DK153526B - FLUIDIZATION PROCEDURE, ISSUED FOR USE OF DIFFICULT FLUIDIZABLE MATERIALS - Google Patents

Description

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Different types of fluidization processes have been used for many years for many different unit operations and / or unit processes, including chemical reactions and drying operations. In the usual fluidized system, a solid phase is suspended in an upward fluid stream, usually a gas stream, whereby the mass of solid particles has the same appearance as a boiling liquid. The solid phase can be a catalyst for promoting a chemical reaction, the reactants being contained in the fluidizing gas, or the solid phase being a material reactive with the fluidizing gas. Alternatively, the solid phase may be a material treated with the fluidizing gas, as is the case with fluidized drying.

One of the main advantages of fluidized bed systems is that the high turbulence occurring in a fluidized bed produces high heat transfer capability. In addition, turbulence in the fluidized bed causes complete mixing of the solids with the fluidizing gas to form a relatively homogeneous gas-solid system.

However, fluidized bed systems are not free from certain disadvantages. Thus, it is well known to those skilled in the art that the use of fluidized systems typically leads to duct formation, a phenomenon caused by the formation of pockets in the solid phase, which in turn causes the gas to pass through the solids as the bed is formed. without intimate contact between the gas and the solid phase.

The problem of duct formation in a fluidized bed system can in part be minimized by the use of many tubular zones through which the fluidizing gas is contacted with the solid phase. Thus, each tube contains an individually fluidized bed with a much smaller TV area in such tubes. Such tubular 35 bed systems have even greater heat transfer capacity because the numerous tubular zones increase the available surface.

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o 2 for heat transfer.

However, the use of many tubular zones has not found recognition or acceptance in the fluidization of materials which, due to their coherence properties, tend to form aggregates and consequently are difficult to fluidize. The difficulty of fluidizing such materials is investigated by Gelhart and discussed in "Types of Gas Fluidization" Powder Technology 7, pages 285-292 (1973). In this publication 10, the author classifies solids in groups A through D, both inclusive, the materials having a smaller 3 average size and / or particle density than 1.4 g / cm are classified as group A materials. Particles having an average size of 40 µm to 500 µm and a density 15 or density of 1.4 to 4 g / cm 3 are described as Group B materials. From a fluidization point of view, materials from Groups A and B do not present unusual problems. On the other hand, materials from Groups C and D present the most serious problems in fluidization, with Group C materials being cohesive, ie. tend to adhere together, and as a result tend to clog small diameter tubes.

Gelhart points out that fluidization of such materials can be made possible or enhanced by the use of mechanical agitators or vibrators to minimize duct formation in the fluidized bed. However, the author points out that one of the most effective means of avoiding difficulties with such materials is the addition of foreign solids, viz. external solids, 30 added to the system.

There are a number of solid materials that fall into the categories C and D. mentioned above. Starch is an example of a Group C material, since starch tends to become quite coherent and thus tends to clog tubes with small diameter. Attempts have previously been made to treat or

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process starches in a fluidized bed system.

In e.g. US 2,845,368 discloses a method for converting starch to dextrin in a fluid bed system, wherein the fluidization reactor includes many heat transfer tubes disposed in the reactor to provide the starch with heat while undergoing conversion. One of the major difficulties of a system of the type described in the above patent is that when contacted with an acidic catalyst, the starch is prone to form lumps or agglomerates within the fluid bed of the reactor to an even greater extent. Thus, the starch's own propensity to clump together with the increased propensity of starch to agglomerate when contacted with a catalyst will lead to quite severe channel formation. In turn, channel formation involves incomplete conversion of the starch to dextrin.

In addition, reactors used in starch dextrinization are frequently characterized by a "dead zone" 20 at the upper end or upper part of the reactor, where the starch may or may not lie or be exposed to high temperatures for extended periods. Self-ignition may occur, causing fire and / or explosions.

This problem can be aggravated in particular in an apparatus of the type disclosed in the above-mentioned patent, where the heat transfer surfaces are present in the fluidized bed of the reactor when sufficient surface area is provided to provide the necessary heat transfer and the fluid flow within the reactor is interrupted. , · 30 so that such "dead zones" are formed.

U.S. Patent No. 3,735,498 relates to an apparatus for fluidizing solid particles so that a very large amount of the particles are continuously circulated within successive circulating zones in the fluidized bed, and the object of the apparatus is to maintain a stable state. of recirculation, with some J "~ * S * r * f <\ S * Λ L; \ ϋ 4 o of the narrow passages between the upper and lower zones serving for upward transport of fluidized particles while the other narrow passages serve for downward transport.

On the contrary, in the process of the present invention, a smooth feed of the particulate material is desired from top to bottom and in countercurrent with the fluidizing gas supplied. This has so far caused great technical difficulties, which, however, are now overcome by the fact that the fluidisation takes place in three superimposed zones with stirring in both the upper and lower zones, which are provided with such narrow passages that the fluidized particles can only be carried in one direction, namely downwards.

The following more detailed description serves to illustrate the invention in more detail by illustrating certain embodiments of the method according to the invention, in particular the embodiment described in the drawing and the accompanying text in more detail.

The invention relates to a fluidization process, especially for use on difficultly fluidizable, highly adherent solid particles such as starch, in which the supplied solid particles are fluidized by an upwardly flowing fluidizing gas in a number of successive flow zones, during the fluidization and subjected to treatment.

The method according to the invention is characterized in that the fluidisation takes place in three adjacent flow zones, a lower zone, an intermediate zone and an upper zone, the intermediate zone being divided into several sub-zones of a smaller cross-section than the upper and lower zones, whereby the solid particles is introduced into the upper or lower flow zone, passed through the intermediate zone to the lower or upper flow zone and discharged therefrom, and that the solid particles in the upper and lower flow zones besides Γ · '-S Λ C y η Γ, r -, ι-Ά; The liquid gas is further mechanically stirred and subjected to a heat exchange in the intermediate zone.

The heat transfer to or away from the fluidized system takes place predominantly in the region of -5. The tubular zones with these diameters forming or forming the intermediate zone are provided with heat exchange means and the many tubular zones small diameters provide a large heat transfer area.

The fluidization method of the present invention is particularly well suited for treating starches, including for use in e.g. dextrinization or oxidation of starches, since starches have cohesive tendencies and are thus difficult to fluidize.

The invention encompasses physical as well as chemical processes such as drying. Starches can be effectively dried using the method of the invention. In addition, other physical and / or chemical processes may be performed on other solids which are difficult to fluidize, including e.g. coal.

As mentioned above, the method according to the invention is described in more detail below in the drawing, in which fig. 1 is a cross-sectional view of a fluidized bed reactor suitable for use in the method of the invention; FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1, for the sake of clarity only four pipes have been selected, and fig. 3 shows an illustration of the method-30 according to the invention reproduced in stylized or schematic form.

According to an embodiment of the process according to the invention, the principles of the invention are applied to the conversion of starch to dextrin in an acid-catalyzed reaction 35 carried out at elevated temperature at which the starch is introduced into a fluidized zone which is stirred continuously.

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From this fluidized zone, the starch is sent, either in a co-flow or preferably in a counter-flow with the fluidizing gas, through many tubular fluidized zones and further into another fluidized zone which is also subjected to stirring.

In the preferred embodiment of the invention, starch is introduced into an upper fluidized zone and continuously stirred in this upper fluidized zone. From the upper fluidized zone, the starch is sent downstream in countercurrent to the fluidizing gas through many tubular fluidized zones and into a lower fluidized zone which is also kept stirred. The resulting product is then withdrawn from the lower fluidized zone.

One of the important features of the process of the invention is that both the upper and lower fluidized zones are kept vigorously stirred to ensure complete mixing in both zones. This stirring not only serves to prevent duct formation and thus to prevent incomplete transformation of the starch, but it is also driven to prevent the build-up and accumulation of the so-called "dead zones" in the reaction chamber, thereby avoiding stinging and unwanted heat degradation of the starch. .

As will be well known to those skilled in the art, dextrins are starch degradation products obtained by heating starch in a relatively dry state in the presence or absence of an acid. Usually cornstarch from approx. 10 to approx. 12% by weight moisture; but during the dry heating of naturally occurring dry starch, this moisture is regenerated, after which dextrinization and branching begin. During the dextrinization reaction, both hydrolysis and condensation occur. Branching occurs as a result of the re-polymerization of partially hydrolyzed starch when the moisture in the starch is below approx. 3% by weight.

The term "dextrose equivalent number" (DE) is used to denote the content of reducing sugars at 0 7 ρ · s -i f 'r η / *! The dissolved solids in a starch hydrolyzate or dextrin expressed as dextrose percentage as measured by Schorrl's method (cf. Encyclopedia of Industrial Chemical Analysis, Vol. 11, page 41-42) Starch dextrins usually have a dextrose equivalent number of less than about 7 and most frequently in the range of about 1 to about 7.

Untreated starch usually has a branching degree of approx. 3.6%. Dextrins, on the other hand, usually have a branching degree of at least 7% and usually from 7% to 16%.

The degree of branching in a dextrin is determined by three types of analysis, viz. the dextrose equivalent number (DE determined according to Schoorl's as mentioned above), the dry matter content and the amount of formic acid formed after oxidation with periodate. The latter analysis is also known as the formic acid number (FAV) expressed in milliequivalents of formic acid per day. grams of dry matter and determined by low temperature oxidation (2 ° C) with sodium metaperiodate under 20 carefully controlled conditions. This method is more completely defeated by R.W. Kerr and F.C. Cleveland, J. Am. Chem. Soc., 74, 4036-4039 (1952) and by the same authors in Die Stårke, 5, 261-266 (1953), where further information on the request can be obtained.

Periodic oxidation produces one molecule of formic acid from each non-reducing terminal glucose unit and two molecules of formic acid from each reducing terminal glucose unit. Thus, changes in formic acid number, when calculated on the basis of one mole, indicate the branching degree of dextrin. From the above three analyzes, the degree of branching is calculated as follows: 1. The average molecular weight by number (Mn) is calculated by the following terms: o =, - 20,500 35 Mn -

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Note: ϋχΕχ is not taken into account for dextrose in dextrin, because the amount of dextrins present in dextrins is negligible.

2. The formic acid number (FAV) is converted from milliequivalents per year. grams of dry matter to equivalents per mol by the following terms: FAV, eg / mol = FAV, meq / g.t.s. x j_ ^ qqq 10 3. The branching number per. moles are calculated by the following terms:

Branches per mol = 3 15 Note: Periodic oxidation produces one molecule of formic acid from each non-reducing end group and 2 molecules of formic acid from each reducing end group.

4. The total number of bonds per mol is calculated: 20 π. . --Η - 18,

Bindings per mol = —— -1 5. The degree of branching is calculated: 25 Branching percentage = ^? - ^ and ^ n ^ is Pr · mo - * - x χοθ 3 3 ^ bonds per moth

The formula for starch dextrin can be written as where n is a variable (closer to a mathematical 6 10 5 n constant) and less than the value for n in starch. Dextrins 30 are available in various grades by heating starch for varying times to temperatures of up to approx. 240 ° C. Amylodextrin, erythrodextrin, achrodextrin etc. prepared by these measures can be roughly divided by molecular size by standard iodine test.

The dextrinization reaction can be catalyzed by treating the naturally occurring dry starch r · ': =' i * <i · -Ί! . ·. \. · '. -. . j

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with an acid either before or during the heating of the starch.

Any acid can be used for this purpose, e.g. sulfuric acid, sulfuric acid, hydrochloric acid and the like. Preferably, aqueous dilute hydrochloric acid is sprayed onto or passed aqueous hydrogen chloride gas through the starch particles before or during the heating process. Other chemicals such as borax can also be incorporated into the starch during the dextrinization treatment.

Referring now to the embodiment of FIG. 1 10 illustrates in detail a cross-sectional view of the fluidization apparatus preferably used for carrying out the method of the invention. The apparatus includes an elongated vertical housing designated 10 which defines in its upper part a chamber 12 provided with input means 14 for supplying starch. The housing 10 also defines a lower chamber 16 located practically at the bottom. Both the upper chamber 12 and the lower chamber 16 include respective stirring means 18 and 20. The stirring member 18 comprises a shaft 22 mounted 20 for rotation within the upper chamber 12. Mounted on the shaft 22 for rotation therewith are many vane plates 24, which can be in the form of flat vanes which can rotate together with the shaft 22. The stirrer 20 in the lower chamber 16 also includes a rotatable shaft 26, 25 on which wing plates 28 can be mounted for rotation therewith.

In the preferred embodiment of the invention, the stirrer 18 is formed with multi-blade upwardly bent wing plates 24 spaced apart, 30 being mounted at an angle of 90 ° between each of the wing plates 24, further wing plates 30 are used when two-blade wing plates are used. The stirrer 20 in the lower chamber 16 preferably has a similar configuration. If desired, some or all of the blade plates may be positioned at a certain angle with respect to those illustrated herein, depending on the number of blades per blade. wing- 10 \. ('! V V; · Γ' '· «1 v v..... J. <0 plate.

Located in a housing 10 in an intermediate section 32 are many tubes 34 having an upper end 36 which communicates with the upper chamber 12 and a lower end 38 which communicates with the lower chamber 16. In this way starch introduced through the inlet 14 by the action of gravity downward through the upper chamber 12 and further through the plurality of tubes 34 into the lower chamber 16.

The lower chamber 16 also includes an output means 40 0 for withdrawing starch dextrin therefrom.

Located below the lower chamber 16 is a housing 42 which defines a pressure chamber 44. Fluidizing gas is introduced into the pressure chamber through a fluidizing gas inlet means 46 and passes through an opening 48 into the lower chamber 16.

The arrangement of the tubes in the intermediate section 32 can be varied considerably. A suitable arrangement for the pipes 34 in section 32 is shown in the drawing of FIG. 2nd

As shown in this figure, the tubes 34 are arranged 20 in a pattern around the center of the section 32.

At least the tubular section is provided with means for supplying and / or removing heat therefrom.

For this purpose, the section 32 preferably defines a heat exchange media sheath which can be fed to the section 32 through an input member 49 and is removed from the section or sheath 32 through an output member 50 as shown in FIG. 1. It is also desirable in many cases to use heat exchange means with the upper and lower chambers. For this purpose, it is generally sufficient to provide a sheath 52 surrounding the upper chamber 12, the sheath 52 including an input means 54 for supplying heat exchanger media to the sheath 52 and a discharge means 56 for withdrawing heat exchange media from the sheath 52.

As shown in Figure 1 of the drawing, it may be sufficient that the heat exchanger sheath 52 to the upper

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11 I "-! V r --- · Γ- '.,., L- A i .....':. J chamber 12 only extends up to the input means 14, or it may be desirable that the sheath cover Generally, however, it is preferred that the upper chamber 12 includes an associated dome portion 58 from which the fluidizing gas may be withdrawn from the reactor by a discharge means 60. As will be understood by In the art, not only the fluidizing gas is withdrawn through the exhaust member 60, but any "fine particles" trapped in the fluidizing gas are entrained therewith and passed through the exhaust member 60. As will be understood by those skilled in the art, it is possible and sometimes desirable to design the upper chamber with an increased cross-sectional area, thereby reducing the linear velocity of the fluidizing gas and thereby assisting in the separation or separation of entrained particles (resulting from the solid phase) from the fluid upon its departure. t for the dome itself may be increased or the cross-sectional area of the entire chamber 12 may be increased for this purpose.

The lower chamber 16 may also be provided with heat exchange media, preferably in the form of a jacket 62, to which the heat exchange media is supplied through an input means 64 and from which heat exchange media can be withdrawn from an outlet means 66.

The process for converting starches to dextrin is illustrated specifically in Figure 3 of the drawing.

As shown in this figure, the supply of starch, preferably containing an acid as a catalyst, is fed from a hopper 70 to the input means 14, through which it is introduced into the upper chamber 12. In the preferred embodiment of the process of the invention, steam is introduced through conduits 72 and 74 in the heat exchange sheath 52 for supplying the upper chamber with heat.

The shaft 22 and the stirring means 18 can be driven by a convenient means 76 as shown in FIG. Third

The catalyst-containing starch is fluidized with 12 i · / / i i - r * /. Humid air entering the pressure chamber 44 through the inlet means 46 and passing upwardly through the lower chamber 16, through the pipes 34 in the intermediate section 32 and into the upper chamber 12. Water vapor is supplied as heat exchange medium additionally through conduits 78 to the sheath in section 32 and further through conduit 80 to sheath 62 surrounding the lower chamber 16. In this way, both the upper and lower chambers and the tubular section are provided with water vapor for heating the starch which passes genius easily to them.

Thus, the acidified starch supplied to the input means 14 is immediately fluidized in the upper chamber 12, while the upper chamber 12 is continuously stirred to counteract the effect of the fluidizing agent downward 16 through the upper chamber while being subjected to stirring.

The acidified starch continues its downward flow under the influence of gravity and in the opposite direction to the suspension action of the air flowing through the tubes 34 in which there is no stirring, except that which occurs naturally due to the inherent turbulence in the tubes containing the fluidized starch. After being sunk down through the tubes 34, where the starch is at least partially converted to dextrin, it continues its downward movement further into the lower chamber 16 still directed against the action of the fluidizing gas and is withdrawn from the lower chamber 16 through the outlet member 40th

According to one embodiment of the practical practice of the method according to the invention, the product taken out of the line 40 is passed through a rotary air lock 82 into a pneumatically driven cooling pipe where the temperature of the product is lowered to below 65 ° C. For this purpose, the product is discharged through the rotary air lock 82 into a cooling pipe 84 and passed to collection equipment 35 through a conduit 86. Dust or fine particles discharged through the access means 60 are removed by a cyclone 88 13 r '. {* C - * ϊ- ο - and are thus conveyed by means of a dust discharge line 90 to the collection equipment through the same line 86.

The starch dextrinized by the process of the invention may be derived from many different starchy materials, including starches of various cereals, starches of wax plants and / or plant roots. Typical of such starch materials are the non-waxy grain starches (e.g. corn starch and wheat starch), potato starch, tapioca starch, starch from the sugar sorghum, rice starch, waxy starches, e.g. starch from wax beans, milo beans, waxy corn starch, etc. The starches of non-waxy cereals are preferred, with corn starch being particularly preferred.

In practicing the process of the invention, the starch is mixed with a catalyst before being introduced into the stirred fluidized bed. Hydrogen chloride or hydrochloric acid is preferred, although any acid may be used for this purpose, including sulfuric acid, sulfuric acid and the like. The acid is mixed with the starch, preferably by spraying a weighed amount of acid over a layer of starch, while the starch is continuously mixed to provide a homogeneous acidified starch mixture. The use of a tape mixer has proved particularly suitable for this purpose. The amount of acid mixed with the starch is not critical and can be varied within wide limits, which depends in part on the type of starch used and the type of dextrin produced. Generally, such amounts of an acid equal to 30 are used in the range of 0.01 to 10 parts by weight of 20 ° Be 'of HCl per liter.

1000 parts by weight of starch, which corresponds to an average acidity expressed as milliequivalents of acid per liter. grams of starch (on a dry basis) between 0.001 and 0.10.

The acidified starch is then passed through the apparatus described above while kept at a temperature which is to some extent dependent on the type of starch.

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creation / to be made. Generally, the starch is maintained at a temperature in the range of 50 to 195 ° C and preferably from 75 to 190 ° C in the fluidized bed of the reactor. In general, the residence time of the starch in the fluidized bed of the reactor is less than 1 hour, and most often the residence time is in the range of 10 minutes to 30 minutes, although longer or possibly shorter residence times may be used, depending on some of the desired dex. degree of trinity and the degree of conversion sought. If desired, the air used as fludizing gas can be heated externally, which depends on the dextrin quality to be produced, although there is often little benefit to be gained from this variant. In general, the fluidized bed can be heated to a temperature in the range of from 15 to 175 ° C. For example, when canary dextrin is prepared, temperatures are usually preferred in the range of 107 to 168 ° C. The air supplied as a fluidizing gas preferably contains moisture to promote the rate of conversion more efficiently.

As will be appreciated by those skilled in the art, other fluidization media may be employed. Eg. For example, water vapor or inert gases such as argon, nitrogen or carbon dioxide may be used, preferably containing a certain amount of moisture. In addition, fuel gases from combustion operations can also be used as the fluidization medium if desired. It is not essential that the fluidization medium supply any free heat to the starch undergoing dextrinization, since the tube section of the reactor used in the ideas of the present invention in the dextrinization of starches is capable of providing all the necessary heat to efficiently to effect the transformation.

According to another embodiment of the invention, the fluidization process described herein can also be used in the treatment of starches to produce bleached starches and oxidized starches. Thus 15 P: f Λ Γ c ~ <'; As it is now well known to those skilled in the art, bleached starches are those starches produced by oxidative treatment which lead to a noticeably whiterer starch. the thoroughness of the oxidation treatment 5 such that the naturally occurring carotene, xanthophyl and related pigments are effectively oxidized to colorless compounds, while the starch produced is only weakly oxidized (ds> 0.1) as defined below (if the starch at all) Bleaching is preferably carried out in a dry state, and accordingly various oxidizing agents may be used, provided that the oxidizing agent is one which is mild enough under the reaction conditions so as to avoid excessive oxidation of the starch, but strong enough to Ensure that the pigments themselves will be oxidized effectively. Examples of useful bleaching agents include, without limitation, chlorine, bromine, alkali metal ypochlorites, alkali metal permanganates, ozone, alkali metal chlorites or alkali metal chlorites in combination with alkali metal persulfates. Methods for bleaching starch are discussed in more detail in "Chemistry and Industries of Starch", second edition, published by R.W. Kerr at Academic Press, Inc., New York, New York (1950).

25 Oxidized starches are such starches produced by oxidative treatment of the starch, leading to chemical changes in the starch. Eg. oxidation of primary alcohol groups to carboxylic acid groups, oxidation of aldehyde groups to carboxylic acid groups, oxidation of secondary alcohol groups to ketone groups, and oxidation of glycolic groups to carboxylic acid groups. The oxidation of starch leads to a more easily soluble starch product which exhibits lower viscosity when dissolved in water. Oxidation can be accomplished using any of several different oxidizing agents. Often, the oxidizing agents used are 16 t 'f:! ! Oxidized starch, the same agents used to bleach starch. Just tougher reaction conditions such as higher temperatures, longer contact times, a different pH, etc. are required to cause these agents to react with the starch molecules rather than merely with carotene, etc. The reagents used in the oxidation of starch include, but are not limited to, air. bleaching powder, halogens, chloramines, chloric acid, chlorates, chromic acid, ferric chloride, hydrogen peroxide, hypochlorite, manganese dioxide, nitric acid, nitrogen dioxide, perborates, periodic acid, persulfates, potassium dioxide, potassium permanganate, silver oxide, p-toluene and zinc oxide. Methods for oxidizing starch are also described in more detail in the above-mentioned literature site "Chemistry and Industry of Starch".

The repeated anhydroglycose units in starch may have different degrees of substitution (ds), ie. from 1 to 3, and the starch derivatives are usually divided into categories by reference to their degree of substitution. In a given amount of a starch derivative, there will generally be some unhydroglucose anhydroglucose units (i.e., ds = 0) present with other anhydroglucose units having different degrees of substitution therefrom, namely from 1 to 3. averages are used to characterize the average portion of the whole portion of the portion, although the number is generally quoted as the degree of substitution and not as the average degree of substitution. The oxidized starch treated by the process of the invention may have a varying range of degrees of substitution (carb-oxyl substitution) which may be as low as 0.0001 and up to a maximum level of 3.0. Regardless of the number of starch molecules reacted, or the order of actual substitution, or the number of anhydroglucose units involved, the general formula is intended to represent products where substitution may occur at varying degrees of substitution at all or fewer anhydroglucose units in all or fewer starch molecules.

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The distinction between oxidized and bleached starches is now well known to those skilled in the art, especially in the grain wet milling industry. Such a distinction is described in e.g.

U.S. Patent No. 3,598,622, in which details of the request may be obtained regarding these terms.

In general, the distinction between starch oxidation and bleaching is directly related to the severity of the reaction conditions. It has been found that starch oxidation generally occurs where the temperature of the starch undergoing conversion is maintained at levels above 93 ° C and preferably at 93 to 204 ° C. However, while the conversion is also related to the amount of oxidizing agent used, it has been found that the reaction temperature largely dictates whether the reaction is a bleaching or oxidation reaction. However, to effect oxidation, it is preferable to use an oxidizing agent in an amount in the range of 0.5 to 20% oxidizing agent based on the weight of the starch on a dry basis. At temperatures below 93 ° C, the reaction is predominantly a bleaching reaction, and the starch itself is only affected to a minimal extent. In general, starch bleaching is carried out at a reaction temperature of at least 25 27 ° C and preferably from 27 ° C to 104 ° C with an amount of oxidizing agent in the range of 0.05 to 2%, based on starch weight on a dry basis.

In carrying out the fluidization process of the invention for oxidation or bleaching of starch, it is usually preferred to introduce the starch mixed with the oxidizing and / or bleaching agent into the upper stirred fluidized zone from which the starch is allowed to pass downward from the upper stirred fluidized countercurrent to the fluidizing gas through many tubular fluidized zones into the lower fluidized zone while the starch is stirred in both the upper 18 f - * r *. ,, -.

1 · * \ t 'V V. . / 0 and lower fluidized zone. Thus, the oxidized or bleached starch is recovered from the lower fluidized zone. As is the case with dextrinization, the violent stirring in the upper and lower fluidized zone 5 not only serves to prevent duct formation and thus to avoid incomplete transformation of the starch, but it is also driven to prevent the formation and accumulation of so-called "dead zones" "in the reaction chamber, thereby avoiding stinging and unwanted heat degradation of the starch.

Alternatively, the starch mixed with the oxidizing agent or bleaching agent may also be applied to the lower fluidized zone, whereby the starch is sent upward from the lower fluidized zone through tubular zones and into the upper fluidized zone in co-flow with the fluidizing gas. Thus, in this practical embodiment of the method according to the invention, the oxidized or bleached starch is recovered from the fluidization system by withdrawal from the upper fluidized zone.

The heat supplied to the bleaching or oxidation reaction 20 is dissipated through the heat exchange media surrounding the tubular zones. Due to the high surface area of the heat transfer provided by the tubular zones, it is unnecessary to heat either the upper or lower stirred fluidized zone.

In general, the starch residence time in the fluidized bed reactor is less than 1 hour, which applies both to the production of oxidized starches and to the production of bleached starches. Most often, the residence time ranges from 10 minutes to 30 minutes-30 hours, depending on whether you want oxidation or bleaching.

According to a further embodiment of the present invention, the fluidization process can also be used in the drying of starch or similar cohesive solid particles. It has been found that in the fluidization method of the invention one is in

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19 OX 15X X '2 C 3 capable of effectively drying starches and similar materials which are coherent and, as a result, difficult to fluidize. The fluidization method of the invention provides remarkable energy savings and thus price reduction over the drying methods currently used for starch treatment.

As is well known to those skilled in the art, lightning drying is a method of drying starches which, incidentally, is very inexpensive because it minimizes the starch's residence time for necessary heat transfer. However, one of the major disadvantages of lightning drying applied to starch or any other material is that a high ΔΤ or high driving force is required for heat transfer, because all the drying energy must enter with the gas or superheated steam. In lightning drying of starches, it has generally been the practice to use hot air with inlet temperatures in the range of 175 to 260 ° C. The thus heated air serves as a heat source 20 as well as the carrier medium for the extracting moisture.

The method of the invention addresses the disadvantages of lightning drying, since the fluidization method of the invention is capable of providing an extremely high surface area for heat transfer as well as high heat transfer coefficients due to the turbulence of the fluidized system's tubular intermediate zones. At the same time, the process of the invention does not make it necessary to use as high ΔΤ as is required for lightning drying, since the driving force needed to effect the required drying degree can be supplied by means of a transfer fluid in contact with the tubular intermediate fluidization zones.

In fact, it has been found that the fluidization method of the invention can be used in drying starch, using as heat transfer fluid waste steam from turbine powered generators used.

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to generate electrical power. Such vapor is usually saturated at only a few atmospheric pressures. Either being able to utilize waste steam in the drying of starch represents a considerable economic advantage, as it avoids the use of extremely high air temperatures which are otherwise characteristic of lightning drying, while utilizing the low residual energy in exhaust steam.

Using the method of the invention for drying, starch or similar material can be applied either to the upper stirred fluidized zone or to the lower stirred fluidized zone, and the dried starch is taken from the opposite zone. The fluidizing gas may be any of the fluidizing gases described above, although it is generally most economical to use air. Heat for the drying operation can be supplied only by means of the heat exchange medium surrounding the central zone formed with tubes providing a high surface area for heat transfer, while at the same time providing high heat transfer coefficients due to the fluidized starch turbulence in the many tubular zones. Generally, heat transfer media having temperatures in the range of 38 ° C to 260 ° C can be used, depending on the material being dried and the amount of moisture present.

Following the above detailed description of the invention, the following specific examples will serve to further illustrate the invention while reviewing some characteristic embodiments of the process of the invention and the product thus produced.

Example 1 35

The present example illustrates the use of a 21 r- 1 / /] i- - ·? r- r. S 'i

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o reactor with a stirred fluidized bed of the type illustrated in the drawing of FIG. 1 and 3, and having 7 tubes in the intermediate section, by dextrinizing starch.

An acidified starch is prepared by feeding raw starch to a covered tape mixer, to which is then added gaseous hydrochloric acid. The amount of hydrochloric acid added is determined by titration and is indicated as a titer representing the number of milliliters of 0.1 N NaOH required to bring 20 g of starch slurried in 100 milli-10 liters of distilled water to a pH of 6. starch is introduced into the fluidized bed through the inlet member 40 and air is introduced into the overpressure chamber 44.

Dextrins can be characterized as either white dextrins or canary yellow dextrins. In addition, white dex-15 steps can be either high-resolution or low-resolution. The solubility is stated as a percentage and denotes the amount of a 2 g sample dissolved after being suspended in 250 milliliters of water at 25 ° C and shaken for 1 hour.

Canary yellow dextrins are classified as either 20 thick (high viscosity) or thin (low viscosity). The viscosity of dextrin is usually stated as its fluidity.

Eg. a fluidity of 3: 4 is calculated as determined by sample 4050 listed in the table below as follows. Three parts by weight of dextrin sample is mixed with four parts by weight 25 parts of water, heated on a steam bath for 30 minutes and then cooled to 25 ° C. Any evaporation of water as determined by weighing is compensated by the addition of water. The material is then pressed through a nylon mesh 5029 into a beaker and held at 25 ° C for a two hour cooling period of 1 hour. The material is then placed in a standard funnel and kept at 25 ° C. The fluidity is usually denoted in milliliter units and represents the amount of material flowing out of the standard hopper in exactly 70 seconds. The borax fluidity method 35 is the same as described above, except that 10% by weight of the sample is replaced by

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22 borax (Na2B40 ^ · 10Η2Ο).

As shown in the table below, a high-resolution white dextrin (sample 4050), a low-resolution white dextrin (sample 4060), a thin canary yellow dextrin (sample 4064) and a thick canary yellow dextrin (sample 4074) are produced.

Sample No. 4050 4060 4064 4074 10 Starch moisture,% 10.7 10.7 10 '11 ·

Starch titre, ml · 4.6 4.2 · 5.3 4.1

Operating temperature, ° C 135 93 · 154 163

Naninel residence time, minutes - 15.3 14.8 13.3 12.6 15 Airflow / pipe, skmnaPipe 0.156 0.156 0.156 · 0.156

Air velocity, n / sec, ^ 0.64 0.64 0.64 0.64

Headdressing pressure, ato 3.87 0.35 7.87 10.55

Product moisture,% · 2.5 5.0 2.2 1.9 20 Product soluble substance,% 94.5 19.8 98.1 97.9

Product fluidity, ml 22c) 25d) 16e) 36f) ► a) foam = standard cubic meter per minute.

b) Calculated on inner tube diameter 7.20 and 25 c) 3: 4 fluidity as it is d) 1: 3 10% borax fluidity as it is e) 2: 3 10% borax fluidity, scan it is f) 1 : 2 10% borax fluidity, if it is 30

The fluid-layer apparatus contains 7 tubes, each of which has an inner diameter of 7.20 cm.

The height of each pipe is 1,524 meters.

35 23

i, · s s.? r- o, - I-, i \ i -J · .- J iJ

island

Example 2

The present example illustrates another dextrinization reaction carried out in a fluidized bed system similar to that described in Example 1. The reactor used is of the same type as illustrated in FIG. 1-3 and has 7 pipes in the middle section.

Using the process described in Example 1, an acidified starch is prepared by feeding 10 raw starch to a mixer with gaseous hydrochloric acid as indicated in the table below. The amount of hydrochloric acid added is determined in the same manner as described in Example 1.

The acidified starch is then introduced into the fluidized layer through the input means 14 and air is introduced into the overpressure chamber 44.

As shown in the table, a high-resolution white dextrin (sample 5170), a low-resolution white dextrin (sample 5268), a thin canary yellow dextrin 20 (sample 5199), and a thick canary yellow dextrin (sample 5198) are prepared.

25 30 35

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24

Sample No. 5170 5268 5199 5198

Starch moisture,% 9.9 12.0 11.3 12.3

Starch titre, ml 4.3 4.5 5.0 4.7 5 Operating temperature, ° C 137 101 162 161

Naninel residence time, minutes 12.0 9.8 23.2 21

Airflow / pipe, sknm3 ^ / pipe 0.093 0.102 0.088 0.088

Air velocity w / sec ^ 0.61 0.61 0.61 0.61 10 Hood steam pressure, ato 4.78 0.98 8.44 8.23 Upper pipes cmdr. per. min (diam 38.1 in) ^ - '42 42 42 42

Lower stirrer cmdr. .pr. min (diam. 25.4 cm) ^ 66 66 66 66 15

Product moisture,% 2.0 5.7 1.7 1.5

Product soluble substance,% 98.3 17.4 98.9 98.5

Product fluidity, ml 27C ^ · 23 ^ 18e ^ 42 ^ 20 a) skimi = standard cubic meter per c) 3: 4 fluidity, if it is d) 1: 3 10% borax fluidity, e) 2: 3 borax fluidity, son. it is 25 f) 1: 2 10% borax flux, so it is.

(g) two 4-blade upward-swinging vanes; h) three 4-blade upward-swinging vanes 30

The fluid-layer apparatus contains 7 tubes, each with an internal diameter of 7.11 cm. The height of each tube is 1.5 meters.

35 Ο 25 V. 'S Λ - *' C; - - Λ

\ i ·,; ... .. J

Example 3

The present example illustrates the use of the fluidization process of the invention in drying 5 starch.

Using the equipment described in Example 1, starch having a moisture content of 12% by weight, based on the weight of the starch on a dry basis, is fed to the inlet 14 and dry air taken from the surroundings 10 is introduced as the fluidizing gas.

Heat to the drying operation is supplied by feeding the vapor sheath 32 with steam at 10.3 ato. The starch is fluidized for an average residence time of 15 minutes and dried to a moisture content of 3.3% by weight on a dry basis.

15

The above examples illustrate the use of the process of the invention in the dextrinization of starch and in the drying of starch. While Example 3 above illustrates what is known in the art as secondary drying of starch, ie. reducing the starch's moisture content from a level of approx. 10 to 14% and down to a level of approx. 3 to 5%, the process of the invention may also be used in the drying of starch containing greater amounts of moisture. Eg. For example, the process of the invention can be used in the drying of starch containing approx. 35 wt% moisture on a dry weight basis. In addition to starch, the process of the invention may also be used in the drying of gluten, germ, corn syrup solids or sugars, dextrose, etc.

The process of the invention is also well suited for use in the preparation of starch derivatives.

Such derivatives are formed by reacting starch containing up to 35% moisture on a dry solids basis with many different reagents according to well-known reactions. Such derivatives are formed by the reaction of starch represented by the general structural formula t - »/ t. * f * ^ «<· · * fc t V_ · V M - - / 26 0

I I

Clio OH! CII2OH! Ciroii I> 1 (^ η / --- 9 η i η J — ο η I i / i 9 π ^ y! [/ ¾ M! Γ «\ 011! 7_J .__ I \ oh n / __. __I \? n γ

HO 9 (^ - '' j OH

H OH 'H OH I H 911 I! L J.

10 with several different reagents, whereby the starch molecule is substituted by either the primary and / or the secondary hydroxyl groups. Eg. For example, starch phosphates can be prepared by reacting starch with an alkali metal tri-polyphosphate, whereby the starch forms a starch phosphate ester. In addition, cationic starches can be prepared by reacting starch with glycidyl trialkylammonium halides, preferably those of the structural formula CH0 - CH - CH ~ - N (R) t X ~ z z ό 0 wherein R represents a lower alkyl group such as methyl, ethyl, propyl, etc., and X represents a halide ion. In addition, other reagents can be used to prepare cationic starches such as β-halogenated amines including 2-dimethylaminoethyl chloride, 2-diethylaminoethyl chloride, 2-dimethylaminoisopropyl chloride, 2-diallylaminoethyl chloride, 2-diisopropylaminoethyl chloride, etc.

Aninonic starch derivatives can be prepared by practicing the process of the invention, reacting starch with an alkali metal salt of an omega-halogenated substituted carboxylic acid. Preferred reagents for use in the preparation of anionic starch

Γ ”', -. · -: - -: -3. \ i * J · ·. · '-. '-J

solutions include sodium chloroacetate, sodium 2,3-epoxypropyl sulfonate, sodium 3-chloro-2-hydroxypropyl sulfonate or propiolacetone. In the above-mentioned reactions to prepare anionic starches, the starch is contacted with the reagent in the presence of a basic catalyst to promote the reaction, which is also well known to those skilled in the art.

Another reaction to which the process of the invention is ideally suited is the preparation of starch carbamate. In this reaction, urea is reacted with starch, whereby the starch is substituted with carbamate groups having the structure 0

II

0 - C - NH,

Other starch ethers can also be prepared by the process of the invention, namely according to well known reactions. In such reactions, starch is reacted with e.g. acrylonitrile, acrylamide, methacrylamide, dialkylmethacrylamides, etc.

In carrying out each of the reactions described above, it has usually been found preferable to bring the starch containing from ca. 3 to approx. 35 wt% 25 moisture, in contact with the reagent to be used in the preparation of the derivative, to ensure intimate mixing of the starch with such a reagent. The starch containing the desired reagent is then added to the fluidized bed system in the practice of the method of the present invention, either to the upper fluidized zone or to the lower fluidized zone as described above, and the reaction is carried out as described in the examples for preparing the desired starch derivatives according to the above general reaction schemes. In practicing the process of the invention, the desired conversion of the starch 28 o to the starch derivative is accomplished over a relatively short period of normally 5 to 30 minutes in the fluidized system, avoiding undesirable heat degradation of the starch and at the same time minimizing the risk of fire 5 and / or explosion as a result of superheating in the fluidized reaction system.

Illustrative of typical reactions may be mentioned that starch can be oxidized by mixing it with a suitable oxidizing agent (NaOCl) in a band mixer 10 in sufficient quantity to provide a starch containing 1.0% oxidant expressed as chlorine on dry basis solids. The resultant mixture of starch and oxidant is then introduced into the fluidized bed through the inlet 14, and a suitable fluidizing gas, preferably air, is introduced into the overpressure chamber 44.

The heat needed to promote the oxidation reaction is supplied by contacting the plurality of tubular zones with an appropriate heat exchange medium such as steam for heating fluidized layers 20 to the desired reaction temperature. The resultant oxidized starch is then removed from the lower fluidized zone, having a viscosity determined according to Scott (of 100 g) of approx. 47 and a carboxyl number of 0.65.

It will be appreciated that the process of the present invention provides a significant improvement in the fluidization of materials which are prone to cohesion and thus are difficult to fluidize. The method of the invention is particularly well suited for the treatment of starch using a system of stirred fluidized bed which includes an upper and lower mechanically stirred zone which serves to maintain the homogeneity of the fluidized bed and to prevent the burning or burning of the starch as it is passed through the middle section of the reactor formed with tubular zones. The method includes the use of an intermediate narrowed 29 Γ-! r, · '-, -. ': -

· '-. \: ·> · ·. · _J

Ο heat exchange zone interposed between the upper and lower stirred fluidized zones, the starch being processed being passed rapidly through the intermediate layer to prevent the starch from burning or burning.

It will also be appreciated by those skilled in the art that the process of the present invention is not limited solely to the treatment of starch. On the contrary, the process of the invention can be used in the treatment of many different materials which tend to be interconnected and thus are difficult to fluidize.

15 20 25 30 35

Claims (1)

u • s - - .-. • ♦ s <- * o Patent claims. Fluidization process, especially for use on difficult fluidizable, highly adherent solid particles such as starch, in which supplied solid particles are fluidized by an upwardly flowing fluidizing gas in a number of successive flow zones, subjected to treatment, and then stripped, characterized in that the fluidization takes place in three superficial flow zones, a lower zone, an intermediate zone and an upper zone, the intermediate zone being divided into several sub-zones of a smaller cross-section than the upper and lower zones, whereby the solid particles are introduced. in the upper or lower flow zone, 15 is passed through the intermediate zone to the lower or upper flow zone and discharged therefrom, and in addition to the fluidization gas, the solid particles in the upper and lower flow zones are further stirred mechanically and in the intermediate zone undergo a heat exchange. 20 25 35