WO2009061169A1

WO2009061169A1 - An improved process to produce biodiesel

Info

Publication number: WO2009061169A1
Application number: PCT/MY2008/000130
Authority: WO
Inventors: Phillip Kooi Jiu Tan; Chiew Peng Haw; Wooi Guan Liang
Original assignee: Grand Inizio Sdn. Bhd.
Priority date: 2007-11-09
Filing date: 2008-11-10
Publication date: 2009-05-14

Abstract

A transesterification process for producing fatty acid methyl ester comprising the steps of reacting oil of plant or animal origin with methanol premixed with an alkaline catalyst in aqueous form at a temperature of 600C to 700C to produce a first reaction products; withdrawing formed glycerol continuously from the first reaction products; reacting additional methanol premixed with the alkaline catalysts into first reaction products by stirring when conversion of fatty acid methyl ester in the first reaction products reached at least 90% to acquire the fatty acid methyl ester with a conversion rate of at least 99%, wherein the alkaline catalyst is dissolved in water with a concentration of 40% to 50%.

Description

AN IMPROVED PROCESS TO PRODUCE BIODIESEL

FIELD OF THE INVENTION

The present invention relates to an improved process to produce biodiesel, namely fatty acid methyl ester (FAME), from methanol and natural oil or fat. The disclosed process can be conducted under high humidity along the transesterification process.

Specifically, the disclosed process able to utilize alkaline catalysts prepared in aqueous form to enhance reaction without the need of maintaining complete dryness during the transesterification reaction proceed.

BACKGROUND OF THE INVENTION

Worldwide demand on biomass energy has been increasing greatly in recent years.

This mainly attributes to the elevating price of the fossil fuel. Fatty acid methyl ester is known to be one of the attractive bio-fuel because purified fatty acid methyl ester can be used directly in existing diesel engines without the need of diesel engines modification or further treatment on this bio-fuel.

Taking into consideration that use of natural sources-derived fatty acid methyl ester as fuel substitutes is set for major development over the coming future, it is desire of the manufacturer to improve present available methods to commercialize this bio-fuel at lower price either via increase the process yield or enhance the reaction rate to reduce the laboring cost. Production of the fatty acid methyl ester normally involves transesterification reaction between methanol and oil or other derivatives thereof such as triglycerides. Along the transesterification process, factors like reaction temperature, reactor pressure, ratio of the initial substrate, types of catalysts, and amount of the existing side products are crucial in determining yield as well as quality of the end products. Numerous improvements on the aforesaid factors have been proposed. For example, European patent application no. 0523767 discloses a method to carry out transesterification process which utilizes a homogenous basic catalysts. Particularly, this invention involves two-staged^{^} conversion that the reactants are intensively mixed in the reactor while the side products are being withdrawn from the reactor. Moreover, end products of the first stage conversion are directed to second stage when the 20% to 60% of the reactants are consumed. The catalysts used in this invention is preferably sodium methylate. Other basic catalysts are proposed but no detailed information are disclosed in preparing the proposed catalysts in liquid form and to be used other than said sodium methylate.

Another European patent application no. 0706988 discloses another method to prepare FAME by dissolving the alkaline catalysts into the glycerol to form mono-alkaline glycerate. Again, sodium methylate is employed in this disclosed invention to avoid soap forming due to the existence of water in sodium hydroxide or potassium hydroxide prepared in the aqueous form.

United State patent application no. 6262285 is related to another method to produce FAME under reduced pressure and continuously separate both FAME and glycerides fraction by a continuous decantation process. With such processing steps, this invention claims that the produced FAME containing only trace amount of water thus further water removal steps can neglected rendering lower manufacturing cost.

Untied State patent application no. 6440057 entails a process for producing FAME at higher rate with shorter time via applying sheering force to emulsify the mixture of Ihe reactants. This invention claims that emulsion formed increases the area of contact among the reactants and consequently lead to faster reaction. The disclosed process includes only single stage transesterification process with a basic potassium solution as the catalysts.

Lee et. al. filed a patent application with publication no. WO2004085585 which proposes to transesterify the reactant in the presence of an alkyl ester. It states that the alkyl ester enables the two immiscible reactants to form a single liquid phase leading to high reaction rate. Acidic catalysts are utilized in this invention. United State patent application no. 6534186 provides another improved process by employing basic glycerin to neutralize available free fatty acids in the reactants to inhibit formation of the unwanted side products. United State patent publication no. 2005204612 offers a process to reuse water and glycerin recovered from the esterification for purification of the end products as well as the reactants. Patent publication no. WO2006089429 utilizes a porous membrane which selectively allows the formed FAME to pass through for collection but not the reactants or the side products

SUMMARY OF THE INVENTION

The present invention provides an improved method for producing FAME that the disclosed process able to produce FAME under high moisture or water content in the reactants.

Further object of the present invention includes providing a process which able to employ basic catalysts prepared in aqueous form without any deteriorating effects towards the FAME produced by end of the process.

Another object of the present invention is to offer a cost effective process to produce FAME as equipment or costly treatment for removing of the water content such as distillation can be omitted via the disclosed process. Thus, no additional cost incurred for water content removal in opposed to the conventional-method.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiment of the present invention is a transesterification process for producing fatty acid methyl ester comprising the steps of reacting oil of plant or animal origin with methanol premixed with an alkaline catalyst in aqueous form at a temperature of 60⁰C to 70⁰C to produce a first reaction products; withdrawing formed glycerol continuously from the first reaction products; reacting additional methanol premixed with the alkaline catalysts into first reaction products by stirring when conversion of fatty acid methyl ester in the first reaction products reached at least 90% to acquire the fatty acid methyl ester, wherein the alkaline catalyst is dissolved in water with a concentration of 40% to 50%. The heating of the reaction can be done using steam.

Further embodiment of the present invention includes a purifying step the acquired methyl ester with magnesium silicate. This purification step can be conducted simply by stirring the acquired methyl ester with magnesium silicate to enhance adsorption of the impurities in the acquired methyl ester onto the magnesium silicate. Subsequently, the adsorbents, magnesium silicate, are removed via filtration or any other known methods in the art.

It is important to have the parameters of the conducted process always in favor of producing fatty acid methyl eater rather than the sides product, thus the initial amount of methanol to the animal fat or plant oil is preferably in stoichiometry of at least 3 mole of methanol to 1 mole of oil. It is most preferred that the amount of methanol is always in excess than the stated ratio. Furthermore, the ratio of the methanol to the animal fat or plant oil is 1 D to 15: 100 by weight.

Preferably the amount of alkaline catalyst (99.95% wt. %) to amount of the methanol (99.95 wt. %) is 5-10 : 120-130 by weight. Practically, alkaline catalyst is mixed in diluted form i.e. 10-20 parts of sodium hydroxide (40%~50% wt %) to 120-130 parts of methanol (99.95% wt %). The amount of the strong basic catalysts presented in the methanol is crucial in determining the amount of methanol to be deprotonaed to form alcoixdes which reacts with the oil to form FAME. It is preferred that the alkaline catalyst is any one or combination of sodium hydroxide or potassium hydroxide. .

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is the flow chart showing the steps to conduct the present invention.

DETAILED DESCRIPTION OF THE INVENTION One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiment describes herein is not intended as limitations on the scope of the invention.

One of the embodiments of the present invention involves a transesterification process for producing fatty acid methyl ester comprising the steps of reacting oil of plant or animal origin with methanol premixed with an alkaline catalyst in aqueous form at a temperature of 60⁰C to 70⁰C to produce a first reaction products; withdrawing formed glycerol continuously from the first reaction products; reacting additional methanol premixed with the alkaline catalysts into first reaction products by stirring when conversion of fatty acid methyl ester in the first reaction products reached at least 85% to acquire the fatty acid methyl ester, wherein the alkaline catalyst is dissolved in water with a concentration of 40% to 50%. It is possible to conduct the disclosed process under pressure higher than the atmospheric pressure as the surface where the reactants contacted are enhanced under high pressure. Nevertheless, it is preferable to conduct the present invention under normal atmospheric pressure.

The oil of plant or animal origin used in the present invention can be of oil palm, soybean oil, coconut oil, groundnut oil, safflower oil, linseed oil, corn oil, sunflower oil, olive oil, canola oil, cottonseed oil, rapeseed oil, tung oil and derivatives thereof. Nevertheless, it is preferred that the oil is in refined form i.e. RBD oil (refined bleached deodorised oil) which contain less impurities. However, crude vegetable oil may also be used with an add-on pre-treatment processing unit.

Attention shall now draw to the fact that the alkaline catalysts used in the present invention is preferably strong base such as sodium hydroxide, potassium hydroxide or any combination thereof. The strong base in the present invention may be acquired in aqueous form i.e. already diluted in water (40% to 50% wt. %) which is lower in costs. Amount of the strong catalysts dissolved in the methanol affects the reactivity of the process, as the dissolved catalysts will deprotonate the methanol to form alkoxides which actually in turn react with the oil of plant or animal origin. Preferably, about 8 to 10 parts of mixture of catalysts and methanol are mixed with 100 parts of RBD Oil by weight in the first reaction. Moreover, approximately 10 to 20 parts of catalysts (40% ~ 50% wt. %) to be mixed in 120 ~ 130 parts of methanol (99.95% wt. %) to perform the disclosed invention. The alkoxides formed in the mixture are highly reactive that it can instantly react with the triglycerides in the oil to produce fatty acid methyl ester and glycerols once these reactants are discharged and heated together in the reactor. In the preferred embodiment, the glycerols produced during the transesterifϊcation is continuously discharged out of the reactants from the beginning of the reaction until end of the reaction. Concentration of the glycerol is most preferred to be maintained at the lowest possible. Presence of the glycerol in the reaction will hinder the production of FAME because the equilibrium of the transesterification may shift from instead of producing FAME back to yielding the original reactants, methanol and the oil of plant or animal origin when the amount of glycerol increases along the reaction. It is important to be noted that the alkaline catalysts may react with the glycerol produced to form alkoxides. These alkoxides of glycerol are in much stable form compared to those of methanol due to the other electron withdrawing hydroxy groups attached on the carbon chain. Henceforth, the amount of catalysts available in the reaction will be decreasing when more glycerol are discharged. Meanwhile, methanol may also be drawn out following the glycerol. Preferably, the withdrawn methanol is further separated from the glycerol mixtures to be reused.

As in the foregoing description, the disclosed process is multi-staged. New batch of methanol premixed with catalysts are loaded into the products of first reaction when the transesterification reaches about at least 85%. Amount of the second batch to be introduced in the second reaction is preferably. About 5 to 6 parts of mixture of the methanol and catalysts is introduced into 100 parts of RBD oil by weight to favor the transesterificaiton reaction to attain about 99% conversion. Again, the mixture of methanol and the strong base contains approximately 10 ~ 20 parts of catalysts (40% ~ 50% wt. %) to be mixed in 120 ~ 130 parts of methanol (99.95% wt. %). Moreover, stirring of the reactants is preferred in the second reaction to ensure a homogeneous mixing achieved thus enhance conversion. Introduction of the second batch of methanol premixed with the catalysts not only aims to provide high concentration of methanol in the reaction which favors the tranesterification, but also restore concentration of the catalysts in the system which is mostly withdrawn away with the glycerol in the first reaction.

In each of the 1^st stage and final pre-reactors, methanol is evaporated and withdrawn from the vessels and is then recycled back. The methanol vapours are passed through vapour condensers. The methanol, which now contains large traces of moisture (approximately 7% - 10% moisture) may be pumped back to methanol storage tanks for reuse in the transesterification process without being rectified as the disclosed process is water tolerant.

It is known in the art that different methods can be employed in purifying the acquired methyl ester from the second reaction. It is the preferable embodiment that magnesium silicate based compounds is used as adsorbents to remove impurities in the acquired FAME. Unlike traditional water washing or bubble washing which would introduce additional water content to be removed by distillation, the magnesium silicate with high surface area and activity is capable of adsorbing impurities such as glycerol, methanol, catalysts or other side products from the FAME without the stated shortcomings. The magnesium silicate adsorbents are stirred with the acquired FAME for removing the impurities. Amount of adsorbents used and time of stirring are subjected to change in accordance with the volume to be treated, physical equipment used, quality required and so on. Subsequently, the impurities and the adsorbents will form by-products, namely cake, which is removed from the purified FAME by any known methods such as Niagara filters, pressure filters or other presses. Though, press filtration at high temperature is preferred for cake removal to further reduce the water content of the purified FAME.

The resultant pure methyl ester is then passed through various dryers to comply to relevant international specifications before being sent to nitrogen blanketed storage tanks.

The following example is intended to further illustrate the invention, without any intent for the invention to be limited to the specific embodiments described therein.

EXAMPLE l

RBD Palm Oil, 1000 kg weight was mixed with 80 kg of Reacting Agents in 1^st stage pre-reactors. The Reacting Agents is a mixture of 10 parts of sodium hydroxide (48% concentration diluted in water) to 120 parts of methanol by weight. The reaction was maintained at atmospheric pressure at a temperature of 65°C to 70⁰C for 2 hours with continuous withdrawal of crude glycerin and water. The conversion to methyl ester was found to be 90% to 93% complete.

This product was then pumped to a compartmentalized reaction attached with a mixer paddle as a stirrer to ensure homogenous mixing and thus result in higher ester conversion. In the final reactors, the esters from first reaction pre-reactors is added with 50 kg of fresh Reacting Agents (10 parts of sodium hydroxide to 120 parts of methanol concentration) and the reaction was allowed to proceed for another 1 hour at a temperature of 65⁰C. Analysis of this product showed a 99% conversion to methyl ester.

This final methyl ester was then purified with addition of 0.5% magnesium silicate giving the final methyl ester in compliance to ENl 4214 and ASTM standards as stated in Table 1 below. Table 2 shows the available carbon chain of the FAME produced by the present invention.

Property Unit Our Specs

Ester Content % (m/m) 99.1

Density Kg/m3 875.8

Viscosity mm2/s 4.59

Flash Point ⁰C 173.0

Sulphur content mg/kg 1

Carbon Residue %(m/m) 0.07

Cetane Number N/A 69.2

Sulphated Ash %(m/m) <0.01

Water content mg/kg 479

Total contamination mg/kg 16

Copper corrosion Rating Ia

Oxidation Stability Hours 12.2

Acid Value mgKOH/g 0.31

Iodine Value g/lOOg 51.6

Linolenic Acid %(m/m) 0.2

Polyunsaturated %(m/m) <1

Methanol content %(m/m) <0.01

Monoglyceride %(m/m) 0.65

Diglyceride %(m/m) 0.18

Triglyceride %(m/m) 0.18

Free Glycerol %(m/m) <0.01

Total Glycerol %(m/m) 0.21

Group Metals (Na₅K) mg/kg <5

Group Metals (Ca₅Mg) mg/kg <5

Phosphorus content mg/kg 1

CFPP ⁰C 12.0

Table 1

Chain No % (m/m)

C12:0 0.3

C14:0 1.1

C16:0 43.1

C16:1 0.2

C18:1 4.7

C18:2 39.4

C18:3 10.5

C20:0 0.4

C22:0 0.1

C22:1 Trace

C24:0 Trace

Table 2 The present 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 present 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.

Claims

CLAIMS:

1. A transesterification process for producing fatty acid methyl ester comprising the steps of (a) reacting oil of plant or animal origin with methanol premixed with an alkaline catalyst in aqueous form at a temperature of 60⁰C to 70⁰C to produce a first reaction products;

(b) withdrawing formed glycerol continuously from the first reaction products;

(c) reacting additional methanol premixed with the alkaline catalysts into first reaction products by stirring when conversion of fatty acid methyl ester in the first reaction products reached at least 85% to acquire the fatty acid methyl ester, wherein the alkaline catalyst is dissolved in water with a concentration of 40% to 50%

2. A process according to claim 1 further comprises the steps of purifying the acquired methyl ester with magnesium silicate.

3. A process according to claim 1 or 2, wherein ratio of the methanol to the animal fat or plant oil is 10 to 15: 100 by weight.

4. A process according to claims 1 to 3, wherein the alkaline catalyst is any one or combination of sodium hydroxide or potassium hydroxide.

5. A process according to claims 1 to 3, wherein the oil of plant or animal origin is RBD oil.