Recently, the US Patent Office has issued a patent (No. 8,420,841) to Texas Tech University that describes a new, efficient method to produce biodiesel. The process has the following key features:
· The transesterification reactions are taking place in a tubular reactor that operates at temperature higher than 110°C (230°F), and
· The unconverted alcohol is recovered in a flash tank installed on the exit of the reactors.
The process provides the following benefits:
· The reactions occur at rates 25 to 50 times faster than those obtained in conventional stirred-tank reactors.
· The transesterificaltion reactions are carried out to completion (at higher temperatures, the equilibrium is shifted towards the production of biodiesel and the reduction of mono-glyceride).
· The removal of the alcohol accelerates the separation of the glycerin from the biodiesel (either by settling or centrifuge), thus requiring smaller equipment (or higher production rates in existing equipment).
· All unconverted alcohol is recovered and recycled.
· Applying heat-integration to minimize operating costs.
The core of the invention is identifying techniques to overcome the main bottlenecks of the current methods to produce biodiesel – (i) the immiscibility of the two reactants (oil and alcohol), and (ii) the need to maintain the reactor temperature below the boiling point of the alcohol. As a consequence of the former bottleneck, the reaction rate is limited by the interfacial surface area between the two reactants, thus requiring large volume reactors. The second bottleneck is imposed to avoid using high-pressure (thus high cost) stirred- tank reactors. Another consequence of the low temperature reaction is a limiting equilibrium conversion (since the reactions are slightly endothermic), thus requiring two-step operations.
The current patent (see Figure 1) is based on generating high interfacial area between the oil and the alcohol. The process utilizes an ultrasonic atomizer to create micro-droplets (~50 microns in diameter) of the alcohol and mix them with the oil to create a homogeneous dispersion without relying on the reactor agitator. The dispersion is then fed into the tubular reactor. The much higher reaction rate (from the high interfacial surface area) enables us to carry out the reaction in a much smaller reactor and to employ a tubular reactor, which can be readily maintained at a higher pressure. Consequently, the reactor can be maintained at higher temperatures (say, above 120°C), thus providing higher reaction rates, beneficial equilibrium conversion.
Cost-effective, continuous biodiesel fuel production
Faster transesterification reaction rate, which produces biodiesel faster than current technologies
- Lower capital investments, as smaller mixing vessels can be used in continuous production
- Lower production costs, because less energy is required to produce the biodiesel
- Lower energy consumption, by using micro-droplets in the gas phase and dispersing them into the reactant mixture
- Ultrasonic atomizer generates alcohol droplets of uniform size, which speeds up fuel separation
- Tubular reaction vessel helps produce biodiesel continuously, dramatically increasing fuel yield
Variations of Process to yield in additional Patents
A forthcoming subsequent patent describes another variation to process. That patent (see Figure 2) is based on the observation that the biodiesel itself is a co-solvent for the oil and alcohol. Hence, a one-phase homogeneous mixture of the reactants can be formed by mixing the reactants with appropriate amount of biodiesel prior to feeding the mixture into the tubular reactor. The limiting reactant (oil) in the homogeneous mixture is then completely converted in the reactor (which operates at selected pressure and temperature). The excess alcohol is removed in the flash tank, and the mixture of biodiesel and glycerin is fed to a separator. A portion of the biodiesel is then recycled to the feed to serve as a co-solvent.