AU639833B2

AU639833B2 - Mercury removal

Info

Publication number: AU639833B2
Application number: AU85557/91A
Authority: AU
Inventors: Patrick John Denny
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Johnson Matthey PLC
Priority date: 1990-10-10
Filing date: 1991-10-03
Publication date: 1993-08-05
Anticipated expiration: 2011-10-03
Also published as: NO913960D0; CA2052888C; NZ240095A; EP0480603A2; AU8555791A; CA2052888A1; DE69109041D1; EP0480603A3; EP0480603B1; NO178427B; NO913960L; GB9022060D0; NO178427C; DE69109041T2

Description

AUSTRALIA

Patents Act 65Qi"l 7~j~ COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: S Imperial Chemical Industries PLC I S* Actual Inventor(s): S, Patrick John Denny Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA I' -Invention Title: :MERCURY REMOVAL 'Our

POF

Or Ref 230420 Code: 1453/1453 s The following statement is a full description of this invention, including S'the best method of performing it known to applicant (3 1- 6006 H35975 Mercury Removal This invention relates to a process for the removal of mercury from a gaseous or liquid stream.

GB-B-1533059 discloses the use of a pre-sulphided absorbent comprising copper f.r th b =orption of mercury from a natural gas stream containing mercury. The pre-sulphided absorbent is prepared by forming a precursor comprising a copper compound, e.g. an extrudate comprising basic copper carbonate and a refractory cement binder, and then contacting the precursor with a gaseous stream containing a sulphur compound, e.g. hydrogen sulphide, so as to fully sulphide the copper compound. The pre-sulphided absorbent is then used to remove mercury from a sulphur-free natural gas stream. It is also shown that an absorbent comprising copper in the reduced, i.e. metallic, state is less effective at absorbing mercury than the pre-sulphided absorbent.

Japanese kokoku JP-75001477 shows that a pre-sulphided absorbent comprising copper sulphide is capable of absorbing mercury from a stream of electrolytic hydrogen containing mercury.

S 20 It has now been found that a pre-sulphided absorbent comprising a metal sulphide, in particular a pre-sulphided absorbent comprising copper sulphide, may exhibit a change in its mercury absorption capacity during storage such that a freshly pre-sulphided absorbent is more readily able to absorb mercury 25 than a similar absorbent which has been stored for subsequent use.

It has also been found that the ability of an absorbent comprising a metal sulphide to absorb mercury is dependent on the conditions under which the sulphiding is conducted. Furthermore, it has also found that it is possible to improve the performance of a mercury removal process using an absorbent comprising a metal sulphide by concomitantly forming the metal sulphide during the absorption of the mercury.

removal process comprising conr rning feed wRnrhni-in mphidc apabl of ja I> /r^ r lB Accordingly the present invention provides a process for the removal of mercury from a gaseous or liquid mercury-containing feed stream comprising forming a sulphided absorbent by contacting an absorbent precursor containing oxides, carbonates and/or basic carbonates of copper and/or iron with a stream containing at least one sulphur compound selected from hydrogen sulphide, carbonyl sulphide, mercaptans, and polysulphides, and then, without exposing the sulphided absorbent to an oxygen-containing gas, contacting said mercury-containing stream with said sulphided absorbent.

The present invention further provides a process for the removal of mercury from a gaseous or liquid mercury-containing feed stream also containing at least one sulphur compound selected from hydrogen sulphide, carbonyl sulphide, mercaptans, and polysulphides, comprising by contacting an absorbent precursor containing oxides, carbonates and/or basic carbonates of copper and/or iron with said feed stream whereby said absorbent 20 precursor is sulphided at the same time as mercury is absorbed.

0665i

S

t T.

H35975 -aborbing prrry anr wherein the absorbent i'P ed by contacting in situ a precurs r prising a metal compound capable of forming the sulphide with a first stream containing a The present invention may be used to treat bc&h liq;'id and gaseous feed streams. Gaseous feed streams which are susceptible to being treated by the present invention include those which inherently contain both mercury and a sulphur compound e.g. certain natural gas riccms, or a mercury containing gaseous stream to which a sulphur compound has been added to effect mercury absorption. Suitable liquid streams include mercury containing LPG and naphtha streams.

As stated above, conventional absorbents comprising copper sulphide are pre-sulphided, i.e. they are sulphided prior to use, and are then often stored in contact with air. It has now 0*

C

e g *e

C

gee g .g

C

g Ce *c S gee C Ce

C

C Ce been found that during storage substantial sulphate are formed which is significantly absorbent than copper sulphide. Thus, the sulphate is undesirable and it is therefore absorbent used in the present invention is free. To avoid the formation of the metal used in the present invention is sulphided pre-sulphided and stored subsequent to use an other oxygen containing gas. Thus, the quantities of copper less effective as a presence of a metal preferred that the substantially sulphate sulphate, the absorbent in situ, i.e. it is not in contact with air or precursor may be fee g sulphided using a first stream which contains a suitable sulphur compound to form the absorbent and then held in-situ in a non-sulphate forming environment. It is preferred, however, that the sulphiding of the precursor and the absorption of mercury occur together, i.e. they are concomitant, thereby avoiding the need for a separate sulphiding process and the subsequent storage difficulties. Thus, the present invention may be advantageously used on streams which contain both mercury and sulphur compounds.

Preferably the concomitant absorption of mercury and sulphur is conducted at a temperature below 100 0 C in that at such temperatures the overall capacity for mercury absorption is ~uU 0 3 H35975 increased. Temperatures as low as 20 0 C may be used to good effect in the present invention.

The mercury may be in the form of mercury vapour, organomercuric, or organomeriurous compounds. Typically the c" n"Ser Pton n of nme.rcir.y in a gaseous feed stream is from 0.01 to 500 ug.Nm- 3 and more usually between 10 to 200ug.Nm 3 The sulphur compound used to sulphide the precursor may be one or more sulphur compounds such as hydrogen sulphide, carbonyl sulphide, mercaptans and polysulphides. Where concomitant sulphiding and mercury absorption occurs the amount of sulphur compound that is present depends on the type of sulphur compound and metal compound used. Usually, a concentration ratio, as defined by the ratio of sulphur compound (expressed as hydrogen sulphide) concentration to mercury concentration of at least one, and preferably of at least 10 is used so that the precursor is sufficiently sulphided. Should the initial concentration of the sulphur compound in the feed stream be below o .the level necessary to establish the desired ratio of sulphur compound to mercury compound concentration then it is preferred 20 that the concentration of the sulphur compound is increased by any suitable method, e.g. by the addition of further quantities of the sulphur compound, or by the use of a molecular sieve or semi-permeable membrane to selectively increase the concentration of the sulphur compound.

goo**: S* 25 The metal may be any which provides a metal compound :which shows a suitable capacity for being sulphided and for mercury abso--' Jn. Examples of suitable metals are iron and see* copper, and in particular copper. Certain other metals, however, are generally unable to provide either compounds which can be suitably sulphided, e.g. aluminium, or sulphided compounds which can adequately absorb mercury e.g. zinc. Nevertheless, a compound of such an other metal may be present as a binding or support agent which improves the structural integrity of the absorbent, and/or as a promoter which enhances the sulphiding of the precursor and/or the absorption of mercury by the absorbent.

4 H35975 A metal compound suitable for use in an absorbent Trecursor is one which may be readily sulphided and may include the oxide, carbonate, and/or basic carbonate. A particularly suitable metal compound is thus basic copper carbonate.

The precursor c.p riiz.g the mital ;ecmpcund may be in any suitable form, e.g. as a granule, extrudate, or tablet.

Particularly effective absorbents are those which are prepared from precursors having a capacity to be highly sulphided. Thus, it is preferred that the amount of sulphide forming compound of the metal present in the precursor is such that the precursor may be sulphided to achieve a sulphur loading of at least 15Z w/w, and particularly at least 20Z w/w.

The present invention is illustrated by the following examples.

Example 1 A freshly sulphided material containing copper and zinc sulphides, having a total sulphur content of 19Z w/w was tested for its ability to remove mercury from a simulated natural gas feed stream. The material had previously been sulphided at 20 0

C

and 1 atm. using a natural gas stream which was saturated with water, and contained 1% v/v hydrogen sulphide.

Mercury removal was assessed at 20 0 C, 1 atm., by contacting the sulphided material at a space velocity of 10000 hr 1 with methane containing 1.8 ppm mercury.

Example 2 Example 1 was repeated except that the sulphided material was stored under ambient conditions, and in contact with air, for 8 months prior to the mercury removal assessment.

The results of Examples 1 and 2 are shown in Table 1.

S. 2 *0 0 aut a So a Sy a 25n a. a H35975 Days on line <1 9 Table 1 Mercury Slip Z Example 1 Example 2 0.0 100.0 0.0

S.

S S

S

S.

s

S

S.

*e S 20 a* 0 a 16 18 19 10.0 It can thus be seen that the ability of the sulphided material to remove mercury diminishes on storage. Analysis of the materials used in Examples 1 and 2 showed the presence of copper sulphate in the material of Example 2 and the absence of copper sulphate in the material of Example 1.

Example 3 Example 1 was repeated using a sulphided material containing 6.2Z w/w of sulphur.

Example 4 Example 3 was repeated except that the sulphiding was conducted at a temperature of 110 0 C, to a sulphur loading of 17.7z w/w.

Example Example 4 was repeated except that the sulphur loading was to 24Z w/w.

The results of Examles 3 to 5 are shown in Table 2.

S

Table 2 Mercury Slip Hours on-line Example 3 Example 4 Example 24 0.0 1.0 0.0 48 0.0 2.4 0.0 72 0.0 3.8 0.0 96 4.5 5.8 0.0 120 9.4 >12.5 0.0 144 12.1 0.6 It can thus be seen that although the material of Example 4 was H35975 laden with more than twice the amount of sulphur than that of Example 3, the material of Example 3 was superior in performance to that of Example 4. Example 5 shows that for materials which have been sulphided under the same conditions, the greater the s~ninhur loading '-hp more mercury can be absorbed before mercury slip occurs.

Example 6 Example 1 was repeated using a material of the same composition as that of Mass A of UK patent, GB-B-1533059.

The freshly sulphided material was similarly assessed for its mercury removal capacity. After 2 days on-line a mercury slip of 2.5Z was observed. The mercury slip increased approximately at a rate of 2.5Z per day until the end of the assessment on the fifth day.

Example 7 In this Example the non-sulphided starting material of Example 1 was placed in sample baskets, and inserted into an industrial operating unit used for the removal of sulphur compounds, principally hydrogen sulphide (60 70 ppm), from natural gas containing 11% v/v carbon dioxide. The natural gas also contained mercury as a trace component. The unit was operated at about 70 0 C, and 50 bar. After a period of time on line, the sample baskets were retrieved and analysis of the material for sulphur and mercury contents performed.

The material was shown to be sulphided and to have a sulphur content of 18.1%. Furthermore, the material was shown to have a mercury content of 2.2% w/w.

Example 8

S.

@0

S

At the same time as the sample baskets of I inserted into the operating unit, additional sample containing a zinc oxide sulphur absorbent were also These were then analysed in the same manner as those The zinc oxide sulphur absorbent was shown sulphur content of 17.3Z w/w. No mercury was shown, have been absorbed by the material.

Example 7 were baskets inserted.

of Example 7.

to have a however, to

Claims

1. A process for the removal of mercury from a gaseous or liquid mercury-containing feed stream comprising forming a sulphided absorbent by contacting an absorbent precursor containing oxides, carbonates and/or basic carbonates of copper and/or iron with a stream containing at least one sulphur compound selected from hydrogen sulphide, carbonyl sulphide, mercaptans, and polysulphides, and then, without exposing the sulphided absorbent to an oxygen-containing gas, contacting said mercury-containing stream with said sulphided absorbent.

2. A process for the removal of mercury from a gaseous or liquia mercury-containing feed stream also containing at least u. sulphur compound selected from hydrogen sulphide, carbonyl sulphide, mercaptans, and polysulphides, comprising by contacting an absorbent precursor containing oxides, carbonates and/or basic carbonates of copper and/or iron with said feed stream whereby said absorbent precursor is sulphided at the same 20 time as mercury is absorbed.

3. A process as claimed in claim 2 wherein the sulphur compound-containing stream contacts the precursor at a temperature not exceeding 100 0 C.

4. A process as claimed in claim 2 or claim 3 wherein 25 ratio of the concentration by volume of the sulphur compound to the concentration by volume of mercury in the feed stream is at least 1:1.

5. A process as claimed in claim 4 wherein the sulphur-compound concentration of a mercury-containing 30 stream having a ratio of the volume concentration of sulphur compound to the volume concentration of mercury below 1:1 is increased to give the feed stream having a sulphur compound to mercury volume concentration ratio of at least 1:1.

6. A process as claimed in any one of claims 1 to wherein the precursor comprises basic copper carbonate.

7. A process as claimed in any one of claims 1 to 6 Swherein the precursor can be sulphided to a sulphur Scontent of at least 15% w/w. Z Si~F 7- -8

8. A process as claimed in any one of claims 1 to 7 wherein the feed stream is gaseous and has a mercury content from 0.01 to 500 pg.Nm 3

9. A process, as claimed in claim 1 or 2, substantially as hereinbefore described with reference to anay one of the examples. DATED: 24 May, 1993. PHILLIPS ORMONDE FITZPATRICK ATTORNEYS FOR:- IMPERIAL CHEMICAL INDUSTRIES PLC 0665i JOCZAA0.2~4 3. 9 H35975 Abstract A process for the removal of mercury from a stream wherein an absorbent comprising a metal sulphide is prepared in situ, sreferably by the stream also containing a sulphur comp:-nd thereby concomitantly preparing the mercury absorbent and absorbing the mercury, such that the formation of ineffective and undesired metal compounds e.g. sulphates is avoided. ae o *5