NO881817L - PROCEDURE FOR RECOVERING HYDROGEN AND SULFUR FROM H2S-CONTAINING GAS. - Google Patents

Description

Background for the invention.

1. Scope of the invention.

The invention relates to the interaction between transition metal complexes, more specifically palladium complexes with H^S.

More particularly, the invention relates to a method for removing H 2 S from a supply such as e.g. natural gas using a palladium metal-metal bonded dimer that extracts the sulfur and evolves hydrogen.

Field natural gas typically contains undesirable components such as

e.g. H^ S which must be removed because of its corrosive and harmful nature. H^S is now removed by treatment with aqueous ethanolamine in a countercurrent cycle followed by regeneration in a stripper column. Amines are often used and typical amines used are diisopropylamine or methyldiethanolamine. B,B'-hydroxyaminoethyl ether known as diglycolamine is also sometimes used.

The preferred alkanolamines typically have a hydroxyl group to lower the vapor pressure and to provide water solubility. The alkaline amine group absorbs acidic pollutant gases.

However, the alkanolamines suffer from several disadvantages and a problematic and expensive disadvantage is the formation of irreversible reaction products with some pollutants such as COS and CS2.

This results in an economic loss from the loss of alkanolamine if these contaminants are present in the well. Other disadvantages of alkanolamines include relatively high corrosiveness, evaporation losses due to their relatively high vapor pressures, and the often occurring need to keep the water content below 5% necessitating high boiler temperatures.

A refining process for sour natural gas which can remove H^S efficiently but without many of the above attendant disadvantages would be an advance in the field. 2. Description of Related Art.

The palladium dimer complexes Pd^Cl^(ju-dppm)^ are rapport-

tart by A.L. Balch, L.S. Benner, and M.M. Olmstead, Inorg. Chem, 1979, 18, 2996, and by CL. Lee, B.R. James, D.A. Nelson, and R.T. Hallen, Organometallics, 1984, 3, 1360.

The present invention teaches a new and useful process utilizing these complexes.

Summary of the invention.

The invention teaches a method for removing H^S from a gas feed and converting H^S to hydrogen and organosulfur compounds.

The invention is based on the discovery of the reaction:

where X = Cl, Br or I.

The palladium complex (1a) is £pd,,X2( ^u-dppm^J

where dppm is bis(diphenylphosphine)methane and X is Cl, Br or I. The complex (1a) is a bridged dppm dimer,

[<p>d2X2(/U-dppm^J, but is written for simplicity

as Pd2X2(dppm)2-All the above-mentioned complexes are to be understood herein and are defined herein as equivalent representations of the same palladium complex.

This reaction can be carried out in solution under normal conditions. Therefore, Pd2Cl2(dppm)^ can be used to

remove H^ S from acidic natural gases.

It has been found that H^ S can be removed from natural gases by bubbling the gas through a CP^C^ solution of Pd2Cl2 (dppm.) ^

at 10"'' to 10"^ M. The palladium complex extracts sulfur with simultaneous liberation of hydrogen. The sulfur-containing palladium complex can then be oxidized with a weak oxidizing agent to a SO2-containing product, Pd2Cl2(yU-dppm)^

(/ U- SO^) which spontaneously releases SO2 with regeneration of the palladium complex.

Detailed description.

When Pd2Cl2(dppm)2 is dissolved in a solvent such as dichloromethane and exposed to U^ S, PD^ Cl^ i^ PP^) 2 is formed

(^,u-S) together with the evolution of hydrogen gas. Essentially, hydrogen is split off from the HjS molecule and sulfur is incorporated between the two palladium atoms. The reaction can be written as:

or generally as:

wherein P P is bis(diphenylphosphine)methane, and X is selected from Cl, Br or I.

Quantitative measurements show that 97% of the theoretical amount of hydrogen is obtained.

The relative reactivities towards H.,S for the different halogen substituents are:

Pd2Cl2(dppm)2>Pd2Br2(dppm)2>Pd2I2(dppm)2

Pd2Br2(dppm)2 reacts significantly more slowly than

Pd2Cl2(dppm)2, and the iodine-substituted complex even

slower.

The commercial importance of the route over Pd2Cl2(dppm)2

to hydrogen evolution becomes obvious by the realization that Pd2Cl2(dppm)2 can be regenerated from Pd2Cl2(dppm)2

(^u-S) by oxidation of the sulfur to SO-,. The complex thus becomes valuable for the quantitative extraction of hydrogen from H2S.

A one-stage hydrogen separation and sulfur extraction from gas mixtures with mixtures similar to those for oxygen-blown coal gas is made possible by the invention. Quite generally, it can be stated that Pd2X2(dppm)2(/U-S02) can be developed from Pd2X2(dppm)2(/U-S) by oxidation where X = Cl, Br

or I. The oxidation can be carried out using oxidizing agents such as H 2 O 3 , pyridinium chlorochromate, pyridinium dichromate and m-chloroperbenzoic acid. The S02~ adduct is formed in high yields when the oxidation is carried out by

-20°C with two equivalents of oxidizing agent. Oxidation of Pd2Cl2(dppm)2(/U-S) with a small excess of m-chloroperbenzoic acid at -20°C followed by addition of hydrazine to eliminate excess oxidizing agent resulted in the formation of Pd2Cl2(dppm)2(/U- S02) with 76%

isolated dividend.

Although the SC^ adduct tends to spontaneously lose SO2

so that the Pd2X2(dppm)2 catalyst is thereby regenerated,

rate and degree of regeneration of Pd2X2( dppm) 2 catalyst can be maximized or increased by using agents that remove SO2 from the SC^ adduct. The remover to

release SC>2 can be selected from N2 gas introduction, heating or application of reduced pressure.

The violet Pd2X2(dppm)2(/U-SC^) (X = Cl, Br, I)

complexes lose S02 when N2 is bubbled through the solution or if exposed to heat or vacuum. The rate of SO2 loss is reduced in the order of I > Br > Cl judged by color change in samples with similar concentration.

Pd2Cl2(dppm)2 has a solubility of 0.15 M in trichloroethane and 0.027 M in trichloropropane.

The choice of solvent appears to have an impact on the lifetime of the complex in solution.

Pd2Cl2(dppm)2 is soluble in dichloromethane to form a 0.05 M solution. The boiling point (39.7 C) and the vapor pressure

(424 torr at 25°C) of dichloromethane, however, does not make it the easiest solvent to work with.

Solvents more suitable for dissolution of PcJ 2 Cl 2 (dppm) 2 can be determined using the concept of solubility parameters as illustrated by Hildebrand, J., and Scott, R.L. The Solubility of Nonelectrolytes, 3rd ed., Reinhold Publishing Corp., New York, 1950, and Hoy, K.L. J. Paint Technol., 42, 1, 1970.

The solubility parameter (cf) depends on the internal pressure or the cohesive energy density

where AE = f vaporization energy, and

V = molar volume.

The solubility parameter of Pd2Cl2(dppm)2 is judged to be about 10 based on its solubility in dichloromethane.

Possible process solvents could be tetralin (although its UV/VIS spectrum overlaps somewhat with that of Pd^Cl^Cdppm)^), dibutyl phthalate or diphenyl ether.

Table 1 lists several possible solvents. Based on cost, 1,1,2-trichloroethane was preferred for Pd2X2(dppm)2, for X = Cl or Br.

The projected profitability for hydrogen separation by the method according to the invention is dependent on the lifetime of the palladium catalyst in solution. The complex lifetime appears to be affected by the chosen solvent. Laboratory experiments with trichloroethane as solvent seem to suggest that the complex lifetime in trichloroethane may be less than optimal for some commercial operations. More favorable complex lifetimes were found with dichloromethane as solvent. The principles, preferred embodiments and working methods in accordance with the invention are described in the preceding description. However, the invention to be protected herewith is not understood to be limited only to the specific structure and the formulas indicated, as these are to be considered illustrative rather than limiting. Variations and changes can be made by the person skilled in the field without going outside the inventive idea and the scope thereof.

Claims (6)

1. Procedure for extracting sulfur and forming hydrogen, characterized by: - dissolution in a solvent of a palladium complex of the formula Pd2X2(ju-dppm)2, where dpm = bis(diphenylphosphine)methane, wherein X is selected from Cl, Br or I, - H2 S is introduced to the palladium complex in solution whereby sulfur is extracted from the complex from H^ S and forms Pd2 X2 (/U -S) (^ u-dppm),, and hydrogen. 2. Method as stated in claim 1, characterized by the further step of oxidizing Pd2 X2 (/U -S) (/U-dppm)2 to form a (/U-SO2 ) complex of formula Pd2 X2 (^ u-S02 ) (/ U-dppm)2 , whereby the (ju-SO2) complex spontaneously loses SO2 and regenerates the palladium complex. 3- Method as stated in claim 2, characterized by the further step of introducing N2~ gas to the (^ u-SO2 ) complex to facilitate the loss of SO2 for regeneration of the palladium catalyst. 4. Process for extracting sulfur from a H2 S-containing gas and forming hydrogen, characterized in that a palladium complex is formed in solution wherein P P = bis(diphenylphosphine)methane, whereby X is selected from Cl, Br or I, - H2 S is introduced to the palladium complex in solution, - the palladium complex is reacted with H2 S according to the reaction, whereby sulfur is extracted and hydrogen is formed. 5. Method as stated in claim 4, characterized by the further step of oxidation of by exposing this to an oxidizing agent for the formation of a SO^ adduct, as the SOp adduct will often spontaneously lose for regeneration of the palladium complex. 6. Method as stated in claim 5, characterized by the further feature of regeneration of the palladium complex by means of removal agents which cause the SO^ adduct to lose S02 , the removal means being selected from the introduction of N^ gas, heating or application of reduced pressure.