GB2423088A

GB2423088A - Removal of impurities from liquids using gaseous nitrogen

Info

Publication number: GB2423088A
Application number: GB0502869A
Authority: GB
Inventors: Ronald John Groves; Daniel John Cross
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-02-11
Filing date: 2005-02-11
Publication date: 2006-08-16
Anticipated expiration: 2025-02-11
Also published as: GB2423088B; GB0502869D0

Abstract

A technique for removing impurities from liquids by passing nitrogen through the liquid. The technique is especially applicable to liquids that are in part organic and in a particularly preferred aspect, nitrogen is passed through biodiesel or other biofuel as a drying procedure. Nitrogen may also be passed through feedstock to dry it prior to cracking.

Description

Impurity Removal From Liquids Using Nitrogen This invention relates to

removing impurities from liquids using nitrogen and in particular, but not exclusively, to drying liquids that have an affinity for or will hold oxygen and/or water Typically the liquids may be at least partly organic The invention also relates to use of nitrogen for mixing such liquids Drying and mixing may take place separately, sequentially and/or repeatedly in the same or different vessels and is accomplished by passing nitrogen through the liquid.

Although described principally in the context of biodiesel production, the present invention is not limited to that application nor within that application to any particular source or feedstock, nor specifically to biodiesel, as the techniques described may be utilised in other systems, especially other biofuels Biodiesel fuel is a clean-burning replacement for petroleum based diesel and can be made from natural renewable sources such as new or used vegetable oils and animal fats. The vegetable oils or fats contain fatty acids which are reacted to form substances such as methyl esters that constitute the biodiesel More generally there are biofuels, such as bioethanol, which can be used to replace other petroleum derived fuels.

There is particular interest in converting used and waste or byproduct oils and fats into biodiesel as this can be more economic than using higher grade or new oils There are various processes that have been described for producing biodiesel. In a typical process a feed stock of oils or fats is cracked, for example by reaction with sodium methoxide. A better reaction may be obtained, especially when the feed stock is a used or waste product, if the feedstock is dried first, but in many prior art systems the pre-drying process is omitted because of its complexity. After cracking, the unwanted products (for example, glycerol) of the cracking are drained off and the biodiesel esters that have been formed are washed with water to remove other byproducts and dried. Drying at this stage is essential for the performance of the biodiesel.

Various drying processes are currently used, such as centrifuging, vacuum drying or distillation. Distillation requires heating to 100 degrees C to steam water from the esters.

This can be problematical in that residual methanol is present which is both a hazard and also forms a constant boiling mixture below 100 degrees C. Centrifugal and vacuum drying require specialised equipment that is costly. Whichever prior art system is used for drying there are potential problems, high costs and high energy consumption.

Similar considerations apply in other production systems, such as for other biofuels or other systems where removal of water and/or oxygen is required.

The present invention provides a technique for removing impurities from liquids by passing nitrogen through the liquid. The technique may be applied to all liquids but is particularly applicable to liquids that are in part organic In a particularly preferred aspect, nitrogen is passed through biodiesel or other biofuel as a drying procedure.

In a further aspect of the invention nitrogen is passed through feed stock to dry it prior to cracking.

In a particularly preferred production system according to the invention, nitrogen is passed through feedstock to dry it prior to cracking, then in the same or a different vessel nitrogen is passed through again to mix together the feedstock and sodium methoxide for the cracking phase, and again in the same or a different vessel after the biodiesel esters produced from cracking have been separated and washed, nitrogen is passed through the biodiesel in a second drying phase Heating is not essential while the nitrogen is passed, but the procedure may be accelerated by higher temperatures The introduction of nitrogen may cause cooling and gentle heating to offset this may be preferred. Temperatures ranging from ambient to near 100 degrees Centigrade have been used, the latter producing a turbulent or violent response due to the speed of elimination of gaseous impurities temperature may be chosen according to suit the scale and containment vessels of a system, but it is convenient to maintain a temperature of around 50 to 55 degrees Centigrade throughout drying and cracking stages The final esters are very dry (99.7 to 99 9% dry), for example holding only 280 milligrams of water per kilogram of ester, and it has further been noticed that esters produced in this way have a longer shelf life, as measured by water content, compared with conventionally produced biodiesel esters.

The invention is now described by way of example with reference to the accompanying drawings in which Figure 1 shows a vessel in the process of drying feedstock; Figure 2 shows a reactor vessel in the process of mixing feedstock and sodium methoxide, Figure 3 shows a vessel in the process of drying biodiesel esters Referring to Figure 1, a vessel I contains feedstock 2 which may be introduced into the vessel by any convenient means. For biodiesel a range of vegetable oil feedstocks are available including, but not limited to, coconut, corn, cotton, flax, palm, rapeseed, sunflower seed and soya. Animal fats and greases may also be used. A process suitable for used vegetable oil is described, but the novel uses of nitrogen according to the invention may be employed in other systems.

The vessel 1 has a tapered or pointed lower portion 3 which is generally convenient for tapping off vessel contents via drain pipe 4. This tapered shape may be conical, pyramidal, wedge or any other suitable shape and the sides are provided with a one or more vents 5 for the introduction of gaseous nitrogen. In the drawing a series of vents is shown Feedstock usually substantially fills the vessel, although this is not essential, and nitrogen is introduced through the vents 5 so that streams of nitrogen bubbles pass through the feedstock. The nitrogen may be introduced at any of a range of pressures varying from that equivalent to the pressure in the vessel at the depth of the vent to a more vigorous injection pressure. It is convenient to adjust the pressure and purity of nitrogen so that the drying process takes about 15 to 30 minutes, although this will also depend on other factors including the type of liquid material, the water saturation and temperature (50 to 55 degrees C being a convenient operating temperature). Pressures ranging from a fraction of a bar to 200 bar direct from a nitrogen cylinder have been used. Samples are taken from the feed stock to monitor the level of moisture At the top of the vessel there are vents 7 and 8 which may be used simply to vent the nitrogen and entrained moisture as it reaches the surface of the feedstock However, it is preferred to cause a cross flow over the surface to speed up the removal of water vapour from the vessel before it condenses on the exposed walls of the top part of the vessel. The cross flow may be produced by suction or by introduction of dry air or nitrogen under pressure or a combination of both For this purpose vents in the side walls of the top portion of the vessel may be provided Heat is applied to the vessel to maintain the feedstock at approximately 50 to 55 degrees C which is both a convenient all round operating temperature and provides a viscosity level in the liquid that aids the moisture removal Modifications to the method of introduction of nitrogen to the liquid may be made rather than it being a simple release For example pulsing may be used, or diffusers to maximise the surface area of the nitrogen, or the nitrogen may move or be moved through the liquid in other than an upward path Once the feedstock is dry, it may either be tapped off from the vessel through drain pipe 4 or other alternative exit and passed to another vessel for the cracking phase, or alternatively it may remain in the same vessel Figure 2 shows the cracking phase. Reactor vessel 1 is similar to, or may be the same vessel, as described for the drying phase of Figure 1. There may be other pipes for introducing liquids to the vessel. Any size of vessel may be used for the reaction phase, for example containing from 1 litre to at least 40,000 litres of feedstock into which a volume of 15 to 25% of sodium methoxide is introduced. Mixing at this stage may be provided by mechanical means (not shown) but it is convenient to mix by introduction of nitrogen through lower ones of the vents 5 to produce a rising column of bubbles in the centre of the vessel. The continuous introduction of nitrogen up the centre of the vessel encourages flow in the liquids as shown by arrows 10 so that a vortex or tonoidal current is established that intimately mixes the liquids together. In some circumstances it may be preferred to use mechanical mixing as well as introduction of nitrogen. Mixing may also be induced during transfer from one vessel to another, for example by blending streams of feedstock and methoxide Heating to about 50 to 55 degrees C is again preferred.

During the cracking process esters and glycerol are formed which separate out when mixing is stopped with the heavier glycerol at the bottom. The glycerol is drained off and usually further sodium methoxide added and the process repeated one or more further times until the feedstock is all reacted After the final draining of glycerol the biodiesel esters need to be washed to remove other residues such as soaps and salts as well as any remaining glycerol Water is introduced, nitrogen and/or mechanical agitation is applied, then the contents are allowed to settle. At this stage water and other residues separate out at the base of the vessel and are tapped off This washing process may be repeated one or more times. Once all the water that can be tapped off has been removed, the remaining biodiesel is then either transferred to another vessel, or again remains in the same vessel, for the final drying phase.

The drying phase is shown in Figure 3 and is similar to the drying phase described in respect of Figure 1, with the nitrogen introduced again over a range of possible pressures Biodiesel dried in this way easily passes the EU standards for dryness of 500 milligrams per kilo of biodiesel, tested samples having dryness levels of 280 milligrams of water per kilo of biodiesel. Sufficiency of dryness can be detected visually when the biodiesel turns from cloudy to clear. Again samples are withdrawn for monitoring purposes.

Biodiesel is hygroscopic and therefore if exposed to air it absorbs moisture. However it has been found that the biodiesel produced with a final drying phase involving passing nitrogen through the liquid is more stable than biodiesel dried by heating methods. This is also found if just the final drying process is applied to biodiesel produced by other methods For example, a sample of nitrogen dried biodiesel left in a petri dish for 3 days remains substantially clear while biodiese! dried by a heating technique left in a similar petri dish in the same environment begins to turn cloudy in a few hours During the nitrogen drying process other impurities are also removed, which provides a deodourising effect that is particularly useful when using recycled or waste materials as feedstock. It is believed that the enhanced stability and other impurity reduction is due to the removal of oxygen and leaving clean open bonds on the ends of the esters. In the drying process it appears that the nitrogen lowers the oxidisation level, which in turn reduces the water saturation point and water is removed as free liquid water that falls to the bottom of the vessel, then on further introduction of nitrogen, oxygen and water vapour are carried to the surface of the liquid.

Due to the superior quality of biodiesel obtained from nitrogen drying, it may be applied as a drying stage to biodiesel produced by other methods either as part of the production or additionally or after storage The use of nitrogen for drying has several other practical advantages It is a more energy efficient process as well as being simpler and/or safer than processes involving heating, centrifuging and distillation It is readily applied within a vessel that may also form the reactor vessel. Nitrogen is usually used for flushing vessels and therefore it does not add substantially to equipment requirements. It may also be used for mixing instead of mechanical agitators, thereby enabling simplification of equipment.

Although described in the context of production of biodiesel, the same procedure may be used for drying or separation of other substances, for example for recovery of methanol

Claims

Claims 1. A method of removing impurities from liquids, the method

comprising introducing a stream of gaseous nitrogen into the liquid
2. A method according to claim I in which the liquid comprises biofuel
3 A method according to claim 2 in which the liquid comprises biodiesel.
4. A method according to claim 1 in which the liquid comprises feedstock for a biodiesel reactor A method according to any preceding claim in which the stream of nitrogen is introduced at a lower or base zone of a vessel containing the liquid.
A method according to any preceding claim in which the nitrogen is introduced at a pressure not significantly greater than the ambient pressure at its point of introduction.
6. A method according to any preceding claim in which the nitrogen is introduced at a pressure significantly greater than the ambient pressure at its point of introduction
7 A method according to any preceding claim in which a plurality of streams of nitrogen are introduced.
8 A method according to any preceding claim in which nitrogen is introduced into a vessel containing the liquid via a plurality of vents distributed over the base of the vessel.
9. A method according to claim 8 in which the base of the vessel comprises tapered sides and the vents are in the tapered sides.

A method according to any of claims 1 to 7 in which nitrogen is introduced into a vessel containing the liquid via at least one pipe or nozzle located proximate the base of the vessel 11 A method according to any preceding claim in which vacuum extraction is applied above the surface of the liquid.

12 A method according to any preceding claim in which dry air or nitrogen is blown over the surface of the liquid 13 Apparatus for drying liquids that are at least in part organic, the apparatus comprising a vessel for containing the liquid and at least one means in the lower part of the vessel for introducing a stream of gaseous nitrogen into the liquid.