Low viscosity stable mixtures of coal and fuel oil containing alcohol

A stable homogeneous liquid fuel composition comprising a petroleum residual oil having a viscosity at room temperature of 1-2.5 poises, an alcohol of 1-2 carbon atoms, and a hydrocarbon coupling agent. This composition has utility as a fuel per se and as a liquid carrier in which powdered coal can be dispered to produce another liquid fuel.

BACKGROUND OF THE INVENTION 
In the past several years petroleum crude oil has increased in price 
many-fold due to the controls in production and price levels established 
by the Middle East countries producing a large percentage of the world's 
crude oil. This has caused a significant increase in research efforts to 
develop alternative fuels. Among the areas investigated has been that of 
pulverizing coal and dispersing it in petroleum oil as an "extender" for 
the oil. Petroleum residual oil, as distinguished from "distillate" from 
which gasoline is produced, is of relatively high viscosity, e.g. 1-10 
poises, and when powdered coal is added the viscosity rises rapidly with 
increasing concentrations of coal. At viscosities above about 5-10 poises, 
the liquid is too difficult to pump to consider the liquid as a practical 
fuel. Accordingly, it has been a difficult problem to produce easily 
pumpable coal in oil slurries at high coal concentrations (e.g. 50% to 60% 
by wt. of coal). 
It is an object of this invention to provide a liquid fuel oil having the 
property of low viscosity. It is another object of this invention to 
provide a liquid fuel oil that is capable of carrying high concentrations 
of pulverized coal at low viscosities. Still other objects will appear 
from the more detailed description which follows. 
BRIEF SUMMARY OF THE INVENTION 
This invention provides a stable, homogeneous liquid fuel blend having a 
viscosity at room temperature of less than 0.6 poise comprising petroleum 
residual oil having a viscosity of 1.0 to 2.5 poises at room temperature, 
an alcohol of 1-2 carbon atoms, and as a coupling agent an aliphatic 
hydrocarbon liquid of 6-16 carbon atoms, preferably kerosene. In a 
preferred embodiment the invention provides a stable homogeneous liquid 
fuel comprising 65-90% by weight of a petroleum residual oil having a 
viscosity at room temperature of 1.0-2.5 poises, 5-25% by weight of an 
alcohol of 1-2 carbon atoms, and 5-15% by weight of a coupling agent 
selected from the group consisting of kerosene, n-alkane of 6-10 carbon 
atoms, and mixtures thereof. 
This invention also provides a heating fuel composition comprising the 
above liquid fuel with pulverized coal dispersed therein, the dispersion 
containing 10-60% by weight of coal and the remaining 90-40% by weight of 
one of the above liquid fuels. Preferably the coal comprises 20-40% by 
weight of the composition with the liquid fuel comprising the remaining 
60-80%.

DETAILED DESCRIPTION OF THE INVENTION 
This invention contemplates both a basic liquid fuel and a heating fuel 
composition wherein that liquid fuel has pulverized coal dispersed 
therein. 
The basic liquid fuel has three components which are mixed in proportions 
which will produce a homogeneous liquid i.e. a single-phase liquid in 
which the components are miscible and do not separate into more than one 
liquid layer over a reasonable period of time, e.g. 24 hours. The 
components are (1) a petroleum residual oil, (2) an alcohol of 1-2 carbon 
atoms, and (3) a coupling agent. The first two components are not miscible 
with each other when used alone, but in the presence of the third 
component, there is a significant range of component concentrations which 
result in a single-phase, homogeneous liquid. This is shown graphically in 
FIG. 1 which is a ternary diagram of these three components wherein the 
alcohol is ethanol and the coupling agent is either kerosene or n-hexane. 
In general, this shows that in the presence of the coupling agent, ethanol 
in concentrations up to about 25% by weight, is miscible in Fuel Oil No. 
6. 
The principal component of the basic liquid fuel is a petroleum residual 
oil. The term "residual oil" is intended to mean a fuel oil remaining 
after removing the light oils and distillate fractions from a crude 
petroleum. This "residual oil" will generally have a flash point above 
about 200.degree. F. and a viscosity of at least about 0.5 to 2 poises at 
100.degree. F. Typical of these residual oils are Fuel Oil Nos. 4,5 and 6. 
The preferred of these oils for this invention is Fuel Oil No. 6. 
The second component is an alcohol of 1-2 carbon atoms, which includes 
methanol and ethanol, the latter being preferred. For some reason which 
has not yet become clear, denatured ethanol appears to function slightly 
better than absolute ethanol in the composition of this invention. 
The third component is a coupling agent which is believed to provide some 
type of bonding between the residual oil and the alcohol to make them 
compatible and miscible. The coupling agent is an aliphatic hydrocarbon of 
6-16 carbon atoms, including materials such as kerosene, n-hexane, hexene, 
heptane, octane, octene, nonane, decane, decene, dodecane, tetradecane, 
tetradecene, hexadecane, or their mixtures. The preferred agents are 
kerosene, n-hexane, and mixtures of these two. 
When these components are mixed in the proportions that fall within the 
"miscible region" of FIG. 1, i.e. between the bottom line of the graph and 
the curved lines labelled "n-Hexane" or "Kerosene", the resulting mixture 
is a single-phase liquid having a viscosity considerably lower than that 
of the fuel oil by itself. As stated above, this generally is a 
composition of about 25% or less ethanol. The ranges of fuel oil and 
coupling agent may vary widely so long as the ethanol is 25% or less by 
weight of the total. However, the most useful compositions as a fuel are 
those of high fuel oil content, which means those in shaded portion in the 
lower right hand corner of the graph. Several compositions that illustrate 
these statements are listed below in Table 1. In each instance the total 
volume of the composition is 100 parts by volume. The data show that the 
viscosity of the miscible composition is many times lower than the 
viscosity of the unmodified fuel oil. 
TABLE 1 
______________________________________ 
Blend Composition 
(% Weight) Ethanol-to- 
Immiscible 
Ethanol + Kerosene Volume Viscosity 
Fuel Oil 
Kerosene Ratio (parts) (cp) 
______________________________________ 
65 35 10.6 2.0 
6.0 1.0 
2.5 0.5 30 
1.33 0 
70 30 14.0 3.0 
5 1.0 
2.75 0.5 42 
1.0 9 
75 25 4.0 1.0 
3.0 0.5 50 
1.0 0 
100 0 0 220 
______________________________________ 
The above described liquid fuel compositions are excellent carriers for 
powdered coal. The low viscosity of the liquid fuel permits a high loading 
of pulverized coal to produce a pumpable blend of coal and fuel oil 
containing a higher percentage of coal than has heretofore been available. 
The coal that is used is crushed to a particle size such that at least 80% 
passes through 200 mesh and the remainder through 325 mesh. Any type of 
coal is suitable. 
In prior art procedures of blending fuel oil with powdered coal, it was 
found that the viscosity of the blend rose rapidly with increasing coal 
concentrations, and in order to retain a pumpable viscosity, it was 
necessary to heat the blend to an elevated temperature. By using the 
liquid fuel composition of this invention (fuel oil/ethanol/coupling 
agent) it has been possible to obtain blends with powdered coal that need 
not be heated to obtain the pumpable viscosity. This is illustrated in 
FIG. 2 which shows graphically the viscosity changes with increasing 
concentration of powdered coal in Fuel Oil No. 6 at 65.degree. F. and 
212.degree. F. as compared to the liquid fuel of this invention using Fuel 
Oil No. 6 as the petroleum oil component. The shear rate in the viscosity 
measurement was kept constant at 0.3 rpm. At approximately 30% coal 
concentration in Fuel Oil No. 6 at 65.degree. F. the viscosity is 
approximately 1700 cp., and if that mixture is heated to 212.degree. F., 
the viscosity drops to approximately 50 cp. If the liquid fuel of this 
invention is used at 64.degree. F., the viscosity can be kept within 
pumpable ranges even at high coal concentrations (50 to 60% of coal ). 
Therefore, the liquid fuel of this invention provides tremendous energy 
savings in eliminating the cost of heating the fuel oil to make it 
suitable for carrying more than 30% of coal. 
It has also been found that the addition of a small amount of any of 
several surfactants lowers the viscosity of the coal/liquid fuel 
compositions of this invention. For example, the addition of 0.25% by 
weight of a surfactant to a coal/liquid fuel composition having a 
viscosity of about 170 cp. at 65.degree. F. lowered the viscosity to 
110-160 cp. using any of four different surfactants. 
The stability of the coal/liquid fuel blend appears to be greatly enhanced 
by the presence of a surfactant. In a test with a blend containing 30% 
coal at 65.degree. F., the blend was permitted to stand without stirring 
over long periods of time and measurements were made of phase separation 
and the loss of coal from the oily upper layer by settling into the lower 
layer. The same measurements were made with the coal/liquid fuel blend 
containing 0.25% by weight of a surfactant and the results showed 
improvement with each surfactant. The preferred surfactant (Triton X-15) 
provided the most stable blend with less than 5% loss in coal from the 
oily layer over a period of 150 hours. 
The surfactants which have been found useful include; Span 20 (Sorbitan 
monolaurate, HLB 8.6), an anionic surfactant Triton X-15 (Alkyl phenoxy 
polyethoxy ethanol), Tergitol (nonionic surfactant) and TRS 10-80, a 
petroleum sulfonate of anionic type. 
This invention includes liquid fuel compositions and coal/liquid fuel 
compositions. The liquid fuel contains 
65-90% by weight of petroleum residual oil; 
5-25% by weight of an alcohol of 1-2 carbom atoms; and 
5-15% by weight of an aliphatic hydrocarbon coupling agent of 6-10 carbon 
atoms 
Preferably, the liquid fuel contains: 
65-75% Fuel Oil No. 6 
10-25% ethanol; and 
5-15% kerosene, n-hexane, or a mixture of the two. 
When the above liquid fuel is blended with powdered coal the blend may 
contain 40-90% liquid fuel and 10-60% coal, with the preferred amounts 
being 60-80% liquid fuel and 20-40% coal. Preferably the blend also 
contains 0.1 to 0.5% by weight of a compatible surfactant. 
The compositions of the present invention provide advantages in the 
conservation of petroleum oils and in general energy consumption. The low 
viscosity liquid fuel can be used for direct consumption in oil-fired 
utility and industrial boilers in place of the petroleum fuel oil now 
used. Ethanol is expected to become available from biomass conversion at a 
low cost. The liquid fuel will provide considerable savings in stretching 
the petroleum oil stocks available today. The coal/liquid fuel blends are 
also attractive boiler fuels. These blends provide even greater savings in 
petroleum oil stocks. They can be pumped or stored at ambient temperatures 
because of their low viscosity and stability. 
While the invention has been described with respect to certain specific 
embodiments, it will be appreciated that many modifications and changes 
may be made by those skilled in the art without departing from the spirit 
of the invention. It is intended, therefore, by the appended claims to 
cover all such modifications and changes as fall within the true spirit 
and scope of the invention.