DE2733105B1 - Process for the production of synthesis gases by partial oxidation - Google Patents

Description

13th

The present invention relates to a continuous process for the production of substantially Synthesis gases containing carbon monoxide, hydrogen and methane, with those contained in the raw synthesis gas Contamination of hydrocyanic acid and ammonia. by catalytic hydrogenation prior to gas scrubbing be eliminated.

The production of synthesis gases is described in Ullmanns Encyklopadie der technischen Chemie, Volume 16, 3rd edition 1965, pages 599 to 635. Newer. 4 ^r > Developments with regard to various areas of application can be found in the supplementary volume, 3rd edition 1970, keyword »ammonia« or »methanol«, in the section »gas generation«, from page 468 ff. And pages 94/95. w

In particular, reference is made to the illustration reproduced on page 601 of the first cited reference 1 referenced, which gives an overview of the gas generation when using different starting materials, such as Contains coal or liquid and gaseous hydrocarbons

Synthesis gases are produced today on an industrial scale through partial oxidation of hydrocarbons or produced by coal or natural gases or LPG with gases containing oxygen Mix can act as a temperature moderator water vapor, nitrogen or another suitable substance be admitted.

In the past, however, increasingly larger proportions of heavier hydrocarbons of the type heavy fuel oil or even residual oils or vacuum reused These heavy oils contain a comparatively larger proportion of organic residual nitrogen compounds and a higher sulfur content.

During the oxidation reaction, therefore, in addition to carbon monoxide, hydrogen and methane, depending on the Raw material and its composition also contain carbon dioxide, hydrogen sulfide and traces of Carbon oxysulphide, ammonia, hydrocyanic acid and formic acid. Part of the carbon contained in the raw material is produced as soot and must be used before the other Work-up of the gas can be removed.

Regardless of the type of further processing, the gas is cleaned at one point in the process the acidic compounds, such as CO2, H2S, HCN and HCOOH, optionally with the exception of the Carbonic acid, and also carbon oxysulphide, are substantially removed. When the said Connections are to be removed together by means of gas scrubbing, arise in particular with higher Contained in hydrogen cyanide considerable difficulties. These are due to the fact that the hydrocyanic acid in is readily soluble in most of the solvents used for gas cleaning and therefore in solvent regeneration is only incompletely removed from the solvent. As a result, it accumulates in the Washing solution on; in aqueous washing solutions it is hydrolyzed to formic acid, which is also enriches

The accumulation of hydrocyanic acid and formic acid in the washing solution assumes their absorption capacity acidic compounds down; it also causes severe corrosion on those used for gas cleaning Apparatus. The amount of formic acid that enters the gas cleaning system from the gas generation stage falls next to the hydrocyanic acid not significant.

It is therefore of interest to remove the hydrogen cyanide from the gas before the remaining acidic compounds, such as H2S or CO2, can be removed. The distance the hydrocyanic acid by means of a cold water wash before carrying out the acid gas wash results in an additional one Expenditure; the washing liquid must be regenerated because it usually does not go into the wastewater can be given; In addition, the operation of the laundry with fresh water alone is uneconomical.

From DE-OS 23 52 425 it is known to convert nitrogen compounds such as NH ₃ and HCN in gases containing H2S over transition metal sulfides as a catalyst (in particular iron sulfide is proposed) to form nitrogen. This reaction is carried out mainly at temperatures of 649 to 815 ° C. Furthermore, the removal of HCN from unspecified gases with the aid of Cr-Ni catalysts at temperatures from 250 to 450 ^° C. is described in SU-PS 4,39,302. According to the information provided by the authors, the activity of the catalyst used drops very sharply after only 20 hours of operation. Finally, from DE-OS 22 45 859 it is known to convert hydrogen cyanide on supported catalysts which contain elements of the 6th and / or 8th subgroup in the oxide form and to remove this from certain gas mixtures. This process is carried out without pressure. In the examples, model gases are used that contain no carbon oxides and no water vapor. The cited DE-OS shows that the reaction only ^{proceeds with the desired conversions from 200 or from 250 °} C. Here, space velocities of at most 1500 per hour can be used.

All of these methods have disadvantages which prevent them from being used in practice. Task of The present invention was to thereby add the hydrocyanic acid to the acid gas scrubber before the gas entered eliminate the fact that the gas is brought into contact with a catalyst with hydrocyanic acid on the surface is hydrogenated with the hydrogen already present in the gas.

Such a catalyst must be resistant to sulfur and, moreover, it must be suitable for the desired reaction, hydrocyanic acid dehydration, act selectively. Because thermodynamically, a number of other reactions are involved Catalysts possible, the composition of the carbon oxides and water vapor containing gas in would change undesirably. On the one hand, the oxides of carbon can be mixed with hydrogen Methane form according to the following equations:

CO + 3 H ₂ O
CO ₂ + 4 H ₂ -

♦ CH ₄ + H ₂ O
CH ₄ + 2 H ₂ O

In addition, if there is a lack of water, soot can develop according to the equation

2 CO - C -I- CO ₂

deposit.

If, on the other hand, the gas contains a high content of water vapor, the conversion of the carbon monoxide can occur according to the equation

CO + H ₂ O- CO ₂ + H ₂

expire.

All of the above-mentioned reactions are undesirable for the present task.

It has now been found that hydrogen cyanide is present even at low temperatures and with high loads can be selectively hydrogenated even in the presence of carbon oxides and water vapor. This was in With regard to the statements in DE-OS 23 52 425 and 22 45 859 were not to be expected.

The present invention therefore relates to a process for the production of synthesis gases containing essentially carbon monoxide and hydrogen by partial oxidation of hydrocarbons or of coal with oxygen-containing gases in the presence of steam or another suitable temperature moderator in a pack-free, non-catalytic synthesis gas reactor at a temperature between 900 and ^{170O 0} C lying (autothermal) temperature and at a pressure lying between 1 and 250 bar with subsequent cooling of the reaction products and deposition of particulate carbon, as well as removal of acidic impurities and further after-treatments, which are carried out in a sequence known per se. The process is characterized in that the reaction products are treated after the deposition of particulate carbon, but before the removal of the acidic gas components in a catalytic hydrogenation zone at temperatures of 100 to 250 ⁰ C and the catalytic hydrogenation zone is equipped with a catalyst that 10 to Contains 45% by weight of hydrogenation-active metals of the 6th and / or 8th subgroup of the Periodic Table in the form of the oxides and sulfides and 90 to 55% by weight of a carrier

In this catalytic hydrogenation zone, the hydrogen cyanide present in traces is mixed with that present in the gas Hydrogenated hydrogen; the concentration of the remaining gas constituents is essentially not in this case changed.

The catalytic hydrogenation zone is equipped with a hydrogenation-active catalyst, which in itself consists of the Refinery technology for longitudinal desulphurisation and denitrification processes is known. Such refining catalysts usually contain at least one element from the 6th or 8th subgroup of the Periodic Table, usually in the form of their oxides or Sulphides on inorganic, refractory oxides as

ι ο carriers are applied.

As elements of the 6th subgroup, chromium, molybdenum and tungsten come into consideration, of which the the latter are preferred. The elements of the 8th subgroup are nickel and cobalt.

The catalysts preferably each contain at least one element of the 6th and 8th subgroup, usually an atomic ratio of 0.8 to 10 atoms of the elements of the 6th group per atom of the Elements of the 8th group is applied. In particular Catalysts, the mixtures of one or more elements of the 6th and 8th group of the Periodic table included are used; here the atomic ratio should expediently be between 1 and 4 lie. Nickel and molybdenum or those containing cobalt and molybdenum are particularly preferred Used catalysts that have such atomic ratios.

The oxides or sulfides of the hydrogenating metals are generally 10 to 45% by weight of the Total catalyst; the remainder from 90 to 55% by weight constitutes the carrier.

In particular, ceramic masses, such as MgO, SiO ₂ , Al ₂ Oi, TiO ₂ , ZrO ₂ or mixtures thereof, such as MgO and Al ₂ O ₃ , are used as carriers for the hydrogenation-active metals.

r> or compounds, namely the Spienlle, also artificial or synthetic magnesium or aluminum silicates, such as clays and bleaching earth; also clays, e.g. B. y- Al ₂ O ₃ and 6- Al ₂ O ₃ or alumina hydrates, such as bayerite, hydrargillite, boehmite or mixtures of alumina or alumina hydrates. The most preferred carriers are clays or alumina hydrates or mixtures thereof.

The catalytic hydrogenation zone is operated at a temperature of 100 to 250 ⁰ C, preferably 150-230 ⁰ C. These temperatures relate to the entry temperature of the reaction products of the autothermal cleavage after the soot has been removed. Since no methanation and also no conversion is desired in the catalytic hydrogenation zone, these are

> o Inlet temperatures practically identical to the outlet temperatures. The pressures in the catalytic hydrogenation zone are from 1 to 250 bar, the pressure is preferably set so that it corresponds to the pressure prevailing in the generator minus the normal pressure loss on the processing path bar and 0 ⁰ C). The catalytic hydrogenation of the hydrocyanic acid is favored at higher pressure, so that the temperature can be adjusted so as to lower and the space velocity is higher, the higher the gasification pressure used is In particular, at low gasification printing should not higher than 200 ⁰ C are chosen temperature.

The following raw materials for autothermal cleavage come into consideration: gases, LPG, petrol hydrocarbons, Heating oils, heavy heating oils, vacuum gas oils, vacuum residues, and coal.

Depending on the raw material used and the process conditions, in particular the gasification pressure, after passing through the gasification zone, i.e. after the water quench or after the waste heat system, a raw gas composition is obtained that is in the range of H ₂ = 62 to 40 percent by volume, CO = 34 to 60 Volume percent and CO ₂ - 2 to 6 volume percent can vary. The other components, such as CH ₄ , N ₂ , H ₂ S, noble gases, etc. are generally less than 1% each. The hydrocyanic acid content of the raw gas depends on the nitrogen content of the starting material and can be from 1 to 50 ppm, in the case of heavy fuel oil in particular from 5 to 25 ppm.

The process according to the invention is illustrated by the following examples. Catalysts A (CoMoZAl ₂ O ₃ ) and B (NiZMoAl ₂ O ₃ ) were prepared as described below and had the following properties:

Catalyst A

Boehmite was precipitated with ammonia from an aluminum salt solution, filtered and washed free of salts. The still moist alumina paste was mixed with cobalt nitrate and a molybdenum salt solution (molybdic acid or Ammonium molybdate). After drying, the powder was kneaded and shaped to form Strands pressed, dried and calcined

A catalyst was obtained which contained 5% cobalt oxide, 13.5% MoO ₃ , the remainder Al ₂ O ₃ as a carrier, the Al ₂ O ₃ still having an impurity of 2% by weight SiO ₂ . The catalyst had a bulk density of 650 kgZm ³ , a specific surface area of 220m ² Zg and a pore volume of 0.5 cm ³ Zg.

Catalyst B

As described above under A, alumina strands were produced from the alumina paste and calcined. The calcined strands were impregnated with a solution containing nickel and molybdenum, then dried and calcined again. A catalyst was obtained which contained 3% by weight NiO and 15% by weight MoO ₃ , the remainder being alumina contaminated _{with SiO 2.} It had a bulk density of 700 kgZm ³ , a specific surface area of 150m ² Zg with a pore volume of 0.6 cm ³ Zg.

In all examples, the gas emerging from the reaction zone had an HCN content of less than 1 vol. ppm and had a composition that was within the analytical accuracy of the composition of the inlet gas. In all experiments the catalyst was used in the sulphurized form. However, it must be taken into account here that even a catalyst used in an oxidic manner for longer periods of time Operation through the sulfur compounds contained in the raw synthesis gas gradually into its sulfidic Form is transferred. To accelerate the reaction, however, the catalyst can be equal to Beginning to be used in its sulfided form.

example 1

Heavy fuel oil (atmospheric residue) was preheated to 110 ° C and introduced via a ring burner into a free-flow, non-catalytic synthesis gas reactor.The density of the oil starting material was 954kgZm ³ at 16 ° C (17 degrees APi), the kinematic viscosity at 80 ° C was 64 , 0 m ² Zs (8.45 degrees Engler) and the upper calorific value was 43 518 kj / kg. An analysis showed in wt .-% - 85.00 C,

ι ο

11.46 H, 1.75 S, 0.35 N, 0.90 0 and 0.09 ash. At the same time, steam with a temperature of 400 ^° C. and practically pure oxygen (99.1 mol%) were fed to the generator. The weight ratio H2 / fuel was 0.40 and the atomic ratio of oxygen to carbon (in the fuel) was 03072.

The reaction between the feed streams took place in the reaction zone under an absolute pressure of about 45 bar and at an (autogenous) temperature of 1306 ^° C. The average residence time in the reaction zone was about 6 seconds. The hydrocarbon feed stream was converted by partial oxidation into a gas stream which, after indirect cooling to 165 ° C. and subsequent separation of the particulate carbon with water, had the following composition in mol% of the dry gas: 3.6 CO ₂ , 47.5 CO, 48 , 0 H ₂ , 0.2 CH ₄ , 0.4 H ₂ S and COS, 0.16 N ₂ and 0.14 Ar. The gas contained the following trace impurities, in ppm by volume:

3 NH ₃ , 18.5 HCN and less than 0.5 HCOOH. It should be noted that some of the trace impurities mentioned are removed as soon as the particulate carbon is precipitated from the gas. Under the operating conditions mentioned, the particulate carbon only made up 1.5% of the carbon used, and since more than 90% of it was returned to the gasification process, it was not noticeably included in the material balance. After the particulate impurities had been separated off, the gas of the above composition was saturated with water, it had a temperature of 82 ° C. and an absolute pressure of about 42.5 bar.

A quantity of

4 kmol / h by indirect heat exchange to 150 ⁰ C. and a hydrogenation zone fed to the 91 the catalyst A contained the operating pressure corresponded to the generator pressure less normal pressure drop in the intermediate apparatus and was absolutely about 42.5 bar. The stated throughput corresponded to a space velocity of 10,000 liters per liter of catalyst per hour.

The following table shows the analytical data before and after the hydrogenation stage.

Before the After Hydrogenation stage Hydrogenation stage CO ₂ % by volume 3.6 3.6 CO vol% 47.5 47.5 H ₂ % by volume 48.0 48.0 CH ₄ % by volume 0.2 0.2 H ₂ S + COS vol .-% 0.4 0.4 N ₂ % by volume 0.16 0.16 Ar vol% 0.14 0.14 HCN vol. Ppm 18.5 <1

Example 2

A gas stream of 4 kmol / h, the production conditions and composition of which corresponded to the gas stream of Example 1, was ^{heated to 150 °} C. by indirect heat exchange and fed to a hydrogenation zone which contained 91 of the catalyst B. The absolute pressure was 42.5 bar, and the said throughput corresponded to a space velocity of 10,000 liters per liter of catalyst and hour. The HCN content after the hydrogenation stage corresponds to the result obtained in the example.

Claims (2)

Patent claims: 1. A process for the production of essentially carbon monoxide and hydrogen-containing syn-, thesegases by partial oxidation of hydrocarbons or coal with oxygen-containing gases in the presence of steam or another suitable temperature moderator in a pack-free, non-catalytic synthesis ι ο gas reactor at a between 900 and 1700 ⁰ C lying autothermal temperature and at a pressure lying between 1 and 250 bar with subsequent cooling of the reaction products and separation of particulate! Carbon ι> and removal of acidic impurities and further aftertreatments, which are carried out in a sequence known per se, characterized in that the reaction product after the deposition of the particulate carbon m substance, but before the removal of the acidic gas components, in a catalytic hydrogenation zone Temperatures of 100 to 25O ° C is treated and the catalytic hydrogenation zone is equipped with a catalyst that contains 10 to 45 wt Contains 90 to 55% by weight of a carrier 2. The method according to claim 1, characterized in that the treatment at temperatures of 150 to 230 ° C is carried out.