Method for measuring the properties of petroleum fuels by distillation
The method for measuring the properties of petroleum fuels by distillation relates to a measuring method for predicting the property values of complex hydrocarbon fuels, such as the property values of gasoline, by distillation. Compensation of boiling point distribution measurements used for the prediction of physical properties of hydrocarbons is further performed.
1. A method for measuring the properties of petroleum fuels by distillation, comprising the steps of:
storing an initial data set of properties associated with a selected light petroleum fraction in computer readable memory, the initial data set of properties including API gravity, RVP, PNA content and true boiling point;
generating a molecular ensemble comprising a plurality of molecular species, each with a known pure component API gravity, RVP, PNA content and true boiling point, and storing a pure component data set in the computer readable memory;
applying at least one mixing rule to the pure component data set to calculate a concentration of light components of the selected light petroleum fraction based upon the pure component API gravity and RVP;
applying the at least one mixing rule to the pure component data set to calculate a concentration of heavier components of the selected light petroleum fraction based upon the pure component PNA content and true boiling point;
comparing the API gravity, the RVP, the PNA content and the true boiling point of the initial data set with the pure component API gravity, RVP, PNA content and true boiling point to form a set of comparison data;
optimizing the set of comparison data, the step of optimization including application of an objective function S;
generating a distribution of the molecular ensemble in terms of volume fractions by minimizing the objective function S as:
S
=
∑
j
=
1
n
(
(
Tb
j
-
T
′
b
j
)
×
W
o
×
100
/
Tb
j
)
2
+
(
(
P
%
-
P
%
′
)
×
W
1
×
100
/
P
%
)
2
+
(
(
N
%
-
N
%
′
)
×
W
1
×
100
/
N
%
)
2
+
(
(
A
%
-
A
′
%
)
×
W
1
×
100
/
A
%
)
2
,
wherein
P
′
v
=
∑
i
=
1
n
P
i
v
;
P
′
%
=
∑
i
=
1
n
P
%
i
=
∑
i
=
1
n
x
i
P
;
N
′
%
=
∑
i
=
1
n
N
%
i
=
∑
i
=
1
n
x
i
N
;
and
A
′
%
=
∑
i
=
1
n
A
%
i
=
∑
i
=
1
n
x
i
A
,
where x i is the mole fraction of pure component i, P %, N %, A % represent mole percent of paraffin, naphthene, and aromatic content, respectively, in the petroleum fraction, P′ t %, N′ t %, A′ t % represent the paraffin, naphthene, and aromatic contents, respectively, for the petroleum fraction calculated from aggregating pure components in the molecular ensemble using the at least one mixing rule, P v is the true vapor pressure of the petroleum fraction, and P′ v is the true vapor pressure of the petroleum fraction, calculated from aggregation of pure components in the molecular ensemble;
generating a set of component concentration data based upon the optimized comparison data; and
displaying the set of component concentration data.
2. The method for measuring the properties of petroleum fuels by distillation as recited in claim 1 , wherein said step of storing the initial data set of properties includes storing estimated values for the API gravity, the RVP and the PNA content.
3. The method for measuring the properties of petroleum fuels by distillation as recited in claim 1 , wherein Σx i =1 and ∀x i ≧0.
4. The method for measuring the properties of petroleum fuels by distillation as recited in claim 2 , wherein the true boiling point of the selected light petroleum fraction is found experimentally by ASTM D86 distillation, the estimated values for the API gravity, the RVP and the PNA content being calculated based upon the true boiling point.
5. A method for measuring the properties of petroleum fuels by distillation, comprising the steps of:
distilling a selected light petroleum fraction to determine at least the true boiling point thereof;
storing an initial data set of properties associated with the selected light petroleum fraction in computer readable memory, the initial data set of properties including API gravity, RVP, PNA content and the true boiling point, wherein said step of storing the initial data set of properties includes storing estimated values for the API gravity, the RVP and the PNA content;
generating a molecular ensemble comprising a plurality of molecular species, each with a known pure component API gravity, RVP, PNA content and true boiling point, and storing a pure component data set in the computer readable memory, wherein said step of generating the molecular ensemble comprises generation of a molecular distribution of the pure components comprising paraffins, olefins and aromatics, wherein generation of the molecular distribution includes a calculation method selected from the group consisting of: optimization, multivariate regression, partial least square regression, principal component regression, topological optimization, genetic algorithms, and combinations thereof, wherein the true boiling point of the selected light petroleum fraction is found experimentally by ASTM D86 distillation, the estimated values for the API gravity, the RVP and the PNA content being calculated based upon the true boiling point;
applying at least one mixing rule to the pure component data set to calculate a concentration of light components of the selected light petroleum fraction based upon the pure component API gravity and RVP;
applying the at least one mixing rule to the pure component data set to calculate a concentration of heavier components of the selected light petroleum fraction based upon the pure component PNA content and true boiling point;
comparing the API gravity, the RVP, the PNA content and the true boiling point of the initial data set with the pure component API gravity, RVP, PNA content and true boiling point to form a set of comparison data;
optimizing the set of comparison data, the step of optimization including:
application of an objective function S;
minimizing a difference between the true boiling points of the pure components with the true boiling points of the initial data set by varying concentration values associated with the pure components; and
minimizing a difference between the RVP of the pure components with the RVP of the initial data set;
generating a distribution of the molecular ensemble in terms of volume fractions by minimizing the objective function S as:
S
=
∑
j
=
1
n
(
(
Tb
j
-
T
′
b
j
)
×
W
o
×
100
/
Tb
j
)
2
+
(
(
P
%
-
P
%
′
)
×
W
1
×
100
/
P
%
)
2
+
(
(
N
%
-
N
%
′
)
×
W
1
×
100
/
N
%
)
2
+
(
(
A
%
-
A
′
%
)
×
W
1
×
100
/
A
%
)
2
,
wherein
P
′
v
=
∑
i
=
1
n
P
i
v
;
P
′
%
=
∑
i
=
1
n
P
%
i
=
∑
i
=
1
n
x
i
P
;
N
′
%
=
∑
i
=
1
n
N
%
i
=
∑
i
=
1
n
x
i
N
;
and
A
′
%
=
∑
i
=
1
n
A
%
i
=
∑
i
=
1
n
x
i
A
,
where x i is the mole fraction of pure component i, P %, N %, A % represent mole percent of paraffin, naphthene, and aromatic content, respectively, in the petroleum fraction, P′ t %, N′ t %, A′ t % represent the paraffin, naphthene, and aromatic contents, respectively, for the petroleum fraction calculated from aggregating pure components in the molecular ensemble using the at least one mixing rule, P v is the true vapor pressure of the petroleum fraction, and P′ v is the true vapor pressure of the petroleum fraction, calculated from aggregation of pure components in the molecular ensemble;
generating a set of component concentration data based upon the optimized comparison data; and
displaying the set of component concentration data.
6. The method for measuring the properties of petroleum fuels by distillation as recited in claim 5 , wherein Σx i =1 and ∀x i ≧0.