Mercury Removal Methods

As mercury and arsenic tend to distribute throughout all the major cuts in an olefin unit (Fig. 18.30) the best or preferred location for contaminants removal for olefin plants is the feedstock before it enters the plant This avoids future problems associated with plant contaminants such as maintenance/health concerns, the possibihty of mercury passing through to selected unprotected product streams, the clean-up of regeneration effluent and plant waste streams, as well as the conventional catalyst/aluminum equipment [121, 122], 

The number of streams feeding the plant, the number of contaminated streams, the mercury concentration and the type of mercury removal system considered aU have a potential impact on the cost of the removal system. For overall economic assessment, one should consider the in-plant impact and the cost of removal systems for regeneration/waste effluent systems as well as down-stream client impacts. One should also consider other contaminants which are present in the natural gas condensate i.e. mainly arsenic but also sometimes phosphorus, lead or sihcon. For these contaminants, there is no removal process which is industrially apphed on the steam-cracker effluents. 

4 Typical RAM II (Removal of Arsenic and Mercury) Process Description 

The RAM II process (Fig. 18.31) developed by IFF is ideally suited for simultaneous removal of arsenic, mercury and lead from contaminated feedstocks, upstream of aromatics complexes or steam-cracking units. Typical results are excellent, less than 3 ppb of each contaminant in the process effluent as threshold limit for analysis, 1 ppb of each as expectation. Mercury removal from a HC cut is not as simple as the same operation from a gas or LPG feed. The very nature of the mercury compounds to be found in such a cut requires a two-step process in which the organo-mercuric species are decomposed into hydrocarbons and 

If needed, gas effluent could be sent to a mercury absorber purge gas reactor where mercury is adsorbed on the trapping mass before release of the gas at battery limits. Liquid effluent is sent to the mercury adsorber reactor where free mercury is adsorbed and the resulting treated product is routed to the downstream unit 

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Effect of Mercury Removal Method on Silica Structure. To... 

Figure 4. Effect of the mercury removal method on the pore structure ofSorbsil C60. Curve a is the material before treatment, and curve b is that after...

Hultbom, K.G. (2003) Industrially proven methods for mercury removal from gases. EPD Congress 2003, ed. Schlesinger, M., TMS, Warrendale, PA, 147 156 www.tms.org... 

Considerable research is being conducted into developing technologies for removal of mercury from flue gas and these are all extremely expensive. The situation for gasification technologies is different. Proven and economic methods for mercury removal are available and have been practiced for many years. Mercury can be adsorbed onto sulfur-impregnated carbon, which can achieve an effluent concentration of less than 0.1 pg/m. ... 

Problem Mercury and its compounds have many uses, from fillings for teeth (as a mixture with silver, copper, and tin) to the industrial production of chlorine. Because of their toxicity, however, soluble mercury compounds, such as mercury(II) nitrate, must be removed from industrial wastewater. One removal method reacts the wastewater with... 

Process sampling campaigns were focused on inlet gas streams, mercury removal unit outlets, treated gas, acid gas and sales gas. The results were used to identify process areas with increased potential for mercury exposure during maintenance events. Sampling methods used for the determination of total mercury (THg) in gas phase streams, were based on the USEPA Methods 30B and EPA 1631 and EPA 1669. 

NcNamara, J.D., and Wagner, N.J., Process effects on activated carbon performance and analytical methods used for low level mercury removal in natural gas applications. Gas Sep. Purif. 10(2), 137-140 (1996). 

The increase in mercury emissions through anthropogenic sources is a challenge for the modern society where environment condition is a vital and crucial issue. The level of mercury emission is quite high in Europe so it is advisable to take up activities which can help to reduce its impact. Currently, the best effective methods to reduce the mercury emissions in the environment are based on the capture of it from emission sources. SSILs seem to be the best available technology to adopt for mercury removal efficiently. 

Mercury inhalation has been linked to Alzheimer disease and autism, and limitation to mercury emissions is currently the subject of legislation by the U.S. Environmental Protection Agency (ERA) who will impose limits on mercury emissions from coal-tired boilers in the utilities industry. Mercury control techniques currently used in the industry include the use of flue-gas desulfurization (EGD) units and, as a result of mercury measurements around these units, it is known that oxidized and not elemental mercury is removed by the EGDs. Consequently, one method to increase mercury removal by this type of unit is to introduce a catalyst to promote the oxidation of mercury. Mercury measurement [128,129] led to the discovery that a gold-coated sand sample in a simulated flue-gas environment absorbed elemental mercury until an equilibrium was established and desorption of oxidized mercury began. Individual components of the simulated flue-gas have been evaluated for their effect on the oxidation of mercury, and it was found that nitrogen dioxide and hydrogen... 

Allyl cyanide. Into a 1 5 litre three-necked flask (1), provided with a mercury-sealed stirrer and two long double surface condensers, place 293 g. (210 ml.) of freshly-distilled allyl bromide, b.p. 70-71° (Section III, 35) and 226 g. of dry cuprous cyanide (Section 11,50,3, Method 1), Remove the mercury-sealed stirrer and replace it by a tightly fitting... 

The toxic nature of mercury and its compounds has caused concern over environmental pollution, and governmental agencies have imposed severe restrictions on release of mercury compounds to waterways and the air (see Mercury). Methods of precipitation and agglomeration of mercurial wastes from process water have been developed. These methods generally depend on the formation of relatively insoluble compounds such as mercury sulfides, oxides, and thiocarbamates. MetaUic mercury is invariably formed as a by-product. The use of coprecipitants, which adsorb mercury on their surfaces facihtating removal, is frequent. 

The mercury contained in the mother Hquid and washings of either method is recovered by treatment with sodium hydroxide solution. Yellow mercuric oxide is precipitated and filtered. The filtrate is treated further to remove the last traces of mercury before it is discarded. 

Soluble sulfides such as sodium sulfide, potassium sulfide, and calcium polysulfides have been used to precipitate mercury salts from alkaline solutions. When this procedure is used, exercise of caution is requked to maintain the pH within a given alkaline range so as to prevent evolution of H2S. Because the solubiUty of mercuric sulfide in water is 12.5 flg/L at 18°C or 10.7 ppb of mercury, use of this method for removal of mercury is adequate for most purposes. However, the presence of excess alkah, such as sodium hydroxide or sodium sulfide, increases the solubiUty of mercuric sulfide as shown ... 

Another method of removing mercury compounds from aqueous solution is to treat them with water-soluble reducing agents, thus hberating metallic mercury (26). The use of formaldehyde (qv) at a pH of 10—12 also is recommended. 

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