U.S. patent application number 13/641591 was filed with the patent office on 2013-02-07 for absorption heat pump with sorbent comprising lithium chloride and an organic chloride salt.
This patent application is currently assigned to EVONIK DEGUSSA GMBH. The applicant listed for this patent is Marc-Christoph Schneider, Rolf Schneider, Matthias Seiler, Olivier Zehnacker. Invention is credited to Marc-Christoph Schneider, Rolf Schneider, Matthias Seiler, Olivier Zehnacker.
Application Number | 20130031930 13/641591 |
Document ID | / |
Family ID | 42647440 |
Filed Date | 2013-02-07 |
United States Patent
Application |
20130031930 |
Kind Code |
A1 |
Seiler; Matthias ; et
al. |
February 7, 2013 |
ABSORPTION HEAT PUMP WITH SORBENT COMPRISING LITHIUM CHLORIDE AND
AN ORGANIC CHLORIDE SALT
Abstract
An absorption heat pump with a sorbent which comprises lithium
chloride and at least one salt Q.sup.+Cl.sup.- with an organic
cation Q.sup.+ and the shared anion chloride, the organic cation
Q.sup.+ having a molar mass of not more than 200 g/mol, exhibits an
improved degassing range of the working medium composed of
refrigerant and sorbent.
Inventors: |
Seiler; Matthias;
(Griesheim, DE) ; Zehnacker; Olivier;
(Recklinghausen, DE) ; Schneider; Rolf;
(Grundau-Rothenbergen, DE) ; Schneider;
Marc-Christoph; (Darmstadt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seiler; Matthias
Zehnacker; Olivier
Schneider; Rolf
Schneider; Marc-Christoph |
Griesheim
Recklinghausen
Grundau-Rothenbergen
Darmstadt |
|
DE
DE
DE
DE |
|
|
Assignee: |
EVONIK DEGUSSA GMBH
Essen
DE
|
Family ID: |
42647440 |
Appl. No.: |
13/641591 |
Filed: |
April 14, 2011 |
PCT Filed: |
April 14, 2011 |
PCT NO: |
PCT/EP11/55897 |
371 Date: |
October 16, 2012 |
Current U.S.
Class: |
62/476 |
Current CPC
Class: |
C09K 5/047 20130101;
F25B 15/14 20130101 |
Class at
Publication: |
62/476 |
International
Class: |
F25B 15/00 20060101
F25B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2010 |
EP |
10160431.2 |
Claims
1-12. (canceled)
13. An absorption heat pump comprising an absorber, a desorber, a
condenser, an evaporator, a volatile refrigerant and a sorption
medium, wherein said sorption medium comprises lithium chloride and
at least one salt Q.sup.+Cl.sup.- comprising an organic cation
Q.sup.+ and the shared anion chloride, and wherein the organic
cation Q.sup.+ has a molar mass of not more than 200 g/mol.
14. The absorption heat pump of claim 13, wherein the sorption
medium contains lithium chloride and the salt Q.sup.+Cl.sup.- in a
molar ratio at which the melting point of the mixture of lithium
chloride and salt Q.sup.+Cl.sup.- is lower than the melting points
of the components lithium chloride and Q.sup.-Cl.sup.-.
15. The absorption heat pump of claim 14 wherein the sorption
medium contains lithium chloride and the salt Q.sup.+Cl.sup.- in a
molar ratio which deviates by not more than 25% from the molar
ratio of a eutectic mixture of lithium chloride and the salt
Q.sup.+Cl.sup.-.
16. The absorption heat pump of claim 13, wherein the proportion of
lithium chloride and the salt Q.sup.+Cl.sup.- in the sorption
medium is more than 50% by weight.
17. The absorption heat pump of claim 13, wherein the refrigerant
is selected from the group consisting of: methanol, ethanol,
2-propanol, trifluoroethanol, sulphur dioxide, carbon dioxide and
ammonia.
18. The absorption heat pump of claim 13, wherein the refrigerant
is water.
19. The absorption heat pump of claim 13, wherein a solution of
lithium chloride in the refrigerant which is saturated at
35.degree. C. has a higher vapour pressure than a mixture of the
salt Q.sup.+Cl.sup.- and the refrigerant having the same proportion
by weight of refrigerant.
20. The absorption heat pump of claim 13, wherein the organic
cation Q.sup.+ is selected from the group consisting of: 1,3
dialkylimidazolium ions; 1,3-dialkyl-imidazolinium ions;
N-alkylpyridinium ions; N,N-dialkylpyrrolidinium ions; and ammonium
ions having the structure R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+,
wherein R.sup.1, R.sup.2 and R.sup.3 are each, independently of one
another, hydrogen, alkyl or hydroxyethyl and R.sup.4 is an alkyl
radical.
21. The absorption heat pump of claim 13, wherein said absorption
heat pump is operated as absorption refrigeration machine and heat
is taken up in the evaporator from a medium to be cooled.
22. The absorption heat pump of claim 13, wherein said absorption
heat pump has a two-stage construction.
23. The absorption heat pump of claim 13, wherein a vapour phase
containing refrigerant and a liquid phase containing sorption
medium are separated from one another by a semipermeable membrane
in the absorber and/or desorber and the semipermeable membrane is
permeable to the refrigerant and impermeable to the sorption
medium.
24. The absorption heat pump of claim 13, wherein at least one of
the components absorber, desorber, condenser and evaporator has a
wall surface made of a polymeric material selected from among
polyamides, polyimides and polyether ether ketone via which heat is
exchanged with the surroundings.
25. The absorption heat pump of claim 15, wherein the proportion of
lithium chloride and the salt Q.sup.+Cl.sup.- in the sorption
medium is more than 50% by weight.
26. The absorption heat pump of claim 25, wherein the refrigerant
is selected from the group consisting of: methanol, ethanol,
2-propanol, trifluoroethanol, sulphur dioxide, carbon dioxide and
ammonia.
27. The absorption heat pump according of claim 25, wherein the
refrigerant is water.
28. The absorption heat pump of claim 17, wherein the organic
cation Q.sup.+ is selected from the group consisting of: 1,3
dialkylimidazolium ions; 1,3-dialkyl-imidazolinium ions;
N-alkylpyridinium ions; N,N-dialkylpyrrolidinium ions; and ammonium
ions having the structure R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+,
wherein R.sup.1, R.sup.2 and R.sup.3 are each, independently of one
another, hydrogen, alkyl or hydroxyethyl and R.sup.4 is an alkyl
radical.
29. The absorption heat pump of claim 18, wherein the organic
cation Q.sup.+ is selected from the group consisting of: 1,3
dialkylimidazolium ions; 1,3-dialkyl-imidazolinium ions;
N-alkylpyridinium ions; N,N-dialkylpyrrolidinium ions; and ammonium
ions having the structure R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+,
wherein R.sup.1, R.sup.2 and R.sup.3 are each, independently of one
another, hydrogen, alkyl or hydroxyethyl and R.sup.4 is an alkyl
radical.
30. The absorption heat pump of claim 29, wherein a vapour phase
containing refrigerant and a liquid phase containing sorption
medium are separated from one another by a semipermeable membrane
in the absorber and/or desorber and the semipermeable membrane is
permeable to the refrigerant and impermeable to the sorption
medium.
31. The absorption heat pump of claim 30, wherein the proportion of
lithium chloride and the salt Q.sup.+Cl.sup.- in the sorption
medium is more than 50% by weight.
32. The absorption heat pump of claim 31, wherein the sorption
medium contains lithium chloride and the salt Q.sup.+Cl.sup.- in a
molar ratio which deviates by not more than 25% from the molar
ratio of a eutectic mixture of lithium chloride and the salt
Q.sup.+Cl.sup.-.
Description
[0001] The invention is directed to an absorption heat pump having
an improved degassing range of the working medium.
[0002] Classical heat pumps are based on a circuit of a refrigerant
via an evaporator and a condenser. In the evaporator, a refrigerant
is vaporised and heat is withdrawn from a first medium due to the
heat of vaporisation taken up by the refrigerant. The vaporised
refrigerant is then brought to a higher pressure with a compressor
and condensed in the condenser at a higher temperature than in the
evaporation, resulting in the heat of vaporisation being liberated
again and heat being passed to a second medium at a higher
temperature level. The liquefied refrigerant is subsequently
depressurised again to the pressure of the evaporator.
[0003] The classical heat pumps have the disadvantage that they
consume a large amount of mechanical energy for compression of the
gaseous refrigerant. Absorption heat pumps, on the other hand, have
a reduced mechanical energy requirement. Absorption heat pumps
have, in addition to the refrigerant, the evaporator and the
condenser of a classical heat pump, a sorption medium, an absorber
and a desorber. In the absorber, the vaporised refrigerant is
absorbed in the sorption medium at the pressure of the evaporation
and the refrigerant is subsequently desorbed again from the
sorption medium in the desorber by introduction of heat at the
higher pressure of the condensation. The compression of the liquid
working medium composed of refrigerant and sorption medium requires
less mechanical energy than the compression of the refrigerant
vapour in a classical heat pump; the consumption of mechanical
energy is replaced by the heat energy used for desorption of the
refrigerant.
[0004] The size of the circuit of sorption medium via absorber and
desorber required for operation of an absorption heat pump is
determined essentially by the degassing range of the working medium
of the absorption heat pump; for the present purposes, the working
medium is the mixture of sorption medium and refrigerant in the
circuit via absorber and desorber of the absorption heat pump and
the term degassing range refers to the difference in the
refrigerant content between refrigerant-depleted working medium and
refrigerant-rich working medium. To be able to construct compact
and inexpensive absorption heat pumps, there is therefore a need
for absorption heat pumps having a large degassing range.
[0005] A large part of the absorption heat pumps used in industry
uses a working medium which contains water as refrigerant and
lithium bromide as sorption medium. However, this working medium
has an unsatisfactory degassing range in many applications, since
in the case of a working medium composed of water and lithium
bromide the water concentration in the working medium must not go
below from 35 to 40% by weight because otherwise crystallization of
lithium bromide and thus solidification of the working medium can
occur.
[0006] Working media which contain water as refrigerant and lithium
chloride as sorption medium are not used industrially in absorption
heat pumps since in the case of such working media in most
applications the degassing range has to be kept even smaller than
in the case of working media composed of water and lithium bromide
in order to avoid crystallization of lithium chloride.
[0007] WO 2005/113702 describes absorption heat pumps which use a
working medium having an ionic liquid as sorption medium, with the
ionic liquid preferably having unlimited miscibility with the
refrigerant. Although the problem of crystallization of the
sorption medium can be avoided when using ionic liquid as sorption
medium, the degassing range achieved is generally no better than in
the case of working media composed of water and lithium bromide,
especially not for working media containing water as
refrigerant.
[0008] WO 2006/134015 describes, in Example VII a), the use of the
ionic liquids 1-ethyl-3-methylimidazolium methylsulphonate,
1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium
hydroxide as additives for a working medium composed of lithium
bromide and water in order to reduce the crystallisation
temperature of the sorption medium. However, the proportions of
water, lithium bromide and ionic liquid which should be present in
the working medium are not disclosed and nothing is disclosed about
the influence of the additive on the degassing range of the working
medium.
[0009] In Korean J. Chem. Eng., 23 (2006) 113-116, K.-S. Kim et al.
propose working media composed of water, lithium bromide and the
ionic liquid 1-butyl-3-methylimidazolium bromide, which working
media contain lithium bromide and the ionic liquid in a weight
ratio of 4:1 and 7:1. In these working media, the ionic liquid acts
as anticrystallisation additive which increases the solubility of
lithium bromide and reduces the crystallisation temperature.
However, nothing about the degassing range of the working media
disclosed can be deduced from the solubilities, viscosities and
surface tensions disclosed.
[0010] It has now surprisingly been found that the use of a working
medium comprising, as sorption medium, lithium chloride and at
least one salt Q.sup.+Cl.sup.- having an organic cation Q.sup.+
having a molar mass of not more than 200 g/mol and the shared anion
chloride makes it possible to achieve a higher degassing range of
the working medium than when using lithium chloride or the salt
Q.sup.+Cl.sup.- alone.
[0011] The invention accordingly provides an absorption heat pump
comprising an absorber, a desorber, a condenser, an evaporator, a
volatile refrigerant and a sorption medium comprising lithium
chloride and at least one salt Q.sup.+Cl.sup.- having an organic
cation Q.sup.+ and the shared anion chloride, where the organic
cation Q.sup.+ has a molar mass of not more than 200 g/mol.
[0012] The absorption heat pump of the invention comprises an
absorber, a desorber, a condenser, an evaporator, a volatile
refrigerant and a sorption medium. The working medium of the
absorption heat pump is a mixture of sorption medium and
refrigerant. During operation of the absorption heat pump of the
invention, gaseous refrigerant is absorbed in refrigerant-depleted
working medium in the absorber to give a refrigerant-rich working
medium with liberation of heat of absorption. In the desorber,
gaseous refrigerant is desorbed from the obtained refrigerant-rich
working medium by supply of heat to give refrigerant-depleted
working medium which is recirculated to the absorber. The gaseous
refrigerant obtained in the desorber is condensed in the condenser
to liberate heat of condensation, the liquid refrigerant obtained
is vaporised in the evaporator, taking up heat of vaporisation, and
the gaseous refrigerant obtained in the process is recirculated to
the absorber.
[0013] The term absorption heat pump, as used in the invention,
encompasses all apparatuses by means of which heat is taken up at a
low temperature level and given off again at a higher temperature
level and which are driven by supply of heat to the desorber. The
absorption heat pumps of the invention thus encompass both
absorption refrigeration machines and absorption heat pumps in the
narrower sense, in which absorber and evaporator are operated at a
lower working pressure than desorber and condenser, and absorption
heat transformers, in which absorber and evaporator are operated at
a higher working pressure than desorber and condenser. In
absorption refrigeration machines, the uptake of heat of
vaporisation in the evaporator is used for cooling a medium. In
absorption heat pumps in the narrower sense, the heat liberated in
the condenser and/or absorber is used for heating a medium. In
absorption heat transformers, the heat of absorption liberated in
the absorber is used for heating a medium, with the heat of
absorption being obtained at a higher temperature level than the
heat supplied to the desorber. In a preferred embodiment, the
absorption heat pump is operated as absorption refrigeration
machine and heat is taken up in the evaporator from a medium to be
cooled.
[0014] The absorption heat pump of the invention comprises a
sorption medium comprising lithium chloride and at least one salt
Q.sup.+Cl.sup.- having an organic cation Q.sup.+. Lithium chloride
and the salt Q.sup.+Cl.sup.- have the anion chloride in common. The
proportion of lithium chloride and salt Q.sup.+Cl.sup.- in the
sorption medium is preferably more than 50% by weight and
particularly preferably more than 80% by weight. The sorption
medium can contain other lithium salts such as lithium bromide,
lithium nitrate, lithium formate, lithium acetate and lithium
carbonate in addition to lithium chloride. The proportion of
lithium chloride in the total amount of lithium salts is preferably
more than 80% by weight, particularly preferably more than 90% by
weight.
[0015] The sorption medium preferably contains lithium chloride and
the salt Q.sup.+Cl.sup.- in a molar ratio at which the melting
point of the mixture of lithium chloride and the salt
Q.sup.+Cl.sup.- is lower than the melting points of the components
lithium chloride and Q.sup.+Cl.sup.-. The sorption medium
particularly preferably contains lithium chloride and the salt
Q.sup.+Cl.sup.- in a molar ratio which deviates by not more than
25% from the molar ratio of a eutectic mixture of lithium chloride
and the salt Q.sup.+Cl.sup.-. At the preferred molar ratios of
lithium chloride and the salt Q.sup.+Cl.sup.-, a particularly wide
degassing range of the working medium is achieved and the working
medium can be used in the absorption heat pump in a particularly
wide temperature range.
[0016] In the salt Q.sup.+Cl.sup.- the organic cation Q.sup.+ has a
molar mass of not more than 200 g/mol and preferably not more than
165 g/mol. The use of one or more salts Q.sup.+Cl.sup.- whose
organic cation Q.sup.+ has a low molar mass according to the
invention is essential for achieving a wide degassing range of the
working medium.
[0017] Suitable organic cations are, in particular, cations of the
general formulae (I) to (V):
R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+ (I)
R.sup.1R.sup.2R.sup.3R.sup.4P.sup.+ (II)
R.sup.1R.sup.2R.sup.3S.sup.+ (III)
R.sup.1R.sup.2N.sup.+.dbd.C(NR.sup.3R.sup.4)(NR.sup.5R.sup.6)
(IV)
R.sup.1R.sup.2N.sup.+.dbd.C(NR.sup.3R.sup.4)(XR.sup.5) (V)
[0018] where
[0019] R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 are
identical or different and are each hydrogen, a linear or branched
aliphatic or olefinic hydrocarbon radical, a cycloaliphatic or
cycloolefinic hydrocarbon radical, an aromatic hydrocarbon radical,
an alkylaryl radical, a linear or branched aliphatic or olefinic
hydrocarbon radical terminally functionalised by OH, OR', NH.sub.2,
N(H)R' or N(R').sub.2 or a polyether radical of the formula
--(R.sup.7--O).sub.n--R.sup.8, where in the case of cations of
formula (V) R.sup.5 is not hydrogen,
[0020] R' is an aliphatic or olefinic hydrocarbon radical,
[0021] R.sup.7 is a linear or branched alkylene radical containing
2 or 3 carbon atoms,
[0022] n is from 1 to 3,
[0023] R.sup.8 is hydrogen or a linear or branched aliphatic or
olefinic hydrocarbon radical,
[0024] X is an oxygen atom or a sulphur atom, and
[0025] where at least one and preferably each of the radicals
R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 is
different from hydrogen.
[0026] Cations of the formulae (I) to (V) in which the radicals
R.sup.1 and R.sup.3 together form a 4- to 10-membered, preferably
5- to 6-membered, ring are likewise suitable.
[0027] Further suitable cations are heteroaromatic cations having
at least one quaternary nitrogen atom in the ring, said atom
bearing a radical R.sup.1 as defined above, preferably derivatives
of pyrrole, pyrazole, imidazole, oxazole, isoxazole, thiazole,
isothiazole, pyridine, pyrimidine, pyrazine, indole, quinoline,
isoquinoline, cinnoline, quinoxaline or phthalazine which are
substituted on the nitrogen atom.
[0028] The organic cation Q.sup.+ preferably contains a quaternary
nitrogen atom. The organic cation Q.sup.+ is preferably a
1,3-dialkylimidazolium ion, 1,3-dialkylimidazolinium ion,
N-alkylpyridinium ion, N,N-dialkylpyrrolidinium ion or an ammonium
ion having the structure R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+, where
R.sup.1, R.sup.2 and R.sup.3 are each, independently of one
another, hydrogen, alkyl or hydroxyethyl and R.sup.4 is an alkyl
radical.
[0029] The organic cation Q.sup.+ is particularly preferably a
1,3-dialkylimidazolium ion in which the alkyl groups are selected
independently from among methyl, ethyl, n-propyl and n-butyl. The
organic cation Q.sup.+ is particularly preferably
1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium,
1-(n-butyl)-3-methylimidazolium or
1-(n-butyl)-3-ethylimidazolium.
[0030] In a further particularly preferred embodiment, the salt
Q.sup.+Cl.sup.- is choline chloride.
[0031] The salt Q.sup.+Cl.sup.- is preferably thermally stable up
to a temperature of 150.degree. C. Preference is given to using
salts Q.sup.+Cl.sup.- which have a solubility in water of at least
500 g/l. Preference is given to using salts Q.sup.+Cl.sup.- which
are stable to hydrolysis. Hydrolysis-stable salts Q.sup.+Cl.sup.-
display less than 5% decomposition by hydrolysis in a mixture with
50% by weight of water when stored at 80.degree. C. for 8000
hours.
[0032] The sorption medium can contain further salts having an
organic cation and other anions such as bromide, nitrate, formate,
acetate or carbonate in addition to the salt Q.sup.+Cl.sup.-. The
proportion of chloride salts Q.sup.+Cl.sup.- in the total amount of
organic salts is preferably more than 80% by weight, particularly
preferably more than 90% by weight.
[0033] The absorption heat pump of the invention preferably
contains water, methanol, ethanol, 2-propanol, trifluoroethanol,
sulphur dioxide, carbon dioxide or ammonia, particularly preferably
water, ethanol, 2-propanol or trifluoroethanol and most preferably
water, as refrigerant.
[0034] In a preferred embodiment, the salt Q.sup.+Cl.sup.- and the
refrigerant are selected so that a solution of lithium chloride in
the refrigerant which is saturated at 35.degree. C. has a higher
vapour pressure than a mixture of the salt Q.sup.+Cl.sup.- and the
refrigerant having the same proportion by weight of refrigerant.
Preference is given to using water, methanol, ethanol, 2-propanol
or trifluoroethanol and particularly preferably water as
refrigerant. Examples of such an embodiment are
1-ethyl-3-methylimidazolium chloride, choline chloride or
tetramethylammonium chloride as salt Q.sup.+Cl.sup.- and water as
refrigerant. A further-improved degassing range of the working
medium can be achieved by a corresponding selection of salt
Q.sup.+Cl.sup.- and refrigerant.
[0035] The absorption heat pump of the invention can contain
further additives, preferably corrosion inhibitors and/or additives
which promote wetting, in the working medium in addition to
sorption medium and refrigerant. The proportion of corrosion
inhibitors is preferably from 10 to 50 000 ppm, particularly
preferably from 100 to 10 000 ppm, based on the mass of the
sorption medium. The proportion of additives which promote wetting
is preferably from 10 to 50 000 ppm, particularly preferably from
100 to 10 000 ppm, based on the mass of the sorption medium.
[0036] All non-volatile corrosion inhibitors, which are known from
the prior art to be suitable for the materials used in the
absorption heat pump, can be used as corrosion inhibitors.
[0037] Preferably one or more surfactants from the group consisting
of nonionic surfactants, zwitterionic surfactants and cationic
surfactants are used as additive which promotes wetting.
[0038] Suitable nonionic surfactants are alkylamine alkoxylates,
amidoamines, alkanolamides, alkylphosphine oxides,
alkyl-N-glucamides, alkyl glucosides, bile acids, alkyl
alkoxylates, sorbitan esters, sorbitan ester ethoxylates, fatty
alcohols, fatty acid ethoxylates, ester ethoxylates and
polyethersiloxanes.
[0039] Suitable zwitterionic surfactants are betaines,
alkylglycines, sultains, amphopropionates, amphoacetates, tertiary
amine oxides and silicobetaines.
[0040] Suitable cationic surfactants are quaternary ammonium salts
having one or two substituents having from 8 to 20 carbon atoms, in
particular corresponding tetraalkylammonium salts, alkylpyridinium
salts, ester quats, diamidoamine quats, imidazolinium quats,
alkoxyalkyl quats, benzyl quats and silicone quats.
[0041] In a preferred embodiment, the additive which promotes
wetting comprises one or more nonionic surfactants of the general
formula R(OCH.sub.2CHR').sub.nOH where m is from 4 to 40 and R is
an alkyl radical having from 8 to 20 carbon atoms, an alkylaryl
radical having from 8 to 20 carbon atoms or a polypropylene oxide
radical having from 3 to 40 propylene oxide units and R' is methyl
or preferably hydrogen.
[0042] In a further preferred embodiment, the additive which
promotes wetting comprises a polyether-polysiloxane copolymer
containing more than 10% by weight of [Si(CH.sub.3).sub.2O] units
and more than 10% by weight of [CH.sub.2CHR--O] units, where R is
hydrogen or methyl. Particular preference is given to
polyether-polysiloxane copolymers of the general formulae (VI) to
(VIII):
(CH.sub.3).sub.3Si--O--[SiR--(CH.sub.3)--O].sub.n--Si(CH.sub.3).sub.3
(VI)
R.sup.2O-A.sub.p-[B-A].sub.n-A.sub.q-R.sup.2 (VII)
R.sup.2O-[A-Z
].sub.p--[B--Si(CH.sub.3).sub.2--Z--O-A-Z].sub.n--B--Si(CH.sub.3).sub.2[Z-
--O-A].sub.qO.sub.1-qR.sup.2 (VIII)
[0043] where
[0044] A is a divalent radical of the formula
--[CH.sub.2CHR.sup.3--O].sub.r--,
[0045] B is a divalent radical of the formula
--[Si(CH.sub.3).sub.2--O].sub.s--,
[0046] Z is a divalent linear or branched alkylene radical having
from 2 to 20 carbon atoms, preferably --(CH.sub.2).sub.3--,
[0047] n is from 1 to 30,
[0048] m is from 2 to 100,
[0049] p, q are each 0 or 1,
[0050] r is from 2 to 100,
[0051] s is from 2 to 100,
[0052] from 1 to 5 of the radicals R.sup.1 are radicals of the
general formula --Z--O-A-R.sup.2 and the remaining radicals R.sup.1
are each methyl,
[0053] R.sup.2 is hydrogen or an aliphatic or olefinic alkyl
radical or acyl radical having from 1 to 20 carbon atoms and
[0054] R.sup.3 is hydrogen or methyl.
[0055] The additives which promote wetting are known to those
skilled in the art from the prior art as additives for aqueous
solutions and can be prepared by methods known from the prior
art.
[0056] In a preferred embodiment of the absorption heat pump of the
invention, the refrigerant-containing vapour phase and the sorption
medium-containing liquid phase are separated from one another by a
semipermeable membrane in the absorber and/or desorber, with the
semipermeable membrane being permeable to the refrigerant and
impermeable to the sorption medium.
[0057] The semipermeable membrane is preferably a solution
diffusion membrane. A solution diffusion membrane has virtually no
pores. For a solution diffusion membrane the selective permeability
of the membrane for the refrigerant is due to the refrigerant
dissolving in the material of the membrane and diffusing through
the membrane, while the sorption medium is insoluble in the
material of the membrane. The suitability of a solution diffusion
membrane for the absorption heat pump of the invention can
therefore be determined by a person skilled in the art by simple
tests on the solubility of refrigerant and sorption medium in the
material of the membrane.
[0058] For the embodiment using water as refrigerant, it is
possible to use any pore-free membrane, known to those skilled in
the art from the technical fields of dialysis, reverse osmosis and
pervaporation as being suitable for the removal of salts from
aqueous salt solutions, as solution diffusion membrane.
[0059] The material used for the solution diffusion membrane is
preferably a hydrophilic or hydrophilically functionalised polymer
containing polyvinyl alcohol, polyimide, polybenzimidazole,
polybenzimidazolone, polyamide hydrazide, cellulose ester,
cellulose acetate, cellulose diacetate, cellulose triacetate,
cellulose butyrate, cellulose nitrate, polyurea, polyfuran,
polyethylene glycol, poly(octylmethylsiloxane), polysiloxane,
polyalkylsiloxane, polydialkylsiloxane, polyester-polyether block
copolymer, polysulphone, sulphonated polysulphone, polyamide, in
particular aromatic polyamide, polyether, polyether ether ketone,
polyester, polyether-urea composite, polyamide-urea composite,
polyether sulphone, polycarbonate, polymethyl methacrylate,
polyacrylic acid or polyacrylonitrile. It is likewise possible to
use mixtures or copolymers of two or more of these polymers.
Particular preference is given to solution diffusion membranes
composed of cellulose acetate, crosslinked polyethylene glycol,
crosslinked polydimethylsiloxane or a polyester-polyether block
copolymer.
[0060] In a further preferred embodiment, the semipermeable
membrane is a microporous membrane. For the purposes of the
invention, microporous membranes are membranes which have pores
extending through the membrane, the pores having a minimum diameter
in the range from 0.3 nm to 100 .mu.m. The membrane preferably has
pores in the range from 0.3 nm to 0.1 .mu.m.
[0061] Preference is given to using a microporous membrane which is
not wetted by the working medium composed of sorption medium and
refrigerant. Here, the term wetting refers to a contact angle
between working medium and microporous membrane of less than 90
degrees, which leads to penetration of working medium into pores of
the membrane as a result of capillary forces. The contact angle
between working medium and microporous membrane is preferably
greater than 120 degrees, particularly preferably greater than 140
degrees. The use of a nonwetting microporous membrane can also
prevent flow of the liquid working medium through the pores of the
membrane to the vapour side of the membrane in the case of a
pressure on the side of the liquid working medium which is higher
than that on the vapour side. The suitability of a microporous
membrane for the absorption heat pump of the invention can
therefore be determined by a person skilled in the art by
determining the contact angle between the working medium and the
membrane.
[0062] For the embodiment using water as refrigerant, preference is
given to using a hydrophobic microporous membrane as semipermeable
membrane. Suitable hydrophobic microporous membranes are known to a
skilled person in the technical field of functional clothing as
membranes which are watertight and permeable to water vapour.
[0063] Preference is given to using hydrophobic microporous
membranes composed of polyethylene, polypropylene,
polytetrafluoroethylene, polyvinylidene fluoride or
fluoroalkyl-modified polymers. It is likewise possible to use
mixtures or copolymers of two or more of these polymers. Further
suitable membranes are inorganic hydrophobic microporous membranes
or composite membranes comprising an inorganic hydrophobic
microporous material, for example membranes whose pores are formed
by silicalite or hydrophobised silica.
[0064] The semipermeable membrane is preferably arranged on a
porous support layer. Arrangement on a porous support layer makes
it possible to achieve a mechanically stable membrane unit even
when using a thin semipermeable membrane. This allows more rapid
mass transfer through the membrane and thus a smaller and more
compact construction of the absorber. The support layer is
preferably arranged on the side of the semipermeable membrane
adjoining the vapour phase. Such an arrangement of the support
layer leads to a lower resistance to mass transfer than arrangement
of the support layer on the side of the membrane facing the liquid
working medium.
[0065] The porous support layer can comprise either inorganic or
organic materials. The membrane is preferably arranged on a porous
support layer composed of a hydrophobic polymer, in particular a
polyolefin, a polyester or polyvinylidene fluoride. The support
layer can additionally contain reinforcements, e.g. by means of
layers of fabric.
[0066] In a preferred embodiment, the semipermeable membrane is
arranged in the form of hollow fibres. The embodiment of the
membrane in the form of hollow fibres allows a particularly compact
construction of absorber and/or desorber and operation with a
higher pressure difference between the vapour phase and the liquid
phase.
[0067] The absorption heat pump of the invention preferably has a
two-stage or multistage, particularly preferably two-stage,
construction, as described, for example, for absorption
refrigeration machines in F. Ziegler, R. Kahn, F. Summerer, G.
Alefeld "Multi-Effect absorption chillers", Rev. Int. Froid 16
(1993) 301-311.
[0068] The absorption heat pump of the invention preferably has an
additional heat exchanger by means of which heat is exchanged
between the refrigerant-depleted working medium which is fed from
the desorber to the absorber and the refrigerant-rich working
medium which is fed from the absorber to the desorber. A
countercurrent heat exchanger is particularly preferably used for
this purpose.
[0069] In a preferred embodiment, at least one of the system
components absorber, desorber, condenser and evaporator has a wall
surface made of a polymeric material via which heat is exchanged
with the surroundings. The polymeric material is in this case
preferably a polyamide, a polyimide or polyether ether ketone. As
polyamide, preference is given to using polyamide 12. As polyimide,
preference is given to using a polyimide of
benzophenonetetracarboxylic dianhydride and a mixture of tolylene
diisocyanate and methylenedi(phenyl diisocyanate), which can be
obtained under the trade name P84 from Evonik Fibres. Corrosion of
the heat-exchanging surfaces can be avoided by the use of a
polymeric material. At the same time, a high heat transfer
coefficient can be achieved by the use of a polyamide, a polyimide
or polyether ether ketone, allowing a compact construction of the
absorption heat pump.
[0070] The following examples illustrate the invention without
limiting the subject matter of the invention.
EXAMPLES
Examples 1 to 6
Degassing Range Using 1-ethyl-3-methylimidazolium chloride (EMIMCl)
as Organic Salt
[0071] The maximum achievable degassing range was determined for
operation of an absorption refrigeration machine at a pressure in
the evaporator and absorber of 10 mbar, a temperature in the
absorber of 35.degree. C., a pressure in the desorber and condenser
of 50 mbar and a maximum temperature in the desorber of 85.degree.
C. For this purpose, the sorption medium was mixed with various
amounts of water, the vapour pressure was measured in each case and
in this way the content of water was determined at which the
mixture with sorption medium had a vapour pressure of 10 mbar at
35.degree. C. or a vapour pressure of 50 mbar at 85.degree. C.
respectively. In addition, the minimum content of water was
determined at which a homogeneous mixture without undissolved
lithium salt is obtained at 35.degree. C. The mixture having a
vapour pressure at 35.degree. C. of 10 mbar corresponds to the most
refrigerant-rich working medium which can be used in operation of
the absorption refrigeration machine. The most refrigerant-depleted
working medium which can be used in operation of the absorption
refrigeration machine is the mixture having a vapour pressure of 50
mbar at 85.degree. C. or, if such a mixture exceeds the solubility
limit of the lithium salt at 35.degree. C., the homogeneous mixture
having the minimum content of water. The degassing range is
calculated as the difference in the mass fraction of the
refrigerant water between the most refrigerant-rich working medium
and the most refrigerant-depleted working medium. The results are
shown in Table 1.
[0072] The data in Table 1 show that, according to the invention, a
higher degassing range is achieved using a sorption medium composed
of 1-ethyl-3-methylimidazolium chloride and lithium chloride than
when using 1-ethyl-3-methylimidazolium chloride or lithium chloride
as sorption medium. An improved degassing range is also achieved
compared to the industrially used sorption medium lithium
bromide.
TABLE-US-00001 TABLE 1 Degassing range of sorption media using
water as refrigerant Mass Mass Mass fraction of fraction of
fraction of water for water for water for solubility Sorption 10
mbar at 50 mbar at limit at Degassing Example medium 35.degree. C.
85.degree. C. 35.degree. C. range 1 * LiCl 0.61 *** 0.53 0.08 2 *
EMIMCl 0.17 0.1 0.07 3 EMIMCl/ 0.45 *** 0.34 0.11 LiCl 1:1 ** 4
EMIMCl/ 0.37 *** 0.24 0.13 LiCl 2:1 ** 5 EMIMCl/ 0.35 0.2 0.03 0.15
LiCl 3:1 ** 6 * LiBr 0.45 0.34 0.34 0.11 * not according to the
invention ** weight ratio of EMIMCl to LiCl *** for homogeneous
mixtures of sorption medium and water, the vapour pressure at
85.degree. C. is always higher than 50 mbar
Examples 7 to 11
Vapour Pressure of Working Media Containing Water as
Refrigerant
[0073] The vapour pressure of working media which contained as
sorption medium an organic salt and lithium chloride in a mass
ratio of 3:1 and as refrigerant water in a proportion by mass of 10
and 40% by weight was determined at 35, 50 and 60.degree. C. In the
case of mixtures which contained undissolved lithium salt, no
vapour pressure was determined. The results are shown in Table
2.
[0074] The experimental data show that in the case of a combination
of lithium chloride and an organic salt having an anion other than
chloride, undissolved lithium salt is present at low contents of
water of 10% by weight in the working medium, while in the case of
a combination of lithium chloride with an organic salt having the
shared anion chloride, a single-phase liquid working medium is
surprisingly obtained even at such low contents of water. In
addition, a lower vapour pressure is achieved using the sorption
media according to the invention even at higher water contents of
40% by weight, which is advantageous for a two-stage absorption
heat pump and allows three-stage operation of an absorption heat
pump.
TABLE-US-00002 TABLE 2 Vapour pressure of working media containing
a sorption medium composed of an organic salt and lithium chloride
in a mass ratio of 3:1 and water as refrigerant Proportion of water
in % Vapour pressure in mbar at Example Organic salt by weight
35.degree. C. 50.degree. C. 60.degree. C. 5 EMIM Cl 10 2.7 3.3 3.6
40 18 46 65 7 BMIM Cl 10 2 4 9 8 Choline 10 <3 4 8 chloride 40
18 48 79 9 * EMIM CF.sub.3COO 10 ** ** 28 40 29 65 109 10 * EMIM
SCN 10 ** ** ** 40 ** ** ** 11 * EMIM CH.sub.3COO 10 ** ** ** 40 26
54 90 * not according to the invention ** undissolved lithium salt
BMIM = 1-butyl-3-methylimidazolium
* * * * *