Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-06-24
2001-06-19
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S087000, C208S091000, C208S211000, C208S25400R
Reexamination Certificate
active
06248230
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to a method for manufacturing a cleaner fuel and, more particularly, to the removal of NPC (Natural Polar Compounds) from petroleum hydrocarbon feedstocks ranging, in boiling point, from 110 to 560° C., in advance of a catalytic hydroprocessing process. The removal of NPC improves the efficiency of the catalytic process and produces environmentally favorable petroleum products, especially diesel fuel with a sulfur content of below 50 ppm (wt) by deep hydrodesulfurization. Also, the present invention suggests the usage of such NPC to improve fuel lubricity.
DESCRIPTION OF THE PRIOR ART
The ever-worsening environmental pollution problem, especially air quality degradation, has brought stringent environmental regulatory policies throughout the world, and developed countries are imposing tight quality regulations upon transportation fuels. Of such fuels, diesel fuel is considered to be a major contributor of such harmful pollutants as SO
x
, NO
x
and PM (particulate matter). The most severe regulatory standards are being applied to diesel fuels.
While such diesel quality specifications as sulfur content, aromatics content, polyaromatics content, cetane number, T95 (95% distillation temperature), density and viscosity are known to affect generation of the aforementioned pollutants, sulfur content has become the most critical issue because it forms sulfur dioxide when combusted. Further, a portion of sulfur dioxide is readily converted to sulfur trioxide, which, with moisture, forms PM. Besides contributing to the formation of PM, sulfur-containing compounds such as sulfur dioxide and sulfate harm automobile emission after-treatment devices by poisoning the noble metal catalysts therein.
Recently, automobile manufacturers have claimed that the sulfur content of diesel fuel should be reduced to below 30 ppm (wt) for their new diesel engines to meet the future tail-pipe emission regulations. Consequently, a ULSD (ultra low sulfur diesel) market is now emerging, especially in Western Europe. Eventually, such fuels are expected to replace the conventional 500 ppm sulfur diesel fuel market.
In keeping up with the tightening regulations, oil companies have been making large investments to produce environment-friendly petroleum products, for example, by revamping existing facilities or installing new processes. From an economic standpoint, however, neither existing nor newly developed processes thus far appear to be economically feasible under the current price structure of petroleum products. Therefore, the United States and many countries in Western Europe have implemented refiner-inducing policies such as tax incentives, which reimburse additional costs incurred in producing cleaner fuels.
An HDS (hydrodesulfurization) process is most commonly used to reduce sulfur content from diesel fuel by converting sulfur compounds into hydrogen sulfide. In the late 1950's, the HDS process was first introduced as a pretreatment for the naphtha reforming process since catalysts were prone to poisoning by sulfur compounds. Since then, various HDS processes have been developed and an HDS process for LGO (light gas oil) appeared in the 1960's. Nowadays, most refineries are equipped with HDS processes, and statistics show that, in 1994, the unit capacity of kerosene and LGO HDS processes in the world amounted to 21% of the crude distillation units.
Many of the HDS processes currently being used by refiners are non-licensed processes, and most of the related patents pertain to catalyst preparation and modification. Generally, when the process variables are properly modified and suitable catalysts are selected, diesel fuel with 0.1 weight percent of sulfur can be produced. In order to reduce the sulfur content below 50 ppm, however, innovative improvement in terms of the following operating parameters is required: catalyst activity, reaction temperature, bed volume and hydrogen partial pressure.
Catalyst activity has been doubled since the first generation LGO HDS catalyst was introduced in the late 1960's. However, the activity has to be further improved to attain deep HDS to desired levels. Deep HDS is understood herein to refer to hydrodesulfurization rates greater than 95%. An improved activity, by a factor of 3.2, compared to that of the first generation catalyst, is required to reduce the sulfur content from 2,000 ppm to 500 ppm, and an improvement in activity by a factor of 17.6 is needed to reach the 50 ppm level. This means that unless the catalyst activity is dramatically improved, the number of reactors must be increased or the charge rate must be decreased to achieve deep HDS. To make matters worse, the catalysts are getting more and more expensive because of the increase in the amount of impregnated metals employed in the catalysts and the sophisticated modification of support structure, while catalyst lifetime is reduced to ½~⅕ of conventional catalysts, as reaction conditions get severe.
Reaction temperatures may be increased to reduce the sulfur content. However, since most HDS processes were designed for a 0.2% sulfur level, the furnace and the reactor cannot be operated exceeding the design limits. In addition, increase in temperature results in product color degradation and/or reduction in catalyst life.
In the past, many refiners opted to install additional reactors to meet the regulatory standards because it seemed to be a simple and straightforward approach. However, only a finite number of reactors can be added because there exist space limitations, pressure drop considerations across reactors, and huge capital costs for additional reactors and compressors.
Increasing the pressure of reactors, as mentioned previously, could be another alternative. Yet, the revamp costs for high pressure reactors, compressors, pumps and heat exchangers are significantly high, not to mention the hydrogen consumption increase.
Besides sulfur, it has long been disputed whether the aromatics content should be a part of the quality standards of diesel fuel. Nevertheless, automotive diesel fuels with low aromatic content are already manufactured and sold regionally in the United States and Northern Europe. To saturate aromatic compounds, however, a large amount of hydrogen is necessary with noble metal catalysts, and energy consumption also increases noticeably. In addition, the use of noble metal catalysts requires an additional HDS process preceding the catalytic hydrotreating process in order to prevent sulfur and nitrogen compounds from deactivating the catalysts.
Of the catalytic hydroprocessing processes that are designed to produce cleaner diesel fuels from LGO by removing sulfur and aromatic compounds, only a few of them are commercially available, and they can be categorized into the following three groups.
First, there is a process in which HDS (hydro-desulfurization) and HDA (hydro-dearomatization) are accomplished simultaneously under a high temperature and high pressure with a nickel-molybdenum-based catalyst of high activity in a single reactor. The process is, however, not widely used because high temperature and high pressure facilities, together with a low processing rate, significantly increase the investment cost and still cannot achieve a desirable aromatics conversion rate.
A second process utilizes two reactors placed in series. Deep HDS is achieved in the front reactor while the rear reactor charged with a noble metal catalyst, reduces aromatic compounds. The process is usually constructed by adding a new HDA unit in the rear of the existing HDS unit. HDA conversion rate is significantly improved compared to a stand-alone HDA unit. However, investment cost and operation cost also increase significantly.
Third, there is the Syn-Sat process in which HDS and HDA are conducted at a high efficiency by utilizing countercurrent flow in a single reactor. The Syn-Sat process enables higher conversion rates than any other processes, and the process economics are superior to two-stage reaction proce
Choi Kyung-Il
Khang Sin-Young
Kim Jyu-Hwan
Min Dong-Soon
Min Wha-sik
Drinker Biddle & Reath LLP
SK Corporation
Yildirim Bekir L.
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