US3231486A - Catalytic hydrogenation of carbonized coal vapors - Google Patents

Description

United States Patent 3,231,486 CATALYTlC HYDROGENATION 0F CARBONIZED COAL VAPORS Richard C. Perry, Charleston, and Charles W. Alhright,

South Charleston, W. Va., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 16, 1960, Ser. No. 76,113

3 Claims. (Cl. 2088) This invention relates to the stabilization of tar vapors resulting from thermal treatment of carbonaceous materials. More particularly, this invention relates to the stabilization of vapors produced by low temperature coal carbonization processes so as to form low molecular weight tar products.

A number of low temperatures coal carbonization processes have been developed in the past. These processes comprise in general heating coal at a temperature of from about 400 C. to about 700 C. and recovering the resulting products: char, gas and tars. In many of these processes the carbonization of the coal is conducted in a fluidized bed, withdrawing the char from the bed, and condensing the vapors that form to recover the carbonization tar. Quite often the fiuidizing gas is air, although nitrogen, steam and hydrogen have also been used. Such processes have not been extensively used in this country because the resulting products are not of sufiicient value to make the processes economically feasible. The main product of these processes, amounting to about 70 to 75 weight percent of the coal carbonized, is a char containing 15 to 20 percent of volatile material. At present, this char can be used as a solid fuel. But the worth of the unit heating value of the char is approximately the same as the coal charged. About 6 to 7 weight percent of the coal carbonized appears as Water, while another 6 to 7 weight percent of the coal forms a gaseous product, which can be used as a fuel, and which has a worth per unit heating value, at something greater than that of the original coal. The remaining product, amounting to about 12 to 15 weight percent of the coal carbonized, is a low temperature tar which basically has the value of a liquid fuel oil. Because the fuel worth of the products is not much greater than that of the coal charged, low temperature carbonization processes have rarely been employed.

Various attempts have been made to upgrade the products of low temperature coal carbonization processes. Many of these attempts have centered on the low temperature tar, because it is known to contain many potentially valuable compounds, such as phenolic compounds, which can be used to manufacture phenolformaldehyde resins. Processing of the tar is difficult, however, because it is heat sensitive, decomposes readily, and polymerizes easily due to its reactivity. Efforts atrevaporization of the tar have not been satisfactory because much of the tar is a heavy asphalt that will not vaporize. It is believed that certain oxygenated materials present in the tars, such as indenols, dihydroxy phenols, ethers and the like, that are easily polymen'zabl'e and are subject to attack by atmospheric oxygen, polymerize in the tar upon condensation, and tie up many of the reactive compounds present in the tar, thereby forming the asphalt.

Secondary treatments of the tar to enable recovery of the various compounds present in the'tar have not, to date, been particularly successful. For example, liquid phase or mixed phase hydrogenation of the tar, using a fixed bed catalyst, is complicated by the short catalyst life normally encountered in such operations. Such short catalyst life requires expensive and time consuming shutdowns of the process for regeneration or renewal of the catalyst.

We have found that the amount of tar residue or asphalt obtained upon condensation of the low temperature tar vapors can be materially reduced, in some cases to less than percent of the low temperature tar produced,

and the quantity of low molecular weight oils correspondingly increased if the vapors from the carbonization are stabilized by subjecting them to a mild catalytic hydrogenation treatment prior to their condensation. By operating in this way we effect the removal, in the vapor phase, of the unsaturated and reactive groups contained by the compounds resulting from the carbonizatiou, making a more stable, lower molecular weight tar which is more amenable to separation. In addition, by operating in accordance with our invention, lower pressures can be employed than in the hydrogenation processes which have been employed for the treatment of the tars prior to our invention. Furthermore, the uncondensed gas recovered from our process has been upgraded and has a substantially higher heating value than the gases obtained from conventional carbonization processes.

The process of our invention essentially comprises stabilizing the tar vapors resulting from the carbonization of carbonaceous material by subjecting said vapors to a catalytic hydrogenation prior to allowing such vapors to condense.

The process of this invention may be carried out with coals of all ranks, including anthracite, bituminous, sub bituminous, and lignitic coals and any other carbonaceous material which, upon carbonization, yields oxygenated compounds which readily polymerize upon condensation.

Catalysts that can be used in the process of this invention are those known as hydrogen-treating catalysts. Such catalysts have been used in the past for desu'lfurization', denitrification, deoxygenation, and hydrogenation of petroleum feed stocks. These catalysts, as commercially obtained, usually comprise oxides or sulfides of metals such as cobalt, molybdenum, nickel, zinc, chromium, and tungsten on a suitable support material. Tyical catalysts of this type are the cobalt molybdate catalysts, which cornprise cobalt and molybdenum oxides on a suitable support. These catalysts contain, in general, from about 1.0 to about 8.1 weight percent of cobalt and from about 5 to about 17 weight percent of molybdenum, based upon the total catalyst weight, the weight ratio of molybdenum to cobalt being, in general, from about 1.621. to about 4.8:1.

These catalysts may also contain other'metal oxides, suchas nickel oxide and sodium oxide, the metal being present in an amount up to about 0.5 Weight percent of the total catalyst Weight or they may contain only cobalt oxide or molybdenum oxide alone.

Sulfide catalysts that are employed for desulfurization, deoxygenation, denitrification or hydrogenation processes are usually either nickel sulfide or a mixture of nickel and tungsten sulfides. Such catalysts may be on a support material but are often used without a support material. A typical catalyst of the latter type is one prepared by the coprecipitation of nickel and tungsten as the metals, followed by a treatment with hydrogen sulfide to convert the metals to the sulfides, giving a final composition having about 40 weight percent of tungsten and about 25 weight percent nickel.

Suitable support materials are bauxite, alumina, fullers earth and montmorillonite. ally employed support material.

A particularly preferred catalyst for use in the process of the instant invention comprises about 0.5 weight percent of nickel, about 1.0 weight percent of cobalt and about 8.3 weight percent of molybdenum: based on the total catalyst weight, onan alumina support, said metals being present as their oxides.

The catalysts described above are reduced before the use in the process of the invention by beating them in a hydrogen atmosphere at a temperature of from about 350 C. to about 400 C. and a pressure of about one atmosphere for from about 4 hours to about 12 hours.

Patented Jan. 25, 1966 Alumina is the most gener The carbonization reaction can be conducted in any manner known to the alt, such as by using fixed beds, moving beds and fluidized beds of the carbonaceous material.

The preferred carbonization process is that employing a fluidized bed of the material to be carbonized. When the process of this invention is employed in conjunction with sucha carbonization process, the hydrogen used in the catalytic treatment can'be employed as the fluidizing gas, thus taking advantage of whatever hydrogenation of char occurs during carbonization.

When the carbonization is conducted in a fluidized bed, the charge, on heating, should not tend to agglomerate or form a coke residue on the walls of the carbonizer. Such behavior can be avoided by including in the charge a nonagglomerating material, such as a lignitic or sub-bituminous coal, whenever the carbonaceous feed has agglomerating tendencies, whereby a non-agglomerating mixture is formed. Another method of avoiding agglomeration of the feed is to subject the feed to a pre-oxidation step in ways known in the art, or by the addition of non-agglomerating agents. Provision should be made to minimize carry over of solid particles to the catalyst bed.

The fluidizing gas is preferably preheated prior to being mixed with the carbonaceous material to be carbonized to fromabout 300 C. to about 700 C. and more preferably to about 400 C. Such preheating is not necessary, however, and the carbonization can be conducted without it.

The catalytic hydrogenation of this invention can be conducted at hydrogen pressures of at least 200 p.s.i.g. This ability to stabilize the coal tars from the carbonization at such low pressures is one of the major advantages of the instant process over those previously employed to treat coal carbonization tars. But the process of our invention is not limited to low pressures and can be applied after such processes as dry coal hydrogenation at about 3000 p.s.i.g. The higher pressures result in higher tar yields and accordingly higher yields of the low molecular weight oils produced by our process. It is preferred, however, to conduct the catalytic. hydrogenation at pressures of from about 200 p.s.i.g. to about 3000 p.s.i.g., with pressures of from about 300 p.s.i.g. to about 1000 p.s.i.g. being particularly preferred.

The coal carbonization can be carried out at temperatures of from about 450 C. to about 600 C.,and preferably at temperatures of from about 500 to 550 degrees centigrade.

It is essential to this invention that the vapors from the carbonization are not permitted to condense prior to the catalytic hydrogenation. Therefore, temperatures of from about 400 C. to about475 C., and preferably from about 420" C. to about 430 0., should be maintained in the catalyst bed as well as in the vapor line from the carbonization reactor to the catalyst bed.

In a particularly preferred embodiment of the process of this invention, particulate carbonaceous material is mixed with hydrogen that has been preheated to about 400 C. at a pressure of about 400 p.s.i.g.,and is passed to a carbonization zone where the carbonaceous material is heated to about 500550 C. The resulting char, or

solid product, is removed from the carbonization-zone and the vapors from the carbonization are passed over a catalyst containing 0.5 part by weight of nickel, 1.0 part by weight of cobalt and 8.3 parts by weight of molybdenum, on an alumina support at a temperature of about 425 C. and a pressure of about 400 p.s.i.g. The vapors are then condensed. Uncondensed gases are mixed with fresh hydrogen and are recycled to the carbonization.

The following examples are illustrative of the process of this invention.

EXAMPLE 1 The apparatus employed comprised two batch coal feed hoppers connected in parallel, each hopper-having a capacity of 3500 grams of coal, suflicient for 6 to 10 hours of operation; Process gas from a gas-cylinder manifold was preheated to about 400 C. and was then mixed with the coal fed continuously from the hopper. The resulting gassolids mixture was conducted to the base of the carbonizer where the coal was fluidized at such a rate that the char retention time within the reactor was about 15 minutes. The carbonizer consisted of an 8-inch long tube having an inside diameter of 1 inch and fitted with an expanded head. The carbonizer was equipped with two electrical heating circuits. Thermocouples located 1, 4, 7, and 12 inches from the bottom of the carbonizer were installed in a Ai-inch outside diameter thermowell placed axially in the center of the reactor. The lower three thermocouples were in the fluidized bed while the upper thermocouple was in the vapor space above the bed. An electrically heated char overflow line at the top of the fluidized bed conducted the char to a char receiver. An electrically heated vapor line conducted the vapors from the top of the carbonizer to the catalyst tube, a metal tube 32 inches high and having an inside diameter of 1 inch. Heat was supplied to the tube through 3 independent electrical circuits. A A-inch outside diameter thermowell was installed along the axis of the catalyst tube and contained 5 thermocouples equally spaced along the length of the tube. Ceramic saddles, used as packing for non-catalytic runs, were replaced with a commercially obtainable catalyst comprising 8.3 weight percent of molybdenum, 1.0 weight percent of cobalt and 0.5 weight percent of nickel, said metals being present as their oxides on an alumina support for the catalytic run. The catalyst was reduced in hydrogen prior to use.

The recovery system consisted of a steam cooled pri mary condenser, a water cooled secondary condenser, a ceramic saddle-packed acetone scrubbing tube to'assure removal of the tar fog, and a final water cooled condenser placed in series. A portion of the uncondensed gas was vented to the atmosphere and the remainder of this gas was recycled for use as the fluidizing gas. Suflicient hydrogen was added to the recycled gas to maintain a hydrogen concentration in the gas stream of at least 60 percent, after which the gas stream was reheated to 400 C., mixed with powdered coal and conducted to the carbonizer.

The coal employed was Elkol coal, a commercial, strip-mined Wyoming coal classified as a sub-bituminous B coal. The coal was pulverized to pass a 40 mesh screen and then oven dried at C. in a nitrogen att mosphere prior to use. The analysis of the feed is summarized in Table I below:

TABLE I Proximate analysis (dry basis): Weight percent Volatile matter 43.3 0.5

Ash 2.8 -0.3

Fixed carbon 539:1.0

Ultimate analysis (moisture, ash free basis):

0 (by difference) 173:0,5

A weighed batch of the dried coal was charged to the feed hopper, the unit was pressurized and the gas flow established. The coal feed from one of the hoppers was set at the desired rate and the coal was mixed with process gas, either nitrogen or hydrogen, that was preheated to approximately 400 C. Since char retention time in the reactor was 15 minutes, the pre-run was continued for 15 minutes after equilibrium was established in the system. At the end of the pre-run period the liquid and char receivers were drained, the coal fiow from the second hopper was started and the run was started.

TABLE II [Operating conditions] Run Number 1 2 *3 Flnidizing Gas N2 H2 H2 Pressure, p.s.i.g 400 400 400 Average Hydrogen partial pressure, p.s.i.g 341 290 Carbonization Temp., C 515 515 515 Catalyst Temp, C 435 Time of Run, hr 8.42 Coal Feed Rate, glILfllI 4G9 Catalyst Space Velocity, lb. tar/ lb. catalyst/hr 0. 42 Linear Gas Velocity (in Carbonizer), itJsec 0.1 0.5 0.5 Hydrogen Circulation Rate, SCFH Nil 100 80 Catalytic Run.

PRODUCTS, WEIGHT PERCENT [Moisture, ash free basis] Run Number 1 2 3 Char 75. 3 72. 2 Water 8. 7 11.7 Tar 8. 2 7.7. Gas 7. 3 8. 8 Hydrogen Reacted 0. 3 1. Unaccounted for 0. 0 0.8 0. 6

After completion of a run, the carbonizer and catalyst bed were cooled. The run char was removed from the char receiver and weighed. The liquid product (tar) from the four condensers was drained into a common vessel.

The char obtained by the above-described procedure is typical of those obtained from low temperature carbonization processes.

The gas recycled to the carbonizer was analyzed and these analyses are shown in Table III below:

hour. The mixture was cooled to room temperature and the hexane extract was poured off, leaving insoluble asphalt as a residue. The hexane extract was distilled in a small laboratory packed column to a kettle temperature of 200 C., removing the n-hexane, which was shown by gas chromatographic analysis to contain a negligible amount or" oil. The oil remaining in the kettle was comb'ned with the earlier-obtained oil from the dewatering step. The yields of tar, asphalt and oil obtained in each 10 run are summarized in Table IV below.

TABLE IV Run Number From Table IV it can be seen that the process of this invention results in an increase in the amount of oil from 66 pounds per ton of the coal charged for the noncatalytic, nitrogen-fluidized run (Run 1) to about 120 pounds per ton of coal charged for the process of this invention (Run 3). There is a corresponding reduction in the amount of asphalt produced from 58 pounds per ton of coal for the nitrogen runs to about 30 pounds per ton of coal for the catalytic hydrogenation runs.

The reduction in the amount of asphalt resulting from the coal carbonization effected by our process is believed TABLE III Run Number 1 2 3 Yield:

Lb./ton of coal 224 142 170 CF/ton of coal 3, 085 1, 810 2, 550

Analysis (H and N2 free basis), Volume Percent Com orent:

do as. 3 32. 2

Heating Value, B

From Table III it can be seen that the heating value of the gas is upgraded by the process of this invention, which upgrading is due primarily to the increase in the ratio of- CO to CO of from 0.77 for the nitrogen run (Run 1) to a value of 2.35 for the catalytic hydrogenation run (Run 3).

The liquid product from the condensers, a mixture of tar, water and acetone, was distilled in a small laboratory packed column to a head temperature of 70 C. at a 6:1 reflux ratio. The distillate consisted of acetone with negligible amounts of oil, as determined by gas chromatographic analysis. The distillation was then continued to a head temperature of 110 C. (maximum kettle temperature of 200? C.). The distillate contained light oil-and water, which were separated by decantation. The tar residue remainIng in the kettle was extracted with 4 parts by weight of n-hexane to 1 part by weight of residue by warming on a steam bath with stirring for 1 to be caused mainly by the reduction of compounds containing hetero atoms, such as nitrogen, sulfur and oxygen, in the tar. The amounts of hetero atoms found in the tar from the various runs are set forth in Table V below:

TABLE v [Hetero atoms, wt. percent of tar] Run Number 1 2 3 Oxygen 10. 6 9; 3' 5. 7 Nitrogen. 1. 0 0. 9 0. 9 Sulfur 0. 7 0; 6 0. 4

From Table V it can be seen that the process of this invention reduces the amount of hetero atoms present in the tar from 12.3 weight percent for the run conducted in nitrogen (Run 1) to 7 weight percent for the catalytic hydrogen-fluidized process (Run 3).

The oil obtained from each run was distilled and the fraction boiling at a temperature of from 110 C. to 260 C. was recovered. This fraction amounted to about 44.5 volume percent of the oil recovered from Run 1, about 42.5 volume percent of theoil recoveredfrom Run 2 and about 46.6 percent of the oil recovered from run 3.

These fractions were then extracted to recover the phenols contained in the oil. The yields are shown in Table VI From Table VI it can be seen that the process of this invention substantially increases the amount of low molecular Weight phenols that can be recovered from the tars produced by coal carbonization processes and particularly increases the amount of phenols, cresols and xylenols (C C phenols) that can be recovered.

EXAMPLE 2 Employing the apparatus'and operating procedures of Example 1, Lake de Smet Coal, a Wyoming coal classified as a sub-bituminous C coal, was carbonized at a hydrogen partial pressure of about 900 p.s.i. The analysis of the feed is summarized in Table VII below:

TABLE VII.-LAKE DE SMET COAL ANALYSIS Proximate analysis (dry basis): Weight percent The operating conditions and product yields of the carbonization are shown in Table VIII below:

TABLE VIIIl-LAKE DE SMET COAL [Operating Conditions] Run Number 1 2 3 Fluidization Gas N2 H H2 Pressure, p.s.i.g 200 1, 000 1, 000 Avg. H2 Partial Pressure, p.s. .g nil 900 920 Carbonization Temp, C. 515 525 515 Catalyst Temperature, C 42 Time of Run, hrs 5. 58 6. 42 7. 58 Goal Feed Rate, gm./hr 560 486 422 Catalyst Space Velocity, lb. tar/lb.

catalyst/hr 0. 82 Linear Gas Velocity (in carbonizer),

itu/sec. O. 23 0. 33 t). 31 Hydrogen Circulation Rate, SCFH nil 165 150 *Catalytic Run.

[Products, weight percent (moisture, ash tree basis)] Run Number 1 2 3 Char 68. 6 42. 43. 1 Water 9. 7 18. 2 21. Tar. 12.5 28. 2 23. 1 Gas 9. 3 13. 4' 14. 4 Hydrogen Reacted -2.0 2.2 Unaccounted for- 0. 0 0. 2 0. 1

The gas yields and analyses of the gas products from each run are shown in Table 1X below:

TABLE IX.GAS YIELD AND ANALYSIS Run Number 1 2 3 Yield:

Lb./Ton of Coal 186 270 288 CF/Ton of Coal 3, 780 4, 520 4, 860

[Analysis (H2 and N2 irce basis), volume percent] From Table IX it can be seen that the process of this invention increased the heating value of the gas from 340 B.t.u. per cubic foot for the nitrogen run and 803 B.t.u. per cubic foot of the n n-catalytic hydr 8 to 918 B.t.u. per cubic foot for the catalytic hydrogenation of this invention. The yields of tar, oil and asphalt are set forth in Table X below:

TABLE X.TAR YIELDS Run NumbeL 1 2 3 Yields, Lb. per Ton of Coal Yield s, percent of tar Oil 49 44 83 Asphalt. 51 56 17 Percent of Tar Distillablm 75. 0 S8. 5 Percent of Tar Boiling 110260 C 31. 0

From Table X it can be seen that the yield of oil was increased both as to absolute yield and as to percent of the tar. Furthermore, the percent of tar distillable at reduced pressures (about 5 mm. of Hg) before decomposition sets in, increased'from percent for the noncatalytic hydrogenation to 88.5 percent for the catalytic hydrogenation.

The elemental analyses of the tars resulting from the hydrogenations are set forth in Table XI below:

TABLE XL-ELEMENTAL ANALYSIS OF TABS FROM LAKE DE SMET COAL From Table XI it can be seen that the catalytic hydrogenation reduces the amount of hetero atoms present in the tar, thus causing a reduction in the amount of asphalt formed. The most striking reduction was that of nitrogen from 0.9 percent to only 0.3 percent.

What is claimed is:

1. A process which comprises mixing a particulate coal with hydrogen gas at pressures of from about 200 p.s.i. to about 3000 p.s.i., feeding the resulting gas-solids mixture to a carbonization zone wherein the solids are present in the form of a fluidized bed, heating the gas-solids mixture in said carbonization zone at temperatures of from about 450 C. to about 600 C., withdrawing the vapors from said heating from said carbonization zone and passing them over a hydrogenation catalyst in a substantially separate hydrogenation zone at a temperature of from about 400 C. to about 475 C. and a pressure of from about 200 p.s.i. to about 3000 p.s.i. prior to the condensation of said vapors.

2. A process which comprises mixing a particulate coal with hydrogen gas at pressures of from about 300 p.s.i. to about 1000 p.s.i., heating the resulting gas-solids mixture in a carbonization zone at temperatures of from about 500 C. to about 550 C., withdrawing the vapors from said heating from said carbonization zone and passing them over a hydrogenation catalyst in a substantially separate hydrogenation zone at a temperature of from about 400 C. to about 475 C. and a pressure of from about 300 p.s.i. to about 1000 p.s.i. prior to the condensation of said vapors.

3. The process of claim 2 wherein the hydrogenation catalyst is alumina impregnated with 0.5 weight percent nickel, 1.0 weight percent cobalt and 8.3 weight percent molybdenum, based on the Weight of alumina, said metals being present as their oxides, which metal oxides have been subsequently reduced.

5 References Cited by the Examiner UNITED STATES PATENTS 5/1934 Grimm et a1 2088 7/ 1937 Pier et a1 208-10 8/1938 Winkler 208-10 10 4/ 1939 Pier et a1 208-10 10 6/1945 Thomas 20810 3/ 1949 Storch et a1 208-10 8/ 1952 Storch et al 208-10 5/ 1953 Kalbach 208-11 10/ 1963 Huntington 208-8 FOREIGN PATENTS 2/ 1929 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

Claims (1)

1. A PROCESS WHICH COMPRISES MIXING A PARTICULATE COAL WITH HYDROGEN GAS AT PRESSURES OF FROM ABOUT 200 P.S.I. TO ABOUT 3000 P.S.I., FEEDING THE RESULTING GAS-SOLIDS MIXTURE TO A CARBONIZATION ZONE WHEREIN THE SOLIDS ARE PRESENT IN THE FORM OF A FLUIDIZED BED, HEATING THE GAS-SOLIDS MIXTURE IN SAID CARBONIZATION ZONE AT TEMPERATURES OF FROM ABOUT 450*C. TO ABOUT 600*C., WITHDRAWING THE VAPORS FROM SAID HEATING FROM SAID CARBONIZATION ZONE AND PASSING THEM OVER A HYDROGENATION CATALYST IN A SUBSTANTIALLY SEPARATE HYDROGENATION ZONE AT A TEMPERATURE OF FROM ABOUT 400*C. TO ABOUT 475*C. AND A PRESSURE OF FROM ABOUT 200 P.S.I. TO ABOUT 3000 P.S.I. TO THE CONDENSATION OF SAID VAPORS.