Manufacture of Biodiesel

Abstract

A continuous manufacturing process is described. Vegetable oil is reacted with methanol and a catalyst such as KOH to produce biodiesel and glycerol. The reactants are passed through a reaction zone with magnetostrictive components (4) in it while subjecting them to a strong alternating rotatory magnetic field, preferably adjusted to produce a resonant acoustic or ultrasonic field in the reaction zone.

Description

This invention relates to the manufacture of biodiesel, i.e. the manufacture of fuel which can be used to power conventional diesel engines but which is derived not by petrochemical processing steps from crude oil, but rather from biologically produced materials, most notably vegetable oils.

The basic method of manufacturing biodiesel is well-established and indeed has been commercialised in a number of countries. It consists in taking vegetable oil and methanol and reacting them together in the presence of a catalyst. A transesterification process takes place giving as the reaction product a mixture of fatty acid methyl esters (FAME, which is the biodiesel itself) and glycerol. In the case of the use of rape oil as starting material, the biodiesel product is often referred to as rape methyl esters (RME).

Commercial manufacture as practised consists in combining the vegetable oil with methanol in a reaction vessel in the presence of a catalyst such as sodium or potassium hydroxide or sulphuric acid. The transesterification reaction strips the fatty acids from the glycerol backbone of the vegetable oil molecules and attaches methanol molecules to them. Extra methanol is put into the reaction cylinder to increase the output of e.g. RME and, following the end of the reaction, the mixture of biodiesel, glycerol and excess methanol, the catalyst and sundry impurities is then removed from the vessel and separated, the methanol and catalyst usually being recycled into the process, and the biodiesel sold as such. The glycerol is a valuable by-product which can be used in various manufacturing processes.

It is well-established that the current methods of manufacturing biodiesel on a commercial scale are not particularly efficient. In particular, the reaction time for the mixture is substantial, usually 1.5 to 10 hours, and power consumption is around 40 Kw so the total energy needed to make the biodiesel is very substantial. Proposals have been made to reduce the reaction time, particularly by adopting a continuous rather than batch approach and pumping the oil and methanol mixed with the catalyst through a reactor chamber at high pressure, for example 80 to 100 Bar. The pressure is required because, operating in this way, as the mixture is passed through a reactor vessel including static reactor elements, there is intimate phase mixing which gives a very high mass transfer between the reactants. The engineering requirements of operating at such high pressures are, however, challenging and the energy consumption correspondingly high.

We have now discovered that the transesterification reaction is driven to completion very much faster by carrying it out in a reactor vessel where the reaction chamber area is subjected to high alternating rotary electromagnetic fields and, in addition to the reactants identified above, the reactor vessel includes a large number of magnetostrictive components.

Operating in this way, a transesterification reaction can be carried out at normal temperature and normal pressure very rapidly, and the excess of methanol needed in traditional operation is unnecessary.

According to the present invention therefore there is provided a method for the continuous manufacture of biodiesel which comprises reacting vegetable oil and methanol in the presence of a catalyst to produce biodiesel and glycerol, wherein the reaction takes place in a reaction zone in which magnetostrictive components are present in the mixture of reactants and the zone is subjected to a strong alternating rotatory magnetic field. The rotation of the magnetic field is preferably at least 3000 rpm. Preferably also the magnetostrictive components are excited by the primary magnetic field to generate a resonant acoustic or ultrasonic field within the chamber. The production of such a resonant field may be assisted by dividing the chamber into sections e.g. by the use of a plurality of perforated baffles or the like through which the mixture of reactants may pass, and the spacing of which is chosen to match the desired resonance.

The precise mechanism by which the reaction speed is materially accelerated is understood now in general outline. It is undoubtedly related to the magnetically generated effects mediated by the individual magnetostrictive pieces of material. These may be particles or, for example, small cylindrical iron bodies. For reasons of economy, iron-based materials are preferred, but ferrous alloys, particularly ones including lanthanides such as dysprosium or terbium may provide enhanced results, as may mixed materials such as alfer. If desired, non-ferrous ferromagnetic elements or alloys may be used.

In the active centre of the reaction zone, high intensive physical fields of different nature are generated, such as electromagnetic, mechanical, acoustical and inertonic. Their specific power is very significant and when they influence species of the substance under consideration, they ensure deep structural and energetic changes including changes in the valence electronic shells of atoms. In our apparatus the electromagnetic field is generated in such a way that in the reaction zone the configuration of the field becomes so effective that the magnetic agents are in a resonant condition, which allows us to maximise the effects of magnetostrictive agents. The resonant effects allow the control of turbulence and hence the agents move along special trajectories, such that they do not practically collide, which preserve their destruction. These effects can be enhanced by the inclusion of resonance sub-chambers in the reaction vessel. The total influence of these factors results in deep excitation over the whole of the cross-section of the reactor and in a strong degree of activation of all components of the substance which participate in the process of the transesterification reactions. This yields significant increases of the surface of interaction or interface of the process.

A very quick intermixing, decomposition and, which is most important, activation of substances in the active centre of the reactor chamber makes it possible to realise physical-chemical processes at a rate that significantly exceeds that achieved in conventional chemical-physical processes. In other words, this allows one to pass from diffusive to kinetic reactions.

The improvement in reaction rate is generally dependent upon the strength of the primary magnetic field and the frequency of its oscillation, and on the mass and dimensions of the magnetostrictive components activated by the magnetic field. In practical terms, however, there is a trade-off between the cost of generating the electromagnetic field and the economic benefits of the faster reaction.

The use of ferromagnetic particles subjected to a rotating magnetic field and being suspended in a liquid has been previously proposed, see “Intensification of technological processes in apparatus with vortex bands”, D D Logvinenko and O P Shelyakov, Technika, Kyiv 1976 and U.S. Pat. Nos. 3,969,129, 4,093,189, 3,869,251 and 3,691,130 for various aspects of this. None of these publications discloses the value of the technique in biodiesel or similar manufacture, or the use of a resonance effect in the reaction vessel, which is found under the influence of the primary non-stationary electromagnetic field, to improve reaction rates. The resonance is produced by means of a special winding for each of the three phases of the reactor. Each phase is fed through a parallel resonant circuit, such that the resonant frequency is within the kilo-Hertz region.

We have found that this can be achieved by winding the coils which produce the rotatory magnetic field in a way which is very different from the conventional approach to winding coils e.g. in an electric motor or generator, and by driving them electrically with different phase shifts, frequencies and amplitudes. Preferred arrangements which may be driven by power suitably modified from that provided by a standard three-phase mains supply include three sets each of two windings, each set being supplied with current derived from each phase of the supply. The coils are not driven in a synchronous manner, and act to produce a controlled chaotic action in the magnetostrictive particles, which individually resonate at high frequency if the drives to the coils are appropriately tuned.

The plant or apparatus used to carry out the process of the present invention may vary in scale, depending on the desired throughput in continuous operation. These are described with reference to the accompanying drawings in which:

FIG. 1 shows, diagrammatically, a central reactor chamber forming part of apparatus for carrying out the invention; and

FIG. 2 is a schematic block diagram of a continuous operation pilot plant for biodiesel production.

Referring to FIG. 1, this shows diagrammatically a core reaction chamber assembly for making biodiesel, together with a power supply, for example a 3-phase 50 or 60 Hz AC mains supply, denoted 1. This feeds current to a set of coils 2 constituting an electromagnetic field generator. The coils 2 are located around a non-magnetic tube 3, e.g. of stainless steel. A reactor chamber 5 in the form of a stainless steel cylinder of capacity of 1.5 litres is located centrally in pipe 3. Reactant mixture may be fed into chamber 5 via an inlet pipe 6 and leave via an outlet 7. Inside the chamber 5 are a large number of cylindrical ferromagnetic/magnetostrictive components as activating agents. Since the chamber 5 is located between the coils 2, when the coils are connected to a suitable source of oscillating electrical power and controlled with a view to providing a rotating magnetic field at the centre of the reaction chamber 5 of strength 0.10 to 0.15 Tesla, the activating agents may be vigorously affected. As the power source 1 is the conventional electric mains, the oscillation frequency is 50 or 60 Hertz, and the rotation rate of the field is 3000 or 3600 rpm.

FIG. 2 shows diagrammatically a complete pilot plant for the continuous manufacture of biodiesel in accordance with the present invention.

Referring to FIG. 2, the actual biodiesel production takes place in a reaction chamber generally denoted 10. This is surrounded by coils 36 energised by a power supply unit 11.

The raw materials of biodiesel manufacture are kept in appropriate storage vessels, viz. a waste oil supply tank 12, a methanol tank 13 and a store for potassium hydroxide 14. Methanol hydroxide may be fed by means of a pump 16 into a mixer unit 18 where the potassium hydroxide is dissolved. The solution is then passed by a pump 17 via one of a pair of metering valves 22 into an emulsifier 24. Separately, oil may be pumped from a holding tank 12 by means of a pump 20 and via a second one of the pair of proportioning valves 22 into an emulsifier unit 24. In the emulsifier unit, the mixture of oil with methanol and potassium hydroxide is emulsified by means of vigorous mechanical agitation.

The emulsion then flows through the reaction chamber 10. Located inside chamber 10 which is generally cylindrical is an axial threaded rod 30 on to which are threaded four metallic perforated discs 32. The positioning of the discs 32 may be adjusted by turning them on the threaded shaft 30 and is adjusted to tune the system so that, during operation, it constitutes an acoustic resonant cavity. Also located in the reactor 10 are ferromagnetic cylinders 34 which can be excited vigorously by means of the magnetic field generated by coil 36 internally of the reactor chamber 10.

The treated emulsion emerges from an outlet port at the end of the reaction chamber 10 and passes into the holding and settling tank 26. Biodiesel may be withdrawn via a valve 27 located part way up the side of tank 26 and glycerol via a valve 28 near the bottom.

The following example, which used the apparatus shown in FIG. 2, will serve to illustrate the invention.

EXAMPLE

The feedstock for conversion to biodiesel was rape seed oil. The dissolution unit 12 was controlled in order to provide an 8% by weight solution of potassium hydroxide in methanol.

The potassium hydroxide solution in methanol and feed oil were then emulsified on a continuous basis at a weight ratio of 122 kilograms of the potassium hydroxide in methanol solution per 1000 kilograms of the rape seed oil.

The flow through the reaction chamber was 5 tonnes per hour of emulsion. During its passage through the reactor chamber, the emulsion was subjected to intense agitation as a result of the application of the rotating magnetic field by means of coils 36. The length of the reaction chamber under the influence of the magnetic field was 670 mm, the inner diameter of the chamber being 100 mm. The reactor chamber was tuned to operate as a resonant cavity. The speed of sound in the emulsion being around 2000 metres per second, the generation of an acoustic standing wave having a wavelength of around 166 millimetres and a fundamental frequency of around 12 KHz was achieved. Measurement showed that there was a certain amount of 24 KHz and higher harmonics were achieved. The chamber included, located captive in each of the sections, 600 gm of magnetorestrictive components in the form of iron cylinders of length 15 mm and diameter 1.0 mm.

The power consumption during continuous operation is around 3 to 4

Kilowatt hours per tonne of biodiesel produced. The amount of methanol in the output is less than one percent by weight. If desired, this may easily be removed from the biodiesel by an appropriate rectification or distillation process and recycled to the methanol storage tank 13.

Claims

1. A method for the continuous manufacture of biodiesel which comprises reacting vegetable oil and methanol in the presence of a catalyst to produce biodiesel and glycerol, wherein the reaction takes place in a reaction zone in which magnetostrictive components are present in the mixture of reactants and the zone is subjected to a strong alternating rotatory magnetic field.

2. A method according to claim 1 wherein the rotation rate of the magnetic field is at least 3000 rpm.

3. A method according to claim 1 or 2 wherein the individual magnetorestrictive pieces of material are small cylindrical iron bodies.

4. A method according to any one of claims 1 to 3 wherein the alternating rotary magnetic field is one which produces acoustic resonance in the active centre of the reaction zone.

5. A method according to claim 4 wherein the reaction zone is divided by a plurality of perforated baffles, spaced to promote the resonance.

6. A method according to any one of claims 1 to 5 wherein the magnetic field strength in the reaction zone is around 0.1 Tesla.

7. A method according to any one of claims 1 to 6 wherein the catalyst is an alkali metal hydroxide.

8. A method according to claim 7 wherein the alkali metal hydroxide is first dissolved into the methanol and the solution then mixed with the vegetable oil and the mixture thereby formed is emulsified prior to entering the reaction chamber.