MXPA00004972A - Improved process for the treatment of waste sulfur gases - Google Patents

Abstract

A process is provided for the removal of trace amounts of aromatic hydrocarbons from a waste gas feed stream comprising sulfur compounds and the aromatic hydrocarbons. An adsorption process employing a high silica zeolite adsorbent having a framework silica-to-alumina ratio greater than about 15 and having a pore size greater than about 6.2 angstroms is used to remove from the feed gas mixture aromatic hydrocarbon contaminants and permit the recovery of a high purity sulfur product from the treated effluent stream. The adsorption zone comprises at least two adsorption beds fora continuous process. The regeneration is performed in a closed system or partially closed system, and prior to returning a regenerated adsorption zone to adsorption conditions the waste feed gas stream is used to cool and purge the regenerated zone. The use of the present invention removes aromatic hydrocarbon contaminants, which are responsible for the degeneration of the performance of the downstream sulfur recovery zone

Description

PERFECTED PROCESS OF SULFUROUS DISPOSAL GAS TREATMENTS BACKGROUND OF THE INVENTION Typically, the management of sulfur in petroleum refineries comprises two basic processes: amine treatment and sulfur recovery. The amine treatment units extract the hydrogen sulfide from the recycle gas streams in hydroprocessing operations, and from recovery units for fuel gases and liquefied natural gas. In the gas recycling treatment, the sulfur in the crude oil portion reacts with the hydrogen at high pressures to form hydrogen sulfide. The product flow of the reactor is expanded and a stream of recycled gases is sent to an amine adsorber, which contains hydrogen, hydrogen sulfide and some hydrocarbons, where the hydrogen sulphide is extracted by the circulating stream of amines. In the recovery units for fuel gases and liquefied natural gas, discharge gases and waste from stabilizers are sent from other units of refining processes, such as coke, cracking and reforming units, to gas recovery units to collect the gas flows. The hydrogen sulfide is extracted from the stream of gases collected by the circulating amine, at low pressure. In any of these cases, the gas extracted from the amine units, which is an aqueous process, is an acid gas saturated in water which generally comprises carbon dioxide, hydrogen sulfide and traces of aromatic hydrocarbons. The effluent from the amine treatment unit is sent to a sulfur recovery unit, which typically converts the hydrogen sulfide to elemental sulfur. The Claus sulfur recovery process, commonly used, comprises a thermal recovery stage followed by two or three stages of catalytic recovery. In the thermal recovery stage, the acid gas is burned with air or oxygen in a reaction vessel to consume approximately one third of the hydrogen sulfide and any hydrocarbon and ammonia in the acid gas. Sulfur dioxide from combustion reacts in the reaction stages with unconverted hydrogen sulfide to form elemental sulfur. The products of combustion and reaction are cooled in a recovery boiler and a sulfur thermal condenser to recover the sulfur. The catalytic recovery zones contain an alumina catalyst, which can undergo a significant reduction in activity and selectivity when aromatic hydrocarbons are present in the waste gas stream. Many other commercial sulfur recovery processes for extracting hydrogen sulfide from waste gas feeder streams include processes in which hydrogen sulfide is oxidized in a gas phase or in an aqueous liquid phase. A vapor phase process, known in the art as the Selectox Process, utilizes a catalyst comprising bismuth and vanadium components supported on a hydrophobic crystalline material. The catalyst is highly active and stable, especially in the presence of water vapor, to oxidize sulfuric acid to sulfur or sulfur dioxide by reacting hydrogen sulphide with oxygen. Another example of a hydrogen sulfide extraction process is the Stretford process, which produces a high purity sulfur product in an aqueous wash solution that absorbs and oxidizes hydrogen sulfide. The washing or absorption step is typically carried out with a water-soluble organic alkaline agent, such as an anthraquinone disulfonic acid (ADA), where the hydrogen sulfide is oxidized into elemental sulfur particles by an oxidation promoter which can be a vanadium compound pentavalent, such as sodium vanadate (NaV03). The recovery of the sulfur is obtained by flotation, using a current of air that is injected into the solution of the process. This injection of air generates a foaming sludge that contains the sulfur particles. Sulfur particles rise to the surface of the solution, where they are skimmed and recovered by filtration or any other liquid and solid separation technique. In this process, the oxygen in the injected air also reoxidates the reduced ions of vanadate, thus regenerating the aqueous alkaline wash solution to be reused in the process. In a similar process, the washing solution comprises a vanadium salt solubilized as an oxidant, an aromatic non-quinone absorption compound, thiocyanate ions and a water-soluble carboxylate complexing agent. Other processes are based on the use of other metal oxidants such as ferrous iron and soluble arsenate and stannates. A relatively recent process for extracting sulfur compounds from the waste gas feed stream comes into contact with the stream with an aqueous solution containing sulphide oxidizing bacteria in the presence of oxygen, to oxidize the hydrogen sulfide to elemental sulfur. A commonly used technique for extracting the sulfur particles from the aqueous solutions is to circulate the washing solution through an oxidizing container in the form of a tank, through which air is pumped in bubbles to regenerate the washing solution and thus form a sparkling silt. When these solutions are new, the elemental sulfur particles that are formed have an average diameter ranging from 0.5 to about 5 microns. These particles typically agglomerate to form sulfur clusters of between 10 to 150 microns. These agglomerated particles float easily to the silt surface and pass through a funnel-shaped opening near the top of the vessel to a sulfur collection vessel. Once there, foam bubbles burst immediately, and the resulting liquid slurry or slurry can be easily pumped to a sulfur separation device, such as a rotary vacuum filter, filter press or centrifuge, from which, after wash to extract the solution retained from the process, you get sulfur of extremely high purity degree. If a non-particulate form of sulfur is desired, a washed filtrate can be sent to an autoclave or other type of sulfur melter. The introduction of pollutants such as aromatic hydrocarbons with six to eight carbon atoms per molecule pose problems for these processes. These hydrocarbons can be introduced by the incomplete or inadequate combustion of the sulfur-contaminated waste stream in an oxidation step, or by incomplete separation in a process plant, as in the case of an amine unit, which supplies the raw material basic of this process. When these contaminants appear, even in trace amounts, they accelerate the rate of formation of certain contaminants, such as thiosulfates, in the wash solution, resulting in the promotion of highly stable and long-lasting foams in the oxidation vessel, which it causes the formation of "sticky" particles of sulfur and makes the subsequent separation and washing of the sulfur in the filter extremely difficult. A solution to the problem makes contact with at least a portion of the incoming stream of contaminated gases or the wash solution already contaminated with a carbon or other adsorbent carbon useful for extracting contaminants. The solution in the Claus process was also the use of an activated carbon protection bed to adsorb the aromatic hydrocarbons. Unfortunately, these carbon adsorbents are ineffective when aromatic hydrocarbons and water are present in the gas stream containing the hydrogen sulfide. "Thermal oscillation processes are often used to dry gases and liquids, and for purification, when traces of impurities must be extracted, thermal oscillation processes are often used when the components to be adsorbed are very adsorbed on the adsorbent, ie water and, therefore, heat is needed for regeneration., the thermal oscillation processes use processes with adsorption steps at low temperature, regeneration at high temperature with a hot purge gas and a subsequent cooling to the adsorption temperature. A generally exemplary gas drying process of the thermal oscillation processes is described in US-A-4,484,933, issued to Cohen. The patent describes basic steps of the thermal oscillation processing coupled with the use of an auxiliary adsorption bed to improve the regeneration step. SUMMARY OF THE INVENTION The present invention relates to a process in which a stream of incoming gases containing hydrogen sulfide comes in contact with a catalyst to convert hydrogen sulfide to elemental sulfur. The gas stream contains organic pollutants, particularly one or more low molecular weight hydrocarbons, such as aromatic hydrocarbons with 6 to 8 carbon atoms per molecule, such as benzene, toluene and Cs aromatics such as ethylbenzene and the para-, meta- and ortho -xylene isomers. The present invention utilizes an adsorption process that contains a high silica zeolite molecular filter adsorbent to enable the production of a high purity sulfur product in the downstream sulfur recovery units. The present invention is a process for rejecting trace amounts of aromatic hydrocarbons from a feed stream of waste acid gases comprising hydrogen sulfide, carbon dioxide, water and the aromatic hydrocarbons. The process comprises passing the stream of waste acid gases under effective adsorption conditions by a high silica zeolitic adsorbent, effective for the adsorption of at least a part of the aromatic hydrocarbons and water, to supply a treated stream of effluents that is essentially free of aromatic hydrocarbons. Specific process steps may include increasing the pressure in an adsorption zone containing the high silica zeolite adsorbent to a desorption pressure and regenerating the high silica adsorbent with a heated stream of regeneration gas to desorb the aromatic hydrocarbons. The adsorption zone is depressurized up to the adsorption pressure, and the steps described above are repeated to form a continuous process. The preferred continuous process passes the feed stream of acid waste gases to a first adsorption zone from at least two adsorption zones. Each adsorption zone contains a regenerable adsorbent comprising a high selective silica and zeolite for the adsorption of water and aromatic hydrocarbons. The adsorption step produces a treated stream of effluents essentially free of aromatic hydrocarbons. A second adsorption zone is depressurized from the desorption pressure to the adsorption pressure. The second adsorption zone has already completed a desorption step and is at a desorption temperature, which is higher than the adsorption temperature. The feed stream of acid waste gases passes into the second adsorption zone to purge and cool the second adsorption zone. A warm purge stream is removed from the second adsorption zone. The warm purge stream is cooled to produce a cooled purge stream, and this cooled purge stream passes into the first adsorption zone and the treated stream of effluent is removed from it until the second adsorption zone returns to the adsorption. The passage of the acid waste gas feed stream to the first adsorption zone is interrupted, and the treated effluent is removed from the second adsorption zone. The first adsorption zone is pressurized to a desorption pressure, which is higher than the adsorption pressure, with a stream of high pressure filling gases. A regeneration gas heated to a desorption temperature is passed to the first adsorption zone to desorb the water and the aromatic hydrocarbons in the desorption step, and produce a stream of regeneration effluents. The stream of regeneration effluents is cooled and is at least partially condensed to produce a stream of water, a stream of aromatic hydrocarbons and a waste stream of regenerating gases. At least a portion of the regenerative gas waste stream is heated to produce the heated stream of regenerants. The previous steps are repeated to produce the continuous process. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flowchart of the process of the present invention. Figure 2 is an isotherm of toluene adsorption in a high silica zeolitic adsorbent. Figure 3 is an isotherm of adsorption of p-xylene in a high silica zeolitic adsorbent. DETAILED DESCRIPTION OF THE INVENTION The present invention is useful for extracting aromatic hydrocarbons from a sulfurous waste gas feed stream in a regenerable adsorbent to produce a purified stream of waste gases, which can subsequently be processed in a sulfur recovery unit for the production of a high purity sulfur product. Generally, the waste gas stream was already processed in an amine treatment unit. The amine treatment units extract hydrogen sulfide from the gas streams by absorption with aqueous solutions of amines such as monoethanolamine, diethanolamine and methyldiethanolamine to obtain treated combustible gases comprising less than 160 parts per million by volume of hydrogen sulfide, and more particularly to produce combustible gases with less than about 10 parts per million by volume of hydrogen sulfide and liquefied natural gas with less than about 50 parts per million by weight of hydrogen sulfide. Although the absorption of amines extracts a significant portion of aromatic hydrocarbons in the feed from the amine unit, the waste gas stream produced by the amine unit will comprise approximately 3 percent of the aromatic hydrocarbons entering the amine unit. with the feeding towards the amine unit. Although the process of the present invention can be applied before the amine unit (in the feed of the amine unit), it is preferred to process the waste gas stream produced by the amine unit. Typically, the waste gas stream comprises carbon dioxide and sulfur compounds. Sulfur compounds in waste gases typically include hydrogen sulfide, sulfur dioxide, carbonyl sulfide and mercaptans. The hydrogen sulfide generally comprises more than 95% of the volume of total sulfur in the waste gas stream, and the waste gas typically comprises more than about 90% of the volume of carbon dioxide. Typically, the total amount of aromatic hydrocarbons in the waste gas stream comprises a concentration ranging from about 1,500 to about 3,000 parts per million of the volume. Preferably, the waste gas comprises about 1,000 to about 2,000 parts per million of the volume of aromatic hydrocarbons, and more preferably the waste gas comprises less than about 2,000 parts per million of the volume of aromatic hydrocarbons. The waste gas is available at a pressure that would range from about 167 kPa to about 310 kPa. The waste gas feeder stream comes into contact with the adsorbent in an adsorption zone of the present invention under conditions effective to adsorb the aromatic hydrocarbons and water, and to produce a stream of treated wastes essentially free of aromatic hydrocarbons. The adsorbent is subsequently desorbed in a thermal oscillation cycle at an effective regeneration temperature with a treated stream of fuel gas. The regeneration gas used is removed from the adsorption zone and cooled to room temperature, typically between about 27 ° C to about 37 ° C. If a part of the waste gas stream to be processed in the adsorption unit comprises aromatic hydrocarbons that do not need to be recovered, a portion of the cooled and used stream of regeneration gases comprising aromatic hydrocarbons passes into the fuel gas system to be used as fuel. As the stream of regeneration gases used is cooled, part of the desorbed water is condensed and withdrawn into the wastewater. To prevent reintroduction of the aromatic hydrocarbons to the downstream sulfur recovery stream, regeneration is carried out in a partially enclosed circle, where a stream of combustible filling gases is combined with a portion of the cooled gas stream. regeneration used and heated to produce the flow of heated combustible gases. By returning the newly regenerated adsorption zone to the adsorption service, the waste gas feed stream is introduced to the feed end of the newly regenerated adsorption zone to cool the adsorption zone, and the hot effluent is cooled and sent to another adsorption zone that operates in the adsorption mode. This operation of guiding and trimming is continued until the regenerated bed reaches effective adsorption conditions, and at the same time the other adsorption bed in the trimming position is regenerated to produce a continuous process. When no fuel is required, or when you want to use an open regeneration system, the regenerative process can transfer regenerants used from the process without the need to cool or separate. The hydrocarbons adsorbed on the adsorbent have the problem that when it is adsorbent it is desorbed at low pressure, the portion of the aromatic hydrocarbons that are condensable is high, and the condensation of these hydrocarbons can adversely affect the operation of the adsorption unit. The purified stream of waste gases produced by the process of the present invention is essentially free of aromatic hydrocarbons such as Ce to C8 hydrocarbons, such as benzene, toluene and xylene isomers, where "essentially free" means a concentration of aromatic hydrocarbons of less than of 500 parts per million of the volume, and preferably a concentration of aromatic hydrocarbons of less than 250 parts per million of the volume. More preferably, the concentration of aromatic hydrocarbons varies between 250 and 500 parts per million of the volume. The purified stream of waste gases can be passed to a sulfur recovery unit by oxidation to produce a high purity sulfur product. A further advantage of the present invention is that the water withdrawn from the waste gas feed stream by the adsorption process can be returned to the amine unit to replenish the water extracted from the amine solution during the aminic adsorption step. The thermal oscillation process of the present invention is related to a conventional thermal oscillation process in which each bed of an adsorption zone undergoes cyclic adsorption at an adsorption temperature, wherein the most readily adsorbable components in the feed stream are selectively adsorbed to produce a stream of adsorption effluents enriched in less adsorbable components, regeneration at a desorption temperature that is higher than the adsorption temperature and which is made by passing through a purge gas at an elevated temperature, that is, equal to or greater than the desired desorption temperature through the bed, and cooling the bed to the adsorption temperature by passing a purge gas through the bed. Generally the thermal oscillation processes are carried out in such a way that the adsorption steps take place at approximately the same adsorption and desorption pressures, or when the adsorption pressure is generally higher than the desorption pressure. In the present invention, in order to recover the aromatic hydrocarbons as liquids, the adsorption takes place at a low adsorption pressure with respect to the desorption pressure. The adsorption of the present invention typically takes place at effective conditions which include an adsorption pressure ranging from 167 kPa to about 310 kPa, and an adsorption temperature ranging from about 5 to about 65 ° C. The desorption step of the present invention is performed at a pressure higher than the adsorption pressure, in order to collect and condense the aromatic hydrocarbons recovered upon desorption from the adsorbent. Preferably, the desorption step of the present invention takes place at a desorption pressure ranging from about 315 kPa to about 1.38 MPa, and more preferably the desorption step takes place at a desorption pressure greater than or equal to about 790 kPa .

The desorption step is performed at a desorption temperature which is effective to desorb the aromatic hydrocarbons from the adsorbent. Preferably the desorption temperature ranges from about 100 to about 300 ° C, and more preferably the desorption temperature ranges from about 150 to about 260 ° C. The desorption zones of the present invention contain desorption beds containing a suitable adsorbent to adsorb the particular components to be adsorbed. The adsorption bed has selectivity for various components of a feed stream over other components, thereby producing a less adsorbable component and a more easily adsorbable component. In the present invention, the more readily adsorbable components are aromatic hydrocarbons and water, and the less adsorbable components are hydrogen sulfide and carbon dioxide. Upon reaching the capacity of the adsorption bed of more easily adsorbable components, ie, preferably before a substantial part of the adsorption guideline has passed through the first adsorption bed, the feed stream is directed to another bed in the adsorption bed. adsorption zone. It will also be understood that the term "countercurrent" denotes that the direction of gas flow through the adsorption bed is countercurrent to the direction of the flow of feed current. The purge gas is at least partially comprised by a stream of effluents, ie the stream of adsorption effluents from the adsorption bed, comprising the less adsorbable component. The term "enriched" should be understood in reference to the composition of the feeder stream, unless noted in another sense. Adsorbents known in the art include crystalline molecular filters, activated carbons, activated clays, activated aluminas, polymer resins and mixtures thereof. Crystalline molecular filters include zeolitic molecular filters. Molecular zeolitic filters in the calcined form can be represented by the general formula: Me2 / nO: A1203: xSi02 where Me is a cation, x has a value ranging from 2 to infinity, and n is the valence of the cation. The adsorbent of the present invention will comprise high zeolitic adsorbents on silica, and mixtures thereof. The high silica zeolites that can be used include: clinoptilolite, boggsite, EMC-2, zeolite L, ZSM-5, ZSM-11, ZSM-18, ZSM-57, EU-1, offretite, faujasite, ferrierite, mordenite, Beta zeolite and silicalite. It is desirable to reduce the aluminum content in the structure or framework, thereby reducing the affinity of the water with the zeolite as long as it retains its ability to retain its hydrocarbon adsorption capacity in the presence of reasonably high moisture levels. For these reasons, zeolites suitable for use in accordance with the present invention are synthetic or natural zeolites with a high silica content, ie those with a silica to alumina ratio of the structure preferably greater than 15. The term "proportion" silica versus alumina of the structure "refers only to the aluminum and silica atoms that are tetrahedrally coordinated within the zeolite structure. Preferably, naturally occurring or synthetically produced adsorbents having a ratio of silica to alumina of the structure of less than 15 will be modified in conventional ways such as steam injection, acid extraction, fluoride treatment and the like to increase the proportion of silica against alumina of the structure to more than about 15. Faujasites with a silica to alumina ratio of the structure greater than 15 are preferable for use with the present invention. Preferred adsorbents have a pore opening of at least about 6.0 angstroms and, preferably, more than about 6.2 angstroms. The pore opening of molecular filters of naturally occurring and synthetically produced zeolites can be increased by any conventional way, as cation exchange, acid leaching and the like. More particularly, synthetic and naturally occuring zeolites are preferred with an FAU structure as defined in the "Atlas of Zeolite Structure Types", by W.M. Meier and D.H. Olson, published by the Structure Commission of the International Zeolite Association, (1987), on pages 53-54 and 91-92. In ZEOLITE MOLECULAR SIEVES, Ed. John Wiley and Sons, New York, 1974, detailed descriptions of some of the zeolites described above can be found. Adsorbents suitable for the process of the present invention may comprise Zeolite Y or various modifications of Zeolite Y in a refractory matrix of inorganic oxide. Zeolite Y can be modified, for example, by increasing the molar ratio of silicon to aluminum. US-A-4,869,803 describes an improved method for calcining zeolites, and presents characterizations of the zeolites Y-82, LZ-10 and LZ-20 in columns 7-8. This reference refers to the US patent. 4,401,556 issued for R.D. Bezman and J.A. Tail that reveals an ultra-hydrophobic Zeolite Y (UHP-Y) characterized by having a molar ratio of silica to aluminum of between 4.5 and 35, the essential X-ray diffraction pattern of the zeolite Y, an ion exchange capacity no greater than 0.070, a unit cell dimension of between 24.20 and 24.45 angstroms, surface area of at least 350 m2 / g (BET), a water vapor sorption capacity at 25 ° C of between 2 to 4 percent of the weight a value p / p ° of 0.10, and a Residual Butanol test value of not more than 0.40 percent by weight. LZ-20 is prepared in a manner similar to LZ-10, except that the final calcination takes place in a single stage. The LZ-15 zeolite is prepared in a similar manner to the LZ-20 zeolite, although LZ-15 has a lower water capacity than the LZ-20 zeolite. The specifications of LZ-20 are a ratio of SÍO2 / AI2O3 of between 5.0 and 6.0 (by volumetric chemical analysis), surface area of between 580 to 650 m2 / g (BET), a unit cell dimension of between 24.33 to 24.41 Angstroms and a water vapor sorption capacity of between 1,361 and 2,494 kilograms per 45 kilograms of adsorbent. Zeolites LZ-10, LZ-20 and LZ-15 are available in UOP from Des Plaines, Illinois, USA. The respective proportions of silica against alumina of the structure of LZ-10, LZ-15 and LZ-20 are: 30-60, 28-66 and 13-22. When using crystalline molecular filters, it is often desirable that the molecular filter be agglomerated with an adhesive, in order to ensure that the adsorbent has an adequate particle size. Although there are a variety of synthetic and natural adhesive materials available such as metal oxides, clays, silicas, aluminas, silica-aluminas, silicozirconias, silicotries, silicoberilias, silicotitanias, silicoaluminotorias, silicoaluminozirconias, mixtures thereof and the like, silica adhesives are preferred. Clay adhesives are preferred, and silica is more preferable since the silica can be used to agglomerate the molecular filter without the adsorptive properties of the zeolite being substantially altered. The experiments showed that high silica zeolites, such as LZ-10, do not show a large reduction in the adsorptive charge of aromatic hydrocarbons in humid air, particularly in the case of air with a relative humidity greater than 50 percent, and more particularly for air with a relative humidity of between 50 and approximately 80 percent. DETAILED DESCRIPTION OF THE DRAWINGS The process of the present invention will be described below with reference to Figure 1, which illustrates various aspects of the process. Referring to Figure 1, a waste gas stream comprising sulfur compounds, water and carbon dioxide with trace amounts of aromatic hydrocarbons passes through line 10, valve VI and line 12 into an adsorption zone 101. In the adsorption zone 101, the waste gas feed stream comes into contact with a selective adsorbent for the adsorption of aromatic hydrocarbons. A stream of adsorption effluents is removed from the adsorption zone 101 on line 14, and passes through the valve V9 and line 16, and is removed from the process as treated waste stream on line 16. At a certain point in the process, before the emergence of aromatic hydrocarbons from the adsorption zone 101, the valve VI and valve V2 is opened, allowing the waste gas feed stream to pass through valve V2 and line 52, and to enter adsorption zone 102 previously regenerated. The adsorption effluent removed from adsorption zone 102 on line 54 passes through valve V8, line 20, air cooler 104, line 22, line 24, valve V5 and line 12 in a step of displacement to purge the regenerated adsorption zone 102 of any aromatic hydrocarbon residue, and pass the aromatic hydrocarbon residues to the adsorption zone 101. This displacement step prevents the release of a slime or a maximum concentration of aromatic hydrocarbons into current processes below, for the recovery of sulfur. At the conclusion of the displacement step, the valve V8 is closed, and the adsorption effluent from the adsorption zone 102 passes through line 54 and the VIO valve, and is removed as the stream of products treated in line 16. In this At the point of the process, the adsorption zone is isolated from the waste gas feed stream by closing valves V5 and V9, and a pressurization step is initiated where the adsorption zone 101 reaches the desorption pressure, which is greater than the Adsorption pressure. In the process of the present invention it is necessary to raise the pressure of the desorption stage above the adsorption pressure, which is considerably lower, to effectively remove the aromatic hydrocarbons from the regeneration gases used. In the pressurization stage, with valve V9 closed, valves V7 and V12 are opened and a filling gas stream, which is available at high pressure and which typically comprises natural gas, nitrogen, carbon dioxide and mixtures thereof, is passed. , by line 48, valve V12, line 50, valve V3 and line 12 to adsorption zone 101. Valve V12 allows a part of the filling gas stream to undergo a pressure reduction until reaching approximately the adsorption pressure, and gradually raises the pressure in the adsorption zone 101 until reaching the desorption pressure in the pressurization stage. When the adsorption zone 101 reaches the desired desorption pressure, a closed regeneration step is carried out. In the closed regeneration stage, a stream of regeneration effluents is removed from the adsorption zone 101 on line 14, and passes through the valve V7 and line 20 to the air cooler 104, which at least partially cools the stream of regeneration effluents to produce an effluent of regeneration cooled in line 22. The cooled effluent of regeneration, at a cold temperature that varies from 35 to about 65 ° C on line 22, goes through lines 22, 25 and 26, valve V16 and line 34 to a refrigerator 106. Refrigerator 106 further reduces the flow of cooled regenerating effluents to a refrigerated temperature ranging from 0 to about 15 ° C, to at least partially condense aromatic hydrocarbons and water, and to produce a cooled effluent stream in line 36. The cooled effluent stream passes to the condenser 112 for phase separation, where the condensed water is withdrawn water stream in line 38, and condensed aromatic hydrocarbons are removed as stream of aromatic hydrocarbons in line 40. The uncondensed portion of the stream of cooled effluents, or regenerant gas used, is removed from condenser 112 and passes through line 42 to compressor 110, which restores the pressure of the flow of regenerating gases used until reaching a pressure approximately equal to the desorption pressure, to produce a pressurized stream of regeneration gases in line 44. The pressurized stream of regeneration gases passes to heater 108 to raise the used regeneration gas to the effective desorption temperature and produce a stream of hot regeneration gases in line 46. The flow of hot regeneration gases passes into the first adsorption zone 101 through line 46, valve V14, line 47, line 50, valve V3 and line 12 to complete the closed circuit of regeneration. The regeneration stage is carried out for a period of between 0.5 to about 8 hours, and more preferably the regeneration stage is carried out for a period of between 0.5 to about 2 hours, to desorb the aromatics and the water in the adsorbent in the first stage. desorption zone 101, while the second adsorption zone 102 adsorbs aromatic hydrocarbons from the waste gas feed stream in an adsorption step. At the conclusion of the regeneration stage, valves V14 and V16 are closed, separating the first adsorption zone 101 from the cooling and heating sections of the process. The first adsorption zone 101 undergoes a depressurization step by releasing the depressurization gas through the valve V7, line 20, the air cooler 104, the lines 22 and 24 and the valve V6 to the gas supply line 52 to the inlet end of the second adsorption zone 102, from which the effluent stream treated by line 54, the valve, is removed.

VIO and line 16. After the depressurization step, the first adsorption zone 101 goes through a cooling stage in which the waste gas feed stream in line 10 is introduced into the first adsorption zone 101 via the line 10, valve VI and line 12, and a warm purge stream is removed on line 14, and passes to air cooler 104 via line 14, valve V7 and line 22 passes to the second adsorption zone 102 through lines 24, valve 26 and line 52, and the effluent stream from second adsorption zone 102 is removed by lines 54, valve 10 and line 16 as treated waste gas stream. Accordingly, the second adsorption zone 102 acts as a secondary adsorption zone while reducing the temperature of the first adsorption zone 101 to the effective adsorption temperature. This configuration of guiding and trimming the adsorption zones during the cooling step prevents setbacks in the plant such as allowing a slurry of aromatic hydrocarbons to be transported to downstream sulfur recovery units. The advantage of this guiding and trimming configuration is that any of the remaining aromatic hydrocarbons in the newly regenerated adsorbent will be removed with the increase of gas flow during depressurization, and will be captured in the bed in a trimming position. The total cycle time of the present invention can vary from about 1 to 24 hours, where the total cycle time is the time for the process to go through a cycle of adsorption and desorption. Preferably, the total cycle time varies from about 2 to about 8 hours. During the regeneration of the second adsorption zone 102, the filling gas at the desorption pressure is introduced into the second desorption zone 102 by line 48, valve V12, line 50, valve V4 and line 52, and the regeneration effluent is removed by the line 54 and is passed to the cooler 104 via the valve V8 to the line 20. When the adsorption zone 102 goes through the cooling stage, the waste gas feed stream passes to the adsorption zone 102 by line 10, valve V2 and line 52 to produce the warm purge stream which is removed by line 54 and passing through valve V8 and line 20 to air cooler 104 to producing the cooled purge stream in line 22. The cooled purge stream passes to the first adsorption zone 101 via line 22, line 24 and valve V5. During the regeneration stage, a portion of the regeneration stream cooled in line 22 can be withdrawn to be used as fuel gas stream by line 22, line 28, valve V18 and line 30 or, if required to maintain the pressure in the sections, cooling and heating, between valve V16 and valve V14, can be passed through line 28, valve V18 and line 30 a portion of regeneration gas to be used as fuel or to a flame ( it is not shown). EXAMPLES Example I The process of the present invention is illustrated for the scheme shown in the drawing. A waste gas feed stream is passed to the process at a rate of about 6.150 Nm3 / hr, a temperature of about 37 ° C and a pressure of about 207 kPa. The waste gas stream is saturated with water and comprises approximately 200 parts per million of the volume of aromatic hydrocarbons. A high pressure gas stream available at a pressure of about 550 kPa and comprising methane is used as the regeneration gas. Two adsorption vessels, each containing approximately 2,680 kg of high silica zeolite molecular filter adsorbent operates in accordance with the present invention, alternatively by processing the waste gas stream and aligning itself in the guiding and trimming configuration so that the waste gas feed enters the newly regenerated bed during the cooling stage and the warm effluent is cooled and then it is passed to the adsorption zone that continues to operate in the adsorption mode during the cooling stage of the process, to prevent a silt from entering. aromatic hydrocarbons to the flow of treated gases. The air cooler reduces the temperature of the regeneration effluent used, from the regeneration stage to a temperature of about 49 ° C, and the cooling zone reduces the temperature of the effluent stream cooled to about 4.5 ° C. The heater operates at a temperature of approximately 260 ° C. The stream of treated gases removed from the process comprises less than about 250 parts per million of the volume of aromatic hydrocarbons. EXAMPLE II Saturation curves were developed experimentally for a high silica zeolite adsorbent with a silica to aluminum structure ratio of about 35. The adsorbent was an acid-washed, dealuminated Y zeolite, commercially known as LZ-15, as described above. . Saturation curves were determined by passing an air stream at a rate of 0.9 Nm3 / hr through an adsorbent column with an external diameter of 16 mm and 0.45 m in length, and containing about 20 grams of adsorbent. Tests were carried out at a pressure of approximately 124 kPa and a temperature of approximately 21 ° C. Air streams, adjusted to have a relative humidity of about 60 and about 80 percent, were separately mixed with a stream of dry air that passed through a vessel containing aromatic hydrocarbons through a conventional bubble machine, to thereby add aromatic hydrocarbons to humid air streams. The feed and effluent concentrations were monitored and analyzed until the exit concentration reached at least 50 percent of the input concentration. Among the analyzes, the column of adsorbent was regenerated with dry air during a period of one hour and a temperature between 175 and 200 ° C. The adsorbent was allowed to cool to room temperature in preparation for the next adsorption process. Periodic measurements of the effluent concentration were taken as a function of the adsorption time. The actual charges in terms of grams of aromatic hydrocarbon adsorbed per 100 grams of adsorbent were calculated based on this saturation curve using feed concentration, feed flow rate and adsorbent weight. The aromatic hydrocarbon concentration was measured with a Perkin-Elmer 392OB gas chromatograph using a flame ionization detector. The relative humidity was measured with a Panametric 1000 relative humidity detector and calibrated with a gravimetric analyzer Nesbitt Figure 2 shows that the loading of adsorbent for toluene over a range of toluene concentration of between 100 to about 800 parts per million volume of toluene in air with relative humidity of 60 and 80 percent increases in an essentially linear manner. Figure 3 shows a similarly linear adsorbent load in air with relative humidity of 60 and 80 percent for p-xylene concentrations of between 40 to about 120 parts per million volume of p-xylene in the humid air stream. Example III Saturation determinations were developed to adsorb an aromatic hydrocarbon, toluene, and carbon dioxide (99.9% carbon dioxide) in the presence of water in a high silica zeolitic adsorbent. The device and adsorbent of Example II were used, substituting the air stream of Example II with carbon dioxide. Analyzes were performed for carbon dioxide temperatures of between 21 and 35 ° C, and relative humidities of between 28 to approximately 80%. Bubbles were produced in a stream of dry carbon dioxide through a chamber containing toluene, and then mixed with the main stream of carbon dioxide that passed through a chamber containing water, to produce the streams of acid gases that contained water and aromatic hydrocarbons. The feed and effluent concentrations were measured until the conditions of the outlet reached at least 50% of the input concentration. The charge of adsorbent for toluene ranged from 430 to about 560 parts per million of volume, and the water content varied from a relative humidity of about 28% at about 35 ° C, to a relative humidity of about 80% at about 21 ° C. The results of the toluene saturation charges appear in the following table.

Three cycles of desorption adsorption were performed at each temperature, and saturation was determined based on the toluene effluent composition which reached 2% of the input toluene composition. Surprisingly, the relative humidity had little influence on the capacity of the adsorbent for toluene as the cycle progressed beyond the first cycle.

Claims (10)

1. CLAIMS 1. A process for the extraction of trace quantities of aromatic hydrocarbons from a feed stream of acid waste gases comprising hydrogen sulfide, carbon dioxide, water and aromatic hydrocarbons, where the gas stream is waste acids comprises a a large amount of acid gases, and where the process involves passing the stream of waste acid gases through effective adsorption conditions through a high silica zeolitic adsorbent, effective for the adsorption of the aromatic hydrocarbons and water to produce a treated stream of effluents essentially free of aromatic hydrocarbons. The process of claim 1, wherein the acidic waste gas feed stream comes into contact with the high silica zeolite adsorbent, at effective conditions including an adsorption pressure in an adsorption zone that increases the pressure in the zone of adsorption after contacting the waste acid gas at a desorption pressure and regenerating the high silica adsorbent to desorb the aromatic hydrocarbons; and depressurizing the adsorption zone to the adsorption pressure and repeating steps (a) and (b) to produce a continuous process. The process of claim 2, wherein the process includes the additional steps of: (a) passing the waste gas feed stream to a first adsorption zone from at least two adsorption zones, where the high silica zeolite produces a effluent treated stream essentially free of aromatic hydrocarbons; depressurizing a second adsorption zone that completed a desorption step, from a desorption temperature and a desorption pressure to the adsorption pressure, the waste gas feed stream passing to the second adsorption zone to purge and cool the second zone of adsorption, and removing a warm purge stream from the second adsorption zone; (c) cooling the warm purge stream to produce a cooled purge stream, and passing the cooled purge stream to the first adsorption zone until the second adsorption zone returns to an effective adsorption temperature; (d) interrupting the passage of the waste gas feed stream to the first adsorption zone, removing the treated stream of effluents from the second adsorption zone, and pressurizing the first adsorption zone to the highest desorption pressure than the adsorption pressure with a stream of high-pressure filling gases; (e) passing the heated stream of regeneration gas to the effective desorption temperature to the first adsorption zone to desorb the hydrocarbons and water in the desorption step and produce the stream of regeneration effluents; (f) cooling and condensing the stream of regeneration effluents to at least partially condense the aromatic hydrocarbons to produce a stream of water, a stream of aromatic hydrocarbons and a stream of regenerating gases used; (g) heating at least a portion of the stream of regenerants used to produce the heated stream of regeneration gases; and (h) repeating steps (a) to (g) to produce a continuous process. 4. The process of claims 1, 2 or 3, wherein the zeolite high in silica is selected from the group consisting of clinoptilolite, silicalite, zeolite Beta, boggsite, faujasite, EMC-2, zeolite L, mordenite, offretite, ferrierite, LZ-10, LZ-15 and LZ-20, ZSM-5, ZSM-11, ZSM-18, ZSM-57, EU-1, and mixtures thereof. The process of claims 1, 2 or 3, wherein the effective desorption temperature ranges from 150 ° C to about 260 ° C, and the desorption pressure ranges from 315 kPa to about 1.38 MPa. The process of claims 1, 2 or 3, wherein the treated effluent goes through a sulfur recovery process comprising an oxidation process of hydrogen sulfide selected from the group consisting of a thermal combustion stage., a stage of catalytic oxidation of the gas phase, an aqueous alkaline washing step, a step of aqueous bacterial oxidation of sulfides and combinations of these. The process of claims 1, 2 or 3, wherein the waste gas feed stream is an effluent from an amine treatment zone. The process of claims 1, 2 or 3, wherein the waste gas stream comprises aromatic hydrocarbons in an amount ranging from 1 part per million volume to about 5,000 parts per million volume and the effluent treated stream , essentially free of aromatic hydrocarbons, comprises less than about 500 parts per million of the volume of aromatic hydrocarbons. The process of claims 1, 2 or 3, wherein the adsorption conditions includes an adsorption pressure ranging from about 167 kPa to about 310 kPa. The process of claims 1, 2 or 3, wherein the acid gas comprises between about 0.5 to about mol-% hydrogen sulfide and between about 10 to about 95 mol-% carbon dioxide, and the substantial amount of gas acid comprises more than 60 mol-% of the waste acid gas stream. A process for extracting trace amounts of aromatic hydrocarbons from a waste gas feed stream comprising sulfur compounds and aromatic hydrocarbons is disclosed. An adsorption process using a high silica zeolitic adsorbent with a ratio of silica to alumina structure greater than 15 and with a pore size greater than about 6.2 angstroms extracts aromatic hydrocarbon contaminants from the feed gas mixture and allows the recovery of a high purity sulfur product from the treated effluent stream. The adsorption zone comprises at least two adsorption beds for a continuous process. The regeneration of the adsorption zones is carried out in a closed or partially closed system, and the waste gas feed stream is used to cool and purge the adsorption zone passing through regeneration. The use of the present invention extracts aromatic hydrocarbon contaminants, which cause the Q degeneration of the operation of the downstream sulfur recovery zone.