JPS5935251B2 - Stirring tank with ribbon type stirring blades and how to use it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved stirring tank with ribbon type stirring blades and a method of using the same.

Ribbon-type stirring blades are mainly used for mixing and stirring high viscosity liquids, and are installed in polymerization reaction vessels, mixing vessels, etc.

The advantage of the ribbon type stirring blade is that the entire liquid in the tank can be fluidized and mixed by the flow shown in FIG. Many studies have been conducted and structural improvements have been made to ideally generate such liquid flow. FIG. 2 shows a conventional example of a ribbon-type stirring blade (hereinafter referred to as a ribbon blade). Figure 2a shows the simplest structure called a single ribbon. FIG. 2b shows what is called a double ribbon, which is often used as a typical ribbon feather, and there are already established techniques for its structure and dimensions. Further, FIG. 2c shows a configuration in which a screw is added to the single ribbon stirring blade shaft in order to increase the efficiency of liquid flow shown in FIG. Although these ribbon blades are very useful for relatively high viscosity liquids having 10 or less Ray nozzles, they cannot always mix and stir high viscosity liquids as designed.

For example, in a polymerization reaction tank, it is normal for the viscosity of the solution in the tank to increase as polymerization progresses, and the viscosity also varies depending on the type of product being produced. It is not possible to perform efficient mixing and stirring. The ideal liquid flow shown in Figure 1 is caused by the ribbon blades in the laminar region [Reynolds number Re(n
d2ρ/μ, where n: stirring rotation speed, d: ribbon blade diameter, ρ: liquid density, μ: liquid viscosity) is generally defined as 10 or less. ], and as it moves to the transition zone and turbulent zone, slippage from the ribbon blade surface increases and the liquid flow deviates from the ideal flow. The present inventors have developed a device that eliminates the above-mentioned drawbacks of ribbon blades, is effective for relatively low-viscosity liquids, and can take advantage of the characteristics of ribbon blades not only in laminar regions but also in transition regions and turbulent regions. I found it.

That is to install baffles at the top and/or bottom of the tank. An example of its structure is shown in FIG.

This shows a structure in which baffles are attached to the upper and lower parts of the inside of a tank having concave surfaces on the upper and lower sides. In the figure, the rotation direction of the ribbon blade 1 is the direction (arrow) that pushes the liquid on the surface of the ribbon blade downward. In the case of this rotation direction, baffle plates 2 are placed radially from the rotating shaft 4 in the radial direction of the tank at the bottom of the tank. In the illustrated example, the length of the baffle plate in the radial direction extends from a position close to the rotating shaft 4 to the outer edge of the ribbon blade, but it is effective if it extends to at least the inner edge of the ribbon blade. Further, the number of baffle plates 2 is preferably up to about four for structural and economical reasons. On the other hand, there is also a rotating shaft 4 in the upper part of the tank.
Baffle plates 3 are provided radially from the tank, and the length in the radial direction can be from the inner surface of the tank to the rotating shaft 4, but as shown in the figure, the baffle plates 3 are provided so as to extend at least from the inner surface of the tank to the inner edge of the ribbon blade. It is effective to place it above the ribbon blade. If the rotation direction is opposite to the above, the upper and lower baffle plates are installed in the opposite direction.

That is, for rotation in the direction of pushing the liquid on the surface of the ribbon blade upward, baffle plates with a length from the rotating shaft 4 to at least the inner edge of the ribbon blade are installed radially in the upper part of the tank, and at least the ribbon is placed in the lower part of the tank. A baffle plate with a radial length comparable to the width of the blade is installed below the position of the ribbon blade.
The installation of such a baffle plate has nothing to do with the amount of liquid in the tank, and can be applied both when the tank is filled with liquid and when there is a free liquid level.

Further, the upper and lower baffle plates may be arranged alternately or may be arranged so as to correspond to the ground. Further, even if the upper and lower surfaces of the tank have any shape, such as a concave shape or a flat plate shape, the objects of the present invention can be achieved by installing the upper and lower baffle plates. The stirring tank of the present invention can be used regardless of whether it is a homogeneous phase system or a heterophase system.

In other words, stirring and mixing of liquid and liquid, or gas and liquid,
Can be used for stirring and mixing solids and liquids. The present invention can be used in stirring and mixing of homogeneous phase systems in reaction tanks for polymerization modes that produce relatively low viscosity liquids (e.g. bulk polymerization, solution polymerization), or in reaction vessels for relatively low viscosity liquids, or for relatively low viscosity liquids. A typical example is a mixing tank for mixing liquids and lower viscosity liquids.

Looking at the usage status of conventional stirring tanks used for such applications, even in the case of stirring and mixing relatively low viscosity liquids, the operating range is often 100 or more in terms of Reynolds number. Therefore, the various ribbon blades shown in FIG. 2 cannot fully demonstrate their original functions. The first thing is liquid flow.
It is thought that this is because solid rotation (a phenomenon in which the liquid appears to be "spinning around" with the stirring blade) becomes dominant rather than as shown in the figure. The baffle plate according to the present invention is useful for preventing this solid rotation, and the stirred tank according to the present invention exhibits a particularly remarkable effect when used in an operating range where the Reynolds number is 100 or more. When solid rotation exists, the time required for the concentration of the liquid in the tank to become uniform becomes longer.

For example, in a blending tank, processing efficiency decreases,
Furthermore, there is a high risk of uneven density. Further, in a polymerization reaction tank, damage caused by solid rotation causes a decrease in heat removal ability and non-uniformity in temperature and concentration, resulting in deterioration in the quality of the polymerization product. These drawbacks occur both in batch operations in blending vessels and polymerization reactors, as well as in continuous operations. As shown in the examples below, these drawbacks were completely eliminated in the stirring tank of the present invention. The present invention also relates to a method of using the stirring tank in heterophase dispersion polymerization such as emulsion polymerization and suspension polymerization. In conventional heterophase dispersion polymerization tanks, determining the stirring intensity,
There are many proposals regarding the selection of stirring blades and the determination of the dimensions and structure of the tank body, baffle plate, stirring blades, etc.
Although it has been put into practical use, it is not completely satisfactory. In the case of heterophasic dispersion polymerization, as in the case of ordinary polymerization reactions, stirring is required during the reaction for the following purposes.

1. Supply of mechanical energy to disperse the monomer2. Ensuring uniformity within the reactor 3. Acceleration of polymerization reaction heat removal These objectives can be achieved by increasing the stirring intensity.

However, in the case of heterophasic dispersion polymerization, excessive stirring strength can be detrimental to maintaining the produced polymer particles in a stable dispersed state. For example, if the mechanical shearing force or stirring intensity of latex obtained by emulsion polymerization is too large, the stability of the latex will decrease, causing coagulation to form on the inner surface of the polymerization reactor or on the surface of the cooling coil. . Further, in the suspension polymerization method, excessive stirring causes particles to coalesce and become uneven in particle size. The stirred tank of the present invention eliminates the production of coagulum, which has been a problem in conventional polymerization reactors (for example, the blue margin, inclined paddle, or Faudler type polymerization reactors shown in Figure 4). We were able to solve the problems such as decreased properties and irregularity of particles all at once. In FIG. 4, 1 is a polymerization vessel, 2 is a cooling pipe, 3 is a stirring blade, 4 is an ammonia gas passage opening/closing valve, 5 is a control means for the opening/closing valve 4, 6 is an accumulator 7 is an ammonia liquid, and 8 is an ammonia liquid. It is the entrance.

In the present invention, the use of ribbon blades eliminates the need for cooling pipes as shown in FIG. 4, and instead employs jacket cooling, which eliminates the drawback of solidified material clogging between the cooling pipes. It became possible to clean the cooling surface by the scraping action. Furthermore, by installing a baffle plate, stirring was performed uniformly and the heterophasic dispersion system was stabilized. The present inventors used the ribbon blade stirring tank of the present invention in the following examples and obtained the desired effects.

Example 1 A double ribbon blade of the type shown in FIG.
Installed in a flat bottom tank with n1 height H: 700 crrL, and installed a lower baffle plate (length l is approximately the same as the radius %D of the tank, center side height h is 40 (1-J mo V1) radially in the tank. Four pieces were placed at equal intervals with the ribbon blades spaced at g: 10 (1-J mo V1).

Using this stirring tank, a liquid with a viscosity of 2000 cp is pumped to a depth of 550.
When the cTn was stirred and mixed, the time required to achieve uniform mixing was reduced to % of that without the baffle plate.
In addition, the Reynolds number in the above-mentioned operation was about 3,000. Example 2 A ribbon blade of the type shown in Fig. 2a (blade width d: 190 CTL, height H': 200 cTn, ribbon width b: 20?) was placed in a polymerization tank with a concave top and bottom surface having a diameter D: 200C, 17L1, and a straight body length of 250 crn. In the tank, install four lower baffle plates (the length is approximately the same as the radius %D of the polymerization tank, the height is 30c7n) radially evenly spaced, and upper baffle plates (the length is from the tank wall to the ribbon). Up to the inner edge, 4 pieces (30cm height in liquid) radially equally spaced and corresponding to the lower baffle plate, each with a ribbon blade and 5CT! They were placed at intervals of 1.

When batch polymerization of polybutadiene solution polymerization was carried out using this polymerization tank, there was no temperature difference between the center and the vicinity of the tank wall, and a product of uniform quality could be obtained.

The Reynolds number was approximately 10,000 at the initial stage of polymerization and approximately 300 after completion of polymerization. Example 3 Fig. 2 A continuous polymerization tank with a concave top and bottom surface and a diameter of 2m and a straight body part of 2m, equipped with a-type ribbon blades (blade width 190?, height 200C1rL, ribbon width 20CTL), is equipped with an upper baffle. Four plates (the length is approximately the same as the radius of the polymerization tank, the height is 20?) are spaced radially evenly, and the lower baffle plate (the length is from the tank wall to the inner edge of the ribbon, the height in the liquid is 20?). Two pieces were installed radially at equal intervals.

When the residence time distribution of this polymerization tank was measured, it was demonstrated that it was closer to an ideal complete mixing tank than a case without baffles. Note that the Reimels number in this example was approximately 1,000. Example 4 The reaction tank shown in Example 2 of the present invention was applied to the following three polymerization reactions.

(1) Emulsion polymerization of carboxyl-modified styrene-butadiene latex (2) Emulsion graft polymerization of styrene and acrylonitrile to polybutadiene latex (3)
Suspension polymerization of acrylonitrile and styrene In (1) above, the frequency of clean-up of the reaction tank is drastically reduced, and
The continuous usable time has been extended by more than three times compared to the previous model.

In (2) above, the inner wall of the reaction tank is almost completely freed, and as a result, as in (1) above, there is almost no need for a clean nap. In (3) above,
Good results were obtained in that the uniformity of the particle diameter of the acrylonitrile-styrene resin produced was extremely good, and no particles were observed that were attached to each other.

[Brief explanation of the drawing]

Figure 1 shows the flow pattern of liquid using ribbon blades, Figure 2 shows a stirring tank equipped with a typical type of ribbon blade, Figure 3a shows one embodiment of the present invention, and Figure 3b is a sectional view showing the lower baffle plate taken along line A-A' in Fig. 3a, Fig. 3C is a sectional view showing the upper baffle plate taken along line B-B' in Fig. 3a, and Fig. 4 is a sectional view showing the conventional baffle plate. It is a diagram showing an example of an emulsion polymerization reaction tank. 1... Ribbon blade, 2... Lower baffle plate, 3... Dobe sha, magic board, 4... Rotating shaft.

Claims (1)

[Claims] 1. In a stirring tank equipped with a ribbon-type stirring blade, a plurality of baffle plates are provided adjacent to the ribbon-type stirring blade in the upper and/or lower part of the tank, and are connected to the rotating shaft of the stirring blade. A stirring tank with ribbon-type stirring blades, which is characterized by being arranged substantially parallel and oriented in the radial direction. 2 Among the above upper and lower baffle plates, one baffle plate extends from a position close to the rotating shaft to the outer edge of the ribbon blade, and the other baffle plate extends from the inner surface of the tank to the inner edge of the ribbon blade. The stirring tank with ribbon-type stirring blades according to claim 1, characterized in that: