Renewable diesel production with very low sulfiding agent addition rates

Abstract

This invention describes a method for producing renewable hydrocarbon fuels from a lipid feedstock. The process involves hydrotreating the lipid feedstock over a bed of sulfided base metal catalyst to convert fatty acids into paraffinic hydrocarbons. The hydrotreating step is conducted at a high weighted average bed temperature, requiring no more than about 50 wppm of a sulfiding agent to maintain catalyst activity. The paraffinic hydrocarbons are then isomerized to produce hydrocarbons in the C3-C18 range, which are fractionated into LPG, naphtha, and a middle distillate fuel fraction. The middle distillate fuel, which can be used as diesel or jet fuel, has a sulfur content of about 1 ppm or less and a total acid number less than 0.02 mg KOH / g.

Description

T-12092-W001PATENT APPLICATIONRENEWABLE DIESEL PRODUCTION WITH VERY LOW SULFIDING AGENT ADDITION RATESFIELD OF THE INVENTION

[0001] The present technology relates to production of hydrocarbon fuels from renewable feedstocks. More particularly, the technology relates to manufacture of renewable diesel from lipid feedstock with low levels of sulfiding agent added to maintain catalyst activity.BACKGROUND

[0002] Methods for production of renewable diesel and jet fuel from lipid feedstocks such as fats and oils have been disclosed in the prior art. These methods comprise a hydrotreating step wherein a lipid feedstock is converted to mainly n-paraffins through hydrodeoxygenation, decarboxylation, decarbonylation, and hydrogenation reactions. The reaction converts C16 and Cl 8 fatty acids to C15-C18 n-paraffins. Although in the diesel boiling range, the product has a high cloud point of around 20° C and needs to be hydroisomerized in order to meet the low temperature flow requirements of diesel and jet fuel.

[0003] The prior art teaches that the hydrotreating step is preferably conducted over sulfided NiMo or CoMo catalyst. Preferred hydrotreating temperatures are said to be in the 250-350° C (482-662° F) range, with pressures in the 435-1450 psi range. Since naturally occurring lipid compositions are generally low in sulfur (typically less than 40 ppm), a sulfiding agent such as dimethyl disulfide is added to the lipid to ensure the hydrotreating catalyst is maintained in the active sulfide state. For example, US Patent 8,859,832 teaches that 50-570 wppm sulfur (total sulfur per total feed) is needed for stable hydrotreater operation.

[0004] The prior art teaches that the subsequent hydroisomerization step is preferably conducted over bifunctional catalyst. These catalysts include a hydrogenation-dehydrogenation activity and acid activity. The former functionality may be provided by either base metals such a tungsten or noble metals like platinum. However, prior art references point to better activity and selectivity when noble metals are used, including platinum and combination of platinum andT-12092-W001 palladium. The acid activity may be provided by a silica-alumina acidic support (including silicoaluminophosphates). The prior art teaches that use of shape selective catalysts minimizes hydrocracking side reactions and thus maximizes yields of the higher value middle distillate fuels (diesel and jet) over lower value LPG and naphtha. A preferred hydroisomerization catalyst disclosed in the prior art is Pt / SAPO-11.

[0005] Since noble metal catalysts can be poisoned by sulfur (e.g., as H2S present in hydrogen treat gas), the prior art teaches that the liquid product from the hydrotreating step is preferably stripped of H2S (and other gas phase byproducts of the hydrotreating) before introduction to the hydroisomerization reaction step. As such, the prior art teaches a “sour” reactor system for hydrotreating and a “sweet” reactor system for the hy droi somerization / hy drocracking step .

[0006] Having to add sulfur to the hydrotreater only to subsequently remove it from the hydroisomerization / hydrocracking reactor system adds operating and capital costs of the process. Thus, there remains the need for a lower cost renewable diesel / jet fuel process wherein sulfiding agent addition is minimized.SUMMARY

[0007] The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.

[0008] An embodiment of the invention is a method for producing renewable hydrocarbon fuels. The method includes the step of initially hydrotreating a lipid feedstock over at least one bed of sulfided base metal catalyst. The hydrotreating step converts the naturally occurring fatty acids in the lipid to paraffinic hydrocarbons that are mainly in the same carbon number range. The weighted average bed temperature is maintained high enough such that no more than 50 wppm sulfiding agent (expressed as unit mass of sulfur per mass of total feed) is required for maintaining catalyst activity stability.T-12092-W001

[0009] Another embodiment of the invention includes the step of isomerizing the paraffinic hydrocarbons. The product stream from the isomerization step comprises hydrocarbons in the C3-C18 range that are fractionated into LPG (C3 / C4), naphtha (C5-C8), and a middle distillate fuel fraction (C9-C18). The middle distillate fuel may be used as diesel, jet fuel, or fractionated into diesel and jet fuel products. All four product fractions have a sulfur content of 1 ppm or less and a total acid number less than 0.02 mg KOH / g.

[0010] An additional embodiment of the invention is to provide conditions for lipid hydrotreating that maintains sulfided catalyst activity stability without addition of more than 50 wppm sulfiding agent, preferably with less than 40 wppm sulfiding agent (expressed as unit mass of sulfur per mass of total feed).

[0011] A further embodiment of the invention is a method of producing renewable diesel / jet fuel process wherein the liquid from the “sour” hydrotreater reactor system is not stripped to remove gas phase byproduct of hydrotreating before introduction to “sweet” hydroisomerization reactor system.

[0012] Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description of the various embodiments and specific examples, while indicating preferred and other embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by referring to the following more detailed description of the presently preferred exemplary embodiments of the invention in conjunction with the accompanying drawings, of which:

[0014] FIG. 1 depicts a flow diagram of one embodiment of the present invention; andT-12092-W001

[0015] FIG. 2 provides a chart showing catalyst activity for different sulfur feeds.DETAILED DESCRIPTION

[0016] The apparatuses and methods disclosed in this document are described in detail by way of examples and with reference to the figures. Unless otherwise specified, like numbers in the figures indicate references to the same, similar, or corresponding elements throughout the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatuses, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific shapes, materials, techniques, arrangements, etc. are either related to a specific example presented or are merely a general description of such a shape, material, technique, arrangement, etc. Identifications of specific details or examples are not intended to be, and should not be, construed as mandatory or limiting unless specifically designated as such. Selected examples of apparatuses and methods are hereinafter disclosed and described in detail with reference made to FIGURES.

[0017] It was surprisingly discovered that by operating the hydrotreating at weighted average bed temperatures (WABT) of 620° F or higher, stable sulfided catalyst activity can be achieved at very low sulfiding agent addition rates of 50 wppm or less. Preferred sulfiding agent addition rates are between 20 wppm and 40 wppm (expressed as unit mass of sulfur per mass of total feed).

[0018] Referring to FIG. 1, a lipid feedstock 101 is introduced to surge drum 10. The lipid feedstock may be an animal fat, a vegetable oil or other plant-based oil, or a used cooking oil (“UCO”). In embodiments, the animal fats and vegetable oils include tallow, lard, poultry, fish, canola, rapeseed, palm, soy, corn, jatropha, carinata, cotton seed, hempseed, sunflower, restaurant and food processing greases, and combinations thereof. In embodiment, the lipid feedstock undergoes a pretreatment step for removal of contaminants prior to hydrodeoxygenation. In embodiments, the pretreated fats, oils, and greases, contain less than 6 ppm phosphorus, less than 2 ppm silicon, less than 100 ppm organic nitrogen, and less than 6 ppm total metals, and the metals include but are not limited to iron, sodium, potassium, calcium, magnesium, and copper. In embodiments, the organic nitrogen content is less than 50 wppm,T-12092-W001 less than 40 wppm, less than 30 wppm, less than 20 wppm, less than 10 wppm, or in a range between any of these two values. For example, the lipid feedstock 101 has a nitrogen content between 10 wppm and 50 wppm. In a preferred embodiment, the lipid feedstock 101 is soybean oil with less 20 wppm nitrogen, less than 3 ppm phosphorus, and less than 3 wppm metals.

[0019] The lipid feedstock 101 may also include small amounts of naturally occurring organosulfur species, typically as less than 40 ppm sulfur. Depending on the concentration of such species, additional sulfiding agent may be required in order to maintain total sulfur to the reactor at up to 50 wppm, preferably in the range of 20 to 40 wppm. Preferred sulfiding agents convert to H2S under hydrotreating conditions and include compounds such as dimethyl disulfide and carbon disulfide.

[0020] The surge drum feedstock 102 is pressurized through pump 12 to provide a pressurized feedstock 103. This stream is diluted with a pressurized recycle product 113 to form diluted feed 103 A. The diluted feed is combined with compressed hydrogen treat gas 133 to provide a two-phase feed 104 comprising hydrogen gas and diluted feedstock. The two-phase feed 104 is heated in a feed-effluent exchanger 30 to provide a partially heated reactor feed 105. This stream is further heated in a heater 46 to provide the reactor feed 106. Although the feedeffluent exchanger is preferably a shell and tube heat exchanger with the two-phase feed flowing through the tubes, the heater 46 may be any number of heat transfer equipment known to persons or ordinary skill in the art. For example, heater 46 may be a fired heater or a shell and tube exchanger with hot oil circulation through the shell side.

[0021] The heated reactor feed 106 enters a hydroconversion reactor 20 where it comes into contact with a bed of hydrotreating catalyst 21. The bed of hydrotreating catalyst includes a sulfided base metal catalyst such as NiMo on alumina support. In embodiments, the bed of hydrotreating catalyst comprises a plurality of catalysts stacked according to activity, with inert media and least active catalyst on top of the bed, and the most active catalyst at the bottom. Preferred catalysts have Mo contents in the 3-20 wt.% range, and Ni content in the 0-5% wt.% range. In embodiments, the hydrotreater bed 21 may comprise different beds of hydrotreating catalyst. For example, hydrotreating bed 21 may have a top bed 21a and a bottom bed 21b (notT- 12092-W001 shown), with the top bed loaded with a 0.5%Ni / 5% Mo catalyst and the bottom loaded with a 3%Ni / 15%Mo catalyst.

[0022] Since lipid hydrotreating is exothermic, the temperature increases across bed 21. A weighted average bed temperature (WABT) value is used to express the “average” temperature of the reactor which accounts for the nonlinear temperature profile between the inlet and outlet of the reactor.

[0023] In the equation above, Tnand Tiolltrefer to the temperature at the inlet and outlet of the bed, respectively, of catalyst bed z. As shown, the WABT of a hydrotreater reactor section with A different catalyst beds may be calculated using the WABT of each bed (WABT,) and the weight of catalyst in each bed (Wet). Referring to FIG. 1, if bed 21 has an inlet temperature of 610 F and an outlet temperature of 720 F, the WABT of bed 21 will be 683 F. To ensure catalyst activity stability under low sulfur conditions, the WABT of bed 21 is maintained above 620 F. For example, the WABT of bed 21 is at 630° F, 640° F, 650° F, 660° F, 670° F, 680° F, 690° F, 700° F, or at a temperature between any two of these values. For example, in a preferred embodiment, hydrotreater bed 1 operates at WABT range of 650-680° F.

[0024] The WABT of bed 21 may be maintained at the range by controlling the heated reactor feed temperature 106 via heater 46, and / or controlling the ratio of pressurized recycle product 113 to pressurized feedstock 103 (thus reducing or increasing the adiabatic temperature rise across bed 21 via controlling the dilution of the reactive feed components).

[0025] The hydrotreated product exiting bed 21 is contacted with a quench hydrogen 107 to cool down the substantially deoxygenated product before it comes into contact with a hydroisomerization catalyst bed 22. Bed 22 is loaded with a bifunctional catalyst such as Pt or Pd / Pt on an amorphous or crystalline acidic support such as silica-alumina. Preferred supportsT-12092-W001 include zeolites such as SAPO-11, ferrierite, and ZSM-48. In embodiments, a layer of noble metal hydrogenation catalyst such as Pd or Pd / Pt on alumina may be included in bed 21.

[0026] The hydroisomerization bed 22 is maintained at a WABT of 590° F to 690° F, preferably between 600° F and 680° F. The amount of hydrogen quench 107 is modified as needed to achieve the desired bed 22 WABT.

[0027] The hydroconversion reactor 20 operate under a pressure of 900-2200 psig, a Liquid Hourly Space Velocity (LHSV) of 0.5-5.0 h'1(vol / h of pressurized feedstock 103 per volume of catalyst in hydrotreating bed 21), preferably 0.5-2.0 h’1, and with a gas to oil ratio (that is, ratio of compressed hydrogen treat gas 133 to pressurized feedstock) between 8,000 and 18,000 SCF / Bbl.

[0028] Due to low levels of sulfur introduced to the reactor system, the hydroisomerization bed 23 containing noble metal catalyst remains stable. This is despite presence of other gas phase byproducts of lipid hydrotreating (i.e., water and CO / CO2).

[0029] The hydroconversion reactor effluent 108 is cooled in the feed effluent exchanger 30 to provide a partially cooled effluent 109 before further cooling in cooler 32. The cooled reactor effluent 110 is preferably at a temperature around 400-440° F before entering a high-pressure separator 34. In the high-pressure separator 34, the reactor effluent is separated into a gas / vapor phase 115 and a liquid phase 111. The gas phase comprises hydrogen and the (by)products of the hydroconversion reactions. These include the propane, CO, CO2, and water produced in the hydrotreating bed 1 and the light hydrocarbons (mainly C4-C9) produced in the hydroisomerization bed 2. The gas / vapor phase 115 is contacted with a wash water steam 118 before cooling in a cooler 36. The cooler 36 condenses the water and light hydrocarbons to provide a three-phase stream 116 that is separated in a cold separator 38. A water stream 134, a light liquid hydrocarbon stream 117, and gas stream 130 exit the cold separator 38. The gas stream 130 includes CO, CO2, and propane, and is partially purged through purge stream 130A to mitigate buildup in compressed hydrogen treat gas 133. A recycle treat gas BOB is combined with a makeup hydrogen 131 to provide a compressor inlet gas 132. The concentration of hydrogen in compressed hydrogen treat gas 133 is thus maintained at 80 mol% or higher, preferably at 85 mol% or higher.T-12092-W001

[0030] Returning to high-pressure separator 34, the liquid phase I l l is partially directed as stream 112 to a recycle pump 46. A high-pressure separator liquid product 114 and the light liquid hydrocarbon stream 117 are transferred to a product fractionator 50. There, the C3-C18 isoparaffmic hydrocarbons product from hydroconversion (hydrotreating followed by hydroisomerization) of the lipid feedstock is separated into LPG overhead 142, a naphtha sidedraw 144, and a middle distillate fuel 146. The middle distillate fuel 146 may be used directly as a diesel fuel or distilled further to provide a renewable jet fuel and a heavy diesel bottoms. The middle distillate fuel has a sulfur content below 1 wppm.EXAMPLE

[0031] Two bench scale isothermal fixed-bed reactors (PSU-B and PDU) were loaded with the same hydrotreating catalysts and activated under the same pre-sulfiding conditions. Upon startup, an oil feedstock spiked with the same DMDS concentration (equivalent to 330 wppm sulfur on total reactor feed basis) was introduced to both reactors at a hydrocarbon dilution ratio of 3: 1 by volume. This was to confirm the same starting activity by verifying that the same conversion was achieved in both reactors at 600° F. The conversion was measured by total acid number (TAN) of the hydrocarbon product, with full lipid conversion to hydrocarbon being characterized by TAN<0.02 mg / g KOH.

[0032] After confirmation of equivalent starting activity, the PSU-B reactor feed was changed to a feedstock spiked with a significantly lower DMDS concentration (equivalent to 48 wppm sulfur on total reactor feed basis). A test matrix with LHSV values of 1, 1.5, and 2, and WABT values of 600°, 625°, 650°, and 670° F (with constant pressure of 1800 psig) was completed, showing that at WABT of 650° F and higher, the hydrotreater catalyst activity is virtually the same (T ANO.03) for the very low sulfur feed and the high sulfur feed for all LHSV value tested. (See FIG. 2.)

[0033] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiment, and that many modifications and equivalent arrangements may be made thereof within the scope ofT-12092-W001 the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products.

Claims

T-12092-W001CLAIMS1. A process for producing a middle distillate fuel comprising the steps of: a. introducing a lipid feedstock and a sulfiding agent to a hydrotreating step over a bed of sulfided hydrotreating catalyst to produce a deoxygenated product; b. introducing the deoxygenated product to a hydroisomerization step over a bed of hydroisomerization catalyst to produce a reactor effluent; and c. subjecting the reactor effluent to a separation step and a fractionation step then recovering a middle distillate fuel; wherein the sulfiding agent has a concentration of less than 50 wppm expressed as weight of sulfur per mass of total feed to the bed of sulfided hydrotreating catalyst, and the bed of sulfided hydrotreating catalyst has a WABT greater than 620° F.

2. The process of claim 1, wherein the WABT of the bed of sulfided hydrotreating catalyst is between 650° F and 680° F.

3. The process of claim 1, wherein the concentration of the sulfiding agent expressed as weight of sulfur per mass of total feed to the bed of sulfided hydrotreating catalyst is between 20 and 40 wppm.

4. The process of claim 1, wherein the middle distillate fuel has a sulfur content of less than 1 wppm and a total acid number less than 0.02 mg KOH / g.

5. The process of claim 1, further comprising fractionating the middle distillate fuel to produce a jet fuel product.T-12092-W0016. The process of claim 1, wherein the hydrotreating catalyst is a sulfided NiMo catalyst and the hydroisomerization catalyst is platinum on a zeolite-containing support.

7. The process of claim 1, wherein the hydrotreating step produces gas phase byproducts, and the process further comprises introducing the deoxygenated product from the hydrotreatment step to the bed of hydroisomerization catalyst without removing the gas phase byproducts.

8. The process of claim 1, wherein the lipid feedstock comprises at least one of tallow, lard, poultry fat, fish oil, canola oil, rapeseed oil, palm oil, soybean oil, corn oil, jatropha oil, carinata oil, cotton seed oil, hempseed oil, sunflower oil, greases from restaurants and food processing operations, and combinations thereof.

9. The process of claim 1, wherein the nitrogen content of the lipid feedstock is less than 20 wppm.

10. A process for producing a middle distillate fuel comprising the steps of: a. introducing a lipid feedstock and a sulfiding agent to a hydrotreating step over a bed of sulfided hydrotreating catalyst to produce a deoxygenated product; b. introducing the deoxygenated product to a hydroisomerization step over a bed of hydroisomerization catalyst to produce a reactor effluent; and c. subjecting the reactor effluent to a separation step and a fractionation step then recovering a middle distillate fuel; wherein the sulfiding agent has a concentration of between 20 and 40 wppm expressed as weight of sulfur per mass of total feed to the bed of sulfided hydrotreating catalyst, and the bed of sulfided hydrotreating catalyst has a WABT between 650° F and 680° F.T-12092-W00111 . The process of claim 10, wherein the middle distillate fuel has a sulfur content of less than 1 wppm and a total acid number less than 0.02 mg KOH / g.

12. The process of claim 10, wherein the nitrogen content of the lipid feedstock is less than 20 wppm.

13. The process of claim 10, further comprising fractionating the middle distillate fuel to produce a jet fuel product.

14. A process for producing a middle distillate fuel comprising the steps of: a. introducing a lipid feedstock and a sulfiding agent to a hydrotreating step over a bed of sulfided hydrotreating catalyst to produce a deoxygenated product, wherein the nitrogen content of the lipid feedstock is less than 20 wppm; b. introducing the deoxygenated product to a hydroisomerization step over a bed of hydroisomerization catalyst to produce a reactor effluent; and c. subjecting the reactor effluent to a separation step and a fractionation step then recovering a middle distillate fuel, wherein the middle distillate fuel has a sulfur content of less than 1 wppm and a total acid number less than 0.02 mg KOH / g; wherein the sulfiding agent has a concentration of less than 50 wppm expressed as weight of sulfur per mass of total feed to the bed of sulfided hydrotreating catalyst, and the bed of sulfided hydrotreating catalyst has a WABT greater than 620° F.

15. The process of claim 14, wherein the WABT of the bed of sulfided hydrotreating catalyst is between 650° F and 680° F.T-12092-W00116. The process of claim 14, wherein the concentration of the sulfiding agent expressed as weight of sulfur per mass of total feed to the bed of sulfided hydrotreating catalyst is between 20 and 40 wppm.

17. The process of claim 14, further comprising fractionating the middle distillate fuel to produce a jet fuel product.

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