WO1988004311A1

WO1988004311A1 - 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: WO1988004311A1
Application number: PCT/NO1987/000077
Authority: WO
Inventors: Kenneth Peter Harris; Gudbrand RØDSRUD; Finn Knut Hansen
Original assignee: Dyno Industrier A/S
Priority date: 1986-12-10
Filing date: 1987-12-07
Publication date: 1988-06-16
Also published as: DK447088D0; JPH01502122A; NO864988D0; EP0292526A1; DK447088A; FI883699A0; AU8338887A; IL84674A0; EP0292526B1; FI883699A; BR8707573A

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

A method for upgrading of waxy oils to products that can be used as light fuel oils, diesel fuel and other upgraded oils, the pro¬ ducts so obtained and an application of the products as substitut¬ es.

The present invention concerns a method for the upgradin of heavy, waxy oil fractions having an al ane content in exces of 50% in such a fashion that the upgraded products can be use for purposes for which light fuel oils (also known as ligh heating oils) and diesel oils are currently employed.

Furthermore the invention describes a method for th preparation of stable emulsions fulfilling these purposes, a well as upgraded oils in the form of stable emulsions prepare by the said process.

In order that crude oil can be used e.g. as an energ source or as chemical feedstock, it must be broken down int specified boiling point fractions by distillation and the 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 some¬ times 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 sale¬ able products in their own right. It is therefore common prac¬ tice that these oils are subjected to further refining pro¬ cesses.

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 espec¬ ially 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 iso- mers 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 pro¬ ducts 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 imply¬ ing 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 _χ) particularly when combustion times are limited, e.g. in a diesel motor.

Whilst the heavy waxy gasoils described herein are un- suited for sale to end users because of the risk of precipita¬ tion 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 manu¬ facturers' 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 heavy, waxy nature such as heavy gasoils having an alkane con tent in e ess of 50%. Neither do the descriptions of thes methods include the use of greater amounts of alcohols in th continuous phase, nor do they claim to effect any upgrading o the oil used in their manufacture in as much as they are base upon oils that would otherwise have been employed for the sam purposes as is claimed for the emulsions themselves.

Norwegian patent application 852637 describes a method fo improving the combustion characteristics of heavy mineral oi fractions to the level of fuel oil by emulsification in wate in -the presence of an emulsifier system containing at least on biologically derived emulsifier. This method is restricted t oils containing less than 50% alkanes.

Norwegian patent application 830785 describes an emul sifier for use in a system where the aqueous phase consists o an alcohol and water mixture. Whilst emulsions of the water-in fuel oil kind are claimed usable as fuel oils, the oil-in-wate emulsions that are described there cannot be employed for suc purposes, nor do they ipso facto result in an upgrading of th oil employed as starting material.

A series of patents (1-11) describe the preparation of emulsified fuel oils, but all of these are highly viscous emul¬ sions containing more than 70% dispersed oil, termed gels or thixotropic emulsions. The use of alcohols is not considered in these patents nor can the fuels described therein, because of their high viscosity, be considered suitable for use as diesel fuel or heating oil. In spite of the claim made in these patents suggesting that the emulsions made thereby can be used as diesel fuel, e.g. aircraft engines applications of this kind are not feasible for the products in existing diesel fuel driven engines without considerable modification of the motor itself.

There are also disclosed 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 pur¬ poses. The invention describes a method of preparing stable oil-in-water type emulsions cotaining 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 proce¬ dure 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 rotatio.n at 1500 g for one hour.

Oil fractions that generally speaking are suitable for up¬ grading 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%, pre¬ ferably 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 only about one half of that of diesel oil and heavy gasoil whilst water detracts from the available energy content of t emulsion. It is especially surprising that an emulsion of thi type can be used as a fuel for standard diesel motor as conve tional wisdom would suggest that an emulsions cetane valu would be too low. As an example for an emulsion with the fol lowing formulation:

60% by volume of oil having a cetane value of approxi mately 50 24% by volume of methanol (60% by volume of the continu ous phase) having a cetane value of 0, the remainder water without cetane value, a normal mixing calculation would yield a theoretical cetan value for the emulsion of less than 30.

The addition of cetane value enhancers could within econo mic limits raise the theoretical cetane value of this system b 2-3 points, i.e. to about 33. Existing norms and standard that govern the cetane value of fuels used to drive autodiese motors recommend a minimum cetane value of 47 implying that th emulsion ought to be unusable for such purpose. In spite o this, the emulsion described above can be used to drive a autodiesel motor.

According to the invention, heavy, waxy oils are converte by emulsification to oil-in-water/alcohol emulsions for use a autodiesel fuels or as light heating oils.

The emulsions contain emulsifier systems that according t the invention consist of one or more non-ionic and anioni emulsifiers and one or more polymeric stabilisers in a quan tity of from 1 to 30 grammes/litre oil preferably non-ioni emulsifiers having an HLB value of from 12 to 17 in a quantit of from 5 to 15 grammes/litre oil.

The emulsions contain nitrate esters and nitrate salts preferably in quantities of from 0.1 to 4.0 grammes/litre emul sion. These function as cetane value enhancers in emulsion used in place of diesel fuels or as combustion catalysts i emulsions used in place of light heating oils.

The process of emulsification can be performed accordin to standard methods. By emulsifying the oil in accordance wit the invention, the oil will be present as finely distributed droplets with a particle size within the range of 1-20 micro¬ metres. 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 combus¬ tion process. This ensures a more optimal size distribution of the oil droplets in the combustion chamber, than is the case when normal oils are ato¬ mised 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 considerable mechanical simplifications to be made to the injec¬ tion 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 obtained according to this invention used as light heating oil or diesel fuel exhibit the following advan¬ tages 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 materia costs and/or lower production costs.

E) Maintenance of stability and properties of use in t presence of modest amounts of moisture.

F) Resistance to bacterial growth.

The following example will serve to describe the inventio more fully. EXAMPLE

A heavy gasoil (Rafinor TG from Statoil's Mongstad, Norwa refinery), having a density of 0.867 g/ml and containin

76.4% alkanes was emulsified in a water/methanol mixtur 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 preemulsio and then homogenising the said preemulsion in an ultrasoni homogeniser.

The emulsion thus prepared had a viscosity of 61 cp, flash point higher than 27°C but lower than 55°C (enabling i to be classed as a B fluid for transportation and storage pur poses 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 diese engine. The same engine was then run on a standard summe diesel fuel having a density of 0.834 g/ml and a viscosity of cp as control.

Exhaust gas analyses showed that the quantities of NOx an soot in the combusted products were always lower when the emul sion was burned than when the control was used, from idlin conditions up to full loading of the engine. Compared to th control, NOx was reduced by from 18% to 87% (according t 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.

R e f e r e n c e s

1. US 4 084 940

2. US 3 490 237

3. US 3 352 109

US 3 756 794

US 3 615 290

EP 0 156 486

CA 1 132 908

8. DE 30 16 544

DE 16 44 942

10. FR 2 548 208

11. US 4 382 802

Claims

C l a i m s Stable oil-in-water/alcohol emulsions for use as a substi¬ tute for diesel fuel and/or light heating oil characteri¬ zed by the emulsions' continuous phase consisting of a water/alcohol mixture and their discontinuous phase con¬ sisting of heavy, waxy oils containing more than 50% alkanes and having a pour point down to 5°C, further that the oil phase volume accounts for from 40 to 65 percent by volume, preferably from 50% to 60% of the total volume of the emulsions and that the emulsions contain emulsifiers and combustion catalysts and/or cetane value enhancers. Stable emulsions according to claim 1, characterized by the alcohol being a low molecular weight alcanol and pre¬ ferably methanol, being present in the emulsions continuous phase in an amount of 5 to 70 percent by vol¬ ume, preferably from 20 to 60 percent by volume. Stable emulsions acording to claim 1, characterized by the emulsifier system consisting of one or more non-ionic emulsifiers or a mixture of one or more non-ionic emul¬ sifiers, one or more anionic emulsifiers and one or more polymeric stabilisers, being present in an amount of 1 to 30 grammes/litre of oil, preferably non-ionic emulsifiers having an HLB value of from 12 to 17 in an amount of from 5 to 15 grammes/litre oil.

Stable emulsions according to claim 1, characterized by containing nitrate esters and/or nitrate salts to the extent of 0.1 to 4.0 grammes/litre that act as cetane value enhancers.

Stable emulsions according to claim 1, characterized by being stable and easy flowing at temperature as low as -40°C having a viscosity at that temperature of less than 300 cp.

Stable emulsions according to claim 1, characterized by the fact that they upon combustion yield exhaust gases containing less NOx and soot than is the case for the com¬ bustion from corresponding diesel fuel of light heating oils.

Stable emulsions according to claim 1, characterized by being resistant to bacterial growth. A method for upgrading heavy, waxy oil fractions, con¬ taining more than 50% alkanes for the preparation of stable oil-in-water/alcohol emulsions as described by claims 1 to 7, characterized 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 volum is emulsified into stable emulsions in a water/alcohol mixture that constitutes the continuous phase by adding emulsifiers and cetane value enhancers and/or combustion catalysts.

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