WO2013050242A1

WO2013050242A1 - Sorbent for absorption heat pumps

Info

Publication number: WO2013050242A1
Application number: PCT/EP2012/068357
Authority: WO
Inventors: Matthias Seiler; Marc-Christoph Schneider; Olivier Zehnacker; Thomas Kuebelbaeck
Original assignee: Evonik Degussa Gmbh
Priority date: 2011-10-04
Filing date: 2012-09-18
Publication date: 2013-04-11
Also published as: DE102011083976A1

Abstract

The use of an ionic fluid, produced by reaction of formaldehyde, at least one C_1-4 alkylamine, at least one C_1-5 carboxylic acid and glyoxal, as a sorbent in a working medium for absorption heat pumps reduces the corrosiveness of the working medium in comparison to commercially available ionic fluids.

Description

Sorbent for absorption heat pumps

The invention relates to a sorbent for a

Absorption heat pump.

The currently used absorption heat pumps use a working medium containing water as refrigerant and lithium bromide as sorbent. In this

Working medium must not fall below a water concentration of 35 to 40 wt .-% in the working medium, otherwise it would lead to the crystallization of lithium bromide and thereby disruption up to a solidification of the

Working medium can come. Another disadvantage is the high corrosivity of the working medium.

In WO 2005/113702 and WO 2006/134015, it has been proposed to use working media to prevent disturbances by crystallization of the sorbent, which comprise an ionic liquid with organic cations as

Contain sorbent. The use of ionic liquids as sorbents also leads to a lower corrosivity of the working media compared to lithium bromide. Nevertheless, these working media show

Use of commercially available ionic liquids still an undesirably high corrosivity.

WO 91/14678 and WO 2009/074535 describe the preparation of 1,3-dialklyimidazolium salts by reacting an alpha-dicarbonyl compound, an aldehyde, a

Alkylamine and an acid. Described is also the

Preparation of mixtures by using two

different alkylamines. Also described is the use of the 1,3-dialklyimidazolium salts as

Synthesis intermediates, polymer precursors and solvents, e.g. for dissolving cellulose.

WO 02/094883 describes the preparation of halide-free hydrophobic 1,3-dialklyimidazolium salts by reaction of aqueous formaldehyde, one or more alkylamines, an acid and glyoxal, and their use as

Electrolyte with improved ionic conductivity and as a microwave absorbing medium.

WO 2011/056924 describes the use of mixtures of ionic liquids obtained by reaction of

Formaldehyde, two different alkylamines, an acid and glyoxal, as solvents for polymers such as cellulose and chitin.

US 4,450,277 describes the preparation of

1-substituted imidazoles by reacting an alpha-dicarbonyl compound, ammonia, an aldehyde and a primary amine in equimolar amounts.

It has now surprisingly been found that by using an ionic liquid which has been prepared by reacting formaldehyde, an alkylamine, a carboxylic acid and glyoxal as sorbent in a working medium for absorption heat pumps, the corrosivity of the working medium in comparison to commercially available

reduce ionic liquids.

The invention accordingly provides the use of an ionic liquid prepared by imple mentation of formaldehyde, at least one Ci-4-alkylamine, at least one Ci-5-carboxylic acid and glyoxal, as a sorbent in an absorption heat pump.

The invention is also a

An absorption heat pump comprising an absorber, a desorber, a condenser, an evaporator and a working medium, the working medium comprising a refrigerant and an ionic liquid prepared according to the invention.

The term absorption heat pump according to the invention includes all devices that absorb heat at a low temperature level and at a higher Temperature level is released again and by

Heat to be driven to the desorber. The

Absorptive heat pumps according to the invention thus include both absorption chillers and absorption heat pumps in the narrower sense, in which absorber and evaporator are operated at a lower working pressure than desorber and condenser, as well as absorption heat transformers in which absorber and evaporator at a higher

Working pressure can be operated as a desorber and a condenser. In absorption chillers, the intake of

Evaporative heat in the evaporator used to cool a medium. In absorption heat pumps in the narrower sense, the heat released in the condenser and / or absorber is used to heat a medium. In

Absorption heat transformers, the absorption heat released in the absorber is used for heating a medium, wherein the heat of absorption at a higher

Temperature level than when the supply of heat to the desorber is obtained.

The ionic liquid used according to the invention is prepared by reacting formaldehyde, at least one

Ci-4-alkylamine, at least one Ci-5-carboxylic acid and glyoxal produced.

As Ci-4-Alkylamin are all primary alkylamines having 1 to 4 carbon atoms. Preference is given to methylamine,

Ethylamine, n-propylamine and n-butylamine, especially

preferably methylamine and ethylamine, and most preferably methylamine. Ionic liquids produced by the reaction of methylamine show in absorption heat pumps an improved COP efficiency, calculated as the ratio of the heat flow used for cooling to the heat flow supplied to the desorber for operation of the absorption heat pump.

In a preferred embodiment, the ionic liquid is converted by reaction of formaldehyde, at least two different Ci-4-alkylamines, at least one Ci-5-carboxylic acid and glyoxal produced. The

different Ci-4-alkylamines can be added in the reaction as a mixture or in succession.

Preferably, methylamine and ethylamine are used as different Ci-4-alkylamines. The molar ratio of methylamine to ethylamine is preferably in the range from 4: 1 to 30: 1. Ionic liquids produced by reacting methylamine and ethylamine in this ratio exhibit improved COP efficiency in absorption heat pumps. In addition, because of their low viscosity, low melting point and high thermal stability in the desorber, the refrigerant can be expelled to a greater degree.

In a further preferred embodiment, in addition to a C 1-4 -alkylamine, ammonia is also used in the preparation of the ionic liquid. The molar

Ratio of alkylamines to ammonia is thereby

preferably in the range of 5: 1 to 30: 1. The ionic liquids produced in this way also show in

Absorption heat pumps improved COP efficiency and allow the expulsion of the refrigerant to a higher degree.

Monocarboxylic acids are preferably used as the Ci-5-carboxylic acid, particularly preferably formic acid, acetic acid and propionic acid, and most preferably propionic acid. By an appropriate choice of the carboxylic acid, a particularly low corrosivity can be achieved. Likewise, it is also possible to use mixtures of two or more C 1 -C 5 -carboxylic acids, preferably mixtures of formic acid with

Acetic acid, of formic acid with propionic acid and of

Acetic acid with propionic acid.

Formaldehyde and glyoxal are preferably used as aqueous solutions. The implementation of formaldehyde, at least one

Ci-4-alkylamine, at least one Ci-5-carboxylic acid and glyoxal can be carried out in a solvent.

Preferably, however, the reaction takes place without addition of an organic solvent. The implementation takes place

preferably at temperatures in the range of 5 to 40 ° C, particularly preferably 5 to 25 ° C. Preferably, formaldehyde is first reacted with alkylamine, then added carboxylic acid and finally added glyoxal. The reaction can be carried out either batchwise or continuously. Preferably, formaldehyde, alkylamine,

Carboxylic acid and glyoxal in a molar ratio of 1: 2: 1: 1, wherein in mixtures of alkylamines or carboxylic acids, the molar ratio in each case to the

Total amount of alkylamines or carboxylic acids relates.

The ionic liquid obtained by the reaction of formaldehyde, at least one C 1-4 -alkylamine, at least one C 1-5 -carboxylic acid and glyoxal can be used as sorbent in an absorption heat pump without further purification

be used. Preferably, however, unreacted starting materials are removed by evaporation from the ionic liquid after the reaction. Likewise, the

ionic liquid are also purified by short path distillation in vacuo as described in WO 2009/027250. In the use according to the invention, the ionic liquid is used as a sorbent together with a

Used refrigerant. Preferably, the ionic

Liquid with the refrigerants water, methanol or ethanol or with mixtures of these refrigerants used. Most preferably, the refrigerant is water. Especially with water as a refrigerant is a particularly high

Efficiency COP achieved. The working medium of ionic liquid and refrigerant includes in the

use according to the invention preferably 4 to 67 wt .-% refrigerant and 30 to 95 wt .-% ionic liquid and particularly preferably from 20 to 67% by weight of refrigerant and from 30 to 80% by weight of ionic liquid.

In the use according to the invention, the working medium may contain, in addition to refrigerant and ionic liquid, further additives, preferably corrosion inhibitors. The proportion of corrosion inhibitors is preferably 10 to 50,000 ppm, more preferably 100 to 10,000 ppm, based on the mass of the ionic

Liquid. Preferred inorganic corrosion inhibitors are Li ₂ Cr0 ₄ , Li ₂ Mo0 ₄ , Li ₃ VO, LiVO ₃ , NiBr ₂ , Li ₃ PO ₄ , CoBr ₂ and LiOH. Suitable organic corrosion inhibitors are amines and alkanolamines, preferably 2-aminoethanol,

2-aminopropanol and 3-aminopropanol, as well as

Fatty acid alkylolamides referred to amides of fatty acids with alkanolamines and their alkoxylates. Suitable is

For example, the mixture available under the trade name REWOCOROS® AC 101 from Evonik Industries AG

2-aminoethanol and oleic amidoethanol polyethoxylate. As corrosion inhibitors are also organic

Phosphoric acid esters, in particular phosphoric acid esters of ethoxylated fatty alcohols, and fatty acid-alkanolamine mixtures. Preferred organic corrosion inhibitors are benzimidazole and especially benzotriazole.

In the use according to the invention, the working medium can also be used as an additive to improve the efficiency of a monohydric aliphatic alcohol having 6 to 10

Carbon atoms, preferably in an amount of 0.001 to 0.1 wt .-%. The alcohol is preferably a primary alcohol having a branched alkyl group, and more preferably 2-ethyl-1-hexanol.

The absorption heat pump according to the invention comprises an absorber, a desorber, a condenser, a

Evaporator and a working medium, wherein the working medium is a refrigerant and a by reacting formaldehyde, at least one Ci-4-alkylamine, at least one Ci-5-carboxylic acid and glyoxal produced ionic

Liquid includes. Preferably, the ionic

Liquid by one of the previously described preferred embodiments of the reaction of formaldehyde,

Ci-4-alkylamine, Ci-5-carboxylic acid and glyoxal produced.

The in the absorption heat pump according to the invention

used refrigerant is preferably water, methanol, ethanol or a mixture of these refrigerants. Most preferably, the refrigerant is water. Especially with water as a refrigerant, a particularly high COP efficiency is achieved. The working medium of ionic liquid and refrigerant in the use according to the invention preferably comprises from 4 to 67% by weight of refrigerant and from 30 to

95% by weight of ionic liquid and more preferably 20 to 67% by weight of refrigerant and 30 to 80% by weight of ionic liquid.

In the operation of the absorption heat pump according to the invention vapor refrigerant is absorbed in low-refrigerant working medium in the absorber to obtain a

refrigerant-rich working medium and releasing heat of absorption. From the thus obtained refrigerant-rich working medium is in the desorber with heat

Refrigerant vapor desorbs to give

low-refrigerant working medium, which is returned to the absorber. The obtained in the desorber vapor refrigerant is in the condenser to release

Condensation heat condenses, the resulting liquid refrigerant is in the evaporator taking up

Evaporated heat evaporates and the resulting

vaporous refrigerant is added to the absorber

returned.

The absorption heat pump according to the invention can be designed both in one stage and in several stages with several coupled circuits of the working medium. In a preferred embodiment, the

Absorption heat pump is an absorption chiller and in the evaporator heat from a medium to be cooled

recorded.

The use of an ionic liquid which has been prepared by reacting formaldehyde, at least one C 1-4 -alkylamine, at least one C 1-5 -carboxylic acid and glyoxal as sorbent in an absorption heat pump permits the corrosion of metallic materials, in particular components of copper and steel, in the

Avoid absorption heat pump. This allows the

Use of easier to process and

cheaper materials when using

Lithium bromide or a commercially available ionic

Liquid can not be used as a sorbent because of their corrosivity in contact with the working medium.

Examples Example 1

Preparation of 1,3-dimethylimidazolium acetate

622 g (8.00 mol) of 40% by weight aqueous methylamine are initially introduced at 5 ° C. in a cooled jacketed reactor. Within 15 min, 325 g (4.00 mol) of 37 wt .-% aqueous formaldehyde are added with stirring and then within 15 min 241 g of acetic acid, wherein the

Reaction temperature is maintained by cooling to 10 ° C. After stirring for 60 minutes, 580 g (4.00 mol) of 40% by weight aqueous glyoxal are metered in at 15 to 20 ° C., and

then stirred for a further 120 min at 20 ° C.

Subsequently, water and unreacted starting materials are distilled off on a rotary evaporator. There are obtained 612 g (98%) of 1, 3-dimethylimidazolium acetate. Example 2

Preparation of 1,3-dimethylimidazolium propionate

Example 1 is repeated, but 296 g (4.00 mol) of propionic acid are used instead of acetic acid. There are obtained 660 g (97%) of 1, 3-dimethylimidazolium propionate.

Example 3

Preparation of 1,3-dimethylimidazolium butyrate Example 1 is mixed with 188 g (2.40 mol) of 40 wt% aqueous methylamine, 98 g (1.20 mol) of 37 wt% aqueous

Formaldehyde, 106 g (1.20 mol) of butyric acid in place of acetic acid and 175 g (1.20 mol) 40 wt .-% aqueous glyoxal repeated. It will be 208 g (94%)

Obtained 1,3-dimethylimidazolium butyrate.

Example 4

Preparation of 1,3-dimethylimidazolium pivalate

Example 3 is repeated, but instead of the butyric acid 123 g (1.20 mol) of pivalic acid is used. There are obtained 206 g (94%) of 1, 3-dimethylimidazolium pivalate.

Example 5

Preparation of 1,3-diethylimidazolium acetate Example 3 is repeated, but instead of the methylamine, 155 g (2.40 mol) of ethylamine are used instead of the methylamine

Butyric acid used 73 g (1.20 mol) of acetic acid. There are obtained 217 g (98%) of 1, 3-Diethylimidazoliumacetat. Example 6

Preparation of a mixture of

1,3-dimethylimidazolium acetate, 1,3-diethylimidazolium acetate and 1-ethyl-3-methylimidazolium acetate. Example 5 is repeated, but instead of the ethylamine, a mixture of 94 g (1.20 mol) 40% by weight is used.

aqueous methylamine and 78 g (1.20 mol) of ethylamine

used. There are 194 g (95%) of a mixture of

1, 3-Dimethylimidazoliumacetat, 1, 3-diethylimidazolium acetate and 1-ethyl-3-methylimidazoliumacetat in the molar ratio 1: 1: 2.

Examples 7 to 27

Corrosivity of ionic liquids mixed with water

For mixtures of ionic liquid, water and optionally corrosion inhibitor, the corrosion rate of copper, material number 2.0060 (E-Cu57 according to DIN) and of stainless steel, was determined by measuring the potentiodynamic polarization resistance and evaluation by panel plot according to the method ASTM G59-97 (2009). Material number 1.4463, determined. The investigated ionic liquids and their trade names, the proportions by weight of ionic liquid and corrosion inhibitor and the specific corrosion rates are summarized in Tables 1 and 2.

In a comparative measurement with a mixture of 55 wt .-% lithium bromide and 45 wt .-% water was for copper,

Material number 2.0060, a corrosion rate of 2.3 mm / year determined. Table 1

Corrosivity to copper, material number 2.0060

* Proportions in weight percent, balance to 100% is water ** not according to the invention

Table 1 (continued)

Corrosivity to copper, material number 2.0060

^ Parts by weight, the rest to 100% is water

Table 2

Corrosivity to stainless steel, material number 1.4463

* Percentages by weight, the rest to 100% is water

L-ethyl-3-methylimidazolium acetate BASIONICS ™ from BASF SE is prepared by ion exchange from 1-ethyl-3-methylimidazolium chloride.

1, 3-dimethylimidazolium acetate and

1, 3-Dimethylimidazoliumpropionat the company Proionic GmbH are by alkylation of methylimidazole with

Dimethyl carbonate and subsequent reaction of the formed 1, 3-Dimethylimidazoliummethylcarbonats with acetic acid or propionic acid.

Claims

Claims:

1. Use of an ionic liquid prepared

by reaction of formaldehyde, at least one

Ci-4-alkylamine, at least one Ci-5-carboxylic acid and glyoxal, as a sorbent in one

Absorption heat pump.

2. Use according to claim 1, characterized in that the ionic liquid by reaction of

Formaldehyde, methylamine, at least one

Ci-5-carboxylic acid and glyoxal was prepared.

3. Use according to claim 1, characterized in that the ionic liquid by reaction of

Formaldehyde, at least two different ones

Ci-4-alkylamines, at least one Ci-5-carboxylic acid and glyoxal was prepared.

4. Use according to claim 3, characterized in that the ionic liquid by reaction of

Formaldehyde, methylamine, ethylamine, at least one Ci-5-carboxylic acid and glyoxal was prepared.

5. Use according to claim 4, characterized in that in the reaction, the molar ratio of methylamine to ethylamine in the range of 4: 1 to 30: 1.

6. Use according to one of the preceding claims,

characterized in that in the implementation

in addition to a Ci-4-alkylamine ammonia is used.

7. Use according to claim 6, characterized in that in the reaction, the molar ratio of alkylamines to ammonia in the range of 5: 1 to 30: 1.

Use according to one of the preceding claims, characterized in that the ionic liquid was prepared by reaction with propionic acid.

9. Use according to one of the preceding claims,

characterized in that the ionic liquid is used with a refrigerant selected from water, methanol, ethanol and mixtures of these refrigerants.

Use according to claim 9, characterized in that the refrigerant is water.

An absorption heat pump comprising an absorber, a desorber, a condenser, an evaporator and a working medium comprising a refrigerant and an ionic liquid prepared according to any one of claims 1 to 8.

12. absorption heat pump according to claim 11, characterized

characterized in that the refrigerant is selected from water, methanol, ethanol and mixtures thereof

Refrigerant.

13. absorption heat pump according to claim 12, characterized

characterized in that the refrigerant is water.

14. Absorption heat pump according to one of claims 11 to 13, characterized in that it has a

Absorption chiller is and absorbs heat from a medium to be cooled in the evaporator.