Method of eliminating mercury from liquid hydrocarbons

Abstract: Activated carbon is prepared specially by means of activating carbonaceous material in a circumstance comprising water vapor less than 15 % on volume basis and providing the thus treated activated carbon to carry alkaline or alkaline earth metal sulfide in it. The thus prepared activated carbon or that carrying these compounds provide for a method of eliminating mercury and its compounds from liquid hydrocarbons substantially completely which are contained in it at a slight amount. Liquid hydrocarbons containing mercury or sulfur will harm catalysts which are often applied during processing such intermediates of petroleum products and petrochemical products. Thus the present method is advantageous to processing of such oil intermediates.

Description: This invention relates to a method of eliminating mercury and its compounds from liquid hydrocarbons, more particularly, to a method capable of substantially completely eliminating mercury and its compounds contained in a slight amount in liquid hydrocarbons which are usually intermediates leading to petroleum products and petrochemical products, by means of contacting the liquid hydrocarbons with activated carbon or activated carbon carrying alkaline metal sulfide or the like. Heretofore, alumina based catalysts carrying palladium, for instance, have been used for the hydrogenation process of reforming liquid hydrocarbons, such as naphtha, wherein the hydrogenation reaction suffers from damage of the catalyst if an impurity of mercury is present in the liquid hydrocarbons. Then, mercury tends to readily form amalgam with many kinds of metals. For such reason, if an apparatus constructed from aluminum based alloys is involved in such a process noted above, there is harm of corrosion due to amalgamation with mercury. Accordingly, there has been strong desire for progress in the elimination of mercury from such hydrocarbons. There have been reported adsorbents for mercury which include a porous adsorbent carrier carrying sulfur. Such adsorbents allegedly effect the elimination of mercury by reaction between mercury and sulfur. Porous adsorbents including conventional activated carbons, zeolite, and alumina with nothing carried thereon can eliminate mercury by action of physical adsorption, but attainment is as low as 30-70 % and adsorption ability drops down extremely when the mercury concentration is less than 10 ppb. These are problems involved in the art heretofore. The art disclosed heretofore concerning adsorbents carrying sulfur is, for example, sulfur-carrying activated carbon which is prepared by mixing activated carbon with fine sulfur particles and heating such mixture at 100-400 °C (Japanese Patent Application Laid Open 59-78915/1984 ); activated carbon carrying organic sulfur compounds (Japanese Patent Application Laid Open 62-114632/1987). As for the choice of sulfur compounds, the use of sulfur or an organic sulfur compound such as thiophene is typical in the art, wherein such porous materials carrying sulfur compounds have been of interest mainly in order to eliminate mercury from a gaseous material, not to eliminate mercury from liquid hydrocarbons. However, the prior art does not disclose the inhibition of the dissolution of the sulfur contained in the adsorbents into the liquid hydrocarbon as contaminants or the elimination of mercury. Liquid hydrocarbons are mostly subjected to the hydrogenation at an intermediate stage wherein sulfur contained in such hydrocarbons as a contaminant or impurity gives serious damage to the hydrogenation catalysts. Therefore, the dissolution of sulfur into such hydrocarbons should be prevented at all. The known activated carbons carrying sulfur or sulfur compounds have been found to dissolve the carried sulfur or sulfur compound into the liquid hydrocarbons (dissolved concentration is about 10-400 ppm). Chemical Abstracts, vol. 121, no. 12, 1994, abstract no. 141156 (JP-A-06 106 161) and Chemical Abstracts, vol. 121, no. 6, 1994, abstract no. 65240 (JP-A-06 100 310) describe a granular activated carbon obtained from carbonaceous material by carbonization in an atmosphere containing 15 % by volume of water vapor. The activated hydrocarbon is used to purify water, in particular from organic halides. It is the object of the present invention to provide a method of eliminating mercury and its compounds substantially completely from liquid hydrocarbons without the problems known in the prior art. The object of the invention is achieved by providing a method of eliminating mercury and its compounds substantially completely from liquid hydrocarbons which contain mercury and its compounds at a slight amount, comprising contacting activated carbon or preferably activated carbon carrying alkaline or alkaline earth metal sulfide with the liquid hydrocarbons, wherein the activated carbon noted has been prepared by activating carbonaceous material with activation gas containing water vapor less than 15 % based on the volume of the activation gas. Said activated carbons are used for elimination of mercury and its compounds in liquid hydrocarbons in this invention. The inventive method eliminates the mercury from the hydrocarbons to such an extent that no substantial harm occurs to the desired hydrocarbons due to either uneliminated mercury or the dissolution of sulfur into the liquid hydrocarbons during subsequent processes which convert the hydrocarbons into petroleum products and petrochemical products. Specifically it has been found that the preparation of activated carbons should be changed, that is, activation conditions should be changed in order to provide a product of activated carbon with the capability of substantially complete elimination of mercury and its compounds, in other words, water vapor should be present less than 15 % based on the volume of the activation gas. The thus obtained activated carbon should act as a carrier for alkaline or alkaline earth metal sulfide, wherein the finished activated carbon preferably has micropore radii: 50-5000 nm (5-500 angstroms) and specific surface of 200-2500 m 2 /g. Other objects and advantages will be apparent through description in this specification. Reference will be made to an activation gas, which normally contains water vapor and carbon dioxide gas. Then, the activation gas of the present invention is not limitative as to a content of carbon dioxide component, but water vapor content should be less than 15 % volume based on the volume of the activation gas. In contrast to the present invention, normal activation gases contain water vapor in the range of 40-60 %, i.e. a much higher level. The background is that the activation rate for carbonaceous materials caused by water vapor is remarkably higher than that by carbon dioxide, so that the composition of the activation gas is normally designated to have a higher content of water vapor than that of carbon dioxide. Therefore, limitation imposed on the present invention provides the subject gas which causes activation conditions which will effect much milder and slower activation rate as compared with normal gases for a similar purpose. As shown hereinafter in Examples 1 - 4 and Comparative Examples 1- 4, and Table 1, the activation under high water vapor contents results in lowering the absorption of mercury. The detailed mechanism to explain why the activation under low water vapor content gives higher mercury adsorption is not clear, though, it is presumed that such activation condition builds up such micropore structures which will adsorb mercury more suitably. In the activation process, it is preferable to maintain similar gas composition to the activation gas even in the step of cooling until activated carbon is cooled under 300°C and then to remove such activated carbon, wherein said similar gas composition does not mean that cooling gas should have the same composition as activation gas, but it means that in the circumstance that nitrogen gas, carbon dioxide gas or mixture thereof ( content of oxygen, hydrogen are less than 1 - 2 % ) is are used for activation, such gas composition is allowable for cooling which continues the process after activation. Raw material for the activated carbon is not limitative, but acceptable where such comes from coal, charcoal, coconut shell, timber or synthetic resin. Regarding the specification of the activated carbon for use as carrier, micropore radii: 5 - 500 angstroms, preferably 10 - 100 angstroms, and specific surface: higher than 200 m 2 /g, more preferably higher than 500 m 2 /g, and in converse, preferably lower than 2500 m 2 /g, more preferably lower than 1500 m 2 /g. Further, a residue after strong heating of less than 10 weight % is preferable. Higher elimination of mercury will be attained with use of activated carbon having its specification in preferable range. The form of activated carbon is not limitative, and any form of powder, crushed particles, cylindrical form, globular form, fibrous form, or honeycomb is acceptable. Such a form as granular or cake is manufactured by the ordinary process including kneading of carbonaceous material ( 100 parts ), mixed with oil pitch or coal tar ( 30 - 60 Parts ) as binder, and then such carbonaceous material is subjected to activation. The present invention allows the activated carbons prepared specifically as noted to be used in the state of simple body or as it is, and further allows such activated carbons to be converted to a carrier carrying a substance, that is, activated carbon with alkaline metal sulfide and/or alkaline earth metal sulfide is preferable. These sulfur containing compounds will enhance the adsorption of mercury with scarce sulfur dissolution into liquid hydrocarbon. Alkaline metal sulfide and alkaline earth metal sulfide as noted are not limitative, of which examples are: lithium sulfide, sodium sulfide, potassium sulfide (alkaline metal sulfide); magnesium sulfide, calcium sulfide (alkaline earth metal sulfide). Sole kind or joint use of two or more kinds is acceptable. As will be shown hereafter, Examples 5 - 8 and Table 2 indicate that, among metal sulfides, carbon carrying sodium sulfide performs optimum results as to elimination of mercury. The range of carried alkaline or alkaline earth metal sulfides is not particularly limited, but the range of 0.1 - 30 weight %, based on the weight of the carrier is prefered. In the range less than 0.1 %, resultant adsorption of mercury is not high enough, and more than 30 %, adsorbability of the carrier is hindered by the carried compound and resultant adsorption of mercury is also not high enough. When the metal sulfide carried on activated carbon of this invention is used to eliminate mercury and its compounds in liquid hydrocarbon as adsorbent, sulfur carried on the activated carbon scarcely dissolves into liquid hydrocarbon during contacting the activated carbon with liquid hydrocarbon. As shown hereinafter in Examples 5 - 8 and Table 2, the amount of sulfur dissolved into liquid hydrocarbon is extremely low level ( less than 1.0 mg/Kg ). This is another advantage of this invention, because liquid hydrocarbons containing sulfur will harm catalysts seriously which are often applied during process for such intermediates of petroleum products and petrochemical products. Activated carbon prepared by conventional process which carries sulfur or its compound, has high adsorbability of mercury in liquid hydrocarbons, as mentioned in prior art description. However, large amount of sulfur and its compound is dissolved into liquid hydrocarbon, during contacting the activated carbon with liquid hydrocarbon, as shown hereinafter in Comparative Examples 5, 6 and Table 2. Therefore, these activated carbons are not allowed to be used for mercury adsorption of liquid hydrocarbons. Reference will be made to the process of providing the carried substance or compound with the activated carbon carrier, a carried compound such as alkaline metal sulfide is dissolved into aqueous ammonia solution, or other inorganic or organic solvent such as acetone, alcohol and into this solution, the activated carbon is submerged into the solution in order to adsorb the compound and then dried in an oven at 110 -400 °C, preferably 110 - 200°C. An alternative method for the submerging noted above is, for example, to apply the compound solution, like shower or spray, onto the activated carbon, wherein stirring the activated carbon improves uniform reception. Regarding the conditions while drying the applied activated carbon as noted, limitation is not present and then, air, nitrogen, or combustion gas from liquefied petroleum gas is usable. Liquid hydrocarbons, objective of the inventive method, are meant to include such broad scope that the adsorption through contact between solid phase activated carbon and liquid phase hydrocarbon is feasible, and they are mainly found in intermediates leading to petroleum products and petrochemical products, for example, naphtha or other petroleum intermediate or in-process goods consisting of hydrocarbons with 6 - 15 carbon atoms and being liquid at ambient temperature. Others are liquefied oil based or coal based hydrocarbons, for example. As for hydrocarbons having not more than 5 carbon atoms and being gaseous at ambient temperature, such hydrocarbons are applied to the inventive method after liquefaction by pressure. In particular, liquefied natural gas ( LNG ), liquefied petroleum gas ( LPG ), liquefied ethylene, liquefied propylene, and naphtha are handled in the liquid state, and such material may be used in the present invention with no preliminary treatment to liquefaction, so that the inventive method provides industrial utility for those hydrocarbons indicated above. These hydrocarbons may be single components or mixtures of two or more components. In the cases that the adsorption is performed using a fixed bed filled with activated carbon, particles size thereof may be 4.75 - 0.15 mm, preferably 1.70 - 0.50 mm. The term mercury referred to in the present invention can be mercury contained in the liquid hydrocarbon in the form of the metal as well as in the form of inorganic or organic compounds of mercury. The concentration of mercury in the liquid hydrocarbon is not particularly limited and with the method of the present invention mercury can be eliminated to reach a trace level or an extremely low level. In the case that the mercury concentration is not at 100 µg/kg, 1 kg of the inventive activated carbon will eliminate about 0.1 - 10 g mercury, though necessary amount of the activated carbon depends upon target elimination amount. Assuming that liquid hydrocarbon is for use as a feed in a reforming process, normally such feed contains mercury at 0.002 - 10 mg/kg. Therein prior filtration of the liquid hydrocarbon is desirable in order to eliminate sludge therefrom wherein the mercury component which is separable together with the sludge is desirably removed. EXAMPLES Example 1 Carbonized coconut shell, mesh cut mass of 4 - 14 mesh ( larger than 1.7 mm, smaller than 4.75 mm ) was used as raw material of activated carbon. This material was activated under conditions of liquefied petroleum gas combustion gas ( gas composition: nitrogen 80 %, oxygen 0.2 %, carbon dioxide 9.8 %, water vapor 10 % ) at 900 °C, and resultant specific surface 1400 m 2 /g was reached and cooled in the same gas down to 300 °C. Thus prepared activated carbon was crushed to mesh range 10 - 32 ( larger than 0.5 mm, smaller than 1.7 mm ). This activated carbon has an ash content ( residue after strong heating ) of 2.5 weight %. Light naphtha ( hydrocarbon C 6 to C 9 ) containing mercury at different levels was used and adsorption on different levels as measured using the activated carbon noted above, wherein 20 % of mercury contained in the light naphtha was shared by organic mercury compound. The light naphtha (100 ml) was contacted with the activated carbon (10g) under mixing. Mercury concentration of the naphtha after the adsorption was measured after 2 hours in the 3 cases of mercury start concentrations of 100, 10, and 1 µg/kg, and thereby the performance was rated and shown in Table 1 wherein O indicates good, or acceptable and × indicates fail or unacceptable. As shown in Table 1, mercury adsorption by the activated carbon is good, and no organic mercury compound is found in the naphtha subsequent to the adsorption. In conclusion, the inventive activated carbon is proved to have superior performance. Example 2 and 3 The activated carbon particles were prepared in the same way as in Example 1 except that a different gas composition was used, and mercury adsorption was measured in the same way as in Example 1. Results are shown in table 1. The performance is rated good at each case. Thus it is proved that the activation gas containing water vapor less than 15 %, based on the volume of the activation gas, leads the performance to be good. Example 4 Phenol resin fiber (NIPPON KYNOL CO., LTD. Brandname KYNOL FIBER ) was used to prepare to the activated carbon. Except that this fiber was used, activated carbon fiber was prepared in the same way as in Example 1. The mercury adsorption by this fiber is proved to be good as shown in Table 1. Comparative Examples 1 to 4 Activated carbon particles and activated carbon fibers made from phenol resin fiber were prepared in the same way as in Examples 1 and 4 except that the activation gas composition was changed, and then mercury adsorption was measured, and results are shown in Table 1. It is proved that the activation gas containing water vapor more than 15%, based on the volume of the activation gas, reduces the adsorption of mercury as well as organic mercury largely, and hence, such activated carbon is not allowed to be used for mercury adsorption. Example 5 The activated carbon obtained in Example 1 was used. Sodium sulfide solution (Na 2 S · 9H 2 O, reagent first class, KATAYAMA KAGAKU KOGYO) wherein 7.5 g was dissolved in 100 ml of water was sprayed onto the activated carbon under mixing. The thus treated activated carbon was dried for 3 hours at 130°C to yield the activated carbon carrying 1 weight % Na 2 S expressed as sulfur. Adsorption of mercury was measured in the same way as in Example 1 and results are shown in Table 2. The activated carbon carrying sodium sulfide shows good performance and no dissolution of sulfur is found, and thus field service for mercury elimination is feasible. Example 6 The activated carbon was prepared in the same way except that the carried sodium sulfide amount was 2 weight %. As shown in Table 2, good mercury adsorption and no dissolution of sulfur is found. Examples 7 and 8 Activated carbons carrying a sulfur containing compound were prepared with potassium sulfide and sodium sulfide wherein the activated carbon with potassium sulfide was prepared in Example 7 and the one with sodium sulfide was prepared in Example 8. These activated carbons show good mercury adsorption as shown in Table 2, and no dissolution of sulfur is found. Comparative Example 5 The activated carbon obtained in Example 1 was used to prepare the activated carbon carrying sulfur, wherein 100 g of activated carbon particles were mixed uniformly with powder sulfur (1g) and heated to yield an activated carbon carrying 1 weight % of sulfur. Adsorption was measured as in Example 1 and results are shown in Table 2. As is indicated in Table 2, the activated carbon carrying sulfur has good mercury adsorption, but dissolution of sulfur is much and therefore unacceptable for mercury adsorption treatment of liquid hydrocarbons including naphtha or other oil products. Comparative Example 6 The activated carbon obtained in Example 1 was used to prepare the activated carbon carrying thiourea, wherein activated carbon particles were sprayed uniformly with thiourea solution and heated and dried at 130 °C, for 3 hours to yield an activated carbon carrying 1 weight % of the organic sulfur compound. Adsorption was measured as in Example 1 and is shown in Table 2. As shown in Table 2, the activated carbon carrying thiourea shows good mercury adsorption, but dissolution of sulfur is much and therefore unacceptable for mercury adsorption treatment of liquid hydrocarbons including naphtha or other oil products. Example 9 The activated carbon obtained in Example 1 was packed uniformly in a column ( diameter: 30 cm, height: 1 m ), whereinto light naphtha containing mercury at a concentration of 6 µg/kg was passed at a LV ( linear velocity) of 0.30 m/min. The thus treated naphtha contained mercury less than 0.1 µg/kg, and substantially complete elimination was proved. Also organic mercury compounds were completely eliminated and dissolution of sulfur into naphtha was less than 0.1 mg/kg, and thus, scarce dissolution was proved. The mercury elimination from liquid hydrocarbons according to the present invention has proved to show superior performance by combining the specially prepared activated carbon or activated carbon carrying alkaline metal sulfide so that a slight amount of mercury contained in liquid naphtha is substantially completely eliminated and that no side effect of dissolution of the carried sulfur component into the liquid hydrocarbon is found. Liquid hydrocarbons containing mercury or sulfur will harm catalysts which are often applied during process for such intermediates of petroleum products and petrochemical products. Thus the present method is advantageous to processing of such oil intermediates.

Claims: A method of eliminating mercury and its compounds contained in liquid hydrocarbons comprising contacting of activated carbon with liquid hydrocarbons, wherein the activated carbon has been prepared by activating a carbonaceous material with activation gas containing water vapor in an amount less than 15% based on the volume of the activation gas. The method of claim 1, wherein the activated carbon carries alkaline metal sulfide or alkaline earth metal sulfide.

Inventors: IKUSHIMA KENJI, MIMOTO KENJI, NAKAYAMA AKINORI, OHTSUKA KIYOTO, IKUSHIMA, KENJI, MIMOTO, KENJI, NAKAYAMA, AKINORI, OHTSUKA, KIYOTO
Applicants: KURARAY CHEMICAL KK, TAIYO ENGINEERING COMPANY LIMI, KURARAY CHEMICAL CO., LTD., TAIYO ENGINEERING COMPANY LIMITED
Application year: 1996
Main classification: C10G25
IPC codes: C10G25, C10G29, B01J20, C01B31