GB2094827A - Catalytic oxycracking of polynuclear aromatic hydrocarbons - Google Patents

Abstract

Phenanthrene, anthracene, fluorene, or mixtures thereof, are converted to fluorenone and biphenyl products by a catalytic oxycracking step using an oxygen-containing gas and steam. The reaction conditions used are 700-1250 DEG F (317-677 DEG C) temperature and preferably 5-50 psia pressure (0.35-3.5 kg/cm<2> absolute). If desired, the intermediate products of fluorenone and biphenyl can be thermally hydrocracked to produce additional benzene. Raw hydrocarbon feed materials having a normal boiling range of 500-900 DEG F (260-482 DEG C) can be treated by hydrodealkylation to provide the fused polynuclear aromatic feedstock to the catalytic oxycracking step. Also, intermediate products from the oxycracking step are preferably hydrocracked in the same hydrodealkylation step to produce a benzene product. <IMAGE>

Description

SPECIFICATION Catalytic oxycracking of polynuclear aromatic hydrocarbons This invention relates to a process for converting fused polynuclear aromatic hydrocarbons or heavy oils containing such aromatic materials either to monocyclic aromatic hydrocarbons such as benzene, or to non-fused bicyclic aromatic compounds such as fluorenone and diphenyl, which are converted to benzene. More particularly, this invention is directed to a process for cleaving the centre ring of tricyclic aromatics by catalytic oxidation and steam-cracking to produce monocyclic aromatic hydrocarbon products such as benzene.

High-boiling hydrocarbon fractions derived from fossil fuel sources, such as coal and petroleum, normally contain substantial quantities of fused polycyclic aromatic hydrocarbons, such as phenanthrene, anthracene, and the like, and their alkylated derivatives. Although these compounds are valuable when purified, the costs and difficulty of purifying them by extraction are usually prohibitive.

For this reason, many investigators have sought to convert such poiycyclic aromatic materials to monocyclic hydrocarbons, such as benzene, by thermal hydrocracking. Some of these prior art processes have been reviewed in U.S. Patent No. 4,139,452 to Beuther et al. Benzene yields from such feedstocks are usually low because only saturated rings are cracked. Hydrogenation usually begins with a terminal ring and degrades the rings successively, as shown by Penninger et al, American Chemical Society Symposium Series, Vol. 32, pp. 444-456 (published 1976). As a result, hydrogen consumption is undesirably high. If a centre ring becomes hydrogenated, it usually undergoes dehydrogenation rather than cracking as reported by Wiser et al, Ind. Eng. Chem. Prod. Res. Develop., 9, 350 (1970).

Conventional catalytic hydrocracking, as described by Langlois et al,Advances in Chemistry Series, Vol.

97, pp. 62-64 (1970), also yields predominantly bicyclic products.

The use of an oxidative process to make polycyclic aromatic hydrocarbons susceptible to thermal hydrocracking has also been proposed. Sakai et al, U.S. Patent No. 4,097,541, describes thermal hydrodecarbonylation of products, such as 9, 1 0-anthraquinone and 9,1 0-phenanthrenequinone, to biphenyl and benzene by reaction with hydrogen at a temperature of from about 932 to about I 6520F (500 to 9000 C) at atmospheric pressure and in the absence of a catalyst. Sakai also described the production of monocyclic aromatics in 38% yield by treatment of a fraction containing naphthalene or more polycyclic aromatic hydrocarbons of a residual oil from a naphtha steam cracker with atmospheric oxygen at 1 500C followed by reaction with hydrogen.However, it was shown by Larsen et al, Ind. Eng.

Chem., 34, 183 (1942), that oxidation of phenanthrene under similar conditions is extremely slow and gives no carbonyl compounds, so that the monocyclic aromatics observed by Sakai et al were probably formed by some route not involving oxidation of phenanthrene. Oxidation of phenanthrene to 9,10phenanthrenequinone requires much more severe conditions as shown by Morotskii et al. Morotskii et al, ChemicalAbstracts, 67, 81 982E (1967) and 68, 68776 S (1968), described the oxidation of phenanthrene over a V205/K2SO4/SiO2 catalyst. Therefore, it is most likely that Sakai in this experiment did not oxidise any aromatic rings, but rather formed benzene from thermal hydrocracking of naphthalene.

Daly, in U.S. Patent No. 4,234,749, described a two-step process by which anthracene, in either pure form or present in mixtures of polynuclear aromatic hydrocarbons with normal boiling points between about 338 and 71 60F (1 70 and 3800C), is oxidised with molecular oxygen in the presence of a cerium salt catalyst, and the product anthraquinone is then thermally cracked at a temperature of about 797 to 14000F (425 to 76O0C) to form benzene. Similarly, Robinson et al, U.S. Patent No.

3,855,252, taught that anthracene can be selectively oxidised to anthraquinone in the presence of phenanthrene in synthetic blends or in middle distillates from coal tar. This demonstrates that anthracene is oxidised considerably faster than phenanthrene.

In most practical feedstocks derived from either coal or petroleum sources, phenanthrene and substituted phenanthrenes are present in significantly higher concentrations than anthracenes and other polycyclic compounds. In an oxidation process for conversion of the three-ring fraction of such feedstocks to benzene or precursors of benzene, it is desirable to effect controlled centre-ring oxidation of phenanthrenes as well as of anthracenes.

We have discovered that, in the presence of suitable catalysts, polycyclic aromatic hydrocarbons such as phenanthrene and mixtures of phenanthrene with anthracene react with oxygen and steam in the vapour phase to form fluorenone and biphenyl. It is known from the work of Richter, U.S. Patent No.

3,210,432, and others that these intermediate compounds can be converted to benzene by thermal hydrocracking. By combining oxidative steam-cracking and thermal hydrodealkylation, a process has been devised to convert 3-ring and 4-ring aromatics into benzene in a high yield. These oxycracking and thermal hydrocracking steps used in combination provide an advantageous and novel method for the conversion of trinuclear aromatics to provide monocyclic aromatic hydrocarbon products such as benzene in high yields.

The present invention provides a process for producing fluorenone and biphenyl products from a polynuclear hydrocarbon feedstock selected from phenanthrene, anthracene, fluorene and technical mixtures thereof, which comprises: (a) heating and vaporising said hydrocarbon feedstock; (b) passing a mixture of the vaporised feedstock with a molecular oxygen-containing gas and steam through at least one catalytic reaction zone at a temperature within the range of 700--12500F (371--6770C); and (c) withdrawing fluorenone and biphenyl products.

A primary object of the present invention is to provide a process for converting fused tricyclic aromatic hydrocarbon feedstock, such as phenanthrene, anthracene, fluorene and mixtures thereof to fluorenone and biphenyl products by catalytic reaction in the vapour phase with a molecular oxygencontaining gas and with steam. The fluorenone and biphenyl intermediate materials produced in the oxycracking step may then be thermally hydrocracked to produce a benzene product. The term "oxycracking" is used herein to denote the basic process of this invention, because the centre ring of a fused polycyclic molecule can be both oxidised and cracked in a single operation. Such fused trinuclear aromatic feed materials to the oxycracking step can be provided by the hydrodealkylation of heavy hydrocarbon materials.The thermal hydrocracking cf fluorenone and biphenyl intermediates from the oxycracking step to produce benzene can be performed in a separate thermal hydrocracking step; however, such thermal hydrocracking is advantageously and preferably performed in the same hydrodealkylation reaction step used to produce the intermediate materials.

While we do not wish to be bound by any particular theoretical explanation, we believe that the following sequence of reaction steps is involved when the feedstock is phenanthrene:

+ H2O + CO I H20 2 Fluorenone phenanthrene + H20 + 0 + Co2 Biphenyl Another object of the invention is to provide novel bifunctional catalysts having activity for both the oxidation and cracking reaction steps referred to above. Such catalysts utilise two or more selected metal oxides deposited on an acidic support such as alumina or silica alumina. Other objects of the invention will become apparent from the description which follows.

Hydrocarbon feedstocks containing fused polynuclear aromatic molecules and which are suitable for reaction in the basic oxycracking step of this invention include phenanthrene, anthracene, fluorene, their alkyl derivatives as further described below, and technical mixtures comprising these substances.

Because aliphatic side chains are subject to oxidation with the undesired formation of carboxylic acids, such side chains should be present in technical feedstocks to an average extent of not more than about one side chain per two trinuclear aromatic molecules. The feedstock composition can be estimated in various ways, for exampie. by means of nuclear magnetic resonance. By way of illustration, a mixture of 2 moles of phenanthrene, 1 mole of methylphenanthrene and 1 mole of ethylphenanthrene has an aromatic proton/aliphatic proton ratio of about 83/17 and an aromatic carbon/aliphatic carbon ratio of about 95/5. The side chains, if present, should be substantially free of unsaturation.

Hydrocarbon raw materials containing trinuclear aromatic hydrocarbons and which can be treated to provide feedstocks suitable for the oxycracking reaction step include the anthracene oil fraction from coke oven tar, heavy distillate oils from coal liquefaction processes, and products of petroleum origin such as pyrolysis tars obtained as by products from steam crackers used to make light olefins, coker gas oils, fluid catalytic cracker decent oils, etc. Other raw hydrocarbon sources include tar and bitumens and shale oils.While the normal boiling points of the most useful raw material feedstock fractions can vary depending on the size and number of aliphatic side chains present, in general the boiling points will be within a broad range of about 500-9000F (260-4820C), and preferably 600-80O0F (316--4270C). Raw materials which contain aliphatic groups in concentrations higher than those defined above should be dealkylated before they are used as feedstocks for the oxycracking reaction step of this invention. The most preferred hydrocarbon feedstocks to the oxycracking step are substantially free of aliphatic side chains.

If the feedstock contains substantial amounts of sulphur in compounds such as dibenzothiophene, these feeds can be hydrodesulphurised prior to hydrodealkylation. It is also possible to let the benzothiophene pass through the hydrodealkylation step for cracking in the oxycracking reactor.

According to the present invention, trinuclear aromatic compounds such as phenanthrene are reacted catalytically with molecular oxygen and steam in the vapour phase to produce fluorenone and biphenyl as principal products. The oxycracking process step can be operated in either of two basic modes. In one mode or embodiment, a single catalytic reaction zone is used containing a single bifunctional oxycracking catalyst. The catalysts may be used in fixed beds, although fluidised catalyst beds can be used to advantage in order to dissipate the exothermic heat of reaction.In the other mode of operation, the reactants pass successively through two catalytic reaction zones; the first zone for the oxidation reaction, and the second zone for the steam cracking reaction. Teach reaction zone may be operated with a different catalyst and at different temperatures and space velocities.

The steam cracking step can be effected at temperatures of about 700-11 1 000F (371-5930C), at space velocities of about 0.2-40 millimoles of hydrocarbon per hour per gram of catalyst, and at water to hydrocarbon molar ratios of at least about 5/1. The process is preferably operated at 5-50 psia pressure (0.35-3.5 kg/cm2 absolute) and is most preferably operated at about atmospheric pressure.

Catalysts useful for the vapour phase oxidation of tricyclic aromatic hydrocarbons include cobalt or nickel molybdate, and oxides of vanadium, molybdenum, titanium, tin, antimony, bismuth, chromium, manganese, iron, cobalt and nickel.

Bifunctional catalysts having activity for both the oxidation reaction and the steam-cracking reaction typically contain two or more metal oxides. In general, these metal oxides are selected for their activity in the separate reaction steps as disclosed above, and may advantageously be deposited on acidic support materials such as alumina or silica-alumina. Particularly useful are catalysts comprising cadmium or zinc oxide or mixtures thereof, and V20s or MoO3 or mixtures thereof, both on a y-alumina support. Techniques for the preparation of such catalysts are generally known to those skilled in the art.

Thus, the support material may be impregnated with an aqueous solution of Cd(NO3)2 or Zn(NO3)2. After drying and calcining to decompose the metal nitrates, these operations may be repeated with a solution of NH4VO3 or ammonium heptamolybdate. Alternatively, the metal oxides may be deposited on the support in the reverse order or simultaneously. Aluminas with relatively large pores, such as greater than about 50 Angstrom units, are preferred in order to permit the polycyclic hydrocarbon molecules to diffuse to and away from the reaction sites.

The molar ratio of oxygen to hydrocarbon feed may range from about 1/1 to about 30/1. Air is the preferred oxygen-containing gas, but mixtures of oxygen and nitrogen containing more or less oxygen than is normally present in air may also be used.

The molar ratio of steam to hydrocarbon in the oxycracking step is not critical, but in general will be at least about 5/1. Reaction temperatures of about 800 to 1 2500 F (42 7--677 OC) are suitable, and space velocities range from about 0.2 to 40 millimoles of hydrocarbon per hour per gram of catalyst.

Substantially atmospheric pressures are preferred.

It will be apparent to those skilled in the art that these operational variables may be combined in a variety of ways. For example, space velocities should typically be increased when reaction temperatures are increased. Also, while it is desirable to effect a high conversion of trinuclear hydrocarbons to biphenyl in a single pass, the process may be operated continuously with separation of the biphenyl product by distillation or partial condensation and recycle of the fluorenone and tricyclic hydrocarbons to the oxycracking reactor.

Reference is now made to the accompanying drawings of preferred embodiments of the invention, in which: Figure 1 is a schematic flow diagram of a process for hydrodealkylation of polynuclear aromatic feedstocks, followed by catalytic oxycracking of the residue, then by a thermal hydrocracking step to produce benzene; and Figure 2 is a flow diagram of the process utilising two catalytic oxycracking steps and additional fractional distillation steps.

As shown by Figure 1, a polynuclear aromatic hydrocarbon feedstock at 10 having a normal boiling range of 500--9000F (260-4820C) is introduced with hydrogen 12 into a hydrodealkylation reactor 1 4 where the feed material is hydrodeallcylated with the hydrogen to substantially remove alkyl side chains. Useful hydrodealkylation reaction conditions are within the range of 1000--15000F (538-81 60C) temperature and 500-1200 psi (35-84 kg/cm2) hydrogen partial pressure.It is important that excess hydrogen be maintained in the reaction to prevent coking by having a relatively high hydrogen circulation rate relative to the feed rate of at least about 5/1, and preferably exceeding about 6/1. A hydrocarbon gas stream is withdrawn at 1 8 and a stream 20 containing a hydrocarbon mixture is passed to successive fractional distillation steps 22 and 28 for removal of benzene at 21 and naphthalene at 27. A stream 29 containing biphenyl and fluorene can be recycled to the hydrodealkylation reactor 14 for further reaction.

After fractionation steps at 22 and 28 to remove lighter fractions, the resulting heavy liquid residue stream 30 containing mainly phenanthrene is heated, vaporised and passed to a catalystcontaining oxycracking reactor 32, along with oxygen at 34 and steam at 35. A desirable catalyst is CdO/MoO3 on y-alumina. The oxycracking reaction conditions used are 800-1 2000F (427--6490C) temperature and 5-50 psia (0.35-3.5 kg/cm2 absolute) pressure. An effluent gas containing CO2 and some SO2 is withdrawn at 33 and the liquid biphenyl-containing product is withdrawn at 36.

If the product stream 36 contains substantial amounts of fluorenone and phenanthrene, these materials can be separated from the liquid product by a distillation step at 40. The resulting biphenyl product withdrawn as stream 41 can be passed to a separate thermal hydrocracking reactor (shown by broken lines) for reaction to produce a benzene product. This is optional if no dealkylation is needed.

Useful hydrocracking reaction conditions are within the range of about 1000--15000F (538-81 60C) temperature and 500-1200 psi (35-84 kg/cm2) hydrogen pressure. The hydrogen circulation rate relative to feed rate to the hydrocracking reactor should be at least about 4/1 and preferably exceeding 5/1 flow ratio to prevent coking. However, the stream 41 containing mainly biphenyl is advantageously and preferably returned to the hydrodealkylation step at 14 for reaction. The bottoms stream 42 containing increased phenanthrene and fluorenone is recycled to the oxycracking reactor 32 for further reaction to increase the yield of fluorenone and biphenyl products.

It is pointed out that the hydrodealkylation reactor 14 used to prepare feedstock for the oxycracking reaction step 32 can also be used for splitting biphenyl, and even for splitting fluorenone, if these materials are substantially free of phenanthrene. However, if the fluorenone contains relatively large percentages of phenanthrene, it is preferable to recycle it back to the oxycracking reactor for further cracking.

As an alternative embodiment, the oxycracking reaction may be carried out in two steps as generally shown in Figure 2. This embodiment is similar to Figure 1 except an additional fractional distillation step is provided at 24 to remove toluene and xylene at 25 for recycle with stream 29 to the hydrodealkylation reactor 14. Also, the heated phenanthrene feed at 50 is passed with air at 52 and optional steam at 53 to a first catalytic reactor 54, which is maintained at reaction conditions within the range of 800-1 2500F (427-6770C) temperature and 5-50 psia pressure (0.35-3.5 kg/cm2 absolute). An effluent gas containing CO2 and some SO2 is withdrawn at 51.The remaining material is passed with additional steam 56 to a second catalytic reactor 58, which is maintained at reaction conditions within the range of 700-11 000F (371 593C C) and 5-45 psia (0.35-3.2 kg/cm2 absolute). If desired, the resulting fluorenone and biphenyl products can be passed to a separate thermal hydrocracking reactor for producing benzene. As in the Figure 1 embodiment, a residue stream 60 containing fluorenone and phenanthrene is cooled at 62 by stream 63 to remove water at 61 and then passed to a fractional distillation step 64.An overhead stream 65 containing fluorenone and biphenyl is returned to the hydrodealkylation reactor 14, and a bottoms stream 66 is recycled to the first oxycracking reaction step 54 for further reaction to increase the yield of fluorenone and biphenyl product.

The present invention is further illustrated by the following Examples, which are illustrative only and should not be construed as limiting the scope of the invention.

EXAMPLE 1 In preparation of a CdO/MoO3/AI203 catalyst, the catalyst support used was a alumina extrudate, 4.7 mm long x 1.6 mm diameter, having a surface area of 96 m2/g, a pore volume of 0.537 cc/g, and a minimum pore diameter about 64 Angstroms. The support (81.0 g) was impregnated with a solution containing 14.49g of Cd(NO3)2.4H2O and 65 ce of water. After drying at22O0F (1040C) and calcining at 9200 F (493 OC), the catalyst weight was 83.4 g. Of this catalyst material, about 67.2 g was impregnated with a solution of 6.9 g of (NH4)6Mo7O24.4H2O in 65 cc of water. The final weight after drying and calcining as above was 74.6 g.This final prepared catalyst sample contained about 6.4 W% of CdO and 7.7 W% of MoO3.

EXAMPLE 2 A catalyst sample of CdO/V2OJAl2O3 catalyst was prepared similarly to Example 1 from Al2O3 (71.2 g),Cd(NO3)2.4H20 (25.46 g) and NH4VO3 (0.965 g).The resulting catalyst contained about 12.8 W% CdO and 0.9 W% V2O5.

EXAMPLE 3 Oxycracking reactions of phenanthrene over CdO/MoOWAl2O3 catalyst were carried out using experimental apparatus fabricated from stainless steel pipe and tubing. Liquid water and compressed air were mixed together and passed through a heated tube in which the water was vaporised. The resulting air-steam mixture was passed through a reservoir containing molten feed material comprising about 90% of phenanthrene, 8% of anthracene, and 2% of other materials. The resulting vapour mixture was passed through a preheater, then into the reactor. The reactor volume was about 30 cc and contained about 25 cc of catalyst comprising CdO/MoO3 on alumina support prepared as described in Example 1.

The reactor was heated uniformly by an electrically heated fluidised sand bath. The vapours exiting the reactor were condensed, and the organic product was separated from water, weighed, and analysed.

Samples of the uncondensed gases were collected periodically for analysis. The water feed rate was measured directly the air flow rate was estimated from flowmeter readings. The dry product weight was used to estimate the phenanthrene feed rate. Reactor temperatures were measured by thermocouples.

Typical results from this run are tabulated in Table 1 below: TABLE 1 Air flow rate (assumed atmospheric pressure), mole/hr 0.303 Water flow rate, cc/hr 171 Reactor temperature, OF(OC) 1040 (560) Reactor pressure, psig (kg/cm2 gauge) 0 Solid organic products collected, gm/hr 1.81 Solid Product Analysis, W% Phenanthrene 67.2 Fluorenone 25.9 Biphenyl 8.4 Off Gases Composition, V% Carbon Dioxide 11.04 Carbon Monoxide 2.03 Oxygen 5.86 Phenanthrene evaporation rate, mole/hr 0.0128 O2/PN mole ratio 4.97 H20/PN mole ratio 740 Space Velocity, total gases at reactor temperature, sex~' 6 Space Velocity, millimoles phenanthrene per gram of catalyst per hour 0.5 Phenanthrene going to respective products, M% Phenanthrene (unreacted) 52.6 Fluorenone 20.0 Biphenyl 7.6 CO by combustion 1.5 CO2 by combustion 18.3 Additional oxycracking runs were made with the same 90% phenanthrene feed using CdO/MoO3/AI203 catalyst. The results are shown in Table 2 below:: TABLE 2 OXYCRACKING P HENANTHREN E WITH CdO/MoO3/AI203 CATALYST Run No. 9C 10B 10C 12C Feedstream flow Rates Air, moles, Hr. 0.31 0.30 0.30 0.30 Water, cc/hr. 157 159 156 150 Reaction Temp., F 1040 1110 1180 1185 Reaction Temp., C (560) (599) (638) (641) Solid Product Yield, g/hr. 8.6 1.6 1.9 4.2 Solid Product Composition, W% Phenanthrene 78 68 69 80 Fluorenone 4.2 18 10 5.9 Biphenyl 1.8 11.5 9.3 3.2 it is noted that using a feed stream of 90 W% phenanthrene, significant amounts of the desired fluorenone and biphenyl products were produced at a reaction temperature within the range of 1040-11 850F (560-641 OC),with the remainder of the solid products being 68-80 W% phenanthrene.

EXAMPLE 4 Further oxycracking runs were made using 90% phenanthrene feedstock with other catalysts comprising CdO/V2O5 on alumina and nickel molybdate. The results of these experiments are shown in Table 3.

TABLE 3 OXYCRACKING PHENANTHRENE WITH OTHER CATALYSTS Run No. 6C 8A 14A Catalyst'a' V V N Feedstream Flow Rates Air, moles, hr. 0.85 0.85 0.475 Water, cc/hr. 138 145 107 Reaction Temp., OF'b' 1240 825 930 Reaction Temp., C (671) (441) (499) Solid Product Yield, g/hr. 1.3 2.2 3.2 Solid Product Composition, W% Phenanthrene 81 66 74 Fluorenone 8.3 20 9.4 Biphenyl 3.1 3.1 1.8 (a) V indicates CdO/V205/Aí203 catalyst N indicates nickel molybdate (H-Coal catalyst) (b) Exothermic reactions Similarly as for Example 4, 90 W% phenanthrene feed was successfully oxycracked using different catalysts to produce significant amounts of fluorenone and biphenyl products.It was observed that the oxycracking reaction with the catalyst containing vanadium was more exothermic than with the other catalysts. Anthracene, naphthalene and one or more unidentified compounds were observed in some of the solid products. Losses of hydrocarbon values due to combustion occurred to some extent.

EXAMPLE 5 This Example describes the oxycracking reaction as used in a commercial-scale, fixed-bed-type reactor. The mole ratio used for phenanthrene/oxygen/water is 1/6/17.

A mixture of air (140 standard cubic feet per second (or 3.96 m3/s) and steam (13,750 pounds per hour or 6237 kg/h) is preheated to about 6000F (31 60C). Phenanthrene feedstock (8000 pounds per hour or 3629 kg/h) is heated to about 400"F (2040C) and pumped into an evaporator, in which it is vaporised by contact with the warmer steam-air mixture. The resulting vapour stream is fed to the reactor, which comprises an array of about 10,000 tubes, each 1 inch (2.5 cm) diameter and containing about 1.2 litres of catalyst. The catalyst consists of cadmium and molybdenum oxides supported on alumina having about 0.060-inch-diameter (1.52 mm) particle size as extrudates.The catalyst-filled tubes are cooled by a fused salt mixture and a maximum temperature is maintained in the range of 1000-11 000F (538-5930C). The molten salt mixture is circulated through heat exchangers in which process steam is generated.

The gases leaving the oxycracking reactor are partially cooled by a heat exchange step to about 180"F (82 0C). The condensable aromatic products are separated from the water and gases, and the resulting condensed organic products are fed into a fractional distillation unit for separation into a biphenyl stream taken overhead and a bottoms stream consisting essentially of fluorenone and phenanthrene. The biphenyl overhead stream is passed to a thermal hydrocracking unit, while the distillation bottoms product of mainly phenanthrene and fluorenone is recycled to the oxycracking reactor for further reaction to increase the product yield.

The mixture of water vapour and gases is further cooled to about 850F (29aC) to effect condensation of biphenyl and most of the water; the composition of the resulting vent gases is shown in Table 4. An approximate material balance for the feed and product streams to the oxycracking step is also provided below in Table 4.

TABLE 4 MATERIAL BALANCE FOR O)(YCRACl(íMG REACTION Feed Reaction Stack Gases Streams Products, Composition, Lb/Hr(kg/h) Lb/Hr(l"g/h) V% Phenanthrene 8000(3529) 320 (145) Water 13753 (6238) 14748(6690) 4.1 Oxygen 8629 (3914) 1622 (736) 3.6 Nitrogen 30202 (13700) 30202 (13700) 77.0 Fluorenone - 243(110) Biphenyl - 4776 (2166) 0.001 CO2 - 7345(3332) 11.9 CO - 1329 (603) 3.4 Total 60584 (27481) 60584(27481) 100.0

Claims (18)

1. A process for producing fluorenone and biphenyl products from a polynuclear hydrocarbon feedstock selected from phenanthrene, anthracene, fluorene and technical mixtures thereof, which comprises: (a) heating and vaporising said hydrocarbon feedstock; (b) passing a mixture of the vaporised feedstock with a molecular oxygen-containing gas and steam through at least one catalytic reaction zone at a temperature within the range of 700-1 2500F (371-6770C); and {c) withdrawing fluorenone and biphenyl products.

2. A process as claimed in claim 1 , wherein the oxygen-containing gas is air and the molar ratio of oxygen to hydrocarbon is from 1/1 to 30/1.

3. A process as claimed in claim 1 or 2, wherein the reaction temperature is within the range of 800-1 2000F (427649OC) and pressure is from 5 to 50 psia (0.35 to 3.5 kg/cm2 absolute).

4. A process as claimed in any of claims 1 to 3, wherein the number of catalytic reaction zones is one and said zone contains a bifunctional oxycracking catalyst.

5. A process as claimed in claim 4, wherein the catalyst comprises a mixture of at least one Group IIB metal oxide with an oxide of molybdenum, vanadium or mixtures thereof on an alumina support.

6. A process as claimed in any of claims 1 to 5, wherein the oxygen-containing gas is air, the reaction pressure is 5-50 psia (0.35-3.5 kg/cm2 absolute), the molar ratio of oxygen to hydrocarbon feedstock is from 1/1 to 30/1, the molar ratio of steam to hydrocarbon feedstock is at least 5/1, the reaction temperature is from 900 to 1200 F (482--6490C), and the space velocity of hydrocarbon feedstock is from 0.2 to 40 millimoles per hour per gram of catalyst.

7. A process as claimed in any of claims 1 to 6, wherein the hydrocarbon feedstock is phenanthrene which is substantially free of aliphatic side chains.

8. A process as claimed in any of claims 1 to 7, wherein said hydrocarbon feedstocks are obtained from raw materials having normal boiling points in the range of from 5000 F to 9000F (260-4820C), and are selected from the anthracene oil fraction from coke oven tar, heavy distillate oils from coal liqufaction, and products of petroleum origin comprising pyrolysis tars, coker gas oils, fluid catalytic cracker decant oils, tar sand, bitumen, shale oils, and the like by a hydrodealkylation reaction prior to the oxycracking reaction step.

9. A process as claimed in claim 8, wherein at least one step of fractional distillation is used between the hydrodealkylation reaction and oxycracking reaction steps to remove light fractions of benzene and naphthalene.

10. A process as claimed in any of claims 1 to 3 and 6 to 9, wherein the number of catalytic reaction zones is two, the oxygen-containing gas is injected into the first zone, and steam is injected between the two reaction zones.

11. A process as claimed in any one of claims 1 to 10, wherein the fluorenone and biphenyl products are further thermally hydrocracked to produce a benzene product.

12. A process as claimed in claim 11, wherein the thermal hydrocracking step is provided by a hydrodealkylation step preceding the oxycracking step.

13. A process for producing fluorenone and biphenyl products from a polynuclear aromatic hydrocarbon feedstock selected from phenanthrene, anthracene, fluorene and technical mixtures thereof together with their alkyl derivatives, in which the average number of side chains is not more than one per two molecules of feedstock, which comprises: (a) heating and vaporising the feedstock; (b) passing a mixture of vaporised feedstock with a molecular oxygen-containing gas and steam through at least one catalytic reaction zone at a temperature of 800--1 1000 F (427--593 OC); (c) withdrawing the fluorenone and biphenyl products; and (d) further thermally hydrocracking the fluorenone and biphenyl intermediate products at a temperature of 1000 to 1 5000F (538-81 60C) to produce a benzene product.

14. A catalyst material comprising a mixture of at least one Group IIB metal oxide comprising from 1 to 15 W% and an oxide of molybdenum or vanadium deposited on a y-alumina support.

15. A catalyst material as claimed in claim 14, wherein the catalyst contains CdO/MoO3/AI203.

16. A process as claimed in claim 1, substantially as hereinbefore described with reference to any of the Examples and/or the accompanying drawings.

1 7. Fluorenone or biphenyl products produced by a process as claimed in any of claims 1 to 1 3 and 16.

18. A catalyst material as claimed in claim 14, substantially as hereinbefore described with reference to any of the Examples.