Patent Publication Number: US-5024823-A

Title: Copper sulfate absorption mass to remove AsH3, PH3, B2 H.sub.4 and SiH4

Description:
BACKGROUND OF INVENTION 
     The invention relates to an absorption mass consisting of an oxidic porous carrier substance saturated with copper sulfate CuSO 4  which is suitable for the elimination of reactive process gases in the electronics industry. 
     The electronics industry makes use of reactive gases in the production of semi-conductors. Commonly used reactive gases are: arsenic hydride AsH 3 , phosphorous hydride PH 3 , boron hydride B 2  H 6 , germanium hydride GeH 4  and silicon hydride SiH 4 . These reactive gases are toxic and tend to spontaneous combustion so that they must be effectively eliminated to prevent any negative effects on the environment. 
     An absorbent for the elimination, for example, of AsH 3  consists of a 60% solution of copper sulfate pentahydrate CuSO 4 . 5H 2  O and silica gel whose residual moisture lies between 10% and 25%, following a drying period of 17 hours at a temperature of 110° C. A disadvantage of this known absorbent is its small absorption capacity and low threshold value. The threshold limit value (TLV value), in other words, the maximum admissable concentration of the substance can be used to establish the threshold value. Both factors mentioned above can easily lead to serious contamination of the environment even when the substance has been subsequently dump-covered as a precaution. An additional drawback is that the absorption front becomes totally blurred so that a visual detection of the degree of exhaustion of the absorption mass contained in a glass tube is more difficult. 
     SUMMARY OF INVENTION 
     The invention is, therefore, based on the object of providing an absorption mass having a substantially increased threshold value capacity. Threshold value capacity refers to the absorption capacity beyond which the threshold values (TLV values) are exceeded. 
     According to the invention, this increased threshold value capacity is achieved by means of an absorption mass consisting of an oxidic porous carrier substance which has been previously saturated with CuSO 4  in the form of a monohydrate or with CuSO 4  free from water of crystallization. 
    
    
     DETAILED DESCRIPTION 
     In accordance with the invention, the saturation is preferably carried out with CuSO 4  free from water of crystallization. Silica gel and aluminum oxide are particularly suitable as carrier substances. 
     The absorption masses according to the invention have a high reproducible threshold value capacity. In addition, they also constitute an absorption front which can be readily detected with the naked eye. 
     Such masses can also be readily used for high concentrations and as a result of their high threshold value capacity facilitate ultimate disposal. 
     The absorption masses according to the invention are produced by saturating the carrier substance with an aqueous solution of CuSO 4 . 5H 2  O, drying and dehydration at a temperature between 150° C. and 200° C. at atmospheric pressure. 
     Less favorable process results are obtained if the above mentioned temperatures are exceeded. At temperatures above 200° C., CuSO 4  can quickly break down to CuO and SO 2 . Dehydration can be quickly and reliably achieved at a temperature of 180° C. with inert gas flushing, a process which takes between one and two hours. 
     Saturation of the carrier substance with CuSO 4  can be carried out, for example, as follows: 
     A total of 1250 g of silica gel E (Manufacturers: BASF and Grace) having a granulate size of 6 mm is saturated with a solution of 1000 ml of hot distilled water and 641 g of CuSO 4 . 5H 2  O, subsequently evaporated in a drying chamber at a temperature of 110° C. and finally dehydrated at a temperature of 180° C. The absorbent can be best used when the pale-blue monohydrate or better still when the white CuSO 4  free from water of crystallization is present. The absorption mass thus produced is then removed from the drying chamber and immediately filled into glass tubes. Finally, it is stored, if possible, free from humidity. 
     The absorption mass is employed at room temperature. 
     The absorption masses according to the invention can be effectively employed to absorb not only arsenic hydride--with its extremely low threshold limit value of 0.01 ppm--but also all other reactive process gases commonly used in the electronics industry. The absorption front can be easily and distinctly detected in most of the investigated gases without indicator additive as a result of the indication of the gas per se. The following examples substantiate the advantages of the absorption masses saturated with CuSO 4 . 5H 2  O according to the invention in comparison with the commonly used absorption masses. In all experiments, the absorption masses were produced as described above and filled into a glass tube measuring 440 mm in length and having an inside diameter of 24 mm. The dumping height was 370 mm which corresponds to a weight of 150 g and a volume of 167.3 cm 3 . The gas flow rate was 50 l/hour. In each example, the first line refers to the data of a commonly used absorption mass and the second line to an absorption mass according to the invention. 
     
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Example 1                                                                 
Elimination of arsenic hydride, AsH.sub.3 : (TLV value: 0.01 ppm)         
          Treatment                  TLV                                  
          duration  temp.            capacity                             
Mass      (h)       (°C.)                                          
                            Indication                                    
                                     (1/kg)                               
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CuSO.sub.4 /silica                                                        
          17        110     blurred grey                                  
                                      3.7                                 
gel E                                                                     
CuSO.sub.4 /silica                                                        
           2        180     black    14.2                                 
gel E                                                                     
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Example 2                                                                 
Elimination of phosphorous hydride, PH.sub.3 :                            
(TLV value: 0.01 ppm)                                                     
          Treatment                  TLV                                  
          duration  temp.            capacity                             
Mass      (h)       (°C.)                                          
                            Indication                                    
                                     (1/kg)                               
______________________________________                                    
CuSO.sub.4 /silica                                                        
          17        110     blurred grey                                  
                                      6.3                                 
gel E                                                                     
CuSO.sub.4 /silica                                                        
           2        180     black    25.2                                 
gel E                                                                     
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Example 3                                                                 
Elimination of diboran, B.sub.2 H.sub.6 : MA (TLV value 10 ppm)           
          Treatment                  TLV                                  
          duration  temp.            capacity                             
Mass      (h)       (°C.)                                          
                            Indication                                    
                                     (1/kg)                               
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CuSO.sub.4 /silica                                                        
          17        110     none      1.0                                 
gel E                                                                     
CuSO.sub.4 /silica                                                        
           2        180     black    19.5                                 
gel E                                                                     
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Example 4                                                                 
Elimination of monosilan, SiH.sub.4 : (TLV value 10 ppm)                  
          Treatment                  TLV                                  
          duration  temp.   capacity                                      
Mass      (h)       (°C.)                                          
                            Indication                                    
                                     (1/kg)                               
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CuSO.sub.4 /silica                                                        
          17        110     none     immediate                            
gel E                                escape                               
CuSO.sub.4 /silica                                                        
           2        180     black    24.5                                 
gel E                                                                     
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     These examples show a substantial increase in the threshold limit value capacities of the absorption masses according to the invention in comparison to the commonly used absorption masses. In addition to the cited reactive gases, dicyanogen, amine, ammonia, H 2  S and NO 2  can also be eliminated with the absorption masses according to the invention but also of course mixtures of any of the cited gases. After absorption of S 2 , the absorption masses according to the invention but also of course mixtures of any of the cited gases. After absorption of S 2 , the absorption mass can be regenerated at a temperature of 80° C. 
     SUMMARY 
     Reactive process gases used in the electronics industry, in particular, AsH 3 , PH 3 , B 2  H 6 , GeH 4  and SiH 4  can be eliminated by means of an absorption mass consisting of a porous oxidic carrier substance, for example, silica gel saturated with CuSO 4  pentahydrate. In order to improve the absorption effect, the CuSO 4  pentahydrate is dehydrated at a temperature between 150° C. and 200° C. to obtain CuSO 4  monohydrate or CuSO 4  free from water of crystallization.