NO823254L - PROCEDURE FOR ELECTROCHEMICAL GASPING OF CARBON-CONTAINING MATERIAL. - Google Patents

Description

The field of the invention

The invention relates to a method by electrochemical gasification of carbonaceous materials in an aqueous acidic electrolyte using an iron catalyst.

State of the art

It is known that carbonaceous materials when mixed with an aqueous, acidic electrolyte in an electrochemical cell through which a direct current is passed react electrochemically and oxidize the carbonaceous material to oxides of carbon on the anode. The electrochemical oxidation of the carbonaceous material on the anode takes place regardless of the nature of the simultaneous cathodic reaction, e.g. may be the production of hydrogen, the electrodeposition of metals, the hydrogenation of unsaturated organic compounds, or any other electrochemical reduction process, or any other process that may take place at the cathode, and furthermore in any compartment of the electrolytic cell in a place other than on the anode, and this will be common knowledge to the person skilled in the art.

In US patent 4268363 is electrochemical gasification

of carbonaceous materials by anodic oxidation described as leading to oxides of carbon on the anode and hydrogen, metallic elements or hydrogenation of coal on the cathode in an electrolytic cell.

In US patent 4279710, electrochemical oxidation of carbon-containing materials on the anode is described and the accompanying formation of hydrogen on the cathode, and also production of electric power by using the hydrogen as fuel in a fuel cell.

In US patent 4226683, hydrogen is produced by reacting coal or carbon dust with hot water which. exists as water at superatmospheric pressure., described. The pressure is regulated by using an inert, dielectric liquid which

. washes the electrodes and which depolarises these by absorption

tion of the gases while the washing takes place.

r US patent document 4233132 describes a method where electrodes are immersed in oil which forms a layer over a

amount of water. When electric current is passed between the electrodes, the water is electrically split. Gaseous hydrogen is collected in the closed space above the oil/water layers, and the oxygen is assumed to react with the constituents of the oil layer.

As recognized in US Patent 4226683, the main problem with the previous application of this principle for the commercial production of hydrogen has been the slow rate of the electrochemical reaction between coal or carbon and water. It has now been found that iron when added to an aqueous acidic electrolyte containing the carbonaceous material, preferably iron in the trivalent form, catalyzes the reaction rate and facilitates the achievement of a more complete oxidation for the electrochemical oxidation of the carbonaceous material on the anode, whereby such processes as the commercial production of hydrogen or electroextraction methods are becoming commercially feasible.

Summary of the invention

As described above, it is well known that carbonaceous materials, such as coal, can be oxidized on the anode in an electrochemical cell containing an aqueous acidic electrolyte, with the simultaneous production of oxides of carbon on the anode and that the anodic half-cell reaction can be utilized in combination with the cathodic half-cell reactions , such as the electrodeposition of a metal M from an aqueous solution of its ions (M<m+>), or production of hydrogen. In the case where e.g.

a metal is electrically deposited, the anodic reaction, with particular regard to the carbon in coal and by representing this with C, can be written as the stoichiometric equation:

in combination with the simultaneous cathodic reaction

The net reaction, i.e. the sum of equations (I) and (II), for the case where m = 1 is:

In the case of electrical separation of e.g. copper, the excretion promoted by the coal can be written in the form of the equation

When producing hydrogen, this anodic reaction,

with particular regard to the carbon in coal and by representing this with C, could be written in the form of the following stoichiometric equation:

in combination with the simultaneous cathodic reaction

The net reaction, i.e. the sum of equations (IV) and (V), is:

In these equations, the symbols (g), (s) and (1) denote gaseous, solid and liquid states, respectively. Equations (I) and (IV), i.e. the reaction between coal and water caused by applying a suitable electrical voltage across a suitable electrochemical cell, represent the reactions which in US patents 4268363 and 4279710 are designated as electrochemical gasification of coal.

A problem with these known methods is the relatively low reaction rate and the incomplete combustion of the carbonaceous material on the anode.

It has now been found that when a sufficient amount of iron is added in elemental form or in the divalent or trivalent valence state or in the form of a mixture of these to the carbonaceous material which is subjected to oxidation in an aqueous, acidic electrolyte at the anode, the reaction rate for the oxidation process increase. The iron catalyst helps complete the oxidation of carbonaceous material and increases the amount of current produced at the anode for a given working voltage.

Detailed description of. the invention

The carbon-containing materials that can be used in the method according to the invention include a wide range of different materials, such as bituminous coal, coal products produced by the dry distillation of coal, lignite, peat, active carbon grades, coke, carbon black grades, graphite, wood or other lignocellulosic materials including forest products, such as wood waste, wood chips, sawdust, wood flour, bark, shavings or wood pellets, including different biomass materials such as land or sea vegetation or waste thereof after other treatment, including grass, various wood chips, crops and waste from crops, waste after ground coffee, leaves, straw, fruit stones, pods, husks, stalks, chaff, cobs or scrap materials including animal faeces, sewage sludge from municipal treatment plants, or plastic or waste or scrap formed during the manufacture of plastics, such as polyethylene or cellulose acetate etc. thus appears that essentially a which h or fuel or waste material. regardless of whether this is a liquid, oil, ash, such as methane or another hydrocarbon or a scrap material containing carbon, with the exception of CC>2/provides a suitable starting material for carbonaceous material for use by the present method.

The special apparatus used to carry out the electrolytic oxidation of the carbonaceous materials is not of decisive importance. The same apparatus and the same methods can essentially be used as used in the electrolytic separation of metals due to the electrolytic splitting of water, as well as those described in US patents 4268363, 4279710, 4226683 and 4233132.

The cells described in US Patent 4,268,363

and 4 2 79710, including "the therein described use of acidic aqueous electrolytes, selection of anode and cathode materials and the optional, but preferred, use of cell membranes to retain the carbonaceous material on the anode side is most preferred,

Although the electrode materials described in US patent documents 4,268,363 and 4,279,710 are suitable for use in carrying out the present method, anode materials that have proved to give particularly good results,

a mixture of RuO2/TiO2 on a Ti substrate and a mixture of TiR02/TiO2 on a Ti substrate, both of these anodes being commercially available.

The preferred acidic, aqueous electrolytes that can be used in the execution of the present method have a pH below 3 and include solutions of strong acids, such as sulfuric acid, nitric acid, hydrochloric acid or phosphoric acid, etc.

Although temperatures from above the freezing point of water and higher can be used, temperatures of 25-350°C are preferred. Temperatures of 120-300°C are most preferred, especially when solid carbonaceous materials, such as coal, are used. At temperatures below 140°C, the reactivity of solid carbonaceous materials, such as coal, decreases steadily as the electrochemical oxidation takes place. This reduced reactivity is believed to be due to surface oxides forming on the coal's surface and preventing further maintained reactivity for the coal. At temperatures of approx. 140°C and above, the coal's reactivity is maintained, and no significant reduction can be observed.

As it is desirable to allow the reaction to proceed in the liquid phase, it is of course necessary that the reaction be carried out at elevated pressure when elevated temperatures are used. In general, pressures of 2-400 atmospheres are satisfactory.

It has also been shown according to the invention that the addition of the iron catalyst to a solid carbonaceous material, such as coal, will maintain the coal's activity for a longer time at temperatures below 120°C compared to systems that do not contain the iron catalyst. Moreover, the catalytic effects of the iron catalyst are more predominant at the higher temperatures.

Although iron can be used in an elemental state, it is preferred to use iron in the bivalent or trivalent, valence state; It is most preferred to use trivalent iron. valence state, . Inorganic iron compounds, such as iron oxides, iron carbonate, iron silicates, iron sulphide, iron oxide, iron hydroxide, iron halides, iron sulphate or iron nitrate etc., can thus be used. In addition, various organic iron salts and complexes, such as salts of carboxylic acids, e.g. iron acetates, iron citrates, iron formates or iron glyconates, etc. or iron cyanide, iron chelate compounds, as chelates with diketones, such as 2,4-pentanedione, iron ethylenediaminetetraacetic acid or iron oxalates, etc., are used.

Although the iron catalyst can be used at a concentration up to the saturation point in the aqueous electrolyte, the preferred concentration of the iron catalyst is 0.04-

0.5 molar, preferably 0.05-0.1 molar.

Although certain carbonaceous materials, such as coal, may contain iron as an impurity, generally an ferrous catalyst from an external source is required to increase the reaction rate, at least initially, to acceptable levels for commercial application. The iron catalyst can be formed in situ by oxidizing sufficient ferrous coal that an effective amount of iron catalyst will be formed in the electrolyte.

Of course, non-iron, carbonaceous materials, such as carbon black, require an iron catalyst added from an external source.

Thus, according to one embodiment of the present invention, a sufficient amount of iron catalyst is added from an external source to provide the preferred catalyst concentration range, ie 0.04-0.5 molar.

According to another embodiment, an effective amount of iron catalyst can be formed in situ by oxidizing a sufficient amount of ferrous coal, albeit at a slower rate initially, to provide the preferred catalyst concentration range.

The catalyst formed will then be freed from the carbon and able to function in a similar manner to an externally supplied iron catalyst.

According to a third embodiment, a combination of iron catalyst supplied from outside and iron catalyst formed in situ can be used to provide. the preferred catalyst concentration range, ie 0.04-0.5 molar. The concentration or amount of carbonaceous material present in the electrolyte can vary within a wide range depending on whether the carbonaceous material is. a liquid, a solid or a gas and depending on the particle size, but the preferred range is 0.1-0.7 g/ml.

In the same way as for the case described in US patent document 4268363, it is possible to electrically recover, electrocoat or electrically deposit any element that can be reduced cathodically from an aqueous solution during simultaneous electrochemical anodic oxidation of carbonaceous material . Typical metallic elements that are often separated in practice from aqueous electrolytes include Cr, Mn, Co, Ni, Pb, Cu, Sn, Zn, Ga, Hg, Cd, Ir, Au, Ag, Os, Rh, Ru, Ir, Pd or Pt. The metallic elements are preferably Cu, Zn, Ag, Ni or Pb.

The invention will be described in more detail using the examples below.

Example 1

Electrical separation of Cu was carried out at constant

(R)

voltage in a cell with a Nafion^ membrane and where the catalyst and anolyte solution was pumped.

The anolyte contained no charcoal and no added iron in the first trial and was pumped through an external circulation system. The catholyte was pumped through a system in a similar manner to the anolyte. The aqueous electrolyte was 0.5 M H 2 SO 4 , and the cathode also contained 0.5 M CuSO 4 . The total volume was 500 ml and the temperature 95°C and 120°C, and the anode had an area of 55 cm 2 and consisted of titanium coated with iridium oxide and titanium dioxide (TIR). The cathode consisted of a copper plate.

Example 2

The apparatus used and the conditions used were the same as in Example 1, except that the pumped anolyte contained 0.5 g/cm<3>coal ("WOW 3932V"). The results were as follows:

Example 3

In the third experiment, the conditions used and the apparatus used were the same as according to example 2, except that the anolyte contained 0.04M Fe3+ due to the addition of Fe2(SC"4)^- The results were as follows:

At 120°C, the Fe<3+-> concentration was increased to 0.1M, while

all other conditions and apparatus were held constant.

The results were:

Example 4

Production of hydrogen by electrical means was carried out

(s)

at constant voltage in a cell with a Nafiorf^ membrane, and where catholyte and anolyte solutions were stirred with magnetic stirring devices.

The aqueous electrolyte had a sulfuric acid concentration. tion of 0.5M E^ SO^ both as regards the catholyte solution and the anolyte solution. The total cell volume was 500 ml and the temperature 180°C. The anode consisted of 98 cm^ titanium coated with iridium oxide/titanium dioxide. The cathode consisted of platinum. The first pre-ash was carried out without coal being added to the anolyte. The results were as follows:

Example 5

The apparatus used and the conditions used were the same as in Example 4, except that the anolyte contained 0.17 g/cm<3>coal ("WOW 3932") or coke (El Segundo).

Example 6

The conditions and apparatus were the same as in Example 5, except that the anolyte was brought to contain -3+

keep 0.07M Fe by adding Fe2(SO4)3.

Claims (10)

1. Procedure for electrochemical gasification of carbon-containing materials in an aqueous, acidic electrolyte by anodic oxidation for the production of oxides of carbon on the anode in an electrolysis cell, characterized in that iron in elemental state, in divalent valence state or in trivalent valence state or mixtures thereof is added to the electrolyte containing the carbonaceous material, in a sufficient amount to increase the oxidation rate of the carbonaceous material on the anode. 2. Method according to claim 1 for producing oxides of carbon on the anode and hydrogen on the cathode in an electrolysis cell, characterized in that carbonaceous materials and the electrolyte are introduced into an electrolysis cell with a cathode electrode and an anode electrode and that an electromotive force is applied over the electrodes so that the carbonaceous materials react on the anode and hydrogen is produced on the cathode in the electrolysis cell. 3. Method according to claim 1 for the production of oxides of carbon on the anode and electrical recovery of a metallic element from an electrolyte containing a metallic component such as a cationic component, characterized in that carbonaceous materials and the electrolyte are introduced into an electrolysis cell with a cathode electrode and a anode electrode and that an electromotive force is applied across the electrodes so that the carbonaceous materials react on the anode and the metallic component is deposited on the cathode. 4. Method according to claims 1-3, characterized in that the iron is added as a salt in a divalent or trivalent oxidation state. 5. Method according to claims 1-4, characterized in that the electrochemical process is carried out at a temperature of 25-350°C. 6. Method according to claims 1-5, characterized in that the temperature is kept within the range 120-300°C. 7. Method according to claims 1-6, characterized in that the iron is added in such an amount that the iron concentration in the electrolyte becomes 0.04-0.5 molar, 8. Method according to claims 1-7, characterized in that the iron is added in such an amount that the iron concentration in the electrolyte is 0.05-0.1 molar. 9. Method according to claims 1-8, characterized in that an aqueous electrolyte is used which is acidic with a pH of 3 or below. 10. Method according to claims 3-9, characterized in that an electrolyte is used in which the metallic element is from the group Cr, Mn, Co, Ni, Pb, Cu, Sn, Zn, Ga, Hg, Cd, Ir, Au, Ag , Os, Rh, Ru, Ir, Pd and Pt, preferably from the group Cu, Zn, Ag, Ni and Pb.