Abstract:
A process for removing undesirable elements, e.g. nitrogen, sulfur, oxygen, from the light organic liquid product derived from a solvent refined coal liquefaction process, while preserving octane number, which comprises the steps of (1) subjecting the light liquids to an ion-exchange resin treatment and (2) contacting the resulting ion-exchanged liquids with a zeolite acting as an adsorbent under specified conditions of space velocity, temperature and pressure.

Description:
This is a continuation, of application Ser. No. 941,437, filed Sept. 11, 1978, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a process for removing undesirable elements from light organic liquid products, obtained as a by-product of solvent refined coal liquefaction processes, while preserving octane number. 
     2. Description of the Prior Art 
     With ever increasing demands on fossil fuels as a source of energy and ever decreasing supplies of crude petroleum within the United States, the nation must turn more and more to the use of coal. Yet the people of this country have mandated through their representatives that they do not want the anticipated use of coal to degrade their environment. 
     The air pollutants of particular concern are nitrogen oxides, sulfur oxides and particulates. Nitrogen oxides are formed from nitrogen in air as well as organic nitrogen in the fuel, and their concentration is primarily a function of combustion parameters. Sulfur oxides and particulates are a function of the chemical composition of the fuel used. 
     Coal is liquefied by exposing it to hydrogen gas or a hydrogen-bearing solvent under pressure and, in many processes, in the presence of a catalyst. Temperatures are kept below 900° F. so that hydrocarbon molecules are not destroyed. Alternately, coal can be destructively distilled by heating in such a way that its volatile components are given off and can be condensed as a liquid. The net result is to add hydrogen or remove carbon, in the process shortening the length of the hydrocarbon molecular chains. Hydrogen is generated by gasifying a portion of the coal or of a coal residue in most schemes, and this is a substantial part of the cost of liquefaction. Sulfur content of the coal is also an important constraint, since hydrogen is also needed to remove this contaminant (as hydrogen sulfide gas) in proportion to the amount of sulfur present. In theory, it is somewhat easier and cheaper to make a heavy oil from coal suitable for a boiler fuel than a synthetic crude oil that can be refined to gasoline, since the crude oil product requires adding about twice as much hydrogen--between 5 and 10 percent of the coal&#39;s weight. Boiler fuels may also have an economic advantage in that they would supply a regulated market--the electric utility industry that now generates about 30 percent of its power with oil and natural gas--making commercial introduction somewhat easier. 
     The three direct general processes for converting coals to liquid fuels are: catalyzed hydrogenation, staged pyrolysis, and solvent refining (1,2). Each of these processes results in the production of a coal liquid which contains a variety of desirable and undesirable components. The desirable coal liquids are the oils-saturated and aromatic hydrocarbons and the resins-polar nonhydrocarbons. 
     The undesirable species are the asphaltenes and the carbenes-high molecular weight highly aromatic solids, and the carboids-polymerized coke-like materials. The undesirable elements: metals, sulfur, nitrogen, and oxygen are generally present in higher concentration in the asphaltene and carboid fractions. Under hydrogenolysis conditions, the conversion of coal to oil has been suggested to proceed via the following sequence (3): Coal→Asphaltene→Oil. Therefore, asphaltene generation and elimination are of great importance in the liquefaction process. 
     One commercial process for coal-to-liquids produces synthetic gasoline and other motor fuels, along with pipeline gas, ammonia, and other products. Coal is gasified to produce synthesis gas (carbon monoxide and hydrogen) and then, using the Fischer-Tropsch process, the synthesis gas is converted to a mixture of hydrocarbons. 
     Another process is the &#34;Solvent Refined Coal&#34; process, which is a method of dissolving coal to remove ash, reducing its sulfur content and lowering its average molecular weight. Pulverized coal is mixed with a solvent and hydrogen and heated until most of it dissolves. Gases including hydrogen sulfide are removed, as are ash and other undissolved solids. A fraction of the remaining liquid is recycled as the solvent, and the rest is product, a low-sulfur boiler fuel that is solid at room temperature but melts readily at about 375° F. 
     It is the light organic liquid derived from the Solvent Refined Coal (SRC) process that is the starting material of this invention. 
    
    
     SUMMARY OF THE INVENTION 
     In accordance with the invention, there is now provided a process for removing undesirable elements from the aforementioned (SRC) light organic liquid, and at the same time preserving, or even enhancing, octane number, which comprises the steps of (1) subjecting the light organic liquids to an ion-exchange resin treatment and (2) contacting the resulting ion-exchanged liquids with a zeolite acting as an adsorbent under specified conditions of liquid hourly space velocity, temperature and pressure. The ion-exchange resin is the class of acid ion exchange resins exemplified by Amberlyst-15 Amberlyst XN-1005, Amberlyst XN-1010, Amberlyst XN-1011, Amberlyst XN-1008, Amberlite 200 and Amberlite IR-120H, with Amberlyst 15 particularly preferred (see U.S. Pat. No. 3,855,342 for further description of the resins), while the zeolite adsorbent is the class of zeolites exemplified by ZSM-5, ZSM-11, ZSM-12 and ZSM-35 with ZSM-5 particularly preferred (see U.S. Pat. Nos. 3,702,886; 3,709,979; 3,832,449; and 4,016,245, respectively). 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Describing now the inventive process in further detail, the light organic liquid product from the solvent refined coal (SRC) liquefaction process is separated from the recycle solvent by flask distillation and amounts to about 10-30 wt % of the total product yield. It boils in the gasoline range; however it has high nitrogen (0.2-0.3 wt %) and oxygen (5-6 wt %) contents along with a reasonable, low sulfur (˜0.5 wt %). Further processing is thus necessary to reduce these heteroatoms down to an acceptable level for use as a gasoline. 
     The high nitrogen content precludes conventional processing using acidic catalysts (such as ZSM-5), since nitrogen compounds poison the acid sites. Also, hydrogenative processing (over Co/Mo/Al 2  O 3 , Pd/Al 2  O 3 , etc) would require such severity to hydrogenate the nitrogen compounds that many of the aromatic rings would also be hydrogenated, giving a low octane gasoline. 
     We have found that the major amount of nitrogen compounds can be selectively removed from the SRC light organic liquid by a simple, room temperature contact with an organic resin, e.g. Amberlyst 15, a registered Trademark of Rohm &amp; Haas, Co. or the like. 
     The remaining liquid, having about the same oxygen and sulfur content as the original liquid, can then be treated with acidic catalysts or hydrogenated under milder conditions to remove oxygen and sulfur without destroying aromatics, thereby preserving high octane number. 
     By gasoline boiling range material is meant any hydrocarbon or petroleum type material boiling in the naphtha or gasoline boiling range (75° to about 440° F.), and includes hydrocarbons in the range C 5  -C 12 . HZSM-5 zeolite which has a wide variety of uses as a catalyst or adsorbent may be found described in U.S. Patent No. 3,702,886. Liquid hourly space velocity is defined as the ccs. of liquid charged per cc of catalyst per hour. 
     In accord with the foregoing, it was found surprising that the Amberlyst ion-exchange resin would be so selective for nitrogen compounds, since in the upper boiling range of the gasoline more than one heteroatom per molecule is common. Subsequent treatment over HZSM-5 removed even more nitrogen, as well as sulfur and oxygen, the later of which was not significantly removed by the ion-exchange resin. 
    
    
     In order to more fully explain the invention, the following non-limitative examples are presented. 
     EXAMPLES 1-3 
     A sample of SRC light organic liquid was passed over HZSM-5 extrudate at 1 LHSV, atmospheric pressure, at temperatures of 703°, 756° and 806° F., respectively, for periods of 4, 51/2 and 16 hours, respectively. Properties of the SRC charging liquid and analytical data from the examples are detailed in Table 1 immediately hereinbelow. 
     
                       TABLE 1______________________________________CATALYST - HZSM-5 Extrudate, (30-60 Mesh)CONDITIONS - 1 LHSV, Atmospheric PressureEXAMPLE                  1       2     3______________________________________Temp., °F.            C       703     756   806Run Time, Hours  h       4       51/2  16Products, Wt %   aC.sub.1 &amp; C.sub.2            r       &lt;0.1    &lt;0.1  &lt;0.1C.sub.3          g       &lt;0.1    0.2   0.6C.sub.4          e       0.2     1.1   1.7C.sub.5                  0.3     1.3   1.7C.sub.6.sup.+    100     99.5    97.4  96.0Liquid Product AnalysisGravity, °API            25.9    --      23.4  23.8Gravity, Specific            .8990   --      .9135 .9111Oxygen, Wt %     5.15    4.85    4.51  4.78Nitrogen, Wt %   0.23    --      0.15  0.20Sulfur, Wt %     0.40    --      0.30  0.32Sim. Dist.IBP              175     165     115   1095%               253     242     239   24410%              283     278     277   27620%              322     319     321   31830%              346     344     354   34940%              357     354     366   36150%              369     368     377   37260%              385     388     397   38970%              399     398     406   40080%              412     410     419   41290%              423     429     441   42495%              450     455     466   45198%              483     503     512   484Octane No., R + O(Minimicro)      99.9    100.5   --    100.5______________________________________ 
    
     It can be seen from the foregoing that essentially no reaction took place, although oxygen, nitrogen and sulfur content were reduced somewhat, and octane number (R+O) was preserved, if not somewhat enhanced. 
     EXAMPLE 4 
     Three hundred cc (268.3 g) of the liquid was poured into a one liter Erlenmeyer flask, 30 g of 16-50 mesh Amberlyst beads added, and the mixture gently agitated on a stir-plate at room temperature overnight (17 hours). A 10 gram sample of supernatant liquid was withdrawn and analyzed; it contained 0.056 wt % nitrogen. Continued contact for an additional four days made no further change (0.055 wt % nitrogen). Recovery of total supernatant liquid (separated from wet Amberlyst beads by filtration through paper) was 221.4 g, or 83 wt %. Analysis compared with the charge is as follows: 
     
         ______________________________________          Untreated  Treated______________________________________Gravity, °API            25.9         24.0Specific         0.8990       0.9100Nitrogen, Wt %   0.23         0.055Oxygen, Wt %     5.15         4.65Sulfur, Wt %     0.40         0.43Boiling Range, °F.IBP              175          1745%               253          25010               283          27520               322          31630               346          33340               357          34150               369          36060               385          37270               399          39080               412          40090               423          41295               450          43298               483          461Octane No., R + O            99.9         98.6______________________________________ 
    
     The 17 wt percent of the SRC light organic liquid adsorbed on the Amberlyst beads (not desorbed) would be expected to contain 1.08 wt percent nitrogen, nearly a 5-fold enrichment. 
     EXAMPLE 5 
     The Amberlyst treated liquid which contained 0.055 wt % nitrogen compared to 0.23 wt % nitrogen in the original liquid (treatment described in Example 4), was passed over HZSM-5 at 700° F. Very little cracking occurred (99 wt % C 5   + ), ani the octane No. (R+O) increased from 98.6 to 100.9. Heteroatom removal (based on original liquid) was as follows: 
     
         ______________________________________                   Then HZSM-5      Amberlyst 15 Treat                   700° F.______________________________________N Removal, wt %        76             87S Removal, wt %        Nil            27O Removal, wt %        10             13Octane No. (R + O)        98.6             100.9______________________________________ 
    
     This example demonstrates very high nitrogen removal with preservation, indeed enhancement of octane number. Sulfur removal over HZSM-5 went from essentially zero originally to 27 wt %. Complete listing of analytical data may be found in Table 2, below. 
     EXAMPLES 6 AND 6A 
     The Amberlyst 15 treatment was made by &#34;dripping&#34; the charge liquid over a column of Amberlyst, rather than agitating on a stir plate as in Example 5. The treated liquid recovery was the same as in Example 5 (83 wt %) but nitrogen removal was more complete (0.036 compared to 0.055 wt %). The treated liquid was then passed over HZSM-5 at 800° F. Again little cracking took place (98 wt % C 5   + ) and the octane number (R+O) increased from 98.1 to 99.2. A difference in this example is that the liquid product boils significantly lower throughout the boiling range which improves its volatility characteristics. Heteroatom removal was as follows: 
     
         ______________________________________      Example 6    Example 6A Then      Amberlyst 15 Treat                   HZSM-5, 800° F.______________________________________N Removal, wt %        84             88S Removal, wt %        Nil            30O Removal, wt %        22             23Octane No. (R + O)        98.1           99.2______________________________________ 
    
     Again this example demonstrates very high nitrogen removal with enhancement of octane number. Sulfur removal over HZSM-5 went from zero to 30 wt. percent. 
     Table 2 set forth immediately hereinbelow sets forth the correlative data obtained from all of the foregoing examples. 
     
                                           TABLE 2__________________________________________________________________________PROCESSING OF SRC LIGHT ORGANIC LIQUID OVER HZSM-5 EXTRUDATEBEFORE AND AFTER TREATMENT OF LIQUID WITH AMBERLYST 15 BEADSEXAMPLE NOS.       1  2      3   4      5   6      6A__________________________________________________________________________Temp. Av. Cat., °F.        Charge              703                 756    806 Charge 701 Charge 798LHSV               1.00                 0.95   0.93       1.03       1.04Pressure              Armospheric       Atmos.     Atmos.Run Time, Hours    4  542    16         21         211/2                            Treated    TreatedProducts, wt %        Untreated           With       WithC.sub.1 + C.sub.2  &lt;0.1                 &lt;0.1   &lt;0.1                            Amberlyst.sup.1                                   &lt;0.1                                       Amberlyst.sup.2                                              0.1C.sub.3            &lt;0.1                 0.2    0.6        0.4        0.9C.sub.4            0.2                 1.1    1.7        0.8        1.1C.sub.5            0.3                 1.3    1.7        1.0        1.6C.sub.6.sup.+      99.5                 97.4   96.0       97.8       96.3Liquid AnalysisGravity, °API        25.9  -- 23.4   23.8                            24.0   24.4                                       24.2   25.6Gravity, Specific        0.8990              -- 0.9135 0.9111                            0.9100 0.9076                                       0.9088 0.9007Boiling Range, °F.IBP          175   165                 115    109 174    51  163    65%           253   242                 239    244 250    240 247    19710           283   278                 277    276 275    287 279    24320           322   319                 321    318 316    330 320    28830           346   344                 354    349 333    344 334    30340           357   354                 366    361 341    362 349    31550           369   368                 377    372 360    377 362    32760           385   388                 397    389 372    389 374    33770           399   398                 406    400 390    411 399    36180           412   410                 419    412 400    421 409    37190           423   429                 441    424 412    440 420    37795           450   455                 466    451 432    458 447    40498           483   503                 512    484 461    486 482    411Octane No., R + O        99.9  100.5                 --     100.5                            98.6   100.9                                       98.1   99.2Nitrogen, Wt %        0.23  -- 0.15   0.20                            0.055  0.031                                       0.036  0.028Sulfur, Wt % 0.40  -- 0.30   0.32                            0.43   0.29                                       0.47   0.28Oxygen, Wt % 5.15  4.85                 4.51   4.78                            4.65   4.50                                       4.04   3.95Nitrogen Removal, Wt %        --    -- 35     13  76     87  84     88Sulfur Removal, Wt %        --    -- 25     20  NIL    27  NIL    30Oxygen Removal, Wt %        --    6  12     7   10     13  22     23__________________________________________________________________________ .sup.1 Recovery of treated liquid 83 wt % of charge (remainder adsorbed o Amberlyst 15) .sup.2 783 g charge liquid &#34;dripped&#34; thru 1759 Amberlyst 15 &#34;Super Resin&#34; in ˜1&#34; dia. glass column in ˜40 hours. Recovery of treated liquid 83 wt % of charge. Resin has 2 meg. acid sites per gram, total meg = 2 × 175 = 350. Charge has 783 × 0.23 ÷ 14 = 128 meg. N. there are thus 2.74 sites available for each N or 174% excess.