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GB2088839A - Borate Sequestered Vanadium Solutions - Google Patents

Borate Sequestered Vanadium Solutions Download PDF

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Publication number
GB2088839A
GB2088839A GB8039130A GB8039130A GB2088839A GB 2088839 A GB2088839 A GB 2088839A GB 8039130 A GB8039130 A GB 8039130A GB 8039130 A GB8039130 A GB 8039130A GB 2088839 A GB2088839 A GB 2088839A
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United Kingdom
Prior art keywords
borate
vanadium
sequestered
ratio
composition
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GB8039130A
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GB2088839B (en
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British Gas Corp
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British Gas Corp
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Priority to GB8039130A priority Critical patent/GB2088839B/en
Publication of GB2088839A publication Critical patent/GB2088839A/en
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Publication of GB2088839B publication Critical patent/GB2088839B/en
Expired legal-status Critical Current

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1493Selection of liquid materials for use as absorbents

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Catalysts (AREA)

Abstract

Sequestered vanadium solutions comprise an aqueous solution of a metal or ammonium vanadate in a concentration of from 1 to 5 gm/litre together with a borate in which the ratio of vanadium to borate is from 2.0:1 to 3.0:1. Alkaline solutions of such borate sequestered vanadium together with at least one salt of an anthraquinone disulphonic acid may be used in the Stretford Process for the removal of hydrogen sulphide from gases or non-polar liquids.

Description

SPECIFICATION Borate Sequestered Vanadium Solutions This invention relates to sequestering or chelating agents, more particularly the invention relates sequestrants for use in redox systems employed for the removal of hydrogen sulphide from gases and non-polar liquids.
In U.K. Patent Specification No. 948270, there is described a process (known as the Stretford Process) for removing hydrogen sulphide from gases or non-polar liquids wherein inter alia the gas is contacted with a redox system comprising an aqueous alkaline solution of a mixture of anthraquinone disulphonic acid salt and an alkali metal or ammonium vanadate. This aqueous alkaline solution is otherwise known as a "Stretform Liquor". In addition to the active redox constituents the Stretford Liquor may contain pH buffering agents to maintain the desired level of alkalinity and sequestrants to maintain the vanadium component in solution. Typical buffering agents include borax in a concentration of from about 5 to 10. gm/litre (calculated as Na2B40,) and typical sequestrants which have been used include citrates and EDTA compositions.
We have surprisingly found that borates have a beneficial sequestering effect upon vanadium in concentrations outside of those required for pH buffering purposes.
Sequestering compounds which contain boron are known. For example U.S. Patent Nos.
3539463 and 3539464 describe the use of borate esters of sodium B-glucoheptonate as sequestrants for alumina and U.S. Patent No.
3852213 describes compositions comprising a copolymer of polyvinyl methyl ether and maleic anhydride and from 3~30% of a borate for use in chelating calcium, magnesium, iron or manganese ions.
However, the use of borates alone for chelating vanadium is not known.
In accordance with the present invention there is provided a chelated vanadium aqueous solution comprising a metal or ammonium vanadate and a water soluble borate wherein the concentration of vanadium in solution is from 1 to 5 gms/litre and the ratio of vanadium to borate is from 2.0:1 to 3.0:1.
The vanadate may be added as an ortho-, meta-, or pyrovanadate. The borate may be added in the form of a tetra-borate, borax being a conveniently available form. Alternative sources of borate ion may be used for example, sodium meta borate.
The invention is particularly useful for the chelation of vanadium in Stretford Liquors and the presence of borates has a beneficial effect upon the operation of the Stretford Process in that vanadium loss can be eliminated or substantially reduced.
Thus the present invention further provides a process for the removal of hydrogen sulphide from gases or non-polar liquids wherein said gas or liquid is contacted with an aqueous alkaline wash liquor comprising at least one salt of an anthraquinone disulphonic acid a vanadate, wherein the concentration of vanadium in the liquor is from 1 to 5 gms/litre and a borate wherein the ratio of vanadium to borate is from 2.0:1 to 3.0:1.
For typical Stretford application the vanadium to borate ratio is preferably about 2.5:1.
The present invention will be illustrated by the following Example in conjunction with the accompanying drawings, in which: Figure 1 is a graph showing the effect of borates on the buffering capacity of Stretford Solutions, Figure 2 is a graph showing the effect of borate on the reoxidation of the Stretford Liquor during the oxidation phase of the redox cycle, and Figure 3 is a graph showing the effect of borate as a sequestrant for vanadium.
A Stretford Solution precursor was prepared containing: 5 gm/l Na2C03-25 gm/l NaHCO3-pH 8.85 4 gm/I-sodium anthraquinone disulphonate M/32-sodium meta-vanadate (1.7 gm/l-- vanadium) a) To each of six samples of the precursor solution was added borax (Na2B4O7) to give the following respective amounts of borate.
Borate Concentration V:B 20 7 ratio (i) O gm/l.
(ii) 2.7gm/l. 2.5:1 (iii) 3.8gm/l. 1.76:1 (iv) 5.0gm/l. 1.32:1 (v) 10.gm/l. 0.66:1 (vi) 15.gm/l. 0.44:1 The acidity of each solution was increased by adding dilute sulphuric acid and the pH measured against increase in acidity. The results of plotting pH change against increase in acidity are shown in Figure 1.
The working pH range for Stretford Liquors is from pH 8.6 to pH 8.85. Thus from a consideration of Figure lit will be apparent that only solutions (v) and (vi) can provide adequate buffering whereas say solution (ii) has little buffering effect.
B) Each of solutions (i), (ii), (iv) and (v) was employed in a redox system wherein each solution was loaded with hydrogen sulphide to a level of 0.5 gm/l and left to stand for 10 minutes.
At the end of the standing period air was blown into the samples for 40 minutes at a rate of 80 mi/min.
During the air-blowing each sample was analysed at intervals to determine the amount of vanadium being reoxidised from vanadium (IV) (vanadium (V) was present prior to H2S loading but was reduced to vanadium (IV) on addition of H2S). The amount of reoxidized vanadium is expressed as a percentage of the V present prior to commencement of H25 loading and is shown plotted against the reoxidation time in Figure 2. It will be seen from Figure 2 that 100% reoxidation can be achieved in 30 minutes with Stretford Liquors containing 2.7 gm/l borate whereas with those solutions having effective pH buffering action the reoxidiation rates are only of the order of 80% at completion of the reoxidation period.
c) Three Stretford Liquors, each comprising the precursor, as described above, and respectively, 0.0 gum/1,1.35 gm/l and 2.7 gm/l of borate were subjected to H2S loading (reduction) for 25 minutes and allowed to stand under reduced conditions, samples being extracted periodically and analysed for total vanadium content. The vanadium loss (calculated as a percentage) was plotted against time and results shown in the graph of Figure 3. It will be noted that the V:B4O7 ratios for the samples containing 1.35 and 2.7 gm/i borate were 5:1 and 2.5:1 respectively.
From a review of the results given in Figure 3, it will be appreciated that significant vanadium loss can be prevented using V:B4O7 ratios in accordance with the invention and it will be seen that several advantages accrue to the Stretford Process in that (a) Vanadium loss is significantly reduced and (b) Effectively complete reoxidation can be speedily achieved.

Claims (5)

Claims
1. A chelated vanadium composition comprising an aqueous solution of a metal or ammonium vanadate wherein the concentration of vanadium is from 1 to 5 gm/litre and a water soluble borate wherein the ratio of vanadium to borate is from 2.0:1 to 3.0:1.
2. A composition as claimed in Claim 1 wherein the borate is borax.
3. A composition as claimed in Claim 1 or Claim 2 which also contains at least one salt of an anthraquinone disulphonic acid and has an alkaline pH.
4. A composition as claimed in any of Claims 1 to 3 wherein the vanadium to borate ratio is about 2.5:1.
5. A process for the removal of hydrogen sulphide from gases or non-polar liquids wherein said gas or liquid is contacted with an aqueous alkaline wash liquor comprising at least one salt of an anthraquinone disulphonic acid, a vanadate, wherein the concentration of vanadium in the liquor is from 1 to 5 gm/litre and a borate, wherein the ratio of vanadium to borate is from 2.0:1 to 3.0:1.
GB8039130A 1980-12-05 1980-12-05 Borate sequestered vanadium solutions Expired GB2088839B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8039130A GB2088839B (en) 1980-12-05 1980-12-05 Borate sequestered vanadium solutions

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8039130A GB2088839B (en) 1980-12-05 1980-12-05 Borate sequestered vanadium solutions

Publications (2)

Publication Number Publication Date
GB2088839A true GB2088839A (en) 1982-06-16
GB2088839B GB2088839B (en) 1984-03-21

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4460554A (en) * 1983-03-31 1984-07-17 Purtec Systems, Inc. Method of removing H2 S from a gas stream utilizing boron-vanadium, quinone solution and iron scavaging composition
US5004588A (en) * 1988-01-15 1991-04-02 Chevron Research & Technology Company Process for removal of hydrogen sulfide from gaseous stream

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4460554A (en) * 1983-03-31 1984-07-17 Purtec Systems, Inc. Method of removing H2 S from a gas stream utilizing boron-vanadium, quinone solution and iron scavaging composition
US5004588A (en) * 1988-01-15 1991-04-02 Chevron Research & Technology Company Process for removal of hydrogen sulfide from gaseous stream

Also Published As

Publication number Publication date
GB2088839B (en) 1984-03-21

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