Patent Grant
11268040
This application is a National Stage of International Application No. PCT/GB2018/051263, filed May 10, 2018, which claims the benefit of GB Patent Application No. GB1707556.5, filed May 11, 2017, the contents of which are herein incorporated by reference.
This invention relates to oil-in-water (water continuous) emulsions that can be used as fuels, and which have high static and dynamic stability. The invention also relates to a process for their preparation and to fuel compositions comprising such emulsions.
Significant changes in the range and use of primary fossil fuels throughout the world over the last years have influenced and altered the way that energy intensive industries source their requirements and operate. These industrial trends have been significantly affected by fuel economics, diversification and availability, as well as by an increasing need to improve environmental performance. Higher prices have resulted in a move away from conventional oil based fuels towards cheaper alternatives with reduced environmental impact. Although feasible primary energy alternatives to oil exist for land-based industries, the shipping market remains predominantly dependent on oil-based products, particularly heavy fuel oil-based products, and is likely to do so for the foreseeable future.
Heavy fuel oils are normally produced by blending viscous refinery residues with higher value distillate fuels to provide the lower viscosity characteristics required for acceptable fuel handling and combustion performance. Direct use of high viscosity refinery residues requires high-temperature storage and handling that limits and complicates their potential use, and consequently lowers their value. As an alternative to blending refinery residues for fuel oil production, further processing (e.g. coking, hydrocracking, etc.) of the residue can be applied at the refinery to yield additional distillate fuels. However this strategy requires large capital investments to be made by the oil refinery, produces some lower value products, generates difficult to market by-products, results in an increase of emissions (including greenhouse and acid gases), all of which can serve to limit the economic advantage of this approach.
Preparation of emulsion fuels has been previously described, for example in Logaraj et al; “Emulsification—A solution to Asphaltene Handling Problems”, presented at the ISSA/AEMA 2nd Joint Conference, Mar. 12-13, 2000, Amelia Island, Fla., GB 2 475 090, U.S. Pat. Nos. 4,776,977, 5,419,852, 5,603,864, 6,530,965 B2, US 2010/0043277 A, U.S. Pat. Nos. 5,411,558, 5,360,458, 5,437,693, 5,976,200 and 6,113,659. Droplet size distribution characteristics of an emulsion fuel and the resulting combustion performance has been previously described in WO 2008/074138, EP 1 935 969 and U.S. Pat. No. 5,603,864. WO 2014/082981 describes Bitumen emulsions, and U.S. Pat. No. 6,194,472 describes colloidal dispersions of hydrocarbons in water, in which softening point of the hydrocarbons in the dispersion exceeds about 95° C.
There remains a need for an oil-in-water emulsion, particularly an oil-in-water emulsion fuel, and more particularly a marine fuel, that has improved stability during storage and handling.
The present invention is directed to an oil-in-water emulsion, particularly a fuel, and a method for its production, whereby the distillates conventionally used for blending down hydrocarbon residue viscosity are not required, and are replaced with water and a small amount of stabilising chemical additives. The invention can be directly applied to a wide range of heavy hydrocarbon and refinery residue streams. Such hydrocarbon-containing materials include: atmospheric and vacuum residues, visbroken or thermally cracked residues, vacuum flashed visbroken residues, and other heavy, viscous residues produced from refinery and/or heavy oil upgrading facilities (such as hydrocracking, de-asphalting and similar conversion processes).
An added benefit of the invention is to provide a means of enhancing the handling and combustion characteristics by emulsification. Although the importance of the droplet size distribution characteristics of an emulsion fuel on its resulting combustion performance has been previously documented (see above), there remains a need to simultaneously control rheological properties in order to produce a fuel that can be handled in a wide range of system applications. For a diesel engine application, for example in a ship's engine system, the rheological properties of the fuel are important in ensuring sustainable hydraulic performance of the fuel handling and injection systems. In the present invention, the droplet size distribution of the oil-in-water emulsion is maintained within particular limits. When used as a fuel, this enables control of both the rheological characteristics during the fuel handling, and the (rapid) burn-out of the fuel to ensure acceptable (if not complete) carbon utilisation in terms of efficiency and resulting emissions.
For an oil-in-water emulsion to be used successfully as a fuel, for example as a marine fuel, it must be robust to both storage (static) stability and handling (dynamic) stability. Although preparation of emulsion fuels has been previously described in some of the documents mentioned above, the stability requirements for their subsequent use have not been established.
It is an advantage of the present invention that the oil-in-water emulsions of the present invention exhibit reduced levels of sedimentation on storage.
Accordingly, a first aspect of the invention provides an oil-in-water emulsion comprising an oil phase; an aqueous phase; a primary surfactant; and a polymeric stabiliser selected from cationic polymers, and in particular cationic polymers containing monomers comprising dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate quaternary salts, or dialkylaminoalkylacrylamides or methacrylamides and their quaternary salts; wherein the oil phase is dispersed in the aqueous phase; and wherein in the oil-in-water emulsion has the following characteristics:
An emulsion having the above characteristics can have a dynamic stability of less than 0.30 μm increase in mean (D[4,3]) droplet size per minute at 50° C. (±10%).
A second aspect of the invention provides an oil-in-water emulsion comprising an oil phase; an aqueous phase; a polymeric stabiliser, wherein the polymeric stabiliser is selected from cationic polymers, and in particular cationic polymers containing monomers comprising dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate quaternary salts, or dialkylaminoalkylacrylamides or methacrylamides and their quaternary salts; and a primary surfactant, selected from one or more from the group consisting of fatty alkyl amines, ethoxylated fatty alkylamines, ethoxylated fatty alkyl monoamines, methylated fatty alkyl monoamines, methylated fatty alkyl amines, and quaternary fatty alkyl amines; wherein the oil phase is dispersed in the aqueous phase; and wherein the oil-in-water emulsion has the following characteristics:
An emulsion having such characteristics can result in high static and dynamic stability, as set out above, in addition to reduced sedimentation on storage
In a third aspect the invention provides a process for preparing the oil-in-water emulsion fuel comprising the steps of:
Values of parameters are sometimes expressed in terms of a particular value ±a percentage. This means that the value of that parameter can be either the value specified, or a range of values either side of the specified value, calculated from the percentage. For example, a viscosity of greater than 50, preferably greater than 100 and up to 700 mPas at 50° C. (±10%) and 20 s−1 (±10%) is referred to above. This means that the viscosity is greater than 50, preferably greater than 100, and up to 700 mPas, at a temperature that is either 50° C., or in the range of from 45 to 55° C., and at a shear rate that is either 20 s−1, or in the range of from 18-22 s−1. Similarly, a static stability of less than 5% residue after centrifugation at 50° C. (±10%) and 2000 g (±10%) for 30 minutes (±10%) means that the static stability is such that less than 5% residue (by weight) is produced after centrifugation at a temperature that is either 50° C. or in the range of from 45-55° C., at a g-force of either 2000 g or in the range of from 1800-2200 g, over a time period that is 30 minutes or in the range of from 27-33 minutes.
The oil-in-water emulsion of the invention may be other than a gas-in-oil-in-water emulsion.
The oil-in-water emulsion of the invention may be one in which the oil phase is substantially free from entrained bubbles or pockets of gas.
The present invention will now be described with reference to the accompanying drawings, in which:
Parameter Measurement
The average droplet size distribution of the oil phase can be measured by conventional techniques, for example using light scattering techniques using commercially and readily available apparatus, such as a Malvern Mastersizer™ instrument. The average droplet size is expressed as the Volume Moment Mean, represented as the D[4,3] mean. In the present invention, the average droplet size is in the range of from 3 to 15 μm, although is preferably in the range of 5 to 10 μm.
Similar light scattering techniques and apparatus can be used to determine the droplet size distribution, and hence the weight %, of droplets with a size of greater than 125 μm based on the volume equivalent sphere diameter. In the invention, the percent of particles having a size of greater than 125 μm is less than 3 wt %. Preferably it is less than 2 wt %, and more preferably less than 1 wt %. In embodiments, less than 0.5 wt % can be achieved.
The dynamic viscosity can also be routinely measured using standard techniques, and equipment such as the Malvern Kinexus™, which measures viscosity at controlled temperature and shear rates. The value is expressed in terms of mPas (cP), and is preferably determined at a shear rate of 20 s−1 and at 50° C., although in one embodiment, the dynamic stability, the shear rate and temperature can each differ by up to ±10%. In the present invention, the value is in the range of from greater than 50 and up to 700 mPas under such conditions, more preferably greater than 100 and up to 700 mPas, more preferably in the range of from 200 to 700 mPas. The dynamic viscosity may be measured after manufacture of the oil-in-water emulsions of the present invention or after storage. The oil-in-water emulsions exhibit dynamic stability of greater than 50 and up to 700 mPas under the above conditions at at least one test point, e.g. after manufacture or after storage for 3 weeks at 50° C., and preferably both after manufacture and after storage for 3 weeks at 50° C. Preferably, the oil-in-water emulsions exhibit dynamic stability of greater than 100 and up to 700 mPas±10% at 50° C.±10% and 20 s−1±10% after manufacture or after storage for 3 weeks at 50° C.
Static stability refers to the stability of the emulsion during storage. This can conveniently be measured by the centrifugation method by determining the amount of material (wt %) that deposits from the oil-in-water emulsion. The method for determining the static stability of an oil-in-water emulsion comprises the steps of:
The centrifuging is typically operated in excess of 1000 g (i.e. g-force), and preferably in the range of from 1000 to 3000 g, for example 1500 to 2500 g. Typically, 2000 g±10% is employed (i.e. 2000 g or in the range of from 1800 to 2200 g).
The temperature is typically in the range of from 40 to 90° C., for example 40 to 60° C., such as 50° C.±10% (i.e. 50° C., or in the range of from 45 to 55° C.).
A typical sample size is in the range of from 1 to 100 mL, for example 5 to 15 mL, e.g. 10 mL±10% (i.e. 10 mL or in the range of from 9 to 11 mL).
A suitable time for centrifugation is from 1 to 60 minutes, for example from 20 to 40 minutes, typically 30 minutes±10% (i.e. 30 minutes or in the range of from 27 to 33 minutes).
Typical conditions include centrifugation at 2000 g for 30 minutes at 50° C., using a sample size of 10 mL.
The static stability is preferably less than 3 wt % residue remaining after centrifugation.
In the oil-in-water emulsion of the present invention, the static stability at 50° C. is such that the residue after centrifugation of a 10 mL sample is less than 5 wt %. Preferably, this quantity is less than 4 wt %, and more preferably less than 3 wt %. In embodiments, a static stability of less than 2.5 wt % can be achieved.
An alternative static stability test is described in U.S. Pat. No. 6,194,472, for example, which involves pouring the emulsion into a 500 mL graduated cylinder, and leaving to stand for 24 hours, after which the hydrocarbon content in each of the top 50 mL and bottom 50 mL is measured, and the difference calculated. This test is qualitative, and does not necessarily provide comparable numerical values. It also takes a long time to complete. The static stability test by centrifugation is advantageous, in that it is rapid, quantitative, and reduces the possibility of degradation or long-term surface wall interactions influencing the results.
Another static stability test is a sieve test for particles greater than 125 μm (120 Mesh), based for example on ASTM tests D4513-85 and D4572-89. An example test (described below) involves passing 100 g of oil-in-water emulsion through a 125 μm sieve, washed with a 2% solution of non-ionic surfactant, such as a nonyl phenol or alkyl ethoxylate, and dried in an oven for 2 hours prior to weighing. Typically, in the compositions according to the present invention, the amount of material captured and remaining on the sieve is preferably less than 3 wt %, more preferably less than 1 wt %, more preferably 0.5 wt % or less. Although this test can provide some information on the extent of larger particles in the emulsion, a “before and after” analysis still has to be conducted over several hours (e.g. 24 hours). In addition, it only provides information on the presence or formation of larger particles, even though smaller droplets may be non-emulsified, and which may settle over longer periods of time.
Dynamic stability is a measure of the stability of the emulsion when under motion or agitation. It can be measured using a Shaker Table test, which employs 100 mg sample, and subjects it to 24 hours of agitation at 3.3 Hz/200 rpm at 40° C. at a stroke setting of 18 mm. Stability is determined by the amount (weight) of material deposited when filtered through a 120 mesh (125 μm) sieve.
U.S. Pat. No. 6,194,472 describes another shaker test, in which 100 g sample is shaken in a Burnell Wrist Action™ Shaker for 24 hours, and then determining the amount of residue remaining on a 50 mesh screen.
Mesh sizes referred to herein are based on US mesh sizes.
Oil Phase
The oil phase of the invention comprises hydrocarbons. Typically, the oil is a source of heavy hydrocarbons, which may have a density slightly lower to significantly higher than water (e.g. 0.95 to 1.15 kg/m3 or 0.95 to 1.25 kg/m3 at 15° C.). The heavy hydrocarbon may have an extremely high viscosity. For example, the viscosity can be up to 300 000 cSt at 100° C. It can employ residues or hydrocarbon sources which have viscosities of 7 cSt or more at 25° C., or 10 cSt or more at 100° C. The invention can also utilise hydrocarbon sources having viscosities of 180 cSt or more at 25° C., and preferably 250 cSt or more at 25° C. The oil-phase hydrocarbons can be sourced from a number of established processes, including:
In one embodiment the oil-in-water emulsion comprises an oil phase which is a hydrocarbon residue, e.g. being sourced from refinery residues with kinematic viscosities of up to 300 000 cSt at 100° C., and preferably above 200 cSt at 100° C., and more preferably above 1 000 cSt at 100° C. Examples of hydrocarbon residues that can be used in the oil-in-water emulsion of the present invention are given in Table 1.
An example hydrocarbon residue that can be used is given in Table 2.
Oil-in-water emulsions according to the invention can typically contain 60% wt or more of the “oil” phase, e.g. the hydrocarbon residue. In embodiments, the emulsion comprises in the range of from 60 to 80 wt % of the oil phase.
Aqueous Phase
The water in the aqueous phase can come from a variety of sources. An example of a water specification that can be used is given in Table 3.
Optionally, the water can be pretreated, for example by filtration and/or deionization. The water can come from a variety of sources, and from number of processes, including;
The water content of the oil-in-water emulsions of the present invention is typically in the range of from 20 to 40 wt %.
Chemical Additives
The oil-in-water emulsion of the present invention comprises a primary surfactant and a polymeric stabilizer and may additionally comprise one or more of the following:
The chemical additives are typically added to the aqueous phase before mixing with the oil phase when preparing the oil-in-water emulsion of the present invention.
The chemical additives can be provided separately, or two or more additives can be provided in the form of a pre-prepared chemical additive package.
Advantageously, the chemistry of the additives is taken into consideration to ensure they do not contribute to any detrimental performance during use, for example as a fuel, such as avoiding negative impact on health and the environment, disadvantageous corrosion both before and post-combustion, and any increased burden of undesirable combustion emissions.
Primary Surfactants
The oil-in-water emulsion of the invention comprises at least one primary surfactant, which is typically added to the aqueous phase before being mixed with the oil phase when preparing the oil-in-water emulsion.
The primary surfactant is typically present in an amount ranging from 0.05 to 0.6% wt of the oil-in-water emulsion. The aim of the primary surfactant is to act as an emulsifier, to stabilise the oil phase droplets in the aqueous phase. A range of from 0.05 to 0.5 wt % primary surfactant can be used, for example 0.08 to 0.4 wt %.
A number of primary surfactants can be employed. They can include non-ionic, anionic, amphoteric, zwitterionic and cationic surfactants. There can be one primary surfactant or more than one primary surfactant. In embodiments, at least one primary surfactant, optionally all the primary surfactants, is selected from one or more of the following:
where;
where;
where;
one or two of the groups R1 to R7 are each selected from aliphatic groups having from 8 to 22 carbon atoms
The aliphatic groups mentioned in the formulae above, including those containing a carbonyl group, can optionally be substituted, typically with one or more, for example from 1 to 3, substituents which are independently selected from hydroxyl, C1-3 alkyl, C1-3 alkoxy, or C1-3 hydroxyalkyl. Preferably, there are no substituents on the aliphatic groups. Each aliphatic group can be saturated, or can comprise double or triple carbon-carbon bonds, for example up to 6 double bonds, for example up to 3 double bonds.
Preferably, R1 has a formula C14-20H24-41, or C(O)C13-19H22-39. More preferably it has a formula C14-20H24-41.
Preferably, each R2 and R3 is independently selected from CH3, H and CH2CH2OH.
Preferably, each R4 is independently selected from CH3 and H.
Examples of fatty alkyl amines include:
In the above, the anion A is preferably selected from those anions which bind more strongly to the quaternary amine than carbonate. Examples include halide, particularly Cl−, and organic anions such as formate (HCOO−), acetate (CH3COO−) and methane sulfonate (CH3SO3−).
In the above, the group “EO” is an ethoxylate group (—CH2CH2O—). The ethoxylate group (or polyether group for more than one linked ethoxylate group) is typically terminated by H, i.e. —CH2CH2OH.
In embodiments, the primary surfactant is selected from one or more fatty alkyl di-, tri- and tetra-amines, ethoxylated fatty alkyl mono-, di- and tri-amines, and quaternary fatty alkyl amines.
In further embodiments, the primary surfactant is selected from one or more fatty alkyl diamines, fatty alkyl tetra-amines, ethoxylated fatty alkyl diamines, and quaternary fatty alkyl amines. Examples include fatty alkyl tripropylenetetramine, such as tallow tripropylenetetramine, fatty alkyl propylene diamines, oleyldiamine ethoxylate.
The term “fatty alkyl” includes not only saturated groups (i.e. C12 to C24 alkyl groups), but also partially unsaturated C12 to C24 groups (i.e. C12 to C24 alkenyl groups), for example having up to six C═C double bonds. Preferred fatty alkyl groups have no more than 3 double bonds. Examples of fatty alkyl groups include oleyl (C18, 1 double bond), and other groups associated with tallow, e.g. palmityl (C16, 0 double bonds), stearyl (C18, no double bonds), myristyl (C14, no double bonds), palmitoleyl (C16, 1 double bond), linoleyl (C18, 2 double bonds) and linolenyl (C18, 3 double bonds).
Secondary Surfactant
The oil-in-water emulsion preferably, comprises a secondary surfactant. Typical amounts present in the oil-in-water emulsion are in the range of from 0 to 2 wt %, and preferably greater than 0.3 wt %, for example at least 0.4 wt %.
Secondary surfactants serve to improve dynamic stability of the resulting oil-in water emulsion, to ensure they remain stable during handling and use. This is advantageous for fuel applications, and particularly for marine fuel applications where the fuel handling conditions are relatively severe in terms of pumping, shearing and large changes in pressure, and also where the fuel is subject to significant motion over extended periods of time.
They can include non-ionic, anionic, amphoteric, zwitterionic and cationic surfactants.
Typically secondary surfactants have larger hydrophilic groups compared to the primary surfactants, and thereby impart a degree of steric stabilisation into the emulsion system. There can be one or more than one secondary surfactant. At least one of the secondary surfactants, optionally all, is preferably selected from one or more lignin amines.
Particularly preferred lignin amines are made by a Mannich reaction, for example between lignin, formaldehyde and a secondary amine, according to the formula;
LR′+CH2O+R2NH→LCH2NR2+R′OH
In the above formula, L represents lignin, and R′ is a displaceable hydrogen or a cation such as an alkali metal (e.g. sodium) on the lignin. Each R on the amine can be independently selected from an optionally substituted aliphatic group having from 1 to 6 carbon atoms. Dimethylamine is an example of a secondary amine which can be used. Although formaldehyde is typically used, aldehydes other than formaldehyde can be employed, for example aldehydes with an aliphatic group having from 1 to 6 carbon atoms.
Optional substituents on the aliphatic group are the same as those identified above for the various exemplary primary surfactants.
The lignin can be used in a salt form, for example in a form where displaceable hydrogens are at least in part replaced with an alkali metal ion, such as sodium.
Production of lignin amines is described for example in U.S. Pat. Nos. 2,709,696, 2,863,780 and 4,781,840.
Polymeric Stabiliser
One or more polymeric stabilisers are added to the aqueous phase when preparing the oil-in-water emulsion of the present invention. They are preferably included in amounts of up to 0.25 wt % of the oil-in-water emulsion. In embodiments, they are present in amounts in the range of from 0.03 to 0.08 wt %.
Polymeric stabilising and flow improvement agents are used to improve static stability in storage by compensating for the density differential between the residue and aqueous phase. They can also modify the viscosity characteristics of the emulsion.
The polymer stabilising additive can form a weakly ‘gelled’ structure in the aqueous additive-containing phase, which helps to improve static stability of the oil-in-water emulsion by holding the hydrocarbon residue droplets apart, preventing sedimentation during static storage conditions. The weak gel structure can also impart low resistance or yield to applied stress to ensure suitable low viscosity characteristics of the emulsion, for example during pumping and handling. This behaviour can also be recoverable, for example once the oil-in-water emulsion fuel is pumped into a tank it can recover its static stability characteristics. The polymer additive can help to achieve this by interacting with the other additives in the formulation through entanglement and bonding mechanisms, forming a molecularly structured gel.
There can be one or more than one polymeric stabiliser and flow improving agent. At least one polymeric stabiliser and flow improving agent is selected from polymers containing monomers comprising dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate quaternary salts, or dialkylaminoalkylacrylamides or methacrylamides and their quaternary salts.
Examples of such polymeric stabilisers and flow improving agents include cationic polymers comprising at least one cationic monomer selected from the group of dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate quaternary salts such as dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt, or dialkylaminoalkylacrylamides or methacrylamides and their quaternary salts such as acrylamidopropyltrimethylammonium chloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide methyl saulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropyl acrylamide hydrochloride salt, methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt, diethylaminoethylacrylate, diethylaminoethylmethacrylate, diallyldimethylammonium chloride, and diallyldimethylammonium chloride.
Additional polymeric stabilisers and flow improving agents may be selected from one or more alkyl hydroxyalkyl cellulose ethers (water soluble), preferably having an alkyl group with 1 to 3 carbon atoms, and an hydroxyalkyl group (e.g., hydroxyethyl or hydroxypropyl), where;
Examples include methyl ethyl hydroxyethyl cellulose ether (water soluble), preferably having
DS represents the degree of substitution of the specified component, and MS represents the extent of molar substitution of the specified component.
Further examples of additional polymeric stabilisers include those where (in the formula represented below) R is H, CH3 and/or [CH2CH2O]nH.
Other examples of additional polymeric stabiliser and flow improvement agent can include guar gum, starch and starch derivatives, hydroxy ethyl cellulose, and ethyl hydroxy ethyl cellulose.
Acid
An acid, i.e. a Brønsted acid, is often used to activate the primary surfactant. The aqueous phase preferably has a pH in the range of pH 2 to 6, and more preferably in the range 2 to 4.5 or 3 to 4.5. This also generally corresponds to the pH of the resulting oil-in-water emulsion.
Acids can be organic or inorganic. Inorganic acids include hydrochloric acid (HCl), sulfuric acid (H2SO4) and nitric acid (HNO3). Organic acids comprise at least one C—H bond, examples of which include methanesulfonic acid, formic acid, acetic acid, citric acid, and benzoic acid. There can be one or more than one acid.
The acid should preferably not be detrimental to the operational or environmental performance of the oil-in-water emulsion fuel, nor be incompatible with any other components of the oil-in-water emulsion, for example the other chemical additives used. In marine fuel applications, for example, inorganic acids are often prohibited, hence organic acids are preferred.
Where organic acids are used, at least one of which (optionally all) is preferably selected from methanesulfonic acid, formic acid, acetic acid, citric acid, and benzoic acid. Preferably at least one (optionally all) of the acids are selected from formic acid and methanesulfonic acid.
Acids that yield a divalent anion (such as sulfuric acid) can act to block the interfacial action of ionic primary and secondary surfactants, hence acids that yield a monovalent anion are preferred.
Oil-in-Water Emulsions as Fuels
In embodiments, an oil-in-water emulsion fuel according to the invention comprises one, more than one, or all of the characteristics defined in Table 4.
up to 0.25
Oil-in-water emulsion fuels according to the invention have properties that enable them to be utilised within existing combustion engines or boilers, for example by being:
The oil-in-water emulsion of the invention can be used as a fuel, or as a component of a fuel composition. It can be used in heating oil applications, for example in boilers, which may otherwise use fuels such as kerosene or gas oil. It can also be used in engines, typically diesel engines that use fuels such as diesel fuel or bunker fuel. The oil-in-water emulsion fuels of the invention are particularly suited for marine vessel applications, where high static and dynamic stabilities are required.
Preparation of an Oil-in-Water Emulsion
The oil-in-water emulsion can be prepared by a process in which water and the one or more chemical additives are mixed to form the aqueous phase; heating a hydrocarbon-containing oil; and blending the hydrocarbon-containing oil and the aqueous phase to form an oil-in-water emulsion.
It is preferred that the chemical additives form an aqueous solution when mixed with water, although a suspension or emulsion can be tolerated provided there is sufficient mixing with the hydrocarbon oil-containing phase to ensure a stable oil-in-water emulsion results.
Examples of the hydrocarbon-containing oil are provided above. It is preferably heated to a temperature sufficient to reduce its viscosity to below 500 cSt, for example in the range of from 100 to 500 cSt or 200 to 500 cSt.
Preferably, it is heated to a temperature such that, when mixing with the aqueous phase, the resulting temperature at the oil-water interface will be such that the viscosity of the oil phase is less than 10000 cSt. This will depend on the heat capacities of the aqueous phase (which incorporates the chemical additives) and the hydrocarbon-containing oil, and also their relative concentrations.
The relationship between the temperature at the interface and the initial temperatures of the aqueous and oil phases can be expressed by the following equation:
In the above equation:
The temperature of the oil phase (Toil) before mixing is preferably such that the hydrocarbon-containing oil viscosity is in the range of from 200-500 cSt. Although this is dependent on the source of hydrocarbons, it is typically in a range of from 110 to 230° C.
The temperature at the oil/water interface after mixing (Ti) is preferably such that the viscosity of the hydrocarbon-containing oil is less than 10 000 cSt. This temperature is preferably less than the boiling point of the aqueous phase, and also a temperature at which the thermal and phase stability of the chemical additives is preserved. Typically, this temperature is in the range of from 70 to 150° C., for example from 80 to 120° C.
The temperature of the aqueous phase before mixing (Taq) is selected according to the above requirements of the Ti and Toil temperatures. Typically, it is in the range of from 30 to 95° C., for example from 50 to 90° C., or 50 to 70° C.
The relative weight ratio of the hydrocarbon-containing oil relative to the aqueous phase are typically in a range of from 5:1 to 1:1, and preferably in a range of from 4:1 to 3:2 or from 4:1 to 2:1.
Mixing to form the emulsion can be achieved using apparatus and technology known to a skilled person, such as high shear mixing apparatus.
In one embodiment of the invention, two separate and different emulsions are separately prepared and mixed to form a composite oil-in-water emulsion, which enables further control over the properties of the desired oil-in-water emulsion to be achieved.
A non-limiting example schematic of a process for preparing an oil-in-water emulsion according to the invention is given in
The area designated (2) represents the source of suitable water.
In the area designated (3), the material from the hydrocarbon-containing oil source (1) may be cooled by a medium to a suitable temperature for storage as required and further temperature control as required, to achieve a viscosity of between 250 to 500 cSt, for direct introduction into the emulsion preparation unit (4). Water (2) is first heated (typically to within the range 50 to 90° C.) in a heat exchanger (5) that is also utilised for cooling the final emulsion product (typically to less than 90° C.) along with supplementary cooling (typically to less than 60° C.) to enable easier handling.
In area (6), a polymer stabiliser is mixed into the aqueous phase, followed by the further addition (7) of additional chemical additives (including one or more of the primary surfactant and secondary surfactant), and optionally also a suitable acid if pH adjustment is required. The chemical additives can be varied if and as required to achieve an emulsion fuel with the required specification and performance criteria.
The chemical additives used preferably do not contain any components or impurities that can negatively affect the use of the resulting emulsion as a fuel. Therefore, preferably, they contribute no more than 50 ppm of halogenated compounds and no more than 100 ppm of alkali metals in the final emulsion fuel specification.
The aqueous phase containing the chemical additives passes through a tank/vessel (8), which provides sufficient residence time for any added acid to fully activate other chemical additives, for example the primary surfactant. Both the aqueous phase and the hydrocarbon-containing oil phase are then introduced into a high-shear colloidal mill (9), the speed of which is adjusted to intimately mix the components. One or more colloidal mills may be employed (10) within the manufacturing process, depending on the number of required emulsion component streams of differing properties (i.e., one for the manufacture of a single component emulsion fuel, or two or more required for the manufacture of a composite, multi-component emulsion fuel). If more than one component is manufactured, then the differing components can be passed through an in-line blender (11) or mixed downstream at the required ratios to achieve the correct properties of the final oil-in-water emulsion fuel. In this way, the characteristics of the final required droplet size distribution, hydrocarbon/water phase ratio (i.e. energy density) and viscosity/rheological characteristics can be effectively controlled.
After production, the emulsion fuel may be stored (12) for subsequent transport and supply for use as a fuel (13).
Process of hydrocarbon residue evaluation, formulation and emulsification
The formulation of the oil-in-water emulsion can be optimised, depending on the nature of the hydrocarbon-containing oil, typically a hydrocarbon residue such as one of those listed in Table 1.
The chemical additives and their concentrations that can be used for different hydrocarbon residues can be optimised by a skilled person, and preferably the components are chosen so as to ensure compliance with any associated operational, performance or legislative requirements.
Taking an example of an oil-in-water emulsion fuel, the formulation can be optimised by hydrocarbon analytical testing, followed by a series of laboratory and pilot scale emulsification and emulsion handling tests. The objectives of these tests are to:
The target specification of the resulting oil-in-water emulsion fuel at each stage is based on correlation with established (acceptable) performance criteria of emulsion fuels during full application (i.e., behaviour during storage, supply and logistics handling, as well as during end-use engine operation). A typical example of an oil-in-water emulsion fuel specification is given in Table 5.
In further embodiments, the oil-in-water emulsion of the invention can have the following characteristics, which is suitable for use as a marine fuel:
Examples of test methods that can be used to measure the above properties are provided in Table 5. The droplet size measurements can be measured using available equipment, such as a Malvern particle size analyser (e.g. using light diffraction methods). The viscosity can be measured using a coaxial cylinder viscometer, and the sieve test can be carried out according to methods such as ASTM D 4513-85, D 4572-89 and ASTMD244/ASTM D6933.
Optionally, the oil-in-water emulsion can also have the properties set out in Table 6.
Quality Assurance
Static stability is a term used to describe the stability that an emulsion requires to remain integral under conditions where there is no externally applied force except for gravity (i.e., stability under static storage conditions over time).
Dynamic stability is a term used to describe the stability an emulsion requires to ensure it can be handled as required within the application for which it is designed. This includes being stable when pumped, heated, and used within specific fuel handling components such as pressure control valves, flow meters, fuel injection equipment, etc. This differs from static stability in that it involves the external impartation of energy to the emulsion system (which includes mechanical energy such as shearing and turbulent flow forces) and heat energy (e.g., heating within heat exchangers). As such the oil-in-water emulsion fuel requires a significantly higher degree of dynamic stability than that needed under static conditions.
The physical and chemical properties of a candidate hydrocarbon residue influence the properties of the resulting emulsions, and hence influence the action and efficiency of the chemical additives used.
Therefore the formulation derived for each residue (i.e., the chemical additives and production process parameters employed for each candidate hydrocarbon residue) needs to ensure that the oil-in-water emulsion fuel has the required droplet size distribution, rheological/hydraulic properties, and both static and dynamic stability. It is also preferred that the resulting oil-in-water emulsion fuel can be blended safely with other emulsion fuels according to the present invention, and/or that are made according to the process of the present invention, but which may have an alternative formulation.
Determination of a desired formulation can be achieved by undertaking a series of matrix screening tests and subsequent optimisation defined within, whereby a sample of a candidate hydrocarbon residue feedstock is used to manufacture a series of emulsions using different process conditions, whilst varying the chemical additives and concentrations to optimise the overall emulsion fuel formulation. The fundamental characteristics of each emulsion batch can be analysed.
One way to characterise the oil in water emulsion is to determine the Droplet Size Distribution (DSD); which provides the distribution profile, median, mean, and span of the hydrocarbon residue once it has been emulsified into the aqueous phase.
The DSD is normally represented as the percentage droplet volume population against size range, from which a number of statistical parameters can be derived. Two common ways of expressing the droplet size distribution include volume or mass moment mean, expressed as D[4,3], and the volume median, which is represented as D[v, 0.5] or D50. The “span” is the difference between the largest and smallest droplets/particles. For practical purposes, it is calculated from D90−D10, where Dx represents the droplet size at which x % of the droplets have that size. The dimensionless unit, relative span, is often calculated as (D90−D10)/D50.
When interpreting and evaluating the response of the hydrocarbon residue emulsification to the formulation applied, the differences between these two statistical averages can be advantageously used, because each provides different insights into the droplet size distribution. The volume median droplet size is the size mid-point of the total size distribution or span. The volume mean droplet size is the statistical average of the whole volume distribution, and as such is more sensitive to the presence of droplets with larger size. Accordingly, a decrease in the volume mean droplet size is normally associated with a decrease in the droplet size distribution span, whereas the droplet size distribution can vary in span and the volume median may stay the same. An example of an oil-in-water emulsion fuel droplet size distribution is shown in
An analytical instrument such as a MALVERN Mastersizer™ can be used to determine the DSD of an oil-in-water emulsion fuel (in the case of MALVERN™ instruments, the size range distribution is determined by standard laser diffraction techniques). In an example analysis, 2.5 ml of 2M formic acid and a 5-8% wt solution of a non-ionic surfactant (e.g., a nonyl phenol or alkyl ethoxylate) are added to 500 ml of clean, finely filtered water. Approximately 0.5 ml of the oil-in-water emulsion fuel sample is mixed with 5 ml of a 2% wt solution of a stabilising agent (such as a fatty alcohol ethoxylate or fatty alkyl diamine) and dispersed under ambient conditions. The purpose of this pre-mixing with stabilising agent is to ensure that the emulsion particle/droplet sizes of the oil-in-water emulsion remain unaltered during the remainder of the analysis process, which involves adding drops of this dispersion to the recirculated 500 ml formic acid/surfactant solution previously prepared until an acceptable obscuration value for the Micro Mastersizer™ is achieved. Typically a measurement cycle of 5 repeats with 2000 sweeps each is then performed to obtain the DSD analysis. Alternative methods for determining droplet size distribution are also available, such as that using a Coulter Counter instrument (which employs the technique of measuring changes in the electrical resistance of a dilute emulsion when a potential difference is applied and the sample is drawn through a microchannel) or by optical image analysis (whereby a microscopic recorded image of the emulsion is analysed using computer algorithm). Similar sample preparation protocols can be used.
The combination of the volume mean droplet size (D[4,3]) range of from 3 to 15 μm and the proportion of droplets having a size of greater than 125 μm being less than 3 wt %, helps to achieve the static and dynamic stabilities required.
Another parameter that can be used to characterise the oil-in-water emulsion is viscosity (typically measured over controlled shear rate and temperature conditions of 10 to 150 s−1 at 50° C.). Oil-in-water emulsions according to the invention can typically contain a high (greater than 60% wt) concentration of hydrocarbon residue. Factors affecting the resulting rheology of such emulsions include;
Such concentrated emulsions normally display non-Newtonian behaviour, whereby the viscosity of the emulsion at any given temperature will vary with the applied level of shear. It is possible to model this non-Newtonian behaviour (e.g., using the Power Law model) and hence quantify and characterise the emulsions' rheological behaviour. Such emulsions can also display time dependent rheological behaviour (such as thixotropy) whereby the viscosity will be influenced by how long shear is applied. This can be a fully or semi-recoverable phenomenon, whereby the viscosity will return to its initial value in part or in full over time.
All of these rheological characteristics can be influenced by the type of hydrocarbon residue being used, and the chemical additives applied.
An analytical instrument such as a MALVERN KINEXUS™ or a HAAKE VT550™ Rheometer can be used to determine the rheological properties (including viscosity) of an oil-in-water emulsion fuel. An example of such a measurement includes the use of a parallel plate configuration (using a 40 mm rotational element, set with a 1 mm gap), in which a sample of temperature controlled (e.g. 50° C.) oil-in-water emulsion fuel sample is subjected to shear cycles, ascending and descending between 15-150 s−1. The corresponding viscosity values, for example at 20 and 100 s−1 on the descending cycle, can then be determined.
Maintaining the viscosity range of greater than 100 to 700 mPas (at 20 s−1 and 50° C.), in addition to maintaining the droplet size distribution characteristics mentioned above, helps to achieve the required dynamic and static stability of the oil-in-water emulsion.
Sedimentation
Static stability can be measured by determining sedimentation during centrifugation. In an example of an analysis, a 10 ml emulsion fuel sample is subjected to 2000 g at 50° C. for 30 mins, using a lab scale centrifuge (e.g., Hettich™ Universal 1200). The sample tube is then carefully washed with a 2% solution of a non-ionic surfactant (e.g., a nonyl phenol or alkyl ethoxylate), to remove non-compacted emulsion from the sediment. The washed tubes are then dried in an oven at 105° C. for 2 hours prior to weighing, so that the % wt. of sediment can be calculated. Alternatively, sedimentation may be assessed by a visual inspection after a period of storage, suitably 3 weeks.
Sieve Testing
Sieve testing can provide a measure of residue droplets greater than 125 μm in the oil-in-water emulsion, thereby providing an indication of emulsion stability post production. The method can be based on the standard ASTM test methods D4513-85, D4572-89 and D6933, and gives a measure of the amount of free oil residue/non-emulsified material present in the sample. A known weight of approximately 100 g is washed though a 125 μm sieve using a 2% solution of a non-ionic surfactant (e.g., a nonyl phenol or alkyl ethoxylate). The sieve is then dried in an oven at 105° C. for 2 hours prior to weighing, so that the % wt. of retained material can be calculated.
Optimisation
A method for optimising the oil-in-water emulsion formulation can include various sequential stages as follows;
Accordingly, a number of experimental test protocols have been developed at laboratory and pilot scale to evaluate the characteristics and stability of the oil-in-water emulsion fuel formulations over a range of representative (typical) operational conditions that would be experienced when used as a marine fuel.
Hydrocarbon Residue Sample Analysis
A hydrocarbon residue can be analysed for the properties indicated in Table 7.
This initial analysis is primarily to establish if the hydrocarbon residue meets the requirements of a feedstock for oil-in-water emulsion fuel production, and to provide information on key composition parameters that may impact the chemical formulation required.
The Simulated Distillation (SIMDIST), water and flash point determination give an indication of the general composition of the residue.
The ash content and elemental analysis of the residue, as well as the calorific value determination, help to evaluate the potential combustion performance and resulting environmental emissions.
Aluminium and silica in a fuel can act as abrasives, hence determination of their content is often a specific requirement if the resulting emulsion fuel is to be used within the marine industry, to ensure the integrity of engine operations.
A higher pour point value can indicate that a hydrocarbon residue is more paraffinic (waxy) in composition, which influences the chemical additives to be used in producing an optimum oil-in-water emulsion fuel. For example, for unbranched paraffinic (waxy) hydrocarbons, it is generally useful to employ a primary surfactant having unbranched paraffinic (waxy) hydrocarbon chains. Further techniques such as low temperature rheological analysis, microscopy, etc., can also assist in determining the potential waxy nature of the sample.
Relatively high TAN/TBN values are an indication of an increased level of heterogeneous/ionic chemical functionality in the chemical composition of the hydrocarbon residue, which is often associated with higher asphaltenes content. As a number of the chemical additives used are ionic in nature, the level of indigenous ionic species present in the residue can affect the optimum combination and concentration of additive chemicals used in the oil-in-water emulsion fuel formulation.
Higher viscosities indicate a need for elevated temperatures for effective emulsification.
Higher densities indicate a need for the use of (or increased use of) polymeric stabiliser agents in the emulsion formulation to offset the density difference between the hydrocarbon residue and aqueous phases.
A high level of alkaline metals (e.g., Na, Ca) and/or halogens (e.g., Cl, which is an undesirable contaminant for fuel combustion emissions) could indicate the presence of salts in the hydrocarbon residue. The presence of such salts can lead to an undesirable osmotic droplet swelling (thickening) process, resulting in a significant increase in viscosity over time. This can be corrected by balancing the ionic content of the hydrocarbon residue and aqueous phases.
Matrix Formulation Screening
‘Matrix’ formulation testing can be used to optimise the oil-in-water emulsion formulation. It is an iterative process. As all the parameters being evaluated are interdependent, optimisation of the emulsification formulation requires determination of the correct balance of all the parameters and variables involved. In this way the response of the candidate hydrocarbon residue to the different process conditions and additives used is evaluated against the target specification. A guideline to this approach to determine the optimum formulation follows, and is illustrated in
Initial Hydrocarbon Residue Emulsification
The first step in the evaluation of the potential to emulsify a refinery residue is to calculate the required temperature to yield a hydrocarbon residue viscosity of 300 to 500 cSt. The temperature of the water/additive phase required is then calculated, which would result in a hydrocarbon residue/water interfacial temperature at which the residue viscosity is less than 10,000 cSt (after correcting for phase ratio and relevant heat capacities), while ensuring the other temperature requirements of the water (such as to avoid boiling, thermal and phase stability of the additives) are met.
The hydrocarbon residue viscosity at 100° C.=1450 cSt. When heated to 130° C. this reduces to 260 cSt. Heating the additive aqueous solution to 55° C. will result in an estimated interfacial temperature of 95° C. (with a hydrocarbon residue content of 70%, taking into consideration hydrocarbon residue/aqueous phase heat capacity values), which corresponds to a hydrocarbon residue viscosity of approximately 2,000 cSt at the residue/water interface.
Hydrocarbon residue viscosity at 100° C.=14670 cSt, when heated to 155° C. this reduces to 400 cSt. Heating the additive solution to 70° C. will result in an estimated interfacial temperature of 115° C. (with a hydrocarbon residue content of 70%, taking into consideration hydrocarbon residue/aqueous phase heat capacity values), which corresponds to a residue viscosity of approximately 4,300 cSt at the residue/water interface.
With these estimated residue and water phase temperatures, a series of emulsion production tests at laboratory scale can be undertaken using a series of generic ‘benchmark’ formulations and conditions (e.g. as shown in Table 8) that represent a starting point for further evaluation and optimisation.
For the preparation of the aqueous phase containing the additives, the following procedure can be used:
The volume of water to be used for the preparation of the test formulation is heated to between 50 to 70° C.
The required amount of polymeric stabiliser is added to the hot water and mixed until completely dissolved.
Using the organic acid, the pH of the solution is adjusted to be within the range 3 to 4.5.
At this stage of the preparation, the required amount of the secondary surfactant (if included in the formulation) is added and the water phase is mixed to ensure the additives are completely dissolved.
This is followed by the addition of the required amount of the primary surfactant and the water phase is mixed while the pH is adjusted using further organic acid until the required pH is achieved. This mixing continues until all the additives are completely dissolved and activated.
The aqueous phase is then transferred to a laboratory scale colloidal mill system (such as the DEMINOTECH™ SEP-0.3R Emulsion Research Plant which is capable of producing emulsions at a maximum capacity of 350 l/h, see
The test emulsion can then be prepared using the following procedure;
Flow of cooling water to the system outlet heat exchanger is started.
Pumping of the prepared water phase through the system via the colloidal mill is started.
The mill is switched on and a suitable mid-range speed selected (e.g., 9000 rpm for the SEP-0.3R system). The back pressure on the system is adjusted to approximately 2 bar.
Once steady flows and temperatures are achieved, the hydrocarbon residue pump is started at a low flow rate, and steadily increased until the required flow rate is achieved (e.g., to give a final hydrocarbon residue content in the emulsion). The backpressure of the system is adjusted to maintain a level of approximately 2 bar. The flow rate of water to the final heat exchanger is adjusted to ensure the emulsion is flowing at the outlet of the system at a temperature less than 90° C.
Once steady state operation of the system is achieved (i.e., in terms of flow rates, temperatures and pressures) a sample of the oil-in-water emulsion is taken for testing and analysis.
To stop production pumping of the residue through the system is stopped, and flow of the water phase maintained to flush the system through.
For the further evaluation and optimisation process the operating procedure of the laboratory scale colloidal mill system will be the same, with the required process and formulation variables being adjusted accordingly.
The principle of the production procedure for the manufacture of an oil-in-water emulsion fuel on a large scale using a continuous in-line plant will be the same as described above.
The analysis of these test emulsion preparations provides an indication as to the potential of a candidate hydrocarbon residue to be used as a feedstock for the production of the oil-in-water emulsion fuel by the process described using ‘generic’ formulation and conditions. Based on the results of these tests, further formulation matrix testing can be carried out if necessary to fine-tune and optimise the response of the residue to emulsification and subsequent stability testing, focusing on specific aspects and variables.
Selection of Primary Surfactant
In the context of an oil/water emulsion system, surfactants can generally be described as molecules that have hydrophilic (water liking) and hydrophobic (oil liking) components. The role of the primary surfactant is to reduce the surface tension at the hydrocarbon residue/water interface such that the surface can be broken up to form droplets. The primary surfactant acts to stabilise the droplet (e.g., by charge density in the case of ionic surfactants) and prevent them from re-coalescing. In order to do this, the hydrophobic part of the primary surfactant molecule must have sufficient affinity for the hydrocarbon residue in order to be fixed (i.e., anchored) at the hydrocarbon residue/water interface. This will depend on the characteristics of the surfactant and the residue alike.
Use of an effective primary surfactant that has sufficient affinity and stabilising properties for the residue results in an emulsion with a smaller average droplet size and a narrower droplet size distribution range. This acts to increase the viscosity of the resulting emulsion, due to its geometrical effect on droplet packing within the emulsion system. The ability to have effective control over droplet size distribution during the emulsification process by influencing, for example, the concentration and pH of the primary surfactant is also a desirable property. In this way, a balance between efficiency of emulsification and required droplet size/rheological properties can be achieved with the correct choice of primary surfactant type.
Examples of the effect of primary surfactant on droplet size distribution and viscosity of the resulting fuel emulsion characteristics are given in
The suitability of primary surfactants is based at this stage on achieving the manufacture of an oil-in-water emulsion fuel with an average droplet size less than 25 μm (D[4,3]), a distribution that has a 90% droplet distribution less than 50 μm (D[v, 0,5]) and a relative span less than 3.5, whilst maintaining a viscosity less than 500 mPas (at 20 s−1, 50° C.), using the method for measuring droplet size distributions given above. Further reduction of viscosity can be achieved by other parameters evaluated at a later stage in formulation matrix testing.
To start the process of optimising the oil-in-water emulsion fuel formulation, testing of the primary surfactants is carried out with an initial concentration range of 0.10 to 0.60% wt adjusted to a pH value of 3 to 4.5, without the addition of the secondary surfactant at this stage, since the influence of this additive component is optimised in a later stage. Any polymeric stabiliser is included, the estimated concentration range of which is be based on the density of the hydrocarbon residue. The emulsification and resulting emulsion droplet size distribution can be varied to achieve the required range, for example by;
Any primary surfactant failing to produce an oil-in-water emulsion or that forms an oil-in-water emulsion that does not show the above variations in viscosity with mill speed or primary surfactant concentration, is discarded at this stage of the formulation tests.
Optimisation of Formulation pH
The next parameter to be optimised is the pH of the aqueous phase during manufacture. A further series of formulation matrix tests is undertaken using the suitable primary surfactants, and varying both the concentration of the surfactant and the addition of acid being tested to achieve a range of pH values between pH 2 and 6. The analysis of the manufactured test batches can include droplet size distribution, viscosity, sedimentation, sieve test and shake table test as indicated above.
The optimum pH is the value at which the lowest average droplet size and viscosity can be achieved that fall within the limits according to the invention. At the same time, static stability must be acceptable as determined by sedimentation, sieve test and shake table results over a nominated period of time (e.g., four weeks at this stage of the evaluation).
Polymeric stabilising and flow improving agent
The selection and use of a polymeric stabilising and flow improving agent is based on its interactions with the other chemical additives. The polymeric agent has the potential to influence droplet size distribution, improve (lower) the viscosity of the final oil-in-water emulsion and enhance the stability of the fuel. This is achieved by changing the density differential between the hydrocarbon and aqueous phases and through the formation of a low yield gel structure as indicated earlier. Introduction of the secondary surfactant
Once the selection and basic behaviour of the primary surfactant with the polymeric agent is established, a further series of formulation tests are undertaken with the inclusion of secondary surfactant if required, and at a concentration within the range indicated in Table 4 or Table 8.
The role of the secondary surfactants is to provide a high degree of dynamic stability. Its inclusion in the formulation is usually required, for example, when the emulsion fuel is intended for use in engines (e.g., for propulsion in ships), where the fuel handling conditions are more severe in terms of pumping, shearing and large changes in pressure.
Typically secondary surfactants have a larger hydrophilic group, and will thereby impart a degree of steric stabilisation into the emulsion system. The secondary and primary surfactants compete for the interface during the emulsification process; which will be influenced by their relative concentrations. Secondary surfactants are not as efficient as an emulsifier as the primary surfactant, so their interfacial displacement of the primary surfactant will result in a tendency to broaden the emulsion droplet size distribution (which will also have the effect of lowering the viscosity of the system). Again, the balance between the components of the required formulation and final emulsion fuel characteristics can be optimised.
Further Optimisation of Temperatures and Mixing (Mill) Speed
With the presence of the primary, and the optional secondary surfactants and optional polymeric stabiliser, a series of matrix formulation tests can be undertaken to fine-tune the balance between the hydrocarbon residue and aqueous phase temperatures during the emulsification process at the optimum identified pH range.
The optimum mixer or milling speed can be determined at this stage, since with increased speed more energy is imparted into the emulsion system during manufacture which will tend to decrease the average droplet size and distribution span, thereby increasing viscosity.
Evaluation of Optimum Emulsion Residue Content
The predominant influence of the hydrocarbon residue content on an oil-in-water emulsion will be on viscosity. As the internal phase of the emulsion (i.e., the hydrocarbon residue content) is increased, the viscosity will also increase, particularly at concentrations greater than 60 wt %.
It is preferred to have as much hydrocarbon residue in the emulsion fuel as possible so as to maximise its energy content, while still retaining the other required characteristics to ensure a stable emulsion.
Optimisation of Emulsion Droplet Size Packing Density
Optimisation of the packing density of droplets using composite emulsion technology can reduce viscosity. A composite emulsion is one that is manufactured from two or more component emulsions of differing droplet size distributions. By their correct combination, it is possible to get improved packing of smaller droplets with larger ones allowing either a decrease in viscosity for a given dispersed (hydrocarbon residue) phase or an increase in the hydrocarbon residue (i.e., energy) content without significantly increasing viscosity. This can arise due from a reduced tendency for inter-droplet impaction and deformation during flow, leading to a reduction in viscosity. This is another factor that can be used in the formulation of emulsion fuels to obtain the best optimisation of required characteristics.
Laboratory and Pilot Scale Dynamic (Handling) Stability Testing
Candidate formulations resulting from the matrix screening and static stability requirement in the specification can be subjected to further dynamic stability testing.
Dynamic stability is important because an emulsion fuel can be subjected to heating as well as high shearing and turbulence during pumping and transportation.
A number of devices can be used to measure dynamic stability (such as controlled speed mixers or rheometers/viscometers) that can impart controlled shear, under temperature controlled conditions, to a sample of an oil-in-water emulsion fuel. Such test conditions are used to make both qualitative and quantitative judgements of the change in emulsion fuel characteristics, particularly those relating to changes in droplet size distribution.
Another example of a laboratory based method for the evaluation of dynamic stability is the Shaker Table test. The test gives an assessment of static/dynamic stability by measuring the comparative amount of residue droplets/particles greater than 125 μm in the bulk emulsion after a 100 mg sample of the emulsion is subjected to a controlled amount of agitation for 24 hours at fixed temperature (40° C.), shaking frequency (3.3 Hz/200 rpm) and shaking stroke setting (18 mm) on a shake table apparatus such as the JulaBo SW-20C.
Example oil-in-water emulsions of the invention were prepared by the process described above and were visually assessed for sedimentation after 3 weeks of storage at 50° C. Results are shown in Table 9.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1707556 | May 2017 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2018/051263 | 5/10/2018 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/206963 | 11/15/2018 | WO | A |
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| Number | Date | Country | |
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| 20210032554 A1 | Feb 2021 | US |
