DE2006632A1 - Electrothermal hypophosphite production - Google Patents

Abstract

Hypophosphites, esp. alkali cpds., are produced by reacting P slurry accruing in electrothermal P manufacture, before pretreatment, using familiar decomposing agent, esp. Ca(OH)2 suspension containing NaOH, giving conc. hypophosphite soln. and PH3-H2 mixture containing P2H4. Thus hypophosphite is produced simply from relatively cheap charge and substantially P-free residue remains. High-grade product is obtained.

Description

Process for the preparation of hypophosphites The invention relates to a process for the production of hypophosphites, especially alkali hypophosphites.

It is already known that hypophosphites can be converted into elemental ones Phosphorus with alkali or alkaline earth hydroxide solutions or suspensions or mixtures allow both (in particular RJaOH + Ca (OH) 2 or Ba (OH) 2) to be produced; also combinations of Na2CO3 and Ca (OH) 2 are already known.

It is now known to be typical for such reactions that the phosphorus used is never exclusively after reacted; rather, a certain proportion of the initially formed hypophosphite is always converted with alkali or alkaline earth metal hydroxide to form phosphite with evolution of hydrogen, so that, for example, if the amounts of metal hydroxide stoichiometrically required for hypophosphite formation according to the above equations are used, unreacted phosphorus inevitably remains in the approach. In addition, according to various authors, a certain proportion of phosphite (in addition to PH3) is formed directly from elemental phosphorus by disproportionation. Technically advanced processes for producing hypophosphite work under reaction conditions which, on the one hand, ensure the most extensive possible conversion of the phosphorus into hypophosphite and, on the other hand, prevent the undesired formation of phosphite, e.g. 13. after / allow to keep within economically acceptable limits; Apart from the reduction in the hypophosphite yield, the formation of phoephite inevitably entails the need to purify such hypophosphite solutions.

In the case of the conversion of the phosphorus carried out exclusively with Ca (OH) 2, after the reaction has ended, the sparingly soluble CaHPO3 present in addition to the soluble Ca (H2P02) 2 is separated off together with the undissolved excess Ca (OH) 2 by means of piltration; this is followed by the precipitation of the dissolved excess Ca (OH) 2 fraction by means of CO2. The conversion of the hypophosphite by means of soda solution now follows at. Similar considerations apply when working with NaOH and Ca (OfI) 2 retaining solutions or. Suspensions, if the Ca (OH) 2 component predominates. The conversion of yellow phosphorus exclusively with IJaOH is only expedient if the formation of phosphite is avoided to a very large extent and thus the phosphite separation which is otherwise necessary is avoided can be bypassed, since the free NaOH formed in this case is used for further processing into crystalline NaH2PO2. H20 necessary concentration of the solution would in the worst case lead to the formation of phosphite again. However, there is the possibility, if necessary, according to to proceed, which, however, presupposes that phosphorus is reacted in batches with the exclusive or predominant use of Ca (OH) 2. It is also known that after fractional crystallization of NaH2PO2. H20, the separate phosphite separation can be dispensed with if the phosphite-containing mother liquor is added to a new batch and the NaOH amount is only reduced in accordance with the Na2HPO3 content and the amount of Ca ++ required for HPO3 precipitation in the form of Ca (OH) 2 additionally brings in zlioh.

It is also known that the inadvertent conversion of the hypophosphite TO phosphite proceeds all the faster. The higher the temperature of the solution and the higher the excess metal hydroxide used or the more concentrated the solution. Above 80 ° C, the secondary phosphite formation takes place, depending on the other reaction conditions, in more concentrated solutions with a noticeable speed; For this reason, the vacuum evaporation of the solution required to produce the crystalline liatric hypophosphite should always take place at (70 ° C. Below this temperature, at least in dilute solutions, even with considerable hydroxyl ion concentrations, hypophosphite does not settle very slowly; the formation of certain, for example after - or a similar scheme - of primarily formed phosphite quantities, on the other hand, does not seem to be avoidable even under mild conditions. However, in order to prevent unnecessary losses of hypophosphite that has already formed, attempts are made to convert the phosphorus at the lowest possible temperatures. However, since at such temperatures (technically advanced processes mainly work in the range between 45 and 80 ° C) the speed of the disproportionation reaction is completely inadequate from an economic point of view, special measures were recommended which essentially increase the surface area of the elemental phosphorus or The aim is to produce phosphor emulsions that are as finely divided as possible. It is known, for example, that the addition of glass dust, charcoal or activated charcoal, especially in connection with correspondingly intensively working stirring devices, influence the speed of the reaction in the desired manner. The use of emulsifier reactors operated at very high speeds is also already known; In this case, the reduction can essentially be carried out at 45 to 50 ° C, but towards the end of the reaction the reaction time must be briefly heated to 85 ° C to destroy polymeric hydrogen phosphides. It is also known that the addition of saturated aliphatic alcohols significantly shortens the reaction times can. It is also known that yellow phosphorus, after special pretreatment, is already below its melting point, ie

at <44 00, able to react with hydroxyl ions; one uses for this purpose an aqueous suspension of pure yellow phosphorus, the e.g. in connection with large-scale phosphorus production by quenching gases containing comparatively little phosphorus vapor with water in the so-called "Cold condensation stage" can be recovered.

However, all hypophosphite production processes adhere in principle Flaws. If, for example, the aim is to fully implement the phosphorus used has to work with a considerable excess of OH and heated accordingly so that finally a phosphorus-free, but comparatively rich in phosphite Digestion solution results; such a solution also contains a considerable amount of Concentration of free Ca (OH) 2 or NaOU. First, the crude solution has to be separated for the purpose of separation the CaHPO3 and the undissolved suspended Ca (OH) 2 are filtered, then follows after the dissolved Ca (OH) 2 fraction has been precipitated by means of CO2, another filtration process. Finally, if necessary after intermediate concentration of the solution, must this during the usual uit-t; els soda conversion of Ca (H2P02) 2 CaCO3 formed are also filtered off. Only in the case of combined use of Na2CO3 + Ca (OII) 2 - the first carbonate precipitation takes place immediately in the approach - you get by with two filtration levels. In all cases the filter cake must In order to avoid major losses of hypophosphite, they should be carefully washed out in this way that there are always larger amounts of very dilute solutions, their concentration require additional energy expenditure.

Excess NaOH must be contained in the crude hypophosphite solution on the other hand generally remain in the solution, eo that produced by crystallization NaH2PO2. H2O often still contains adhering ITaOII and that which is considerably enriched in ITaOII Mother liquors are not again evaporated and crystallized can, but usually take a fresh approach before starting the implementation of the elementary Phosphorus must be added; in the following reaction becomes inevitable a certain proportion of the H2PO2 introduced with the mother liquor converted to IIP03.

If, on the other hand, the secondary phosphite formation is to be suppressed to a large extent, so you have to work at the lowest possible temperatures and roughly stoichiometric Use amounts of hydroxide; in this case there are considerable amounts of unreacted Blementary phosphor, the separation of which is considered quite unpleasant and dangerous must be taken up in T3. Romlilt added that especially in such palls the Digestion material to destroy the iui course of side reactions arising polymeric phosphine, at least for a short time, heated comparatively high must become; otherwise these compounds end up in the finished product (NaH2PO2 . H20) and have a highly toxic effect there due to the gradual decomposition. It is essential to achieve an economically viable rate of implementation necessary measures to increase the surface area of the reacting phosphorus also require additional technical and economic ones in almost all cases Expenditure. In addition, all known methods exclusively from as possible pure elemental phosphorus to prevent contamination of the end product.

Another great disadvantage is that it is used to avoid hypophosphite decomposition is worked in very dilute solutions.

So are approaches with 10 to 20 parts by weight of water (total weight of the suspension and dilution water)) to 1 part by weight of elemental phosphorus has been recommended in connection with optimization studies and accordingly technical quite common; accordingly, considerable amounts must always be diluted Solutions are concentrated at reduced pressure in order to produce the desired end product, crystalline NaH2PO2. H20 to arrive.

The purpose of the present invention is to eliminate the quoted tones Disadvantage.

The invention is based on the object in a simple way Use of impaired process-specific input products to produce hypophosphite and at the same time to arrive at a largely phosphorus-free residue.

It has been found that very heavily contaminated with particular advantage Phosphorus - specifically in the form of phosphorus sludge - for hypophosphite production can be used, the known disintegrating agents (NaOH and / or Ca (OH) 2) are used. Such sludge falls as extremely undesirable and by-product which is difficult to work up inevitably in the course of the electrothermal Phosphorus production in not insignificant amounts. Phosphorus sludge is as one stabilized by highly dispersed solids, partly of a colloidal character, to understand by simple means non-destructible phosphorus-water emulsion; the in particular hydrated Si02, P205, alkali and alkaline earth ions, fluoride and soot-like carbon-containing solid fractions give the rapidly aging, Hate that is crumbly in the cold and thick and pulpy in the warmth is usually one deep black color. A typical aged phosphor sludge contains about 30 to 50% P, 50 to 30% water and 10 to 20% solids. All known work-up methods assume that the phosphorus content in the sludge is somehow for safety and water hygiene reasons, as quantitatively as possible, must be separated and / or unset to P205 or H3P04.

This goal is usually only partially achieved.

In contrast, the method according to the invention permits extensive conversion of the yellow phosphorus contained in the phosphorus sludge becomes industrially particularly valuable Hypophoephit and a phosphine-hydrogen mixture, which is known per se Way can be burned to phosphoric acid. It is particularly noteworthy that that for the implementation of the method according to the invention in particular, more aged Phosphorus sludge is suitable, dease processing @ according to the previously known method is extraordinarily uneconomical and, moreover, on particular technical difficulties bumps; in addition, the end products obtained by the process according to the invention are surprisingly pure. 1, Thus, the inventive method allows manufacture high quality products using a previously extremely undesirable and heavily contaminated by-product of the electr @ -thermal phosphorus production.

The input product does not need to be prepared in any way; The low expenditure on equipment during the implementation is of particular advantage of phosphorus sludge. On special measures to increase the reactive surface due to the high degree of dispersion of the phosphorus in the phosphorus sludge, which is typical for the process and omitted because of the unusual stability of the emulsion. For example A gas-tight steel agitator tank with jacket heating is sufficient, the one with a stuffing box for the agitator shaft, lockable loading opening, Inlet nozzles for the cover nitrogen, outlet nozzles for the reaction gas and Inlet nozzle for the NaOH or Ca (OH) 2 solution is given away, completely meeting the requirements. The agitator can, for example, with 60 revolutions / min. work. Advantageously the crude reaction gas mixture is used to remove the impurities carried along (yellow phosphorus, diphosphine, traces of so-called "suboxides") through a water reserve directed; the phosphorus components are condensed, the suboxides are retained, and the diphosphine largely decomposes to polymeric solid hydrogen phosphide and phosphine.

The resulting water vapor-containing PH3-H2 mixture can now be used in It is known that it has been burned to form phosphoric acid, and it is of particular importance It is advantageous if - due to the spatial height of a phosphoric acid plant - can be done on separate equipment. The content of the water reserve is expediently drained from time to time and a new batch is added.

The gray-black to deep black containing significant amounts of solids Digestion solution can be easily filtered. The rather voluminous filter cake is expedient washed only briefly, then mashed with fresh water and filtered again; the remaining filter cake is practically free of elemental phosphorus. Both Filtrates are combined and finally processed further in a manner known per se. Of particular advantage il is also the fact that the digestion in comparatively concentrated solution can be worked. The further processing known per se the Ca (H2PO2) 2 solution has been improved in that the so far Commonly used precipitation of the dissolved excess Ca (OH) 2 content by means of CO2 could be saved. According to the invention, the hypophosphite confrontation is with coupled to the Ca (OH) 2 conversion; the resulting HaOH is better known per se Hypophosphorous acid produced in a way that is saturated to NaH2PO2. Furthermore, was in the vacuum evaporation stage, not steam on the energy side, but in the interest an improvement of the network economy given by the process hot phosphoric acid used.

The invention is described below with reference to a few exemplary embodiments are explained in more detail. As is still common practice, it is assumed that that in the production of hypophosphite only 25% of the elemental phosphorus used to be implemented to PH3. The calculation of the hypophosphite yield is thus based on the amount of phosphorus present in the solution as a whole in compound form, whereby the more or less inevitable primary phos-phite formation is not taken into account remain; accordingly, the values calculated in this way are always inevitable for the yields too low. However, it is not advisable to use any other method of calculation, since the proportion of the primarily formed phosphide is not constant, but 3. 3.

depends significantly on the NaOH: Ca (OH) 2 ratio used.

Example 1: 25 kg of phosphorus sludge (P content 40%) after adding 40 1 of water while stirring (20 rpm) with a mixture of 5.5 1 50%. NaOH, 11.9 kg Ca (OH) 2 and 20 1 water overcittened suspension (hol ratio OH # as NaOH: OH # as Ca (OH) 2 = 1: 3) reacted over the course of a total of 6 hours; the The temperature was kept at 60 ° C. with the aid of a heating mantle. before the start of In the reaction, the apparatus was flushed with nitrogen. The hydroxide suspension was added continuously over the course of 2 hours; that mainly from PH3 and H2 existing reaction gas was passed over a water reservoir and finally burned in a known manner to form phosphoric acid, the direct coupling riit The physically adjacent phosphoric acid plant has a separate absorption device made redundant.

76 l of a black-gray digestion solution resulted. To the balance sheet attempt 1000 ml were removed. There were 675 ml of filtrate (# = 1.098 g / n1) with 35.5 g of P (I), 460 ml hypophosphite wash water (# = = 1.067 g / ml) with 16.3 g P (I) and 298 g of moist filter cake with 39 g of total P (P (I), P (III) and P (V) as P205 Oxidation determined). In this balance attempt, therefore, were 35.5 + 16.3 = 51.8 g P (I) l or a total of 3.94 kg P (I) found; this corresponds to a hypophosphite yield of 52.5,) of the theory, taking into account the aspects listed above must be that the highly active and voluminous filter cake after a single wash by no means can be obtained already hypophosphite-free.

After the Ca (H2PO2) 2 had been converted using soda solution, the precipitated CaCO3 was filtered off; taking into account the fact that during the hypophosphite conversion the dissolved excess Ca (OH) 2 inevitably follows reacted, the free NaOH was now neutralized by adding H3PO2, which had previously been prepared in a manner known per se from Ca (H2P02) 2 solution and oxalic acid.

After vacuum evaporation of the solution and subsequent crystallization eventually became NaH2PO2. H20 received. That for the purpose of electroless nickel plating the most suitable product is colorless; chromatographically, neither P (V) nor P (III) can be detected, a P (IIIt content of 0.06% was determined by titration. The crystals are arsenic-free.

Example 2: 25 kg of phosphorus sludge (2 content 40%) were used in the same Way implemented as in Example 1, but not at 60 ° C, but at 80 00. The The reaction time totaled 3 hours, with the NaOH-Ca (OH) 2 suspension could be added completely in the course of the first hour. It resulted 80.5 l of a black-gray dissolving solution. 1000 @@ @ @@ er @ öunn; @ ogenom @ en. There were 640 ml of filtrate (# @: @@@@@@@) m @@ @ (I), @@ 0 ml @ popho @@ @ thaltig @@ washing.

water (= = 1.065 g / ml) with 20.8 g P (I) and 395 g moist filter cake obtain. This corresponds to 58.8 g P (I) / 1 bzi.

4.73 kg total P (I); the hypophosphite yield is therefore 63 % of theory.

The black-gray filter cake obtained during the balance test contained as expected, in addition to the solid impurities originating from the phosphorus sludge still undissolved Ca (OH) 2, also considerable amounts of CaHPO3, some Ca (H2PO2) 2 and Traces of elemental phosphorus. Only the completely dried dilter cake was smoking little in the air.

For the complete conversion of the elemental phosphorus, like some Hand tests showed the heating of the suspended with a little water for one hour Filter cake at about 100 ° C. optionally after adding some NaOH.

Example 3: 29.6 kg of phosphorus sludge (P content 40%) were, as in Example 2 described, unset at 80 ° C. with an NaOH-Ca (OH) 2 suspension; the The molar ratio OH # as NaOH: OH # as Ca (OH) 2 was 1: 1 in this case; as dilution water was that during the previous experiment (Example 2) when cleaning the raw PH3-H2 gas mixture in the water reserve and low-grade phosphorus Water containing phosphorus compounds is used. In this attempt as in the aforementioned examples were each with a total ratio of about 7 parts by weight Water worked on 1 part by weight of phosphire; 103 l of deep black digestion solution fell at.

1000 ml of the digestion solution resulted in 500 ml of filtrate (t = 1.135 g / ml) with 39.2 g (P (I), 690 ml hypophosphite-containing wash water (# = = 1.068 g / ml) with 28.6 g of P (I) and 490 g of moist filter cake. This corresponds to 39.2 + 28.6 .67.8 g P (I) / 1 or a total of 6.98 kg P (I); the pituitary yield is thus 78.3 5 the theory. The considerable hypophosphite concentration is particularly noteworthy in the first step; it amounts to 25 wt .-; A, calculated on NaH2PO2. H2O.

Example 4: As described in Example 1, both work-up the solution to NaH2PO2. H2O predominantly known methods are used.

In order to improve the network economy possible from the process, was, however, in the stage of operating at about 65 ° C vacuum concentration of On the energy side, the NaH2PO2 solution does not use heating steam, but rather hot phosphoric acid (> 90 ° C) worked; the acid was removed from the circulation line for this purpose Phosphoric acid factory branched off and after passing the evaporator apparatus the circulation fed back. Thus, an energy source was used that does not incur any costs.

Claims (6)

Patent claims: 1. Process for the preparation of hypophosphites, in particular of Alkali hypophosphites, characterized in that in the course of the electrothermal Phosphorus production inevitably results in phosphorus sludge without pretreatment taking Use of disintegrating agents known per se, in particular using NaOH-containing ones Ca (OH) 2 suspensions, to a concentrated hypophosphite solution and a diphosphine-containing one Phosphine-hydrogen mixture is implemented. 2. method according to claim 1, characterized in that the rche Phosphine-hydrogen mixture passed through a water seal for cleaning and which gradually becomes enriched with phosphorus and low-valent phosphorus compounds Water is added to a new batch. 3. The method according to claims 1 and 2, characterized in that that the purified gas mixture is burned to form phosphoric acid in a manner known per se will. 4. The method according to claim 1, characterized in that after filtration the digestion mass in the filtrate after the conversion, known per se, has ended of the Ca (H2P02) 2 to NaH2PO2 by the parallel Ca (OH) 2 conversion resulting ITaOll neutralized using H3202 before further processing of the solution will. 5. The method according to claims 1 and (, characterized in, that the further processing of the previously purified hypophosphite solution in itself takes place in a known manner. 6. The method according to claim 5, characterized in that in the step vacuum evaporation uses hot phosphoric acid as an energy source.