DE1645851A1 - Process for the production of methanol synthesis gas - Google Patents

Description

METALLGESELLSCHAFT Frankfurt (Main), Jan. 3, 1968

Aktiengesellschaft ■ DrWer /

Prov. No. 5460

Process for the production of methanol synthesis gas

Recently, natural gas, which is generally made available free of sulfur, has been increasingly used for the production of synthesis gas. Most of the practically usable natural gases consist primarily of "methane and, due to their C ^ H ratio, are not suitable for the production of methanol in the case of water vapor splitting in the tube furnace without the addition of extraneous carbon or without the elimination of excess hydrogen refrains from the possibility of producing methanol from a completely unstoichiometric mixture of CO and H _9. In the production of methanol, the following reactions primarily take place;

(1) CO + 2 H ₂ CH ₃ QH

(2) CQ ₉ + 3 H ₉ - »CH« OH + • H ₉ Q

Two moles of H 2 are therefore required for each mole of CO and three moles of H _{3 are} required for each mole of CO. In the synthesis gas for the production of methanol, the molar ratio H ₉ : C should be at least 2.0. Taking into account this CO _o proportion in the raw gas, it is preferable to work with a gas mixture that meets the condition.

fH ₂ - CQ ₂ ): (CQ + CO ₂ ) = 2: 1 to 2.4; 1

enough. '

When methane is split with steam, three moles of H ₀ are produced per mole of CO and four moles of H ₀ per mole of CO, according to the reactions:

Ci £ Cj

(3) CH ₁ + H ₀ O - 4CO + 3H-

TC Ct Ct

(4) CH ₄ + 2H ₂ O-4 CO ₂ -Η 4 H ₂

When methane is split with oxygen, two moles of H ₀ are formed per mole of CO according to the reactions;

(5) CH ₄ + j O ₂ - * CO + 2H ₂

(6) CH ₄₊ O ₂

When splitting with water vapor, there is an excess of hydrogen in the cracking gas, and when splitting with oxygen, there is an excess of carbon. The excess of carbon can easily be eliminated in a known manner _{by washing out CO 0 from the cracked gas.} hydrogen

to remove from a gas mixture, is encountered in practice to considerable Difficulty and is uneconomical, even if the excess Hydrogen is used for other purposes.

In practice, therefore, the reverse route is preferred and leads to carbon that is foreign to the cracking process of methane cracking with steam instead of removing hydrogen from the cracking gas. This carbon supply usually takes place by adding carbon dioxide, which from the excess of other processes, e.g. from the production of NH " Synthesis gas, can be taken, but preferably from the flue gases of the tube furnace in which the methane is split up will. Since the tubular furnace is also heated with natural gas, the flue gas is sulfur-free.

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* · Ο -

A number of chemical scrubbing processes are known for obtaining CO ₃ from flue gases, in which aqueous solutions of alkali carbonates, of alkali salts of weak organic acids or organic bases, optionally in aqueous solution, are used as absorbents.

While washing out the CO "from flue gas with soda or potash solution As a result of their low loading capacity, it requires large amounts of detergent and involves expensive apparatus and high steam and electricity consumption leads to the use of alkaline absorbing solutions with organic Components such as alkylamines. Alkanol mines or alkali salts of weak organic acids, which contain a lot of oxygen in the flue gas Decomposition of the absorbent and thus ongoing losses detergent as well as a considerable risk of corrosion.

It now became an extremely simple and economical option to remove the oxygen from the flue gas with the company's own resources found, through which the plant costs and the operating costs of the COg-WäsdB can be significantly reduced. This is done from the furnace of the gap Exiting mixture preheater and bare in the waste heat boiler to temperatures between 100 and 450 ° C cooled flue gas, which contains approx. 1-5% oxygen, inside the so-called flue gas duct with a burning

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mixed gas and arranged via one in the same flue gas duct platinum-containing catalyst passed. The contained in the flue gas becomes acidic Oxidation of the supplied combustible gas used up. The temperature increase in the flue gas that occurs during this oxidation becomes the additional one Steam generation made usable. A carbon-rich gas is preferably used as the fuel gas Waste product from methanol production, e.g. B. expansion gas from the methanol distillation or from the distillation of the raw methanol used dimethyl ether.

The invention relates to a method for producing methanol synthesis gas by splitting gaseous hydrocarbons with water vapor and carbon dioxide.

The inventive method is characterized in that the in the Fission process to be introduced carbon dioxide from oxygen-free made flue gas of the cracking furnace is obtained.

The free oxygen still contained in the raw flue gas is thereby passed through thermal or catalytic conversion with flammable gases in the hot, raw flue gas is mixed in, preferably consumed with residual gases from methanol synthesis and / or from the distillation of the raw methanol, before the carbon dioxide is removed from the flue gas by washing it out by means of a Absorption solution and regeneration of the same is obtained.

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As much of the carbon dioxide obtained from the oxygen-free flue gas is added to the gaseous hydrocarbons to be split, as is necessary to establish a molar ratio H 1: C = 2: 1 in the synthesis gas. For this it can be sufficient to use only a partial flow of the cracking furnace flue gas for CO ₂ extraction and to make it oxygen-free;

A significant advantage of the process according to the invention is that a synthesis gas with the correct H ₀ : G ratio is obtained directly from the cracking furnace, which only needs to be compressed for the synthesis, which is done only after cooling with the separation of vapor condensate.

Since the tube furnace generally works with the gaseous hydrocarbons, which are also the feedstock for the cleavage, is heated, is the flue gas sulfur free. Should the available natural gas or the like still contain sulfur it can be desulfurized in a known manner, e.g. on zinc oxide masses will.

From the smoke made free of oxygen in the manner according to the invention carbon dioxide can with the known alkaline absorbing solutions such as alkanolamftien, which are characterized by a ^ xohe capacity.

0 0982 0/086 7

be washed out without the fear of oxidizing damage to the absorbent and an increased risk of corrosion.

Since the scrubbing of the CO _{0 is} only aimed at obtaining the same, but not at a minimal _{residual CO 0} concentration in the scrubbed flue gas, no intensive regeneration of the absorbent is required. Therefore, the gas scrubbing system can be used simply and comparatively _{to obtain the CO 0} be designed small.

In the figure is the flow diagram of a plant for the implementation of the invention Procedure shown for example. May it be used in conjunction with two Examples serve to explain the invention in more detail.

The system essentially consists of the tube furnace 6, the gas washing system with the absorption tower 45 and the regeneration tower 52, the steam boiler 32 with the heaters 25 and 28 in the flue gas duct 24 of the tubular furnace and from the actual synthesis plant 15,

Pure methanol is released from the synthesis plant at 16. On line 26 the exhaust gases that are produced during the distillation of the raw methanol are directed to the flue gas duct.

management
In the / L7, the exhausted synthesis cycle gas is transferred to the fuel line 18

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admixed to the tube furnace. The combustion air is passed through line 21 introduced by means of the compressor 20. The feed water supply to the steam boiler 32 is denoted by 33. The gaseous hydrocarbons to be split are introduced into the system through line 1.

A catalyst bed arranged in the flue gas channel is designated by 27, in FIG the oxidation of the residual gases from the methanol distillation (from line 26) takes place with the residual oxygen of the flue gas.

Example 1

3 Under a pressure of H atü, an amount of methane of 4000 Nm / h from line 1 is mixed with a CO "amount of 100 Nm / h from line 58 and fed to the preheater 2, in which the CH ^ / COq- Ge. is heated to approx. 250 ° C.

After exiting the preheater through line 3, this mixture is an amount of 7000 kg / h of steam at 11 atm from line 35 is added. The mixture of methane, carbon dioxide and water vapor enters the heater 4, is heated there to 450 ° C and passes through line 5 into the gap tubes of the tube furnace 6, where they are subjected to the supply of heat from the outside at a pressure of 7 atü and a reaction temperature of 850 C to a gas about the following composition is split:

: - 8 009820/0987

5851

., ■ CO ₂ 8.24 vol.%

CO 20, 85 vol.%

H ₂ 6 9.81VoI. %

CH 2.10% by volume

The amount of cracked gas formed of 16,500 Nm / h contains approx. 4,000 kg / h of water vapor. The cracked gas / steam mixture passes through line 7 to cracked gas waste heat boiler 8, where it is cooled to approx. 480 ° C. in the heat exchange against boiling water. From there the cracked gas passes through line 7 to the heater 4 and from there through line 7 to the preheater The cracked gas then enters a cooler 11 through line 10, where the remaining heat that is not in the heater 4 and the preheater 2 is preheated the feedstock has been used, discharged to cooling water or air or feed water and the water vapor contained in the cracked gas is condensed. The gas passes through the line 12 to the compressor 13 in which it is compressed to approximately 320 atmospheres and is fed to the methanol synthesis 15 via the line 14.
* In the methanol synthesis, the reaction partners CO 2, CO and H are converted into crude methanol in a known manner, which is broken down into its main components CH OH, HO and (CH) O by distillation in a known manner.

3 B

16,500 Nm / h of cracked gas produce 6,250 kg / h R / nmethanol and 1,000 kg / h water and 72 kg / h dimethyl ether. In addition, the

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Methanol synthesis plant 1,000 Nm purge gas per hour with the following Composition relaxed g>

CO ₂ =. . 1.0 JVoI. %

GO = 6.0 vol.%

H ₂ = 75.0% by volume

= 18.0% by volume

When relieving the crude methanol on the used in the distillation Pressure of about 5 atmospheres and in the work-up by distillation of the

3 crude ethanols also accumulate 280 Nm / h expansion gas, which is composed as follows:

CO ₂ - 26.0% by volume

CO = 6.0 vol.%

H ₂ = 36.0 Vol. %

CH ₄ = 32.0 vol.%

While the methanol leaves the plant through line 16, this is Purge gas supplied via line 17 to a heating gas line 18, there with

3
1 720 Nm / h methane mixed and the burners 19 of the tubular furnace 6

leads. The supply of 23,000 Nm / h of combustion air to the burners takes place through the blower 20 via line 21 through the air preheater

and the subsequent line 23. The combustion produces 25,600 Nm / h Flue gas of the following composition:

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₂ = 8.05 vol. %

O ₂ * 1.73 VoI,%

N ₂ = .71 * 67 vol% ■

H ₀ O = 18.55

The flue gas leaves the furnace of the tubular furnace through the flue gas duct 24 at a temperature of 970 ° C. and is in a first waste heat boiler 25 cooled to approx. 38 ° G by heat exchange with boiling water The uchgas are in the flue gas duct via the line 26 from the

> 3

The methanol plant supplied 280 Nm / h of expansion gas and 72 kg / h Dimethyl ether added, and this mixture is then the int flue gas duct arranged platinum-containing catalyst 27 with the one contained in the flue gas Oxygen needed to react. Due to the combustion of the expansion gas and the dimethyl ether which takes place with consumption

3 of the oxygen, the amount of flue gas increases to 25 780 Nm / h and the. Composition changes as follows?

GO ₂ = 8.9% by volume

N ₂ =. 71.2 VoI,%

H ₀ O = 19.9% by volume

Due to the released heat of combustion, the Rauchgästemperatur increased to 600 ⁰ C, the Bi is likewise arranged in the flue gas channel _r 'second waste heat boiler 2NC is the flue gas, again by releasing heat ati

-Ii--

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boiling water, cooled to 380 ° C. The two waste heat boilers 25 and 28, like the cracked gas waste heat boiler 8, are via the rising and falling conduit pairs 29; 30 and 31 are connected to the steam drum 32, which is charged with preheated feed water via line 33 and from which the steam generated is withdrawn through line: 34. The vapor is partly added to the ^ methane / CO ₂ mixture via line 35 and partly via the line 36 to other consumers, such as the methanol distillation, and the CO ₂ scrubbing supplied.

The flue gas flows through the air preheater 22 where it is at simultaneous heating of the combustion air to 325 C cools to about 150 C and passes through the line 37 to the flue gas fan 38, which the maintains the desired negative pressure in the furnace of the tubular furnace.

Of the 25,780 km / h flue gas, 13,080 Nm / h are generated without further cooling

3 passed through line 39 into the atmosphere, the remaining 12 700 Nm / h fed through line 40 to a cooler 41, where the im. Flue gas contained Water vapor condenses and the flue gas is cooled to approx. 40 C. The amount of smoke gas remaining after the separation of the water vapor

of 10 200 Nm / h with the following composition:

CO = 11.1 vol.%

N ₂ «88.9% by volume

If a fan 43 is fed via the line 42, it experiences a Pressure increase by about -900 mm WS and is through the line 44 in the Washer 45 introduced.

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In this washer, the flue gas is freed _{from CO 0} by trickling down absorption solution down to a residual content of approx. 2%. Be there

.et

• 3 ■

1 lOÖ Niii GO ₀ absorbed by the absorption solution, the remaining 22

Nm CO "go together with the remaining 9 078 Nm / h nitrogen via line 46 to the atmosphere. _{The CO 0} -loaded absorption solution draining from the scrubber through line 47 is fed with the aid of the pump 48 through line 49 to a heat exchanger 50, where it is heated, and then passes through line 51 into the upper part of regenerator 52, which it trickles through from top to bottom. By means of the steam-heated reboiler 53 arranged on the lower part of the regenerator, the absorption solution is brought to the boil and the rising water vapor causes this in the washer to boil

■ - 3

_{The CO 0} absorbed by the lye is released. The free 1 100 Nm / h

CO ₀ , together with the water vapor that has not condensed in the regenerator, pass via line 54 to cooler 55, where they are cooled and the water vapor is condensed. _{The CO 0} , which is under a slight overpressure of approx. 100-500 mm water column, is transferred to the cooler through line 56

Compressor 57 supplied, from which it after compression to .11 atü through the line 58 enters the line 1, where it is used with the natural gas is mixed.

The absorption solution, which runs out of the regenerator through line 59 and has largely been _{freed from CO 0} , is passed through the line with the aid of pump 60

-13 -

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- ia «

61 fed to the heat exchanger 50 * Where they are in heat exchange to the "loaded" solution is precooled. Then the regenerated solution arrives through the line 62 to the cooler 63 * in which it is brought to the "Vfesch temperature is cooled from about 45 C, and then through line 64 into the Daredevil

Example 2,. ■

With the omission of the platinum-containing catalyst 27 and mentioned in Example I

when burning the 280 Nm / hEnt from the methanol distillation «

¹ 3 ■ ·

tension gas and 75 kg / h Dimethy lather together with 2 180 Nm / h air, which are fed to the combustion chamber by self-priming burners is, but with otherwise the same type of process management increases the smoking

3 3

gas volume from 25 600 Nm / h to 28070 Nm / h with simultaneous temperature rise in the flue gas to 525 ⁰ C ₄ The flue gas contains oxygen and has the following composition:

CO ₂ - 8 * 2 vol.%

O ₂ = 1, 1 VoI,%

N ₂ = 71.8% by volume

H ₂ O ..--. '■ 18.3% by volume

This flue gas is as in Example 1 by heat transfer to boiling Water in the waste heat boiler 28 and to the combustion air in the air preheater 22 is cooled to approx. 160 ° C and passes through line 37 to the flue gas fan 38 i ..

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■ - u-

3 3

Of the 28,010 Nm / h, 14,320 Nm / h are now transmitted via line 39

into the atmosphere, while the remaining 13,750 Nm / h through the Line 40 are fed to the cooler 41, where the flue gas is cooled and the water vapor contained therein is condensed * After separation

of the steam, the remaining gas volume of H 240 Nm / h with the following combination:

CO ₂ - 10.0 vol.%

Ο. = 2.1 % by volume

k "■ -_ * _ ■ - ■

W ^N 2 ^{= 87} ' ⁹

fed through the line 42 to the blower 43, where it increases the pressure of 900 mm WS, to then pass through the line 44 into the washer 45 to get. Here from the trickling down absorption solution 11QO

m. '/ h CO ₂ absorbed. The remaining gas passes through line 46 to the atmosphere, solvent circuit, regeneration and recirculation of the CO ₀ to the natural gas used in line 1 take place as described in Example 1.

W In both experiments the absorbent was an aqueous solution of

ο
Alkali salts of simple amine acids (alkazides).

The oxygen-containing flue gas of experiment 2 caused an hourly loss of 3.5 kg of the absorbent due to oxidizing changes in the absorbent and also required a corrosion-resistant design of the CO ₉ recovery system:

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645851

If one adds that, compared to example 1, the waste heat boiler arranged in the flue gas duct generate about 30% less steam, that the partial pressure CO ₉ in the flue gas is 11% lower and that accordingly the sorbent _{circulation in the CO 2} recovery is 11% higher , which also increases the power requirement of the compressors and pumps
it can be calculated that the low oxygen concentration in the flue gas causes an increase in operating costs of around DM 25 per hour, which means 0.2 million for 8,000 operating hours per year.

■ - 16 - Patent applications

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Claims (7)

-ie- patent claims 1.) 1 process for the production of methanol synthesis gas by cleavage of gaseous hydrocarbons with water vapor and carbon dioxide, characterized in that the to be introduced into the cracking process Carbon dioxide made deoxygenated flue gas from the cracking furnace is won. 2.) "The method according to claim 1, characterized in that the im raw flue gas containing free oxygen with in.this introduced Separable gases or vapors thermally or on catalysts that Platinum or a metal of the platinum group contained is implemented. 3.) Method according to claims 1 and 2, characterized in that Residual gases rich in carbon from methanol synthesis as flammable gases and / or the subsequent methanol distillation into the crude flue gas to be introduced. 4.) Process according to claims 1 and 2, characterized in that that the dimethyl ether formed in the methanol synthesis and obtained in the subsequent methanol distillation is the combustible vapor is introduced into the raw flue gas. 009820/0967 5.) Process according to claims 1 to 4, characterized in that the Wash carbon dioxide from the flue gas in a known manner using Ais by means of organic bases or aqueous solutions of organic Bases or alkali salts of weak organic acids is obtained. 6,) Process according to claims I to 5, characterized in that so much carbon dioxide is added to the hydrocarbon to be split is how to adjust the molar ratio H «: C of at least 2, ο is required - 7.) Process according to claims 1 to 6, characterized in that that a partial flow of the flue gas withdrawn from the cracking furnace made oxygen-free and worked up to carbon dioxide. · 009820 / Q967 Blank page