Stability of hydrocarbons containing asphal tenes

Abstract

Heavy fuel oils or residual fuel oils can be stabilized with magnesium over-based compounds such as magnesium overbased carboxylates. It was surprisingly discovered that adding magnesium overbased carboxylates to the residual fuel oils shortly after thermal cracking gave much better results than can be achieved after the application of the carboxylates to the fuel oil after storage. Further, compounds containing at least about 21 wt % magnesium also give better results than compounds with 18 wt % or less, in one non-limiting embodiment. Magnesium overbased compounds can also be added to coker feedstocks to reduce coker furnace fouling. Treatment with the methods of this invention reduces asphaltene deposits and sludges.

Description

FIELD OF THE INVENTION The present invention relates to methods and compositions to stabilize hydrocarbon streams containing asphaltenes, and more particularly relates, in one embodiment, to methods and compositions to stabilize residual fuel oils and coker feedstocks using readily available materials. BACKGROUND OF THE INVENTION The stability of heavy fuel oils obtained from thermally cracked residual oils is a well known problem with significant economic ramifications. Residual fuel oil consists predominantly of an oil phase, the composition of which is almost entirely related to the crude oil from which it originates. In this oil phase are dispersed relatively large hydrocarbon molecules called asphaltenes. It is the nature of asphaltenes to be attracted to one another, and it is this tendency, along with size and concentration of the asphaltene molecules, that are consequences of both the crude oil type and the thermal cracking manufacturing process. The compositions of the va...

AI Technical Summary

Benefits of technology

Accordingly, it is an object of the present invention to provide a chemical composition for improving the stability of thermally cracked residual fuel oils.

There is additionally provided in another non-restrictive form of the invention a stabilized heavy fuel oil that includes a thermally cracked residual oil. The stabilized heavy fuel oil also includes a magnesium overbased compound in an amount effective to improve the stability of the fuel oil. The magnesium overbased compound is added to the thermally cracked residual oil sufficiently soon after thermal cracking to produce the residual oil to improve stability. The magnesium overbased compound may be a magnesium overbased carboxylate, a magnesium overbased sulfonate, and / or a magnesium overbased phenate.

Problems solved by technology

The stability of heavy fuel oils obtained from thermally cracked residual oils is a well known problem with significant economic ramifications.

The effects of sludge formation in a residual fuel oil in systems where that fuel oil is used to power an engine can result in choked centrifuges, filter blocking, heater fouling, and ultimately, engine shut down and damage.

However, the simple formation of sediment over time in the bottom of storage tanks causes problems because these sludge layers are difficult to remove.

However, these techniques have the disadvantage of having to be customized for each particular fuel oil.

If such streams are not available, any attempt to blend unstable cracked fuel with atmospheric or vacuum gas-oil will result in a de-stabilization of asphaltenes.

Addition of chemicals in storage tanks also requires good mixing, which is seldom available.

Similar stability problems affect visbreaking and delayed coking processes, and potentially any bottoms upgrading process where the feed is stored at elevated temperatures prior to processing.

Although delayed coking is used herein as a specific embodiment, as delayed cokers are units where the problem is often seen, it will be appreciated that the problem is present in any operation where feed is preheated and heat exchangers experience fouling.

A common problem with this process is the formation of fouling (coke formation) in the process furnace.

Any of several changes to which the feedstock is exposed can disturb this colloidal state, with precipitation of the asphaltenes on the furnace tubes.

The primary economic impact of this furnace coking or fouling includes lost production penalties and potentially shorter furnace tube life.