VERY LOW-SULFUR FUEL OIL AND METHOD FOR PRODUCING THE SAME

Abstract

The present invention relates to a method for producing very low-sulfur fuel oil having high compatibility and high stability, comprising: mixing petroleum residua obtained from at least two different petroleum refining processes, adding a hydrocarbon solvent to the residual petroleum mixture, heating the mixture of the petroleum residua mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions and the hydrocarbon solvent from the mixture of the petroleum residua mixture and hydrocarbon solvent with raffinate having asphaltenes therein being left, and removing the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil, wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt % or less bared on the total weight of the very low-sulfur fuel oil, and very low-sulfur fuel oil produced by the production method.

Claims

1. A method for producing very low-sulfur fuel oil, comprising steps of: mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture; adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent; heating of the mixture of the residual petroleum mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions from the petroleum residua mixture and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and removing the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil; wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt % or less based on the total weight of the very low-sulfur fuel oil.

2. The method of claim 1, wherein the petroleum residua are selected from the group consisting of atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DAO), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), t-VGO (hydrotreated VGO vacuum gas oil), high-sulfur diesel (HSD), and ultra-low-sulfur diesel (ULSD).

3. The method of claim 1, wherein the hydrocarbon solvent is C.sub.3-C.sub.5 hydrocarbon solvent or a mixture of two or more thereof.

4. The method of claim 3, wherein the C.sub.3-C.sub.5 hydrocarbon solvent is selected from the group consisting of n-propane, n-butane, i-butane, n-pentane, and i-pentane.

5. The method of claim 1, wherein the hydrocarbon solvent is added with the volume ratio of 1 to 4:1 of the hydrocarbon solvent to the petroleum residua mixture in an extraction column at a pressure ranging from 30 to 50 barg and a temperature ranging from 100° C. to 230° C.

6. A very low-sulfur fuel oil which is obtained by a method for producing very low-sulfur fuel oil, comprising steps of: mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture; adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent; heating of the mixture of the residual petroleum mixture and hydrocarbon solvent to extract and recover a mixture of oil fractions from the petroleum residua mixture and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and removing the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil, wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt % or less based on the total weight of the very low-sulfur fuel oil.

7. The very low-sulfur fuel oil of claim 6, wherein the petroleum residua are selected from the group consisting of AR, VR, t-AR, t-VR, DAO, t-DAO, UCO, VGO, t-VGO, HSD, and ULSD.

8. The very low-sulfur fuel oil of claim 6, having an asphaltene content of 0.01 to 0.6 wt % based on the total weight of the very low-sulfur fuel oil.

9. The very low-sulfur fuel oil of claim 6, wherein the hydrocarbon solvent is C.sub.3-C.sub.5 hydrocarbon solvent or a mixture of two or more thereof.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is photographs showing the spot rating of a spot test (ASTM D4740) for evaluating the stability of fuel oil.

[0022] FIG. 2 is a flowchart showing a production process of very low sulfur-fuel oil by separating and removing asphaltenes from a petroleum residua mixture according to the present invention.

MODE FOR THE INVENTION

[0023] A method of very low-sulfur fuel oil according to the present invention comprises steps of:

[0024] mixing petroleum residua obtained from at least two different petroleum refining processes for production of relatively high quality fuel oils to obtain a petroleum residua mixture;

[0025] adding a hydrocarbon solvent to the petroleum residua mixture to obtain a mixture of the petroleum residua mixture and the hydrocarbon solvent;

[0026] heating the mixture of the petroleum residua mixture and the hydrocarbon solvent to extract and recover a mixture of oil fractions and the hydrocarbon solvent with raffinate having asphaltenes therein being left; and

[0027] recovering the hydrocarbon solvent from the mixture of the oil fractions and the hydrocarbon solvent, thereby obtaining very low-sulfur fuel oil, wherein the very low-sulfur fuel oil has a sulfur content of 0.5 wt % or less based on the total weight of the very low-sulfur fuel oil.

[0028] The petroleum residua may be selected from the group consisting of atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DM)), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), hydrotreated vacuum gas oil(t-VGO) high-sulfur diesel (HSD), and ultra-low-sulfur diesel (ULSD).

[0029] In the present specification, the term “high-quality oils” refers to oils such as jet aircraft oil and gasoline, which have low boiling points and high economic values, and the expression “petroleum residuum” as used in the present invention refers to an oil fraction, which is obtained from a petroleum refining process for production of relatively high quality fuel oil fractions, mainly in the form of residuum, and have a high sulfur and asphaltene content.

[0030] Specifically, according to the present invention, very low-sulfur fuel oil may be produced by adding a C.sub.3-C.sub.5 hydrocarbon solvent to a mixture obtained by mixing different kinds of petroleum residua at a predetermined ratio and separating asphaltenes, which is a source material that causes aggregation and precipitation, from the mixture of petroleum residua The C.sub.3-C.sub.5 hydrocarbon solvent may preferably be selected from the group consisting of n-propane, n-butane, i-butane, n-pentane, i-pentane, and a mixture of two or more thereof, may more preferably be selected from the group consisting of n-pentane, i-pentane, and a mixture thereof, most preferably n-pentane.

[0031] For separation of asphaltenes in an extraction column, the ratio of the C.sub.3-C.sub.5 hydrocarbon solvent to the petroleum residua mixture is 1 to 4:1, more preferably 2 to 3:1, the pressure that is used for the separation is 30 to 50 barg, more preferably 35 to barg, most preferably 38 to 43 barg, and the temperature that is used for the separation may be T.sub.c(critical temperature of the hydrocarbon solvent) minus 20° C. to T.sub.cplus 20° C., more preferably T.sub.c−5° C. to T.sub.c+15° C., most preferably T.sub.c−10° C. to T.sub.c+1.0° C. The temperature may range from 100° C. to 230″C.

[0032] After separation of the asphaltenes, the hydrocarbon solvent is removed from the extract stream, thereby obtaining very low-sulfur fuel oil. The recovered hydrocarbon solvent may be reused, and a stream of raffinate may be used as a blending stock for conventional coker unit.

[0033] Through several repeated experiments, the present inventors have found that hydrocarbon solvents exhibit a stronger solvent effect as the number of carbon atoms in the hydrocarbon solvents increases, but when a hydrocarbon solvent having, a high solvent effect, such as hexane having 6 carbon atoms, is used, the efficiency of removal of asphaltenes from the petroleum residua mixture is greatly reduced, and in the case of hydrocarbon solvents having the same carbon number, a linear hydrocarbon (e.g., n-pentane) exhibits a stronger solvent effect than a branched hydrocarbon (e.g., i-pentane). In addition, the present inventors have found that the yield of VLSFO increases at low temperature and high pressure depending on the density change and thermodynamic preference of the supercritical hydrocarbon solvent in the extraction column in which the extraction of oil fractions is performed. The present inventors have found that a proper hydrocarbon solvent needs to be used to maximize the yield of VLSFO while preventing the loss of oil fractions, and in particular, have found that it is necessary to select a suitable hydrocarbon solvent to increase the stability of the mixture of oil fractions.

[0034] The very low-sulfur fuel of the present invention may have a sulfur content of 0.001 to 0.5 wt %, preferably 0.05 to 0.49 wt %, most preferably 0.1 to 0.48 wt %, based on the total weight of the very low-sulfur fuel.

[0035] The very low-sulfur fuel according to the present invention produced from the mixture of petroleum residua exhibits improved storage stability.

[0036] That is, the petroleum residuum have a high content of saturates and/or a high content of asphaltene, and hence when this petroleum residuum are used as a raw material to produce fuel oil, the stability of the fuel oil is low. However, according to the present invention, when two or more petroleum residua selected from among atmospheric residuum (AR), vacuum residuum (VR), hydrotreated atmospheric residuum (t-AR), hydrotreated vacuum residuum (t-VR), deasphalted oil (DAO), hydrotreated deasphalted oil (t-DAO), unconverted oil (UCO) (or HCR process residuum), vacuum gas oil (VGO), t-VGO (hydrotreated VGO (vacuum gas oil), high-sulfur diesel (HSD), and ultra-low-sulfur diesel (ULSD) are mixed together at a predetermined ratio and the mixture is treated with a hydrocarbon solvent to remove asphaltenes, very low-sulfur fuel oil having high stability and meets specifications on the very low-sulfur fuel oil.

[0037] Hereinafter, the present invention will be described in detail with reference to examples.

EXAMPLE 1

[0038] In an extraction column, 1,457,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1:1, was mixed with n-pentane solvent at a solvent/petroleum residua mixture volume ratio of 2 under conditions of 42 barg and 205° C., and extracted for 60 minutes (extraction column residence time). Total extraction process operation time was 660 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 1,394,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below. The sulfur content was measured in accordance with ASTM D4294, and the asphaltene content was measured in accordance with ASTM D6560.

EXAMPLE 2

[0039] In an extraction column, 1,643,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1:1, was mixed with n-pentane solvent at a solvent/petroleum residua mixture volume ratio of 2 under conditions of 42 barg and 185° C., and extracted for 40 minutes (extraction column residence time). Total extraction process operation time was 480 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 1,615,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below.

EXAMPLE 3

[0040] In an extraction column, 1,325,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1:1, was mixed with i-pentane solvent at a solvent/petroleum residua mixture volume ratio of 1 under conditions of 42 barg and 220° C., and extracted for 90 minutes (extraction column residence time). Total extraction process operation tune was 600 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 958,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below.

EXAMPLE 4

[0041] In an extraction column, 1,656,000 liter of petroleum residua mixture, obtained by mixing t-AR and t-DAO at a volume ratio of 1:1, was mixed with an n-pentane solvent at a solvent/petroleum residua mixture volume ratio of 1 under conditions of 42 barg and 220° C., and extracted for 70 minutes (extraction column residence time). Total extraction process operation time was 600 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fractions from the petroleum residua mixture and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of oil fractions and solvent, thereby obtaining 1,495,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 1 below.

Comparative Example 1

[0042] In an extraction column, 1,325,000 liter of t-AR as single petroleum residuum instead of petroleum residua mixture was mixed with an n-pentane solvent at a solvent/petroleum residuum volume ratio of 3 under conditions of 42 barg and 190° C., and extracted for 70 minutes (extraction column residence time). Total extraction process operation time was 600 minutes. Asphaltenes were removed therefrom so that it remained in raffinate. The mixture of oil fraction from the petroleum residuum and the solvent was extracted and recovered, and then the solvent was separated from the recovered mixture of the oil fraction and the solvent, thereby obtaining 1,176,000 liter of fuel oil. The obtained fuel oil was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, and the results of the measurement are shown in Table 2 below.

Comparative Example 2

[0043] Low-sulfur AR without removing asphaltenes was measured for its sulfur content, asphaltene content and spot rating by a spot test, and the results of the measurement are shown in Table 2 below. Here, the low-sulfur AR was an unhydrotreated atmospheric residuum having low sulfur content.

Comparative Example 3

[0044] A mixture of petroleum residua, obtained by mixing low-sulfur AR and ULSD at a volume ratio of 91: 9, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 2 below.

Comparative Example 4

[0045] A mixture of petroleum residua, obtained by mixing low-sulfur AR and ULSD at a volume ratio of 76:24, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 2 below.

Comparative Example 5

[0046] A mixture of petroleum residua, obtained by mixing AR, ULSD and UCO1 at a volume ratio of 91:4.5:4.5, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 3 below.

Comparative Example 6

[0047] A mixture of petroleum residua, obtained by mixing AR, ULSD and SLO at a volume ratio of 72:20:8, was measured for its sulfur content, asphaltene content, spot rating by a spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 3 below. Here, the SLO was residuum in a fluidized catalytic cracking (FCC) process.

Comparative Example 7

[0048] A mixture of petroleum residua, obtained by mixing t-AR, LCO, SLO and H-Aro at a volume ratio of 80:9:6:5 was measured for its sulfur content, asphaltene content, spot rating by spot test immediately after asphaltene removal, and spot rating by a spot test during storage, in a state in which asphaltene was not removed therefrom. The results of the measurement are shown in Table 3 below. Here, the LCO was a kind of low-price oil fraction produced in a fluidized catalytic cracking process, and the H-Aro was a by-product in an aromatic production process.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Petroleum residuum t-AR t-DAO t-AR t-DAO t-AR t-DAO t-AR t-DAO Petroleum residuum S % (wt %) 0.65 0.27 0.65 0.25 0.7 0.23 0.72 0.2 As % (wt %) 3.21 0.1 3.12 0.1 3.08 0.05 3.25 0.06 S.R. (1-5) 4 1 4 1 4 1 4 1 Mixing ratio (v/v) 50 50 50 50 50 50 50 50 Petroleum residua S % (wt %) 0.48 0.46 0.47 0.47 mixture (before As % (wt %) 1.51 1.56 1.39 1.53 treatment with solvent) S.R. (1-5) 3   3   4   3   Solvent/petroleum residuum (v/v) 2   2   1   1   Solvent n-pentane n-pentane i-pentane n-pentane Process conditions (barg/° C.) 42/205 42/185 42/220 42/220 Oil fraction (after S % (wt %) 0.48 0.47 0.46 0.46 treatment with solvent) As % (wt %) 0.24 0.60 0.16 0.57 S.R. (1-5) 1   1   1   1   Storage stability (days) 30+   30+   30+   30+   Yield (%) 96    98    72    90   

TABLE-US-00002 TABLE 2 Comp. Comp. Comp. Comp. Example 1 Example 2 Example 3 Example 4 Petroleum residuum t-AR LSAR LSAR USLD LSAR USLD Petroleum residuum S % (wt %) 0.67 0.48 0.53 <0.001 0.58 <0.001 As % (wt %) 4.03 0.51 0.53 <0.01 0.51 <0.01 S.R. (1-5) 4   1 1 1 1 1 Mixing ratio (v/v) — — 91 9 76 24 Petroleum residua mixture S % (wt %) — — 0.48 0.45 (before treatment As % (wt %) — — 0.48 0.4 with solvent) S.R. (1-5) — — 1 2 Solvent/petroleum residuum (v/v) 3   — — — Solvent n-pentane — — — Process conditions (barg/° C.) 42/190 Oil fraction (after S % (wt %) 0.65 with solvent) As % (wt %) 0.26 S.R. (1-5) 1   Storage stability (days) 30+   14-18 14-18 14-18 Yield (%) 89    — — —

TABLE-US-00003 TABLE 3 Comp. Example 5 Comp. Example 6 Comp. Example 7 Petroleum residuum LSAR USLD UCO LSAR USLD LSO t-AR LCO SLO H-Aro Petroleum residuum S % (wt %) 0.55 <0.001 <0.001 0.56 <0.001 1.15 0.45 0.67 1.12 <0.001 As % (wt %) 0.55 <0.01 <0.01 0.52 <0.01 3.52 3.48 <0.01 3.45 <0.01 S.R. (1-5) 1 1 1 1 1 1 4 1 1 1 Mixing ratio (v/v) 91 4.5 4.5 72 20 8 80 9 6 5 Petroleum residua S % (wt %) 0.49 0.5 0.48 mixture (before As % (wt %) 0.51 0.68 3.04 treatment with solvent) S.R. (1-5) 2 3 4 Solvent/petroleum residuum (v/v) — — — Solvent — — — Process conditions (barg/° C.) — — — Oil fraction (after S % (wt %) — — — treatment with solvent) As % (wt %) — — — S.R. (1-5) — — — Storage stability (days) 14-18 i i Yield (%) — — —

[0049] In Tables 1 to 3 above, S % denotes sulfur content, As % denotes asphaltene content, and S.R. denotes spot rating. In Table 3 above, “i” denotes immediately after mixing, and indicates that storage stability was not determined due to high spot rating immediately after mixing.

[0050] Based on the results shown in Tables 1 to 3 above, the effects of the present invention will be described hereinbelow.

[0051] 1. It could be confirmed that the Examples, in which asphaltene was removed from the petroleum residua mixture, all exhibited high stability after asphaltene removal from low stability before asphaltene removal, suggesting that these Examples demonstrate the stability of the oil fraction according to the present invention. In addition, it could be confirmed that, in the storage stability of the oil fraction, due to removal of asphaltene, the Examples showed a spot rating of 1 without time-dependent changes even after 30 days, suggesting that the storage stability of the oil fraction was also greatly improved.

[0052] 2. It could be confirmed that Example 1, in which asphaltene was removed from the mixture of two petroleum residua, exhibited the stability and storage stability comparable to Comparative Example 1, in which asphaltene was removed from a single petroleum residuum. In addition, it could be confirmed that the yield of Example 1 was higher than that of Comparative Example 1 with a reduced solvent amount and elevated process temperature compared to Comparative Example 1.

[0053] 3. When comparing Examples 1 and 2, in which asphaltene was removed from the same petroleum residua mixture and the same solvent was used in the same amount, it could be confirmed that the yield was improved by lowering the process temperature. This suggests that the yield may vary depending on the density of the supercritical solvent in the extraction column.

[0054] 4. Then comparing Examples 3 and 4, in which asphaltene was removed from petroleum residua mixture and the solvent was used in the same amount, it could be confirmed that the yield of Example 4, in which n-pentane is used, was greatly improved compared to that of Example 3 in which i-pentane was used. This also suggests that the yield may vary depending on presence of branching in the solvent and the density of the supercritical solvent in the extraction column.

[0055] 5. Comparative Examples 2 and 3, in which asphaltene was not removed, showed a spot rating of 1 immediately after mixing, and thus exhibited stability, but the spot rating was degraded to 2 after 14 to 18 days of storage after mixing.

[0056] 6. Comparative Examples 4 and 5, in which asphaltene was not removed, showed a spot rating of 2 immediately after mixing, but the spot rating was degraded to 3 alter 14 to 18 days of storage after mixing. Thus, it could be confirmed that the Comparative Examples (Comparative Examples 2 to 5), which showed high stability immediately after mixing, showed deterioration in storage stability.

[0057] 7. The petroleum residua mixtures of Examples 6 and 7, from which asphaltene was not removed and which included the petroleum residuum having a high asphaltene content, showed low stability even immediately after mixing.

[0058] Although only the petroleum residua mixture comprising t-AR and t-DAO was described in the above Examples, similar results could also be obtained for other mixture of petroleum residua as listed above, remaining after producing high-quality oils.

[0059] While the present invention has been described above with reference to the specific embodiments, it is to be understood that various modifications are possible without departing front the scope of the present invention. Therefore, the scope of the present invention should not be limited by the described embodiments, but should be defined not only by the appended claims, but also the equivalents of the claims.