Process for effecting deep HDS of hydrocarbon feedstocks

Details Process for effecting deep HDS of hydrocarbon feedstocks Process for effecting deep HDS of hydrocarbon feedstocks

1998-03-30

2003-03-11

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Refining

Sulfur removal

C208S210000, C208S213000, C208S217000

Reexamination Certificate

active

06531054

ABSTRACT:

The present invention relates to a process for effecting deep HDS of hydrocarbon feedstocks and additionally obtaining an efficient removal of nitrogen.
In an effort to regulate SO
2
emissions from the burning of fuels, the environmental regulations as to the sulphur content of fuels, in particular diesel fuels, are becoming more and more strict. Until recently, a sulphur content for diesel fuel of between 0.05 and 0.1 wt. % was acceptable, but for the near future it is expected that diesel fuels will be required to have a sulphur content of less than 500 ppm, while for the more distant future a requirement of a maximum sulphur level of 350 ppm or even lower is foreseen. In consequence, there is an increasing need for catalyst systems which can decrease the sulphur content of a hydrocarbon feedstock with a 95% boiling point of 450° C. or less and a sulphur content of 0.1 wt. % or more to a value of less than 500 ppm (0.05 wt. %), preferably to a value of less than 350 ppm, or even to a value of less than 200 ppm, calculated as elemental sulphur on the total liquid product.
EP 0 464 931 describes a process for the concomitant hydrodesulphurisation and aromatics hydrogenation of a diesel boiling range feedstock which contains 0.01-2 wt. %, preferably 0.05-1.5 wt. % of sulphur, in which the feedstock is contacted with a catalyst comprising Ni, W, and optionally P on an alumina support, after which the feedstock is led to a second catalyst comprising Co and/or Ni, Mo, and optionally P on an alumina carrier.
EP-A 0 523 679 describes a process for the production of low-sulphur diesel oil in which the feedstock is contacted in two steps with a hydrotreating catalyst, the first step being carried out at a temperature of 350-450° C. and the second step at a temperature of 200-300° C. In the first step, the sulphur content of the feedstock is reduced to 0.05 wt. % or less. In the second step, the Saybolt colour is brought to a value of −10 or higher. The catalyst is stated to be a conventional hydrotreating catalyst. In the examples catalysts containing Ni and/or Co and Mo on an alumina carrier are applied.
However, it has been found that the catalyst systems described in the above references are not active enough. That is, they do not provide sufficient removal of sulphur and nitrogen. There is need for a catalyst system which, at comparable conditions, can better effect deep HDS and nitrogen removal from hydrocarbon feedstocks with a 95% boiling point of 450° C. or less.
In the context of the present specification the term deep HDS means the reduction of the sulphur content of a hydrocarbon feedstock to a value of less than 500 ppm, preferably less than 350 ppm, and optionally to a value of less than 200 ppm, calculated by weight of elemental sulphur on the total liquid product, as determined in accordance with ASTM D4294. The present invention provides a process which applies a catalyst system which meets this demand.
The present invention accordingly is directed to a process for reducing the sulphur content of a hydrocarbon feedstock to a value of less than 500 ppm, comprising contacting a feedstock with a 95% boiling point of 450° C. or less and a sulphur content of 0.1 wt. % or more in the presence of hydrogen under conditions of elevated temperature and pressure with a first catalyst comprising a Group VI hydrogenation metal component and a Group VIII hydrogenation metal component on an oxidic carrier, after which at least part of the effluent from the first catalyst is led to a second catalyst comprising a Group VI hydrogenation metal component and a Group VIII hydrogenation metal component on an oxidic carrier which comprises 1 to 15 wt. % of silica, calculated on the weight of the catalyst.
Incidentally, EP 0203228 describes a process for catalytically hydrotreating hydrocarbon oils, in which heavy hydrocarbon feedstocks are contacted with a two-bed catalyst system in which the first bed contains a phosphorus compound while the second bed comprises less than 0.5% of said phosphorus compound. In the example the reaction is steered to obtain 0.3 wt. % of sulphur (3000 ppm). Further, GB 2057358 describes a process for lowering the sulphur content and pour point of heavy hydrocarbon feedstocks, such as vacuum gas oils, applying a first catalyst comprising hydrogenation metals on an oxidic carrier, after which the effluent is contacted with a second catalyst having a silica-content higher than 5 wt. %. The sulphur contents obtained in that reference with a second stage catalyst containing less than 15% silica are above 1600 ppm.
Neither of these references teaches obtaining sulphur contents less than 500 ppm with a catalyst containing less than 15 wt. % of silica in the second bed.
The feedstock suitable for use in the process according to the invention has a 95% boiling point, as determined according to ASTM D-1160, of 450° C. or less, preferably 420° C. or less, more preferably 400° C. or less. That is, 95 vol. % of the feedstock boils at a temperature of 450° C. or less, preferably 420° C. or less, more preferably 400° C. or less. Generally, the initial boiling point of the feedstock is above 100° C., preferably above 180° C. The feed contains 0.1 wt. % or more of sulphur, preferably 0.2 to 2.5 wt. % of sulphur, more preferably 0.5 to 2.0 wt. % of sulphur. The feedstock generally contains 20-1200 ppm nitrogen, preferably 30-800 ppm, more preferably 70-600 ppm. The metal content of the feedstock preferably is less than 5 ppm, more preferably less than 1 ppm (Ni+V). Examples of suitable feedstocks are feedstocks comprising one or more of straight run gas oil, light catalytically cracked gas oil, and light thermally cracked gas oil.
The catalyst to be used in the first step of the process according to the invention comprises a Group VI hydrogenation metal component and a Group VIII hydrogenation metal component on a porous inorganic oxide carrier. As examples of suitable carriers may be mentioned carriers comprising alumina, silica, magnesium oxide, zirconium oxide, titanium oxide, as well as carriers comprising combinations of two or more of these materials. Preference is given to carriers comprising alumina or alumina combined with silica, i.e., silica-alumina in which the amount of silica may be up to 10 wt. %, and more particularly up to 5 wt. %. More preferably, the carrier substantially consists of alumina. By “substantially consists of alumina” is meant that the carrier basically consists of alumina, but may contain minor amounts of other components as long as they do not substantially influence the catalytic properties of the catalyst. In general, carrier materials which show limited cracking activity are preferred.
The Group VI metal preferably is molybdenum, tungsten, or a mixture thereof. Generally, molybdenum is preferred. The Group VIII metal preferably is nickel, cobalt, or a mixture thereof, with nickel being preferred. The Group VI hydrogenation metal component generally is present in an amount of 5-50 wt. %, preferably 10-40 wt. %, more preferably 15-30 wt. %, calculated as trioxide. The Group Vil metal component generally is present in an amount of 0.5-10 wt. %, preferably 2-7 wt. %, calculated as oxide. In addition to the Group VI hydrogenation metal component and the Group VIII hydrogenation metal component, the catalyst may contain phosphorus. If the catalyst contains phosphorus, this compound generally is present in an amount of 0.5-10 wt. %, preferably 3-8 wt. %, calculated as P
2
O
5
.
The catalyst to be used in the second bed of the process according to the invention comprises a Group VI hydrogenation metal component and a Group VIII hydrogenation metal component on an oxidic carrier which comprises 1-15 wt. % of silica, calculated on the weight of the catalyst.
The upper limit of 15 wt. % for the silica-content of the second bed catalyst is governed by the desire to minimise the hydrocracking of the hydrocarbon feedstock. As indicated earlier, the process of the present invention is intended to effect removal of sulphur and nitrogen from a hyd

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