DE3842130C1 - Process for preparing calcium hydrogen diphosphate - Google Patents

Abstract

Process for preparing calcium hydrogen diphosphate by dehydration of thin layers of calcium dihydrogen phosphate in a closed reactor.

Description

In baking technology, besides the known leavening agents, baker's yeast is also used and sourdough the chemical dough loosening agents are of central importance. The release of carbon dioxide has proven to be optimal soluble carbonates, especially sodium bicarbonate, by exposure of substances which release protons in aqueous solution, proven. Substances of this type are usually called Baking acids or driving acids.

Recently, in addition to the standard bakery products that are in the Household or commercial operation immediately after the dough is finished be baked, even such baked goods of greater importance received, in which the finished dough either in the course of Processing itself or as part of the distribution channel up to recycling by processors or the end user refrigerated or frozen for a long time.

So far, sodium aluminum phosphates are used for this application approximate composition

NaAl₃H₁₄ (PO₄) ₈ × 4H₂O

only used as baking acid, provided there is a legal authorization to do so.
However, the use of sodium aluminum phosphate is impaired by its hygroscopicity, the tendency to cake that results from this and, in particular, the unsatisfactory flow behavior in mechanical transport systems.

Of particular importance is the fact that according to recent knowledge an influence of aluminum on the emergence of certain Central nervous system disorders cannot be excluded is. Although the previous knowledge on this require further investigation, but is still from existing ones legal application bans within most EC countries going out.

There was therefore a need to use sodium aluminum phosphate as Baking acid for finished doughs through technologically analogue, to replace physiologically harmless substances.

Surprisingly, calcium dihydrogen diphosphate (acid Calcium pyrophosphate) as excellent for this purpose proven. It has long been known that acidic alkali and alkaline earth pyrophosphates can be used as leavening acids to release carbon dioxide from alkali carbonates in doughs (DE-P 30 26 672). Due to the high response rate (30-50) such compounds were only used as baking acid for "Baking powder" used for doughs for immediate processing are determined.

Such is a high level for the above-mentioned types of frozen dough However, the reaction rate is not suitable.

It has now been found that calcium dihydrogen diphosphate, which special purity requirements are sufficient on sodium bicarbonate a form that acts for the purposes described required reaction rate of about 20 is reached and is also suitable with regard to all other requirements that To replace aluminum phosphates as baking acids.  

It is known from DE-P 41 00 98, 2 moles of primary ammonium phosphate with neutral metal pyrophosphate to acidic pyrophosphates to implement (Eq. 1). There is also an implementation of secondary Orthophosphates with 1 mol ammonium phosphate possible (Eq. 2).

Me₄P₂O₇ + 2 NH₄H₂PO₄ → 2 Me₂H₂P₂O₇ + 2 NH₃ + H₂O (Eq. 1)

Me₂PO₄ + NH₄H₂PO₄ → Me₂H₂P₂O₇ + NH₃ + H₂O (Eq. 2)

From DE-P 30 26 72 it is known to use 2 moles of ammonium phosphate To convert 1 mol of carbonate to pyrophosphate.

2 (NH₄) H₂PO₄ + Me₂CO₃ → Me₂H₂P₂O₇ + 2H₂O + 2NH₃ + CO₂ (Eq. 3)

The reaction proceeds in two stages, initially with the escape of Ammonia and carbon dioxide to the orthophosphate and then at further increased temperature with elimination of water to the pyrophosphate. The conversion of monocalcium phosphate to calcium dihydrogen diphosphate is intensive by Hill (Ind. Eng. Chem. 39 (1947), 12, 1667-1672). After that it turns out that even at Use of only small amounts (20-100 g) in a thin layer and with precise control of the heating conditions, this pyrolytic Splitting of water to the acid pyrophosphate only incomplete expires, d. H. in the end product even after a long reaction time up to 10 or 20% orthophosphate can be included, and on the other hand "Amorphous" products are formed, which are analytical as metaphosphates and polyphosphates prove what a indicates significant overreaction. An improved response leaves reach themselves by passing water vapor, but also below under these conditions an "amorphous" product is formed and that The end product is not finely powdered, but falls into baked goods Lump on. Undetected reaction and clumping are intensified, if you start with an orthophosphate containing water of crystallization and the crystal water does not initially at temperatures from approx. 150-180 ° C is slowly removed. For technological processes this method is therefore unsuitable.  

The aforementioned reactions with ammonium phosphate prove themselves in technical process is also unsuitable because, in addition to contamination due to residues of the ammonium salts or carbonates these processes in larger quantities in addition to more acidic orthophosphates metaphosphates and polyphosphates are already formed, the use of such products as baking acids in the food sector hinder.

The object of the present invention is therefore a method for the production of a pure calcium dihydrogen pyrophosphate To provide that can be used as baking acid can.

The process according to the invention consists in the condensation of Monocalcium phosphate and / or monocalcium phosphate monohydrate Calcium dihydrogen pyrophosphate in a reactor under heat, the starting material in a reactor in a thin layer the reactor wall heated to 255-230 ° C is pressed and the heated layer immediately detached from the wall and with the remaining reaction material is mixed. The reactor is there sealed so that gas exchange with the environment is prevented and the reaction product in the vapor atmosphere of the formed Water of reaction is produced.

The heat transfer takes place from the outside via the reactor wall e.g. B. by means of a tempering medium such as thermal oil, metal melting or molten salt, the temperature control within narrow limits must be regulated. A device is preferred according to DE-A 29 07 453 used. The reactor is modified so that gas exchange with the environment is prevented and the reaction product is produced in the steam atmosphere of the water of reaction formed.  

In addition to the main purpose, the production of pure calcium pyrophosphate, advantages of this reaction management are the savings of steam and heating energy to be supplied, as well as avoidance of environmental pollution caused by vapor vapors containing dust.

Commercially available pure monocalcium phosphates and / or monocalcium phosphate monohydrates with a residual water content of 0.1 to 5.0% (dry loss), preferably 1.0 to 3.0%, are used as raw materials. These have pH values (1% in water) of 3.8 to 4.0 and lose 15.4 +/- 0.3% water or 21.4 +/- 0 when annealed to 800 ° C. 3% for monocalcium phosphate monohydrate within one hour. The molar Ca / P ratio should be in the range from 0.40 to 0.60, preferably in the range from 0.45 to 0.55. For the continuous production process, a monocalcium phosphate and / or monocalcium phosphate monohydrate with an average grain size of less than 1000 μm, and in particular a D ₅₀ between 50 μm and 500 μm, is advantageous in order to ensure a uniform transport of the product through the reactor.

The identity of the starting material is determined using an X-ray diffractogram approved. To track the reactions

Ca (H₂PO₄) ₂ → CaH₂P₂O₇ + H₂O

Ca (H₂PO₄) ₂ × H₂O → CaH₂P₂O₇ + 2 H₂O

X-ray diffractometry also serves up to complete conversion, one uses the disappearance of the characteristic Diffraction peaks of the starting materials and the emergence of the typical diffraction peaks of the product (X-ray radiation Cu K-alpha-1, wavelength 1.5405 Ångstroem).  

X-ray reflections, angular degrees (°) and grid spacing (Ångstroem):

The rise of the signal at 23.6 ° is decisive for a complete Sales.

As a further, very simple indication of the course of the reaction the loss on ignition of the product material is measured, however this is Decrease in ignition losses of 15.4 and 21.4% for the monohydrate to the theoretical value of 8.3% for the calcium dihydrogen pyrophosphate only a necessary, but not a sufficient condition for the purity of the product as an incomplete Implementation does not rule out the presence of metaphosphate components.

Surprisingly, one after thin film analysis and ion chromatography obtained pure product by this procedure which is not clumped, but as usable Powder with grain sizes approx. 80% from 40 µm to 200 µm is obtained. You have to set the reaction temperature so that a product temperature under a batch process in the temperature range between 230 ° and 275 ° C, preferably 240 ° and 260 ° C is set with a residence time of one hour. If the reaction is carried out continuously, the temperature range is due to the heat dissipation by the product for the reactor wall between 255 ° and 330 ° C, preferably 265 ° and 300 ° C at a Residence time of two hours.  

At different dwell times and / or at different temperatures either further reaction to higher condensed products or one incomplete implementation, both if necessary.

For static manufacturing trials in the furnace without mechanical Mixing of the reaction material gives strongly clumped Products.

Experiment description

In a pre-heated double-jacket laboratory kneader with four liters Capacity, with temperature sensor for product and steam room temperature as well as with a condensate outlet connection becomes monocalcium phosphate and / or monocalcium phosphate monohydrate. The steam room temperature and the product temperature are recorded. During the implementation, certain regular Samples are taken at intervals and their purity is and examined by ion chromatography. Through a separate one Nozzle can be added to the nozzle (quantity determination by weight loss of water and counterweighing the condensed Water vapor discharge). After the reaction, the product removed from the kneader, cooled to room temperature and analyzed.

During the reaction it is observed that the volume of the Starting material expands by about 40% after 15 minutes to after Return to its initial volume for 45-60 minutes.

In addition to ion chromatography, thin layer chromatography was also used checked for ortho-, pyro- and meta-phosphate content. The full implementation is in the X-ray diffractogram, due to lack of orthophosphate in the ion and thin layer chromatogram as well by matching the measured and the calculated ignition losses proven.  

To determine the optimal temperature interval, the Times to complete implementation at various constant Temperatures measured without adding steam or water (see Fig. 1: Loss on ignition / temperature in a batch process).

Under the conditions of the batch process the optimal temperature interval between 240 ° and 260 ° C. In the continuous process it is between 265 ° and 300 ° C. Only at the temperature that should preferably be maintained yields of 95-99.9% of theory.

If the condensation temperatures are too low, the theoretical 8.33% exceeded due to residual orthophosphate content, in case of over-drying due to the formation of metaphosphates undershot. Losses on ignition of 8.20-8.45% are obtained from the temperature to be maintained according to the invention.

The attempts to determine the reaction time in the discontinuous Processes up to the complete implementation result in an optimum in terms of duration and temperature, preferably to be observed Temperature range (see Fig. 2: reaction time / temperature). Furthermore, to determine the optimal reaction time in ideal temperature range at different times the compositions of the reaction product determined (see Fig. 3: loss on ignition / reaction time).

Acid pyrophosphates show lower pH values than the corresponding ones primary orthophosphates and the more condensed meta or Polyphosphates. So there is a drop in the pH value of the Formation of calcium dihydrogen pyrophosphate expected. The minimum the pH value of the products is for the pure pyrophosphates in the temperature range proposed by the invention 240 ° -260 ° C with discontinuous procedure (see Fig. 4: pH values / temperature).  

1. Static tests (comparative test)

Monocalcium phosphate and / or monocalcium phosphate monohydrate is used in a heated muffle furnace in a steam atmosphere on one Porcelain bowl heated for several hours. Then will the material is crushed in the mortar, mixed and airborne cooled down; pH value (1% in water), loss on ignition, Ca / P ratio, Pyrophosphate content and the reaction rate (ROR value) determined. For reaction parameters and analysis results, see Tab. 1.

2. Trials in the laboratory mixer

In a preheated double-jacket laboratory kneader with four liters Capacity, with temperature sensor for product and steam room temperature as well as with a condensate outlet connection becomes monocalcium phosphate and / or monocalcium phosphate monohydrate. The steam room temperature and the product temperature are recorded. During the implementation, certain regular Samples are taken at intervals and their purity is and examined by ion chromatography. Through a separate one Nozzle can be added to the nozzle (quantity determination by weight loss of water and counterweighing the condensed Water vapor discharge). There may also be water during the reaction be added. After the reaction has ended, the product turns off removed from the kneader and cooled to room temperature and how analyzed under 1. Reaction parameters and analysis results see table 2.

3. Production trials

In a temperature-controlled kneader system according to DE-A 29 07 453 becomes monocalcium phosphate and / or monocalcium phosphate monohydrate fed continuously. The reaction material is during the Implementation mixed and carried out continuously. The steam room the kneader is sealed from the environment and additionally with a device for dosing water vapor  fitted. That under the different reaction parameters discharged product is analyzed as under 1. Reaction parameters and analysis results see table 3.

In the experiments with pure calcium dihydrogen diphosphate according to the invention as baking acid in frozen doughs using the example the use of frozen dough bases shows clear advantages on, in comparison with the baking acid disodium dihydrogen diphosphate, acidic, normally reacting, as well as disodium dihydrogen diphosphate, acidic, delayed in reaction and not according to the invention Calcium dihydrogen diphosphate according to the prior art, which Contains metaphosphate and orthophosphate.

The baked dough patties are in their surface texture more even, their crumb is looser and better structured, the taste is good and aromatic.

In comparison with sodium aluminum phosphate, acidic, it turns out that the dicalcium dihydrogen diphosphate as the sodium aluminum phosphate Baking acid is equivalent in its baking technology, however, unlike sodium aluminum phosphate, toxicologically is harmless.  

Table 1: Static tests in the drying cabinet

Table 3: Experiments with a continuous procedure

Claims (7)

1. Process for the technical production of practically pure calcium dihydrogen diphosphate from monocalcium phosphate and / or monocalcium phosphate monohydrate by condensation in a reactor with the supply of heat, characterized in that the reactor contents are mixed, pressed in a thin layer against the reactor wall and then the condensed hard layer is again removed from the reactor wall peels off and returns to the inside and seals the reaction chamber against gas exchange with the environment with a residence time of 0.5-3 hours and carries out the reaction under the vapor pressure of the escaping condensation water. 2. The method according to claim 1, characterized in that the Heat by means of a temperature-controlled medium through the reactor wall is fed. 3. The method according to claims 1 or 2, characterized in that that as a heat transfer medium for the reactor thermal oil, a Molten metal or a molten salt used. 4. The method according to any one of claims 1 to 3, characterized in that the reaction is carried out continuously and the reactor is continuously charged with monocalcium phosphate and the reaction product is continuously discharged becomes. 5. The method according to any one of claims 1 to 4, characterized in that additional water vapor during the reaction or water is being fed in or an excessive water vapor pressure is drained.   6. The method according to any one of claims 1 to 5, characterized in that that monocalcium phosphate with a medium grain size smaller than 1000 µm, especially between 50 and 500 µm, and a residual moisture content of 0.1 to 5.0%, preferably of 1.0 to 3.0% is used. 7. The method according to any one of claims 1 to 6, characterized in that that a monocalcium phosphate with a molar Ca / P ratio from 0.40 to 0.60, preferably from 0.45 to 0.55 is used.