FIELD OF INVENTION

The invention relates to a field of biodiesel production. In particular, the present invention relates to a method of producing biodiesel from high sludge content oil without using catalyst and consequently, eliminates the generation of by-product, glycerine.

BACKGROUND OF THE INVENTION

Biomass or biomass-derived materials are used as replacements to petroleum fuel due to the depletion of fossil resources. Biodiesel is a mixture of mono alkyl esters with long-chain fatty acids that is derived from vegetable oils, animal fats, tallow, waste cooking oil or microbial oils (algae, bacteria and fungi). The raw materials are converted to biodiesel through a process called transesterification. Biodiesel has several advantages such as: it is an eco- friendly and biodegradable fuel, it is non-toxic and free of sulphur components and aromatic s and it has a favourable energy balance.

Recently, transesterification has garnered research attention as the most desired method to convert vegetable oils or animal fats into fatty acid methyl esters (FAME). Transesterification involves alcohol such as methanol or ethanol and an acid or base catalyst. Base catalyst such as sodium or potassium hydroxide, and sodium or potassium methoxide, are commonly used for transesterification while acid catalyst gained less attention due to its relatively slow reaction rate and its corrosive characteristic to equipment. The raw materials (a triglyceride) will react with an alcohol to form esters and glycerol. The triglycerides reacts step by step with alcohol, and converts to diglycerides (DG), monoglycerides (MG), and finally glycerol. The reaction is affected by contact between the two immiscible phases during mixing, the type of catalyst and alcohol used, molar ratio of alcohol to triglyceride, content of free fatty acids (which are natural degradation products of oils), water content and reaction temperature.

Since the oils or fats used are immiscible with catalyst-alcohol-solution, mixing is an essential factor in the transesterification process which will improve the yield of the transesterification. Vigorous mixing is important to create sufficient contact between the two immiscible phases because the insolubility of alcohol in the oil phase obstructs the progress of the transesterification reaction. Increasing the speed of mixing will reduce the reaction time and increase the conversion till an optimum limit; wherein any increment in mixing speed thereafter will not show any significant effect on the yield of the reaction. Once methyl esters are formed, they act as a joint solvent for the reactants and a single-phase system is formed.

Ultrasonic is an advantageous device known for lowering processing costs, speeding up transesterification process, reducing amount of catalyst required and produces higher quality of biodiesel. Ultrasonic can also reinforce the mass transfer of liquid-liquid heterogeneous systems wherein this enhances the mixing of oils and alcohol. Ultrasonic waves are longitudinal mechanical waves which generate cavitation bubbles as they transmit through a liquid medium. Ultrasonic waves travel as a successive series of compressions and rarefactions along the direction of wave propagation through the liquid medium. A cavity will be created and is filled with vapor from the liquid when the attraction forces between the liquid molecules became weaker and less than the negative pressure of the cyclic rarefaction. At the beginning of its existence, the cavity starts tiny and grows to form acoustic cavitation bubble within other successive cycles. These cavitation cause a limited increase in temperature near the boundary layer and this increment will change the sequence of transesterification reaction that cancel the external heating step in the production process.

The transesterification process can be conducted in two ways that is with or without incorporating catalyst. Although catalyst accelerates the transesterification process, there are several disadvantages that are associated with the incorporation of catalyst such as high production costs. Recent research has shifted its direction to non-catalytic routes to accelerate transesterification process. There are two different non-catalytic routes, namely biox process and supercritical method. The biox process involves the use of a co-solvent in the transesterification process. The co-solvent functions to increase the solubility of methanol in oil. The process takes place at a low temperature (i.e. 30 °C) and short reaction time. The biox process is able to convert oil with high percentage of FFA into biodiesel in two steps; wherein co-solvent is added in each step. The co-solvent can be recycled and reused in the process. However, the main drawback of this method is the difficulty in separating methanol and co-solvent because their boiling points are extremely close. The co-solvent is hazardous and toxic; hence, it needs to be removed completely from the product.

In the supercritical method, the transesterification process takes place under extremely high temperature and pressure. A liquid or gas exposed to these extreme conditions formed a single supercritical fluid phase. Oils and methanol are immiscible liquids at room temperature; which will create a homogeneous fluid due to sharp drop in the solubility of methanol and reduction in dielectric constant making methanol a non-polar substance. Hence, the transesterification process is accelerated because no mass transfer restriction is expected under such state. The main advantages of supercritical method are it is not affected by free fatty acids (FFA) and no soap is generated because no catalyst is involved. Thus, biodiesel and glycerine has better quality and lower reaction time than for a catalysed reaction. However, the supercritical method requires high pressure and temperature which indicates the need for high energy input for the process. Under high temperature, undesired by-products formed from unavoidable degradation of triglycerides can influenced the biodiesel quality. Besides, the extreme reaction condition indicates that the operating procedure is complicated and needs specially designed equipment.

To overcome the drawbacks of the existing technology, it is desirable to come out with a simple, low processing cost and non-toxic biodiesel production method which is able to solve the abovementioned problems. This invention provides a solution to the problems.

SUMMARY OF THE INVENTION

One of the objects of the invention is to provide a method for producing biodiesel from high sludge content oil without the use of catalyst to eliminate the generation of by-product, glycerine. Another object of the invention is to provide a low-cost method for producing biodiesel from high sludge content oil.

Still another aspect of the present invention is to provide a continuous process in biodiesel production. At least one of the preceding aspects is met, in whole or in part, by the present invention, in which the embodiment of the present invention describes a method for biodiesel production from waste oil comprising the steps of mixing waste oil and alcohol; and performing transesterification in a reactor comprising a combination of a high speed mixer operating at 1000 to 5000 rpm and a sonic mixer operating at 1.5 to 2.4 MHz wherein the mixture is passed through a plurality of reactors connected in series.

In a preferred embodiment of the invention, the alcohol is methanol or ethanol.

In another preferred embodiment of the invention, the volume ratio of waste oil to alcohol is 1: 1.3-1.5.

Still in another preferred embodiment of the invention, the waste oil and alcohol are mixed at temperature ranging from 50 to 60 °C.

Yet in another preferred embodiment of the invention, the unreacted mixture is heated to 45 to 55°C before being passed to the reactor. The preferred embodiment of the invention consists of novel features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings and particularly pointed out in the appended claims; it being understood that various changes in the details may be effected by those skilled in the arts but without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim. The invention relates to a field of biodiesel production. In particular, the present invention relates to a method for producing biodiesel from high sludge content oil without the use of catalyst and eliminates the generation of by-product, glycerine.

In the preferred embodiment of the invention, a method for biodiesel production from waste oil comprising the steps of mixing waste oil and alcohol; and performing transesterification in a reactor comprising a combination of a high speed mixer operating at 1000 to 5000 rpm and a sonic mixer operating at 1.5 to 2.4 MHz wherein the mixture is passed through a plurality of reactors connected in series.

According to the preferred embodiment of the invention, the alcohol used can be methanol or ethanol. The type of alcohol has an impact on the yield and rate of reaction. Preferably, methanol is used in biodiesel production. This is because the yield of biodiesel obtained is higher than ethanol. Moreover, the recovery of methanol from the final product is easier than ethanol. The waste oil used can be any non-edible oil containing high sludge content but it shall not be limited thereto. Low sludge content can be processed using a simpler yet cheaper solution compared to high sludge content. Typically, this invention can treat waste oil containing up to 45 % of free fatty acids. In the preferred embodiment, the volume ratio of the waste oil to alcohol is selected from a range of 1 : 1.3 to 1: 1.5.

As described by the preferred embodiment of the invention, the waste oil and alcohol are mixed at temperature ranging from 50 to 60 °C to separate solid impurities from the waste cooking oil. Any temperature greater than 60 °C will cause vaporization of alcohol from the mixture. The mixture is heated to reduce the viscosity of the waste oil. In accordance to the preceding description, the step of mixing alcohol and waste oil is preferably conducted in a mixing vessel under mixing at speed ranging from 50 to 100 rpm for 30 to 45 minutes. Thereinafter, solid impurities are allowed to settle for about 20 minutes. Preferably, solid impurities are removed from waste oil by passing through a plate & frame filter press and returning the recovered waste oil back to the mixing vessel. As depicted in the preferred embodiment of the invention, the unreacted waste oil and alcohol is heated at temperature ranging from 45 to 55 °C. Preferably, the heater is made of granite enclosed by heating coil. The heating process is conducted to reduce the viscosity of the waste oil to facilitate the pumping process.

In accordance with the preferred embodiment of the invention, the transesterification process is performed in a reactor comprising high speed mixer operating and sonic mixer. Preferably, high speed mixing is conducted at 1000 to 5000 rpm while sonic mixing is carried out at 1.5 to 2.4 MHz. In the present invention, it is preferred that the transesterification process is conducted in a plurality of reactors connected in series to increase the yield of biodiesel produced. Preferably, the amount of reactors used is 3. It is preferred that the reactor is insulated with coconut coir or concrete or any other available insulating materials can also be used. The waste cooking oil and alcohol enters the reactor from the bottom and is exposed to sonic waves wherein mixing of waste cooking oil and alcohol is initiated. Mixing is further enhanced by exposing the mixture to a high speed mixer at the top of the reactor. Since transesterification is an exothermic process, the temperature of the mixture increases to 70 °C during transesterification. The residence time of the transesterification process can be varied depending on the size of the reactor and flow rates of the mixture entering the reactor.

In an exemplary embodiment of the invention, whereby 3 reactors are put to use, waste cooking oil and alcohol enters the first reactor. A mixture of biodiesel and also unreacted waste cooking oil and methanol leaves the first reactor and is passed on to the second and third reactors, respectively. The design and fabrication details of the reactors are similar. Further, the mixture is subjected to a similar transesterification process which takes place in the first reactor. In the present invention, it is preferred that the final product is separated based on boiling point of a substance wherein methanol, whose boiling point is at 70 °C vaporizes and is recycled back to the system leaving only biodiesel which is collected from the bottom of the separation vessel. Example

An example is provided below to illustrate different aspects and embodiments of the invention. The example is not intended in any way to limit the disclosed invention, which is limited only by the claims. Example 1.

Biodiesel produced using method from the present invention. As described in preceding descriptions, waste cooking oil and methanol are mixed in a mixing vessel at volume ratio of 1: 1. The waste cooking oil and methanol are gently mixed at 50 rpm under heating at 55 °C. Solid impurities are then allowed to settle for about 20 minutes. The solid impurities are pumped to a plate and frame filter press and the recovered waste cooking oil is recycled back to the mixing vessel. The recycled waste cooking oil is mixed with the waste cooking oil and methanol at 100 rpm before passing through a heater at temperature 50 °C. Transesterification process takes place in a reactor wherein the waste cooking oil and methanol enters the reactor from the bottom and is exposed to sonic waves with frequency of 2.0 MHz. Mixing of waste cooking oil and methanol is then initiated and further enhanced by exposing the mixture to a high speed mixer at 2500 rpm at the top of the reactor. The residence time that the mixture spends in each tank is 5 minutes. The temperature of the mixture increases to 70 °C when transesterification occurs. The transesterification process is repeated in 3 identical reactors connected in series. The mixture containing biodiesel and unreacted waste cooking oil and methanol are passed to the second and third reactors of similar designs and process parameters. The similar process as in first reactor takes place in both second and third reactors. The final product undergoes a separation process which is based on boiling point of a substance wherein methanol vaporizes and is recycled back to the system. Biodiesel is collected from the bottom of the separation vessel. Example 2.

Comparison between biodiesel produced from the present invention and conventional invention. In the conventional invention, similar raw materials, waste cooking oil and methanol are used at a volume ratio of 1: 1. However, the transesterification process is carried out in the presence of catalyst, sodium hydroxide wherein sodium hydroxide is dissolved in methanol and the methanol solution is added to the waste cooking oil. The biodiesel produced using method from the present invention as described in example 1 is compared to the biodiesel produced using method from conventional invention as described in example 2. The results are shown in Table 1.

Table 1: Comparison between the biodiesel produced from the present and conventional invention.

Properties Biodiesel Biodiesel

(Present invention) (Conventional invention)

Yield (%) 98 90

Water content (%) 0 0

Surface tension (mN/m) 29.50 31.74

Viscosity 4.58 4.66

Density (g/ml) 0.80 0.87

Calorific value (kj) 43.8 43.7

Flash point (°C) 140 147

Pour point (°C) 9 8

From Table 1, it is observed that the present invention achieves nearly 100% biodiesel yield and is slightly higher than conventional invention. Other properties including surface tension, viscosity, density, calorific value, flash point and pour point are comparable to the properties of biodiesel produced using conventional invention. This shows that the quality of biodiesel produced using the present invention is of the same standard as the conventional invention.

The disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.