Short residence hydropyrolysis of residues from aromatic carboxylic acid manufacture
FIELD OF INVENTION 
     The invention relates to the recovery of aromatic compound values from residues obtained in the manufacture of an aromatic di- or tricarboxylic acid. More specifically the present invention pertains to a short residence time hydropyrolysis conducted at an elevated temperature above 500° C. with a mixture of oxygen-containing derivatives of benzene and toluene containing a cyclic ester group (e.g., as in phthalide) and one or more aldehydo-, methylol-, carboxy-nuclear substituents. 
     STATE OF THE ART 
     The thermal decomposition of benzoic acid to benzene and carbon dioxide begins non-catalytically at 370° C. in a glass bulb and is substantially complete at 400° C. (Chemical Abstracts, vol. 41, 646) according to the original article of Wolfgang Mosher in Helv. Chem. Acta. 14, 971-97 (1931) and such dissociation is accelerated by copper and cadmium catalysts. Said dissociation occurs at temperatures as low as 245° to 250° C. in the presence of Zn--Cu--Cr oxide-type catalysts according to Corliss R. Kinney and David P. Langlois in J. Am. Chem. Soc. vol. 53, 2189-2192 (1931). Decarbonylation of benzaldehyde to high yields of benzene is aided by plasma of glow discharge according to German Published Patent Application (&#34;Offenlegungschrift&#34;) No. 2,038,272 of the Federal German Republic published Mar. 16, 1972. According to British Pat. No. 735,300 published Aug. 17, 1955 toluic acids heated to 400° in the presence of chromites of Zn, Cd, Zn--Cd, Zn--Fe or ZnO with either CuO or CdO are converted to toluene. 
     The preparation of benzoic acid by the thermal decarboxylation of phthalic acids in the presence of steam is known to be generally conducted in the presence of a catalyst such as nickel phthalate at 175° to 350° C. according to U.S. Pat. No. 1,962,175; 1 to 2% ammonia in the steam according to British Pat. No. 469,541 published July 27, 1932; V 2  O 5  or ZnO on Al 2  O 3  or Al 2  O 3  alone according to Chemical Abstracts vol. 37, Col. 5383; carbon catalyst impregnated with hydroxides of both alkali and alkaline earth metals to effect the decarboxylation at temperatures at and below 400° C. according to U.S. Pat. No. 2,470,688; cobalt carbonyl, Co 2  (CO) 8  used in an atmosphere of carbon monoxide and hydrogen converts phthalic acids and substituted phthalic acids to benzoic acid and substituted benzoic acid or cobalt carbonyl modified by trialkylphosphine ligands converts benzene polycarboxylic acids having COOH groups on adjacent ring carbon atoms to iso- and terephthalic acids according to Chemical Abstracts vol 81 entry 52064r. Also heating trimellitic acid to temperatures of 300° to 375° C. converts the tricarboxylic acid to o-phthalic acid according to U.S. Pat. No. 3,862,145. 
     From the state of the art at the time of making the present invention it appears that the main interest in decarboxylation of benzene carboxylic acids was to prepare a higher quality benzene carboxylic acid of lesser COOH group content from a benzene carboxylic acid of higher COOH group content and lower quality such as a coal acid or to obtain a benzene carboxylic acid of exceptionally high quality; e.g., pharmaceutical quality benzoic acid, from phthalic anhydride by converting it to o-phthalic acid and decarboxylating it. But there was no apparent interest in the decarboxylation of benzene carboxylic acids to aromatic hydrocarbons. 
     In an altogether different environment a new problem has arisen. In the commercial manufacture of benzene di- or tricarboxylic acids (e.g., isophthalic acid, terephthalic acid or trimellitic acid) there is obtained, after maximizing recovery of such acid and recovery for reuse the reaction solvent, a residue which is a mixture of oxygen-containing derivatives of benzene and toluene which are mono-, di- and tricarboxylic acids, aldehydo-carboxylic acids, and methylol-substituted benzene or toluene or their carboxylic (benzoic or toluic) acids and which also contains components of catalysis. Usually such components of catalysis are Co--Mn--Br or Co--Mn--Ce--Br from liquid phase oxidation of a xylene or pseudocumene (1,2,4-trimethylbenzene) with air in the presence of acetic acid reaction solvent. A similar residue is also obtained from the next oxidation of liquid o-xylene with air in the presence of Co--Mn--Br catalyst system after dehydrating the o-phthalic acid formed to its anhydride under conditions which vaporizes the anhydride, water and materials boiling between the anhydride and water. While such residues amount to from 2 to 25 weight percent of the benzene di- or tricarboxylic acid produced, such residue production annually is substantial in view of the millions of kilograms of the benzene di- or tricarboxylic acids produced annually. 
     Such residues contain water soluble benzene carboxylic acids and water soluble forms of the components of catalysis. Landfill disposal of such residues is undesirable because rain and ground water leach out those carboxylic acids and soluble forms of the components of catalysis and can contaminate surface run off water and eventually streams as well as below surface aquafiers. Disposal of such residues can be made by incineration and use made of the resultant heat produced but the catalyst components are converted to forms in the resultant ash which are difficult and/or expensive to convert to reusable forms for the oxidation of the methyl-substituted benzenes. Although in such residues the substituted benzene and toluene compounds whose substituents are the carboxy-, aldehydo- and methylol substituents are individually desirable and useful commercial products it is not economically feasible to separate and recover the individual compounds from the residues. 
     Based on the knowledge that most of the oxygen-containing aromatic compounds in the residue can be decarboxylated and/or decarbonylated by thermal means, it would be desirable to devise a decarboxylation and/or decarbonylation process which would convert the oxygen-containing aromatic compounds to aromatic hydrocarbons which are volatile under such process conditions so that the hydrocarbon vapors can be readily removed and condensed for their recovery. It is also known that under the severe thermal conditions required for substantially complete decarboxylation and/or decarbonylation to convert the oxygen-containing substituted aromatics to benzene and toluene there can also occur ring coupling (e.g. to form biphenyl) and ring fusion as well as charing of some of the organic compounds. 
     To use a decarboxylation and/or decarbonylation catalyst for the thermal conversion of the foregoing residues to easily recoverable and useful aromatic hydrocarbons would be desirable providing the use of catalyst does enhance the production of the aromatic hydrocarbons but does not make useless the resulting char or further contaminate the catalyst components present so as to make the recovery of cobalt, the most expensive component, technically and commercially unattractive. 
     We have in our laboratories investigated the use of various compositions previously suggested as decarboxylation catalyst and found the resulting thermal conversions to be unattractive. However, the present inventive non-catalytic thermal conversion of the foregoing residues to useful aromatic hydrocarbons is technically and commercially attractive as a step in a route for disposal of such residues. 
     SUMMARY OF THE INVENTION 
     According to the present invention the aforementioned residue or the water-insoluble portion thereof from the manufacture of a benzene di- or tricarboxylic acid is quite rapidly heated to a temperature in the range of from 700° C. up to 900° C. for a short, less than one second down to 0.1 second, residence time in contact with a pressurized hydrogen atmosphere under pyrolysis conditions in the absence of a catalyst. By such short duration hydropyrolysis the aforementioned residue is converted into two hydrocarbon-containing products. The first product comprises in addition to carbon oxides and hydrogen the normal gaseous hydrocarbons methane, ethane and ethylene. The second product comprises mainly the normally liquid aromatic hydrocarbons benzene and toluene together with small amounts of biphenyl and lesser amounts of higher molecular weight multi-ring hydrocarbons containing two, three or more aromatic rings as in terphenyl, or anthracene. It is believed the contact between hydrogen gas and the decarboxylated and decarbonylated aromatic ring entities in the vapor state, although for a rather short time as well as in the absence of a catalyst, minimizes the formation of biphenyl and the multi-ring compounds. 
     Any feasible means for rapidly heating the residue to a temperature of from 700° C. up to 900° C. can be used. For example, small amounts of residue can be moved by belt, or screw, or paddle or bucket conveyor through a tube or tubes externally heated; e.g., by a furnace or a kiln in a hydrogen atmosphere. Heating the residue at a rate above 600° C. per second, for example, at 650° to 700° C. per second will provide adequately rapid heating for the purposes of this invention. The hydrogen gas atmosphere for the 700° to 900° C. temperature used in the hydropyrolysis process of the present invention can be in the range of from 80 up to 150 kg/cm 2  pressure. Suitable contact time between hydrogen and the decarboxylated and/or decarbonylated ring entities vaporized from the residue can be in the range of from 0.7 second down to 0.2 second. 
     The resulting mixture of gases and vapors from the present inventive hydropyrolysis are cooled to about 75° C. or below to condense the aromatic hydrocarbons as a liquid product. The uncondensed mixture comprises mainly oxides of carbon together with the hydrogen and some methane and even ethylene, ethane and propane. 
     The hydropyrolysis also produces a solid product, char, which contains catalyst metals, bromine if used for catalysis, but is mainly carbon with some hydrogen and oxygen. Unlike an incineration ash, the char can be extracted with acetic acid to remove most of the catalyst metals and, if present, a portion of the bromine. The extracted char together with the uncondensed gases can be burned as fuel to supply the heat for pyrolysis. 
     Residues from the manufacture of benzene di- and tricarboxylic acids in general contain from zero to five weight percent total of water and acetic acid, from three up to five weight percent total of components of catalyst and associated with the metals (usually in the plus two valence state) from three to ten weight percent acetate radical. Thus, the oxygen-containing aromatic compounds can comprise from 79 to 96 weight percent of the residue. 
    
    
     More specifically, the oxygen-containing aromatic compounds which can be present in the residues subjected to hydropyrolysis of this invention can be illustrated by the identified compounds present in the residue from the manufacture of terephthalic acid by the air oxidation of p-xylene in acetic acid as reaction solvent and in the presence of cobalt, manganese and bromine as components of the catalyst system. Such identified compounds are now known to be: terephthalic acid and its precursors p-toluic acid, p-formylbenzoic acid, p-tolualdehyde, terephthalaldehyde and p-methylbenzyl alcohol by-products including methylphthalic acids, ortho-and isophthalic acids (from o- and m-xylene impurities in the p-xylene), trimellitic acid, as well as benzaldehyde and benzoic acid (from ethylbenzene impurity in p-xylene); and co-products including 4,4&#39;-bibenzoic acid; 1,2-bis(p-carboxyphenyl)ethane; 2,5,4&#39;-tricarboxybiphenyl; 2,6-dicarboxyfluorenone; and 4,4&#39;-stilbene dicarboxylic acid. On a water and acetic acid-free basis one such residue contains the weight percentages of the foregoing compounds and groups of compounds as shown in TABLE I to follow. 
     
                       TABLE I                                                     
______________________________________                                    
COMPONENTS OF RESIDUE FREE OF                                             
OF WATER AND ACETIC ACID                                                  
______________________________________                                    
Terephthalic Acid     26.4%                                               
p-Toluic Aids         20.8%                                               
p-Formylbenzoic acid  9.1%                                                
p-Tolualdehyde        0.51%                                               
Terephthalaldehyde    1.20%                                               
p-Methylbenzyl Alcohol                                                    
                      2.06%                                               
Reaction By-Products  36.9%                                               
Co-Products           4.12%                                               
______________________________________                                    
 
    
     Another such residue has the composition including the catalyst components: cobalt, manganese and bromine and metals or corrosion as shown in TABLE II to follow. 
     
                       TABLE II                                                    
______________________________________                                    
RESIDUE FROM TEREPHTHALIC ACID MANUFACTURE                                
ON ACETIC ACID AND WATER-FREE BASIS                                       
Component             Weight Percent                                      
______________________________________                                    
Phthalic Acids        19.0                                                
Benzoic Acid          14.8                                                
Toluic Acids          26.7                                                
Methyl Phthalic Acids 2.65                                                
Trimellitic and Trimessic Acids                                           
                      4.32                                                
4-Carboxybenzaldehyde 9.09                                                
Tolualdehydes         0.40                                                
Benzaldehyde          0.004                                               
Terephthalaldehyde    0.27                                                
Methylbenzyl Acetate  0.02                                                
Formyl Acetate        0.15                                                
Benzylbenzoate        0.07                                                
Phthalide             2.04                                                
Co-Products           4.24                                                
Cobalt                1.51                                                
Manganese             2.53                                                
Bromine               2.20                                                
Iron                  0.09                                                
Aluminum              0.00022                                             
Calcium               0.02                                                
Chromium              0.007                                               
Copper                0.0001                                              
Magnesium             0.0028                                              
Molybdenum            0.0035                                              
Sodium                0.30                                                
Nickel                0.0052                                              
Silica                0.0025                                              
Anion of Metals       9.04                                                
______________________________________                                    
 
    
     The first four elements are determined by X-ray fluorescence and the remaining elements are determined by emission spectroscopy. The foregoing more detailed identification of organic components and metals is not one usually made by terephthalic acid manufacturing facilities but is made for research purposes as a starting point, for example, to identify extractable components, or to evaluate the completeness of commercial oxidation of the xylene feed, or to evaluate potential increase of phthalic acids production by some additional oxidation of the phthalic acid precursors present in such residue. 
     However, the terephthalic acid manufacturing facilities will obtain a partial analysis of the residue to include at least the phthalic acids, toluic acids, benzoic acid and catalyst components to determine on a day-to-day basis the approximate oxidation efficiency, and catalyst metal and solvent discard. Such partial analytical inspections of the residue are as shown in TABLE III to follow. 
     
                       TABLE III                                                   
______________________________________                                    
PARTIAL ANALYTICAL RESULTS OF RESIDUE                                     
FROM TEREPHTHALIC ACID MANUFACTURE                                        
Components   Sample Number                                                
In Weight %  1        2        3      4                                   
______________________________________                                    
Acetic Acid  0.22     3.23     3.74   3.24                                
Phthalic Acids                                                            
             45.8     31.4     33.4   26.0                                
Toluic Acids 5.2      12.3     12.8   22.6                                
4-CBA.sup.(1)                                                             
             1.05     4.56     4.82   9.1                                 
Benzoic Acid 20.2     27.6     26.0   19.8                                
Trimellitic Acid                                                          
             5.4      4.0      4.3    3.8                                 
OLB Compounds.sup.(2)                                                     
             5.4      4.1      4.4    0.9                                 
HB Compounds.sup.(3)                                                      
             0.26     7.5      5.8    0.4                                 
Cobalt       0.69     0.49     0.5    1.35                                
Manganese    1.79     1.22     1.3    2.48                                
Bromine      2.59     1.49     1.5    2.5                                 
______________________________________                                    
 .sup.(1) &#34;4CBA&#34; is 4carboxybenzaldehyde (pformylbenzoic acid).           
 .sup.(2) &#34;OLB Compounds&#34; are other lower boiling compounds.              
 .sup.(3) &#34;HB Compounds&#34; are higher boiling (higher than trimellitic acid)
 compounds.                                                               
 
    
     The residue from manufacture of isophthalic acid by air oxidation of m-xylene in an acetic acid reaction medium and in the presence of catalysis provided by cobalt, manganese and bromine is quite similar to the residue from the manufacture of terephthalic acid by the same oxidation of p-xylene. The manufacture of the anhydride (intramolecular) of trimellitic acid (TMA) can produce two residues. One residue is obtained after precipitating and separating impure trimellitic acid from the acetic acid solution of the catalyst (Co--Mn--Br) system and then evaporating the acetic acid. The second residue is obtained after dehydration of impure trimellitic acid (TMLA) to its impure anhydride and evaporating a partially purified anhydride. The compositions of such TMLA and TMA residues and the residue from isophthalic acid (IA) manufacture are characterized in TABLE IV to follow. 
     
                       TABLE IV                                                    
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CHARACTERIZATION OF RESIDUES FROM THE                                     
MANUFACTURE OF ISO-PHTHALIC ACID                                          
AND TRIMELLITIC ANHYDRIDE                                                 
             RESIDUE                                                      
Component      IA        TMLA      TMA                                    
______________________________________                                    
In Weight %                                                               
Acetic Acids   0.11      1.58      0                                      
Phthalic Acids 39.8      12.3      1.0                                    
Toluic Acids   1.8       0         0                                      
Aldehydes      0.09      0.53      1.4                                    
Benzoic Acid   24.1      0.5       0                                      
Trimellitic Acid                                                          
               2.5       38.6      65.2.sup.(1)                           
OLB Compounds.sup.(2)                                                     
               1.7       4.7       1.9                                    
HB Compounds.sup.(3)                                                      
               5.3       0.94      0.4                                    
Cobalt         0.48      1.17      2.51                                   
Manganese      1.27      0.28      0.87                                   
Bromine        2.6       0.94      0.15                                   
______________________________________                                    
 .sup.(1) Trimellitic acid anhydride?                                     
 .sup.(2) See TABLE III?                                                  
 .sup.(3) See TABLE III?                                                  
 
    
     The residues from the manufacture of phthalic anhydride of interest for use in the practice of the present invention are obtained from two different oxidation processes. The residue from the first of such processes is obtained after evaporation of acetic acid and water from the liquid portion of the oxidation effluent from the air oxidation of o-xylene in an acetic acid solution of the Co--Mn--Br catalyst system after precipitating and recovering o-phthalic acid or its anhydride from the oxidation effluent. Such residue contains the components and their concentrations substantially the same as in the residues characterized by TABLES I through III. The residue from the second type of oxidation process is obtained by heating the oxidation effluent to convert o-phthalic acid to its anhydride and evaporate the anhydride and water when such effluent is produced by the air oxidation of liquid o-xylene in liquid o-phthalic acid containing the Co--Mn--Br system of catalysis. Since such oxidation does not use an extraneous solvent, it is hereafter sometimes referred to as the &#34;neat oxidation&#34; process. Such residue from the second type of oxidation process comprises 50 to 85 weight percent phthalic anhydride as a flux for higher boiling materials; e.g., iso- and terephthalic acid, trimellitic acid, metal (Co and Mn) phthalates or acetates, and oxygen-containing both coupled and fused ring compounds: di-, tri- and tetracarboxy-substituted biphenyl and benzophenone and dicarboxyfluorenone. In TABLE V to follow there are given the components and their concentrations in weight percent of such residues from said second type of o-xylene oxidation process. 
     In TABLE V &#34;PAN&#34; is used to designate phthalic anhydride and &#34;2-CBA&#34; is used to designate 2-carboxybenzaldehyde. 
     
                       TABLE V                                                     
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NEAT OXIDATION RESIDUES                                                   
Component    Residue Number                                               
Weight %     1       2       3     4     5                                
______________________________________                                    
PAN          72.2    77.4    65.7  84.5  57.3                             
o-Toluic Acid                                                             
             0.03    0.23    0.15  0.04  0.1                              
Phthalide    0.01    0.2     0.18  0.001 0.3                              
2-CBA        0.77    1.0     1.03  0.41  1.65                             
Benzoic Acid 0.56    1.03    0.69  0.60  1.8                              
Other Aromatics                                                           
             20.7    16.0    26.8  11.5  22.7                             
Cobalt       1.14    1.08    1.36  0.62  0.58                             
Manganese    3.38    2.29    3.34  1.85  1.13                             
Bromine      1.32    0.90    0.78  0.87  1.01                             
______________________________________                                    
 
    
     Also useful in the practice of the present inventive hydropyrolysis are the undissolved solids portion of the residues after the extraction of the residues with water to remove catalyst metals for reuse in the oxidation from which the metal-containing residue originated. Such undissolved solids portion is hereafter referred to as &#34;extracted residue.&#34; In TABLE VI to follow characteristics of such extracted residues are given. 
     
                       TABLE VI                                                    
______________________________________                                    
EXTRACTED RESIDUES                                                        
Components Of Sample 1                                                    
                      Of Sample 3                                         
                                 of Neat Oxidn.                           
Weight %   TABLE III  TABLE III  Residue                                  
______________________________________                                    
Aldehydes  1.57       5.84       1.03                                     
Benzoic Acid                                                              
           18.1       31.4       1.7                                      
Toluic Acids                                                              
           1.61       16.0       0                                        
Phthalic Acids                                                            
           56.4       37.6       5.6                                      
OLB Compounds                                                             
           0.4        0.78       41.0                                     
HB Compounds                                                              
           8.0        3.6        0.2                                      
Cobalt     0.18       0.03       0.16                                     
Manganese  0.49       0.10       0.28                                     
Bromine    0.51       0.09       0.35                                     
______________________________________                                    
 
    
     There follows in TABLES VII and VIII the results of vapor phase decarboxylation of a single benzene carboxylic acid by vaporizing the acid at one temperature and then contacting the vapors with a catalyst sometimes at a second temperature as indicated. Further, in such decarboxylation the catalyst is first placed in a quartz tube, the tube is heated in two zones with electric furnaces, and the benzene carboxylic acid sample is inserted into the vaporizing section of the tube in a ceramic boat, said boat is moved into and out of the vaporizing portion of the tube by a nichrome wire attached to the boat. Vaporization of the sample is accomplished in 5 to 15 minutes at the 500° C. temperature. A small nitrogen gas flow (about 3 ml/sec) through the tube is used to sweep the vapors through the hot catalyst and out of the tube. Products of the decarboxylations are collected by transport of the gaseous mixture after contact with the catalyst through two cooled traps, then through a drier to remove water vapor and then to a gas collector. At least one of the traps is cooled with a mixture of crushed solid CO 2  and isopropyl alcohol. Measured samples of the collected gas are analyzed by mass spectrometry. For the present purpose of illustrating the effectiveness of prior suggested catalysts, only the total amount of liquid aromatic hydrocarbons collected in the cooled traps and the amount of CO 2  generated expressed as weight percentages of the benzene carboxylic acid used are reported. 
     Except for two decarboxylations in TABLE VII illustrating the use of zinc oxide and zinc oxide supported on alumina as the catalyst, the benzene carboxylic acid samples subjected to decarboxylation were about one gram in size. Those two exceptions used five gram samples supplied by five one gram samples successively introduced into the vaporizing portion of the tubes. 
     
                       TABLE VII                                                   
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DECARBOXYLATION OF TEREPHTHALIC ACID                                      
               Temper-   Product,                                         
               ature, °C.                                          
                         Wt. %                                            
Catalyst         Vap.   Catalyst Liquid                                   
                                       CO.sub.2                           
______________________________________                                    
4789-151                                                                  
       Ba Promoted                                                        
       Cu Chromite   352    352    3.97  64.5                             
150     &#34;            399    399    7.99  127.7                            
156    Cu.sub.2 O.sub.3 -Zno                                              
                     400    400    11.9  102.3                            
147    Ni Oxide on                                                        
       Alumina       446    446    18.0  45.4                             
155    ZnO           511    511    24.0  39.9                             
165    ZnO-Chromia   499    499    35.8  49.2                             
184    Zn Chromite   499    499    21.8  67.9                             
185    Chromia-Alumina-                                                   
       Magnesia      500    500    17.7  46.3                             
188    K Promoted                                                         
       Chromia-Alumina                                                    
                     499    499    20.8  66.1                             
195    ZnO-Alumina   498    498    33.9  29.0                             
200    Zno-MoO.sub.2 on                                                   
       Molecular Sieve                                                    
                     499    499    31.7  26.8                             
204    ZnO-Co.sub.2 O.sub.3 -                                             
       W.sub.2 0.sub.3 on                                                 
       Molecular Sieve                                                    
                     500    500    33.0  48.8                             
5065-001                                                                  
       Zn0-Co.sub.2 0.sub.3 -Mo0.sub.2                                    
       on Molecular                                                       
       Sieve         500    500    22.0  39.3                             
005    Chromia on                                                         
       Molecular Sieve                                                    
                     499    499    17.0  41.3                             
006    ZnO*          501    501    24.3  23.0                             
007    ZnO on Alumina*                                                    
                     500    500    32.9  36.3                             
010    ZnO-Alumina   500    500    33.0  47.9                             
022     &#34;            499    498    36.9  47.3                             
023      &#34;           501    399    0     19.9                             
025     &#34;            500    451    26.9  40.6                             
030    CaO           500    502    25.9  0.04                             
031    CaCO.sub.3    499    501    5.0   29.9                             
036    CdO           502    22.0   38.8                                   
______________________________________                                    
 *Five grams terephthalic acid                                            
 
    
     The theoretical amounts of benzene and carbon dioxide from the complete decarboxylation of terephthalic acid are, respectively, 47 weight percent and 53 weight percent. The above amounts of CO 2  reported in excess of said 53 wt.% may be from partial combustion of the benzene produced. 
     
                       TABLE VIII                                                  
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DECARBOXYLATION AND/OR DECARBONYLATION OF                                 
BENZOIC ACID AND SUBSTITUTED BENZOIC                                      
ACIDS IN THE PRESENCE OF ZINC OXIDE                                       
ON ALUMINA                                                                
               Temper-   Product,                                         
               ature, °C.                                          
                         Wt. %                                            
Acid             Vap.   Catalyst Liquid                                   
                                       CO.sub.2                           
______________________________________                                    
4789-149                                                                  
       Benzoic Acid* 399    399    19.9  12.26                            
5065-037                                                                  
       Benzoic Acid  501    501    53    29.7                             
011    Isophthalic Acid                                                   
                     500    500    33    45.4                             
012    o-Phthalic Acid                                                    
                     497    499    24    37.2                             
014    p-Toluic Acid 501    501    21    21                               
015    Trimellitic Acid                                                   
                     502    502    13    32.8                             
016    4-Carboxy-                                                         
       benzaldehyde  500    500    18.4  31.1                             
017    Phthalic                                                           
       Anhydride     502    502    20    36                               
035    Trimellitic Acid                                                   
       Anhydride     499    500    12.8  53.2                             
______________________________________                                    
 *Catalyst is Ni Oxide on Alumina?                                        
 
    
     In TABLE IX to follow terephthalic acid process residue (TAR) unextracted or water extracted (TARX) is decarboxyl- and decarbonylated in the presence of various catalysts at various temperatures. Again only the total liquid aromatic hydrocarbons and CO 2 , both in weight percent of sample, are reported. Also a slight flow (about 3 ml/sec) of nitrogen gas is used for the purposes before described. 
     
                       TABLE IX                                                    
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DECARBOXYLIC AND DECARBONYLATION                                          
OF TEREPHTHALIC ACID PROCESS RESIDUES                                     
               Temper-   Product,                                         
               ature, °C.                                          
                         Wt. %                                            
Catalyst         Vap.   Catalyst Liquid                                   
                                       CO.sub.2                           
______________________________________                                    
4789-124                                                                  
       Copper Wool   353    353    0     2.29                             
125    Cu.sub.2 O-wire                                                    
                     350    350    0     10                               
126     &#34;            400    400    0     16.6                             
134    Ba Promoted                                                        
       Cu Chromite   500    500    0     105.6                            
132    Gamma Alumina 500    500    0     19.8                             
128    Chromia on Gamma                                                   
       Alumina       400    400    0     14.5                             
136    ZnO-Alumina                                                        
       Co Gel        500    500    0     3.58                             
137    Chromia Promoted                                                   
       Fe.sub.2 O.sub.3                                                   
                     400    400    0     18.4                             
131    Co-Molybdate on                                                    
       Gamma Alumia  397           0     1.64                             
142    Co.sub.2 O.sub.3 on                                                
       Keiselguhr    398    398    0     30.34                            
145    Ni Oxide on                                                        
       Refractory                                                         
       Support       399    399    10.96 15.8                             
171    ZnO           499    499    28.0  23.4                             
196    ZnO on Alumina                                                     
                     500    500    26.0  22                               
5065-009                                                                  
       .sup.(1)                                                           
       ZnO on Alumina                                                     
                     499    499    26.2  30.0                             
008    .sup.(1,2)                                                         
       ZnO on Alumina                                                     
                     502    502    27.7  26.2                             
041    .sup.(3)                                                           
       ZnO on Alumina                                                     
                     501    501    24.0  26.7                             
044    .sup.(4)                                                           
       ZnO on Alumina                                                     
                     501    501    28.0  31.0                             
026    .sup.(2)                                                           
       ZnO on Alumina                                                     
                     501    502    30    35.8                             
027    ZnO on Alumina                                                     
                     503    500    26    36.4                             
034    .sup.(5)                                                           
       ZnO on Alumina                                                     
                     499    504    22.9  40.4                             
______________________________________                                    
 .sup.(1) Sample is five grams?                                           
 .sup.(2) Residue from terephthalic acid process after being? extracted   
 with water.?                                                             
 .sup.(3) Sample is 40.76 grams?                                          
 .sup.(4) Sample is 28.85 grams?                                          
 .sup.(5) Residue from ophthalic acid process after being? extracted with 
 water.?                                                                  
 
    
     In general, the use of prior suggested decarboxylation catalysts did cause carbon dioxide to be liberated or produced but not all such catalysts caused an attractive co-production of liquid aromatic hydrocarbons. Of those prior suggested decarboxylation catalysts Zinc oxide alone; or zinc oxide in admixture with or supported by chromia or alumina; or a mixture of zinc oxide with either molybdena, or with oxides of cobalt and tungsten supported on molecular sieves in general were found to produce liquid aromatic hydrocarbons in yields upward from about 50 percent of the theoretical yield at temperatures above 450° C. However, the effective life of such better liquid aromatic hydrocarbon producing catalyst was short. 
     The consistently better prior suggested catalyst was found to be the combination of zinc oxide and alumina. Such catalyst is used at 500° C. with one to two gram samples of terephthalic acid process residues introduced consecutively at about 5-minute intervals into the heated quartz tube containing said catalyst over a five day period. The liquid aromatic hydrocarbon yield decreases from 26.4 weight percent down to 14.6 weight percent of residue fed over the five day period and considerable blackening of the catalyst is observed. Said liquid aromatic hydrocarbon decrease occurs with a residue to catalyst weight ratio of no more than about 2:1. Such results indicate a very short life for the ZnO- alumina catalyst and that frequent regeneration thereof would be necessary for such catalyst to be used commercially. 
     Thus, non-catalytic pyrolysis of the before described residues from benzene di- and tricarboxylic acid manufacture would be more attractive commercially, provided the yield of liquid aromatic hydrocarbons would be equal to or better than the liquid aromatic hydrocarbon yield from the long term (five day) test of the ZnO on alumina catalyst. 
     The conduct of the illustrative non-catalytic hydropyrolysis to follow are conducted in apparatus devised for small scale operation of the present inventive hydropyrolysis. Said apparatus comprises: a tubular reactor which is a 316 stainless steel tube 304.8 mm long having a 6.35 mm outside diameter and a 1.245 mm wall thickness. Two type K thermocouple wires are spot welded to the center of the tube. One thermocouple is connected to a high temperature cut-off control and the other thermocouple is connected to a temperature recorder. The tube is heated by two copper electrodes each having a groove of the tubes&#39; curvature to which the reactor tube is clamped by grooved brackets. During operation only 203 mm (101.5 mm each side of center) of the tube is heated. Power is supplied to the electrodes by a first transformer and timer combination to heat the tube at a rate of 650° C./sec. The second transformer provides a more gradual heating over a 4 second period to the final temperature. The reactor tube is adapted at one end to be attached to a metered supply of compressed hydrogen through pressure control valves and at the other end to be attached to a gas chromatograph column 3.175 mm internal diameter and 1219 mm long packed with Poropak Q. Analysis of the products is accomplished by cooling the column with liquid nitrogen to 15° C. 
     The reactor tube is packed with quartz wool 146 mm from the center on the discharge portion of the tube. The sample (4 to 10 mg), preferably ground to 270 mesh (U.S. Standard Sieve Size) or less, is inserted from the inlet end of the tube and deposited on the front face of the quartz wool plug. Quartz wool is then loosely packed into 152 mm of the inlet length from the center of the tube. The packed tube is then inserted into the flow system and compressed hydrogen is passed through the gas chromatograph. 
     The illustrative examples use terephthalic acid process residue (TAR) and insolubles (TARX) remaining after water extraction of such residue. Said insolubles were, of course, dried before use in the present inventive process. TABLE X provides the operating conditions of, and TABLE XI provides the results from the hydropyrolysis of the unextracted residue (TAR) and the extracted residue (TARX). 
     
                       TABLE X                                                     
______________________________________                                    
OPERATING CONDITIONS FOR                                                  
THE HYDROPYROLYSIS                                                        
          Example                                                         
                 Feed       Temperature, °C.                       
            Number   Type    Mg.  °C./sec.                         
                                         Max.                             
______________________________________                                    
May 78 Mo.PR                                                              
            1        TARX    11.6 697    895                              
4667-061B6  2        TARX    4.8  703    830                              
061B5       3        TARX    7.8  661    805                              
061B1       4        TARX    9.7  703    703                              
061B4       5        TARX    5.4  726    867                              
1753        6        TAR     9.6  714    873                              
1754        7        TAR     7.9  727    869                              
1756        8        TAR     7.8  738    897                              
1755        9        TAR     7.8  709    879                              
061B3       10       TAR     13.0 678    822                              
061B        11       TAR     12.6 661    810                              
______________________________________                                    
          Example  H.sub.2 Press.                                         
                               VRT,                                       
          Number   kg/cm.sup.2 sec.                                       
______________________________________                                    
          1        107.6       0.27                                       
          2        105.5       0.34                                       
          3        105.5       0.34                                       
          4        108.3       0.4                                        
          5        105.5       0.4                                        
          6        105.5       0.4                                        
          7        105.5       0.4                                        
          8        107.6       0.45                                       
          9        105.5       0.5                                        
          10       109.7       0.66                                       
          11       108.3       0.66                                       
______________________________________                                    
 
    
     
                       TABLE XI                                                    
______________________________________                                    
 RESULTS OF THE HYDROPYROLYSIS                                            
Hydrocarbon Products, wt. %                                               
Examples                                                                  
        Aromatic      Alkane                                              
Number  C.sub.6 H.sub.6                                                   
                 C.sub.7 H.sub.8                                          
                          CH.sub.4                                        
                                 C.sub.2 H.sub.6                          
                                        C.sub.3 H.sub.8                   
______________________________________                                    
1       24.7     6.5      5.1    2.0    1.3                               
2       23.7     5.5      3.6    2.5    ND                                
3       14.8     5.9      2.2    1.2    ND                                
4       15.6     5.5      2.3    2.0    ND                                
5       23.2     5.9      3.9    3.6    ND                                
6       17.3     3.6      3.1    2.0    ND                                
7       18.9     4.5      3.5    3.4    1.5                               
8       18.8     2.8      4.4    NM     NM                                
9       15.8     2.9      2.9    NM     NM                                
10      20.6     2.5      4.4    NM     NM                                
11      23.0     8.4       0.15  NM     NM                                
______________________________________                                    
 &#34;ND&#34; is not detected.?                                                   
 &#34;NM&#34; is not measured.?