WO2010011123A1

WO2010011123A1 - Method for production of alkyl ester

Info

Publication number: WO2010011123A1
Application number: PCT/MY2008/000074
Authority: WO
Inventors: Sze Wai Low
Original assignee: Sze Wai Low
Priority date: 2008-07-22
Filing date: 2008-07-22
Publication date: 2010-01-28

Abstract

It is therefore the objective of this present invention to provide a method of processing free fatty acid from low cost vegetable oil and animal oil sources to alkyl esters with the following advantage a) Reaction rate is much faster than previous invention. Reaction completed in 1-2 hours. b) Reduction in salts, soap stocks and aqueous waste or even total elimination of waste. c) Reduction in energy usage. On one option does not require vacuum for operation and hence save capital and operational cost as well. d) Does not requires methanol on first process stage and eliminate the requirement of fractional distillation with is associate capital and operational cost. These and other advantages are accomplished by converting the vegetable or animal oil source free fatty acid content to glycerides in the first step and in the second step convert the created glycerides together with the original oil to fatty acid alkyl ester which is commonly called biodiesel. The converted oil in the first step may be monoglyceride, diglyceride or triglyceride or a mixture of the above. It can be either animal or vegetable base sources. The converted oil is then reacted with methanol to form biodiesel and glycerin thru known process in the art such as using alkaline catalyst. The invention different from previous inventions by using entrainer to removed water of reaction and this enable much faster reaction time. The invention also different from others in that the oil is pretreated to removed dissolved oxygen so operation can proceed at much higher temperature without oxidation taking place and degrade the oil. This step is optional if the oil and it component mixtures have extremely little dissolved oxygen and absence of degummed products or organic components that will discompose at the reaction temperature forming gum in the reactor.

Description

Method for production of Alkyl Ester

Field Of Invention

The present invention relate to a method of making Alkyl ester from either a mixture of glycerides and free fatty acid or any oil with content of free fatty acid from 0% to 100%. Suitable oil are Palm Fatty Acid distillate, high fatty acid crude palm oil, grease trap wastes, tallow, animal fats, used vegetable lipid and other high fatty acid lipids.

Background of Invention

Alkyl esters make from natural lipid or vegetable oil, commonly known as biodiese! are now a viable alternative as fuel for diesel engines. The alkyl ester know better as biodiesel are knows to have better properties that petroleum diesel such as reduction of particulate output, hydrocarbon pollutants and improve lubrication of diesel engine when used as a fuel or mixed with petroleum diesel.

Alkyl ester that is derived from low-grade oil used vegetable based oil or oil sub products are attractive from commercial and environmental viewpoints, as the raw lipid material has low value and is not suitable for human consumption. However the technology for such production have a lot of problems such as high soap stocks, produce huge volume of aqueous methanol for recovery and high salt disposal problem. Thus, it is barely commercially viable due to the above problems.

Presently most biodiesel are manufacture from virgin vegetable oils and this is true for almost all the biodiesel plants in the world. The usage of biodiesel was found to have contributed towards increase in the price of vegetable oil by as much as three fold for the past 3 years. This was partly attributed to biodiesel production and it use as an accepted alternative fuel for commercial diesel.

Crude oil price in 2007 and 2008 has risen dramatically from USD50 per barrel to USD130 per barrel and the demand is commonly attribute to rising demand from developing China and India and the inability of world oil supply to satisfy the demand. At the same time, the demand for vegetable oil for food products is even more than the demand from biodiesel, which resulted in vegetable oil price rising to level uncompetitive for biodiesel plant to operate except for those countries with high subsidies foe biodiesel such as US and Europe.

The current biodiesel plant uses 1^st generation technologies such as liquid acid and base process. These processes were limited by incomplete esterification of all the free fatty acid in the feedstock oil and hence cannot use lower grade low cost, but high free fatty acid oil for biodiesel production without large economical and environmental problems. The disadvantages include long purification methods, relative long reaction times, contamination and separation difficulties, high energy cost as well as requiring much more methanol to be recovery from the waste stream plus much higher capital cost. This is due to the process sensitivity to even small quantity of water making it expensive to purify aqueous methanol to high level of purity and excessive salt deposition.

Current invention such as Boocock method, using solvent to enhance the reaction rate requires excessive methanol and solvent separation. The method can only handle limited amount of FFA and cannot handle FFA greater that 40%. The method of producing methyl ester in patent no US 6822105 Bl published in 2004 overcome the limitation of excessive methanol and acid neutralization but required 5-12 hours for production of oil from 13% free fatty acid to less that 0.5% free fatty acid content oil which is suitable for biodiesel production. It also requires vacuum and continuous nitrogen purge. This requirement of a large vacuum system with excessive power consumption to remove the nitrogen used and operate over long period. The patent illustrates operation time of 450 minutes to reduce FFA from 12% to 0.5 % show the patent limitation.

Brief Description of the Drawings

Vegetable oil and animal oil fatty acid component can be represent by the following reaction schematic

Diagram A

The following invention process as follows (reference Diagram A.) Step l a) Free fatty acid reacts with glycerin to from Monoglyceride. b) Monoglyceride react with fatty acid to form Diglyceride and water c) Diglyceride reacts with fatty acid to form Triglyceride and water. d) The reaction can be speed up by using alkaline or its salts as catalyst. Step 2 e) The formed Monoglyceride, diglyceride and triglyceride oil together with the original glycerides oil is react with alcohol in the presence of alkaline catalyst to form Alkyl ester and glycerin.

Where monoglyceride, diglyceride or triglyceride may be any aliphatic chain typically found in vegetable oil or animal fats with carbon typically from C8 to C22.

The reaction of Step 1 can be typically conducted as referenced in Fig 1. The steps are as follows a) The Fatty acid rich oil can be from 0-100% free fatty acid or anywhere in between. b) The oil have been degυmmed and /or bleached and filtered to removes non-oil components. c) Glycerin and the Fatty acid rich oil are mixed, in proportion suitable for complete conversion of fatty acid to glycerides. The mixture was heated to 100-120 deg C and preferably to 120 deg C in reactor 2. Optional Nitrogen is purged thru the solution during this period to ensure removal of dissolved oxygen and blanket the oil with nitrogen to prevent oil oxidation. The reactor is stirred to ensure mixing of the component. Stirring is optional as the reaction proceed as the product of reaction dissolves the components of the mixture. d) The first step of the reaction in which the fatty acid is converted into glycerides can be performed at temperature of 120-370 deg C. Preferable temperature is 230-280 deg C. The first step can further be perform at reduce pressure ranging from 760mm HG to 0.01mm HG. e) The oil is mixed proportional with the approx. correct amount of glycerin for complete reaction to removes the fatty acid, plus a few percentage more glycerin to provide 99%+ conversion of free fatty acid to glycerides. The percentage increase is preferred 1-5% more of oil volume but can be any volume that is economical to use. f) The present invention could use cheaper Crude glycerin recovered from the biodiesel manufacturing process. It is effective except the product produced is darker in color due to higher presence of color organic product in the glycerin, g) Using crude glycerin can cause the deposition of salts in the process, which may be corrosive to the reaction vessel. h) Trace amount of salts if presence in the final biodiesel product is removed thru a water washing process or by filtration. i) Distilled glycerin can be used for the process without the salt problem, j) The raw material used for the invention such as darker color glycerin, formed glycerides, fatty acid may be bleached to reduce the color of the final product. Commonly available bleaching agent such as bleaching earth, hydrogen peroxide or any bleaching agent that has no adverse effect on the product can be use. The final biodiesel product can also be bleached and filtered to acceptable color if required. k) The final biodiesel product can also be distilled to provide colorless biodiesel. I) Catalysts can be added to speed up the reaction. Catalysts that could be used are alkali metal oxides and salts such as potassium and sodium hydroxide or it salts such as potassium acetate or tin compound. m) A Volatile entrainer that is immiscible with water was introduced into the mixture in the proportion of 1-30% of the lipid volume. The entrainer can be heated to vapor form before introducing into the reaction chamber. Due to it higher vapor mass when entrainer evaporate, it will drive off even trace amount of water vapor that is generated by the reaction and the vapor will co condenses in condenser 3. The condense liquid will separate into a water layer and a liquid layer in container 4. Water layer is removed and the organic liquid layer that floats on top is removed and filtered by a hydrophobic filter to removed trace amount of colloid water in the filter 5. n) The entrainer is then feed to optional water absorbent 10 such as molecular sieve and feedback either directs to the reactor 2 or preheats to vapor form, o) The vapor form have the advantage to separate the entrainer vapor from organic portion such as fatty acid that co distill over with the entrainer when the pressure is set low enough, p) This co distilled fatty acid also act as entrainer to drive off liquid water and the fatty acid removal enable very low level of fatty acid remaining in the reactor such as 0.1 to 0.01%

Free fatty acid level. This important methodology and fact is not utilized in any previous patent on conversion of fatty acid to glycerides. q) More preferable the amount of entrainer used is just enough to drive off the water generated. The amount of entrainer used depends on the volatility of the entrainer and the operating temperature of the reactor 2. The entrainer used can be petroleum diesel, petroleum products, and all products that have no reaction with the compound in the reactor and have low solubility in water. It can even be the free fatty acid or any free fatty acid added such as lauric acid. As the process is very sensitive to even small amount of water present, low water solubility entrainer such as cyclohexane, propyl acetate, octanol, toluene, hexane and petroleum diesel is preferred. r) Diesel as a volatile entrainer is especially useful, as it need not be taken out of the final product, thus removing a production step to remove the entrainer. However, diesel does have relatively higher water content both in emulsion form and in dissolved form. The water in the diesel is reduced by two methods, a) lowering the entrainer temperature by designing a counter flow condenser to get the lowest diesel temperature and using hydrophobic filter to remove suspended colloidal water. s) It is known that hydrocarbon, and most organic liquid that by lowering the temperature from say 250deg C to 50 deg C lower the solubility with water by 30 fold or more and the condenser is designer to achieved lowest temperature possible including using chiller (if required) to lower temperature, such as including minus 10 deg C or include 2 separate condenser. t) In the case of certain entrainer, which tend to form a colloid mixture with the condense water, a hydrophobic filter is to be used to removed suspend water before reintroducing the entrainer back into the reactor. u) The entrainer is preferred heated to vapor form to removed trace amount of distilled over free fatty acid, thru this is not absolutely necessary, before reintroducing back into the reaction chamber. This ensures rapid removal of free fatty acid. The free fatty acid removed can be reused in the next batch. v) The reaction is fast, approx 1 hour to reduce 100% free fatty acid to 1% Fatty acid content when operating at 260 deg C and at atmospheric pressure. It will be even faster in a vacuum environmental due to lower surface vapor pressure and faster removal of water vapor that was form. The vacuum system also has the advantage of automatically removing the entrainer at the same time the operation is running. A suitable entrainer has to be selected for the vacuum system. w) Liquid Counter flow column packed system is useful to enhance removal of moisture and

Free Fatty acid that distilled over, x) The resultant glycerides are then subject to alkaline catalyzed tranesterification process to form alkyl ester and glycerin as a byproduct, using known process in the art. y) The glycerin from this step is semi-purified by neutralization and decolorized using the normal procedure knows in the art such as acid treatment, distillation and bleaching. z) The glycerin generated in this second step of the process can be recycle for use in the first step to form glycerides from fatty acid, aa) It is understood that any alcohol can be used in the second step of the process. It preferred that lower molecular weight alcohol be used such as methanol, ethanol, isopropanol, propanol and butanol. Alcohol used in the second step of the process is in an excess between equivalent about 1 to 10 equivalent molar excess. bb) The reaction scheme particular the first step of the reaction scheme may be performed with a catalyst. Contemplated catalysts include but not limited to organotin compounds (eg dibutyltin oxide), organo titanium compound (e.g. tetrabutly titanate), alkali acetates, earth alkali acetate, lewis acid, alkali carbonate, alkali oxide and combination thereof. cc) The advantage of the method of the present invention can be summarized as follows: a. The use of altered or unaltered glycerin fraction obtain thru glycerin fraction of biodiesel production, will lower the production cost but this does not limit the type of glycerin that can be used. b. Close cycle of removing water product of reaction in which the water vapor is removed by an entraining solvent hence easily removed from the condense liquid as two separate liquid layer. c. Preheat the entrainer to vapor form also removed distilled over free fatty acid ensure very low level of FFA in the glycerides product. d. The entrainer layer was feedback to the bottom of the reactor was found to dramatically increases the reaction rate while removing the water rapidly. e. Removal of the entrainer is not required if the entrainer used is commercial diesel or higher boiling organic liquid that above diesel flash point. f. All trace entrainer is removed by higher boiling Free fatty acid acting as entrainer to remove the actual entrainer residue hence no entrainer trace remain in the product, g. Enhance rate of reaction by a combination of catalyst and higher operating temperature of up to 330 deg C. That is possible thru removal of trace amount of dissolved oxygen in the mixture to prevent oxidation of the product. This is a particular important step of the process to provide low color oil. Note removal of trace oxygen is optional if product color is acceptable. h. The process can also be done in a continuous reactor or a counter flow reactor, or column in know process in the art commonly such as used for removal of odor, water or dissolved fatty acid from oil.

Example 1 The following are example of the invention but is not limited to the example shown.

1000 kg of Palm Fatty Acid distillate with 92% free fatty acid content and 150 kg of industrial 95% grade glycerin was charge into an airtight stir reactor. The catalyst use is 5 kg of potassium acetate. Nitrogen is first send to displace completely the oxygen content as well as dissolved content of oxygen by bubbling nitrogen thru the liquid. This step is preferably done in a vacuum but is not done here due to equipment restriction. This was done for a minimum of 15 minutes and continues until the temperature of the reactant reached about 120 deg C. Nitrogen purge was stopped at that point. The reactor used is as shown in figl. The entrainer used consists of 140 I of diesel. The reactor was initially heated to 190 deg C where the mixture starts to evaporate and temperature slowly rises to 270 deg C within 1 hour. The entrainer evaporates and the water of reaction was removed by the entrainer vapor at the same time. The vapor mixture was condensed, and the water forms a lower layer, which was drained. The diesel condensed was send thru a hydrophobic filter to remove the colloid water in suspension and the diesel is then fed back to the reactor thru the bottom of the reactor. The reaction proceed rapidly and reached 99% conversion within 1 hour, measure from the time temp reach 190deg C

Table 1 is the result for the reaction parameter and measure water removed (which is proportional to removal of free fatty acid.), and illustrated the progress of conversion of Palm Fatty Acid Distillate to glycerides oil.

The sample tested before and after the above from step 1 was found with approx 95% and 1% free fatty acid respectively. The product from step 1 was reacted with alkaline methanol 200 Litres and 6kg of sodium hydroxide under reflux. The product was allowed to settle for 2 hours and the glycerin separated. The resultant methyl ester was washed and dried. The final product contains approx 93% methyl ester and approx 5-7% diesel that have not been evaporated off.

Example 2 1000 gm of Indonesia Sludge oii was degummed with phosphoric acid and bleached with 2% bleaching earth. The resulting oil was filtered and has 40% FFA content. 66 gm of 95% glycerin was added. Catalyst was potassium acetate of 5.12 gm. The entrainer used is of food grade propyl acetate 100 m

The sample tested before and after the above was found with approx 40% and 0.5% free fatty acid content respectively. The product above was subsequent vacuum to remove the propyl acetate. 80ml. of propyl acetate was recovered at 180 deg C. Approx. 0.1-5 ml remains in the oil, by raising temperature to 250 deg C in a vacuum to drive off the remainder propyl acetate and also removal of trace free fatty acid. The oil is cooled to 60 deg C.

The oil is reacted with alkaline methanol 200 ml with 6gm sodium hydroxide for 1 hour in a reflux condition. The reacted products are allowed to settle for 2 hours and glycerin was separated out. The methyl ester formed was washed and dry to form biodiesel of high quality with 0 to 1% propyl acetate still in the product. Most of the trace propyl acetate was removed together with the methanol during distillation to remove the methanol from the alkyl ester. Propyl acetate was an acceptable impurity as it 100% hydrocarbon.

The entire reaction can be operated in a vacuum environment and the reaction will proceed much faster and trace Propyl acetate will be removed by the distilled over free fatty acid acting as entrainer for the lower boiling point propyl acetate. Free fatty acid is not reintroducing back into the reactor by heating the propyl acetate to vapor form. The vapor then sends back to reaction chamber.

Claims

The invention claims is a) A method of making alkyl ester comprising the following steps

1. Providing an oil sources, an oil sources containing free fatty acid of any amount.

2. Providing a molar equivalent of Glycerin that can react completely with the free fatty acid content plus a slight excess equal to one to 30% by volume of the fatty acid.

3. An entrainer of volume low enough to provide a continuous evaporation below the boiling point of the free fatty acid, oil and glycerin in the reaction vessel in order to remove the reaction water produced. The entrainer is reintroduce back to the reactor after condensation to the lowest temperature practical and the water is removed by liquid-liquid separation. The condense entrainer may contain water emulsion is removed by hydrophobic filter or any method know in the art. The entrainer may also pass thru absorbent to removed trace of water.

4. The entrainer used can either enter the reactor as a gas or a liquid when introduce into the reactor. As a gas, the distilled over free fatty acid is not reintroduce back to the reactor. We need not reheat the reactor otherwise needed due to the entrainer latent heat absorbing the chamber heat. The practical amount of entrainer is approx 2-10% of the product weight.

5. The operation can operate either at atmospheric pressure, pressurized environmental or in a preferred vacuum environment. The vacuum environmental will allow faster reaction and lower operation temperature for a given product process rate. The pressure environmental can also be used in the reaction environment and will allow lower boiling point entrainer to be used as well as higher reaction temperature.

6. The reaction time is of sufficient time to allow complete reaction of 99% or more of the free fatty acid to a mixture of monoglyceride, di-glycerides and tri-glycerides.

7. The residue free fatty acid is distiller over and removed, enabling only very little free fatty acid residue of 0.1% or less in the reaction product.

8. The practical reaction time of step 1 is approx 0.5-6 hours, depending on the selection of entrainer and operating temperature plus design of the equipment such as utilizing micro bubble vapor.

9. Providing an alcohol with an excess of 3-20 molar or more preferable at 6 molar

10. Reacting the mixture of glycerides and alcohol for an effective conversion to alkyl ester of 98% or more of the glycerides with known method such as "catalyst free high temp reaction" or "Solid catalyst assisted reaction, liquid alkaline catalyst assisted reaction" to produce alkyl ester.

11. Recovering the alkyl ester using known process such as washing, dry cleaning, using absorbent such as bleaching earth, magnesium silicate, bleaching, filtering, or distillation. b) The method of claim A where the entrainer selected can be commercial diesel with boiling point from 130 to 350 deg C, toluene, propyl acetate, cyclohexane, hexane, octanol or any products with boiling point from 20 deg C to 300 deg C including the existing free fatty acid or any introduce free fatty acid and immiscible with water. The entrainer could be separate from water by merely liquid-liquid separation and is not reactive with the product of the reaction. The entrainer shall boil in the reaction liquid in step 1 and assist in ^removal of the reaction water c) The method of claim A where the alcohol can be simple alcohol or complex alcohol such as methanol, ethanol, isopropanol, propanol, butanol, tert butanol. d) The method of claim A where the alcohol can be in 1 to 20 molar equivalent amounts. e) The method of claim A where one example of the invention, where no vacuum is required to provide effective reaction for the process in step 1. f) The method of claim A in an example of the invention where vacuum is provided in a close system, in which the reaction product is reacted in a vacuum and the evaporated water and entrainer is condense in a vacuum environment. This will enable faster removal of reaction water due to lower vapor pressure and thus speed up the reaction of the system. g) The entrainer is preferred heated to vapor to removed distilled over free fatty acid, to avoid reintroducing it back into the reaction chamber. h) The method of claim F where vacuum is applied either immediately or gradually to less than 10mm hg. i) The method of claim F where vacuum is applied in separate reactor with different vacuum level. This is to optimized removal of free fatty acid residue and entrainer. j) The method of claim F where at the end of reaction, a stream of nitrogen or steam can be used to removed excessive entrainer still in the liquid mixture if required and to removed trace free fatty acid residue at high vacuum.. k) The method of claim F where temperature is raise up to 330 deg C and the product is flashed to removal volatile compounds, enough of it, to meet diesel flash point specification in a non vacuum reactor.

I) The method of claim A where a vacuum is provide near the end of the reaction to removed dissolved entrainer and residue entrainer. m) The method of claim A where the entrainer is not removed but become part of the product, n) The method of claim A where vacuum is used to reduce usage of entrainer which can be at the beginning of reaction or end of reaction period to provide a low entrainer usage system. The entrainer can also remain as part of the product. o) The method of claim A where the raw input material dissolved oxygen is removed to prevent oxidation during the process of the invention.