DE1165002B - Process for removing sulfur compounds that are difficult to convert from gases to be methanized, essentially only containing carbon dioxide and hydrogen - Google Patents

Description

Process for removing sulfur compounds that are difficult to convert from, essentially only carbon dioxide and hydrogen containing, to be methanized Gases The conversion of gases over highly active cobalt and nickel catalysts requires A purification of the reaction gases that goes far beyond the normal level is mandatory of sulfur and its compounds. Especially the removal of organic sulfur compounds offers difficulties here.

According to French patent 59 614 (addition to patent 1 010539) should the sulfur compounds with nickel, cobalt or iron catalysts 350 to 5000 C are decomposed and then the hydrogen sulfide with lux mass be bound.

The German patent 966 539 used to decompose the organic Sulfur compounds exhausted catalysts of the carbohydrate hydration, which with Air were oxidized. Here, too, the hydrogen sulphide that is produced becomes iron oxide bound. The German patent 906 606 leads the implementation of the organic sulfur compounds with the help of sulphurized nickel catalysts and binds the hydrogen sulphide by alkaline masses at elevated temperature.

The situation is essentially different in the case of a particular one Case of carbohydrate hydrogenation as described in patent 1,110,147.

The patent 1110 147 has a method for catalytic Methanation of essentially only carbon dioxide and hydrogen Gas that works with two nickel catalysts connected in series. Of the Fresh catalyst is used in the second methanation stage and transferred from there to the first catalyst stage after a reasonable period of use. Both stages work at 180 to 2500 C with a load of 300 to 3000 parts of the room of the gas measured under normal conditions per part of the space of the catalyst (i.e. load = 300 to 3000 VlV / h).

In the first stage, a (CO + H2) conversion of over 75e / o and in the second stage a conversion of over 80% is observed. To achieve a possible long service life of the catalytic converter is a high degree of purity of the gases processed, in particular a practically complete removal of any sulfur compounds that may be present, necessary.

The desulfurization of the CO2 / H2 gas mixture or the two gas components, d. H. of carbon dioxide and / or hydrogen, according to the additional patent 1128 417 with the nickel catalyst used up and reduced in the first methanation stage take place. For this desulfurization, below 1000 C, have been preferred temperatures below 500 C are suggested.

Hardly unsettable sulfur compounds, for example from thiophene and thiophene derivatives exist, can be at temperatures below 1000 C. do not remove sufficiently in this way. In any case, small Amounts of hydrogen present that are approximately 0.5 to 5 percent by volume, preferably 1 to 3 O / o, of the gas to be purified, especially if the gas to be cleaned consists essentially only of carbon dioxide.

It has been found that the process for the desulfurization of im essential technical gases containing only carbon dioxide and hydrogen, the then methanized in two stages over nickel catalysts according to patent 1,110,147 are, according to patent 1128 417 by passing over the carbon dioxide and / or hydrogen before they are mixed in separate operations over those in the first methanation stage according to patent 1 110 147 spent nickel catalyst with particular success so can perform that to remove difficult to implement, especially thiophene-like Sulfur compounds desulfurization at 150 to 4000 C, preferably above of 2000 C, and at catalyst loads of 500 to 1500 parts by volume of gas per part by volume Catalyst and hour is made. In the temperature range between 150 and 4000 C, especially above 2000 C, thiophenes and similar sulfur compounds can be found easily hydrogenate to hydrogen sulfide, which in turn immediately follows is bound as nickel sulfide by the nickel content of the catalyst. Small amounts of hydrogen sulfide, which may still remain in the treated gas can be used in the customary manner easily remove.

The gas cleaning according to the invention is at atmospheric pressure or carried out at elevated gas pressures of, for example, 5 to 20 kg / cm2. It can but can also be used at even higher gas pressures. As a catalyst is a exhausted, nickel-containing methanation catalyst used.

For sulfur-containing impurities of less than 10 g S per 100 m3 of gas, preferably at less than 5 g S per 100 m3 of gas, is exposed to a gas load worked from 500 to 1500 VlV / h. An even higher load on the catalyst is unfavorable because of the catalytic conversion of the sulfur compounds in this case decreases considerably. The catalyst fillings do not need a heat exchange medium To be cooled, because only small amounts of heat in the desulfurization according to the invention develop. For this reason, you can work with simple shaft furnaces and need Do not put the catalyst used for desulphurisation in the usual tube furnaces to fill in.

With the method according to the invention one can thiophenes and others Remove up to 90% sulfur compounds that are difficult to convert from the gas to be cleaned. The sulfur or hydrogen sulphide produced during the cleaning process is used here taken up immediately by the catalyst. After a certain period of operation it makes However, a slow decrease in catalyst activity is noticeable. Through appropriate The catalyst activity can be improved again by increasing the temperature. To longer operating times and depending on the sulfur content of the gas, the catalyst must however to be renewed.

In some cases one observes before the normal one has finished Catalyst service life as a result of the saturation with sulfur that occurs. It is caused by it. that carbon dioxide acts as an oxidizing agent and the nickel metal present in the catalyst more or less largely in nickel oxide convicted. This will result in a corresponding decrease in sales of thiophene and Thiophene compounds with a simultaneously decreasing cleaning effect caused.

Example One made from 100 parts of nickel, 50 parts of diatomite and 10 parts MgO (parts by weight) existing catalyst was made in a known manner by precipitation from a nitrate solution with soda solution, stirring in kieselguhr, filtering and washing out of the filter cake with subsequent deformation and drying of the moist mass manufactured. The catalyst was turned off at 3500 C for one hour 75 75 ° / nH2 and 250/0 N2 existing mixture and then had a reduction value from 800io.

This catalyst was used to methanate a gas mixture, the 10.10 / o carbon dioxide and 40.10 / 0 hydrogen (remainder methane and a little nitrogen) contained (volume percent). This gas came from the second stage of carbon dioxide methanation.

After an operating time of 31 / e months, the catalyst was in the first stage of methanation is switched and a gas is applied there, which consisted of 19.1% carbon dioxide and 80.1% hydrogen (remainder nitrogen).

After another operating time of about 41/2 months, the Catalytic converter exhausted. It was now used to purify the carbon dioxide substream used and for this purpose poured into a shaft furnace of suitable size. The carbon dioxide came from the pressurized water scrubbing of a converted water gas. Besides 97.5 per cent of carbon dioxide, this gas contained about 20 per cent of hydrogen and about 20 per cent 0.5 ovo nitrogen. It also had a thiophene content of approximately 1 to 2 g per 100 m3 of gas.

At a working temperature of 2000 C the thiophene content could be reduced to about a tenth of its initial value.

After an operating time of 4 weeks, the thiophene conversion decreased slowly after, and the cleaning effect was correspondingly lower.

Claims (1)

Claim: Process for the desulfurization of substantially only technical gases containing carbon dioxide and hydrogen, which subsequently according to patent 1 110 147 are methanated in two stages over nickel catalysts, according to patent 1128417 by passing over the carbon dioxide and / or hydrogen before they are mixed in separate operations over those in the first methanation stage according to patent 1 110 147 exhausted nickel catalyst, d a d u r c b g e k e n n z e i c h ne t that for the removal of difficult to implement, especially thiophene-like Sulfur compounds, desulfurization at 150 to 4000 C, preferably above of 2000 C, and at catalyst loads of 500 to 1500 parts by volume of gas per part by volume Catalyst and hour is made. Documents considered: German Patent No. 906 606; German patent application R 2666 IV b / 120 (published October 9, 1952); French additional patent specification No. 59 614 (addition to French patent specification No. 1 010 539). Older patents considered: German patents No. 1110 147, 1 128 417.