WO2011099871A1

WO2011099871A1 - Saturated fatty acid ester phase change materials and processes for preparing the same

Info

Publication number: WO2011099871A1
Application number: PCT/NZ2011/000011
Authority: WO
Inventors: Mohammed Farid
Original assignee: Auckland Uniservices Limited
Priority date: 2010-02-15
Filing date: 2011-02-07
Publication date: 2011-08-18

Abstract

The invention relates to a process of preparing saturated fatty acid esters suitable for use as PCMs (phase change materials). The process comprises the step of hydrogenating fatty acid esters that have been obtained by processing of a triglyceride-containing starting material. In preferred embodiments, the fatty acid esters that are to be hydrogenated have been obtained by transesterification of the triglyceride-containing starting material with an alcohol, preferably in the presence of catalyst. The invention also relates to PCMs comprising a mixture of saturated fatty acid esters derived from animal fat or vegetable oil or a blend of one or more animal fats and/or vegetable oils.

Description

SATURATED FATTY ACID ESTER PHASE CHANGE MATERIALS AND PROCESSES FOR

PREPARING THE SAME

FIELD OF THE INVENTION

The present invention relates to new processes of preparing phase change materials

(PCMs), to PCMs obtainable by or obtained by such processes, to compositions containing the PCMs, and to methods of using the compositions for latent heat storage or removal in various applications.

BACKGROUND OF THE INVENTION Phase change materials (PCMs) are substances that use phase changes to absorb or release heat at a relatively constant temperature. Typically the phase changes are fusion (or

melting) with an associated latent heat.

PGMs have many applications. They are commonly used to improve .thermal performance of buildings, for example by use in walls, ceilings or flooring. Other applications are as food storage coolers or other types of coolers, and devices used to keep food warm.

PCMs are also used to keep the temperature of electtonic devices relatively constant and prevent overheating of batteries during discharge. They may also be used with cloths for human protection in fire and harsh environments.

PCMs can be classified into three different types: organic, inorganic and eutectic

compounds. Paraffins and non-paraffin compounds are two major groups of the organic phase change materials. Inorganic phase change compounds consist of salt hydrates and metallic compounds. A large number of organic and inorganic substances are known to melt with a high heat of fusion in a required operational temperature range. However,

some requirements need to be fulfilled for their application as phase change materials. The suitable phase change materials must exhibit certain desirable thermodynamic, kinetic and chemical properties. In addition, economic considerations of cost and large scale

availability of the materials must: be taken into accoun

The melting and freezing characteristics of phase change materials can be determined by the. following factors: melting and free2ing temperature ranges, congruency of melting, nucleation characteristics, supercooling and stability to thermal cycling. Moreover, the stability of the phase changes is also essential for the long-term performance of the phase change materials. Two measurement techniques can be applied for the detennination of the above factors: differential scanning calorimetry (DSC) and thermal cycling analysis (TCA).

Fatty acid esters have heats of fusion tha t are reasonably high and comparable to those of paraffins. They can be produced from oil and fat as renewable and environmentally friendly sources. Because of their stability and ability to freeze with little or no subcooling, fatty acid esters are good phase change materials. However, existing fatty acid esters suitable for use as PCMs are expensive, which limits their potential applications as PCMs.

It is an object of the present invention to provide a process of preparing fatty acid esters suitable for use as PCMs, that goes some way to o

\'ercoming the disadvantages of the prior art, or at least to provide the public with a useful alternative.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a process of preparing saturated fatty acid esters suitable for use as PCMs, wherein the process comprises the step of hydrogenating fatty acid esters that have been obtained by processing of a triglyceride-containing starting material.

In preferred embodiments, the fatty acid esters that are to be hydrogenated have been obtained by transesterification of the triglyceride-containing starting material with an alcohol, preferably in the presence of catalyst.

In alternative embodiments, the fatty' acid esters that are to be hydrogenated have been obtained by hydrolysis of the triglyceride-containing starting material to form free fatty acids and esterification of the free fatty acids with an alcohol.

In preferred embodiments, the process comprises the steps of (1) transesterifying a triglyceride-containing starting material with an alcohol to produce fatty' acid esters; and (2) hydrogenating the fatty' acid esters obtained from step (1) to produce saturated fatty acid esters suitable for use as PCMs. The ttiglyceride-containing starting material preferably comprises a fat or oil, or any mixture of fat and/or oils. In certain embodiments, the fat or oil may be animal fat, such as tallow, or vegetable oil, such as palm oil, coconut oil, rapeseed oil, sunflower oil, canola oil or soybean oil, or any mixture or animal fat and/ or vegetable oil.

In certain preferred embodiments, the alcohol is a CI to C4 alcohol, such as methanol, ethanol, propanol or butaiiol.

In a further aspect, the invention provides PCMs comprising fatt acid esters obtained by or obtainable by a process as described above.

In certain preferred embodiments, the PCMs obtained have a latent heat of fusion of at least about 120 J/g, such as at least about 130 J/g, such as at least about 140 J/ g. In certain preferred embodiments, the PCMs obtained have a phase transition temperature in the range of from about 18°C to about 25°C.

In certain preferred embodiments, the PCMs obtained comprise fatty acid esters selected from the group consisting of hydrogenated tallow methyl, ethyl, propyl and butyl esters (that is, fatty acid esters obtained by hydrogenation of tallow that has been esterified with methanol, ethanol, propanol or butanol), hydrogenated palm oil methyl, ethyl, propyl and butyl esters, hydrogenated coconut oil methyl, ethyl, pi'opyl and butyl esters and hydrogenated rape seed oil methyl, ethyl, propyl and butyl esters, hydrbgenated sunflower oil methyl, ethyl, propyl and butyl esters, or a blend of any two or more of the foregoing.

In certain preferred embodiments, the PCMS obtained comprise hydrogenated tallow butyl or propyl esters.

In other preferred embodiments, the PCMs obtained comprise hydrogenated palm oil butyl or propyl esters.

In other preferred, embodiments, the PCMS obtained comprise hydrogenated palm oil or tallow methyl esters, or a blend of either of these with coconut oil methyl esters. In a further aspect, the invention provides a PCM comprising a mixture of saturated fatty acid esters derived from animal fat or vegetable oil or a blend of one or more animal fats and/or vegetable oils. In preferred embodiments, the proportions of individual saturated fatty acid esters in the mixture correspond to the proportions of individual fatty acids in the animal fat or vegetable oil, or blend thereof, from which the saturated fatty acid esters are derived.

In a further aspect, the invention provides a method of storing or removing thermal energy, the method comprising incorporating a PCM as denned above or a PCM comprising fatty acid esters obtained by or obtainable by a process as defined above into a bunding or other structure or device.

In a further aspect, the invention provides a composition for storing or removal of thermal energy, the composition comprising a PCM as defined above or a PCM comprising fatty acid esters obtained by or obtainable by a process as defined above.

In certain embodiments, the composition includes a nucleating agent. In certain embodiments, the composition may be in the form of a device comprising the PCM encapsulated within a material such as a metallic or plastics material.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention. The disclosures and descriptions herein are illustrative only and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE FIGURES The invention will no be described in more detail, and with reference to the

accompanying drawings, in which:

Figure 1 shows the equipment arrangement of a hydrogenation unit suitable for use in carrying out the hydrogenation of free fatty esters according to the present invention. Figure 2 is a melting DSC analysis of fresh tallow.

Figure 3 shows DSC melting curves of tallow methyl ester before and after hydrogenation and their comparison: (a) before hydrogenation (b) after hydrogenation. Figure 4 is a melting DSC analysis of fresh palm oil.

Figure 5 shows DSC melting curves of palm oil methyl ester before and after

hydrogenation and their comparison (a) before hydrogenation (b) after hydrogenation. Figure 6 is a melting DSC analysis of fresh coconut oil.

Figure 7 shows DSC melting curves of coconut oil methyl ester before and after hydrogenation and their comparison: (a) before hydrogenation (b) after hydrogenation (c) comparison.

Figure 8 shows DSC melting curves of hydrogenated tallow and coconut oil methyl esters blends with a mixing ratio of 0.76:0.24. Different mixing ratios with different sources of esters will provide PCMs having different melting temperatures. Figure 9 is a DSC curve for hydrogenated tallow butyl ester.

Figure 10 is a DSC curve for hydrogenated palm oil butyl ester.

Figure 11 is a DSC curve for hydrogenated tallow propyl ester.

Figure 12 shows cyclic measurements conducted in a computer controlled water bath in which its temperature was cycling between 12"C and 30"C. More than 300 cycles were done on the ester and the results show no change in its characteristics, indicating that the ester produced is stable. Figure 13 shows the mass loss of gypsum boards impregnated with fatty acid esters produced according to the present invention and the commercially available paraffin RT21 after being kept in an oven at 30°C for one month. Figure 14 shows a comparison between the vapour pressure of paraffin and fatty acid esters produced according to the present invention, at different temperatures.

Figures 15 A to D show fire testing for composites of (1) fatty acid esters produced according to the present invention in high density polyethylene (HDPE) and (2) RT21 in HDPE, using Con Calorimeter.

DESCRIPTION OF THE INVENTION The present invention relates to processes for preparing PCMs comprising fatty acid esters. In broad terms, a process of the invention involves hydrogenating fatty acid esters that have been produced by converting a fat or oil, or mixture of fats and/ or oils, to fatty acid esters, to produce fatty acid esters that have properties that make them useful as PCMs. The triglyceride feed matenal

Triglyceride-containing starting materials suitable for use in the process of producing PCMs of the present invention may be selected from a variety of fats and oils including but not limited to animal fat such as tallow, and vegetable oils such as palm oil, coconut oil, canok oil, rapeseed oil, sunflower oil and soybean oil. Blends of fats and/ or oils may also be used.

Different fat and oil starting materials may result in the fatty acid esters PCMs having different properties, in particular different latent heat and melting point profiles. The particular fats or oils selected for use as starting materials will therefore depend to some extent upon the desired end use of the PCMs to be produced by the process, as will be discussed in more detail below.

In preferred embodiments, the triglyceride feed material comprises a naturally occurring fat or oil, or blend thereof, for example selected from those listed above, on which no fractionation step which modifies the fatty acid composition of the fat or oil has been performed.

In an alternative embodiment, the triglyceride containing feed material may be a low quality cooking oil or fat, which has been reacted with glycerol to convert free fatty acids in the oil or fat to mono and diglycerides. In still a further embodiment, the triglyceride containing feed material may be a waxy waste product obtained from the refining of some vegetable oils, for example sunflower oil.

The alcohol to be reacted with the triglyceride

The triglyceride-containing starting material is converted to fatty acid esters of an alcohol. Alcohols suitable for use in the conversion process include, but are not limited to, methanol, ethanol, propanoL butanol, isobutanol, pentanoL hexanoL cyclohexanol, phenol and others. In certain preferred embodiments, the alcohol is a C1-C4 alcohol, such as methanol, ethanol, propanol or butanol.

The particular alcohol used to form the free fatty acid esters from the starting triglycerides may affect the properties, and in particular the melting point, of the resulting free fatty acid esters. The particular alcohol chosen may therefore depend to some extent on the desired end use of the PCMs, as will be discussed in more detail below.

Conversion of triglyceride feed to fatyt add esters

The fat or oil may be converted to fatty acid esters using any suitable method known in the art. In preferred embodiments, the conversion is carried out using transesterification, which is a stepwise reaction that breaks down triglyceride to form alcohol esters. Methods of transesterification of fats and oils are well known, and in general terms involve the reaction of the fat or oil with an alcohol, preferably in the presence of a suitable catalyst, such as a metal hydroxide, such as sodium hydroxide or potassium hydroxide, or a sodium or potassium alkoxidc, such as sodium methoxide, sodium ethoxide, sodium propoxide and sodium butoxide.

In principle, any known transesterification method , such as the liquid-liquid phase reaction, can be used in the process of this invention. Purely by way of example, one mediod of transesterification that can be used is the method described in PCT

International Patent Publication WO 2007/049979, and also as described in Behzahdi, S. and Farid, M.M. "Production of biodiesel using a continuous gas-liquid reactor", ioresor e Technology! 100 (2009): 683-689, the mil contents of both of which are incorporated herein by reference. That method involves spraying an atomised feed of vegetable oil and/or meat fat into gaseous alcohol in a reaction vessel, preferably in the presence of a transesterification catalyst, whereupon the transesterification occurs substantially instantaneously. In alternative embodiments, the triglyceride can be converted to fatty acid esters by a sequential method comprising first hydrolysing the triglycerides, to produce free fatty acids and glycerol, followed by esterification with an alcohol to produce fatt)' acid esters. Again, such methods are known in the art:

Hydrogenation of free fatty acid esters

The fatty acid esters produced are then subjected to hydrogenation. It will be appreciated that naturally occurring fats and oils contain both saturated and unsaturated fatty acids. Hydrogenating the fatty acid esters converts any unsaturated fatty acids to saturated fatty acids. This in turn significantly increases the latent heat of the fatt)-' acid esters, making them more suitable as PCMs. Hydrogenation also both increases the melting point and narrows the melting point range of the fatty acid esters. A narrow melting point range is a desired characteristic of a PCM.

Methods of hydrogenation are known in the art and in principle any such known method may be used. For example, the hydrogenation may be carried out in a commercially available hydrogenation apparatus, such as a Parr 3921 Hydrogenation Apparatus. The hydrogenation is carried out at a suitable temperature and pressure and preferably in the presence of a suitable catalyst (such as palladium on active carbon powder). The hydrogenation is preferably continued until completion to achieve full saturation of the fatty acid esters.

It is preferred that the process of the present invention does not include any fractionation or separation step which alters the naturally occurring proportions of the fatty acids either in the triglyceride feed material or in the mixture of fatty acid esters obtained by the esterification, or which alters the proportions of the hydrogenated fatty acids in the mixture of hydrogenated fatty acid esters obtained by the hydrogenation step. Thus, in preferred embodiments, the proportions of different fatty acids in the mixture of saturated fatty acid esters product will correspond to the proportions of the fatty acids in the triglyceride feed material, taking into account that the unsaturated fatty acids in the triglyceride feed material will be converted to saturated fattv acids of the same carbon chain length in the final product.

Accordingly, the process of the present invention allows production of PCMs using the entire fatty acid composition of the triglyceride feed material, widiout the need for a fractionation or separation step to obtain fatty acid esters in a pure form. As is described in more detail below, mixtures of hydrogenated fatty acid esters obtained from different triglyceride feed materials and/ or alcohols may be blended to obtain a PCM with specific desired properties for a particular application. Alternatively, two fats and/or oils with different fatty acid compositions may be blended to obtain a triglyceride-containing feed material having a fatty acid composition that is desired in the final PCM fatly acid ester composition to be produced.

PCMs produced and properties thereof

It is preferred that PCMs produced by the process of the present invention have a latent heat of fusion of at least about 120 J/g, such as at least about 130 J/g, such as at least about 140 J/g. The desired phase transition temperature or melting point of the fatty acid esters PCMs will vary, depending on the application to which the PCM is to be put, for example whether it is to be used in a building application or some other application. The desrired melting point may vary from about -20°C to about 90°C, depending on the desired application. For a building application, it is preferred that fatty acid esters PCMs produced by the process of the present invention have a phase transition temperature of between about 18°C and 25°C. It is also preferred that the melting range for the fatty acid esters is narrow, for example a melting range of less than about 2-3°C is desirable.

The compositions of fatty acid esters vary based on the compositions of the fats and oils and alcohols that they arc produced from. For example, based on the thermal properties of different esters, for saturated esters, the longer the fatty acids chain the higher the melting point. In addition, butyl ester has a lower melting point compared to methyl ester for the same fatty acid carbon chain. For example, methyl stearate (CI 8) has a melting point of 38°C which is higher than the one of methyl palmitate (CI 6) which is 29°C, while the melting point of butyl stearate is only 19°C. Accordingly, the tiiglyceride-containing feed material and alcohol chosen for use in producing the fatty acid esters will depend on the desired end use of the PCMs and therefore the desired latent heat and melting point range properties. It will be appreciated that a blend of two or more different oils and/or fats may be used as the starting triglyceride containing feed material, to obtain a fatty acid ester composition having the desired properties for use as a PCM in a particular application.

It will also be appreciated that different fatty acid ester compositions obtained by the process of the present invention can be blended to achieve a PCM having properties that are desired for a particular application.

By way of example, methyl esters from animal fat such as tallow and vegetable oils such as palm oil after hydrogenation contain mainly stearate and palmitate and hence have melting ranges higher than 30°C, making them unsuitable PCMs for building application, but suitable for certain other applications. However, certains blend of hydrogenated tallow methyl esters and coconut methyl esters with a certain mixing ratio, or certain blends of hydrogenated palm oil methyl esters and coconut methyl esters with certain mixing ratio have desired thermal properties. For example, blends having melting point ranges and latent heat suitable for use in building applications may comprise blends of hydrogenated tallow methyl estersxoconut oil methyl esters in a ratio of about 0.72:0.28 to 0.88:0.12, such as about 0.76:0.24 to about 0.80:020, or blends of hydrogenated tallow methyl esters: palm oil methyl esters in a ratio of about 0.72:0.28 to 0.88:0.12, such as about 0.80:0.20 to 0.84:0.16.

Also, because stearate is the predominant ester produced after hydrogenation from tallow and palm oil and the melting point of butyl stearate is 1 °C which is within the desired range, hydrogenated butyl esters from tallow and palm oil produced according to the invention have been found to have melting points between 18°C and 25°C. Accordingly, hydrogenated palm oil butyl esters and hydrogenated tallow butyl esters produced according to the present invention are very suitable PCMs for building applications. It is sometimes desirable to have the indoor temperature slightly higher than 21"C, especially in low humidity areas. In this case, butyl ester may be replaced by propyl ester, which has a melting point around 25"C. - Similarly, other alcohols may be used to produce esters suitable for other applicadons. Applications of the PCMs

PCMs produced according to the invention can be used in a variety of applications. As described above, certain PCMs according to the present invention are particularly suitable for use in building applications, for example, for use. in walls, ceilings and flooring. Other PCMs produced according to the present invention may have thermal properties that make them suitable for use in alternative applications, for example in food storage or other types of coolers, and devices used to keep food warm. PCMs according to the invention can also be used to keep the temperature of electronic devices relatively constant and to regulate the temperature of batteries.

Publications describing the wide range of use of PCM in buildings are:

Qureslii, W.A., Nair, N.K.C and Farid, M.M. "Phase change material application for electricity demand side management options" Accepted for publication in "Energy Conversion and Management", 2010.

Farid, M.M., Khudhair, A.M., Razak, S.A. and Al-Hallaj, S. "A review on phase change energy storage: materials and applications", Energy Conversion & Management, 45, 1597-1615, 2004. .

Farid, M.M. and Kong, W.J. "Underfloor heating with latent heat storage", journal of Power and ' Energy, Proc histn Mecb Eng Part A, 215, 601-609, 2001.

Methods of using PCMs in the above applications are known in the art and the PCMs of the present invention can be used according to such methods. For example, the PCMs can be encapsulated, conveniently in the form of small containers or cells, within a suitable packaging material. Suitable packaging materials include stainless steel and plastics materials such as polypropylene and polyolefin. If desired, a nucleating agent may be incorporated in the PCM. Microencapsulation is another method of containing the PCMs. Publications describing microencapsulation of PCMs include:

Rami Sabbah, Mohammad Farid and Said Al Hallaj "Micro-channel heat sink with slum' of water with microencapsulated phase change materials: 3D Numerical Study", Applied Energy, 29, 445-454, 2008, and Smith, M.C., Farid, M.M., and Easteal, A.J. "Review of microencapsulated phase change materials for thermal energy storage applications" IIR/IRHACE Conference, 16-18 February 2006, Auckland, New Zealand. Publications describing the use of PCMs for cooling batteries and electronics include: Khateeb, S.A., Farid, M.M., Selman, J.R. and Al-Hallaj, S. "Mechanical Electrochemical Modeling of Li-Ion Battery Designed for an Electric Scooter", Journal of Power Sources, 158: 673-678, 2006, and

Khateeb, S.A., Amiruddin, S., Farid, M.M., Selman, J.R. and Al-Hallaj, S. "Thermal management of Li-ion battery with phase change materials for electric scooters:

experimental validation". Journal of Power Sources, 142: 345-353, 2005.

Publications describing the use of PCM in cold stores include:

Gin, B and Farid, M.M. "The use of PCM panels to improve storage condition of frozen food", Journal of Food Engineering, 100, 372-376, 2010, and

Gin, B., Farid,M.M., and Bansal,P.K. "Effect of door opening and defrost cycle on a freezer with phase change panels, Energy Conversion and Management, 51, 2698-2706, 2010. A publication describing the use of PCM for keeping food warm is

Smith, M.C. and Farid, M.M." Phase change material containers for improved fast food delivery "First Australasian Workshop on Phase Change Materials for Thermal Storage in Buildings and Other Applications. Auckland, New Zealand, 2 December 2003. The present invention provides, at least in preferred embodiments, an efficient and relatively low cost process of producing high quality fatty acid ester PCMs from a variety of readily available fats and oils. The inventive process docs not require any initial separation or fractionation of the triglyceride feed material, thereby avoiding these steps. It also does not require the use of solvent which would require later energy-intensive separation.

Further, the process of the present invention does not require separation of the different fatty acid esters obtained and mixing them in proportions to form a suitable PCM. Again, such a process requires the use and removal of solvent, which is eneigy expensive. Instead, fatty acid esters produced from different vegetable oils or fats may be mixed in suitable proportions to give a required PCM, or the oils and fats may be mixed in the required proportions before esterification.

It will be appreciated that the structures of the fatty acid esters produced by the processes of the present invention will depend on the feedstock used. Accordingly, the product of the process of the invention will usually not be a single, pure ester but will instead be a mixture, typically of esters of stearic, palmitic and other fatty acid esters in a proportion which will vary according to the fatty acid composition of the feedstock. In addition, hydrogenating fatty acid esters is relatively straightforward compared with hydrogenating triglycerides, as fatty acid esters have a lower melting point and lower viscosity than triglycerides. Similarly, it is significantly easier to esterify the triglyceride before hydrogenation. Oil is predominantly liquid at room temperature and if

hydrogenatcd it will tend to become solid, making the esterification process less efficient and more energy consuming. The time needed to hydrogenate triglycerides will typically be of the order of about four times longer than that need to hydrogenate esters at similar hydrogenation temperature.

It should be noted that hydrogenation changes the proportion of the individual fatty acids in the mixture (see Tables 2 and 3 in the Experimental section below), as any unsaturated fatty acids will be converted to saturated fatty acids of the same carbon chain length. This should be taken into account in the formulation of the required PCM.

Another advantage of the present invention is that it allows all of the triglyceride feed material to be used, eliminating wastage. Suitable initial feedstock is chosen to produce PCM having desired properties. Further, as discussed above, two or more PCM can be blended to modify the properties of a particular PCM to make it more suitable for a particular application. A further advantage of the present invention, at least in certain embodiments, is that the esterification step may be carried out using existing plants for the manufacture of biodiesel. The esters produced may be hydrogenated for use as PCMs according to the process of the present invention, or used without hydrogenation for fuel as biodiesel, depending on market requirements. The invention will now be described in more detail, with reference to the following non- limiting experimental section.

EXPERIMENTAL

Example 1 - Production of fatty acid ester PCMs from fats and oils

Transesterification

Fresh methyl esters were produced from various fats and oil such as tallow and palm oil ' using methanol, ethanol, propanol or butanol and sodium methoxide/hydroxide catalyst or enzymes. For the base catalysed transesterification reaction, a given quantity of fats or oils was used and heated initially to 100°C for 30 minutes to remove water residue. The catalyst methanol mixture was prepared by dissolving 0.5wt% sodium methoxide or sodium hydroxide based on the mass of fats or oils for the reaction. For these experiments a 6:1 methanol to fats or oils molar ratio was used. Methanol and catalyst were added to the fats or oils into the reactor, which was provided with baffles and a stirrer. The temperature of the reaction mixture was maintained below 65 °C for about 45 minutes. After about 10 minutes, the mixture settled into two distinct layers. The light yellow layer on top is the methyl ester from fats or oils and the dark orange layer at the bottom is glycerol. The methyl ester produced was purified and neutralized by washing three times with deionised water. A few drops of pure hydrochloric acid were added during the first wash to neutralize the product.

Butyl esters were also produced from tallow and palm oil. The operational procedure was identical except for the catalyst and operating temperature. A 0% catalyst butanol mixture was prepared by dissolving pure sodium in butanol which produced sodium butoxide, the catalyst. Because the boiling point of butanol under atmospheric pressure is about 118°C, the reaction temperature was close to 115°C.

Propyl ester was produced following the same procedure,

Hydrogenation

The washed methyl esters, butyl esters and propyl esters produced from various fats and oils were fuEy saturated via hydrogenation using Parr 3921 Fiydrogenation Apparatus. A gas detector was used to identify any leakage in the system. Hydrogen was supplied from a gaseous hydrogen cylinder. A heating jacket and temperature controller was applied to maintain the temperature required for the hydrogenation reaction. Borosilicate glasses in different sizes were used as the reaction containers. After each hydrogeriation reaction completed, a vacuum filtration system with filtration aid Celite was employed in order to separate the catalyst from the products. Figure 1 illustrates the equipment used. About 5 wt%. Palladium on active carbon powder was used as the catalyst in the hydrogenation reaction. Washed methyl, propyl or butyl esters from various fats and oils were placed in Botosilicate glass with 2 wt% catalyst. The reaction pressure and temperature were set to 40psig and approximately 60°C. The glass container was kept shaking by an electric motor. As the reaction proceeded, the hydrogen was consumed and - hence the pressure in the Borosiltcate glass decreased. The hydrogen was refilled to 40psig accordingly to provide enotigh driving force for the hydrogenation reaction. The catalyst was filtrated out and the compositions and thermal properties of the final products were analysed using GC-FID and DSC. Blends of Hydrogenated Methyl Esters from Vanous Fats and Oils

In order to obtain a fully saturated methyl esters mixture that has a melting range in between 18°C and 25°C, hydrogenated methyl esters from tallow and palm oil were blended with hydrogenated methyl esters from coconut oils. Firstly, samples with different ratios were prepared and their thermal properties were analysed using DSC. Based on the results, samples with more detailed and desired mixing ratios were prepared and further

DSC analyses were performed.

Analysis Using Differential Scanning Calorimetty (DSC)

Thermal behaviours of various esters were determined by DSC analysis. A Shimadzu DSC- 60 differential scanning calorimeter equipped with a thermal analysis data station was employed. The calorimeter was calibrated according to standard procedures established in the manufacture user manual.

Analysis using Gas Chromatography with Flame Ionization Detector (GC-FID)

In order to determine the compositions of esters from various fats and oils, a gas chromatograph with flame ionization detector (GC-FID) Shimadzu GC-17A was employed. A 15m x 0.32mm x Ο.ΙΟμτη MXT-Biodiesel TG GC metal column from Restek was used. For each analysis, about 0.6ul of the sample was injected into the column by an automatic injector attached to the machine. Results

Tallow

The thermal properties of fresh tallow were analysed using DSC and the results are shown in Figure 2. Due to complexifies of the fatty acids composition, the distribution of fatty acids chains of triglycerides, the DSC melting curve shows many endothermic peaks over wide range of temperatures. These endothermic peaks are separated by an exothermic peak above the baseline at about 18^*C Based on research from Tan and Che Man

{Differential scanning calorimetric analysis of palm oil. palm oil based products and coconut oil: effects of scanning rate variation. Food Chemistry, 2002. 76: p. 89-102), this exothermic change is due to the polymorphic transition and recrystallizadon of triglycerides. The sizes of the two major peaks are quite similar because the concentration of the unsaturated components of tallow is close to that of the saturated components, which confirms the fatty acid compositions of tallow shown by Bockisch {Fats and Oils Handbook. 1998, Champaign, Illinois: AOCS Press). From this DSC curve, it can be seen that tallow exhibits extremely complex thermal behaviour that makes it not suitable for use as a PCM.

DSC melting analyses for taUow. methyl esters before and after hydrogenation are shown in Figure 3. There are two major endothermic peaks before hydrogenation: one is at a higher temperature of about 12 °C and it can be seen that the melting range for this peak is very wide, while the other peak is at much lower temperature, close to -40 °C. The peak at higher temperature represents the melting of mainly methyl stcarate and methyl palmitate. while the lower temperature endothermic peak corresponds to mostly methyl oleate. After hydrogenation, there is no peak shown on the low temperature range which indicates diat all unsaturated methyl esters were converted to saturated esters. The latent heat of the hydrogenated methyl esters Was 187.93] /g and a peak melting, temperature of 31.46° C, which make them good PCMs, but not for a building application.

RBD Palm Oil

The RBD palm oil sample was obtained from Golden Jomalina Food Industries Sdn. Bhd. Figure 4 is the DSC melting curve for this palm oil.

The methyl esters produced were saturated and the DSC analyses for the methyl esters before and after hydrogenation were performed, as shown in Figure 5. The methyl ester was fully converted to saturated ester with a latent heat and melting peak of 133.33kJ/kg and 29.05"C, respectively, similar to the hydrogenated tallow methyl ester. The extra peak ar 18.9 "C indicates that the product could be further improved with regards to its latent heat.

Coconut Oil

Unlike tallow and palm oil, most carbon chains in the coconut oil triglyceride structure are shorter than C16, and most of them are CI 4 and CI 2 as noted by Bockisch (Fats and Oils Handbook. 1998, Champaign, Illinois: AOCS Press). Figure 6 is the DSC melting curve of coconut oil, showing only one single peak at 22.95°C with latent heat of 1 16.60)/g.

Although melting range and latent heat are suitable for the PCM application for buildings, coconut oil cannot be applied as a PCM material due to its instability and because it is easy to oxidise.

The composition, of coconut oil methyl esters is illustrated in Table 1 (Bockisch; Fats and Oils Handbook. 998, Champaign, Illinois: AOCS Press). It can be seen that coconut oil is a nearly fully saturated oil and contains only about 9% carbon unsaturated chains.

Figure 7 shows the DSC melting curves of the coconut methyl esters before and after hydrogenation. Because coconut oil methyl esters are quite saturated, there is only a small degree of hydrogenation; latent heat rose from 112.0lJ/g to 124.36] /g. However, the melting point of the coconut methyl ester is as low as -10°C.

Hydrogenated Tallow and Palm Oil Butyl and Propyl Esters

Butyl esters from tallow and palm oil were hydrogenated and their thermal properties were determined following a heating-cooling-heating cycle with DSC. The results are represented in Figures 9 and 10. The peak melting point for both esters was 22 °C, while the latent heats were 124.5 and 106.2 kj/kg for tallow and palm oil butyl esters, respectively. These properties make them ideal PCM products for building applications. Figure J 1 shows the DSC of the hydrogens ted tallow propyl ester. The peak melting temperature of 25 "C, narrow melting range and moderate latent heat make it ideal PCM for building application.

Figure 12 shows cyclic measurements conducted in a computer controlled water bath in which its temperature was cycling between 12"C and 30"C. The esters were placed in a test tube and their temperatures were recorded as shown. These measurements show that palm oil and tallow esters have melting and freezing points of 21.5°C and 23.5"C respectively.

Example 2- Blends of Hydrogenated Methyl Esters from Fats and Oils

Table 2 shows the composition of most common oils and fats, while Table 3 shows the composition after hydrogenation. Canola oil, sunflower oil and soybean oil consist of mostly stearic acid after hydrogenation and hence their esters will have high melting points,„ usually above 30°C. Palm oil and tallow have a reasonable proportion of palmitic fatty acid and hence their esters, such as butyl and propyl esters, will have a melting point between 22 "C and 25 "C On the other hand, methyl esters from coconut oil, which has about 50% lauric fatty acid, will have a very low melting point, close to -10°C. Rapeseed oil could be used to produce high melting PCM. Mixing coconut oil with any of the other oils followed by cstcrification and hydrogenation will produce PCMs suitable for different applications.

Our experience in working on the use of PCM in buildings in New Zealand and Spain shows that comfort level may vary between the different countries. For example, a comfortable temperature in New Zealand is at least 2 "C lower than that found in dry climate locations in Spain. This suggests that PCMs suitable for building applications may need to be produced widi different melting temperatures. Table 3 shows that tins is possible. For example, if tallow is mixed with coconut oil in proportion of 3:1 , based on . Table 3, the composition of the fatty acids in the mixture will be 57% stearic, 24%palrnitic, 13% lauric and 5% myristic.

Figure 8 shows the DSC melting curve for the 3:1 mixture of hydrogenated tallow and coconut oil methyl esters. It was possible to lower the peak melting temperature by increasing the ratio of coconut ester in the mixture. For example, the ratio of tallow to coconut oil esters of 0.76:0.24 provides more suitable PCMs having peak melting point of 27"C and latent heat of about A 30] /g.

Example 3 - Impregnation of fatty acid esters PCMs produced according to the invention in gypsum board

Two small gypsum boards were impregnated, one with 30wt% commercial paraffin RT21 and the other with 30wt% tallow propyl ester produced according to Example 1 and were . hung in an oven at 30°C and the mass losses from the samples were, monitored for one month.

Figure 13 shows that the gypsum board was losing RT21 continuously, suggesting that it is not suitable for direct impregnation in gypsum board and there is a need for

microencapsulation. On the contrary, the gypsum board impregnated with the esters of the invention did not lose any mass suggesting that that ester could be directly impregnated in gypsum board with no risk of it leaving to the environment.

These results are confirmed by the vapour pressure of a mixmre of methyl paknitate/ methyl stearate and octadecane, which is closest paraffin to RT21 as measured at different temperatures. Figure 14 shows that the vapour pressure of the ester is almost three orders of magnitude lower than that of paraffin. Propyl ester will have even lower vapour pressure. Ester causes less firs hazard than paraffin

Figures 15 A to D show fire testing for composites of (1) tallow propyl ester produced according to the present invention in high density polyethylene (HDPE) and (2) RT21 in HDPE, using Con Calorimeter. Peak heat release rate (PHRR) of the above mentioned ester of the invention in HDPE without fire retardant was 1109 kW/m² (compared to 1507 kW/m² for RT 21). The PHRR of esters of the invention in HDPE with fire retardant was 783 kW/m² (compared to 1107 kW/m² for RT 21 with the same fire retardant). Based on this information it can be concluded that fatty acid esters produced according to the present invention is a more fire safe PCM than RT 21 due to a lower PHRR.

Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth.

Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/ or improvements may be made without departing from the scope or spirit of the invention. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognise diat the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

Claims

1. A process of preparing saturated fatty acid esters suitable for use as PGMs, wherein the process comprises the step of hydrogenating fatty acid esters that have been obtained by processing, of a triglyceride-containing starting material.

2. A process according to claim 1, wherein the fatty acid esters to be hydrogenated have been obtained by transesterification of the triglycxiidc-containing starting material with an alcohol, preferably in the presence of catalyst.

3. A process according to claim 1, wherein the fatty acid esters to be hydrogenated " have been obtained by hydrolysis of the triglyceride-containing starting material

, to form free fatty acids and esterification of the free fatty acids with, an alcohol.

4. A process according to claim 1, comprising the steps of (1) transesterifying a tiiglyceiide-containing starting material^' with an alcohol to produce fatty acid esters; and (2) hydrogenating the fatty acid esters obtained from step (1) to produce saturated fatty acid esters suitable for use as PCMs.

5. A process according to any one of the preceding claims, wherein the triglyceride- containing starting .material comprises a fat or oil selected from animal fats and vegetable oils, or any mixture of animal fats and/or vegetable oils.

6. A process according to claim 5 wherein the fat or oil is selected from the group consisting of tallow, palm oil, coconut oil, rapeseed oil, canola oil, sunflower oil and soybean oil, and mixtures of any two or more of the foregoing.

7. A process according to any one of the preceding claims, wherein the alcohol is a CI to C4 alcohol, selected from medianol, ethanol, propanol or butanol.

8. A PCM comprising fatty acid esters obtained by or obtainable by a process according to any one of the preceding claims.

9. A PCM according to claim 8, having a latent heat of fusion of at least about 120 J/g, preferably at least about 130 J/g, more preferably about 140 J/g.

10. A PCM according to claim 8 or 9, wherein the PCM has a phase transition temperature in the range of from about 18°C to about 25°C.

11. A PC according to any one of claims 8 to 10, comprising fatty acid esters selected from the group consisting of hydrogenated tallow methyl, ethyl, propyl and butyl esters, hydrogenated palm oil methyl, ethyl, propyl and butyl esters, hydrogenated coconut oil methyl, ethyl, propyl and butyl esters, hydrogenated rape seed oil methyl, ethyl, propyl and butyl esters, and hydrogenated sunflower oil methyl, ethyl, propyl and butyl esters.

12. A PCM according to claim 11 , comprising hydrogenated tallow butyl or propyl esters.

13. A PCM according to claim 11, comprising hydrogenated palm oil butyl or propyl esters.

14. A PCM according to claim 11, comprising hydrogenated tallow methyl esters.

15. A PCM according to claim 11, comprising hydrogenated palm oil methyl esters.

16. A PCM according to claim 11, comprising a mixture of hydrogenated coconut oil methyl esters and hydrogenated tallow or palm oil methyl esters.

17. A PCM according to claim 1 1 , comprising a blend of any tvvo or more of the following: hydrogenated tallow methyl, ethyl, propyl and butyl esters, hydrogenated palm oil methyl, ethyl, propyl and butyl esters, hydrogenated coconut oil methyl, ethyl, propyl and butyl esters, hydrogenated rape seed oil methyl, ethyl, propyl and butyl esters, and hydrogenated sunflower oil methyl, ethyl, propyl and butyl esters.

18. A PCM comprising a mixaire of saturated fatty acid esters derived from animal fat or vegetable oil or a blend of one or more animal fats and/or vegetable oils.

19. A PCM according to claim 18, wherein the proportions of individual saturated fatty acid esters in the mixture correspond to the proportions of individual fatty acids in the animal fat or vegetable oil, or, blend thereof, from which the saturated'fattv acid esters are derived.

20. A method of storing or removing thermal energy, the method comprising

incorporating a PCM according to any one of claims 8 to 19 into a building or other structure or device.

21. A composition for storing or removal of thermal energy, the composition

comprising a PCM according to any one of claims 8 to 19.

22. A composition according to claim 21, further comprising a nucleating agent.

23. A composition according to claim 21, comprising the PCM encapsulated within a material such as a metallic or plastics material.