TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Reactor: In reactor (R1), the static mixers in the first and second zones are different to account for differences in physical properties of the reaction mixture in the zones.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In method (M1), the diameter of the tubular reactor in the exit zone is greater than in the intermediate zone, the higher diameter facilitating the transition from the turbulent flow to the laminar or transitional flow. The flow in the entrance zone is turbulent, laminar or transitional, where diameter of the tubular reactor in the entrance zone is adjusted to provide the laminar or transitional flow. The viscosity of the reaction mixture increases between entrance zone and intermediate zone and increases between intermediate zone and exit zone. The reaction mixture in the entrance zone comprises dispersed phase in continuous phase, majority of the continuous phase is triglyceride and majority of the dispersed phase is alcohol. The reaction mixture in the intermediate zone comprises two dispersed phases in continuous phase, majority of one dispersed phase comprising alcohol, majority of the other dispersed phase comprising glycerin, and majority of the continuous phase comprising triglycerides and alkyl ester. The reaction mixture in the exit zone comprises dispersed phase in continuous phase, majority of the dispersed phase comprising glycerin and majority of the continuous phase comprising alkyl ester. The Reynolds number in the exit zone is less than or equal to 4000. The flow in the entrance zone is laminar or transitional and changes to turbulent in the intermediate zone. The diameter of the tubular reactor in the intermediate zone is less than that in the entrance zone so as to provide turbulent flow in the intermediate zone. The static mixer is positioned in the entrance zone and/or the intermediate zone that modifies flow of the reaction mixture, increasing the homogeneity of the reaction mixture and increasing conversion and/or yield of transesterification reaction. The reaction mixture along majority of the entrance zone comprises two phase mixture including the reactants, the reaction mixture along majority of the intermediate zone comprises three phase mixture including the products and the reactants, and the reaction mixture along majority of the exit zone comprises two phase mixture including the products. The length of the static mixer is 4-95% is positioned in the entrance zone. At least two static mixers are positioned in the intermediate zone. The distance between the mixers is 0.5-2 times length that the flow modification deteriorates to zero. The differences in physical properties comprise lower viscosity in the entrance zone than the intermediate zone. The mixers comprise number of mixers in each zone, mixer type, mixer length, and spacing of mixers. The static mixers each comprise several pitched blades that modify the flow. The length of static mixer in the entrance section is longer than static mixer in the intermediate zone to account for lower miscibility of dispersed phase in continuous phase in the entrance zone. The droplet size of the dispersed fluid phase of less than or equal to 20 microns is maintained in both the entrance zone and the intermediate zone. The viscosity of the reaction mixture increases between the entrance zone and the intermediate zone due to change in chemical composition arising from transesterification reaction. The maintained droplet size facilitates mass transfer of alcohol and catalyst in dispersed phase to continuous phase comprising triglycerides to increase conversion of transesterification reaction. The dispersed phase along majority of the entrance zone comprises alcohol in continuous phase comprising triglyceride and the intermediate zone comprises dispersed phase including alcohol and dispersed phase including glycerin in continuous phase including triglycerides and alkyl ester. The entrance zone and the intermediate zone each include at least one static mixer to maintain the droplet size, the characteristics of the mixers in the zones are different to account for difference in properties of the reaction mixture in the zones. The length of static mixer in the entrance zone is longer than static mixer in the intermediate zone to account for lower miscibility of the dispersed phase in the continuous phase in the entrance zone. The viscosity of the reaction mixture increases between the entrance zone and the intermediate zone due to change in chemical composition arising from transesterification reaction. The dispersed phase along majority of the entrance zone comprises alcohol and continuous phase comprising triglyceride. The dispersed phase along majority of the intermediate zone comprises dispersed phase including alcohol and dispersed phase including glycerin and continuous phase including triglycerides and alkyl ester. The mixing is performed as the reaction mixture flows though at least one static mixer in each of the entrance and intermediate zones. The length of static mixer in the entrance zone is longer than static mixer in the intermediate zone due to lower miscibility of the dispersed phase in the continuous phase in the entrance zone. The flow of the product stream through the coalescer is sub-turbulent. The dispersed glycerin phase (at least 99%) is separated from the alkyl ester phase in less than or equal to 1 minute in the decanter. The ratio of alcohol in the separated alkyl phase to alcohol in the separated glycerin phase is increased due to the use of the coalescer. The average droplet size of the glycerin phase in the product stream passed from the coalescer to the decanter is at least 100 microns. The volume of the second coalescer is equal to or larger than volume of the first coalescer. The diameter of the first coalescer is the same as diameter of the second coalescer. The length of the first coalescer is equal to or shorter than length of the second coalescer. The degree of conversion in the product stream from the first tubular reactor is at least 86% and the degree of conversion in the product stream drawn off from the first decanter is at least 90%. The yield in the product stream from the first tubular reactor is at least 78% and yield in the product stream drawn off from the first decanter is at least 88%. The degree of conversion in the product stream from the second tubular reactor is at least 99.1% and the degree of conversion in the product stream drawn off from the second decanter is at least 99.8%. The yield in the product stream from the second tubular reactor is at least 98.4% and yield in the product stream drawn off from the second decanter is at least 99.7%. The alkyl ester product stream corresponds to product stream subsequent to separation from glycerin phase. The alkyl ester product stream corresponds to product stream prior to separation from glycerin phase. The reactor feed to the reactors comprises triglycerides and alcohol. The total glycerol content of the alkyl ester product stream is less than or equal to 0.05 wt.%. The entrance zone and the intermediate zone each include at least one static mixer that modifies flow of the reaction mixture to increase the homogeneity of the reaction mixture and increase conversion and yield of a transesterification reaction. The static mixers in the entrance and intermediate zones are different to account for differences in physical properties of the reaction mixture in the zones. The reaction mixture along majority of the entrance zone comprises majority of reactants and the reaction mixture along majority of the intermediate zone comprises products and reactants, maintaining droplet size of the dispersed fluid phase of less than or equal to 50 microns in both the entrance zone and the intermediate zone. The method involves producing alkyl ester from transesterification reaction in first tubular reactor and second tubular reactor in series, where product stream from the first tubular reactor and product stream from the second tubular reactor each comprise alkyl ester phase and dispersed glycerin phase; passing the product stream from the first tubular reactor through first coalescer unit to increase droplet size of the dispersed glycerin phase followed by passing the product stream through first decanter to separate the glycerin phase from the alkyl ester phase; and passing the product stream from the second tubular reactor through second coalescer unit to increase droplet size of the dispersed glycerin phase followed by passing the product stream through second decanter to separate the glycerin phase from the alkyl ester phase. The method involves producing alkyl ester product stream from production system, where alkyl ester in the product stream is generated by transesterification reaction in at least one tubular reactors in series of the production system, where a concentration of monoglycerides, diglycerides, and triglycerides in the alkyl ester product stream is, upon removal of excess alcohol, less than or equal to 0.1 wt.%, less than or equal to 0.1 wt.%, and less than or equal to 0.2 wt.% respectively. In method (M2), the flow of the liquid mixture through the coalescer is sub-turbulent. The dispersed glycerin phase (at least 99 vol.%) is removed from the alkyl ester phase in less than or equal to 1 minute in the decanter. The ratio of alcohol in the separated alkyl ester phase to alcohol in the separated glycerin phase is increased due to the use of the coalescer. The average droplet size of the glycerin phase provided by the coalescer is at least 100 microns. The degree of phase separation of the alkyl ester phase from the glycerin phase is greater than the phase separation performed in process without the coalescer, the degree of phase separation is ratio of separated glycerin phase drawn off the decanter to the glycerin phase in the fluid mixture exiting the reactor. The amount of the alcohol in separated glycerin phase drawn off the decanter is less than that obtained in process employing the decanter for phase separation without the coalescer. Flowing the liquid mixture through the coalescer reduces decanter length required to achieve selected phase separation of the glycerin phase from the alkyl ester phase. The flowing the liquid mixture through the coalescer reduces residence time required in the decanter required to achieve selected phase separation of the glycerin phase from the alkyl ester phase. EXAMPLE - No suitable example given.