Process for the Removal of Hydrocarbonaceous Compounds From an Aqueous Stream and Hydrogenating These Compounds

The field of art to which this invention pertains is the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream. More particularly, the invention relates to the removal of trace quantities of hydrocarbonaceous compounds which are hazardous or otherwise obnoxious. More specifically, the invention relates to a process for the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream which comprises the steps of: (a) contacting the aqueous stream with an adsorbent to remove trace quantities of hydrocarbonaceous compounds from the aqueous stream to provide an aqueous stream having a reduced concentration of hydrocarbonaceous compounds; (b) contacting spent adsorbent which has accumulated the hydrocarbonaceous compounds from the aqueous stream with an elution solvent to remove the hydrocarbonaceous compounds from the spent adsorbent thereby regenerating the adsorbent; (c) contacting the elution solvent in admixture with the hydrocarbonaceous compounds which were removed from the spent adsorbent in step (b) in the presence of hydrogen with a hydrogenation catalyst in a hydrotreating reaction zone; (d) contacting the hydrotreating reaction zone effluent with an aqueous scrubbing solution; and (e) introducing a resulting admixture of the reaction zone effluent and the aqueous scrubbing solution into a separation zone to provide a hydrotreated elution solvent and a spent aqueous stream.

In U.S. Pat. No. 3,919,398 (Davis), a method is disclosed for recovering bromine as hydrogen bromide from aromatic bromides. The method involves reacting the aromatic bromide with hydrogen at a temperature within the range from about 200.degree. to about 600.degree. C. in the presence of a palladium activated catalyst.

In U.S. Pat. No. 3,892,818 (Scharfe et al), a method is disclosed for the conversion of hydrocarbon chlorides in the presence of hydrogen to hydrocarbons and hydrogen chloride wherein the process takes place in a gaseous phase and in the presence of a rhodium-containing catalyst.

The invention provides a process for the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream by contacting the aqueous stream with an adsorbent to remove trace quantities of hydrocarbonaceous compounds from the aqueous stream and whereby the spent adsorbent is regenerated by removal of accumulated hydrocarbonaceous compounds from the adsorbent by means of an elution solvent and subsequent processing of these hydrocarbonaceous compounds in a hydrotreating reaction zone. The present invention also contemplates the recycle of hydrotreated elution solvent to a spent adsorbent for removal of hydrocarbonaceous compounds.

One broad embodiment of the invention may be characterized as a process for the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream which comprises the steps of: (a) contacting the aqueous stream with an adsorbent to remove trace quantities of hydrocarbonaceous compounds from the aqueous stream to provide an aqueous stream having a reduced concentration of hydrocarbonaceous compounds; (b) contacting spent adsorbent which has accumulated the hydrocarbonaceous compounds from the aqueous stream with an elution solvent to remove the hydrocarbonaceous compounds from the spent adsorbent thereby regenerating the adsorbent; (c) contacting the elution solvent in admixture with the hydrocarbonaceous compounds which were removed from the spent adsorbent in step (b) in the presence of hydrogen with a hydrogenation catalyst in a hydrotreating reaction zone; (d) contacting the hydrotreating reaction zone effluent with an aqueous scrubbing solution; and (e) introducing a resulting admixture of the reaction zone effluent and the aqueous scrubbing solution into a separation zone to provide a hydrotreated elution solvent and a spent aqueous stream.

Another embodiment of the invention may be characterized as a process for the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream which comprises the steps of: (a) contacting the aqueous stream with an adsorbent to remove trace quantities of hydrocarbonaceous compounds from the aqueous stream to provide an aqueous stream having a reduced concentration of hydrocarbonaceous compounds; (b) contacting spent adsorbent which has accumulated the hydrocarbonaceous compounds from the aqueous stream with an elution solvent to remove the hydrocarbonaceous compounds from the spent adsorbent thereby regenerating the adsorbent; (c) contacting the elution solvent in admixture with the hydrocarbonaceous compounds which were removed from the spent adsorbent in step (b) in the presence of hydrogen with a hydrogenation catalyst in a hydrotreating reaction zone; (d) contacting the hydrotreating reaction zone effluent with an aqueous scrubbing solution; (e) introducing a resulting admixture of the reaction zone effluent and the aqueous scrubbing solution into a separation zone to provide a hydrotreated elution solvent and a spent aqueous stream; and (f) recycling at least a portion of the hydrotreated elution solvent from step (e) to provide at least a portion of the elution solvent utilized in step (b).

Other embodiments of the subject invention encompass further details such as potential hydrocarbonaceous compound contaminants, aqueous scrubbing solutions, hydrotreating catalysts, adsorbents, elution solvents and operating conditions, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.

The drawing is a simplified process flow diagram of a preferred embodiment of the present invention.

There is a steadily increasing demand for technology which is capable of eliminating trace quantities of hydrocarbonaceous compounds from aqueous streams such as waste water and potable water, for example. Once an organic phase is decanted from a water phase, the remaining water may potentially contain trace quantities of organic compounds such as hydrocarbonaceous compounds for example. Before waste water can be discharged into the environment, these trace quantities of hydrocarbonaceous compounds must be reduced or eliminated. In the event that these trace hydrocarbonaceous compounds are toxic, carcinogenic or otherwise obnoxious, it is preferred that the hydrocarbonaceous compounds not only be removed from the aqueous phase but converted into less noxious compounds. Therefore, those skilled in the art have sought to find feasible techniques to remove trace amounts of hydrocarbonaceous compounds from an aqueous phase. Although simple in concept, conventional liquid-liquid extraction often is not practical for the removal of hydrocarbonaceous compound contaminants at the parts-per-million level or even lower concentrations.

The present invention provides an improved process for the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream. A wide variety of hydrocarbonaceous compounds are to be considered candidates for removal from an aqueous stream in accordance with the process of the present invention. Examples of compounds which are suitable for treatment by the process of the present invention are halogenated hydrocarbons. Certain halogenated hydrocarbons having demonstrated or potential toxicity include but are not limited to kepone, halogenated biphenyls, halogenated cyclodienes, such as aldrin, dieldrin, and hexachlorocyclopentadienes, dibromochloropropane, halogenated phthalic anhydrides, such as polybromophthalicanhydride, tetrachloroethylene, polychlorodioxins such as tetrachlorodibenzodioxin, halogenated organic phosphates such as 2,2 dichlorovinyldimethyl phosphate. Additional examples of compounds which are suitable for treatment include organometallic compounds and especially those which contain metals such as lead, mercury, cadmium, cobalt, arsenic, vanadium, and chromium. Contaminating hydrocarbonaceous compounds may comprise sulfur, oxygen, metal or nitrogen components. In accordance with the present invention, generally any hydrocarbonaceous compound may be removed from an aqueous stream. It is preferred that the trace quantities of hydrocarbonaceous compounds are present in the aqueous stream in an amount less than about 10,000 PPM and more preferably in an amount less than about 5,000 PPM.

In accordance with the subject invention, an aqueous stream containing trace quantities of hydrocarbonaceous compounds is contacted with a suitable adsorbent which selectively retains the trace hydrocarbonaceous compounds and produces an aqueous stream with a reduced concentration of hydrocarbonaceous compounds. Suitable adsorbents may be selected from materials which exhibit the primary requirement of hydrocarbonaceous compound selectivity and which are otherwise convenient to use. Suitable adsorbents include, for example, molecular sieves, amorphous silica-alumina gel, silica gel, activated carbon, activated alumina and clays. Of course, it is recognized that for a given case, a particular adsorbent may give better results than others.

The selected adsorbent is contacted with an aqueous stream containing trace quantities of hydrocarbonaceous compounds in an adsorption zone. The adsorbent may be installed in the adsorption zone in any suitable manner. A preferred method for the installation of the adsorbent is in a fixed bed arrangement. The adsorbent may be installed in one or more vessels and in either series or parallel flow. The flow of an aqueous stream through the adsorption zone is preferably performed in a parallel manner so that when one of the adsorbent beds or chambers is spent by the accumulation of hydrocarbonaceous compounds thereon, the spent adsorbent zone may be bypassed while continuing uninterrupted operation through the parallel adsorbent zone.

During adsorbtion, the adsorption zone is preferably maintained at a pressure from about atmospheric to about 1500 psig (10342 k Pa gauge), a temperature from about 32.degree. F., (0.degree. C.) to about 300.degree. F. (149.degree. C.) and a liquid hourly space velocity from about 0.1 hr.sup.-1 to about 500 hr.sup.-1. The flow of the aqueous stream containing trace quantities of hydrocarbonaceous compounds through the adsorption zone may be conducted in an upflow, downflow or radial flow manner. The temperature and pressure of the adsorption zone are preferably selected to maintain the aqueous stream in the liquid phase. As used herein, the term "essentially hydrocarbon-free" connotes a hydrocarbonaceous compound concentration of less than about 10 PPM.

The spent zone of adsorbent is regenerated by isolating the spent adsorption zone and contacting the adsorbent with an elution solvent to remove the hydrocarbonaceous compounds thereby regenerating the adsorbent. In general, an elution solvent is utilized which possesses a high solvent selectivity towards the hydrocarbonaceous compounds adsorbed on the adsorbent and which has no deleterious effect on the adsorbent. Preferred elution solvents comprise naphtha, kerosene, diesel fuel, gas oil or mixtures thereof. During regeneration of the adsorbent, the adsorption zone is preferably maintained at a pressure from about atmospheric to about 1500 psig (10,342 k Pa gauge), and a temperature from about 32.degree. F. (0.degree. C.) to about 300.degree. F. (149.degree. C.). The flow of the elution solvent through the adsorption zone during regeneration thereof may be conducted in an upflow, downflow or radial flow manner. The elution solvent during the regeneration of adsorbent may be present in a liquid phase or a gas-liquid mixed phase.

The resulting elution solvent containing the hydrocarbonaceous compounds is introduced into a hydrotreating or hydrogenation zone and is contacted with a hydrogen-rich gaseous phase and a hydrogenation catalyst. The catalytic hydrogenation zone may contain a fixed, ebulated or fluidized catalyst bed. This reaction zone is preferably maintained under an imposed pressure from about 100 psig (689 k Pa gauge) to about 2000 psig (13,790 k Pa gauge) and more preferably under a pressure from about 200 psig (1379 k Pa gauge) to about 1800 psig (12,411 k Pa gauge). Suitably, such reaction is conducted with a maximum catalyst bed temperature in the range of about 350.degree. F. (177.degree. C.) to about 850.degree. F. (454.degree. C.) selected to perform the desired conversion to reduce or eliminate the undesirable characteristics or components of the hydrocarbonaceous compounds. Further preferred operating conditions include liquid hourly space velocities in the range from about 0.2 hr.sup.-1 to about 10 hr.sup.-1 and hydrogen circulation rates from about 200 standard cubic feet per barrel (SCFB) (35.6 m.sup.3 /m.sup.3) to about 10,000 SCFB (1778 m.sup.3 /m.sup.3), preferably from about 300 SCFB (53.3 m.sup.3 /m.sup.3) to about 8000 SCFB (1422 m.sup.3 /m.sup.3).

The preferred catalytic composite disposed within the hereinabove described hydrogenation zone can be characterized as containing a metallic component having hydrogenation activity, which component is combined with a suitable refractory inorganic oxide carrier material of either synthetic or natural origin. The precise composition and method of manufacturing the carrier material is not considered essential to the present invention. Preferred carrier materials are alumina, silica and mixtures thereof. Suitable metallic components having hydrogenation activity are those selected from the group comprising the metals of Groups VI-B and VIII of the Periodic Table, as set forth in the Periodic Table of the Elements, E. H. Sargent and Company, 1964. Thus, the catalytic composites may comprise one or more metallic components from the group of molybdenum, tungsten, chromium, iron, cobalt, nickel, platinum, iridium, osmium, rhodium, ruthenium, and mixtures thereof. The concentration of the catalytically active metallic component, or components, is primarily dependent upon a particular metal as well as the physical and/or chemical characteristics of the particular hydrocarbon feedstock. For example, the metallic components of Group VI-B are generally present in an amount within the range of from about 1 to about 20 weight percent, the iron-group metals in an amount within the range of about 0.2 to about 10 weight percent, whereas the noble metals of Group VIII are preferably present in an amount within the range of from about 0.1 to about 5 weight percent, all of which are calculated as if these components existed within the catalytic composite in the elemental state. In addition, any catalyst employed commercially for hydrotreating middle distillate hydrocarbonaceous compounds to remove nitrogen and sulfur should normally function effectively in the hydrogenation zone of the present invention.

The hydrocarbonaceous effluent from the hydrogenation zone is contacted with an aqueous scrubbing solution and the resulting admixture is admitted to a separation zone in order to separate a spent aqueous scrubbing solution, a hydrogenated hydrocarbonaceous phase comprising hydrotreated elution solvent and hydrotreated hydrocarbonaceous compounds which formerly contaminated the waste water charge stock and a hydrogen-rich gaseous phase. The contact of the hydrocarbonaceous effluent from the hydrogenation zone with the aqueous scrubbing solution may be performed in any convenient manner and is preferably conducted by co-current, in-line mixing which may be promoted by inherent turbulence, mixing orifices or any other suitable mixing means. The aqueous scrubbing solution is preferably introduced in an amount from about 1 to about 40 volume percent based on the hydrocarbonaceous effluent from the hydrogenation zone. The aqueous scrubbing solution is selected depending on the characteristics of the hydrocarbonaceous compounds which are entrained in the contaminated waste water charge stock. For example, if the hydrocarbonaceous compounds present in the waste water charge stock comprise halogenated compounds, the aqueous scrubbing solution preferably contains a basic compound such as calcium hydroxide, potassium hydroxide or sodium hydroxide in order to neutralize the acid which is formed during the hydrogenation of the halogen compounds. In the event that the hydrocarbonaceous compound contaminants contain only sulfur and nitrogen compounds, pure water is a suitable aqueous scrubbing solution. The resulting hydrotreated hydrocarbonaceous phase is recovered and the hydrogen-rich gaseous phase may be recycled to the hydrogenation zone if desired. In a preferred embodiment of the subject invention, at least a portion of the recovered hydrocarbonaceous phase is recycled as at least a portion of the elution solvent mentioned hereinabove. A portion of the aqueous scrubbing solution recovered in the separation zone may be recycled to contact the hydrocarbonaceous effluent from the hydrogenation zone. The spent aqueous scrubbing solution may be neutralized or otherwise treated to provide a more environmentally acceptable effluent.

In the drawing, the process of the present invention is illustrated by means of a simplified flow diagram in which such details as pumps, instrumentation, heat-exchange and heat-recovery circuits, compressors, surge tanks and similar hardware have been deleted as being non-essential to an understanding of the techniques involved. The use of such miscellaneous appurtenances are well within the purview of one skilled in the art.

With reference now to the drawing, an aqueous charge stock contaminated with trace quantities of hydrocarbonaceous compounds is introduced into the process via conduit 1 and is passed via conduit 2, valve 3 and conduit 4 into adsorption zone 5. Alternatively, the contaminated waste water charge stock is introduced via conduit 6, valve 7, and conduit 8 into adsorption zone 9 which is located in parallel with adsorption zone 5. An aqueous stream having a reduced concentration of hydrocarbonaceous compounds is removed from adsorption zone 5 via conduit 10, conduit 11, valve 12, conduit 13 and recovered. In the alternative, an aqueous stream having a reduced concentration of hydrocarbonaceous compounds is removed from adsorption zone 9 via conduit 14, valve 15, conduit 16, conduit 13 and recovered. In the event adsorption zone 9 is to be regenerated, valves 7 and 15 are closed for isolation and an elution solvent is introduced via conduit 17, valve 20, conduit 17, and conduit 14 into adsorption zone 9. An elution solvent rich in hydrocarbonaceous compounds which have been extracted from adsorption zone 9 is removed via conduit 8, conduit 21, valve 22 and conduit 21 and is introduced into hydrotreating reaction zone 25. In the event that adsorption zone 5 is to be regenerated, valves 3 and 12 are closed for isolation and an elution solvent is introduced via conduit 17, conduit 18, valve 19, conduit 18 and conduit 10 into adsorption zone 5. An elution solvent rich in hydrocarbonaceous compounds is removed from adsorption zone 5 via conduit 4, conduit 23, valve 24, conduit 23, and conduit 21 and introduced into hydrotreating reaction zone 25. A hydrogen-rich gaseous stream which is derived in a manner hereinafter described is introduced via conduit 32 and conduit 21 into hydrotreating reaction zone 25. Make-up hydrogen is introduced via conduit 33, conduit 32 and conduit 21 into hydrotreating reaction zone 25. The admixture of elution solvent and hydrocarbonaceous contaminants is hydrogenated in hydrotreating reaction zone 25 in the presence of a hydrogenation catalyst maintained at hydrogenation conditions as described hereinabove. The resulting hydrotreated elution solvent and hydrocarbonaceous compounds and a gaseous phase are removed from hydrotreating reaction zone 25 via conduit 26 and contacted with an aqueous scrubbing solution introduced via conduit 27. The resulting mixture is introduced via conduit 26 into high pressure separator 28. A hydrogen-rich gaseous phase is removed from high pressure separator 28 via conduit 32 and recycled as described hereinabove. A detoxified hydrocarbonaceous stream comprising hydrotreated elution solvent is removed from high pressure separator 28 via conduit 29 and recovered. At least a portion of the detoxified hydrocarbonaceous stream comprising hydrotreated elution solvent is recycled via conduit 31 to provide at least a portion of the elution solvent which is provided via conduit 17. A spent aqueous scrubbing solution is removed from high pressure separator 28 via conduit 30 and is recovered.

The process of the present invention, is further demonstrated by the following illustrative embodiment. This illustrative embodiment is however not presented to unduly limit the process of this invention, but to further illustrate the advantages of the hereinabove described embodiments. The following data were not obtained by the actual performance of the present invention, but are considered prospective and reasonably illustrative of the expected performance of the invention.

This illustrative embodiment describes the removal of poly chlorinated biphenyl (PCB) from an aqueous stream which contains 500 weight PPM of PCB in an adsorption zone, the subsequent elution of the PCB from an adsorbent contained in the adsorption zone and the conversion of the eluted PCB by hydrotreating to produce innocuous hydrocarbonaceous compounds.

An aqueous stream of water containing 500 weight PPM of PCB is introduced into an adsorption zone containing activated carbon particles at conditions including a temperature of about 100.degree. F. (38.degree. C.), a pressure of about 10 psig (69 k Pa gauge), and a liquid hourly space velocity of about 10. The resulting aqueous phase is found to contain less than 1 PPM of PCB. Another adsorption zone containing activated carbon particles which is located in parallel with the hereinabove mentioned adsorption zone and is regenerated to remove previously adsorbed PCB by contacting the activated carbon containing PCB with an elution solvent comprising heptane, a component of naphtha, at conditions which include a temperature of about 100.degree. F. (38.degree. C.), and a pressure of about 10 psig (69 k Pa gauge) for a time sufficient to elute or remove substantially all of the transient PCB from the activated carbon adsorbent. The resulting admixture of elution solvent and PCB removed from the adsorbent is then introduced together with a gaseous hydrogen-rich stream into a hydrotreating reaction zone loaded with a catalyst comprising alumina, cobalt and molybdenum. The hydrotreating reaction is conducted with a catalyst peak temperature of 750.degree. F. (399.degree. C.), a pressure of 900 psig (6205 k Pa gauge), a liquid hourly space velocity of 1 based on fresh feed and a hydrogen circulation rate of 2500 SCFB (444 std m.sup.3 /m.sup.3). The effluent from the hydrotreating reaction zone is contacted with an aqueous sodium hydroxide solution in an amount of 10 volume percent based on the hydrocarbonaceous effluent from the hydrotreating zone. The admixture of the hydrotreating reaction zone effluent and the aqueous scrubbing solution is introduced into a separation zone to provide a spent aqueous stream and a hydrotreated elution solvent having less than 1 PPM of PCB.

The foregoing description, drawing and illustrative embodiment clearly illustrate the advantages encompassed by the process of the present invention and the benefits to be afforded with the use thereof.