Ind. Eng. Chem. Res. 1996, 35, 3697-3701
3697
Mercury Removal from Oil by Reactive Adsorption Tsoung Y. Yan Mobil Technology Company, P.O. Box 1025, Princeton, New Jersey 08543-1025
Mercury in heavy condensate or oil causes marketing, processing, and environmental concerns. We have developed an effective process to remove mercury from oil. Laboratory tests show that the process is capable of removing up to 99% of mercury. The process is based on hightemperature chemisorption for selective adsorption of mercury and uses a special CuS/C adsorbent which is effective for removal of most types of mercury compounds. The process is simple and lends itself to integration into the existing LNG plant systems. In the process, the condensate from the stabilizer at 400-500 °F and 220 psi is directly passed over the adsorbent at about 10 liquid hourly space velocity (LHSV) for mercury removal before normal heat exchange and storage. At the contemplated operating conditions, the adsorbent can last more than 1 year. Extensive laboratory tests have been conducted to verify the technical feasibility of the process. The adsorbent has been produced using a commercial process in a commercial unit and evaluated in the laboratory thoroughly. Introduction Crude oil and liquid condensate produced around the world can contain small quantities of mercury (Phannenstiel et al., 1975; Smith et al., 1975). For instance, the Algerian condensate contains 26-40 ppb of mercury (McIntire et al., 1989). The mercury contents of North Sea and San Joaquin crudes are 55 and 110 ppb, respectively. The mercury in crude oil and condensate can cause processing and environmental concerns. Mercury can attack process equipment made of copper and especially aluminum. McIntire et al. (1989) attribute the failure of the aluminum heat exchangers in the ethylene plant of Cain Chemicals to mercury attack. At that time the plant was processing Algerian condensate containing 26-40 ppb of Hg. To protect the equipment and the environment, it is desirable to remove the mercury from hydrocarbon condensates and crude oils or reduce it to levels that are as low as possible. In fact, it is becoming an important issue in petrochemical industry to develop an effective technology to remove mercury from condensate because of the gradual shift of ethylene plant feedstocks from naphtha to condensate. The mercury in the oil and condensate can be emitted in air upon combustion, causing concerns in air pollution. Upon processing, the mercury in the crude oil and condensate can also end up in wastewater, leading to contamination of waterways and soil. The nature of mercury compounds in the oil is not well-known. Based on studies of its chemical reactivity, the mercury in condensate should be mostly in the form of metal with minor amounts of inorganics, such as mercuric chloride, and organics, such as dimethyl- and diethylmercury. The distribution of mercury compounds in the condensates has been studied by Sarrazin et al. (1993). Even though their reactivities are significantly different, all forms of mercury have to be removed to achieve a high level of overall removal efficiency. Mercury in the oil can be removed up to 80-90% by washing it with a dilute aqueous solution of sodium polysulfide (Yan, 1990a). Apparently, there are mercury compounds which are not reactive with the polysulfide, so that the degree of mercury removal could not be increased further by increasing the process severity, such as increasing the concentration of the polysulfide solution and increasing the contact time. Indeed, S0888-5885(95)00630-0 CCC: $12.00
organic mercury, e.g., dimethylmercury, was found to be not reactive with an aqueous solution of sulfides (Furuta et al., 1990). To achieve a high level of mercury removal, Japan Gas Co. (JGC) employs a two-step process, namely, liquid extraction followed by solid adsorption (JGC Corp., 1989). To achieve the same goal, Institut Francais du Pe´trole (IFP) also proposed a twostep process (Sarrazin et al., 1993). The condensate is mixed with H2 and passed over an organic metal converter for a hydrodemetallation operation. The effluent is cooled and passed over a mercury adsorber for mercury removal. For removing mercury from gases and liquids, the use of various adsorbents has been proposed. The useful adsorbents are copper sulfide on alumina or silica alumina (Sugier and LaVilla, 1978), silver, silver/gold, nickel or copper on support (Sugier and LaVilla, 1976), and sulfur on zeolites (Ambrosini et al., 1978). Even though these adsorbents are generally quite effective in removing mercury from condensate, their cycle life for mercury adsorption is only about 1-3 months depending on the mercury concentration of the oil, and is too short to be commercially useful. We have developed an effective and simple process to remove mercury from oil and condensate. The development of this process is summarized in this paper. Principles of Process Development. Adsorption Process. Since it is intended to be an add-on to an existing system, the mercury removal process has to be simple to operate and easy to integrate into the existing system. Thus, the use of a solid adsorption system was chosen. This adsorber has to be placed in the system with little impact on process configuration and without significant alteration of process conditions. The choice of adsorbents are CuS/C, CuS/Al2O3, Ag/Al2O3, etc. The mechanisms of mercury adsorption by use of CuS are not well-known. Beside physisorption on the surface, chemisorption becomes an important mechanism for mercury adsorption at high temperatures. Since the mercury in the spent adsorbent is mainly in the form of HgS, we are tempted to postulate that the reaction involved is:
CuS/support + Hg T Cu/support + HgS It should be pointed out that the reaction between mercury and the adsorbent is a reversible reaction. In © 1996 American Chemical Society
3698 Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996
this mechanism, sulfur is the real active component for reaction with mercury. The presence of copper makes the sulfur insoluble in oil and active for reaction with mercury. As to the mechanism of mercury adsorption by Ag/ Al2O3, it is believed to be amalgamation, i.e., Ag/support + Hg T Ag-Hg/support. The choice of Ag/Al2O3 in this study was based on the patent literature (Sugier and LaVilla, 1976, 1978). Adsorption Capacity and Cycle Life. Long cycle life is an important process requirement. With long cycle life, the unit operation cost is minimized and the spent adsorbent disposal cost is reduced. It is desirable to have the adsorbents with a cycle life of 1 year or longer at a reasonable flow rate, say, 10 LHSV. Thus, the adsorbent should have a treating capacity of 87 000 bed volume of oil. Unlike the gases, the condensate from some gas fields can contain high-boiling heavy + + ends, e.g., 20 and 5% of C10 and C20 , respectively. In addition, it also contains significant amounts of impurities, particularly, polar compounds, which can be strongly adsorbed by the adsorbent. These heavy ends and impurities compete too favorably with mercury, leading to a low adsorption capacity for mercury. When the conventional sulfur on activated carbon was used as the adsorbent in a fixed-bed reactor, the mercury breakthrough occurred after only 300 bed volumes. To achieve the desired capacity of the adsorbent for mercury, i.e., 1 year cycle life at 10 LHSV for a feed containing 220 ppb of mercury, the mercury selectivity of the adsorbent has to be improved to a level of 1/220 × 10-9, i.e., about 5 × 106. High-Temperature Adsorption. When metal sulfide on support is used as the adsorbent, the adsorption mechanisms of heavy hydrocarbons and mercury are different. Heavy hydrocarbons are physisorbed, while the mercury can be both physisorbed and chemisorbed. As the temperature is increased, physisorption decreases while the chemisorption can increase. Thus, by increasing the adsorption temperature, the mercury selectivity of the adsorbent can be increased to a high level, leading to increased adsorption capacity. In the chemisorption of mercury, chemical bonds are formed between the mercury and the metal sulfides on the support. Thus, the high-temperature process is called reactive adsorption. In addition to improved selectivity for mercury, the increased temperature speeds up the reaction and adsorption rates of mercury so that the feed rate can be increased to, say, greater than 10 LHSV. Even though the adsorption reaction is highly favoring formation of HgS for mercury removal, it remains a reversible reaction, and there is an equilibrium constant which is temperature dependent (Yan, 1994). High temperature decreases the chemical equilibrium constant, leading to high residual mercury levels in the product. Thus, there is an optimum temperature which balances the mercury selectivity and the equilibrium constant. This optimum temperature is higher, the higher the boiling range of the feed is. Activated Carbon Support. The organic mercury reacts with metal sulfide on the support. For example, (CH3)2Hg + CuS/support f Cu/support + HgS + C2H6. This reaction is much slower than that between the metal sulfide and metallic or inorganic mercury. At a high flow rate, removal of organic mercury cannot be complete, leading to a low overall mercury removal efficiency. By use of a proper support, such as activated carbon, the organic mercury can be more strongly
adsorbed. The organic mercury adsorbed near the active site reacts with sulfide slowly to form HgS, leading to removal of organic mercury. In essence, the use of the activated carbon increases its effective residence time to facilitate the mercury reaction, leading to a more complete reaction. Thus, the high-temperature reactive adsorption using metal sulfides on activated carbon adsorbent was devised for removing mercury from oil and condensate. Experimental Section Feed. The condensate used in this study was obtained from a U.S. refinery. The properties of the condensate are as follows: API gravity, 53°; saturates, + + 52.1 wt %; C10 , 20 wt %; C20 , 5 wt %; sulfur, 0.025 wt %; H2O, 169 ppm, Hg, 220 ppb. To speed up the test for mercury loading capacity of the adsorbent, the mercury content in the condensate was increased to 1400 ppb by dissolving additional amounts of metallic mercury. Since the concentration was so low, the dissolved mercury remained in the solution as evidenced by the constancy of the mercury concentration throughout the test period. In this feed, the solubility of mercury was about 5000 ppb. Adsorbents. The following adsorbents were prepared by catalyst manufacturers according to the proprietary procedures: 1. copper oxide on alumina (CuO/Al2O3) 2. copper sulfide on alumina (CuS/Al2O3) 3. silver on alumina (Ag/Al2O3) (SN651A-6-11) 4. copper sulfide on activated carbon (CuS/C) Testing Procedure. As the reactor, a 1/4 in. stainless steel tube of 0.035 in. wall thickness was packed with 0.25 cm3 of the adsorbents of 18 × 40 mesh size. The condensate was pumped downflow through the fixed bed of the adsorbent using a positive displacement (ISCO) pump. The adsorbent bed was heated and controlled at the desired temperature using a temperature controller. The reactor pressure was controlled by use of a NUPRO externally adjustable relief valve. This valve is reliable and inexpensive and has essentially no dead volume. The products at various onstream time or bed volume of oil treated were collected for material balances and mercury analyses. Except for the mercury removal, there was no apparent difference in properties between the feed and the products. The mercury contents were analyzed using the analytical procedure developed at this laboratory which has been adopted for commercial application. This procedure has been cross-checked and verified with the neutron activation analysis. Results and Discussion 1. Effect of Temperature on Mercury Adsorption. The mercury adsorption on the adsorbent and, in turn, mercury removal from the condensate increase with temperature, indicating that it is a reactive adsorption involving chemical reaction and not a simple physisorption. The effect of temperature on Hg removal at high LHSV using CuS/Al2O3 is shown in Table 1. At 75 °F, there was hardly any mercury removal. Mercury removal became significant at 200 °F and increased as the temperature was increased to 400 °F. As can be seen from the increase in bed volume of oil passed, these data were obtained by increasing temperatures in a single run and obtained under non-steady-state operation. Since the samples were taken after several hours
Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996 3699 Table 1. Effect of Temperature on Reactive Adsorption (Feed, Condensate, 220 ppb Hg; LHSV, 80 v/v h; Adsorbent, CuS/Al2O3) experiment
temp (°F)
bed volume no.
Hg in prod. (ppb)
Hg removal (%)
1 2 3 4 5 6
75 200 300 300 300 400
232 1872 2024 2196 2344 2424
210 92 28 32 31 23
4.5 58.2 87.3 85.5 85.9 89.5
Table 2. Effect of Temperature on Hg Removal (Adsorbent, CuS/C; Feed, Condensate, 220 ppb Hg; Pressure, 220 psi) unit
date
temp (°F)
LHSV (v/v h)
28 28 29 29
6/29 6/28 6/29 6/28
400 450 500 450
80 80 80 80
Hg (ppb) prod. feed 20 9 283 17
108 108 1889 1889
Hg removal (%) 81.5 91.7 85.0 99.1
of operation, they are adequate to show the impact of temperature on mercury removal and suggest that the mercury adsorption mechanism is not a simple physisorption but is a chemisorption. Since mercury is adsorbed by activated chemisorption, its adsorption rate is increased greatly as the reaction temperature is increased. Thus, by operating at high temperature ranges in this study, the throughput of the reactor can be increased. The reaction between mercury and metal sulfides on the adsorbent is a reversible process. As the temperature is increased, the relative rate of the reverse reaction also increases, leading to a lower equilibrium constant. Thus, the equilibrium concentration in the oil becomes high, and eventually the degree of mercury removal becomes equilibrium limited. Thus, there is an optimum temperature which balances adsorption rate and mercury selectivity (see the next paragraph) and the equilibrium constants. The effect of temperature on Hg removal using CuS/C is shown in Table 2. The mercury contents of the products decreased when the temperature was increased from 400 to 450 °F but increased when the temperature was increased further to 500 °F. The residual mercury content in the product at the high temperature of 500 °F is limited by thermodynamics due to increased dissociation of the mercury sulfide compounds; while at the lower temperature of 400 °F, it is limited by kinetics due to the decreased rate constant at lower temperatures. For CuS/C, this optimum temperature appears to be about 450 °F, which is exactly the temperature prevailing at the stabilizer bottoms at a LNG plant. 2. Efficacy of High-Temperature Reactive Adsorption for Mercury Removal. The high-temperature reactive adsorption process is effective for removal of mercury from the condensate. By use of CuS/C at 450 °F, 20 LHSV, and 220 psig, the mercury content in the feed was lowered from 220 to 2 ppb, corresponding to 99% of mercury removal (Figure 1). The mercury content of the treated condensate at 2 ppb is significantly lower than that of the typical crude oils and condensates in the world. The efficacy of this process was to remove mercury in the condensate to a low level of about 2 ppb; the experiments were conducted repeatedly using the same batch of the adsorbent. The mercury removals from the repeated runs were 99 ( 1%. In addition, the same results were also obtained
using the adsorbents prepared by the manufacturers in a commercial facility. In this laboratory test, the length of the adsorbent bed was only 1 in., and the flow rate was high at 20 LHSV. There is the potential of flow bypassing in such laboratory units. It is, therefore, possible that the degree of mercury removal could be higher in the commercial unit than that in the laboratory test due to improved flow pattern and solid-liquid contact. Thus, this treating process can bring the mercury content of the condensate down to a level below those of typical crude oil and condensate. 3. Life of the Adsorbent and Reaction Temperature. The long life of the adsorbent is the most critical factor in making this process technically and economically viable. Figure 1 shows that CuS/C is effective and removes 99% of mercury. When the test was terminated arbitrarily, the adsorbent had treated over 18 000 bed volume of condensate, which is equivalent to 15 months of operation life with the regular feed at the contemplated LHSV of 10. Thus, CuS/C is an excellent adsorbent for removal of mercury from condensate. The long life of the adsorbent is achieved due to the increased selectivity for mercury at high reaction temperatures. At high selectivity for mercury, the active sites were used almost exclusively to adsorb and react with mercury rather than adsorbing the impurities and heavy hydrocarbons. For the adsorbent to last 1-2 years of the operation cycle, the selectivity for adsorption of mercury over hydrocarbons and other impurities in the condensate must be 1-10 million. We recognized that the mercury and heavy hydrocarbons in the oil compete for adsorption sites through different adsorption mechanisms. The hydrocarbons are adsorbed by physisorption, and its adsorption isotherm decreases rapidly as the temperature is increased. On the contrary, mercury is adsorbed by chemisorption and its isotherm is little affected by temperature. Thus, by increasing the reaction temperature, the selectivity for mercury is greatly increased and the life of the adsorbent is extended to 1-2 years. 4. Kinetics of Mercury Removal. The kinetics of mercury removal using both Ag/Al2O3 and CuS/Al2O3 do not follow the simple first order with respect to mercury concentration (Figure 2). The rate of mercury removal is rapid on the initial contact and slows down as the contact time is increased or the LHSV is decreased. In fact, the improvement in mercury removal is quite limited when the LHSV was reduced from 80 to 10. It is noted that a high level of mercury removal was not achieved. These results suggest that the feed contains several types of mercury compounds with different reactivities with the adsorbents. To test the reactivities of different mercury compounds, dimethylmercury was compared with the mercury compounds in the condensate. In preparing the testing feed, the mercury compounds in the condensate were removed completely and then doped with dimethylmercury to a mercury level of 300 ppb. When CuS/C was used as the adsorbent, the mercury removal was 85 and 99% for the dimethylmercury and the mercury compounds in the feed, respectively. This result indicates that dimethylmercury is more difficult to remove than the indigenous mercury compounds in the condensate tested. JGC also found that the organic mercury is more difficult to remove than either metallic or inorganic mercury (JGC Corp., 1989). Based on these results, the organic mercury, which is difficult to remove
3700 Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996
2
Figure 1. Hg removal vs bed volume.
Figure 2. Hg in product vs 1/LHSV.
in the condensate, was estimated to be about 2 ppb, i.e., 10% of the total mercury. 5. Nature of Support on Mercury Removal. The organic mercury can be removed effectively by using activated carbon as the support of the CuS adsorbent. Both activated carbon based adsorbents, CuS/C and Ag/ C, were effective in removing the refractory dimethylmercury to about 85%. In contrast, CuS/Al2O3 and Ag/ Al2O3 removed about 10-20% of dimethylmercury at the same conditions. Because the activated carbon based adsorbents are effective for removing all types of mercury compounds including refractory organic mercury, they are effective in removing mercury from condensate to a level of 99%. On the other hand, alumina-based adsorbents, CuS/Al2O3 and Ag/Al2O3, are not effective for removing organic mercury and can remove only up to 95% of mercury from the condensate. The effectiveness of activated carbon based adsorbents for removing refractory organic mercury is due to the strong and selective adsorption of organic mercury by the activated carbon. The activated carbon concentrates and increases the residence time of the organic mercury on the surface to facilitate its reaction with the
active metals, CuS and Ag. The organic mercury must react with metal sulfides to form HgS and leaves the organic part of the molecule in the product because there would not be surface area on the adsorbent to accommodate the adsorbed organic mercury. Adsorption of mercury compounds from air by activated carbon, silver coating, and gold coating was studied by Dumarey et al. (1985). The specific mercury compounds tested were Hg°, HgCl2, (CH3)2Hg, CH3HgCl, (C2H5)2Hg, and C2H5HgCl. Gold is effective for removing all mercury compounds. Silver is effective except for organic mercury, while activated carbon is effective for organic mercury. Obviously, the silver and activated carbon are complementary in mercury removal, so that adsorbents effective for removing all mercury compounds can be prepared by combining silver and activated carbon. Indeed, Ag/C is an effective adsorbent. We believe that the CuS becomes more effective for removing mercury from condensate by changing the support from alumina to activated carbon based on the same principle. Apparently, the CuS/Al2O3 adsorbent is ineffective for removing the organic mercury in the feed, which can be removed effectively by the presence of activated carbon. 6. Regenerability of the Spent Adsorbents. To extend the ultimate life of the adsorbent and to alleviate the problems in disposal of the spent adsorbent, it is desirable to regenerate the mercury-laden adsorbent. The spent Ag/C adsorbent can be regenerated. The regeneration procedure involves passing hot inert gas, flue gas, or natural gas at about 340 °C to strip off the mercury. In the laboratory experiments, over 99% of the mercury on the spent Ag/C was stripped off at 340 °C. The activity of the adsorbent for mercury adsorption was restored. As can be expected, the spent CuS/C is not easily regenerated. Little mercury was stripped off using hot N2 gas at 340 °C. Substantial decomposition of HgS only takes place at temperatures above 500 °C. After heat treating at such a high temperature, the activity of CuS/C for mercury adsorption was greatly reduced. Fortunately, with a long life of more than 1 year, regeneration of the adsorbent using an elaborate operation is not economically justified, and it should be disposed of.
Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996 3701
7. Disposal of the Spent Adsorbents. With 1-10% of mercury content, the spent adsorbents can be safely disposed of and the valuable mercury reclaimed in the process. One of the mercury reclaiming processes is to burn the spent adsorbent at high temperatures (Yan, 1987). The activated carbon is burned to generate hightemperature heat. At high temperatures, the mercury compounds or amalgam is decomposed into mercury vapor which is condensed to recover metallic mercury. Commercial Application Since it is a simple fixed-bed adsorption process, the process can be readily used in commercial applications, such as refineries, LNG plants, and petrochemical complexes. A U.S. patent with broad coverage on this technology has been issued (Yan, 1990). Refineries. It can be used in a refinery to remove mercury from any hydrocarbon stream including naphtha and crude oil. The feed is heated to the required temperature and passed over a fixed bed of the adsorbent. The effluent is free of or low in mercury and can be used for the intended purpose directly without further treatment. LNG Plant. The LNG plants or gas process plants, in general, produce liquid condensate as the byproduct. Some liquid condensates contain mercury. The liquid condensate is stabilized to remove light ends before shipping or storage. The high-temperature mercury removing process can be integrated into such a system readily. At the outlet of the stabilizer, a reactor filled with the adsorbent is installed. The stabilizer bottom at ∼500 °F and ∼250 psi is passed directly through the reactor without changing temperature or pressure. The reactor is sized to obtain the desired LHSV of about 10. The effluent is passed through heat exchangers as usual and sent to storage or shipping. Petrochemical Complex. Liquid condensate and naphtha are important feeds to ethylene crackers. Upon cracking, the mercury contained in the feeds can reach the cold box to damage the aluminum heat exchangers. For application in the ethylene cracker system, the feed is heated to the desired temperature and passed through a reactor filled with the adsorbent. The low mercury oil is subsequently heated to the cracking temperature and cracked as usual. It is noted that the mercury content of the effluent from hightemperature adsorption can be as low as 1 ppb. However, this low level can be too high for the aluminum heat exchanger to tolerate. In this case, the effluent from the cracker can be dried in a drier with 4 Å sieves modified with silver to remove the trace mercury to about 1 ppt. This technology has been described previously (Yan, 1994). Thus, it is possible to reduce the mercury level of the feed to the cold box to 1 ppt for complete protection of the aluminum heat exchanger by combining the high-temperature adsorption and Ag/4 Å sieve technologies.
Acknowledgment The author is grateful to R. K. DeMura and C. D. Taylor, who conducted the experiments effectively and with enthusiasm. Literature Cited Ambrosini, R. F.; Anderson, R. A.; Fornoff, L. L.; Mauchands, K. D. Selective Adsorption of Mercury From Gas Streams. U.S. Patent 4,101,631, July 19, 1978. Dumarey, D.; Dans, R.; Hoste, J. Comparison of the Collection and Desorption Efficiency of Activated Charcoal, Silver, and Gold for the Determination of Vapor Phase Atmospheric Mercury. Anal. Chem. 1985, 57 (No. 13), 2638-2643. Furuta, A.; Sato, K.; Sato, K.; Matsuzawa, T.; Ito, H. A Process for Removal of Mercury from a Liquid Hydrocarbon. European Patent Application 0-352 420 A1, Jan 31, 1990. JGC Corp. Mercury Removal From Natural Gas Liquid. Presented at the LNG-9 Conference, Nice, France, Oct 17-20, 1989. McIntire, D.; English, J. J.; Kobrin, G. Mercury Attack of Ethylene Plant Alloys. Presented at the Corrosion/89, National Association of Corrosion Engineers, New Orleans, LA; April 17-21, 1989; Paper 106. Phannenstiel, L. L.; McKinely, C.; Sorensen, J. C. Mercury in Natural Gas, Progress in Refrigeration Science and Technology. Proceedings of the XIV International Congress of Refrigeration, Moscow, 1975. Sarrazin, P.; Cameron, C. J.; Barthel, Y.; Morrison, M. E. Process Prevent Detrimental Effect from As and Hg in Feedstocks. Oil Gas J. 1993, 25, 86-90. Smith, I. C.; Ferguson, T. L.; Carson, B. L. Metals in New and Used Petroleum Products and By-Products, Quantities and Consequences. In The Role of Trace Metals in Petroleum; Yen, T. Y., Ed., Ann Arbor Science Publishers: Ann Arbor, MI, 1975; Chapter 7, p 136. Sugier, A.; LaVilla, F. Elimination of Mercury Present in a Gas or Liquid by Adsorption on a Solid Mass Containing a Support and a Metal Capable of Forming an Alloy with Mercury. French Patent No. 2,310,795, Dec 10, 1976. Sugier, A.; LaVilla, F. Process for Removing Mercury from Gas or Liquid by Adsorption on a Copper Sulfide Containing Solid Mass. U.S. Patent, 4,094,777, June 13, 1978. Yan, T. Y. Recovery of Mercury and Heat Energy From Waste Using Fluidized Beds. U.S. Patent 4,701,212, Oct 20, 1987. Yan, T. Y. Method for Removing Mercury from Hydrocarbon Oil by High Temperature Reactive Adsorption. U.S. Patent, 4,909,926, March 20, 1990. Yan, T. Y. Use of Dilute Aqueous Solutions of Alkali Polysulfides to Remove Trace Amounts of Mercury from Liquid Hydrocarbons. U.S. Patent 4,915,818, 1990a. Yan, T. Y. A Novel Process for Hg Removal from Gases. Ind. Eng. Chem. Res. 1994, 33, 3010-3014.
Received for review October 16, 1995 Revised manuscript received April 4, 1996 Accepted April 4, 1996X IE950630N
X Abstract published in Advance ACS Abstracts, June 1, 1996.
