Field of the Invention

The present invention relates to a process for upgrading residual hydrocarbonaceous feedstock.

Background of the Invention

A number of schemes for the upgrading 'bottom of the barrel' residues (residual hydrocarbonaceous feedstocks) in refinery processes are commercially available. Of these, delayed coking and Shell visbreaking are considered 'carbon rejection' processes, whereas residue

hydrotreating and hydrocracking are considered 'hydrogen addition' processes. Solvent de-asphalting can be used as feed preparation unit for either of these type of residue upgrading processes. Visbreaking technologies are

relatively low cost but generally result in low distillate yields compared to using a delayed coker. Ebullated bed and Slurry hydrocracking are also known hydroprocessing technologies generating higher yields but at greater cost.

Cracked residue, which may be vacuum flashed, from thermal conversion of residual hydrocarbonaceous

feedstock in a visbreaker is generally routed to a fuel oil pool or as power plant or gasifier feed stock. Part of the undiluted cracked residue may also be used for bitumen blending or as internal refinery fuel.

It is important for refinery processes to extract maximum value from the crude input by achieving a balance between conversion and cost. The conversion of all possible stream to valuable products is an on-going challenge .

The object of the invention is, therefore, to provide a process for upgrading a residual hydrocarbonaceous feedstock in order to extract valuable components .

Summary of the Invention

Accordingly, the present invention provides a process for upgrading residual hydrocarbonaceous

feedstock, said process comprising the steps of:

a) subjecting the residual hydrocarbonaceous feedstock to thermal cracking and separation in a visbreaker to produce a one or more top stream comprising light

hydrocarbon products and gas oil and a bottom stream comprising cracked residue;

b) subjecting the cracked residue product of step a) to a solvent deasphalting process with a deasphalting solvent, to obtain a deasphalted product, which is soluble in said deasphalting solvent; and an asphaltic product which is insoluble in said deasphalting solvent; c) separating the deasphalted product into deasphalted oil and resin; and

d) subjecting the resin to further thermal conversion. Detailed Description of the Invention

The present inventors have developed an innovative line-up for upgrading residual hydrocarbonaceous

feedstock. The residual hydrocarbonaceous feedstocks to be used in accordance with the present invention can suitably be residual hydrocarbon oils, such as those obtained in the distillation of crude oils at atmospheric or reduced pressure and, optionally subjected to further treatment. Residual hydrocarbonaceous feedstock obtained from a process comprising distillation of crude oils at reduced pressure generally has a boiling point of above 550 °C. Residual hydrocarbonaceous feedstock obtained from a process comprising distillation of crude oils at atmospheric pressure generally has a boiling point of above 370 °C. In step a) of the process of the present invention, the residual hydrocarbonaceous feedstock is subjected to thermal cracking in a visbreaker. This process is carried out a high temperature and pressure. Preferably, the thermal cracking is carried out at a temperature in the range of from 440 to 490 °C, more preferably at a temperature in the range of from 450 to 470 °C. Also preferably, the thermal cracking is carried out at a pressure in the range of from 400 to 1300 kPa, preferably in the range of from 500 to 900 kPa.

The feed to the visbreaker is pre-heated and fed to a fired heater where it is further heated to temperature at which thermal cracking reactions occur. Effluent from the fired heater may be provided additional residence time in a soaker vessel where cracking reactions will progress further. The effluent from the heater and soaker is preferably separated into vapour and liquid products in a cyclone. The vapour product of the thermal cracking is then preferably subjected to distillation at atmospheric pressure (101 kPa) and the liquid product is preferably distilled at reduced pressure (in the range of from 1.0 to 2.5 kPa) to produce gas oil and lighter hydrocarbon products as one or more top streams and cracker residue as the bottoms stream.

The gas oil and lighter hydrocarbon products are treated before they can be used as refinery internal fuel or for blending as final products from the refinery

The cracked residue is then subjected to a solvent deasphalting process using a deasphalting solvent in step b) .

In solvent deasphalting the hydrocarbon feed, in this instance, the cracker residue, is treated counter- currently with an extracting medium, comprising a deasphalting solvent, which is usually a light

hydrocarbon solvent containing paraffinic compounds.

Commonly applied paraffinic compounds include C3-8 paraffinic hydrocarbons, such as propane, butane, isobutane, pentane, isopentane, hexane or mixtures of two or more of these. For the purpose of the present

invention, it is preferred that C3-C5 paraffinic

hydrocarbons, most preferably butane, pentane or a mixture thereof, are used as the deasphalting solvent.

In general, the extraction depth increases at increasing number of carbon atoms of the extracting solvent. In this connection it is noted that the higher the

extraction depth, the larger the amount of hydrocarbons being extracted from the residual hydrocarbonaceous feedstock, the smaller and more viscous the asphaltic product will be, whereby the heavier the asphaltenes will be in the asphaltic product to be obtained in step b) .

The viscosity index, V50, of the asphaltic product will suitably be in the range of from 55 to 62,

preferably in the range of from 58 to 62. V50 is a temperature independent measure of viscosity of a stream of a particular chemical composition. V50 can be

calculated from kinematic viscosity as measured by standard test method D445A.

In a solvent deasphalting treatment a rotating disc contactor or a plate column can be used with the vacuum flashed cracker residue (VCFR) entering at the top and the extracting solvent entering at the bottom. The lighter hydrocarbons which are present in the vacuum flashed cracker residue (VCFR) dissolve in the extracting solvent and are withdrawn as the deasphalted product at the top of the apparatus. The asphaltenes which are insoluble in the extracting solvent are withdrawn in the form of the asphaltic product at the bottom of the apparatus. The conditions under which deasphalting takes place are known in the art. Suitably, deasphalting is carried out at a total extracting solvent to residual hydrocarbon oil ratio of 1.5 to 8 wt/wt, a pressure of from 1 to 60 bara and a temperature of from 40 to 200°C. Preferably, the pressure is in the range of from 3500 to 4500 kPa. Preferably, the temperature is in the range of from 100 to 135°C.

The deasphalted product of step (b) is a pure and heavy deasphalted product. This means that preferably at least 40 wt%, more preferably at least 50 wt%, even more preferably at least 70 wt%, and most preferably at least 80 wt% of the deasphalted product of step (b) has a boiling point of above 520°C.

The deasphalted product produced in step b) is then separated into deasphalted oil and resin. Resin as used herein, means resins that have been separated and

obtained from a SDA unit. Resins are denser and/or heavier than deasphalted oil, but lighter than the aforementioned asphaltic product. The resin product usually comprises more aromatic hydrocarbons with highly aliphatic substituted side chains, and can also comprise metals, such as nickel and vanadium. Generally, the resin comprises the material from which asphaltenes and DAO have been removed. The separation may be carried out by any known means, preferably by using critical

temperature separation. In critical temperature

separation, the mixture of deasphalted oil in the solvent present from the deasphalting step is cooled. The resin then precipitates at the critical temperature and can be separated .

The deasphalted oil will be present as a mixture with the solvent, which can then be removed by any known means, for example by steam stripping.

The deasphalted oil may then also be subjected to further upgrading steps. Suitable methods for further upgrading of this stream include thermal cracking, hydrocracking and fluidised bed catalyst cracking. Such processes and suitable conditions for them are well-known in the art .

Following step c) and any necessary solvent removal, the resin is subjected to further thermal conversion.

Any suitable thermal conversion process, such as coking or heavy hydrocarbon cracking, is envisaged herein. In one preferred embodiment of the present invention said thermal conversion is carried out by recycling the resin stream and combining it with the residual

hydrocarbonaceous feedstock for use in step a) .

The asphaltic product of step b) is preferably subjected to a high temperature treatment in the presence of oxygen deficient flue gas or hydrogen. Such a process results in the liberation of residual volatile

hydrocarbon molecules. Said residual volatile

hydrocarbon molecules may be subjected to hydrocracking or incinerated to produce steam. The remaining material is suitable for use as coke.

Alternatively, the asphaltic product may be

pelletized and sold in the market or may be used as feed for a gasifier or power plant.

Detailed Description of the Drawings

Referring to the drawings, Figure 1 illustrates an embodiment of the invention. Residual hydrocarbonaceous feedstock (1) is subjected to thermal cracking and separation in visbreaker (2) to produce gas oil and lighter products (3) and vacuum flasher cracked residue (4) . The vacuum flasher cracked residue product (4) is deasphalted in a deasphalting unit (5) to obtain a deasphalted product (6) and an asphaltic product (7) .

The deasphalted product (6) is then separated by means of separator (8) into deasphalted oil (9) and resin (10) .

The resin (10) is then subjected to further thermal conversion. In this embodiment of the invention, the asphaltic product (7) is subjected to a calcination process (11) to produce volatile hydrocarbons or steam ( 12 ) and coke ( 13 ) .

Figure 2 illustrates the embodiment of the invention wherein the resin (10) is recycled to form part of the residual hydrocarbonaceous feedstock (1)

For the visbreaker (2) .

Figure 3 illustrates a further embodiment of the invention, wherein the deasphalted oil (9) is subjected to thermal cracking in cracker (14), the lighter (15) and heavier (16) products of said cracking process being provided to the gas oil and lighter stream (3) and the vacuum flasher cracked residue product (4) respectively for any further processing.

Examples

A residual hydrocarbonaceous feedstock was converted in a visbreaker to cracked residue in approximately 70 weight %; and gas oil and lighter products in

approximately 30 weight%.

Subjecting the cracked residue from visbreaking to two step solvent de-asphalting and recycling the resin product as thermal cracking feed stock, as shown in figure 2, results in an increase of gas oil and lighter products to approximately 35 weight % besides producing approximately 32 weight % de-asphalted oil which is further converted to gas oil and lighter products in hydroconversion or catalytic cracking units.

In case hydroconversion or catalytic cracking is not feasible, de-asphalted oil can be subjected to thermal cracking as shown in figure 3. This results in gas oil and lighter product yield of approximately 60 weight! from the combined thermal cracking stage.