Continuous production of phosphine
The present invention relates to a process for producing a continuous stream of highly concentrated phosphine (hydrogen phosphide), wherein a mixture containing elemental yellow phosphorus, an aqueous alkali metal hydroxide solution and at least one alcohol with at least 5 carbon atoms is reacted with agitation in a reaction zone. The resulting gaseous reaction products with the phosphane therein are collected, the reaction residue is separated into an aqueous phase and alcoholic phase, and the latter phase is recycled to the reaction zone. 
     A process of this kind has been described, e.g. in German Patent Specification &#34;Offenlegungsschrift&#34; No. 26 32 316. In carrying out this process, it has turned out that it is impossible to avoid adverse effects on the quantitative ratio of PH 3  :H 2  in the gaseous reaction product unless the reaction medium, which is recycled, is carefully purified alcohol. Careful purification of the alcohol can only be achieved, however, by allowing emulsified water to settle over a period of several weeks, for example. 
     Further adverse effects reside in the following points: Whenever the starting reactants cease to be used in stoechiometric proportions or whenever water in excess gets into the reaction zone together with recycled alcohol, the salt suspension which is being formed inside the reactor commences caking together and then naturally ceases to be conveyable. As a result, it is necessary for the production unit to be frequently stopped and cleaned by expensive methods. 
     In accordance with our present invention, we have now unexpectedly found that the prior art process described above can be considerably improved by using the reactants in admixture with 0.01-2, preferably 0.1-0.4, weight %, based on the alcohol, of a surfactant. 
     Use can more specifically be made of known non-ionic, cationic or anionic surfactants which primarily comprise: ethoxylated C 4  -C 22  alcohols; alkyl phenols with 8 to 12 carbon atoms in the alkyl group; phosphoric acid monoesters and diesters of these alcohols or phenols; ammonium salts containing at least one alkyl group with 12 to 18 carbon atoms; ether sulfates or alcanols; alkylbenzene sulfonates; alkenyl sulfonates; or sodium salts of these compounds with 8 to 18 carbon atoms in the alkyl or alkenyl group. 
     The process of the present invention inter alia offers the following technically beneficial effects: 
     (a) the salt suspension which is being formed is easy and reliably to convey and transport; 
     (b) alcohol and aqueous phase are easier to separate after the reaction and the separated alcohol can more readily be used again; 
     (c) the concentration of PH 3  in the gaseous reaction product remains sufficiently high even in those cases in which the starting reactants are used outside the stoechiometric ratio, and 
     (d) the concentration of PH 3  in the gas stream and yield of desirable product are increased. 
    
    
     The following Examples illustrate the invention and technically beneficial effects which are associated therewith. 
     EXAMPLES 1 to 20 
     Yellow elemental phosphorus and a sodium hydroxide solution of 70% strength were reacted, with agitation, in an apparatus such as that described in Example 3 of German Patent Specification &#34;Offenlegungsschrift&#34; No. 26 32 316. The dispersant and reaction medium was a 1:1 (ratio by weight) mixture of n-octanol and n-decanol which was used as such and in admixture with 0.1 weight % of surfactant, respectively. The yield of hydrogen phosphide, its concentration in the resulting gas, and the nature of the particular surfactant used are indicated in the following Table, in which ethylene oxide is briefly termed EO. 
     
                       TABLE 1:                                                    
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                                     % P in                               
                             vol %   form of                              
Ex.                          PH.sub.3                                     
                                     PH.sub.3                             
No.  Surfactant              in gas  P used                               
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1    None                    91.0    28.8                                 
2    Addition product of 6 mols                                           
     EO and nonylphenol      94.0    29.0                                 
3    Addition product of 10                                               
     mols EO and nonylphenol 93.6    31.2                                 
4    Addition product of 6 mols                                           
     EO and 1 mol mixture of li-                                          
     near C.sub.12 -C.sub.15 alcanols                                     
                             92.1    30.9                                 
5    Addition product of 5 mols                                           
     EO and 1 mol mixture of                                              
     C.sub.16 -C.sub.20 alcanols                                          
                             93.0    31.4                                 
6    Sodium salt of alkenylsul-                                           
     fonic acids with 14 to 17                                            
     carbon atoms            91.5    30.2                                 
7    C.sub.12 H.sub.25 --(OCH.sub.2 --CH.sub.2).sub.n                     
     SO.sub.4.sup.- Na.sup.+ n = 2 to 5                                   
                             93.0    29.9                                 
8    Sodium salt of dodecylben-                                           
     zene-sulfonic acid      92.4    29.8                                 
9    An about equimolar mixture                                           
     of phosphoric acid mono-                                             
     and diesters of an addition                                          
     product of 4 mols EO and 1                                           
     mol n-dodecanol         92.5    29.0                                 
10   An about equimolar mixture                                           
     of phosphoric acid mono-                                             
     and diesters of an addition                                          
     product of 6 mols EO and                                             
     1 mol nonylphenol       94.3    32.1                                 
11   An about equimolar mixture                                           
     of phosphoric acid mono-                                             
     and di-2-butoxyethyl esters                                          
                             94.0    29.8                                 
12   An about equimolar mixture                                           
     of phosphoric acid mono-                                             
     and diesters of an addition                                          
     product of 2 mols EO and 1                                           
     mol of a commerical mixtu-                                           
     re of fatty alcohols with a                                          
     chain length of C.sub.16 to C.sub.20                                 
                             94.7    32.2                                 
13   Addition product of 4 mols                                           
     EO and 1 mol n-dodecanol                                             
                             93.0    31.5                                 
14   An about equimolar mixture                                           
     of phosphoric acid mono-                                             
     and diesters of an addition                                          
     product of 4 mols EO and 1                                           
     mol nonylphenol         94.4    30.7                                 
15   Same as in Ex. 14, but                                               
     with 8 mols EO          94.2    31.2                                 
16   Same as in Ex. 14, but                                               
     with 15 mols EO         94.0    32.1                                 
17   Same as in Ex. 14, but with                                          
     10 mols EO              93.8    32.1                                 
18   Same as in Ex. 14, but with                                          
     23 mols EO              93.0    30.7                                 
19   (CH.sub.3).sub.2 N(C.sub.12 H.sub.25).sub.2.sup.+ Cl.sup.-           
                             93.0    31.5                                 
20   C.sub.12 H.sub.25 N(CH.sub.3).sub.2 (CH.sub.2 --C.sub.6 H.sub.5).sup.
     + Cl.sup.-              92.8    30.9                                 
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     EXAMPLES 21 to 29 
     Hydrogen phosphide was produced in a pilot plant which comprised two double-walled glass vessels, of which each had a capacity of 50 liters, provided with agitator, reflux condenser, bottom outlet valve and various dosing means for metered supply of the reactants. To this end, elemental yellow phosphorus was reacted with sodium hydroxide solution of 70% strength in an alcohol mixture which was composed of 35% of n-pentanol, 15% of 2-methylbutanol, 25% of n-octanol and 25% of n-decanol, and was additionally admixed with about 0.1 weight %, based on alcohol, of one of the surfactants specified hereinabove. Phosphorus, sodium hydroxide solution and alcohol mixture were used in a ratio by volume of 1:1.4:12 and continuously metered into the first of the above two vessels. A continuously flowing stream of hydrogen phosphide was formed. It was cooled and purified with the use of an active carbon filter, and determined quantitatively and qualitatively. 
     The dispersion, which was not fully reacted in the first vessel reactor, still contained elemental phosphorus together with phosphite and hypophosphite. It was discontinuously introduced into the second vessel reactor and admixed therein with fresh sodium hydroxide solution so as to obtain a light grey to light beige colored dispersion free from elemental phosphorus. The resulting gas which substantially consisted of hydrogen with varying proportions of hydrogen phosphide, was used for further reaction or incinerated. The salt dispersion which substantially contained sodium phosphite Na 2  HPO 3  was discontinuously introduced into a stirring vessel, admixed therein with a quantity of water just sufficient to dissolve the salts. The resulting emulsion was placed in a phase separating means and alcohol mixture and aqueous phase were separated from one another. The alcohol was suitable for further use. 
     The results obtained and test parameters relevant in the present process are indicated in the following Table. 
     
                       TABLE 2                                                     
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                                 NaOH                                     
     NaOH    Vol %   PH.sub.3    2nd                                      
Ex.  70%     PH.sub.3                                                     
                     yield                                                
                          Sur-   reactor                                  
No.  (l/h)   in gas  %    factant                                         
                                 (l/h) Observations                       
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21   2.8     90      28.8 none   2.3    Discharge un-                     
                                       affected; al-                      
                                       cohol turbid                       
22   2.4     91      26.7 none   2.9   Viscous dis-                       
                                       persion in 1st                     
                                       reactor; re-                       
                                       luctant dis-                       
                                       charge; salts                      
                                       coalesce; poor                     
                                       discharge from                     
                                       2nd reactor;                       
                                       gas-evolving                       
                                       sludge in se-                      
                                       parator                            
23   3.0     87      28.0 none   2.1   Discharge from                     
                                       1st reactor                        
                                       obstructed;                        
                                       test stopped                       
                                       after 2 hours                      
24   2.8     94      34.0 0.1%   2.4   Reliable;                          
                          sur-         clear alcohol;                     
                          factant,     little sludge                      
                          Ex. 17                                          
25   2.4     94      31.0 0.1%   3.0   Same result                        
                          sur-         as in Ex. 24                       
                          factant,                                        
                          Ex. 17                                          
26   3.0     91      32.0 0.1%   2.0   Same result as                     
                          sur-         in Ex. 24                          
                          factant,                                        
                          Ex. 17                                          
27   2.8     95      33.7 0.1%   2.3   Same result as                     
                          sur-         in Ex. 24                          
                          factant,                                        
                          Ex. 10                                          
28   2.4     93      30.5 0.1%   3.1   Same result as                     
                          sur-         in Ex. 24                          
                          factant,                                        
                          Ex. 10                                          
29   3.0     91      31.0 0.1%   1.9   Same result as                     
                          sur-         in Ex. 24                          
                          factant,                                        
                          Ex. 10                                          
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     Used in all of the Examples: 
     2 l/h of phosphorus 
     24 l/h of alcohol 
     Test conducted over period of 8 hours