FIELD OF THE INVENTION The present invention generally relates to a method for producing fatty acid methyl ester. More particularly, the present invention relates to an improved method for producing fatty acid methyl ester, which includes esterification reaction and transesterification reaction under microwave heating system, for use in biofuel production.

BACKGROUND OF THE INVENTION

Biodiesel production is expected to be beneficial from low quality waste feedstock. However, the presence of high free fatty acid content in waste feedstock renders the process for obtaining biodiesel to be difficult, especially by performing conventional transesterification reaction with base catalyst (e.g. sodium hydroxide). The transesterification reaction with the base catalyst leads to soap formation, which leads to increase in catalyst consumption, thus lowering catalytic efficiency and increasing viscosity of the biodiesel mixture. The transesterification reaction also leads to formation of gels, thus complicating purification of crude biodiesel. Further, base catalyzing process is very sensitive to presence of water and free fatty acids, thus leading to more usage of methanol. Brown grease obtained from the low quality waste feedstock contains high percentage of free fatty acids and water. Upon transesterification, the base catalyst will react with the free fatty acids to form soaps.

On the other hand, homogeneous catalysis system is too complicated due to the high amount of steps involved in the process. Transesterification reaction with homogenous catalysis system involved usage of neutralization agent to neutralize catalyst used and requires high amount of water to purify the product. Consequently, it will produce a large amount of waste water. Moreover, such type of catalyst could not be generated and reused. This system is also expensive due to the large amount of water usage. Further, due to oils and methanol being not completely miscible, the mixing efficiency was stated as one of the most important factors affecting the yield of biodiesel. The conventional heating method for biodiesel production requires long reaction time and high energy consumption to achieve high yield of biodiesel. Transesterification reactions under conventional heating method take more than 1 to 12 hours to get result.

See, for example, in the China patent publication no. CN 105536822, there is provided a synthesis of solid acid catalyst, Fe2(S0 ₄ )2 loaded with ΤΊΟ2, resulting in catalytic activity of the catalyst being significantly increased. The substance was thoroughly mixed by a certain percentage and stirred in 3 hours, dried at 1 10 °C and sieved through 50 mesh sieve. The catalyst was calcined at 350 °C in 2.5 hours. However, the time taken for preparing the catalyst is fairly long and the usage of T1O2 is costly.

Thus, there is a need for an improved method for producing fatty acid methyl acid for biofuel production that overcomes the problems or at least mitigate the disadvantages of the prior art. SUM MARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

Accordingly, the present invention provides a method of producing a fatty acid methyl ester for use in biofuel production from a domestic waste grease.

The present invention can be characterized by the method comprising the steps of conducting esterification reaction to the domestic waste grease under a first microwave radiation catalyzed with a solid sulphated-ferric(l l l) oxide/alumina oxide catalyst for producing an esterified domestic waste grease and conducting transesterification reaction to the esterified domestic waste grease under a second microwave radiation catalyzed with a solid potassium oxide/silica oxide catalyst for producing the fatty acid methyl ester.

Preferably, the domestic waste grease is a waste grease having free fatty acid content ranging from 15 to 100 wt% such as brown grease, yellow grease, animal fats, jatropha oil and palm fatty acid distillate.

Preferably, the first microwave radiation is induced by a microwave device. Preferably, the second microwave radiation is induced by a microwave device.

Preferably, the first microwave radiation and the second microwave radiation are induced by the same microwave device.

Preferably, the microwave device is set at a power ranging from 1 10 to 770 Watt and a wavelength of 2.45 Ghz for conducting the esterification reaction and transesterification reaction. Preferably, the esterification reaction and transesterification reaction is conducted with an alcohol such as methanol, ethanol, or propanol.

Preferably, the molar ratio of alcohol to free fatty acid for use in the esterification reaction and transesterification reaction ranges from 15: 1 to 30: 1 .

Preferably, the alcohol used in the esterification reaction and transesterification reaction is recoverable, reusable, and recyclable.

Preferably, the solid sulphated-ferric(ll l) oxide/alumina oxide catalyst and the solid potassium oxide/silica oxide catalyst is used in the esterification reaction and transesterification reaction respectively at an amount ranging from 1 -5% of wt%.

Preferably, the solid sulphated-ferric(ll l) oxide/alumina oxide catalyst is separable from the esterified domestic waste grease by filtration. Preferably, the solid potassium oxide/silica oxide catalyst is separable from the fatty acid methyl ester by filtration.

In another aspect of the invention, there is provided a fatty acid methyl ester for use in biodiesel production produced from domestic waste grease, wherein the fatty acid methyl ester is produced by the abovementioned methods.

It is therefore an advantage of the present invention that the method allows production of biofuel from low cost waste grease having high free fatty acid content in a short time. Further, the method allows lesser energy consumption due to the methods performed at a relatively low temperature and operation time.

It is therefore another advantage of the present invention that the catalyst used in the method of the present invention can be recycled for up to ten times, thus reducing manufacturing cost. Further, the method to produce biofuel from waste grease having high free fatty acid does not form any soap or white precipitation, which eases catalyst recovery and separation of product and byproduct. It is therefore another advantage of the present invention, wherein the filtration method employed in separating the solid acid and base catalyst from the esterified domestic waste grease and fatty acid methyl ester requires no additional purifying steps, thereby reducing operational cost. It is yet another advantage of the present invention, wherein there is no wastewater produced by the esterification reaction and transesterification reaction method utilized in the present invention.

The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein:

Figure 1 is a flow chart of the method of the present invention, according to an embodiment of the present invention.

Figure 2 is a chromatogram of fatty acid methyl ester produced by the method of the present invention, according to an embodiment of the present invention.

Figure 3 is a 1 H-NMR spectrum of fatty acid methyl ester produced from the method of the present invention, according to an embodiment of the present invention.

Figure 4 is a FT-IR spectrum of fatty acid methyl ester produced from the method of the present invention, according to an embodiment of the present invention.

It is noted that the drawing may not be to scale. The drawing is intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a method that allows efficient production of biofuel from low cost waste grease with high free fatty acid content in a relatively short amount of time. It is another object of the present invention that the method, which produces no wastewater, consumes lesser energy in producing fatty acid methyl ester as the method is performed at a relatively low temperature and operation time. It is also an objective of the present invention that the catalyst used may be recycled up to ten times.

The method of the present invention relates to production of fatty acid methyl ester for use in biofuel production from domestic waste grease with high free fatty acid content. The method comprises the steps of conducting esterification reaction 4 to the domestic waste grease under a first microwave radiation catalyzed with a solid sulphated-ferric(l l l) oxide/alumina oxide catalyst for producing an esterified domestic waste grease and conducting transesterification 6 reaction to the esterified domestic waste grease under a second microwave radiation catalyzed with a solid potassium oxide/silica oxide catalyst for producing the fatty acid methyl ester.

The method of the present invention utilizes domestic waste grease having free fatty acid content ranging from 15 to 100 wt% such as brown grease, yellow grease, animal fats, jatropha oil and palm fatty acid distillate. The esterification reaction 4 is conducted in the first microwave radiation, which is induced by a microwave device. The transesterification 6 reaction, which is conducted in the second microwave radiation, was also induced by a microwave device, which is similar to the microwave device used to induce the first microwave device. The microwave device is set at a power ranging from 1 10 to 770 Watt with a wavelength of 2.45 Ghz.

The esterification reaction 4 and transesterification reaction 6 conducted to the free fatty acid of the present invention is preferably conducted with alcohols such as methanol, ethanol, or propanol. The molar ratio of alcohol to free fatty acid for use in the esterification reaction 4 and transesterification reaction 6 ranges from 15: 1 to 30: 1. The alcohol used by the method of the present invention is recoverable, reusable, and recyclable.

The solid sulphated-ferric(lll) oxide/alumna oxide catalyst and the solid potassium oxide/silica oxide catalyst that are used for the esterification reaction 4 and transesterification reaction 6, respectively are provided at an amount ranging from 1-5% wt%. The solid sulphated-ferric(lll) oxide/alumna oxide catalyst used for the esterification reaction 4 of waste grease is separable and recoverable from the esterified waste grease via filtration, which allows reusing of the catalyst. Further, the solid potassium oxide/silica oxide catalyst is also separable from the end product, which is fatty acid methy ester by use of filtration.

Obtained raw domestic waste grease with high free fatty acid content, which includes brown grease, is first pre-treated to prepare it for esterification reaction 4. Typically, the raw domestic waste grease will be heated, filtered, and stored accordingly. The methods of the present invention is preferably carried out in a certain condition, whereby the temperature used in pretreating the brown grease is preferably above 100 °C. The temperature used in heating the esterified brown grease and the fatty acid methyl ester for alcohol separation is preferably around 64 °C to 70 °C. The alcohol to oil molar ratio is preferably above 10: 1. Further, the amount of catalyst used in the esterification reaction 4 and transesterification reaction 6 are preferably above 1 wt% of the domestic waste grease. By way of example, and not necessarily of limitation, the method of the present invention may be provided as follows:

EXAMPLE 1

Methods of Producing a Fatty Acid Methyl Ester for Use in Biofuel Production from

Brown Grease

In accordance to an embodiment of the present invention, there is provided a method for producing the fatty acid methyl ester for use in biofuel production from brown grease. Firstly, the brown grease is pretreated 2 by heating the brown grease above 100 °C, filtered, and stored accordingly. Next, a solid heterogeneous base catalyst (solid sulphated-ferric(l ll) oxide/alumina oxide catalyst) and a solid heterogeneous acid catalyst (solid potassium oxide/silica oxide catalyst) is prepared. Esterification reaction 4 is then carried out to the pretreated brown grease in a 42 L domestic microwave, which is connected to a reflux condenser. 2L of the pretreated brown grease was poured into a 5 L reaction flask. Next, 3 wt% of solid potassium oxide/silica oxide acid catalyst and 30: 1 methanol to free fatty acid molar ratio is added to the reaction flask. Next, the reaction flask is placed in the domestic microwave that is connected to a cooling condenser. The reaction is carried out at a period of 30 minutes with microwave powered to 1 10 watt. The catalyst is then removed from the reaction flask by filtration. The remaining content in the reaction flask is then heated at a temperature ranging from 65 °C to 70 °C to remove excess methanol. Water, which is the by-product of the esterification is separated from the reaction flask by gravity separation and discharged. The final product, esterified brown grease, is then used for transesterification reaction 6.

Transesterification reaction 6 is then conducted, whereby the reaction starts with pouring the esterified brown grease into a 5 L reaction flask. Then, 1 wt% of a solid potassium oxide/silica oxide catalyst and 30: 1 methanol are added into the reaction flask. The reaction flask is then placed in a domestic microwave with a power of 550 watt and connected to a cooling condenser for a period of 90 minutes. The solid potassium oxide/silica oxide catalyst is then removed from the reaction flask by filtration. Excess methanol is also removed from the reaction flask by heating the content of the reaction flask at a temperature ranging from 65- 70 °C. The remaining mixture in the reaction flask is then left overnight in a separating funnel, whereby a fatty acid methyl ester and glycerol produced by the transesterification 6 reaction are separated into two layers. The upper layer of fatty acid methyl ester is then removed for use as an ingredient of biodiesel fuel.

By way of example, and not necessarily of limitation, the properties of the fatty acid methyl ester prepared by the above method may be provided as follows: EXAMPLE 2

Properties of the Prepared Fatty Acid Methyl Ester in Accordance with ASTM Standard A biodiesel product quality test is conducted on the fatty acid methyl ester produced by the above method. The table of characterization of the fatty acid methyl ester produced by the method is shown below:

An analysis result of biodiesel produced by using the fatty acid methyl ester of the present invention is shown in Figure 1 , 2, and 3.

While this invention has been particularly shown and described with reference to the exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.