EP0292526B1

EP0292526B1 - A method for upgrading of waxy oils to products that can be used as light fuel oils, diesel fuel and other upgraded oils, the products so obtained and an application of the products as substitutes

Info

Publication number: EP0292526B1
Application number: EP87907992A
Authority: EP
Inventors: Kenneth Peter Harris; Gudbrand Rodsrud; Finn Knut Hansen
Original assignee: Dyno Industrier AS
Current assignee: Dyno Industrier AS
Priority date: 1986-12-10
Filing date: 1987-12-07
Publication date: 1991-06-19
Anticipated expiration: 2007-12-07
Also published as: WO1988004311A1; JPH01502122A; DK447088D0; EP0292526A1; DK447088A; FI883699A; BR8707573A; AU8338887A; NO864988D0; FI883699A0; IL84674A0

Abstract

Stable oil-in-water/alcohol emulsions. Useful as substitutes for diesel fuel and/or light heating oil. Continuous phase is a mixture of water/alcohol. Discontinuous phase consists of heavy, waxy oils whith more than 50 % alkanes and a pour point down to 5°C. Oil phase volume accounts for 40 to 65 % of the emulsions total volume, emulsifiers and cetane value enhancers are added. Emulsions are easily flowing at -40°C having a viscosity of less than 300 cp, combustion yields lower degree of soot and NOx than traditional fuels. Emulsions are resistant to bacteria growth.

Description

The present invention concerns a method for the upgrading of heavy, waxy oil fractions having an alkane content in excess of 50% in such a fashion that the upgraded products can be used for purposes for which light fuel oils (also known as light heating oils) and diesel oils are currently employed.
Furthermore the invention describes a method for the preparation of stable emulsions fulfilling these purposes, as well as upgraded oils in the form of stable emulsions prepared by the said process.
In order that crude oil can be used e.g. as an energy source or as chemical feedstock, it must be broken down into specified boiling point fractions by distillation and then refined by a variety of special techniques. A group of products termed gasoils or middle distillates form one or more of these refining fractions. Whilst some of these fractions can sometimes be used as such or with relatively little additional treatment, e.g., diesel oil, others, particularly those termed heavy or wide-range and/or vacuum gasoil often have a high wax content that effectively precludes their use as generally saleable products in their own right. It is therefore common practice that these oils are subjected to further refining processes.
This requirement for additional refining is reflected in a lower economic value for these oils than for lighter oils. On the other hand, their chemical structure may make them especially well suited for use in a specific application, as heating oils or fuel for diesel driven motors. For instance, many of the said oils have a high content of linear alkanes and a low content of aromatics, which provide high cetane values.
The development of improved refining techniques for oils of this type is therefore a matter of continuing interest for the petroleum industry.
A well known and much used method involves a cracking process, i.e. converting these oil fractions to branched isomers and cyclic hydrocarbons by the application of heat and sometimes also in the presence of catalysts. These processes have however several disadvantages:

1) There is often a residue of coke and/or heavier products that have a lower economic value than the feed-stock. This detracts from the profitability of these techniques.
2) There is a considerable capital investment required, and also a great amount of energy consumption implying a high economic risk during times of fluctuating oil prices.
3) Cracked products burn more slowly than their linear counterparts. This can during combustion result in increased emissions of soot particles, polycyclic aromatic hydrocarbons and nitrogen oxides (NO_x) particularly when combustion times are limited, e.g. in a diesel motor.

Whilst the heavy waxy gasoils described herein are unsuited for sale to end users because of the risk of precipitation of wax, it is the case that even conventional oil products from time to time are subject to user related problems. These can be caused by a variety of factors, e.g.:

A) Excessive moisture absorption that leads to the formation of a discrete layer or larger droplets of water during storage. This can result in transport problems, bacterial growth, corrosion of metal surfaces, combustion irregularities, etc.
B) The minimum storage and use temperatures are closely related to the pour point, the lowest temperature where the oil is fluid, and the cloud point, the temperature where wax begins to precipitate. As it is economically desireable from the oil product manufacturers' point of view that as high a cloud point as possible can be tolerated by the user at the time of use, this often leads to the sale of different grades of the same product for use under different climatic or storage conditions. An example is the sale of summer and winter qualities of diesel fuel. This can lead to suboptimal employment of storage and transport capacity.

Methods are described whereby oils are converted to oil-in-water emulsions in order to achieve claimed improvements in combustion properties, but the effectiveness of these methods is also subject to considerable restrictions in practise. Furthermore, descriptions of these methods preclude oils of a heavy, waxy nature such as heavy gasoils having an alkane contents in excess of 50%. Neither do the descriptions of these methods include the use of greater amounts of alcohols in the continuous phase, nor do they claim to effect any upgrading of the oil used in their manufacture in as much as they are based upon oils that would otherwise have been employed for the same purposes as is claimed for the emulsions themselves.
Norwegian patent application 852637 describes a method for improving the combustion characteristics of heavy mineral oil fractions to the level of fuel oil by emulsification in water in the presence of an emulsifier system containing at least one biologically derived emulsifier. This method is restricted to oils containing less than 50% alkanes.
Norwegian patent application 830785 describes an emulsifier for use in a system where the aqueous phase consists of an alcohol and water mixture. Whilst emulsions of the water-in-fuel oil kind are claimed usable as fuel oils, the oil-in-water emulsions that are described there cannot be employed for such purposes, nor do they ipso facto result in an upgrading of the oil employed as starting material.
A series of patents, US 4084940, US 3490237, US 3352109, US 3756794, US 3615290, EP 0156486, CA 1132908, DE 3016544, DE 1644942, FR 2548208, and US 4382802 describe the preparation of emulsified fuel oils, but all of these are highly viscous emulsions containing more than 70% dispersed oil, termed gels, solid fuel or thixotropic emulsions. In US 4084940 the use of organic solvents to improve the ignition of the solid fuel is claimed. In US 3615290 the use of polar solvents with smaller amounts of water as continuous phase is claimed. The use of ammonium nitrate as a freezing point depressant is described in US 3756794. Because of their viscosity the fuels described in these patents cannot be considered suitable for use as diesel fuel without considerable modification of the motor itself, nor be considered as heating oil.
There are also water-in-oil type emulsions, which may be used in order to improve the combustion process, however they provide for the use of conventional diesel or light heating oil, which means that they cannot be used for upgrading heavier fractions.
The main purpose of the present invention is to improve the characteristics of heavy, waxy oil fractions having an alkane content of more than 50% and that have hitherto been considered unsuitable for use as light fuel oil and/or diesel oil, to such an extent that they can be used for these purposes. The invention describes a method of preparing stable oil-in-water type emulsions containing 40-65 percent by volume of oil, preferably 50-60 percent by volume, that are usable as diesel oils or light fuel oil substitutes.
A stable emulsion is defined within the context of the present invention as an emulsion that does not show visible signs of destabilisation, i.e. the formation of a separate phase consisting only of oil, after the following test procedure is performed:

(i) Standing for two months, followed by
(ii) Agitation for 24 hours at 500 rpm with a magnetic stirrer, followed by
(iii)Centrifugal rotation at 1500 g for one hour.

Oil fractions that generally speaking are suitable for upgrading by the techniques described herein include, but are not limited to:

a) Heavy gasoil
b) Vacuum gasoil
c) Slack wax
d) Coker heavy gasoil

It is not unlikely that oils and fats of both vegetable and animal origin either alone or admixed with mineral oil can be upgraded to diesel-like and light heating oil-like products by use of the techniques described herein.
The invention as described below, is characterized by the fact that the aqueous phase, which is the continuous phase in the emulsions, contains an alcohol to the extent of 5-70%, preferably 20-60% by volume of the total volume of the water/alcohol phase, where the alcohol can be an alkanol, preferably methanol.
It has been demonstrated that emulsions made according to the invention suprisingly, in view of their high proportion of water/alcohol phase can be used for conventional diesel fuel or heating oils in typical applications for these oil products.
This is unexpected because the energy content of methanol is only about one half of that of diesel oil and heavy gasoils, whilst water detracts from the available energy content of the emulsion. It is especially surprising that an emulsion of this type can be used as a fuel for standard diesel motor as conventional wisdom would suggest that an emulsions cetane value would be too low. As an example for an emulsion with the following formulation:

60% by volume of oil having a cetane value of approximately 50
24% by volume of methanol (60% by volume of the continuous phase) having a cetane value of 0,

the remainder water without cetane value, a normal mixing calculation would yield a theoretical cetane value for the emulsion of less than 30.
The addition of cetane value enhancers could within economic limits raise the theoretical cetane value of this system by 2-3 points, i.e. to about 33. Existing norms and standards that govern the cetane value of fuels used to drive autodiesel motors recommend a minimum cetane value of 47 implying that the emulsion ought to be unusable for such purpose. In spite of this, the emulsion described above can be used to drive an autodiesel motor.
According to the invention, heavy, waxy oils are converted by emulsification to oil-in-water/alcohol emulsions for use as autodiesel fuels or as light heating oils.
The emulsions contain emulsifier systems that according to the invention consist of one or more non-ionic and anionic emulsifiers and one or more polymeric stabilisers in a quantity of from 1 to 30 grammes/litre oil preferably non-ionic emulsifiers having an HLB value of from 12 to 17 in a quantity of from 5 to 15 grammes/litre oil.
The emulsions may contain nitrate esters and/or nitrate salts, preferably in quantities of from 0.1 to 4.0 grammes/litre emulsion. These function as cetane value enhancers in emulsions used in place of diesel fuels or as combustion catalysts in emulsions used in place of light heating oils.
The process of emulsification can be performed according to standard methods. By emulsifying the oil in accordance with the invention, the oil will be present as finely distributed droplets with a particle size within the range of 1-20 micrometres. This enables the emulsions to exhibit important and particularly advantageous characteristics, e.g.:

1) Separation of wax is no longer a problem. Although wax may still crystallise at sufficiently low temperatures, this will occur within each droplet, the continuous aqueous phase effectively isolating the droplets from one another and thereby avoiding the formation of agglomerates that would cause flow and transport problems.
2) The oil phase is finely divided prior to the combustion process. This ensures a more optimal size distribution of the oil droplets in the combustion chamber, than is the case when normal oils are atomised via an injection nozzle, with the result that the combustion process is more complete during the time that the combustibles are in the combustion chamber. One consequence of this advantage is that when injecting emulsions the fuel injection nozzle's atomising function is no longer critical for good combustion performance. This may permit considerably mechanical simplifications to be made to the injection systems of oil burning machinery.
3) The viscosity of the emulsions described in this invention is maintained at low levels, even at very low temperatures. This is because the emulsions' viscosity is determined by the continuous water/alcohol phase viscosity and by the volume proportion of oil.

Emulsions can be formulated according to this invention from materials for use as light heating oil or diesel fuel which inhibit the following advantages compared to conventional oil products:

A) Reduced polluting emission of NOx and soot upon combustion.
B) The ability to be used and stored at temperatures lower than-40°C (depending on type and amount of alcohol in the continuous phase), and with a pour point down to 5°C.
C) Viscosities of below 300 cp at-40°C (See par. B).
D) The possibility of achieving lower raw materials costs and/or lower production costs.
E) Maintenance of stability and properties of use in the presence of modest amounts of moisture.
F) Resistance to bacterial growth.

The following example will serve to describe the invention more fully.

EXAMPLE

A heavy gasoil (Rafinor TG from Statoil's Mongstad, Norway refinery), having a density of 0.867 g/ml and containing 76.4% alkanes was emulsified in a water/methanol mixture as follows:,

97.5 litres Rafinor TG
36 litres methanol
24 litres water
0.3 kilogrammes nitrate salts
2 kilogrammes emulsifier system
0.045 kilogrammes organic nitrate ester

The mixture was emulsified by first making a preemulsion and then homogenising the said preemulsion in an ultrasonic homogeniser.
The emulsion thus prepared had a viscosity of 61 cp, a flash point higher than 27°C but lower than 55°C (enabling it to be classed as a B fluid for transportation and storage purposes in Norway) and a density of-0.894 g/ml.
This emulsion was then used as fuel in a turbocharged, high speed, fully instrumented Scania Vabis DS 11 diesel engine. The same engine was then run on a standard summer diesel fuel having a density of 0.834 g/ml and a viscosity of 5 cp as control.
Exhaust gas analyses showed that the quantities of NOx and soot in the combusted products were always lower when the emulsion was burned than when the control was used, from idling conditions up to full loading of the engine. Compared to the control, NOx was reduced by from 18% to 87% (according to loading) whilst soot emissions, measured by the Bosch method, were from 1.00 to 1.76 units lower.
Methanol has an energy content of approximately 50% that of diesel fuel and heavy gasoil. According to calculation, the above prepared emulsion would have an energy content of approximately 74% that of diesel fuel. By way of confirmation hereof, the yield of the engine per litre fuel was measured for the emulsion as being from 70% to 75% of that of the diesel fuel used as control.

Claims

1. Stable oil-in water/alcohol emulsion suitable for use as a substitute for diesel fuel and/or light heating oil characterised in that the emulsion continuous phase consisting of a water/alcohol mixture and its discontinuous phase consisting of heavy, waxy oil containing more than 50% alkanes and having a pour point down to 5°C, the oil phase volume accounts for from 40 to 65 percent b, volume, preferably from 50 to 60% of the total volume of the emulsion and the emulsion contains emulsifier and combustion catalyst and/or cetane value enhancer.

2. Stable emulsion according to claim 1, characterised by the alcohol being a low molecular weight alkanol and preferably methanol, being present in the emulsion continuous phase in an amount of 5 to 70 percent by volume, preferably from 20 to 60 percent by volume.

3. Stable emulsion according to claim 1, characterised by the emulsifier being present in an amount of 1 to 30 grammes/litre of oil and comprising at least one non-ionic emulsifier optionally mixed with at least one anionic emulsifier and/or at least one polymeric stabiliser.

4. Stable emulsion according to claim 3, characterised by the non-ionic emulsifier having an HLB value of from 12 to 17 and being present in an amount of from 5 to 15 grammes/litre oil.

5. Stable emulsion according to claim 1, characterised by containing nitrate ester and/or nitrate salt to the extent of 0.1 to 4.0 grammes/litre to act as cetane value enhancer or combustion catalyst.

6. A method for upgrading heavy, waxy oil fractions, containing more than 50% alkanes for the preparation of stable oil-in-water/alcohol emulsion as described by claims 1 to 5, characterised by the fact that oil in an amount of 40-65 percent by volume and preferably 50-60 percent by volume calculated on the total emulsion volume is emulsified into stable emulsions in a water/alcohol mixture that constitutes the continuous phase by adding emulsifier and cetane value enhancer and/or combustion catalyst.

7. Application of oil-in-water/alcohol emulsion as described in claims 1 to 5 as substitutes for light heating oils and/or diesel fuels.