FI58110B - REFRIGERATION FOR MONO-CALCULATION OF MONOCALCIUM PHOSPHATE / ELLER DICALCIUM PHOSPHATE FOR EXHAUST GENERATION OF MONO-CALCIUM - Google Patents

Description

-I r-1 ANNOUNCEMENT _ Q „. _ (11) UTLÄGGNINGSSKMFT 5 8 1 1 0 C Patent granted 10 12 1030

Patent coddslat ^ (51) K *.! K? /H*.a.3 c 01 B 25/32

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(22) HikemhplW * - An * ekning * d «g 18.03.75 (23) Alkuptlvi — GIWgh« * Ug 18.03.75 (41) Tullut luiki * · lui - Bllvlt offontllg 20.09.75

National Board of Patents and Registration (44) Nihttviluipvmn] KuulLiulksiau date.

Patents and registration authorities * 6k * n utiagd och uti. * Krtft * n pubUc «nd 29.08.80 (32) (33) (31)» tuolkeu »—Begird prlorlm 19.03.7 ^

Norway-Norge (NO) 7 ^ 098U

(71) Norsk Hydro a.s, Bygdöy alle 2, Oslo 2, Norway-Norway (NO) (72) 0yvind Skauli, Forsgrunn, Jan Birger Isaksen, Porsgrunn,

Norway-Norway (NO) (7 * 0 Oy Kolster Ab (5 **) Method for the production of monocalcium phosphate and / or dicalcium phosphate and plant for the implementation of the method

The invention relates to a process for the preparation of monocalcium phosphate and / or dicalcium phosphate by a direct reaction between a preheated phosphoric acid and a preheated aqueous suspension of finely divided calcium carbonate.

The phosphates according to the invention are so-called feed phosphates, which contain P and Ca in a more defined ratio and in a form in which the phosphorus component can be easily taken up by the animal organism. Such mineral feed compounds are required to meet certain purity requirements, e.g. fluorine, arsenic and heavy metals. For further processing and use, it is important that these feed phosphates are in the form of storage-stable, strong and free-flowing granules with a suitable bulk density and a suitable grain size.

It is known to prepare such feed phosphates by the reaction between phosphoric acid and fine-grained, mineral calcium compounds.

It is further known to carry out the reaction directly between pure, preferably concentrated phosphoric acid and a pure calcium component, which may optionally be in the form of an aqueous suspension. During the reaction, the resulting reaction mass passes through 2

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the first tough and sticky phase. Thereafter, the reaction mass hardens as the reaction is complete. This causes specific consistency and handling problems.

When the silicon component is in the form of CaCO 3, the reaction takes place under strong gas evolution, leading to a further increase in consistency and processing problems in the equipment. This is probably the reason why many previously known processes for the preparation of feed phosphates describe the use of other calcium compounds which are not as problematic in terms of consistency and processability.

The sticky reaction mixture formed is so tough and heavy flowing that it requires very high mixing forces during further processing. With known granulation methods, the mixture is difficult to handle unless significant amounts of finished product are returned.

The above consistency problems also make it difficult to cause the reaction mass to mix homogeneously. Local acid concentrations due to poor mixing again result in a product with poor handling and storage properties.

Due to these particular difficulties, it has not yet been possible to develop a simple and reliable method for preparing granulated feed phosphates from phosphoric acid and CaCO 2. According to South African Patent 66/777 **, which relates to such a reaction process, the granulation step is omitted and instead a sticky and heavy-flowing reaction mass is passed to a slow-moving conveyor belt where the reaction is completed as the reaction product cures. The solid mass is then crushed using a rotary crusher. However, this gives a less satisfactory product with faceted grains of uneven size and a lot of dust.

According to Norwegian patent 100875, the reaction is carried out batchwise without the presence of an aqueous phase and by rapidly mixing the limestone flour and 80-¾ phosphoric acid in a plate mixer. In this case, agglomerates are present for a short time, but the mixer continuously disintegrates these so that a weakly plastic powder is formed. A particular disadvantage of this method is the time, since the reaction takes up to 50 hours. In addition, the powdered product is not sufficiently free-flowing and is not suitable for mixing with commonly used feed materials.

It is also known to shorten the reaction time by working in a more aqueous system and using a known granulation technique. The aqueous reaction components are then decomposed into a larger amount of fully reacted feedback. Swedish publication 3 ** 0 * t ** 3 relates to such a method, but its implementation depends on the use of substantial amounts of feedstock in the granulation process, always 25 times the amount of the reaction mixture while decomposing the reaction mixture.

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3 components for this feedback material. The use of such a feedstock complicates the process and greatly reduces the production capacity of the granulation section. Accurate control of the reaction conditions in terms of water / acid ratio, reaction times and temperature is also difficult to perform in this method.

The process according to the invention is characterized in that the reaction components are introduced into a short tubular reaction zone, one end of which is closed and the other end open, whereby the reaction mixture is depressurized from the open end to give the reaction product in the form of a free-flowing granular product.

The reaction between phosphoric acid and calcium carbonate to monocalcium phosphate (MCP) or Dicalcium phosphate (DCP) takes place according to the following general reaction schemes: MCP: CaCO3 + 2Η ^ Ρ0 ^> Ca ^ PO ^ + CO2 + 1 ^ 0 DCP: CaCO ^ + 1 ^ When using another phosphoric acid containing, for example, calcium from a neutralization plant or an odd solution of the Odda process 1, it has been found that in the process according to the invention Caih ^ PO ^) ^ reacts even in the doped mixture. in accordance with the following reaction scheme:

Ca (H2PO1 +) 2 + CaCO3 -> ZCaHPO4 + CO2 + H2O When using preheated reactants, an aqueous suspension of finely ground calcium carbonate can be reacted very rapidly with phosphoric acid to form a large amount of gas and foam. Such a rapid reaction between warm reactants is used according to the invention in a very special way, whereby very thorough mixing of the reactants takes place, without energy-intensive mechanical stirrers and in a short time the reaction mixture decomposes into air. Most of the reaction takes place as the reaction mixture floats in air in the form of discrete droplets of foamable mass. Normally a sticky mass is generated in this phase and what has been described above is crucial in terms of miscibility, energy requirements, etc. When this short-term suspension has ceased, the reaction mixture appears as a semi-moist non-stick granular substance.

The process and associated apparatus for carrying out the process will now be described in detail with reference to the accompanying drawings, in which Figure 1 schematically shows a simplified process diagram, while Figure 2 shows a schematic section of a tubular reaction structure that can be used to carry out the process.

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Figure 3 shows a cross-section through the same reactor along line a-a in Figure 2.

Figure 1 shows a supply line 1 for a suspension and a second supply line 2 for phosphoric acid. Pump 3 pumps the warm suspension through line 1 to a short tube reactor in 5, the design and operation of which are described in more detail below.

Warm phosphoric acid is pumped via line 2 to reactor 5 by means of pump 6 and the two reactants are thoroughly mixed together in the reactor under intense gas and foam formation. The reaction mixture then protrudes through the open end of the reactor into the chamber 7 and floats freely falling in the chamber until the reaction product collects in the collecting device 8. The upper end of the chamber is provided with a gas outlet communicating with a vortex separator 9a and an outlet vacuum 9. in the form of a fluid product. By appropriately controlling and adjusting the reaction conditions, the product to be easily treated can be obtained with all possible Ca / P ratios.

Due to the evolution of gas during the reaction between phosphoric acid and calcium carbonate, the product has a somewhat porous structure, so it can be light in type for direct mixing with other components of simple compound feed types.

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However, the semi-moist primary material obtained after completion of the first process step is excellent for further processing and also for co-granulation with other minerals and spores which can be efficiently mixed in the reflux stream before the mixing and assembly device 8. The process can therefore be further processed and breaking the pore structure to produce granules with a higher liter weight. The intermediate is fed from the tank 8 via a plate feeder 10 which ensures free flow from the wide opening. The desired level of material on the plate is achieved by the surface adjuster (not shown) controlling the position of the feeder scraper. In addition, the instrumentation of the chamber makes it possible e.g. that the regulated air flow can pass through the porous, warm and somewhat moist product at the outlet. The product is then pressed in a single or multi-stage press 11, from which the substance in the form of compressed flakes is introduced into a granulator 12, where it is granulated in a moist state. In this case, a large, low-dust fine grain is obtained, which is passed through a dryer 13 and a subsequent screen 14, after which the product enters the warehouse in the form of free-flowing non-sticky granules.

The tubular reactor 30 is shown in more detail in Figures 2 and 3.

It comprises three main parts, a mixing chamber 55 * a pressure 56 and a push tube 53, two separate ignition tubes 51 and 52 bring the reactants tangentially into the mixing chamber 55 (Fig. 3) so as to form a strong vortex and mixing, as the force of gas evolution increases. An overpressure develops in the pressure chamber 56, which accelerates the foamed mass through a somewhat narrower outlet to the outlet pipe 53 * This pipe is preferably connected to the pressure chamber so that it can be detached and can be shaped differently. The cross-section and the total reactor volume can be selected so that the exit rate of the reaction mixture becomes optimal in relation to the reaction sensitivity of the reactants used. The choice of material is less decisive and the removal part can be made of stainless steel, Teflon or made of other plastic or rubber materials. Plastic and rubber materials can be advantageously used if the components of the mixture tend to deposit on the inner wall of the reactor as well. At the closed rear end of the reactor is a rod 54 which can be used to hold the reactor open if it fills and clogs in unexpected operating stops.

Performance examples:

Example 1 (MCP)

The ground chalk, which had been ground to an average grain size of 15-20 μm and a maximum particle size of about 50 μm, was used at 55.1 kg / h 60 fox in the form of its aqueous suspension. The temperature was 90-3 ° C and the suspension was continuously fed to the reactor together with 127.5 kg of phosphoric acid per hour at 6,581,106> 2 ° C. The acid contained $ 82.8 Η ^ ΡΟ ^.

184 kg / h of product with $ 21.8 HgO before granulation was obtained. The carbonic acid content was $ 0.6 and the material was very suitable for granulation and onward transport and handling. The product was continuously dried to a water content of $ 1.4. After drying, the particles had good strength and density. The P content of the dried granules was $ 22.6. The weight ratio Ca / P was 0.71 *

Example 2 (MCP ^

A chalk having the same degree of roughness as in Example 1 was reacted with less concentrated phosphoric acid to give a more aqueous reaction product. 141 »θ kg of 74» 5 $ phosphoric acid and 88.8 kg of 64.5- $ lithium suspension per hour were fed to the reactor and the reactor was operated at a filling pressure of 3.2 atm. This gave a particularly fine-grained reaction product, the properties of which made it suitable for further processing in the granulation process.

Example 3 (MCP)

In the same experimental set-up used in Example 1, a chalk with the same fluidity but an average grain size of about 50 microns was used. The concentration and amount of the suspension were the same as in Example 1 and the temperature was 87 ° C. The amount of acid was the same as in Example 1 and the temperature was 117-1 ° C.

The drying process was time consuming and gave an incompletely dried product. The product was sticky and corrosive and contained $ 3.7 COg · Stickiness interfered with granulation.

Example 4 (DCP)

The following example and Example 7 show how DCP was prepared: In the same apparatus used in the previous examples, a particularly P-poor product was prepared by reacting an increased amount of carbonate with phosphoric acid.

The conversion chalk, which was 98- $ ground to a grain size of less than 20 yum, which corresponded to an average grain size of 4-5 yum, was used as the 59- $ aqueous suspension. The feed was heated to only 65 ° C and was fed at 177 kg / h.

87.6- $ phosphoric acid was fed at 113 ° C at 110 kg / h.

The reaction product contained $ 33 HgO and $ 1.8 CO 2 and was then suitably plastic for granulation. A Ca / P weight ratio of 1.4 gave analysis of the dried product at $ 18.8 P and $ 25.6 Ca.

Example 5 (MCP ^

A 42.6- $ aqueous suspension of the conversion chalk having approximately the same roughness as in Example 1 was prepared and fed to the reactor at a rate of 34.0 kg / h at 92 ° C. To prepare a feed phosphate having a P content of about $ 24, this amount of chalk was reacted with F-free, Ca-containing phosphoric acid at 128 ° C at a rate of 128.6 kg / h. The acid P analysis gave $ 25.9 and the weight ratio Ca / P was 0.43, so that the Ca / P of the product was about 0.70.

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The reaction rate was satisfactory and the plasticity of the reaction product was very suitable for subsequent granulation, the H 2 O content of 16.5 l · CO 2 could be indicated to be 0.6 l from unreacted CaCO 3.

Example 6 (MCP)

The same chalk as in Example 5 in a less aqueous suspension, 60 l of CaCO 3, was reacted with the same acid under the same conditions and temperatures. The reaction was slow and incomplete. The product was not suitable for granulation and a total of 2.5 i of CO2 was found. · Substantial post-reactions could be demonstrated in additional processing experiments.

Example 7 (DCP)

Chalk with an average grain size of 10-15yu, but as a 46.8 · $ suspension in an amount of 159.6 kg, could be reacted with 129.1 kg of Ca-phytic acid, which had a Ca / P was -0.522 and the total concentration of P was 25.6 i ». The acid temperature was 152 ° C. The somewhat longer reaction does not prevent the assembled reaction product from being further treated with about 39 μg of HgO. With a Ca / P ratio of 1.22, no interfering acid residue remained, although the unreacted amount of carbonate in the CO2 analysis was 1.7 i ·

Due to the higher amount of water removed during drying, the product was given a bulk density of 790 g / liter when all less than 0.1 mm and more than 1.5 mm were removed. The particle strength was also somewhat poor compared to the product with a lower Ca / P ratio. The product sample dried in 3 g of H 2 O (determined after drying for 5 hours at 105 ° C) had a P analysis of 20.1

Example 8 (storage test)

A number of different prepared feed phosphates were experimentally stored for 12 weeks under varying climatic conditions. The sacks were attached to hydraulic sack presses, which gave a load of about 1500 kptn to each sack. The Ca / P weight ratio of calcium phosphates was between 0.7-1 »5» The products had 1.5 nm larger particles than 0.1 mmm, the proportion of particles was 1-23 i and the water content, determined by drying for 3 hours at 105 ° C, was between 0.4 and 4.9.

Mixtures of up to 39 germs of finely divided lime flour and up to 6 germs in MgO powder form had also been prepared from the same products.

Only one variation showed curing after 12 weeks of storage. This was demonstrably a poorly dried and high dust MCP mixture with lime flour flour (16 i dust and 4 i water).

In the presence of MgO, this mixture was also completely loose. Loose was also MCP alone, containing up to 23 i of dust and 5 i Η ,, Ο.

All percentages given above are percentages by weight.

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It is important that the calcium carbonate used is sufficiently finely divided. Experiments have been carried out with different grain sizes and it has been found that it is necessary for the grain size of the substance to be substantially less than 50 [mu] m, preferably so that at least 98 weights consist of granules less than 50 [mu] m. The preferred grain size is between 5 and 20. The highly ground quality with 98 wt% less than 20 μm and an average grain size of 4-5 μm also gave a completely satisfactory final product. This is a much finer granular material than is used in other known commercial processes, where coarser particles are used to prevent rapid completion, taking into account consistency problems. The added amounts of water result in a faster reaction. However, it is not possible to take advantage of this to use a substantially coarser chalk, as the chalk then becomes less reaction sensitive.

Both mineral chalk and doped chalk can be used. The latter may be calcium carbonate, which is formed as a by-product of the conversion of Ca (NO 2) 2 from the Odda process with NH 3 and CO 3.

As mentioned earlier, the method is also flexible with respect to products, insofar as MCP or DCP or intermediate grades can be produced. The flexibility of the process on the raw material side has been discussed above. Both Cat-free and Ca-containing phosphoric acid have been shown to be useful, while the amount of CaCO 2 added is reduced accordingly if the phosphoric acid contains calcium.

In either case, the Ca / P ratio of the product can be chosen freely.

Useful, commercially available grades of phosphoric acid that meet the above purity requirements are preferably concentrated. Most of the experiments have been performed with two main types of phosphoric acid, pure phosphoric acid containing 74-88 wt.% H 2 PO 4 and Ca-containing acid prepared from the extraction solution of the Odda process. Both grades were used undiluted and both gave a satisfactory reaction.

Acid grades with more water can also be used if they also meet the quality requirements that can be set. Adjusting the water content of the slurry suspension and adjusting other process variables ensures the desired reaction rate and composition while maintaining the course of the described process.

Ca-containing acid, which leads to greater consistency problems when used in conventional feed phosphate production, can surprisingly be easily used in the new process. In this context, however, it is important that the Ca / P weight ratio does not become too high - and according to the invention it has been found that it is most advantageous to work with a Ca / P ratio = 0.45 *

Both the phosphoric acid and the suspension suspension are preheated when introduced into the reaction zone. Temperatures between the? 58110 to 60-100 ° C and phosphoric acid temperatures between 113-132 ° C. This satisfies the requirements for reaction rate and product consistency for calcium carbonate with reasonable degrees of roughness. In the case of particularly fine grades of calcium carbonate, the temperatures can be correspondingly lowered so that the desired reactivity can always be easily achieved.

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Claims (10)

A process for the preparation of monocalcium phosphate and / or dicalcium phosphate by direct reaction between preheated phosphoric acid and a preheated water suspension ion of finely divided carbon in carbonate, characterized in that the reaction components are initiated in a short tubular reaction zone, each of which is a reaction zone, the other end is open, the foamy reaction mixture discharging through the open end due to the pressure of the formed carbon dioxide, and a reaction product in the form of a free-flowing granular product is obtained. 2. A process according to claim 1, characterized in that in the calcium carbonate suspension at least 97% by weight of the particles has a grain size less than 50 µm. Process according to Claim 1 or 2, characterized in that the average grain size of the calcium carbonate is below 20 µm. Process according to any one of claims 1-3, characterized in that the cesium carbonate suspension is preheated to a temperature between 60 and 100 ° C. Process according to any of claims 1-4, characterized in that the phosphoric acid is preheated to a temperature between 113 and 132 ° C. 6. A process according to any one or more of claims 1 to 5, characterized in that a pure phosphoric acid containing 74 to 83% by weight H 2 PO 3 is used. Process according to any of the claims 1-5, characterized in that calcium-containing phosphoric acid is used. 8. A process according to any one of claims 1-7, characterized in that a calcium-containing phosphoric acid having a Ca / P ratio does not exceed 0.45. An installation for carrying out processes according to claims 1 to 8 comprising a reaction zone coupled with separate feed lines for both calcium carbonate suspension and phosphoric acid and devices for collecting and further processing the formed reaction product, characterized in that the reaction zone is designed as a reaction zone. a known pipe reactor (5) having an open end portion forming a discharge pipe, said discharge pipe being arranged for cooperation with a drop chamber (7) and a collection device (8) arranged in the lower end of the chamber 11. Installation according to claim 9, characterized in that the pipe reactor (5) consists of 3 sections arranged one after the other, a first mixing chamber (55), a reaction or pressure chamber (56) and a discharge pipe (53), and the mixing chamber is closed to tangentially arranged supply lines (52, 57) for the reaction components.