Method and apparatus for esterifying fatty acid

1. A method for the synthesis of biodiesel comprising a first step esterifying free fatty acid in natural oil, comprising heating the natural oil to a first temperature above a reaction temperature, feeding the heated natural oil into an acid-resistant pipe reactor, providing a mixture of acid catalyst and short chain alcohol at a second temperature below the reaction temperature, and feeding the mixture of acid catalyst and short chain alcohol at the second temperature into the natural oil in the acid-resistant pipe reactor, pumping the heated natural oil and the mixture of acid catalyst and short chain alcohol through the pipe reactor from the inflow end to the outflow end to cause the short chain alcohol and free fatty acid to react at the reaction temperature to form an ester within the natural oil, thereby forming a treated natural oil, and a second step of providing a mixture of alkaline catalyst and short chain alcohol, mixing the treated natural oil with the mixture of alkaline catalyst and short chain alcohol, and feeding a mixture of natural oil, short chain alcohol and alkaline catalyst in one direction along a second pipe reactor under transitional or turbulent conditions, thereby synthesising biodiesel by transesterification.

2. A method according to claim 1 in which the reaction temperature is in the range 100° C. to 200° C.

3. A method according to claim 2 in which the first temperature is higher than the reaction temperature by a temperature difference in the range 10° C. to 50° C.

4. A method according to claim 3 in which the second temperature is less than 70° C.

5. A method according to claim 1 in which the mixture of acid catalyst and short chain alcohol is fed into the natural oil in the acid-resistant pipe reactor at a pressure greater than 0.5 bar gauge.

6. A method according to claim 1 in which the mixture of acid catalyst and short chain alcohol is fed into the natural oil in the acid-resistant pipe reactor at an angle to the direction of flow of the natural oil.

7. A method according to claim 1 , further comprising reducing the pressure of reactants at an outlet of the acid-resistant pipe reactor to remove excess short chain alcohol by evaporation.

8. An apparatus for synthesis of biodiesel, comprising an apparatus for esterifying free fatty acid in natural oil, comprising a heater for heating natural oil to a first temperature above a reaction temperature, a feed for feeding the heated natural oil into an acid-resistant pipe reactor, a feed for a mixture of acid catalyst and short chain alcohol at a second temperature below the reaction temperature, the feed for the mixture of acid catalyst and short chain alcohol being configured to feed the mixture into the natural oil in the acid-resistant pipe reactor, a pump for pumping the heated natural oil and the mixture of acid catalyst and short chain alcohol through the pipe reactor from the inflow end to the outflow end to cause the short chain alcohol and free fatty acid to react at the reaction temperature to form an ester within the natural oil, thereby forming a treated natural oil, and an apparatus for synthesising biodiesel by transesterification comprising a second pipe reactor, a feed for the treated natural oil, a feed for a mixture of short chain alcohol and alkaline catalyst, the feed being arranged to feed the reactants in one direction along the pipe reactor, and a turbulence generator being provided so that the reactants are fed in transitional or turbulent conditions.

9. An apparatus according to claim 8 in which the heater is configured to heat the natural oil to a first temperature providing reaction temperature reaction temperature in the range 100° C. to 200° C.

10. An apparatus according to claim 9 in which the heater is configured to heat the natural oil to a first temperature that is higher than the reaction temperature by a temperature difference in the range 10° C. to 50° C.

11. An apparatus according to claim 10 in which the feed for the mixture of acid catalyst and short chain alcohol is configured to provide a second temperature of less than 70° C.

12. An apparatus according to claim 8 in which the feed for the mixture of acid catalyst and short chain alcohol is configured to feed the mixture into the natural oil at a pressure greater than 0.5 bar gauge.

13. An apparatus according to claim 8 in which the feed for the mixture of acid catalyst and short chain alcohol is configured to feed the mixture into the natural oil in the acid-resistant pipe reactor at an angle to the direction of flow of the natural oil.

14. An apparatus according to claim 8 , further comprising a pressure reducing valve for reducing the pressure of reactants at an outlet of the acid-resistant pipe reactor to remove excess short chain alcohol by evaporation.

15. An apparatus according to claim 8 , in which the acid-resistant pipe reactor includes a corrosion-resistant lining.

16. A method according to claim 2 in which the reaction temperature is in the range 120° C. to 170° C.

17. A method according to claim 1 in which the first temperature is higher than the reaction temperature by a temperature difference in the range 10° C. to 50° C.

18. A method according to claim 3 in which the first temperature is higher than the reaction temperature by a temperature difference in the range 20° C. to 40° C.

19. A method according to claim 3 in which the second temperature is less than 60° C.

20. A method according to claim 1 in which the mixture of acid catalyst and short chain alcohol is fed into the natural oil in the acid-resistant pipe reactor at a pressure in the range 1 to 20 bar gauge.

21. A method according to claim 1 , wherein the reactants are mixed in the second pipe reactor in a direction normal to the flow direction, such that the time taken for 90% of the reactants to pass through the second pipe reactor is within 20% of the mean residence time of reactants in the second pipe reactor.

22. An apparatus according to claim 8 , wherein the reactants are mixed in a direction normal to the flow direction, such the time taken for 90% of the reactants to pass through the second pipe reactor is within 20% of the mean residence time of reactants in the reactor.

23. A method for the synthesis of biodiesel, including:

a first step of esterifying free fatty acid in natural oil, comprising: heating the natural oil to a first temperature above a reaction temperature; feeding the heated natural oil into an acid-resistant pipe reactor; providing a mixture of acid catalyst and short chain alcohol at a second temperature below the reaction temperature; said second temperature being below 70° C.; feeding the mixture of acid catalyst and short chain alcohol, at the second temperature, into the natural oil in the acid-resistant pipe reactor; and pumping the heated natural oil and the mixture of acid catalyst and short chain alcohol through the pipe reactor from an inflow end to an outflow end to cause the short chain alcohol and free fatty acid to react at the reaction temperature, said reaction temperature being in the range of 100° C. to 200° C., to form a treated natural oil having an ester within the natural oil; and

a second step of transesterification, comprising: providing a mixture of alkaline catalyst and short chain alcohol; mixing the treated natural oil with the mixture of alkaline catalyst and short chain alcohol; and feeding a mixture of natural oil, short chain alcohol and alkaline catalyst in one direction along a second pipe reactor under transitional or turbulent conditions, thereby synthesising biodiesel by transesterification.