Mineral oils: processes and products – Paraffin wax; treatment or recovery – Chemical treatment
Reexamination Certificate
1997-02-21
2001-01-30
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Paraffin wax; treatment or recovery
Chemical treatment
C208S127000, C585S648000
Reexamination Certificate
active
06179993
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for obtaining a substantial amount of olefinic products from a residual feedstock by use of a vapor short contact time conversion process unit comprised of a bed of fluidized heat transfer solids. The vapor short contact time process unit is operated at conditions which includes steam dilution to reduce partial pressure of hydrocarbon vapors and a vapor residence time less than about 0.5 seconds.
BACKGROUND OF THE INVENTION
In a typical refinery, crude oils are subjected to atmospheric distillation to produce lighter fractions such as gas oils, kerosenes, gasolines, straight run naphtha, etc. Petroleum fractions in the gasoline boiling range, such as naphthas, and those fractions which can readily be thermally or catalytically converted to gasoline boiling range products, such as gas oils, are the most valuable product streams in the refinery. The residue from the atmospheric distillation step is then distilled at a pressure below atmospheric pressure. This later distillation step produces a vacuum gas oil distillate and a vacuum reduced residual oil which typically contains relatively high levels of asphaltene molecules. These asphaltene molecules are responsible for most of the Conradson carbon residue and metal components in the resid. They also contain relatively high levels of heteroatoms, such as sulfur and nitrogen. These feeds have little commercial value, primarily because they cannot be used as a fuel oil owing to ever stricter environmental regulations. They also have little value as feedstocks for refinery processes, such as fluid catalytic cracking, because they produce excessive amounts of gas and coke. Also, their high metals content leads to catalyst deactivation. Thus, there is a great need in petroleum refining for greater utilization of such feedstocks for example by upgrading them to make them more valuable cleaner and lighter feeds.
A significant amount of feedstock in the gas oil boiling range is used to make olefins in steam cracking process units which contains a furnace comprised of fired tubes, or coils in which the feedstock is thermally cracked at temperatures of about 540° C. to 760° C. in the presence of steam. While gas oils are adequate feedstocks for such purposes, they are also relatively expensive feedstocks because of their preferred use for the production of transportation fuels. Residual feeds, which are substantially cheaper than gas oils, are typically unsuitable for use in steam crackers because of excessive cracking and coke formation in the furnace tubes leading to overheating and equipment plugging.
An attempt to overcome these problems was made in U.S. Pat. No. 2,768,127 which teaches the use of residual feedstocks for the production of aromatic and olefinic product streams. This was accomplished by contacting the residua feedstock in a fluidized bed of coke particles maintained at a temperature from about 675° C. to 760° C. While such attempts have been made to overcome these problems, there remains a need for improved processes having better control of solids and vapor residence times.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a process for producing olefins from a residual feedstock, which process comprises converting the feedstock in a process unit comprised of:
(i) a heating zone wherein heat transfer solids containing carbonaceous deposits thereon are received from a stripping zone and heated in the presence of an oxidizing gas;
(ii) a vapor short contact time reaction zone containing a bed of fluidized solids comprised of heat transfer solids recycled from the heating zone; and
(iii) a stripping zone through which solids having carbonaceous deposits thereon are passed from the reaction zone and wherein lower boiling additional hydrocarbons and volatiles are recovered with a stripping gas; which process comprises:
(a) feeding the residual feedstock to said vapor short contact time reaction zone wherein it contacts the fluidized heat transfer solids and catalytic component, which reaction zone is operated at a temperature from about 760° C. to about 790° C. and under conditions such that the solids residence time and the vapor residence time are independently controlled, which vapor residence time is less than about 0.5 seconds, and which solids residence time is from about 5 to about 60 seconds, thereby resulting in a material being deposited onto said solids, and a vaporized fraction containing olefinic products, which material is characterized as a combustible carbonaceous metal-containing material, and wherein steam is fed at a rate from about 0.2 to 0.5 lbs per lb. of residual feedstock;
(b) separating the vaporized fraction from the solids;
(c) separating an olefin-rich fraction from said vaporized fraction;
(d) passing the separated solids to said stripping zone where they are contacted with a stripping gas, thereby removing any remaining volatile material therefrom;
(e) passing the stripped solids to said heating zone where they are heated to an effective temperature that will maintain the operating temperature of the reaction zone; and
(f) recycling heated solids from the heating zone to the reaction zone where they provide the heat of reaction and are contacted with fresh feedstock.
In a preferred embodiment of the present invention, the vapor short contact reaction zone is comprised of a horizontal moving bed of fluidized heat transfer solids.
In other preferred embodiments of the present invention the residence time in the reaction zone for the solids is about 10 to 30 seconds and the residence time for the vapor is less than 1 second.
In still other preferred embodiments of the present invention, the feedstock is selected from the group consisting of vacuum resids, atmospheric resids, heavy and reduced petroleum crude oil; pitch; asphalt; bitumen; tar sand oil; shale oil; coal; coal slurries; and coal liquefaction bottoms.
In still other preferred embodiments of the present invention, the reaction zone is fluidized with the aid of both a mechanical means and a fluidizing gas comprised of vaporized normally gaseous hydrocarbons, hydrogen, hydrogen sulfide, and steam.
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Cheng Tony T.
Jacobson Mitchell
Ladwig Paul K.
Pagel John F.
Parrish Michael R.
Exxon Chemical Patents Inc.
Myers Helane E.
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