Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B15/00—Sorption machines, plants or systems, operating continuously, e.g. absorption type
  • F25B15/02—Sorption machines, plants or systems, operating continuously, e.g. absorption type without inert gas
  • F25B15/06—Sorption machines, plants or systems, operating continuously, e.g. absorption type without inert gas the refrigerant being water vapour evaporated from a salt solution, e.g. lithium bromide
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C277/00—Preparation of guanidine or its derivatives, i.e. compounds containing the group, the singly-bound nitrogen atoms not being part of nitro or nitroso groups
  • C07C277/08—Preparation of guanidine or its derivatives, i.e. compounds containing the group, the singly-bound nitrogen atoms not being part of nitro or nitroso groups of substituted guanidines
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C279/00—Derivatives of guanidine, i.e. compounds containing the group, the singly-bound nitrogen atoms not being part of nitro or nitroso groups
  • C07C279/02—Guanidine; Salts, complexes or addition compounds thereof
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B15/00—Sorption machines, plants or systems, operating continuously, e.g. absorption type
  • F25B15/002—Sorption machines, plants or systems, operating continuously, e.g. absorption type using the endothermic solution of salt
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2315/00—Sorption refrigeration cycles or details thereof
  • F25B2315/001—Crystallization prevention
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A30/00—Adapting or protecting infrastructure or their operation
  • Y02A30/27—Relating to heating, ventilation or air conditioning [HVAC] technologies
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
  • Y02B30/62—Absorption based systems
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency

Definitions

• TECHNICAL FIELD This invention relates to guanidinium-based ionic liquids, such as
• This invention also provides a method for synthesizing N,N,N',N',N",N"- hexamethylguanidinium acetate.
• Absorption chillers are designed to generate cooling (chilling) effect by means of generating chilled water which can be used to extract heat from an air flow (e.g. in an air conditioning system).
• Absorption chillers create a chilling effect by going through a complete absorption-refrigeration cycle.
• the simultaneous heat and mass transfer of the refrigerant to and from its mixture with the absorbent is the main mechanism of producing the chilling effect in an absorption chiller.
• the absorbent in the system should have a great tendency towards the refrigerant by dissolving it readily under the operating conditions of the system.
• the absorption process will make it possible for the system to work at sub-atmospheric pressures (between 0.01-0.1 atm for a water-based absorption chiller) leading to the evaporation of the refrigerant at much lower temperatures than its normal boiling point.
• the need for an electricity consuming part (i.e. a compressor) to pressurize the refrigerant is addressed through the use of an appropriate absorbent.
• Latent heat is consumed for the evaporation of the refrigerant, which provides a means of chilling.
• the low pressure in the evaporator provides the benefit of easy evaporation of the refrigerant (i.e. liquids evaporate easier at lower pressures), thereby making the system capable of producing a chilling effect at low temperatures.
• the very low pressure of the evaporator makes the condensation process of the vapor phase (in order for the cycle to be continued) more challenging.
• absorption chillers have their own drawbacks and limitations. Certain factors such as the crystallization of the absorbent in the system, or the heat loss from different compartments of the system, can make the system deviate from the ideal performance predicted by thermodynamic-based models. The benefits and drawbacks of conventional absorption chillers are described as follows.
• LiBr salt Water-lithium bromide (LiBr) salt is a commonly used refrigerant-absorbent (working) pair in absorption chillers. LiBr is a very efficient absorbent for water refrigerant due to its high hygroscopicity. LiBr, which as a pure salt has a melting temperature of 552°C, can absorb water to a high enough degree such that it becomes completely dissolved in the water it has absorbed. [1]
• LiBr concentration in the water is typically required to produce an acceptable amount of cooling load while preventing the solution from being too concentrated or too dilute.
• Another drawback of LiBr salt as an absorbent is its corrosiveness, necessitating the use of costly corrosion inhibitors and copper piping. Due to the corrosive nature of LiBr and the involved control procedures needed to avoid its crystallization within the system, there is a need for absorption chillers having less problematic absorbent materials compared with LiBr.
• FIG. 1 illustrates an absorption chiller
• FIG. 2 shows the reaction scheme for synthesis of N- [chloro(dimethylamino)methylene]-N,N-dimethylchloride (4MeUCl) from 1,1,3,3- tetramethylurea (4MeUrea) and oxalyl chloride (OxalylCl).
• FIG. 3 shows the reaction scheme for synthesis of N,N,N',N',N",N"- hexamethylguanidinium chloride (6MeGuaCl) from 4MeUCl in presence of 1 :2 excess N,N- dimethyltrimethylsilylamine (TMSN2Me), using extra-dry TUF as solvent.
• FIG. 4 shows the reaction scheme for synthesis of N,N,N',N',N",N"- hexamethylguanidinium acetate (6MeGuaOAc) from 6MeGuaCl via a metathesis reaction in presence of equimolar amount of silver acetate.
• the present invention relates to a mixture of a refrigerant and a guanidinium-based ionic liquid and the use of the mixture in an absorption chiller.
• the present invention provides an absorption chiller comprising an absorber compartment and a generator compartment, wherein both compartments comprise a guanidinium-based ionic liquid as an absorbent and water as refrigerant.
• the present invention provides an efficient absorption chiller by substituting the common LiBr absorbent with a non-corrosive, hygroscopic ionic liquid (IL).
• FIG. 1 illustrates the schematic of an absorption chiller.
• An absorption chiller is a machine that utilizes a heat source (e.g., direct flame, hot water, steam, solar energy, waste heat etc.) to drive a cooling process.
• a mixture of a refrigerant and an absorbent is present in the absorber compartment and the generator compartment of the system.
• a working pair comprises an absorbent, which is paired (dissolved) with a liquid refrigerant.
• a refrigerant is a liquid compound used to undergo evaporation in the evaporator compartment of an absorption chiller to produce a chilling effect.
• a refrigerant in general has appropriate properties for use in such a system, such as low melting point, low-to-medium boiling point, low toxicity, low flammability, low corrosivity, low viscosity, high thermal conductivity, high wettability, and high heat of evaporation.
• An absorbent has the role of absorbing the refrigerant vapor in the absorber compartment and transferring the refrigerant from a vapor phase to a liquid phase.
• the generator compartment has the sole role of transferring a portion of the refrigerant from the liquid phase (in solution with the absorbent) to the vapor phase (partial evaporation), thereby performing a vapor-liquid separation procedure.
• a pure refrigerant is needed for chilling purposes in the evaporator compartment, and therefore, needs to be evaporated from the liquid solution containing the absorbent.
• the absorbent material generally has a negative role in the generator compartment, since it decreases the vapor pressure of the refrigerant, hindering its evaporation.
• the existence of absorbent in the generator compartment cannot be avoided due to the fact that it is dissolved in the refrigerant stream (working pair solution) incoming from the absorber compartment.
• An absorption-refrigeration cycle can be accurately modeled using fundamental thermodynamics.
• An ionic liquid is a multi-atomic salt with organic or inorganic cations and anions, usually defined as having a melting temperature of 100°C or lower.
• Many ionic liquids (ILs) are not strongly hydrophilic due to the organic nature of their cations, the larger size of both their cations and anions compared to water molecules, and the limited amount of mass-based solubility of water in ionic liquids due to their relatively large molecular weight. This renders most ILs unsuitable to use as absorbents with water as the refrigerant in an absorption chiller, and the identification of suitable ILs for this purpose is not a simple task.
• l-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Bmim] + [Tf2N] " ) is a well-known ionic liquid with a molecular weight of 419.4 g/mol.
• the high molar mass of this ionic liquid means that an equimolar solution with water (1 : 1), in which 1 mole of ionic liquid is dissolved in 1 mole of water, is equivalent to a solution with only 4.11% by mass of water.
• the "working pair" of Bmim Tf2N (absorbent) and water (refrigerant) contains an insufficient amount of refrigerant (water) to be of practical use in absorption chillers.
• the ionic liquid suitable for the present invention has a high hygroscopic effect comparable to that of LiBr; it has a reasonably low viscosity when diluted with water, and it exhibits desired properties such as non-corrosiveness and a lower risk of crystallization when compared with LiBr.
• Suitable ionic liquids for the present invention include a non-corrosive ionic liquid with a melting point (T m ) lower than 400 K, preferably lower than 350 K, and kinematic viscosity of lower than 25 centistokes, preferably lower than 15 centistokes, when in solution with water.
• the mass basis concentration of the refrigerant (e.g. water) in the absorbent-refrigerant mixture needs to be reasonably high. This is important to ensure that the working pair can have a suitably low viscosity and that the system can achieve a sufficiently high coefficient of performance (COP). Therefore, suitable ionic liquids for the present invention in general have low molecular weights, preferably lower than 350 g/mol, and more preferably lower than 250 g/mol. Also, it is more preferable to use an ionic liquid absorbent with relatively higher hygroscopic properties (greater affinity for water).
• the guanidinium cation is functionalized with one or more alkyl groups (e.g., one to six methyl, ethyl, propyl, or any combination thereof).
• the guanidinium cation is functionalized with one to six methyl or ethyl groups or a combination thereof, or more preferably, with one to six methyl groups.
• the ionic liquid has a hexamethylguanidinium cation. In another embodiment, the ionic liquid has a hexaethylguanidinium cation. In yet another embodiment, the ionic liquid has an anion with a high tendency toward water such as an acetate anion.
• a preferred ionic liquid for the present invention is hexamethylguanidinium acetate.
• ionic liquids with guanidinium-based cations show a higher potential for water absorption.
• the melting point and viscosity of pure ionic liquids, such as guanidinium-based ionic liquids are typically lower than those of pure LiBr salt. Therefore, unlike LiBr-water pair, in order to produce operable ionic liquid-water working pairs including those incorporating guanidinium-based ionic liquids, a mixture of ionic liquid and water with 40% or 50% mass of water (as is the case of for the LiBr-water working pair) in the solution is not required.
• a solution of ionic liquid with water in which at least 10% (by weight) of water is present in the concentrated solution, and at least 15% (by weight) in the diluted solution, would be sufficient to meet the viscosity and melting point requirements for use in absorption chillers.
• Guanidinium-based ionic liquid-water working pairs are particularly preferable for use in absorption chillers because (i) guanidinium-based ILs have a high affinity for water compared to common ionic liquids such as l-butyl-3- methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (Bmim Tf2N), l-butyl-3- methylimidazolium tetrafluorob orate (Bmim BF 4 ), l-butyl-3-methylimidazolium
• the working pair has a sufficiently low viscosity such that the circulation of the absorbent-refrigerant mixture within the system does not create an unreasonable strain on the system components, and (iii) the crystallization temperature of a guanidinium-based IL in a refrigerant is low to avoid the crystallization of the ionic liquid in the system.
• the present application also provides a method for synthesizing N,N,N',N',N",N"- hexamethylguanidinium acetate (6MeGuaOAc).
• the method comprises the steps of (a) reacting 1,1,3,3,-tetramethylurea with oxalyl chloride to form N-
• step (a) 1, 1,3,3,-tetramethylurea is reacted with oxalyl chloride in a first organic solvent to form N-[chloro(dimethylamino)methylene]-N,N-dimethylchloride (4MeUCl) at room temperature for 12-36 hours (e.g., 24 hours).
• a first organic solvent includes, but is not limited to toluene, xylene, benzene, or any combination thereof. After the reaction, the excess amount of oxalyl chloride is removed.
• step (b) 4MeUCl is reacted with a molar excess of N,N-dimethyltrimethylsilylamine in a second organic solvent to form N,N,N',N',N",N"-hexamethylguanidinium chloride (6MeGuaCl) at 20-40 °C for 2-6 hours.
• a second organic solvent includes, but is not limited to tetrahydrofuran, acetonitrile, 1,4-dioxane, or any combination thereof.
• 6MeGuaCl is reacted with about equimolar amount of silver acetate in a third organic solvent at 40-60°C for 16-30 hours.
• a third organic solvent includes, but is not limited to acetonitrile, methanol, acetone, or any combination thereof.
• thermo-dynamic COP Coefficient of Performance of an absorption chiller is defined as the amount of cooling load generated in the evaporator, Q E , (in kilowatt [kW]) divided by the amount of thermal/heat energy, Q G , (in kilowatt [kW]) used to heat up the dilute solution in the generator in order to release refrigerant vapor.
• Q E the amount of cooling load generated in the evaporator
• Q G the amount of thermal/heat energy
• thermodynamic ECOP Exploc COP
• T 0 298 K is the room temperature
• T E the temperature in the evaporator
• T h To + (5 to 10 K) is the heat source temperature, with TQ being the temperature in the generator compartment.
• Example 1 Performance comparison of guanidinium-based ionic liquids and LiBr as absorbents in an absorption chiller
• guanidinium-based ILs hexaalkylguanidinium-based ILs and LiBr are shown.
• the guanidinium-based ILs in water are less corrosive working pairs than LiBr in water.
• CSM Continuum Solvation Model
• DFT density functional theory
• Table 1 lists the theoretical values of COP and ECOP along with the concentration of absorbent (Mass% Ionic Liquid or LiBr) in both diluted and concentrated mixtures in an absorption chiller with different guanidinium-based ionic salts. As shown in Table 1, in the case of having a large and highly hydrophobic anion such as
• hexamethylguanidinium acetate ionic liquid has a predicted melting point of 335.3 K, which is significantly lower than the melting point of LiBr (825 K).
• a lower melting point of an ionic liquid is desirable because it decreases the risk of crystallization of the absorbent within the system.
• hexamethylguanidinium acetate ionic liquid-water mixture is concentrated down to 13% mass of water, a kinematic viscosity of 10.84 est at 60°C is achieved. This viscosity value is lower than the viscosity of other concentrated ionic liquid-water pairs listed in Table 1.
• TMSN2Me ⁇ , ⁇ -dimethyltrimethylsilylamine
• 6MeGuaOAc was synthesized from 6MeGuaCl via a metathesis reaction in presence of equimolar amount of silver acetate, as shown in FIG 4.

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• 2017
  • 2017-05-26 JP JP2018562045A patent/JP2019517654A/ja active Pending
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