PROCESS FOR REDUCING ULTRA LOW SULFUR DIESEL COLOR

The present invention is a process for preparing ultra low sulfur diesel. The steps include reacting a feedstock of petroleum crude oil with hydrogen in the presence of a hydrodesulfurization catalyst under hydrodesulfurization conditions, fractionating the reaction products, flash distilling the bottoms fraction, condensing the volatile distillate fraction as ultra low sulfur diesel, and recycling the distillation bottoms fraction for further reacting with hydrogen.

DETAILED DESCRIPTION

In an embodiment, the present invention is a process for preparing ultra low sulfur diesel which is diesel having a sulfur content of less than 15 parts per million. The process steps include (a) reacting a feedstock of petroleum crude oil with hydrogen in the presence of a hydrodesulfurization catalyst under hydrodesulfurization conditions, (b) fractionating the reaction products into a naphtha fraction, a kerosene fraction, and a first bottoms fraction, (c) flash distilling the first bottoms fraction in a distillation column having at least one stage and a total stage efficiency of less than about 99%, thereby yielding a volatile distillate fraction and a second bottoms fraction, (d) condensing the volatile distillate fraction as ultra low sulfur diesel, and (e) recycling the second bottoms fraction into the feedstock of petroleum crude oil for further reacting of the second bottoms fraction with hydrogen in the presence of the hydrodesulfurization catalyst. The volatile distillate fraction should have an ASTM Color of less than or equal to 2.5 and a sulfur content less than 15 ppm. More preferably, the volatile distillate fraction will have an ASTM Color of less than or equal to 1.5.

The hydrodesulfurization catalyst can include, but is not limited to, at least a first metal component selected from Groups 8-10 (IUPAC) metals such as iron, cobalt, and/or nickel, and at least a second metal component selected from Group 6 (IUPAC) metals such as molybdenum and/or tungsten, on a high surface area support material such as alumina. Other suitable desulfurization catalysts include zeolitic catalyts as well as nobel metal catalyts where the noble metal is palladium or platinum. More than one type of hydrodesulfurization catalyst can be used in the same reaction vessel or zone to remove sulfur. In a preferred embodiment, the hydrodesulfurization catalyst is a nickel molybdenum catalyst.

In a preferred embodiment, the hydrodesulfurization conditions are the following operation conditions:

With consideration ofFIG. 1, the flow of a process according to the present invention includes providing a feedstock of petroleum crude oil via a line10into a main reactor20wherein hydrogen and a hydrodesulfurization catalyst are provided. The main reactor20may be a hydrotreater or other reactor as known in the art. Under hydrodesulfurization conditions, the sulfur-containing components of the feedstock and the hydrogen react.

The reaction products flow through line25into the product fractionator30, wherein products are fractionated into a naptha fraction40, a kerosene fraction50, and a first bottoms fraction60. The naptha fraction40is collected via line45. The kerosene fraction is collected via line55. For convenience, line45and line55may be a single line.

The first bottoms fraction60flows through line65into a flash distillation column or flash tank70to separate the volatile distillate fraction80from a second bottoms fraction90containing heavy diesel, sulfur, colorants, and other impurities. Depending upon the stage efficiency of flash distillation column70, the volatile distillate fraction80may contain at least about 80% of the first bottoms stream's diesel having an ASTM Color of less than or equal to 2.5 and a sulfur content of less than 15 ppm. The corresponding second bottoms fraction90may contain up to about 20% of the first bottoms stream's heavy diesel.

Preferably, the the distillation column for the flash distilling step will have a stage efficiency in the range of about 80% to about 99%. More preferably, the distillation column for the flash distilling step will have a stage efficiency of about 95%.

EXAMPLES

The following non-limiting examples illustrate the invention.

Samples of a first bottoms fraction were collected from a hydrodesulfurizing manufacturing plant. Each sample was evaluated for initial ASTM Color and post-treatment ASTM Color according to ASTM D6045, the contents of which are incorporated herein by reference in its entirety.

The post-treatment methods were either (a) flash distilling the sample with a single-stage flash distillation column to 99% efficiency (i.e., 99% volatile distillate fraction and 1% bottoms fraction) or (b) reacting the sample with hydrogen in the presence of a hydrodesulfurization catalyst under hydrodesulfurization conditions in a pilot plant hydrotreater. The flash distillation method demonstrated that the volatile distillate fraction satisfies the ASTM Color requirement, and the additional hydrotreatment method showed conversion of the sample into ULSD that satisfies the ASTM Color specification.

Flash Distillation

Although the invention has been described in considerable detail by the preceding specification, this detail is for the purpose of illustration and is not to be construed as a limitation upon the following appended claims. All cited ASTM standards, reports, references, U.S. patents, allowed U.S. patent applications, and U.S. Patent Applications Publications are incorporated herein by reference.