Agitator vessel and a scaled agitator vessel set Field of the invention

The invention relates to an agitator vessel for mixing chemicals in liquid slurries, wherein the vessel comprises a substantially cylindrical vertical vessel wall and at least two vertically extending baffles formed on an inner surface thereof. More specifically, the invention relates to agitator vessels for manual, lab scale preparation of automotive catalysts.

Description of the prior art

Mixing of chemicals in liquid slurries is an important step in the preparation of automotive catalysts. Known agitator vessels for mixing chemicals on industry scale are, for instance, stationary metallic tanks with baffles. Baffles are generally used in agitator vessels to change laminar flow to turbulent flow, and a typical baffle design is a flat metallic plate forming a 90° angle with the vessel wall. So, for example, US 2007/081419 A discloses a portable DC motor driven laboratory assembly for uninterrupted stirred processes comprising a vessel having a capacity of 0.1 to 20 L, an agitator assembly having an agitator shaft and a plurality of impellers provided at an end of the agitator shaft, and a removable baffle plate assembly having a plurality of vertically positioned sheet metal baffles plates symmetrically spaced apart. In industrial mixing applications, it is common to use this kind of baffles within a glass lined (e.g. fermentation processes) or steel lined reactor.

However, for manual, lab scale preparation in the range of 1 up to 120 L, there is a need for adequate agitator vessels allowing for a more precise, reproducible, and safe preparation of varying working volumes within this broad range. Summary of the invention

To solve this problem, an agitator vessel for mixing chemicals in liquid slurries and a corresponding scaled agitator vessel set are provided as defined in the independent claims. Further embodiments are specified in the dependent claims.

According to a first aspect, an agitator vessel for mixing chemicals in liquid slurries is provided, wherein the agitator vessel comprises:

a substantially cylindrical vertical vessel wall, which confines a bottom of the vessel, and

at least two vertically extending baffles formed on an inner surface of the vessel wall.

A horizontal cross section of each baffle has an approximately triangular shape whose vertex angle is in a range from 30° to 90°, from 40° to 80°, from 50° to 70°, or from 55° to 65°. More specifically, the vertex angle of the approximately triangular horizontal cross section of each baffle may be approximately 60°.

(Herein, the expressions "substantially" and "approximately" may, in particular, be understood as including possible manufacturing and constructional tolerances of up to 10% of a concerned dimension.)

It was surprisingly found out that this baffle structure promotes mixing very well, also in comparison with the known flat baffle plates at 90° to the vessel wall. Furthermore, baffles having triangular horizontal cross sections and vessels with such baffles turned out to be easier to produce and much easier to handle and to clean than in the case of flat plate baffles. This may particularly facilitate manual, lab scale preparation of mixed chemicals, such as washcoats or automotive catalysts, which involves many manual steps and changes. Easier cleaning an decanting of the agitator vessel may also significantly reduce an overall amount of cleaning water as well as its contamination with chemicals. Apart from the novel baffle structure, the geometry of the vessel may, in particular, be close to a known state-of-the-art geometry.

In a specific embodiment, the agitator vessel is produced of a plastic material by a rotary moulding process. By rotary moulding, agitator vessels having baffles structured as disclosed herein (in particular, having any of the specific features disclosed herein below) can be produced. A wall thickness of thus produced vessels may be, for instance, suited for slurries up to a specific weight of 2.0 kg/L and may be further increased if needed. Rotary moulding allows producing seamless and smoothly shaped vessels, in an almost pressure-less production process. Thereby, vessels nearly free of mechanical stress may be produced. They may, thus, be particularly pressure- and shock-resistant in use.

Suited plastic material is, for instance, polyethylene, in particular LLPE (Linear Light Density Polyethylene). Vessels made of polyethylene are chemically resistant to a wide range of chemicals typically used in preparation of automotive catalysts. Such vessels may be used in a temperature range of e.g. -20°C to +60°C.

Specifically, the at least two baffles and the vessel wall may be formed as a monolithic piece. This may result in a particularly robust and durable agitator vessel.

In a specific embodiment of the agitator vessel, at least one of the baffles or each baffle is shaped as a vertically extending prism whose crest is slightly rounded so as to form a soft edge. This baffle shape may be particularly easy to produce by rotary moulding. It also may be particularly facilitating in respect of handling and cleaning the vessel.

As a further development of this embodiment, in a vertical direction, the prism ends at one or both of its ends in a bevel forming an angle in a range from 90° to 150°, from 100° to 140°, from 1 10° to 130°, or from 1 15° to 125° with a portion of the vessel wall bordering on the bevel. Here, the bevel may have a substantially flat triangular shape, possibly having a rounded vertex or all corners. Also, this bevelled structure may further promote mixing and/or cleaning of the vessel.

In a specific embodiment of the agitator vessel, at least one of the baffles is hollow inside and open to an outer surface of the vessel wall, being formed by a recess in the outer surface of the vessel wall. Therein, the shape of the recess is substantially complementary to the shape of the baffle inside the vessel. In this embodiment, the baffles may be easily formed by pushing the vessel wall of a regular cylindrical vessel in its plastically deformable state radially from the out- side, for instance, using a suited tool shaped as a desired baffle. Thereby, each baffle is formed.

Specifically, at least one of the baffles may have a predetermined bottom distance from a bottom of the vessel and/or a predetermined top distance from an upper edge of the vessel. This configuration may further facilitate decanting and cleaning of the agitator vessel. The predetermined bottom distance and/or the predetermined top distance may be defined to be in a predetermined proportion to an inner diameter of the vessel wall.

Further, the at least two baffles may be spaced apart by substantially equal distances in a circumferential direction of the vessel, so as to achieve a mostly homogeneous mixing.

Specifically, the at least two baffles may be exactly two, three, four, five, or six baffles. The baffles may - though need not - be all substantially identically shaped. For example, a configuration of four identical baffles in a vessel may be a good compromise of mixing efficiency, on the one hand, and handling and cleaning the vessel, on the other hand.

For improved mechanical stability and especially to support installation of dedicated lids that may e.g. act as mounting aids for injections lances, sensors etc., an upper edge of the vessel may be dilated, for instance, in a predetermined proportion to an inner diameter of the vessel wall. Furthermore, agitator vessels having a total effective inner volume smaller than or equal to 26 L may have a pouring lip for easier decanting of washcoat.

Herein, the agitator vessel may

have a total effective inner volume of the vessel in a range from 1 L to 200 L, from 2 L to 180 L, or from about 3 L to about 160 L; and/or allow for a working volume of a liquid slurry in a range from 0.5 L to 180 L, from 1 L to 160 L, or from about 1 .3 L to about 140 L.

Specifically, vessels may be provided with Min/Max markings for allowed working volume and/or with volume scales serving in particular as an assessment value for vessel selection. Volume scales or markings may be, for instance, engraved on an outer surface of the vessel wall. Even though such a scale itself does not need to have an analytical accuracy, it may serve as an aid for filling in or decanting the chemicals.

Providing adequate agitator vessels suited for a standardization of washcoat preparation throughout these volume ranges, comparability, transfer, and reproducibility of washcoat recipes from lab till pilot scale may be realized. This may be, for instance, achieved using a scaled agitator vessel set as disclosed in the following.

As a further aspect, a scaled agitator vessel set comprising a number of differently sized agitator vessels as disclosed herein is provided. In this set, at least one vessel dimension which is relevant for mixing is substantially identically scaled (i.e. calculated by the same equation) with respect to an inner diameter of a vessel wall of a respective vessel for all the differently sized agitator vessels. The number of differently sized agitator vessels may be, for instance, equal to three, four, five, six, seven, eight, or more.

Therein, the at least one vessel dimension which is relevant for mixing may, for instance, comprise one or more of the following vessel dimensions: total vessel height, minimum working vessel height, maximum working vessel height, radial depth of each baffle in the vessel, horizontal base site of each baffle in the vessel wall, total vertical length of each baffle (as measured, for instance, in the vessel wall), total effective volume of the baffles in the vessel, a predetermined bottom distance of a baffle to a bottom of the vessel, a predetermined top distance of a baffle to an upper edge of the vessel, an effective total inner vessel volume, an effective minimum working volume, an effective maximum working volume.

In a specific embodiment, the vessels of the number of differently sized agitator vessels are continuously scaled-up in that a maximum working volume of a smaller vessel is substantially equal to or overlaps to an amount of no more than 10% with a minimum working volume of the next larger vessel. An example for a scaled set of seven agitator vessels having such a continuous scale-up is shown further below in a table, a calculation example, and the figures. An example for a scaled set of seven agitator vessels according to a continuous scale-up is shown in Table 1. The table shows effective volume values, where a contribution of a volume occupied by the baffles inside the vessel is subtracted. A corresponding example for calculation steps and results for relevant dimensions of a mid-sized vessel having a total effective volume of approximately 26 L are set forth further below in connection with an exemplary embodiment shown in the figures.

Table 1 (exemplary embodiment, suited as best mode)

Specifically, the scaled agitator vessel set may further comprise a smaller or same number of correspondingly differently sized agitators. Therein, at least one agitator dimension which is relevant for mixing is substantially identically scaled (i.e. calculated by the same equation) with respect to an inner diameter of a vessel wall of a respective corresponding vessel for all of the number of correspondingly differently sized agitators.

Therein, the at least one agitator dimension which is relevant for mixing comprises may be one or more of the following agitator dimensions: total agitator diameter, agitator blade width, agitator blade thickness, agitator hub height, predetermined distance of agitator to a bottom of the vessel, height of an agitator shaft mark defining a predetermined vertical position of the agitator shaft with respect to an upper edge of the vessel. An example is shown further below for calculating these dimensions and is, additionally, illustrated in the figures. In sum, a novel standardized and easily scalable baffled vessel design for manual mixing of chemicals, e.g. for automotive catalyst or washcoat preparations, from lab scale till pilot plant stations is provided. Especially for the standardization of washcoat preparation, the disclosed vessels allow for an improved comparability, transfer, and reproducibility of washcoat recipes from lab till pilot scale. A typical lab-scale preparation workflow contains many manual changes and movements of agitator vessels. Therefore, the vessels should be light, durable, and stable. In particular, polyethylene vessels produced by rotary molding fulfill these requirements. The disclosed vessels may be made as one piece and without sharp edges, which is easy to handle and to clean within varying process steps during washcoat preparation.

With the vessel and scaled vessel set design as disclosed herein, in particular, the following may be achieved:

Providing adequate agitator vessels for manual, lab scale preparation in the ranges of 1 up to 120 liters fulfilling several or all of the following requirements:

• Similar vessels of different sizes for uniform scaling, which make it easy to scale up and down reproducible preparations in the 1 to 120 L range.

• Safety considerations for the workers, such as break resistance, chemical resistance.

• Environmental safety. A low break resistance lowers a chance of undesired liquid loss by accident. Easy cleaning of the vessels leads to less waste of cleaning water.

• Working ergonomics. The vessels made of plastic material may be particularly light-weight, which is important since they are carried around a lot in the course of lab preparation of chemicals.

• Price. A low price per piece is desired because this also allows to often use the vessels for temporary storage.

• Also in the lab scale, it is nowadays required to inject chemicals more precisely, and defined vessels make it easier to standardize tool, such as stirrers injection lances, sensor location, etc.

With agitator vessels produced of polyethylene by a rotary moulding process, no compromises need to be made regarding safety and working ergonomics. Polyethylene is light and has an excellent chemical resistance against a big variety of chemicals. The rotary moulding process offers the production of strong and durable vessels having a consistent wall thickness and being virtually stress free.

Brief description of the drawings

The above-mentioned exemplary embodiment (Table 1 ) is explained in the following in more detail, accompanied by the schematic drawings. In particular, the drawings need not be understood as true to scale. Therein

Fig. 1 a top view of an agitator vessel of a scaled agitator vessel set according to an exemplary embodiment;

Fig. 2 a side view of the agitator vessel of fig. 1 with a dedicated lid added;

Fig.3 an enlarged view of a baffle portion of fig. 1 ;

Fig. 4 a vertical cross-section of the agitator vessel of fig. 2;

Fig. 5 a perspective side view of a further, smaller agitator vessel of the scaled agitator vessel set of the exemplary embodiment;

Fig. 6 a perspective top view of the agitator vessel of fig. 5.

Detailed description of an embodiment of the invention

Figs. 1 -4 show in more detail an exemplary embodiment of an agitator vessel which, for instance, may be part of a scaled set of similarly or identically scaled agitator vessels, such as the set of seven agitator vessels for a continuous scale- up shown above in Table 1. The vessel shown in figs. 1 to 4 may e.g. have a total effective filling volume of approximately 26 L. Fig. 1 shows a top view of an agitator vessel 1 , which may e.g. be produced of polyethylene by rotary moulding. Agitator vessel 1 possesses four identical vertically extending baffles 2 equidistantly spaced apart on an inner surface 3 of a cylindrical vertical vessel wall 4. A horizontal cross section of each baffle 2 has an approximately triangular shape whose vertex is slightly rounded due to manufacturing tolerances and has a vertex angle P = 60° in this example. In this example, baffles 2 and vessel wall 4 may are formed as a monolithic piece.

Fig. 2 shows a side view of vessel 1 of fig. 1 with a dedicated lid 5 added. Dedicated lid 5 may, for instance, act as a mounting aid for injections lances, sensors etc.. For an improved mechanical stability and to support installation dedicated lid 5, an upper edge 6 of vessel 1 is dilated.

As recognisable in figs. 1 and 2, baffles 2 are hollow inside and open to an outer surface 7 of vessel wall 4. Baffles 2 are formed by recesses 8 in outer surface 7 of vessel wall 4, wherein the shape of each recess 8 is substantially complementary to the shape of respective baffle 2 inside vessel 1. In this example, each baffle 2 is shaped as a vertically extending prism whose crest 9 is slightly rounded so as to form a soft edge. This can be particularly well seen in fig. 3, which shows an enlarged view of an upper right baffle portion of fig. 1 .

Fig. 4 shows a vertical cross-section of vessel 1 of figs. 1 and 2. In a vertical direction, each baffle 2 ends at both of its ends in a bevel 10 enclosing with a vertical axis approximately the same acute angle of P = 60°, i.e. forming an angle of 120° with a portion 1 1 of vessel wall 4 bordering on bevel 10. Here, each bevel 10 has a flat triangular shape, having a rounded vertex (as crest 9 does) due to manufacturing.

Dimensions of vessel 1 , which are relevant for mixing efficiency and handling, may be, for instance, calculated in a continuously scalable manner suited for a scaled agitator vessel set for lab use as follows:

For the design of an agitator vessel, the ratio r _sy n=B/Ai of a vertical height B of the vessel to its inner diameter Ai is known to be important. In the state of the art, a known minimum value of this ratio is r _syn min =0.75 and a known maximum value is r _sy n max =1 .5. Additionally providing a fill level reserve of 0.25, the ratio may be set in this example to reserve =1 .75:

Tsyn max■ ^— Ί■¾

m

Treserve■ ^— \ . Ι Ό

m anglebaffie := 60°

P := anglebaffie

n urn be r ₀ f baffles :=

For an exemplary mid-sized vessel 1 of Table 1 , as shown in figs. 1 -4, an exemplary thickness of vessel wall 4 equal to approximately 4.5 mm and an outer diameter outerd = 281 mm may be chosen: outerd := 281 mm

wallthickness := 4.5 mm

With thus chosen constants and parameters, the following relevant dimensions Ai, A2, B, C, D, E, F, G, H, I, J, K, M, N, and O (as summarized further below) of vessel 1 may be calcuted by the following exemplary equations:

Calculations

Vessel inner _d := outer _d - 2 ^■ wallthickness

innerd := 272 mm A1

hideai := Reserve ^■ innerd

hideal = 476 mm B

hmin . ^— inneTd ^■ Tsyn min

hmin := 204 mm C

hmax . ^— inneTd ^■ Tsyn max

hmax := 408 mm D As shown in fig. 1 , markings for thus calculated minimum and maximum working heights C and D are provided in this example on outer surface 7 of vessel 1 , e.g. by engraving.

Further, depending on inner diameter Ai of vessel wall 4, in the present example, the following relevant dimensions of baffles 2 may be calculated as follows:

Baffles inner d inner ^

Oeptnone Baffle in vessel ■ ~ ~

depthone_Baffle_in_vessel = 40.8 mm

E := depth one Baffle in vessel

\ angle b _a ffi _e ^~ \

base _S ite_baffie := tan rad ^■ depth _{one Ba} ffi _e 2

in_vessel

base _s ite_baffie = 47.1 1 18 mm

F:= base _s ite baffle

Hbaffies := 0.95 ^■ reserve mnerd

Hbaffies = 452.2 mm

G := Hbaffies

Γ depth _one Baffle_in_vessel _n

Vbaffles■- I oase _{site ba} ffi _e 1 ^■ Mbaffles " numDer ₀ f_baffies

Vbaffles = 1 .7384 L

hbaffle_eff 0.91 ^■ innerd ^■ Reserve

hbaffie_eff = 433.16 mm

Γ depth _one Baffle_in_vessel

Vbaffles_eff .- \ DClSe _site _ _ba ff _le · 1 ^■ nbaffle_eff " nUmDer ₀ f_baffles

Vbaffles_eff = 1 .6652 I

H := Vbaffles_eff

Here, G denotes a total vertical height of baffle 2, as measured at outer surface 7 of vessel wall 4. Having thus calculated relevant baffle dimensions E, F, and G, (cf. fig. 3 and 4), an effect of the volume occupied by baffles 2 inside vessel 1 onto an effective filling volume of vessel 1 at relevant filling height values C and D may be estimated as follows:

distancebaffie to bottom wall := 0.04 ^■ [r _reserve ^■ inner _d ]

distancebaffie to bottom wall ^— 19.04 mm

I = distancebaffie to bottom wall

distancebaffie to bottom inside - ^— 0.09 ' ' ΪΪΤ·71β7¾]

distancebaffie to bottom inside = 42.84 mm

J := distancebaffie to bottom inside

Note: Minimal Distance for I is 19 mm according to vessel supplier

For vessels < 26 L use:

3.25 L Behalter- 0.08 * (1.75*ID)

6.46 L Behalter - 0.065 * (1.75*ID)

13.02 L Behalter- 0.05 * (1.75*ID)

V

syn min baffles .—

dist nce _{¾a ie toJ)0ttom waii} ]-number ₀ f_baffies-ABaffleSeff

Vsyn min baffles ^— 0.6744 L depth _one Baffle_in_vessel

syn_max_baffles .- Oa-Se _s ite_baffle ~ ₂ J ^' ['' ^■ max ~ ^aistance baffle_to_bottom_wall\ ^' number ₀ f baffles" ABaffleSeff

Vsyn max baffles ^— 1.4587 L

Vvessei ^' .= - 4-innerd ² -n-hideai

Vvessei = 27.6589 L K := V _ve ssei

Vvessel eff - ^— Vvessei ^— Vbaffles eff

Vvessei eff = 25.9937 L M := Vvessei eff

Vsyn min ^— 11.1794 L N .— Vsyn min

Vsyn max ^— 22.2489 L O .— Vsyn max innerd_with_baffies Ai - 2 E

innerd_with_baffies = 190.4 mm A2 := innerd_ _W ith_baffies

The calculated results for vessel 1 shown in figs. 1-4 may be summarized as follows:

Ai = 272 mm A1 = Inner diameter without Baffles

A ₂ : = 190.4 mm A2 = Inner diameter with Baffles

B = 476 mm B = Ideal vessel height

C = 204 mm C = Height minimal volume for preparation

D = 408 mm D = Height maximal volume for preparation

E = 40.8 mm E = Depth one Baffle in vessel

F = 47.1 1 18 mm F = Base site Baffle at wall

G = 452.2 mm G = Total height Baffle

H = 1 .6652 L H = Effective volume Baffles

I = ^: 19.04 mm I = I Distance Baffle to bottom (wall side)

J ^: = 42.84 mm J = Distance Baffle to bottom (inside vessel)

K = 27.6589 L K = Vessel volume without Baffles

M = 25.9937 L M = ^: Vessel volume with Baffles

N = 1 1 .1794 L N = Minimal vessel volume for preparation

0 = 22.2489 L 0 = Maximal vessel volume for preparation

P = 60° P = Angle Baffle in vessel

Here, in particular, the effective total filling volume M of approximately 26 L is determined. As is readily recognized, all these relevant dimensions of vessel 1 are calculated based on a single predetermined dimension, e.g. inner diameter Ai=innerd. Scaling this dimension, similar vessel of a different size may be obtained in the same manner.

Figs. 5 and 6 show a perspective side and top view of a further, smaller agitator vessel 12, which may also be part of the scaled agitator vessel set of the exemplary embodiment according to Table 1. For instance, vessel 12 may have an effective total filling volume of approximately 3.25 L.

For agitator vessels having a total effective inner volume smaller than 26 L, such as vessel 12, a pouring lip 13 for easier decanting of washcoat may be provided at outer edge 6. For the rest, the above description of vessel 1 applies here by analogy.