loop reaction zone continuously.

8. polymerization process, described method comprises:

The loop reaction zone that provides a common cylinder tube wall to determine, the nominal outside diameter of the length of wherein said loop reaction zone and described common cylinder tube wall is determined the length-to-diameter ratio greater than 800, wherein nominal outside diameter is at least 0.56 meter;

In described loop reaction zone,, generate the fluid slurry that contains liquid diluent and solid olefin polymer particles with the polymerization in liquid diluent of at least a olefinic monomer;

By the weight of described polymer beads and described liquid diluent, the concentration of described solid olefin polymer particles in described slurry is remained on more than the 40 weight %;

Under the speed of the speed of beating greater than slurry by impeller by the loop reaction zone described slurry that circulates; And

Take out continuously the described slurry of the solid polymer particle of the liquid diluent that contains taking-up and taking-up.

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