GB2465412A

GB2465412A - Biodiesel production in a downflow gas contactor reactor

Info

Publication number: GB2465412A
Application number: GB0821045A
Authority: GB
Inventors: Sugat Raymahasay
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-11-18
Filing date: 2008-11-18
Publication date: 2010-05-26
Also published as: GB0821045D0

Abstract

The invention provides a method and apparatus for the production of biodiesel, the method comprising the following steps:(a) mixing methanol and a transesterification catalyst in a mixing vessel [OCV];(b) transferring oil from an oil storage vessel [OSV] to a reactor feed vessel [RF];(c) pumping the oil from [RF] by means of a second pump [P1] into a downflow gas contactor [DGC] reactor comprising a column configured to allow at least one liquid input and at least one gas input into the upper section of said column via an orifice or nozzle configured such that at least one liquid stream can flow downwards through said column and the turbulence and shear at the interface results in mixing and highly efficient mass transfer, said oil being pumped downwards through said column until the total volume of the [DGC] reactor is filled with oil;(d) recirculating the total oil volume between the reactor feed vessel and the [DGC] reactor, the recirculating liquid entering the [DGC] reactor via a liquid input;(e) adding the methanol-catalyst mixture to the oil by either of the following methods (i) and (ii): (i) adding the methanol-catalyst mixture directly to the reactor feed vessel [RF] from the mixing vessel [OCV] by means of a third pump [P3] containing the oil recirculated through the [DGC] reactor in (d) above, or(ii) adding the methanol-catalyst mixture directly to the [DGC] reactor through inlet [l] while the oil is recirculated as described in (d) above, the recirculating liquid entering the [DGC] reactor via a liquid input;(f) recirculating the reaction mixture between [RE] and the [DGC] reactor continuously by means of pump [P1] after initiation of the reaction has taken place in step (e) above, the recirculating liquid entering the [DGC] reactor via a liquid input; and(g) on completion of the transesterification reaction, shutting down the pump recirculating the reaction mixture. The method and apparatus have advantages including low mass transfer resistance, high ester content in biodiesel product and fast reaction speeds with yields in the region 95-99%.

Description

BIODIESEL PRODUCTION N A DOWNFLOW GAS CONTACTOR

REACTOR

Background to the Present Invention

Alternative energy sources are nowadays being extensively investigated due to the very high energy demand worldwide. Intensive research into fuel sources other than petroleum and fossil fuels is being undertaken, in order to find an alternative fuel that is easily available, economically feasible to produce and non-polluting to the environment.

One of the more attractive and possible viable alternatives is "Biodiesel" which is a fuel oil derived from renewable biological feed sources of plant origin like vegetable oils and oil seeds, or animal fats. Several methods of producing biodiesel exist [e.g. see Ma, F. & Hanna, M. A., Biodiesel production: a review, Bioresource Technology, 70, 1-15, (1999)1, blending, microemulsions, thermal cracking (pyrolysis), and catalysis (biocatalysts, supercritical reactions etc) with transesterification (alcoholysis) being the most common at present.

Chemically, the oils/fats consist of triglyceride molecules of three different long chain fatty acids that are ester bonded to a single glycerol molecule. Direct use of these oils (both edible and non-edible) for energy is possible but is cost prohibitive and problems arise with use in engines and therefore slight chemical modification is required. This is done either by transesterification of the triglycerides with lower alcohols (e.g. methanol) or by esterification of fatty acids to obtain the biodiesel. The resulting biodiesel is composed of the fatty acid methyl esters of the fatty acids and has characteristics which are fairly similar to conventional diesel fuel and is considered as an acceptable alternative, As lower alcohols are sparingly soluble in the oil phase, transesterification is initiated by the mixing and reaction of the triglycerides with the alcohol in the presence of a catalyst (usually a strong acid or base). The reaction is step-wise and reversible and intermediates like diglycerides and monoglycerides are initially formed with the final reaction product being fatty acid alkyl esters and glycerol. The reaction is undertaken with an excess of alcohol, when the forward reaction is pseudo-first order, in order to move the equilibrium towards the formation of the desired esters. Use of an alkali as a catalyst also increases rate of the transesterification [e.g. see Ma, F. & Hanna, M. A., Biodiesel production: a review, Bioresource Technology, 70, 1-15, (1999)].

A majority of the existing processes for biodiesel production both industrially [e.g. see J. Van Gerpen, B. Shanks, R. Pruszko D. Clements and G. Knothe, Biodiesel Production Technology, Renewable Products Development Laboratory, USDAINCAUR, NREL/SR-510-36244, July 20041 or for research studies [e.g. see Alcantara, R. et al. Catalytic production of biodiesel from soy-bean oil, used frying oil tallow, Biomass and Bioenergy, 18, 515-527 (2000); Allen CAW, Watts KC. A batch type transesterification unit for biodiesel fuels, Technical paper, 96-404, Canadian Society of Agricultural Engineers, (1996); Ma, F., Clements, L. D. & Hanna, M. A. The effect of mixing on transesterification of beef tallow, Bioresource Technology, 69, 289-293 (1999); Mittelbach, M. Diesel fuel derived from vegetable oils, VI: specifications and quality control of biodiesel., Bioresource Technology, 56, 7-11 (1996); Peterson, C. L., Reece, D. L., Thompson, J. C., Beck, S. M. & Chase, C. Ethyl ester of rapeseed used as a biodiesel fuel -a case study, Biomass and Bioenergy, 10, 331-336 (1995); Schwab, A.W., M.O. Bagby, and B. Freedman, "Preparation and Properties of Diesel Fuels from Vegetable Oils," Fuel, V. 66, October, 1372-1378 (1987); and Muniyappa, P. R., Brammer, S. C. & Noureddini, H. Improved conversion of plant oils and animal fats into biodiesel and co-product, Bioresource Technology, 56, 19-24 (1996)] has been performed with edible oils like canola, rapeseed, soybean, sunflower, etc. Very few cases or reports are available on the non-edible oils obtainable from wastelands, like Jatropha curcas, Simarouba glauca, etc. or oil from Algae like Scenedesmus dimorphus, Chlorophyceae (green algae) etc. Crude oils and fats have also been used [e.g. see Alcantara, R. et al. Catalytic production of biodiesel from soy-bean oil, used frying oil tallow, Biomass and Bioenergy, 18, 515-527 (2000); and Ma, F., Clements, L. D. & Hanna, M. A. The effects of catalyst, free fatty acids, and water on transesterification of beef tallow., American Society of Agricultural Engineers, 41, 1261-1264 (1998)] but need pre-treatment before reaction and purification of the products is required.

Existing Production methods The production of biodiesel by transesterification has usually in the past been undertaken in a batch, stirred tank reactor. The stoichiometric ratio for transesterification is 3 moles of alcohol to I mote of triglyceride, to obtain a yield of 3 moles of the fatty acid alkyl ester. However, use of alcohol to triglyceride ratios varying from 4:1 to 20:1 (mote: mole) have been reported, with the most common being a 6:1 ratio where the maximum conversion to esters is achieved [e.g. see Ma, F. & Hanna, M. A., Biodiesel production: a review., Bioresource Technology, 70, 1-15, (1999)]. The most commonly used catalyst is sodium hydroxide, although potassium hydroxide is also used.

Typical catalyst loadings range between 0.25% to about 2.0%.

In this prior art technique the alcohol has been thoroughly mixed with the catalyst separately before addition to the triglyceride oil. Reaction temperatures varying from 25°C to 85°C have been reported, though 65°C is the temperature usually used. Higher reaction temperatures and higher alcohol: oil ratios can also enhance the yield of esters.

In this most common prior art technique, the reaction is facilitated by intensive mixing of the oil, catalyst and alcohol in the reactor as the oils are generally immiscible with the methanol-hydroxide solution. On completion of the reaction when the formation of the esters has reached equilibrium yield, generally reported to be between 85% to 94% [e.g. see J. Van Gerpen et al above] the mixing is stopped. The glycerol, which is also formed, can then be separated from the ester phase due to its higher density. This is done in the same reactor or by transferring the reaction mixture into a separate vessel where the glycerol layer settles down at the bottom of the vessel or by separation in a centrifuge.

The separated glycerol can then purified, processed and refined as required.

There are some reports [e.g. see J. Van Gerpen et a! above] of research being undertaken where a two-step reaction is used and glycerol is removed between steps. This allows a high yield of >95% ester formation as the presence of glycerol reverses the formation of esters back to oil. Typical reaction times range from twenty minutes to more than one hour at temperatures around 50°C.

Any unreacted and residual alcohol in the reaction mixture is thereafter removed in an evaporator or by flash evaporation. The esters are neutralized, washed using warm, slightly acidic water which also removes any residual alcohol and salts, and then dried. Refined biodiesel is then obtained for storage and use.

Drawbacks of Current Process of Manufacture of Biodiesel Though various methods exist in the art for the production of biodiesel on a large scale, research still continues as the current processes, mainly batch, have various disadvantages and deficiencies, the major ones being as follows: * Due to the characteristics of the process liquids, oil and aqueous sodium or potassium methoxide, which are basically immiscible, there is inefficient mixing on scale up of the stirred reactors used in the laboratory to industrial production scale.

o There is a very high mass transfer resistance which results in a product that contains a lower ester content, the main constituent of biodiesel.

o The reaction initially is mass transfer controlled.

* Back mixing occurs in the stirred vessels used in the prior art processes.

Though the stoichiometric ratio of alcohol: oil is 3:1, a higher ratio of alcohol to oil (6:1) is required due to inefficient mass transfer. An excess of alcohol (methanol or ethanol) is used to achieve the required degree of conversion.

* Use of an excess of methanol causes problems of separation of the glycerol as there is an increase in solubility and associated cost of the excess methanol.

* Heat load (reactions generally undertaken at 65 °C) incurs heating costs.

* In most current processes, different vessels are used to separate the two layers, glycerol and biodiesel (esters).

* Washing of the esters due to unreacted methanol also requires additional vessels.

Recovery of the excess methanol, an almost 30% excess from the waste stream, is required adding to capital and operational costs.

* Longer production times for the biodiesel.

High capital costs.

High operating costs.

* Non-achievement of the statutory standards of the ester content.

What is needed is a new process and apparatus that addresses the problems such as inefficient mixing, low ester content and excess amounts of methanol required that are associated with the prior art biodiesel production techniques described above. The present applicants have achieved this through the use of a novel approach to biodiesel production.

Detailed Description of the Invention

The present invention describes an apparatus and method for production of biodiesel from oil using a downflow gas contactor (DGC) reactor comprising a column configured to allow at least one liquid input and at least one gas input into the upper section of the column, oil being pumped into the column via one of said liquid inputs and the alcohol-catalyst mixture being brought into contact with said oil either via one of said liquid inputs or by being brought into contact with the oil that is circulated from the downflow gas contactor (DGC) reactor to a reactor feed vessel via a pump.

Thus, in a first aspect of the present invention there is provided: (1) An apparatus suitable for the production of biodiesel which comprises the following units: (i) storage vessels for a mixture of methanol and a transesterification catalyst, and for oil to be converted into biodiesel [OCV and OSV respectively]; (ii) a reactor feed vessel [RF] connected to the storage vessels in (i); (iii) a reactor vessel that is connected to both the reactor feed vessel [RF] in (ii) and the storage vessel [OCV] for the mixture of methanol and catalyst in (I); and (iv) a centrifugal pump [P1, P2, P3], characterised in that said reactor vessel is a downflow gas contactor [DGC] reactor comprising a column configured to allow at least one liquid input and at least one gas input into the upper section of said column via an orifice or nozzle which is configured such that at least one liquid stream and optionally at least one gas stream can flow downwards through said column and the turbulence and shear at the interface between the orifice or nozzle and the column results in mixing and highly efficient mass transfer.

This apparatus, which does not have a stirrer in the reaction vessel as in the prior art apparatus, when used in the production of biodiesel from a vegetable oil or animal fat and methanol in the presence of a suitable catalyst, provides a low mass transfer resistance, gives a high ester content in the final biodiesel product, a near stoichiometric ratio (i.e. near 3: 1) methanol: oil in the reaction mixture may be employed, and a fast reaction speed with biodiesel yields in the range 95-99% are obtained. Hence, significant disadvantages associated with apparatus and methods used in the prior art are overcome. Other advantages are discussed below.

Preferred embodiments of the first aspect of the present invention include: (2) an apparatus suitable for the production of biodiesel according to (1) wherein the apparatus is configured for use in a single batch operation mode, a multiple batch operation mode or a continuous mode; (3) an apparatus suitable for the production of biodiesel according to (1) wherein the apparatus is configured for use in a single batch operation mode; (4) an apparatus suitable for the production of biodiesel according to any one of (1) to (3), wherein said column of said downflow gas contactor reactor has an internal diameter of between 5 cm and 1.0 m; (5) an apparatus suitable for the production of biodiesel according to any one of (1) to (4), wherein said column of said downflow gas contactor reactor has a height of between 1.0 m and 25 m; (6) an apparatus suitable for the production of biodiesel according to any one of (1) to (5), wherein the column of said downflow gas contactor [DGC] reactor comprises a cylindrical upper section and an inverted conical lower section; (7) an apparatus suitable for the production of biodiesel according to any one of (1) to (6), wherein the apparatus is configured such that the mixture of methanol and the transesterification catalyst can be pumped directly from its storage mixture [OCV] by means of a pump [P3] to said reactor feed vessel [RF]; (8) an apparatus suitable for the production of biodiesel according to any one of (1) to (6), wherein the apparatus is configured such that the mixture of methanol and the transesterification catalyst can be pumped directly from its storage mixture [OCV] by means of a pump to said downflow gas contactor [DGC] reactor; (9) an apparatus suitable for the production of biodiesel according to any one of (1) to (8), wherein said apparatus is configured such that when it is used in the production of biodiesel it is first fully flooded with the oil to be converted to biodiesel before transesterification is initiated; and (10) an apparatus suitable for the production of biodiesel according to any one of (1) to (9), wherein the ratio of the internal diameter of the orifice or nozzle used at the entry point of said downflow gas contactor [DGC] reactor to the internal diameter of the column is from 1:6 to 1:25.

(11) In a second aspect of the present invention, there is provided a method for the production of biodiesel, comprising the following steps: (a) mixing methanol and a transesterification catalyst in a mixing vessel [OCV]; (b) transferring oil from an oil storage vessel [OSV] by means of a first pump [P2] to a reactor feed vessel [RF]; (c) pumping the oil from said reactor feed vessel [RF] by means of a second pump [P1] into a downflow gas contactor [DGC] reactor comprising a column configured to allow at least one liquid input and at least one gas input into the upper section of said column via an orifice or nozzle which is configured such that at least one liquid stream and optionally at least one gas stream can flow downwards through said column and the turbulence and shear at the interface between the orifice or nozzle and the column results in mixing and highly efficient mass transfer, said oil being pumped downwards through said column until the total volume of the downflow gas contactor [DGC] reactor is filled with oil; (d) recirculating the total oil volume between the reactor feed vessel and the downflow gas contactor [DCC] reactor, the recirculating liquid entering the downflow gas contactor [DCC] reactor via a liquid input; (e) adding the methanol-catalyst mixture to the oil by either of the following methods (i) and (ii): (I) adding the methanol-catalyst mixture directly to the reactor feed vessel [RF] from the mixing vessel [OCV] by means of a third pump [P3] containing the oil recirculated through the downflow gas contactor [DCC] reactor in (d) above, or (ii) adding the methanol-catalyst mixture directly to the downflow gas contactor [DCC] reactor through inlet [I] while the oil is recirculated as described in (d) above, the recirculating liquid entering the downflow gas contactor [DGC] reactor via a liquid input; (f) recirculating the reaction mixture between the reactor feed vessel [RF] and the downflow gas contactor [DGC] reactor continuously by means of pump [P1] after initiation of the reaction has taken place in step (e) above, the recirculating liquid entering the downflow gas contactor [DGC] reactor via a liquid input; and (g) on completion of the transesterification reaction, shutting down the pump recirculating the reaction mixture.

The method of the present invention for the manufacture of biodiesel from a vegetable oil or animal fat and methanol in the presence of a suitable catalyst,

has many advantages over the prior art processes:

It provides a low mass transfer resistance * It gives a high ester content in the final biodiesel product * only a near stoichiometric ratio (i.e. near 3: 1) methanol: oil in the reaction mixture is needed * a fast reaction speed with biodiesel yields in the range 95-99% are obtained * the amount of catalyst required is minimised * the range of different oils and fats that can be used as starting materials for the production of biodiesel is maximised and the reaction can be performed at ambient temperature * the methanol utilisation is greater than 99% and there is a very low concentration of residual methanol (typically 0.08% -2.0% v/v) present in the biodiesel produced there is very easy settling of the two phases in the downflow gas contactor biodiesel and glycerol -which allows quick and simple phase separation of the glycerol produced from the biodiesel no residual glycerol is obtained in the separated biodiesel o the biodiesel consists of between 94% 98% of the desired esters; this product can be used directly without further purification (such as washing and drying) and still meets the required specification o the downf low gas contactor reactor can be scaled up very easily without loss in efficiency o the low inventory of the feed [methanol, catalyst], intense mixing in the downflow gas contactor reactor, very low reaction times, low power and energy requirements, minimal or no requirement of purification and high conversion to production of the desired product ensures a reduced cost of production of the biodiesel Preferred embodiments of the method of the present invention include: (12) a method for the production of biodiesel according to (11) wherein said column of said downflow gas contactor reactor has an internal diameter of between 5cm and 1.0 m; (13) a method for the production of biodiesel according to (11) or (12), wherein said column of said downflow gas contactor reactor has a height of between 1.0 m and 25 m; (14) a method for the production of biodiesel according to any one of (11) to (13), wherein the ratio of the internal diameter of the orifice or nozzle used at the entry point of said downflow gas contactor [DCC] reactor to the internal diameter of the column is from 1:6 to 1:25; (15) a method for the production of biodiesel according to any one of (11) to (14), wherein the rate at which liquid is circulated around the apparatus is at a velocity of from 0.04 metres/second to 0.30 metres/second; (16) a method for the production of biodiesel according to any one of (11) to (15), wherein the column of said downflow gas contactor [DGC] reactor comprises a cylindrical upper section and an inverted conical lower section; (17) a method for the production of biodiesel according to any one of (11) to (16), wherein after the transesterification reaction has been stopped, the resulting transesterified reaction mixture containing the biodiesel is then either: (i) transferred to a separate settling vessel [SVI] by pump [P2] and allowed to settle, or (ii) allowed to settle in the reactor feed vessel [RF] and the downflow gas contactor [DGC] reactor; (18) a method for the production of biodiesel according to any one of (11) to (17), wherein after stopping the transesterification reaction and allowing the phases to settle in the reactor feed vessel [RV] and downflow gas contactor [DGC] reactor or in the settling vessel [SVI], the glycerol is obtained from the bottom layer and the desired biodiesel product is obtained from the top layer; (19) a method for the production of biodiesel according to (18), wherein said glycerol is transferred to a storage vessel [SV2] and, optionally, may be further processed; (20) a method for the production of biodiesel according to any one of (11) to (19), wherein said desired biodiesel product is transferred to a storage vessel [SV3]; (21) a method for the production of biodiesel according to any one of (11) to (20), wherein said method is performed in a batch operation mode, a continuous operation mode or a multiple batch operation mode; (22) a method for the production of biodiesel according to any one of (Ii) to (21), wherein said transesterification catalyst is a base; (23) a method for the production of biodiesel according to (22), wherein said transesterification catalyst is sodium hydroxide or potassium hydroxide; (24) a method for the production of biodiesel according to (23), wherein the ratio of methanol to sodium hydroxide or potassium hydroxide used in the reaction is from 1:0.01 wt%tol: 0.02 wt%; (25) a method for the production of biodiesel according to any one of (11) to (24), wherein the ratio of oil to methanol used in the reaction is from 3: 1 vol% to 10: 1 vol%; (26) a method for the production of biodiesel according to any one of (11) to (25), wherein the transesterification reaction is performed at a temperature of from 20-40 °C; (27) a method for the production of biodiesel according to any one of (11) to (26), wherein the transesterification reaction is performed at a pressure of from 2x105 to6x i05 Pa; and (28) a method for the production of biodiesel according to any one of (11) to (27), wherein the oil used is selected from corn oil, sunflower oil, rapeseed oil, algal oil, jatropha oil and waste cooking oil.

The present invention may be further understood by consideration of the following embodiments of the present invention, with reference to the following drawings in which: Figure 1 is a schematic diagram of a downflow gas contactor [DGC] reactor suitable for use in the apparatus and method of the present invention; and Figure 2 is a flow diagram of a batch production unit according to the present invention.

Figure 3 is a side section view of an orifice in place in the entry to a downflow gas contactor [DGC] reactor according to the invention and the orifice itself in detail.

Figure 4 is a side section view of a nozzle in place in the entry to a downflow gas contactor [DCC] reactor according to the invention.

A critical factor in the present invention is the replacement of stirred reaction vessels with a downflow gas contactor [DGC] reactor. Downflow gas contactor [DGC] reactors are well known in the art. In most of these, the liquid flows downwards and the gas flows upwards. However, such reactors would not be suitable for use in the method and apparatus of the present invention.

In downflow gas contactor [DGC] reactors suitable for use in the present invention, the liquid and gas or liquid and liquid are made to flow downwards together at specific rates depending on the specific application. Downflow gas contactor [DCC] reactors of this type are disclosed in, for example, GB 1,596,738 A, GB 2,117, 618 A and US 4,834,343.

Downflow gas contactor [DGC] reactors of this type are an efficient mass transfer device for contacting liquids and/or gases. It is a downflow co-current device and typically consists of a cyclindrical column (4) with an inverted conical lower section (7) with a specialised orifice or nozzle (1, 2) at its entry section (see also Figures 3 and 4), allowing both liquid and gas inputs into the reactor. The dimensions and configuration of the downflow gas contactor [DGC] reactor depend on the application and operating conditions and are designed accordingly.

Liquid enters the top of the fully flooded column via one or more liquid inputs (1, 2) in the form of one or more high velocity liquid streams. No foaming is possible as no free liquid interface is obtained at the inlet. An additional liquid or gas stream can be fed into the incoming liquid stream immediately prior to the column inlet through the nozzle/orifice concurrently. As the liquid continuous phase expands into the column, part of the kinetic energy imparted to the fluid on its passage through the orifice or nozzle is used in the formation of interfacial area. The high velocity liquid (3) passing through the nozzle/orifice generates intense shear and energy and a large interfacial area is generated in a small containment volume without any mechanical aid and a minimum expenditure of energy over than that required for motive power. The interface is subjected to rapid surface renewal through repeated rupture and coalescence, resulting in intense mixing and highly efficient mass transfer to approach equilibrium in a very short time of contact. The energy of the jet breaks up the gas into very small bubbles and an enormous interfacial area is generated in a small operating volume and also prevents any coalescence of the gas bubbles. It also prevents the formation of a permanent gas space at the top of the column thus maintaining a fully flooded situation. No mechanical aids such as stirrers or baffles are required.

The downflow liquid velocity in the column is maintained at a value below the rise velocity of the gas bubbles so that there is no tendency for the bubbles to be carried downwards. Hence there is no net movement of the gas phase whilst the liquid phase flows downwards through the inter-bubble spaces. The gas-liquid bubble dispersion slowly expands down the fully flooded column and the level of dispersion (and thereby volume of the gas-liquid dispersion) can be controlled by control of the operating conditions (liquid and gas flowrates).

In the lower section of the column as the dispersion proceeds downwards, there is a degree of bubble coalescence since it is no longer within the region of direct inlet steam impingement. This coalescence produces larger bubbles, which rise up the column where they are broken up by the shear of the high velocity inlet liquid jet. The presence of the conical lower section results in disengagement of the bubbles (6) in said section and reduced turbulence in the lower part of the upper cylindrical portion (5). As a consequence, the reaction mixture that is ejected from the end of the downflow gas contactor [DGC] reactor [whether it is liquid and dissolved gas or liquid only (8)] is bubble free (9).

The specific shape, dimensions and configuration of the downflow gas contactor [DGC] reactor depend on the application and operating conditions required.

In one example of the production of biodiesel according to the present invention, the column used as the DGC reactor was of 50 mm internal diameter and I 0 meter in length. Different diameters of the orifice or nozzle sizes were used varying between 2 mm to 8 mm. Liquid flowrates used, varied between 4 litres/mm and 12 litres/mm.

With regard to suitable orifices or nozzles, the internal diameter chosen should be calculated to meet the mixing requirement based on factors such as volume and flow rate. Typical nozzles are depicted in Figures 3 and 4.

The orifice in Figure 3 comprises a threaded fitting, the internal diameter of which is chosen according to factors such as flow rate, volume and the like.

The orifice is screwed into a hole in a flange 10 fitted at the entry of the downflow gas contactor [DGC] reactor shaped to receive said fitting. Bolt inlets 13 are included at the extremities of the flange. The inlet direction 11 is shown.

The orifice has a threaded inlet entry point 12 where the liquid and gas are directed.

The nozzle inlet 17 in Figure 4 has a substantially cylindrical upper section, a conical lower middle section and finally a much narrower substantially cylindrical distal section. The exact dimensions are chosen depending upon the precise requirements for the biodiesel preparation. The nozzle inlet 17 is welded into a suitably configured opening drilled into the centre of a flange 16 at the entry of the downflow gas contactor [DGC] reactor. Bolt inlets 18 are included at the extremities of the flange. The inlet direction 15 is shown.

The transesterification reaction can be carried out with the lowest ratios of alcohol [methanol]:oil [stoichiometric values] and lowest catalyst [NaOH] concentrations. Different types of oil such as edible [sunflower, corn, rapeseed], waste oil /crude oil, or non edible [algal, jatropha] can be used. The reaction can be undertaken at ambient temperatures with no additional heating required.

The reaction is undertaken in a downflow gas contactor [DGC] reactor in which liquid/liquid or liquid/gas are made to flow downwards at high speed and in which there is intense mixing and mass transfer, with the reaction being generally reaction rate controlled. There is no need for the use of an impeller as in the prior art processes. Use of a downflow gas contactor [DGC] reactor in the transesterification reaction of the present invention ensures no loss of mixing or reaction efficiency on scale up that is generally associated with stirred reactors.

The reaction is fast and overall contact times are low and ester or biodiesel yields are high [>95%]. Methanol utilisation is greater than 99% and there is a very low concentration of residual methanol in the biodiesel produced. Due to low concentrations of methanol and catalyst being used there is easy settling and quick phase separation of the glycerol produced. The downflow gas contactor [DCC] reactor can also be used as a settling and separation vessel with quick turnaround times. The bottom layer constitutes the higher density glycerol with the top layer being biodiesel. No residual glycerol is obtained in the separated biodiesel. The biodiesel obtained can be used directly without further washing and drying and meet the required specifications.

It can be concluded that use of the downflow gas contactor [DGC] reactor in accordance with present invention for the transesterifcation of oils would be greatly beneficial for the production of biodiesel. The intense mixing and high mass transfer properties available in the downflow gas contactor [DGC] reactor lead to higher yields [95-99%] even without further purification, in shorter operating times, reduced capital costs, lower operating and inventory costs and a purer and cheaper biodiesel product can be obtained.

The unit for the production of biodiesel comprises chiefly of the following units: a reactor feed vessel; a downflow gas contactor [DCC] reactor unit; and a centrifugal pump The reactor feed vessel [RF] is typically a jacketed, flanged, cylindrical column of suitable dimensions, with inlet and outlet connections. Instrumentation for measurement and control is attached to the column as required. The downflow gas contactor [DGC] reactor is as described above.

All the items are connected together by suitable piping, control valves and instrumentation and incorporated into a modular structure. The feed vessel is connected to a catalyst-alcohol mixing vessel and raw material feedstock storage vessels. A settling vessel is also connected to the reactor feed vessel and the downflow gas contactor [DGC] reactor.

At its simplest, the batch production unit of the present invention includes a feed vessel and a downflow gas contactor [DGC] reactor and a suitable pump for circulation of reactants, all specifically designed depending upon the nature of the nature of the oil to be converted, the reaction conditions to be employed and the operation mode to be employed. The complete processing plant also includes storage vessels for the raw material feedstocks with suitable pumps attached for delivery as required and a mixing vessel for mixing of the alcohol and catalyst before addition to the feed vessel. All the units and vessels are connected, as required, by suitable piping and are fitted with additional components and instrumentation both for process control and safety, as is necessary to provide a complete biodiesel processing plant.

As an example of the complete apparatus according to the present invention, the whole reaction unit is shown in Figure 2, when operating in a batch operating mode. Suitable systems for measurement and control (for heating, cooling, dispersion level, pressure, liquid flowrate control etc.) are included as required.

Production units to operate in a Multiple batch mode or in a Continuous mode, can also be designed as required.

[A] Batch Operating Mode (i) The methanol and catalyst was mixed together in a mixing vessel [OCV] fixed with a stirrer.

(ii) The oil was transferred from the oil storage vessel [OSV] by a suitable pump [P2] to a reactor feed vessel [RF].

(iii) The oil from the reactor feed vessel [RF] was then pumped into a downflow gas contactor [DGC] reactor [D] through a suitable pump [P1] so that the total volume of the DGC [D] was filled with oil.

(iv) Recirculation of the total oil volume was then performed between the reactor feed vessel [RF] and the downflow gas contactor [DGC] reactor unit [D].

(v) The operating in the downflow gas contactor [DGC] reactor [0] was maintained by controlling an outlet control valve [VI].

(vi) The reactor feed vessel [RF] was heated as required until the oil reached the desired reaction temperature.

(vii) The total alcohol-catalyst mixture was then added to the oil by either of the following methods: (a) directly to the reactor feed vessel [RF] from the mixing vessel [OCV] by pump [P3] containing the oil which was being recirculated through the downflow gas contactor [DGC] reactor [D], or (b) directly to the downflow gas contactor [DGC] reactor [D] through inlet [I] while the oil was being recirculated.

(viii) On addition of the alcohol-catalyst mixture to the oil, reaction was initiated and the reaction mixture of oil-alcohol-catalyst was recirculated between the reactor feed vessel [RF] and the downflow gas contactor [DGC] reactor [D] continuously by pump [P1].

(ix) On completion of the transesterification reaction, the pump [P1] was shut down and recirculation was stopped.

(x) The transesterified reaction mixture was then either (a) transferred to a separate settling vessel [SVI] by pump [P2] and allowed to settle, or (b) allowed to settle in the reactor feed vessel [RF] and the downflow gas contactor [DGC] reactor [D].

(xi) On separation of the phases in the downflow gas contactor [DGC] reactor [D] and reactor feed vessel [RV] or in the settling vessel [SVI}, the glycerol is obtained from the bottom phase and the ester from the top layer.

(xii) The glycerol was transferred to storage [SV2] and subjected to further processing if required.

(xiii) The ester (biodiesel) was transferred to storage [SV3].

The simple, compact and flexibile design along with easy automation and control with low engineering and fabrication costs ensures low capital investment. As previously noted, the transesterification reaction can be carried out at ambient temperatures if required, with no additional heating requirement, ensuring that power and energy consumption for the process is very low.

Again, as previously noted, the efficient mixing and mass transfer obtained in the downflow gas contactor [DGC] reactor ensures that, if required, a low alcohol [methanol] requirement of only 10 % the total volume of oil used [only stoichiometric proportions -3 moles alcohol to 1 mole of oil] is sufficient, without need for excess quantities of methanol to be used as is usually required in present production processes [generally ratio of 6: I upto 20: 1 moles of alcohol: mole of oil]. The highly efficient contact and mass transfer between the oil and the alcohol with catalyst, ensures that reaction times required for completion and high conversion to the desired product FAME, are very low.

The reaction and operating conditions can be controlled to operate the system in a continuous operating mode by contacting the required volumes of oil and alcohol in the downflow gas contactor [DGC] reactor.

The final reaction product mixture of the fatty acid methyl esters [FAME] and glycerol produced can be easily separated in the downflow gas contactor [DGC] reactor or reaction feed vessel [RV] or a separate settling vessel [SV] as used, in very short residence times, ensuring simple draining out of the bottom phase layer of glycerol. The top layer of esters, being the residual reaction product after removal of the bottom phase, does not contain any glycerol. The unreacted residual methanol quantity after completion of the reaction is very low and very low percentages of methanol are present in (8% -2.0% v/v, depending on operating conditions) the final ester product [FAMEs].

The transesterified reaction product obtained -in the separated biodiesel comprises between 94% and 98% of the esters or FAME's [depending on optimum operating conditions]. These are the main constituent of biodiesel, due to the very efficient mixing and mass transfer in the DGC reactor. The percentage values of esters or FAMEs reported in the product of the present invention, are of the biodiesel after separation of the glycerol from the settling vessel and without any further processing or purification.

The DGC reactor can be scaled up very easily without loss in efficiency and without the use of mechanical mixing. The low inventory of the feed (methanol, catalyst), intense mixing, very low reaction times, low power and energy requirements, minimal or no requirement of purification and high conversion to production of the desired product ensures a reduced cost of production of the Biodiesel.

It can be concluded that using the downflow gas contactor [DGC] reactor is highly beneficial for the production of biodiesel from edible, non edible or crude oil. The very high mass transfer capabilities in the downflow gas contactor [DGC] reactor can result in shorter operating times, reduced capital costs, reduced energy requirements, lower operating costs and a purer and cheaper biodiesel product can be obtained.

The DGC reactor can also be used for other oxidation and hydrogenation reactions as well as in effluent treatment processes.

Claims

Claims 1. An apparatus suitable for the production of biodiesel which comprises the following units: (i) storage vessels for a mixture of methanol and a transesterification catalyst, and for oil to be converted into biodiesel [OCV and OSV respectively]; (ii) a reactor feed vessel [RF] connected to the storage vessels in (i); (iii) a reactor vessel that is connected to both the reactor feed vessel [RF] in (ii) and the storage vessel [OCV] for the mixture of methanol and catalyst in (i); and (iv) a centrifugal pump [P1, P2, P3], characterised in that said reactor vessel is a downflow gas contactor [DCC] reactor comprising a column configured to allow at least one liquid input and at least one gas input into the upper section of said column via an orifice or nozzle which is configured such that at least one liquid stream and optionally at least one gas stream can flow downwards through said column and the turbulence and shear at the interface between the orifice or nozzle and the column results in mixing and highly efficient mass transfer.
2. An apparatus suitable for the production of biodiesel according to claim 1, wherein the apparatus is configured for use in a single batch operation mode, a multiple batch operation mode or a continuous mode.
3. An apparatus suitable for the production of biodiesel according to claim 1, wherein the apparatus is configured for use in a single batch operation mode.
4. An apparatus suitable for the production of biodiesel according to any one of claims I to 3, wherein said column of said downflow gas contactor reactor has an internal diameter of between 5 cm and 1.0 m.
5. An apparatus suitable for the production of biodiesel according to any one of claims 1 to 4, wherein said column of said downflow gas contactor reactor has a height of between 1.0 m and 25 m.
6. An apparatus suitable for the production of biodiesel according to any one of claims 1 to 5, wherein the column of said downflow gas contactor [DGC] reactor comprises a cylindrical upper section and an inverted conical lower section.
7. An apparatus suitable for the production of biodiesel according to any one of claims I to 6, wherein the apparatus is configured such that the mixture of methanol and the transesterification catalyst can be pumped directly from its storage mixture [OCV] by means of a pump [P3] to said reactor feed vessel [RF].
8. An apparatus suitable for the production of biodiesel according to any one of claims 1 to 6, wherein the apparatus is configured such that the mixture of methanol and the transesterification catalyst can be pumped directly from its storage mixture [OCV] by means of a pump to said downflow gas contactor [DGC] reactor.
9. An apparatus suitable for the production of biodiesel according to any one of claims I to 8, wherein said apparatus is configured such that when it is used in the production of biodiesel it is first fully flooded with the oil to be converted to biodiesel before transesterification is initiated.
10. An apparatus suitable for the production of biodiesel according to any one of claims I to 9, wherein the ratio of the internal diameter of the orifice or nozzle used at the entry point of said downflow gas contactor [DGC] reactor to the internal diameter of the column is from 1:6 to 1:25.
11. A method for the production of biodiesel, comprising the following steps: (a) mixing methanol and a transesterification catalyst in a mixing vessel [OCV]; (b) transferring oil from an oil storage vessel [OSV] by means of a first pump [P2] to a reactor feed vessel [RF]; (c) pumping the oil from said reactor feed vessel [RF] by means of a second pump [P1] into a downflow gas contactor [DGC] reactor comprising a column configured to allow at least one liquid input and at least one gas input into the upper section of said column via an orifice or nozzle which is configured such that at least one liquid stream and optionally at least one gas stream can flow downwards through said column and the turbulence and shear at the interface between the orifice or nozzle and the column results in mixing and highly efficient mass transfer, said oil being pumped downwards through said column until the total volume of the downflow gas contactor [DGC] reactor is filled with oil; (d) recirculating the total oil volume between the reactor feed vessel and the downflow gas contactor [DCC] reactor, the recirculating liquid entering the downflow gas contactor [DCC] reactor via a liquid input; (e) adding the methanol-catalyst mixture to the oil by either of the following methods (i) and (ii): (i) adding the methanol-catalyst mixture directly to the reactor feed vessel [RE] from the mixing vessel [OCV] by means of a third pump [P3] containing the oil recirculated through the downflow gas contactor [DCC] reactor in (d) above, or (ii) adding the methanol-catalyst mixture directly to the downflow gas contactor [DGC] reactor through inlet [I] while the oil is recirculated as described in (d) above, the recirculating liquid entering the downflow gas contactor [DGC] reactor via a liquid input; (f) recirculating the reaction mixture between the reactor feed vessel [RE] and the downflow gas contactor [DGC] reactor continuously by means of pump [P1] after initiation of the reaction has taken place in step (e) above, the recirculating liquid entering the downflow gas contactor [DCC] reactor via a liquid input; and (g) on completion of the transesterification reaction, shutting down the pump recirculating the reaction mixture.
12. A method for the production of biodiesel according to claim 11 wherein said column of said downflow gas contactor reactor has an internal diameter of between 5cm and 1.0 m.
13. A method for the production of biodiesel according to claim 11 or 12, wherein said column of said downflow gas contactor reactor has a height of between 1.0 m and 25 m.
14. A method for the production of biodiesel according to any one of claims 11 to 13, wherein the ratio of the internal diameter of the orifice or nozzle used at the entry point of said downflow gas contactor [DCC] reactor to the internal diameter of the column is from 1:6 to 1:25.
15. A method for the production of biodiesel according to any one of claims 11 to 14, wherein the rate at which liquid is circulated around the apparatus is at a velocity from 0.04 metres/second to 0.30 metres/second.
16. A method for the production of biodiesel according to any one of claims 11 to 15, wherein the column of said downflow gas contactor [DGC] reactor comprises a cylindrical upper section and an inverted conical lower section.
17. A method for the production of biodiesel according to any one of claims 11 to 16, wherein after the transesterification reaction has been stopped, the resulting transesterified reaction mixture containing the biodiesel is then either: (i) transferred to a separate settling vessel [SVI} by pump [P2] and allowed to settle, or (ii) allowed to settle in the reactor feed vessel [RF] and the downflow gas contactor [DGC] reactor.
18. A method for the production of biodiesel according to any one of claims 11 to 17, wherein after stopping the transesterification reaction and allowing the phases to settle in the reactor feed vessel [RV] and downflow gas contactor [DGC] reactor or in the settling vessel [SVI], the glycerol is obtained from the bottom layer and the desired biodiesel product is obtained from the top layer.
19. A method for the production of biodiesel according to claim 18, wherein said glycerol is transferred to a storage vessel [SV2] and, optionally, may be further processed.
20. A method for the production of biodiesel according to any one of claims 11 to 19, wherein said desired biodiesel product is transferred to a storage vessel [SV3].
21. A method for the production of biodiesel according to any one of 11 to 20, wherein said method is performed in a batch operation mode, a continuous operation mode or a multiple batch operation mode.
22. A method for the production of biodiesel according to any one of claims 11 to 21, wherein said transesterification catalyst is a base.
23. A method for the production of biodiesel according to claims 22, wherein said transesterification catalyst is sodium hydroxide or potassium hydroxide.
24. A method for the production of biodiesel according to claims 23, wherein the ratio of methanol to sodium hydroxide or potassium hydroxide used in the reaction is from 1:0.01 wt%to 1: 0.02 wt%.
25. A method for the production of biodiesel according to any one of claims 11 to 24, wherein the ratio of oil to methanol used in the reaction is from 3: I vol%to 10: 1 vol%.
26. A method for the production of biodiesel according to any one of claims 11 to 25, wherein the transesterification reaction is performed at a temperature of from 20-40 °C.
27. A method for the production of biodiesel according to any one of claims 11 to 26, wherein the transesterification reaction is performed at a pressure of from 2 x i05 to 6 x i05 Pa.
28. A method for the production of biodiesel according to any one of 11 to 27, wherein the oil used is selected from corn oil, sunflower oil, rapeseed oil, algal oil, jatropha oil and waste cooking oil.