DE1954781A1 - Solvent preparation for removing acidic impurities from gaseous mixtures - Google Patents

Description

! CHS LUMtfJS COMPAHX, Bloomfield, N.J. / UNITED STATES

Solvent preparation for the removal of acids Impurities from gaseous mixtures

The invention relates to the absorption of acidic impurities, such as carbon dioxide, sulphurous water hydrogen or the like, from gases.

There are many cases in which neutral oasis with acidic Gases are contaminated. The aim of the invention is to create a solvent which, when used, preferably removes such acidic gases. Through the

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Invention, a solvent is made available that removes essentially all of the COg present in the hydrogen is included, the "in a hydrocarbon reforming accrues. This solvent is also capable of COg and HgS Remove natural gas. The solvent according to the invention can be regenerated in a simple manner at the operating temperatures stable and shows good pump and heat transfer properties. The scope of the invention also includes a method in which this solvent is used can be used.

Glycols were previously known as GOg solvents. You own however, they have poor solubility because they are too strongly hydrogenated. This hydrogen bond is also conditional a high viscosity, which stands in the way of a rapid mass transfer between gas phase and liquid phase. Dieters of Mono- and polyglycols have also been proposed, but they are poor in volatility on their molecular weight. Aqueous solutions of alkanolamines have also been used for this purpose. The same thing came a variety of other compounds are used.

The invention provides a new solvent posed, with the help of which acid gases in large quantities have it removed. This solvent is also suitable for painful cleansing. The solvent has both a. good physical solubility for the acidic gases and good chemical affinity. The efficiency of the procedure that can be carried out using the solvent according to the invention, depends, if a distance is greater Quantities intended will depend on the physical solubility of the acidic gases in the solvent. To carry out a

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Fine cleaning removes the last traces of acidic gases removed a chemical affinity. The solvent can be regenerated by flashing and / or by heating and stripping.

According to the invention, solvents are primarily composed of Materials of the formula

where R is a lower alkyl radical, preferably methyl, and E ₁ and R _{2 are} either methylene or lower gem-divalent monoalkyl groups, while η is preferably between 1 and 4. A preferred solvent of this group is 2- (ß-methoxyethoxy) ethanol (hereinafter referred to as BMÄ *.), Where R is methyl, R ₁ and R _{2 are} methylene and η is the number 2. These solvents can optionally contain water and / or one or more alkanolamines. According to. In a preferred embodiment of the method, the gaseous mixture to be purified is contacted in countercurrent in succession with semi-regenerated solvent and then with the same solvent in highly purified form. The enriched solvent is expanded to produce a semi-regenerated solvent, while a smaller portion of the semi-regenerated solvent can be converted into a highly regenerated form by heating and stripping.

An advantage of this solvent and this process is that the water vapor requirement for either the direct stripping or indirect reboiling to remove all acidic gases is much lower

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than when operating a conventional system in which, for example an aqueous alkanolamine system is run.

Another advantage is that this solvent and the method that is carried out using this solvent are suitable for a pump / expander combination for removing the majority of the acidic gases, so that the net energy consumption is also reduced. Because of the high physical solubility of CO ₂ in the solvent mixture, the energy consumption is lower than when using other solvents,

Furthermore, the invention offers the advantage that, although the solvent circulation rate in the section in which the bulk of the sour sas removed is, high, that required Tower diameter is smaller than, for example, in the case of a hot carbonate system. This is a result of the lower operating temperature and the absence of significant amounts of water in the feed gas.

Another advantage is that to perform the Procedure an upright system is to be used, this system only requires low operating costs, and because of the small Xurm diameter as well as because of the small heat transfer surface,

The invention will be explained in more detail with reference to the accompanying drawings explained.

Figure 1 is a logarithmic plot of the history between pressure and solubility when using a commercially available pure B.M.Ä.

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Figure 2 is a log plot of the dependency between pressure and solubility when using 1.25m monoethanolamine with 1.25m triethanolamine and 10 weight- # Water in B.M.Ä.

Figure 3 is a log plot of the relationship between pressure and solubility using a 0.5m Monoethanolamine with 2.5m iriethanolamine and 10 weight ^ Water in B.M.ÄY

Figure 4 is a log plot of the relationship between pressure and solubility using a 0.3m Monoethanolamine with 2.5m triethanolamine and 20 weight ^ Water in B.M.Ä.

FIG. 5 shows a flow diagram of a system which is suitable for carrying out the method according to the invention.

In some cases, for example where there are high COg partial pressures in the feed and moderate pressures in the product, the compounds of the invention are suitable on their own. Other cases may require a two or more component solution. In some cases it is convenient to add water in amounts up to about 20% by weight. In other cases it may appear expedient to add one or more alkanolamines. The preferred concentration ranges vary between 0 and 20% by weight of water and an amount of alkanolamine of 0.5-5.0 molar. As mentioned above, the most preferred material of the form RO (R ₁ R ₂ O) _n H is one in which R is methyl, R ₁ and R _{2 are} methylene and η is the number 2.

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Other compounds of this class which have proven to be particularly suitable are, for example, the following: 2-methoxyethanol (R stands for methyl, R ₁ and R ₂ are methylene and η is 1), 2-methozypropanol (R stands for methyl, R ₁ means ethyl, R ₂ represents methylene and η means 1), 2-ethoxypropanol (R and R ₁ are ethyl, R ₂ stands for methylene and η means 1) and the monomethyl ethers of triethylene glycol (R stands for methyl, R ₁ and R ₂ mean methylene and η is 3).

Solvents of the formula RO (R ₁ R ₂ O) _n H are suitable for sole use when relatively dry gases are processed and when the gas is under a very high pressure and / or when the acidic gas is not to be completely removed . This is generally the case when natural gas is treated. If wet gases are to be treated, then small amounts of water may be present in the solvent. The amount of water present can be up to 40 volumes, but 5-15 volumes are preferred. By suitably controlling the stripper, the water content of the solvent that is fed into the absorber can be lower than that of the enriched solvent, so that the product gas is dehydrated.

Suitable amines are mono-, si- and triethanolamine, diisoproponolamine, N-methylethanolamine, N-methylisopropanolamine ,. N-ethylisopropanolamine and mixtures thereof · Concentrations between 1 and 3 molar of alkanolamine are preferred. Primary, secondary and tertiary amines can be used in place of the alkanolamines. You adding amines to that Solvent depends on the type of gas to be treated. A combination that proved to be particularly suitable has, consists of the solvent, water, a primary

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Alkanolamine (for example monoethanolamine) and a tertiary alkanolamine (for example iriethanolamine). The figures 2-4 show the relationships between pressure and solubility using such solvents. Another Such a combination contains a secondary alkanolamine (e.g. diethanolamine) together with a tertiary one Alkanolamine (e.g. iriethanolamine).

Such solutions are very stable and superior to other amine-containing organic systems, for example those systems in which the solvent contains a carboxyl group, as is the case, for example, with esters, ketones, amides or the like, since amines and HpS react with these materials . The solvents according to the invention are also superior to glycols in terms of both solubility and viscosity. Furthermore, they are more suitable as solvents which contain sulfur, since sulfur, in a known manner, has an adverse effect on catalytic operations which consume fuel. The solvents according to the invention are also superior to aqueous oc "T largely aqueous solvents due to their higher solubility and their higher dissolution rates. The solvents according to the invention combine favorable properties in an optimal way, since of the amine-compatible stable solvents they have the best solubility and at the same time a low solubility The solvency for CO _{2 of} a solvent of the formula RO (R ₁ R ₂ O) _n H (namely (CH 1 OCH ₂ CH ₂ OH)) is shown in Table X below , with comparative values given for other solvents with similar molecular weights.

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Table I.

öOp resolving power (at normal temperature) as well as other properties of organic compounds falling in the pentane molecular weight range

! solvent COo dissolution Kp., ⁰ C
ability ge »* Solution remarks
heat,. 1.4 2.2 high viscosity 103 / atm Kcal / mole 1.4 3.2 ™ .- 2.7 CO ₂ Decomposition 2.5 strong volatile
speed HOOH ₂ CH ₂ OH ₂ OH 5.7 Decomposition 1.7 124.0 2.8 contains sulfur CH ₃ OHOHOH ₂ CH ₃ 7.4 99.5 80.0 low curse
activity, stable C ₅ H ₁₀ 10.0 30.0 2.6 reacts with
Amines, big ones CH ₃ SOCH ₃ 10.7 35.0 Heat of solution CH ₃ OCH ₂ CH ₂ OH 15.4 strong volatile
ability, great CH ₃ COCH ₂ CH ₃ 47.0 Heat of solution 15.9 strong volatile
speed, reacts CHgCHgOCHgCHg with water and 17.5 Amines, big ones CH ₃ COOCH ₃ Heat of solution - Mole - CO ₂ Comment: *

Moles of solution-atm

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As can be seen from FIG. 5, which shows a preferred embodiment of the method according to the invention, the mentioned solvents are used, a gas charge 1, the undesired components (COp and / or HgS and / or other acidic impurities), the Bottom part of the absorption tower 2 supplied, in which the feed in countercurrent with the semi-regenerated solvent 3 will be contacted. The gas flows upwards through it the tower up to the upper section 4, in which a Countercurrent contact with highly regenerated solvent 6 takes place. The purified gas 7 obtained exits from the top of the absorption tower.

The enriched solvent 8 is fed to an expander turbine 9 in which energy is generated. The two-phase mixture is then fed to a pricing drum 11, in which CO ₂ and / or H ₂ S are drawn off via line 12. The main amount of the semi-regenerated solvent 3 is then fed again to the upper part of the bottom section of the absorption tower 2 without further regeneration. The remainder of the semi-regenerated solvent flowing in the line is preheated through the charge effluent exchanger 14 and then passed into the regenerator 16.

In the regenerator 16, the semi-regenerated solvent to remove the residual acidic components using either water vapor or gas or Stripped of indirectly generated steam. The one pouring down overhead Steam 17 from the regenerator 16 is cooled in the cooler 18, whereby the condensable and gaseous products

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* leads.

products are separated in the drum 19. The acid gas will Deducted via line 21. The condensate is together with any fresh water that is at the point 22 on the Pump 23 is fed again to the upper part 14 of the regenerator 16, in which it is used as reflux for organic volatile constituents that may be present in the vapor are used.

The highly regenerated solvent 6 then flows through the BesoMokung effluent heat exchanger 14 through a cooler and is added to the upper section 4 of the absorption tower

As can be seen from Figure 5, both for the distance of acid gases in large quantities as well as for fine cleaning a single solvent used. However, this is only useful if the solvent is both a good ' possesses physical resolving power for the acidic gases as well as a chemical affinity for these gases. at the procedure depends on removal in larger quantities the physical solubility of the acidic gases in the solvent. To be able to carry out a painful cleansing the last traces of the acid gas removed by chemical affinity. This solvent is produced by heating and Stripping regenerates.

Of course, modifications of the method of operation described above can also be carried out without departing from the scope of the invention. If, for example, the BeaoMokung is a methane gas that contains CO ₂ , and if the desired methane recovery is good, then it is possible to find the right solution from the lower absorption tower 2 in a Flaehtroaeel near a Zwieohendruok

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and then to feed the methane-rich gas from the flash tank again to the feed 1 via a compressor. This procedure can also be applied to systems in which the feed gas consists of hydrogen containing _{CO 2;} if the pressure of the feed gas is high and the separation of hydrogen in large quantities is desired. Furthermore, the enriched liquid exiting the expander can be fed to a small stripping tower, whereby some waste nitrogen, for example from an air separation plant, can be used to strip the main part of the solution before it is again pumped back into section 2, in which the removal of the major amount of contamination takes place.

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Claims (2)

- 12 claims' 1. Solvent preparation for removing acidic impurities, such as CO2 and H ₂ S, from gaseous mixtures, characterized by a) a compound of the formula EO (E ₁ E ₂ O) _n H, in which E stands for a lower alkyl radical, E ₁ and E _{2 represent} methylene groups or lower monoalkyl groups and η is an integer, b) water, o) a primary alkanolamine and d) either a secondary or tertiary alkanolamine. 2. A method for removing acidic contaminants, such as CO ₂ and H ₂ S, from a gaseous mixture, characterized in that a) the gaseous mixture is first contacted in countercurrent successively with a solvent which is composed of a compound of the formula EO (E ₁ E ₂ O) _n H, where E is a lower alkyl radical, E ₁ and E _{2 represent} methylene groups or lower monoalkyl groups and η is an integer, where the contact with the solvent is carried out in the semi-regenerated state of the same, and then contact with the solvent in a highly regenerated state to obtain sweet gas and enriched solvent takes place, b) the enriched solvent to remove the gaseous acidic impurities and to transfer the Solvent is expanded to a semi-regenerated state, and c) a small rope of the solvent in the semi-regenerated State, which has been generated in step b), to be converted into a hoohregeneratedji state, which for level a) required, iat. heated and stripped.