SYNTHESIS OF BASE OILS AND FUELS FROM FATTY ACIDS

Abstract

Processes and systems for producing base oils and fuels from fatty acids comprising, in an embodiment, oligomerizing at least one unsaturated fatty acid to provide a mixture of fatty acid oligomers, wherein the mixture of fatty acid oligomers comprises fatty acid trimers and heavier molecules; and hydrotreating the mixture of fatty acid oligomers to provide a product comprising hydrotreated fatty acid oligomers including hydrotreated trimers and heavier molecules, wherein the product has a pour point and other characteristics suitable for use as a base oil, and wherein such processes for base oil production do not require an isomerization step.

Description

TECHNICAL FIELD

This disclosure relates to processes and systems for synthesizing base oils and fuels from fatty acids.

BACKGROUND

Previous attempts to use dimeric fatty acids prepared from vegetable oils or other fatty biomass as base oils and fuels have failed. For example, vegetable oils have been reacted at relatively low conversion to produce fatty acid dimers in a product that is typically waxy and requires dewaxing, e.g., in an additional, separate isomerization step.

There is a need for processes and systems for efficiently producing a base oil product from fatty acid feedstocks.

SUMMARY

In an embodiment there is provided a process comprising oligomerizing at least one unsaturated fatty acid to provide an oligomerization product comprising a mixture of fatty acid oligomers; and hydrotreating at least a portion of the oligomerization product to provide a base oil product having a pour point less than −12° C. (10.4° F.), wherein the process does not include a step for isomerizing the oligomerization product.

In another embodiment there is provided a process comprising contacting a fatty acid feed comprising at least one unsaturated fatty acid with an oligomerization catalyst in an oligomerization zone under oligomerization conditions to provide a mixture of fatty acid oligomers; and contacting the mixture of fatty acid oligomers with a hydrotreating catalyst in a hydrotreating zone under hydrotreating conditions to provide a base oil product having a pour point less than −12° C., wherein the process is performed in the absence of an isomerization step.

In a further embodiment there is provided a process comprising oligomerizing at least one unsaturated free fatty acid to provide an oligomerization product comprising a mixture of fatty acid oligomers, wherein the mixture of fatty acid oligomers comprises fatty acid trimers and heavier molecules; and hydrotreating the mixture of fatty acid oligomers to provide a base oil product, wherein the base oil product comprises hydrotreated fatty acid trimers and heavier molecules, the hydrotreated fatty acid trimers and heavier molecules jointly represent from 10 to 20 wt % of the base oil product, and the base oil product has a pour point less than −12° C.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 schematically represents a process and system for the production of base oil from fatty acids without an isomerization step or an isomerization zone, according to an embodiment of the present invention.

DETAILED DESCRIPTION

Applicant has discovered a new route to make a base oil product by hydrotreating an oligomerization product obtained by catalytic oligomerization of a feedstock comprising at least one unsaturated fatty acid. The base oil product, which comprises hydrotreated fatty acid oligomers larger than dimers, has an unexpectedly low pour point and other characteristics which make it suitable for use as a base oil without isomerization dewaxing. Due to the presence of oligomers larger than dimers, e.g., trimers and heavier molecules (in addition to dimers), the oligomerization product has a sufficiently high average molecular weight with sufficient branching in the oligomer molecules to provide a product with a pour point suitable for use as a base oil without the need for further processing beyond hydrotreating, i.e., the base oil product may be obtained, in the absence of an isomerization step.

In processes as disclosed herein, branches may be introduced into the fatty acid oligomers as a result of the oligomerization reaction, instead of by a separate isomerization step as taught by the prior art. In an embodiment, the oligomerization step does not take place under hydrogen pressure, since hydrogen pressure could lead to the saturation of the olefinic bond in the fatty acid feedstock, thereby preventing oligomerization from occurring. In an embodiment, the oligomerization step and the hydrotreating step may be conveniently and advantageously performed in separate vessels (separate reactors). The use of separate reactors for the oligomerization and hydrotreating steps allows much more control over the oligomerization reaction, thereby enabling the production of an oligomeric mixture comprising a suitable amount of trimers and heavier molecules, such that hydrotreatment of the oligomeric mixture provides a low pour point base oil product without the need for an isomerization step. Similarly, the use of separate reactors for oligomerization and hydrotreating allows the hydrotreatment temperature to be carefully controlled so as to be high enough to remove all of the oxygen from the oligomeric mixture, and at the same time low enough to prevent excessive cracking

“Oligomerization,” as defined herein, refers to an additive reaction of like or similar molecules (e.g., unsaturated fatty acids) to form larger, oligomeric molecules. For example, unsaturated fatty acids of the present invention can react or combine via the double bonds in their structures. When two or more such fatty acid species combine to form a larger molecule, the larger molecule may be referred to herein as a fatty acid “oligomer.”

A fatty acid oligomer or mixture of fatty acid oligomers that has undergone hydrotreating may be referred to herein as “hydrotreated fatty acid oligomer.” Hydrotreated fatty acid oligomers may comprise saturated and deoxygenated derivatives of fatty acid oligomers. It is to be understood that the number of carbon atoms in the hydrotreated fatty acid oligomers may not be an exact multiple of the number of carbon atoms in the fatty acid monomeric unit(s); for example, a hydrotreated fatty acid oligomer may have lost a carbon atom as CO₂ or CO during hydrotreating.

The term “fatty acid oligomer” may include fatty acid dimers formed from two fatty acid molecules, as well as larger fatty acid oligomers. In an embodiment, processes for base oil production as disclosed herein may be particularly concerned with hydrotreated mixtures of fatty acid oligomers comprising fatty acid trimers and larger fatty acid oligomers.

Base Oil Production by Fatty Acid Oligomerization and Hydrotreating

In an embodiment, a process for base oil production may comprise oligomerizing at least one unsaturated fatty acid to provide an oligomerization product comprising a mixture of fatty acid oligomers, and hydrotreating at least a portion of the oligomerization product to provide a base oil product. In an embodiment, the oligomerizing may be performed in a first reactor or vessel and the hydrotreating may be performed in a second reactor or vessel. In an embodiment, the first and second vessels may be separate from each other such that the oligomerizing may be performed in the absence of hydrogen pressure while the hydrotreating may be performed under hydrogen pressure, e.g., in the range from 400 to 2000 psig hydrogen pressure. In an embodiment the base oil product, which may be obtained in the absence of an isomerization step, may have a pour point less than −12° C. (10.4° F.), or less than −18° C. (−0.4° F.), or −23° C. (−9.4° F.) or less. In a sub-embodiment, the base oil product may have a pour point in the range from −12° C. to −50° C. (10.4 to −58° F.).

In an embodiment, the base oil product may comprise at least 10 wt % of hydrotreated fatty acid trimers and heavier molecules. The expression “fatty acid trimers and heavier molecules” may be used herein to refer to fatty acid oligomers that are at least as large as trimers of fatty acid molecules. Or, stated differently, the expression “fatty acid trimers and heavier molecules” may be used to refer to a mixture comprising: i) fatty acid trimers and ii) fatty acid oligomers larger than trimers. In a sub-embodiment, the base oil product may comprise from 10 to 20 wt % of hydrotreated fatty acid trimers and heavier molecules, and often the base oil product may comprise from 15 to 20 wt % of hydrotreated fatty acid trimers and heavier molecules.

In an embodiment, the base oil product prepared as disclosed herein may have a kinematic viscosity at 100° C. in the range from 4 to 10 cSt, or from 4 to 8 cSt. In an embodiment, the base oil product constituents may have an average molecular weight in the range from 400 to 800, or from 500 to 800. In an embodiment, the base oil product may have a Viscosity Index in the range from 120 to 150, or from 120 to 140.

In an embodiment, the base oil product may have an NMR branching index in the range from 10 to 30, or from 10 to 30. In an embodiment, the base oil product may have an average degree of molecular branching in the range from 2 to 4 alkyl branches per 100 carbon atoms. The extent of branching and branching position can be determined by NMR branching analysis (see, for example, Example 5, infra). The NMR Branching Index may be calculated from ¹H NMR analysis as the ratio in percent of non-benzylic methyl hydrogen in the range of 0.5 to 1.0 ppm chemical shift, to the total non-benzylic aliphatic hydrogen in the range of 0.5 to 2.1 ppm chemical shift.

In an embodiment, the oligomerizing step may comprise contacting the at least one unsaturated fatty acid with an oligomerization catalyst in an oligomerization zone under oligomerization conditions to provide the mixture of fatty acid oligomers. In an embodiment, the at least one unsaturated fatty acid may be contacted with the oligomerization catalyst in the presence of a defined amount of water during the oligomerization step, e.g., water may be present in an amount in the range from 0.5 to 3.0 wt % of the fatty acid feed to the oligomerization zone, or from 1.0 to 2.5 wt %.

In an embodiment, the oligomerization conditions may comprise a temperature in the range from 350 to 525° F. (177-274° C.), or from 400 to 500° F. (204-260° C.), or from 400 to 475° F. (204-246° C.). In an embodiment, the oligomerization conditions may further comprise a pressure in the range from 0 to 500 psig, and a LHSV in the range from 0.05 to 1.0 hr⁻¹. In an embodiment, a suitable oligomerization catalyst may comprise an acidic clay catalyst, e.g., as described hereinbelow. In an embodiment, the oligomerization conditions will not include hydrogen pressure, since hydrogen pressure could prevent fatty acid oligomerization by saturating olefinic bonds in the unsaturated fatty acid feedstock.

In an embodiment, the hydrotreating step may comprise contacting the mixture of fatty acid oligomers with a hydrotreating catalyst in a hydrotreating zone under hydrotreating conditions to provide the base oil product. In an embodiment, the hydrotreating catalyst may comprise a metal and a support material, wherein the metal may be selected from Ni, Mo, Co, W, and combinations thereof, and the support may comprise a refractory oxide, such as alumina.

During the hydrotreating step oxygen is removed from the fatty acid oligomers. In addition, during the hydrotreating step olefins and aromatics may be converted to saturated compounds (e.g., isoalkanes and cycloalkanes). However, any isomerization of the fatty acid oligomers during hydrotreating is expected to be minimal and insufficient to significantly affect pour point, since the hydrotreatment catalyst will typically lack substantial isomerization activity for the fatty acid oligomers under the hydrotreating conditions. Instead, sufficient branches are introduced into the fatty acid oligomers as a result of the earlier oligomerization reaction such that subsequent isomerization of the fatty acid oligomers is unnecessary. Accordingly, processes for base oil production as disclosed herein may be performed in the absence of a step for isomerizing the oligomerization product or the mixture of fatty acid oligomers, either before or after hydrotreating.

Exemplary hydrotreating conditions for producing base oil from oligomerized fatty acids may comprise a temperature in the range from 550 to 800° F. (288 to 427° C.), a pressure generally in the range from 400 to 2000 lb·in⁻² gauge (psig), a LHSV in the range from 0.25 to 5 hr⁻¹, and a hydrogen flow rate typically in the range from 300 to 6000 SCF/bbl, or from 500 to 5000 SCF/bbl.

It is to be understood that the oligomerization conditions for producing base oil from oligomerized fatty acids according to the instant disclosure may be distinct from, and may be controlled independently of, the hydrotreating conditions, or vice versa. As a non-limiting example, the oligomerization step is typically performed in the absence of hydrogen pressure. Exposure to hydrogen pressure during the oligomerization step may cause saturation of the olefinic bond in unsaturated fatty acid components of the feedstock, thereby preventing fatty acid oligomerization from occurring.

In an embodiment, the whole liquid (initial) product from the oligomerization step may comprise various amounts of unconverted fatty acid monomers in addition to fatty acid oligomers. Processes for base oil production may further comprise separating the unconverted monomeric fatty acids from the mixture of fatty acid oligomers, and recycling at least a portion of the unconverted fatty acids to the oligomerization zone (see, for example, FIG. 1).

In an embodiment, the step of hydrotreating the mixture of fatty acid oligomers may be performed after separation (removal) of the unconverted fatty acids monomers. Alternatively, the oligomerization product comprising unconverted fatty acid monomers as well as fatty acid oligomers may be hydrotreated en masse, and the hydrotreated product may subsequently undergo separation to remove one or more lighter fractions including monomeric fatty acid materials. Such separation of unconverted monomeric fatty acids may involve various types of distillation including vacuum distillation.

In an embodiment, the hydrotreated material comprising hydrotreated fatty acid oligomers may be further processed to remove water, either before or after the separation of unconverted monomeric material, to provide a dried hydrocarbon fraction comprising hydrotreated fatty acid oligomers. As noted previously herein, such hydrotreated fatty acid oligomers typically include at least 10 wt % of hydrotreated fatty acid trimers and heavier molecules.

In an embodiment, the fatty acid feed to the oligomerization zone may comprise at least one unsaturated free fatty acid. In an embodiment, the fatty acid to be oligomerized may be combined with from 0.5 to 3.0 wt % water, and in a sub-embodiment the fatty acid to be oligomerized may be combined with from 1.0 to 2.5 wt % water. In an embodiment, a fatty acid feed to the oligomerization zone may comprise at least one unsaturated free fatty acid selected from a C₁₂ to C₂₂ fatty acid. In an embodiment, the fatty acid feed to the oligomerization zone may comprise at least 50 wt % C₁₆-C₂₀ free fatty acids, or at least 75 wt % C₁₆-C₂₀ free fatty acids, or at least 90 wt % C₁₆-C₂₀ free fatty acids. In an embodiment, at least 20 wt % of a base oil product produced from a feed comprising C₁₆-C₂₀ free fatty acids according to processes disclosed herein will boil at a temperature above 900° F.

It is to be understood that processes as disclosed herein are not limited to any particular fatty acid(s), but rather that base oil products may be prepared using a range of different fatty acid containing feedstocks. Furthermore, boiling point data for the various base oil products may vary depending on the nature (e.g., carbon chain length) of the starting materials (e.g., fatty acid feed) used in particular embodiments of such processes.

In contrast to prior art processes, the base oil product, having a suitable pour point and other characteristics as disclosed herein, may be prepared by fatty acid oligomerization to provide an oligomerization product and hydrotreating at least a portion of the oligomerization product to provide the base oil product in the absence of an isomerization step, e.g., without isomerizing either the initial (non-hydrotreated) oligomerization product or the hydrotreated oligomerization product.

Catalysts for Oligomerization

Catalysts for oligomerization can be almost any acidic material including zeolites, clays, resins, and acidic ionic liquids. In an embodiment, the oligomerization catalyst may comprise montmorillonite clay. The oligomerization catalyst may be disposed within an oligomerization zone. The oligomerization catalyst and the oligomerization zone will typically be separate from the hydrotreating catalyst and the hydrotreating zone. The oligomerization zone may also be referred to herein as an oligomerization reactor. The oligomerization zone is not limited to any particular reactor type. For example, the oligomerization zone may comprise a fixed-, fluidized-, or moving bed reactor. The oligomerization stage or step may be performed in batch or continuous mode, with recycling of unconsumed starting materials if required.

Catalysts for Hydrotreating

In an embodiment, the hydrotreating catalyst may comprise a metal and a support material, wherein the metal may be selected from Ni, Mo, Co, W, and combinations thereof, and the support may comprise a refractory oxide, such as alumina. The hydrotreating catalyst may be disposed within a hydrotreating zone. The hydrotreating zone may also be referred to herein as a hydrotreating reactor.

The hydrotreating zone is not limited to any particular reactor type. For example, the hydrotreating zone may comprise a fixed-, fluidized-, or moving bed reactor. The hydrotreating stage or step may be performed in batch or continuous mode. The hydrotreating catalyst and the hydrotreating zone will typically be separate from the oligomerization catalyst and the oligomerization zone. For example, the hydrotreating zone will typically be housed in a vessel that is separate from that housing the oligomerization zone (see, for example, FIG. 1).

Feedstocks for Base Oil Production

In an embodiment, feedstocks for oligomerization may comprise at least one fatty acid reactant or a mixture of fatty acid reactants. In an embodiment, the at least one fatty acid reactant for oligomerization may comprise a mixture of at least two (2) fatty acids. In an embodiment, reactants for oligomerization may comprise C₁₂-C₂₂ unsaturated fatty acids. In an embodiment, feedstocks for oligomerization as disclosed herein may be derived from a triglyceride-containing biomass source such as oils or fats from plants, animals, and/or other biological organisms or biological systems. In an embodiment, a fatty acid feed may comprise at least 90 wt % free fatty acids, or at least 95 wt % free fatty acids, or at least 97 wt % free fatty acids. In an embodiment, the fatty acid feed to the oligomerization zone may comprise at least 90 wt % C₁₆-C₂₀ free fatty acids.

In an embodiment, fatty acid-containing feedstocks for oligomerization may be derived from one or more triglyceride-containing materials including, but not limited to, canola oil, soy oil, rapeseed oil, palm oil, peanut oil, jatropha oil, and the like, and their respective fatty acid constituents, and combinations thereof. Additional or alternative sources of triglycerides, which can be hydrolyzed to yield fatty acids, include, but are not limited to, algae, animal tallow, and zooplankton, or the like. Some non-limiting examples of unsaturated fatty acids include, without limitation, palmitoleic acid, oleic acid, and linoleic acid.

In an embodiment, in situations where a fatty acid feedstock may contain a mixture of saturated fatty acids, mono-unsaturated fatty acids, and polyunsaturated fatty acids, one or more techniques may be employed to isolate, concentrate, or otherwise separate one or more types of fatty acids from one or more other types of fatty acids in the mixture (see, e.g., U.S. Pat. No. 8,097,740 to Miller).

Systems for Base Oil Production by Fatty Acid Oligomerization and Hydrotreating

Systems and processes for base oil production will now be described with reference to the drawing. FIG. 1 schematically represents a process and system, according to the instant disclosure, for the production of base oil from fatty acids without an isomerization step or an isomerization zone. In system 110, a fatty acid feedstock 12 (e.g., as described hereinabove) may be fed to an oligomerization reactor 120. Oligomerization reactor 120 may also be referred to herein as an oligomerization zone. Feedstock 12 may be contacted with an oligomerization catalyst (e.g., as described hereinabove) under oligomerization conditions within oligomerization reactor 120 to provide an oligomerization product 122. Suitable oligomerization conditions are described hereinabove. In an embodiment, oligomerization reactor 120 is not under hydrogen pressure, since hydrogen pressure in the oligomerization zone may saturate the olefinic bond, thereby preventing fatty acid oligomerization.

The oligomerization product 122 (e.g., effluent from oligomerization reactor 120) may be fed to a fractionation unit 130 for the separation of oligomerization product 122. For example, a lighter fraction comprising unconverted fatty acid monomers 12′ may be separated from a heavier fraction comprising a mixture of fatty acid oligomers 132 via fractionation unit 130. The unconverted fatty acid monomers 12′ may be recycled to oligomerization reactor 120. As a non-limiting example, fractionation unit 130 may comprise one or more distillation columns.

The heavier portion of the oligomerization product may be fed from fractionation unit 130 to a hydrotreating unit 140 for hydrotreating the mixture of fatty acid oligomers 132, i.e., for the removal of oxygen, using a suitable hydrotreating catalyst (e.g., as described hereinabove) to provide a base oil product 142 having the characteristics as described herein, without the need for isomerization or other dewaxing step(s). In an alternative configuration for base oil production, the oligomerization product may be hydrotreated prior to separating the lighter fraction from the heavier base oil containing fraction.

Suitable hydrotreating conditions are described hereinabove. In addition to the removal of oxygen, the hydrotreating catalyst in hydrotreating reactor 140 may also saturate olefins or other unsaturated constituents of the oligomerization product to saturated hydrocarbons under the hydrotreating conditions disclosed herein. However, the hydrotreating catalyst in hydrotreating reactor 140 will typically lack any substantial isomerization activity for the oligomerization product under the hydrotreating conditions disclosed herein.

The use of separate reactors for oligomerization and hydrotreating, as shown in FIG. 1, allows much more control over the oligomerization reaction so as to obtain a mixture of oligomeric fatty acids containing a suitable amount of trimers and heavier molecules and having a suitable degree of branching in the trimers and heavier molecules as a result of the oligomerization reactions per se. In this manner, a low pour point base oil product can be conveniently prepared solely by hydrotreating the oligomeric fatty acid mixture and in the absence of an isomerization step. Obtaining such a mixture of oligomeric fatty acids using a single reactor to house both the oligomerization and hydrotreating catalysts would be difficult or impossible, since hydrogen pressure used for hydrotreating may eliminate olefins from the feedstock and so prevent oligomerization, and furthermore since during hydrotreating the temperature needs to be carefully controlled so as to be high enough to remove all of the oxygen but low enough to prevent excessive cracking.

Thus, according to systems and processes as disclosed herein, the efficient production of base oil product 142 from fatty acid containing feedstock 12 may be achieved in the absence of an isomerization step, i.e., without a step for isomerizing either the oligomerization product or its constituents either before or after the hydrotreating step. In an embodiment, base oil product 142 may be blended with other base oils and/or combined with various additives to provide finished lubricants.

EXAMPLES

Example 1

Oligomerization of Oleic Acid Using a Batch Reactor

In this Example 1, 90% technical grade oleic acid was used (Alfa Aesar®, Ward Hill, Mass.). The composition and properties of this material were as follows:

Fatty Acid, total %   100.0
Fatty acid composition:
Linoleic acid, %      5
Oleic acid, %         93
Other fatty acid, %   2
Acid number, mg KOH/g 188
Bromine number        54

One hundred grams (100 g) of the technical grade oleic acid was mixed with 8 wt % Montmorillonite K-10 powder (Sigma-Aldrich Corp., St Louis, Mo.) and 2 wt % water. The mixture was introduced into a 300 ml autoclave and heated to 400° F. in 60 minutes. After 4 hours at 400° F. the reactor was cooled to room temperature. The Montmorillonite K-10 powder was then filtered out to provide liquid products only.

The conversion of the technical grade oleic acid was 55.9% and the oligomer yield was 50.9%, expressed as conversion of the technical grade oleic acid to fatty acid oligomers. Simulated distillation (SimDist) analysis (ASTM D-2887) of the whole liquid product of Example 1 is presented in Table 1.

TABLE 1
Simulated distillation analysis of the whole liquid product of Example 1
SimDist (D2887) (vol %, ° F.)
0.5/5   546/644
10/30   665/681
50      709
70/90   960/988
95/99.5 1043/1123

Example 2

Oligomerization of Oleic Acid Using a Continuous Stirred Reactor

The 90% technical grade oleic acid (as described in Example 1) was mixed with 4 wt % Montmorillonite K-10 powder and 2 wt % water, and the mixture was stirred continuously to prevent settling. The stirred mixture was introduced into a 300 ml autoclave at a feed rate of 5 cc/hr. The autoclave was equipped for continuous stirring and with a dip tube for products to flow out of the reactor. The equilibrium liquid level inside the reactor was 60 cc. The autoclave was blanketed with nitrogen at a flow rate of 15 cc/min to maintain the unit pressure at 500 psig. Once the autoclave was filled with the fatty acid mixture, the autoclave was heated to 400° F. in 60 minutes and held at 400° F. throughout the run. Products were collected once the unit was line out. The Montmorillonite K-10 powder was then filtered out to obtain liquid products only. The properties of the whole liquid product of Example 2 are presented in Table 2.

TABLE 2
Properties of the whole liquid product of Example 2
Oligomer Yield, wt %       35.0
API                        23.4
C, wt %                    77.3
H, wt %                    12.2
O, wt %                    10.5
Acid number, mg KOH/g      169
Bromine number, g-Br/100 g 35
SimDist (D2887) (vol %, ° F.)
0.5/5                      485/641
10/30                      659/683
50                         692
70/90                      795/964
95/99.5                    998/1143

It was observed that the oleic acid conversion and oligomer yield was much higher in Example 1 than in Example 2. However, based on SimDist analysis the amount of fatty acid trimers produced in Example 2 was higher than in Example 1. While not being bound by theory, the increased production of fatty acid trimers observed in Example 2 as compared with Example 1 may be due to the longer residence time in the CSTR as compared with the batch reactor (Example 1).

Example 3

Hydrotreating of Whole Liquid Product from Example 2

In this Example 3, the whole liquid products collected in Example 2 were used as feed for hydrotreating. A conventional Ni/Mo hydrotreating catalyst was loaded into a down-flow fixed bed reactor. The catalyst was presulfided prior to introducing the feed into the hydrotreating reactor. The run conditions were as follows: a pressure of 1000 psig, a temperature of 575° F., a LHSV of 1.0 h⁻¹, and an inlet H₂ flow rate of 5000 scf/bbl. The properties of the effluent from the hydrotreating reactor (hydrotreated mixture) are presented in Table 3.

TABLE 3
Properties of hydrotreated mixture from Example 3
CO, wt %          0.05
CO2, wt %         0.74
H2O               8.41
C4−, wt %         0.1
C5−180° F., wt %  0.2
180-700° F., wt % 60.4
700+ ° F., wt %   30.1
C5+, wt %         90.71
SimDist (D2887) (vol %, ° F.)
0.5/5             512/565
10/30             576/593
50                606
70/90             660/890
95/99.5           915/1044

Example 4

Separation of Fatty Acid Oligomers from Hydrotreated Mixture

The effluent from the hydrotreating reactor (Example 3) was subjected to gas-liquid separation at a pressure of about 1000 psig to provide a liquid fraction comprising a hydrotreated mixture of fatty acid oligomers and unconverted fatty acid monomers. After the removal of water, the hydrotreated mixture was distilled under vacuum at 285° F. to separate unconverted monomers from the fatty acid oligomers. Properties of the hydrotreated fatty acid oligomer fraction from the vacuum distillation are presented in Table 4. The combined yield of hydrotreated fatty acid trimers and higher oligomers was determined to be about 16.55 wt % of the total yield of hydrotreated fatty acid oligomers based on SimDist analysis.

TABLE 4
Properties of hydrotreated fatty acid oligomers (700+ ° F.)
VI                130
Vis @40° C., cSt  42.96
Vis @100° C., cSt 7.208
Cloud, ° C.       18
Pour, ° C.        −23
SimDist (D2887) (vol %, ° F.)
0.5/5             658/771
10/30             828/867
50                881
70/90             904/1054
95/99.5           1129/1284

Example 5

NMR Analysis of Hydrotreated Fatty Acid Oligomers

¹H NMR analysis of the hydrotreated fatty acid oligomers (base oil product) from Example 4 was performed using a Bruker Avance 500 MHz spectrometer operating at 500.11 MHz and using 50% solutions in CDCl₃. All spectra were obtained under quantitative conditions using 30° pulse (9.0 μs), recycle delay of 2 second and 128 scans to ensure good signal-to-noise ratios. TMS was used as an internal reference. The results of the NMR analysis are presented in Table 5.

In Table 5, the Branching Index (BI) is the percent methyl hydrogens among the total aliphatic hydrogens, the Branching Proximity (BP) is the percent epsilon-CH₂ carbons among the total carbons, the Free Carbon Index (FCI) is the total number of epsilon-CH₂ carbons, and the term “epsilon-CH₂” carbons is defined as recurring CH₂ carbon located five or more (5+) CH₂ carbon atoms away from a branched carbon along the hydrocarbon chain.

TABLE 5
1H NMR analysis of hydrotreated fatty acid oligomers (base oil product)
NMR Analysis:
2-methyl                        0.25
3-methyl                        0.06
4-methyl                        0.11
5+ methyl                       0.30
Internal ethyl                  0.13
Adjacent methyl                 0.00
Internal propyl                 0.07
Sum                             0.92
Branching Index (BI)            20.19
Branching Proximity (BP)        18.61
Alkyl branches per molecule     0.92
Methyl branches per molecule    0.71
BI − 0.5BP                      29.50
BI + 0.85BP                     36.01
Free Carbon Index (FCI)         5.62
FCI/END methyl ratio            1.75
Alkyl branches per 100 carbons  3.05
Methyl branches per 100 carbons 2.36
% Branches at 2 position        27.11
% Branches at 3 position        6.06
% Branches at 2 + 3 positions   33.17
% Branches at 4 position        12.19
% Branches at 5+ positions      32.20
% Olefins                       0.99

The data presented in Table 5 indicate that the hydrotreated fatty acid oligomeric mixture comprises mostly singly branched molecules with various branching positions, which is consistent with the observed low pour point of the base oil product. The small amount (0.99%) of olefinic materials in the sample may also contribute to the low pour point of the base oil sample from Example 4.

For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Furthermore, all ranges disclosed herein are inclusive of the endpoints and are independently combinable. Whenever a numerical range with a lower limit and an upper limit are disclosed, any number falling within the range is also specifically disclosed. Additionally, chemical species including reactants and products designated by a numerical range of carbon atoms include any one or more of, or any combination of, or all of the chemical species within that range.

Any term, abbreviation or shorthand not defined is understood to have the ordinary meaning used by a person skilled in the art at the time the application is filed. The singular forms “a,” “an,” and “the,” include plural references unless expressly and unequivocally limited to one instance. All publications, patents, and patent applications cited in this application are incorporated by reference herein in their entirety to the extent not inconsistent herewith.

Modifications of the exemplary embodiments disclosed above may be apparent to those skilled in the art in light of this disclosure. Accordingly, the invention is to be construed as including all structure and methods that fall within the scope of the appended claims. Unless otherwise specified, the recitation of a genus of elements, materials or other components, from which an individual component or mixture of components can be selected, is intended to include all possible sub-generic combinations of the listed components and mixtures thereof.

Claims

1. A process for base oil production, comprising:

a) oligomerizing at least one unsaturated fatty acid to provide an oligomerization product comprising a mixture of fatty acid oligomers; and

b) hydrotreating at least a portion of the oligomerization product to provide a base oil product having a pour point less than −12° C., wherein the process does not include a step for isomerizing the oligomerization product.

2. The process according to claim 1, wherein the base oil product has a pour point less than −18° C.

3. The process according to claim 1, wherein the base oil product comprises at least 10 wt % hydrotreated fatty acid trimers and heavier molecules.

4. The process according to claim 1, wherein:

step a) comprises contacting the at least one unsaturated fatty acid with an oligomerization catalyst in the presence of water in an oligomerization zone under oligomerization conditions to provide the mixture of fatty acid oligomers; and

step b) comprises contacting the mixture of fatty acid oligomers with a hydrotreating catalyst in the presence of hydrogen gas in a hydrotreating zone under hydrotreating conditions to provide the base oil product.

5. The process according to claim 4, wherein:

the oligomerization conditions comprise a temperature in the range from 400 to 500° F., a pressure in the range from 0 to 500 psig, and a LHSV in the range from 0.05 to 1.0 hr−1, and

the oligomerization catalyst comprises an acidic clay catalyst.

6. The process according to claim 4, wherein:

the oligomerization zone is separate from the hydrotreating zone, and

step a) is performed in the absence of hydrogen pressure.

7. The process according to claim 1, wherein the oligomerization product further comprises unconverted fatty acids monomers, and the process further comprises:

c) separating the unconverted fatty acids from the mixture of fatty acid oligomers, and wherein step b) comprises hydrotreating the mixture of fatty acid oligomers after step c).

8. The process according to claim 1, wherein the base oil product has a kinematic viscosity at 100° C. in the range from 4 to 10 cSt.

9. The process according to claim 1, wherein the base oil product constituents have an average molecular weight in the range from 400 to 800.

10. The process according to claim 1, wherein the base oil product has a Viscosity Index in the range from 120 to 150.

11. The process according to claim 1, wherein the base oil product has an NMR branching index in the range from 10 to 30.

12. The process according to claim 1, wherein the base oil product has an average degree of molecular branching in the range from 2 to 4 alkyl branches per 100 carbon atoms.

13. A process for base oil production, comprising:

a) contacting a fatty acid feed comprising at least one unsaturated fatty acid with an oligomerization catalyst in an oligomerization zone under oligomerization conditions to provide a mixture of fatty acid oligomers; and

b) contacting the mixture of fatty acid oligomers with a hydrotreating catalyst in a hydrotreating zone under hydrotreating conditions to provide a base oil product having a pour point less than −12° C., wherein the process is performed in the absence of an isomerization step.

14. The process according to claim 13, wherein:

the oligomerization conditions comprise a temperature in the range from 400 to 500° F., a pressure in the range from 0 to 500 psig, and a LHSV in the range from 0.05 to 1.0 hr−1,

step a) is performed in the absence of hydrogen pressure, and

the fatty acid feed comprises from 0.5 to 3.0 wt % water.

15. The process according to claim 13, wherein the base oil product has a kinematic viscosity at 100° C. in the range from 4 to 10 cSt, a Viscosity Index in the range from 120 to 150, an NMR branching index in the range from 10 to 30, and an average degree of molecular branching in the range from 2 to 4 alkyl branches per 100 carbon atoms.

16. The process according to claim 13, wherein:

the fatty acid feed comprises at least 90 wt % C16-C20 free fatty acids, and

at least 20 wt % of the base oil product boils at a temperature above 900° F.

17. A process for base oil production, comprising:

a) oligomerizing at least one unsaturated free fatty acid to provide an oligomerization product comprising a mixture of fatty acid oligomers, wherein the mixture of fatty acid oligomers comprises fatty acid trimers and heavier molecules; and

b) hydrotreating the mixture of fatty acid oligomers to provide a base oil product, wherein:

the base oil product comprises hydrotreated fatty acid trimers and heavier molecules,

the hydrotreated fatty acid trimers and heavier molecules jointly represent from 15 to 20 wt % of the base oil product, and

the base oil product has a pour point less than −12° C.

18. The process according to claim 17, wherein the base oil product is obtained in the absence of an isomerization step.

19. The process according to claim 17, wherein:

the at least one unsaturated free fatty acid is selected from a C12 to C22 fatty acid,

step a) comprises contacting the at least one unsaturated free fatty acid with an oligomerization catalyst in an oligomerization zone under oligomerization conditions in the absence of hydrogen pressure to provide the mixture of fatty acid oligomers,

the oligomerization catalyst comprises an acidic clay catalyst,

the oligomerization conditions comprise an oligomerization temperature in the range from 400 to 500° F., and

the base oil product constituents have an average molecular weight in the range from 400 to 800.

20. The process according to claim 19, wherein the base oil product, as provided by step b) and in the absence of an isomerization step, has a kinematic viscosity at 100° C. in the range from 4 to 10 cSt, a Viscosity Index in the range from 120 to 150, and a pour point less than −18° C.