Process for reclaiming used hydrocarbon oils
This invention relates to a process for reclaiming used hydrocarbon oils through pre-purification by means of coagulation, adsorption, filtration, distillation, and after-treatment. 
     As used herein and in the claims, the term &#34;hydrocarbon oils&#34; may include motor oil, transmission lubricant, hydraulic oil, turbine oil, cutting oil, hardening oil, heat-transfer oil, and industrial oils. The used oils to be reclaimed may be contaminated by, among other things, water, solvents, dirt, abraded metal, soot, oil carbon, and oxidation and decomposition products of hydrocarbon oils and their additives. 
     Among the additives of processed hydrocarbon oils are, for instance, viscosity-index improvers, pour-point depressants, anti-oxidants, anti-corrosion additives, high-pressure (EP) and anti-wear additives, bactericides, fungicides, detergents, dispersing agents, emulsifiers, etc. The following elements are to be found in these additives, among others: Ba, Mg, Na, Ca, P, S, Cl, Pb, Zn, Sb, N, Cd, Mo. 
     The following elements may be found, among others, deriving from the abraded metal: Fe, Cu, Cr, Ni, Al. 
     The methods currently in use for reclaiming used hydrocarbon oils have numerous drawbacks, the effect of which is, for example, that the oils thus obtained--referred to in the trade as re-refined or secondary refined products--clearly differ qualitatively from the primary refined products as regards a number of analytic data. 
     Furthermore, with the reclaiming methods applied heretofore, residues are obtained, the processing, dumping, or incineration of which presents numerous new problems. Whereas incineration incurs high expense and is no longer possible in many countries for reasons of environmental protection, dumping of the residues which endanger the ground-water is now permitted only in a very few special pits. 
     At the present time, the following processes for the reconditioning of used hydrocarbon oils find technical application, among others. 
     Reconditioning with sulfuric acid: 
     A mechanical pre-purification of the contaminated oil is followed by separation through distillation of the light hydrocarbons, the solvents, and the water. Thorough separation of the water in particular is absolutely necessary for the next process step. 
     Concentrated sulfuric acid is thoroughly mixed with the oil in a reaction container. Reaction, precipitation, and extraction of the major part of the contaminants, the consumed, converted, and non-consumed additives then takes place. These materials can be separated from the oil in separators or, more timeconsuming, in settling tanks, and they form the highly-viscous so-called acid tar. Since sulfuric acid in excess is used, the separated oil still contains acid and must be neutralized with alkaline solutions or lime prior to further processing. This step is followed by fractional distillation. The distillates are subjected to bleaching, e.g., hot-contact bleaching, for the purpose of improving their color. As compared with primary refined products, used oil treated in this way may still exhibit numerous negative aspects, such as a marked specific odor, dark color, and a high content of elements foreign to hydrocarbon oils. Particularly because of the content of chlorine or chlorine compounds, virtually unchanged during the course of the process, and the relatively high residual metal content, hydrogenation is practically not possible. Only such an after-treatment would lead to qualities equal to those of primary refined products. 
     Reconditioning with liquid propane: 
     The Institut Francais du Petrole, des Carburants et Lubrifiants has developed a process for regenerating used oil with liquid propane. This method is described in French Pat. No. 1,516,733 and U.S. Pat. No. 3,773,658, among others. 
     In the first step of the process, water, low-boiling hydrocarbons, and solvents are separated from the used oil by distillation. The heated oil is mixed with liquid propane under pressure. The proportion of oil to propane by weight may amount to from 1:5 to 1:16 and depends upon the contamination of the used oil. The propane acts as a coagulant for the additives and contaminants in the used oil, the amount of propane, the temperature, and the pressure being variable factors for the effectiveness of the precipitation. The separation of liquid propane, oil, and residue may take place in a single step, but also in several stages. Under certain circumstances, an after-treatment with sulfuric acid is necessary for reasons of quality. The purified oil is then subjected to fractional distillation, followed by hot-contact bleaching of the fractions. 
     For reconditioning with hydrated alkaline-earth oxides, East German Pat. No. 59,356 teaches a method for reconditioning used lubricating oils. The mechanically pre-purified and fuelfree oil is heated and mixed with, preferably, calcium hydroxide and then immediately distilled. The contaminants and additives coagulated by the calcium hydroxide are drawn off as residue in the distillation column. After this treatment, the distillates are supposed to be substantially free of additives. However, a conventional after-treatment of the distillates is necessary. The treatment with sulfuric acid or with lime and bleaching earth, optionally after solvent extraction with furfurol or sulfur dioxide has taken place, may be used for this purpose. 
     It is an object of this invention to provide a process for reconditioning used oils which eliminates the drawbacks of the prior art methods. At the same time, it is intended that intensive pre-purification of the used oils shall make hydrogenation technically and economically possible. Only in that way are qualities achieved which are comparable to those of modern primary refined products. A further object is to ensure that the resulting residues no longer present costly problems of disposal and pollution as has hitherto been the case with the known processes. 
     To this end, in the process according to the present invention, the oils are pre-purified and then dehalogenated, fractionally distilled, and hydrogenated. 
     All liquid products produced on a hydrocarbon-oil basis can be recycled at qualities comparable to those of primary refined products. 
     The invention will now be described in detail with reference to specific embodiments thereof. First the individual steps for the intensive pre-purification will be set forth. 
     It has proved possible to precipitate and remove a large proportion of the matter suspended in the used oil by means of coagulation with appropriate agents. It has been found that very good coagulation is achieved with solvents, such as esters, ethers, and ketones of low molecular weight, preferably ethyl acetate (EtAc) and acetone, or mixtures thereof in the ratio of used oil to solvent of from 3:1 to 1:10 by weight. Preferably a ratio of 1:3 is used. The values in Table 1 below illustrate the effectiveness of ethyl acetate as compared with n-heptane, which is non-coagulant in this sense. 
     
                       Table 1                                                     
______________________________________                                    
           Used            Used                                           
           Oil I   Used    Oil II                                         
                                 Used  Used                               
           with-   Oil I   with- Oil II                                   
                                       Oil II                             
           out     pre-    out   pre-  pre-                               
Samples    pre-    treated pre-  treated                                  
                                       treated                            
Analyt-    treat-  with    treat-                                         
                                 with  with                               
ical Values                                                               
           ment    EtAc    ment  EtAc  n-heptane                          
______________________________________                                    
Oil: solvent                                                              
ratio by    --     2:5      --   2:5   2:5                                
weight                                                                    
TBN mg KOH/g                                                              
ASTM D 2896                                                               
           6.1     3.0     5.2   2.5   5.3                                
Ash                                                                       
% by weight                                                               
           1.26    0.51    1.16  0.44  0.84                               
ASTM D 482-63                                                             
Appearance black,  brown,  black,                                         
                                 brown,                                   
                                       black,                             
of Oil     opaque  clear   opaque                                         
                                 clear opaque                             
______________________________________                                    
 
    
     In each case, the used oil samples I and II were mixed with the coagulant at room temperature and, after being allowed to stand for 24 hours, were filtered using a filter aid. 
     The liquids or mixtures thereof listed in Table 2 below also exhibit good coagulating properties. In all cases, the ratio of used oil II to coagulant by weight was 1:2. The conditions were otherwise the same as in the tests with ethyl acetate. 
     
                       Table 2                                                     
______________________________________                                    
 Data     TBN       Ash                                                   
Coagulant mg KOH/g  % by weight                                           
                               Appearance of Oil                          
______________________________________                                    
Butanone  3.10      0.75       clear, brown                               
1,4-dioxane                                                               
          2.80      0.50       clear, brown                               
Ester mixture.sup.1                                                       
          2.76      0.53       clear, brown                               
Amine mixture.sup.2                                                       
          39.20.sup.4                                                     
                    0.61       cloudy, brown                              
n-Butanol.sup.3                                                           
          2.83      0.57       cloudy, brown                              
Untreated 5.20      1.16       opaque, black                              
sample                                                                    
______________________________________                                    
 .sup.1 Mixture of ethyl acetate and methyl acetate in a ratio of 1:1 by  
 volume.                                                                  
 .sup.2 5% n-butyl-diethanol amine and 5% isopropanol by weight in        
 n-hexane.                                                                
 .sup.3 According to Chemical Engineering, 13 May 1974, the firm of M.Z.F.
 Los Angeles, California, has developed a process in which aqueous        
 isopropanol is used as an extractant and coagulant. It is also known that
 Exxon Research Engineering uses C.sub.4 - and C.sub.5 -alcohols in       
 laboratory experiments; the results are not known.                       
 .sup.4 The increase in the total base number is attributable to entrained
 amine.                                                                   
 
    
     Further tests have been carried out with 2-methylpentanone-(4), isobutanol, 1,1,1-trichloroethane, benzene chloride, isopropyl acetate, isobutyl acetate, and butyrolactone. These substances, however, did not exhibit good coagulating action. 
     The monophase ternary system of ethyl acetate/acetone/used oil may be mentioned as an example of the aforementioned mixtures of solvents. Various monophase mixtures from the phase diagram of this system have been tested. Examples of such mixtures yielding good results are shown in Table 3 below. The reaction conditions and recovery are the same as in the tests with ethyl acetate. 
     
                       Table 3                                                     
______________________________________                                    
 Data         TBN       Ash %     Appearance                              
Samples       mg KOH/g  by weight of Oil                                  
______________________________________                                    
24% used oil II by wt.                                                    
60% ethyl acetate by wt.                                                  
              1.73      0.38      clear,                                  
                                  brown                                   
16% acetone by weight                                                     
15% used oil II by wt.                                                    
59% ethyl acetate by wt.                                                  
              1.17      0.28      clear,                                  
26% acetone by weight             brown                                   
______________________________________                                    
 
    
     Tests analogous to those of Table 3 have also been carried out with good results at an increased reaction temperature, e.g., at 50° C. 
     It may be taken as certain that in the coagulations with solvents as described, not only are the ash-forming constituents and the solids comprised, but also resin- and asphalt-like products are precipitated out (see, for example, Abtrennung und Identifikation grenzflachenaktiver Substanzklassen aus Roholen, dissertation of H. J. Haardt, Clausthal Technical University, 1973). 
     Besides coagulation with solvents, good pre-purification has also been achieved through coagulation and/or adsorption by hydroxides of the earth and heavy metals, preferably aluminum hydroxide or ferric hydroxide. The earth, aluminum, or heavy metal hydroxides may be used in an amount of from 0.5 to 5.0%, by weight, of hydroxide relative to said used oil, preferably from 1 to 2% by weight. This treatment may be a temperature of from 20° C. to 200° C., preferably from 50° C. to 150° C. The following chemicals were used for obtaining the hydroxides: 
     Dispersion I: 175 g. Ca(OH) 2  per liter (aqueous) 
     Dispersion II: 526 g. Al 2  (SO 4 ) 3 .18H 2  O per liter (aqueous) 
     Dispersion III: 320 g. Fe 2  (SO 4 ) 3 .2H 2  O per liter (aqueous) 
     Assuming the formation of Al(OH) 3  and Fe(OH) 3 , respectively, the equivalent amount for 1 ml. of dispersion I is 1 ml. of dispersion II or dispersion III, respectively. Otherwise, the structure and stoichiometry of the adsorbents were not further investigated. 
     The tests listed in Table 4 below provide information concerning the effectiveness of aluminum hydroxide as an adsorbent and also concerning the most effective proportions of dispersions I and II. Both agents were added to the used oil and thoroughly mixed at room temperature for 5 min. After being allowed to stand for 20 min., the samples were filtered through filter paper. 
     
                                           Table 4                                 
__________________________________________________________________________
                      Ash pH of                                           
Data      TBN   T A N*                                                    
                      % by                                                
                          Water                                           
                               Appearance                                 
Samples   mg KOH/g                                                        
                mg KOH/g                                                  
                      wt. Extract**                                       
                               of Oil                                     
__________________________________________________________________________
Used oil II,                   opaque,                                    
untreated 5.2   4.7   1.16                                                
                          --   black                                      
Used oil II,                   opaque,                                    
filtered  5.6   2.9   1.08                                                
                          --   black                                      
50 ml. used oil II             clear,                                     
 5 ml. dispersion II                                                      
          2.4   3.1   0.74                                                
                          9.4  brown                                      
 8 ml. dispersion I                                                       
50 ml. used oil II             clear,                                     
 5 ml. dispersion II                                                      
          2.2   4.0   0.59                                                
                          8.3  brown                                      
 6 ml. dispersion I                                                       
50 ml. used oil II             clear,                                     
 5 ml. dispersion II                                                      
          2.1   2.5   0.62                                                
                          7.4  brown                                      
 5 ml. dispersion I                                                       
50 ml. used oil II             clear                                      
 5 ml. dispersion II                                                      
          0     2.8   0.40                                                
                          6.0  brown                                      
 4 ml. dispersion I                                                       
50 ml. used oil II             clear,                                     
 5 ml. dispersion II                                                      
          0     5.9   1.4 4.4  brown                                      
 2 ml. dispersion I                                                       
__________________________________________________________________________
 *Titration with tetramethyl ammonium hydroxide in a mixture of dimethyl  
 sulfoxide and benzene chloride.                                          
 **Water extract: 10 ml. of the unfiltered sample shaken with 40 ml. of   
 water.                                                                   
 
    
     It clearly follows from Table 4 that the optimum purification effect is obtained with an excess of about 25% by weight of aluminum sulfate. The increase in the values for TAN and oxide ash in the last test indicates that excess aluminum sulfate passed the filter. 
     The attempt to improve the results still further by choosing other reaction temperatures proved negative. 
     Table 5 below shows that the results can be further improved by combining the process steps of Tables 1 and 4. After the aluminum hydroxide precipitate had been obtained as described above, the mixture was diluted with ethyl acetate to three times its original volume and stirred again for 5 min. The ethyl acetate was evaporated off, and the sample was filtered through filter paper. 
     
                       Table 5                                                     
______________________________________                                    
                                Ash   Appear-                             
Data        TBN       T A N     % by  ance of                             
Samples     mg KOH/g  mg KOH/g  weight                                    
                                      Oil                                 
______________________________________                                    
Used oil II,                          opaque,                             
filtered    5.6       2.9       1.08  black                               
50 ml. used oil II                    clear,                              
 5 ml. dispersion II                                                      
            0         0.44      0.41  brown                               
 3.6 ml. dispersion I                                                     
50 ml. used oil II                    clear,                              
 5 ml. dispersion II                                                      
            0         0.44      0.39  brown                               
 4 ml. dispersion I                                                       
50 ml. used oil II                    clear,                              
 5 ml. dispersion II                                                      
            0         0.29      0.38  brown                               
 4.2 ml. dispersion I                                                     
50 ml. used oil II                    clear,                              
 5 ml. dispersion II                                                      
            0         0.73      0.39  brown                               
 4.4 ml. dispersion I                                                     
50 ml. used oil II                    clear,                              
 5 ml. dispersion II                                                      
            0         --        0.35  brown                               
 4.8 ml. dispersion I                                                     
50 ml. used oil II                    clear,                              
 5 ml. dispersion II                                                      
            2.4       0.87      0.51  brown                               
 5.4 ml. dispersion I                                                     
______________________________________                                    
 
    
     The values obtained in this manner are move favorable than those given in Tables 1 and 4. It is possible that the values listed in Table 5 may be improved still further by prolonging the duration of action of the acetate up to several hours. 
     Tests analogous to those combining adsorbent and ethyl acetate were carried out with ferric hydroxide. The results may be seen in Table 6 below. 
     
                       Table 6                                                     
______________________________________                                    
              TBN      T A N    Ash   Appear-                             
Data          mg       mg       % by  ance of                             
Samples       KOH/g    KOH/g    weight                                    
                                      Oil                                 
______________________________________                                    
Used oil II,                          opaque,                             
filtered      5.6      2.9      1.08  black                               
 50 ml. used oil II                                                       
 5 ml. dispersion I                                                       
              2.0      0        0.37  clear,                              
 3.9 ml. dispersion III               brown                               
150 ml. ethyl acetate                                                     
 50 ml. used oil II                                                       
 5 ml. dispersion I                                                       
              1.1      --       0.26  clear,                              
 4.5 ml. dispersion III               brown                               
150 ml. ethyl acetate                                                     
 50 ml. used oil II                                                       
 5 ml. dispersion I                                                       
              1.4      --       0.32  clear,                              
 5 ml. dispersion III                 brown                               
150 ml. ethyl acetate                                                     
______________________________________                                    
 
    
     A further series of tests has shown that the residual metal content is further reduced by hot-contact bleaching following the adsorption by ferric hydroxide. The adsorption by ferric hydroxide took place according to the process described in connection with Table 4. Thereafter, bleaching earth and a filter aid were added to the samples, and the mixture was heated to 140° C for 30 min., followed by cooling and filtering. 
     
                       Table 7                                                     
______________________________________                                    
Sample       Ash, % by weight                                             
                          Appearance of Oil                               
______________________________________                                    
50 ml. used oil II                                                        
 4 g. bleaching earth                                                     
             0.30         clear,                                          
 2 g. filter aid          light brown                                     
50 ml. used oil II                                                        
             0.28         clear,                                          
 4 g. bleaching earth     light brown                                     
50 ml. used oil II                                                        
 5 ml. dispersion I                                                       
 5.3 ml. dispersion III                                                   
             0.14         clear,                                          
 2 g. bleaching earth     light brown                                     
 0.4 g. filter aid                                                        
50 ml. used oil II                                                        
 5 ml. dispersion I                                                       
 5.3 ml. dispersion III                                                   
             0.1          clear,                                          
 2 g. bleaching earth     light brown                                     
 2 g. filter aid                                                          
50 ml. used oil II                                                        
 5 ml. dispersion I                                                       
 5.3 ml. dispersion III                                                   
             0.06         clear,                                          
 4 g. bleaching earth     light brown                                     
 2 g. filter aid                                                          
______________________________________                                    
 
    
     The values show that a relatively high proportion of bleaching earth must be used in order to obtain a very low-ash oil. 
     Experimentation has indicated that for reasons of economy, optimum results are achieved when the following amounts of adsorbent are not exceeded since larger amounts do not lead to any greater purifying effect: 
     50 ml. used oil 
     3.3 ml. dispersion I 
     3.5 ml. dispersion III 
     i.e., 
     100 kg. used oil 
     1.3 kg. calcium hydroxide (as an aqueous dispersion) 
     2.5 kg. dihydrous ferric sulfate (as an aqueous dispersion) 
     The numerous coagulation tests carried out show that extensive purification of used oil was achieved using the agents tested. Furthermore, in contrast to the technical processes currently in use, no polluting residues are formed when the abovedescribed coagulation treatments are carried out. 
     Because of the low ash content, oil pre-purified as described can be directly subjected to fractional distillation. An after-treatment with a very small amount of sulfuric acid and with bleaching earth leads to a secondary refined product of good quality. Since neither the secondary refined products commercially available at present nor the oil obtained after the treatments described above comes up to the quality standards of today&#39;s modern primary refined products, after-treatment tests have been carried out. 
     In the present state of the art, hydrogenation represents the most convenient and most economical process of aftertreatment; therefore, the further work undertaken concentrated on making this after-treatment applicable to pre-purified used oils. Tests have shown that a relatively high residual metal content and, above all, the virtually unchanged proportion of halogen compounds remaining after the processes described above, make hydrogenation technically and economically impossible. These facts called for an additional process step for the purpose of removing the remaining foreign matter. 
     It has been found that through treatment with the agents listed below, a reduction of the disturbing foreign matter, in some cases a substantial reduction, can be achieved: 
     alkali metal, especially Na or K; alkaline-earth metal, especially Mg or Ca; alkali, alkaline-earth, or aluminum alcoholate; alkali hydride or amide; an organic base, especially pyridine or piperidine; or metallic aluminum or anhydrous aluminum chloride. These treating agents may be used in the proportion of from 1 to 2000 moles of treating agent per metric ton of used oil in the absence of air and humidity and at a reaction temperature of from 15° C. to 300° C. 
     Investigations have shown that the combined-chlorine content in used oils from various western European countries may vary between 500 and 5000 ppm (parts by weight per million parts by weight) and is only inappreciably reduced by means of the usual reconditioning processes. 
     The investigations to be described below relate to a used oil III having a chlorine content of 1180 ppm. This oil was subjected to vacuum-distillation for the pre-purification. 
     In order for hydrogenation to be carried out in a technically and economically feasible manner, the chlorine content should not exceed 5 ppm according to the consensus of those skilled in the art (cf. Die Verarbeitung des Erdols, by Bruno Riediger, Springer-Verlag, Berlin-Heidelberg-New York, 1971, pp. 692ff.). 
     The following tables indicate that the aforementioned agents bring about an albeit differing reduction of the chlorine content under variable conditions. 
     
                                           Table 9                                 
__________________________________________________________________________
Effect of the Alkali Metals on the Chlorine Content                       
           Conc.                                                          
           Agent     Reac-                                                
                         Reac-                                            
                             Cl - mmole/  tion tion Con-                  
Test                                                                      
   Equip-  100 g.                                                         
                Recov-                                                    
                     Time                                                 
                         Temp.                                            
                             tent                                         
No.                                                                       
   ment                                                                   
       Agent                                                              
           oil  ery  min.                                                 
                         ° C                                       
                             ppm                                          
                                Remarks                                   
__________________________________________________________________________
1.11                                                                      
   N.sup.9                                                                
       Na  100  WA.sup.11                                                 
                     30  110 157                                          
1.12                                                                      
   N   Na  100  WA   30  150 100                                          
1.13                                                                      
   N   Na  100  WA   30  200  60                                          
1.14                                                                      
   N   Na  100  WA    5  250  9                                           
1.15                                                                      
   N   Na  100  WA   30  250  7                                           
1.16                                                                      
   N   Na  100  WA   30  300 &lt;5 Decomposition                             
                                of Oil                                    
1.17                                                                      
   D.sup.10                                                               
       Na  100  DIST.sup.12                                               
                      2  250  9                                           
1.18                                                                      
   D   Na  100  DIST 10  250 &lt;5                                           
1.19                                                                      
   D   Na  100  WA   10  250 &lt;5                                           
1.20                                                                      
   D   Na   20  WA    5  250  7                                           
1.21                                                                      
   D   Na   10  WA    5  250 230                                          
1.210                                                                     
   N   K   100  WA   30  200 &lt;5                                           
1.220                                                                     
   N   K   100  WA   30  250 &lt;5                                           
__________________________________________________________________________
 .sup.9 Sulfonating flask, N.sub.2 bubbler, laboratory                    
 .sup.10 Sulfonating flask, N.sub.2 bubbler, dispersing apparatus (25,000 
 rpm, 2 cm. φ)?                                                       
 .sup.11 Excess agent destroyed with water, oil washed with dilute sulfuri
 acid, then washed several times with water, dried, and                   
 .sup.12 Excess agent allowed to settle, oil decanted off and             
 vacuum-distilled                                                         
 
    
     As may be seen from Table 9, the reaction temperature should be about 250° C in order to reach the desired reduced chlorine content of maximum 5 ppm. 
     The dependence upon reaction time and concentration of the alkalis may also be seen from Table 9. It is worthy of note that with the extremely small amount of 20 millimoles of Na per 100 g. of oil (corresponding to 4.6 kg. of Na per 1000 kg. of oil), sufficient dechlorination can be achieved in an extraordinarily economical manner. 
     Moreover, the treatment with sodium brings about a 50% reduction of the sulfur content in the oil. 
     Another substantial advantage of this treatment is that viscosity-index improvers of the polymethacrylate type can no longer be detected in the distillates. When distillation takes place without the sodium pre-treatment, about 50% of the original amount of viscosity-index correctives are still contained in the distillates. 
     
                       Table 10                                                    
______________________________________                                    
Effect of Alcoholates on the Chlorine Content                             
                     Conc.                                                
                     Agent        Reac- Reac- Cl                          
                     mmole/       tion  tion  Con-                        
Test Equip-          100 g. Recov-                                        
                                  Time  Temp. tent                        
No.  ment    Agent   oil    ery   min   ° C                        
                                              ppm                         
______________________________________                                    
2.1  N.sup.9 sodium  200    WA.sup.11                                     
                                  150    200   110                        
             ethyl-                                                       
             ate                                                          
5.1  N       Al iso- 100    WA     30    200  1050                        
             pro-                                                         
             pylate                                                       
5.2  N       Al iso- 100    WA     30    250   100                        
             pro-                                                         
             pylate                                                       
______________________________________                                    
 
    
     
                                           Table 11                                
__________________________________________________________________________
Effect of Alkali Hydrides on the Chlorine Content                         
           Conc.                                                          
           Agent    Reac-                                                 
                        Reac-                                             
                            Cl-                                           
           mmole/                                                         
                Re- tion                                                  
                        tion                                              
                            Con-                                          
Test                                                                      
   Equip-  100 g.                                                         
                cov-                                                      
                    Time                                                  
                        Temp.                                             
                            tent                                          
No.                                                                       
   ment                                                                   
       Agent                                                              
           oil  ery min.                                                  
                        ° C                                        
                            ppm                                           
                               Remarks                                    
__________________________________________________________________________
8.1                                                                       
   N.sup.9                                                                
       NaH 100  WA.sup.11                                                 
                    30  150 170                                           
8.2                                                                       
   N   NaH 100  WA  30  200 100                                           
8.3                                                                       
   N   NaH 100  WA  30  250 &lt;5                                            
8.4                                                                       
   N   NaH 100  WA  20  300 &lt;5 Decomposi-                                 
                               tion of Oil                                
__________________________________________________________________________
 
    
     As may be seen from Table 11, here, too, the reduction of the chlorine content is highly dependent upon the reaction temperature. 
     Other tests, not listed here, have shown that reductions in the amount of sodium hydride and in the reaction time are possible with adequate dechlorination. Furthermore, the sodium hydride treatment has the effect of reducing the sulfur content of the starting material by about 90%. 
     
                                           Table 12                                
__________________________________________________________________________
Effect of Anhydrous Aluminum Chloride on the Chlorine Content             
           Conc.                                                          
           Agent    Reac-                                                 
                        Reac-                                             
                            Cl                                            
           mmole/                                                         
                Re- tion                                                  
                        tion                                              
                            Con-                                          
Test                                                                      
   Equip-  100 g.                                                         
                cov-                                                      
                    Time                                                  
                        Temp.                                             
                            tent                                          
No.                                                                       
   ment                                                                   
       Agent                                                              
           oil  ery min.                                                  
                        ° C                                        
                            ppm                                           
                               Remarks                                    
__________________________________________________________________________
6.1                                                                       
   N.sup.9                                                                
       AlCl.sub.3                                                         
           40   WA.sup.11                                                 
                    30  100 760                                           
                               relatively                                 
                               light-colored                              
6.2                                                                       
   N   AlCl.sub.3                                                         
           55   WA  30  100 570                                           
                               relatively                                 
                               light-colored                              
6.3                                                                       
   N   AlCl.sub.3                                                         
           40   WA  30  150 460                                           
                               relatively                                 
                               light-colored                              
6.4                                                                       
   N   AlCl.sub.3                                                         
           55   WA  30  150 220                                           
                               relatively                                 
                               light-colored                              
6.5                                                                       
   N   AlCl.sub.3                                                         
           80   WA  180 150  50                                           
                               relatively                                 
                               light-colored                              
__________________________________________________________________________
 
    
     
                                           Table 13                                
__________________________________________________________________________
Effect of Other Agents on the Chlorine Content                            
            Conc.                                                         
            Agent                                                         
                 Reac-                                                    
                     Reac-                                                
                         Cl                                               
            mmole                                                         
                 Re- tion                                                 
                         tion                                             
                             Con-                                         
Test                                                                      
   Equip-   100 g.                                                        
                 cov-                                                     
                     Time                                                 
                         Temp.                                            
                             tent                                         
No.                                                                       
   ment                                                                   
       Agent                                                              
            oil  ery min.                                                 
                         ° C                                       
                             ppm                                          
                                Remarks                                   
__________________________________________________________________________
7.1                                                                       
   PR.sup.13                                                              
       Pyridine                                                           
            400  WA.sup.11                                                
                     120 200 730                                          
                                app. 8 atm                                
                                gauge pressure                            
7.2                                                                       
   PR  Piper-                                                             
            400  WA  120 200 130                                          
                                app. 8 atm                                
       idine                    gauge pressure                            
3.1                                                                       
   N.sup.9                                                                
       Mg   400  WA  150 200 730                                          
9.1                                                                       
   N   NaNH.sub.2                                                         
             7   WA   30 150 910                                          
9.2                                                                       
   N   NaNH.sub.2                                                         
             7   WA   30 250 260                                          
__________________________________________________________________________
 .sup.13 Pressure vessel, no stirrer                                      
 
    
     
                                           Table 14                                
__________________________________________________________________________
Data Comparisons of Various Oils                                          
                                Comm.                                     
                   Test                                                   
                       Test                                               
                           Comm.                                          
                                Avail.                                    
         Used oil                                                         
              Used oil                                                    
                   1.15                                                   
                       6.4 Avail.                                         
                                Second.                                   
         III not                                                          
              III  (Tab.                                                  
                       (Tab.                                              
                           Neutral                                        
                                Refined                                   
Specifications                                                            
         dist.                                                            
              dist.                                                       
                   9)  12) Oil  Product                                   
__________________________________________________________________________
Color                                                                     
ASTM D 1500                                                               
         --   3.5  &gt;8  3.5 1    3.5                                       
Density 20° C                                                      
         --   0.882                                                       
                   0.882                                                  
                       0.851                                              
                           0.875                                          
                                0.880                                     
Viscosity                                                                 
cSt 50° C                                                          
         44.3 28.1 34.0                                                   
                       30.0                                               
                           38.0 47.0                                      
Viscosity                                                                 
cSt 37.8° C                                                        
         --   47.9 57.7                                                   
                       51.2                                               
                           68.0 85.0                                      
Viscosity                                                                 
cSt 99° C                                                          
         --   6.9  7.3 6.9 8.1  9.5                                       
VI.sub.E                                                                  
ASTM D 2270-64                                                            
         --   107  93  98  95   100                                       
Ash                                                                       
% by weight                                                               
         0.47 0.007                                                       
                   0.003                                                  
                       0.009                                              
                           0    &lt;0.02                                     
CCT                                                                       
ASTM D 189-65                                                             
         1.09 0.14 0.15                                                   
                       0.10                                               
                           0.05 0.10                                      
Aniline Point                                                             
° C                                                                
         --   100  --  102 107  105                                       
Acid Number                                                               
mg KOH/g 1.01 0.33 &lt;0.03                                                  
                       0.12                                               
                           &lt;0.03                                          
                                &lt;0.10                                     
Saponification                                                            
No. mg KOH/g                                                              
          --  1.85 0.5 --  --   8.2                                       
Iodine Number                                                             
g I.sub.2 /100 g                                                          
         --   3.17 9.5 --  4.5  8.5                                       
Copper Strip Test                                                         
100° C / 3 hr.                                                     
         --   2    1   1   1    1                                         
ASTM D 130-68                                                             
S Content                                                                 
% by weight                                                               
         1.03 0.77 0.40                                                   
                       --  0.11 0.6                                       
Cl Content ppm                                                            
         1400 1180 7   220 &lt;5   400                                       
TBN                                                                       
ASTM D-2896                                                               
         --   0.3  0.2 --  0.1  0.05                                      
__________________________________________________________________________
 
    
    
    
     A preferred embodiment of the invention will now be described in detail with reference to the accompanying drawing, which is a flow sheet. 
    
    
     As a pre-treatment, the used oil, free of coarse, solid contaminants, is rid of water, solvents, and light hydrocarbons by distillation according to known methods, then further distilled in vacuo until a residue I of about 10% by weight remains. The resulting residue I is, at room temperature, a highly-viscous oil which can then be combusted. 
     The distillate is treated with 1-2 kg. of metallic sodium, for example, to remove the halogen compounds, residual metals, and part of the sulfur compounds. This treatment must be carried out in the total absence of air and humidity and with thorough mixing at a temperature of about 250° C. 
     In the next process step, excess sodium and the reaction products are separated by mechanical means, e.g., by centrifuging. The excess sodium may be recycled. The separated reaction products (residue II) are also combusted. 
     The separated oil is fractionally distilled in vacuo. Residue III is combusted. 
     The individual fractions are subjected to catalytic hydrogenation as an after-treatment. 
     The yield of refined product recovered according to the invented process amounts to about 81% by weight relative to used oil free of water and light hydrocarbons.