PROCESS FOR THE PREPARATION OF A HYDROCARBONACEOUS DISTILLATE AND A RESIDUE

Abstract: Process for the preparation of a hydrocarbonaceous distillate and a hydrocarbonaceous residue, which comprises mixing a residual fraction of a product obtained by catalytic cracking or hydrocracking a hydrocarbonaceous feedstock, with a second hydrocarbonaceous fraction having such a boiling range that at least 50%w boils at a temperature above 400°C, and subjecting the resulting mixture to a subatmospheric distillation yielding at least one distillate fraction and one residue. The residue this prepared is a suitable component in bitumen compositions.

Description: The present invention relates to a process for the preparation of a hydrocarbonaceous distillate and a hydrocarbonaceous residue from a residual fraction of a product obtained by catalytic cracking or hydrocracking a hydrocarbonaceous feedstock. In the refining of crude oil cracking is a widely used operation. Cracking is a method to obtain lighter products from a relatively heavy feedstock. Cracking operations include thermal cracking, catalytic cracking and hydrocracking. After the cracking operation the cracked products are separated, generally by distillation, in at least one distillate fraction and a residual fraction. This latter fraction is frequently used as a fuel oil component. This residual fraction, however, contains several relatively light hydrocarbons which have a higher intrinsic value than just that of a fuel oil component. This is especially the case in residual fractions obtained after hydrocracking and catalytic cracking operations. These relatively light hydrocarbons are the main reason why these residual fractions are unfit for use in bitumen compositions. So, it would appear that separation of these relatively light hydrocarbons would be beneficial since then not only relatively valuable hydrocarbons would be obtained, but also a fraction suitable for use as bitumen component. Separation of these relatively light hydrocarbons from the residual fraction by vacuum distillation appears to be troublesome, since fouling and plugging problems may arise. These problems are due to the fact that at the desired distillation conditions a big proportion of the residual fraction evaporates thereby entraining heavier products. The latter products not only cause a relatively bad separation but may also cause plugging problems in discharge conduits at the top of the distillation column. The bottom fraction of the distillation may give rise to troubles, too, since fine particles of the catalyst, applied in catalytic and/or hydrocracking, which are present in the residual fraction, are concentrated in the bottom fraction of the vacuum distillation, which tends to be rather viscous, and causes fouling of the conduit system for removing this bottom fraction. The present invention provides a solution to these problems. Accordingly, it relates to a process for the preparation of a hydrocarbonaceous distillate and a hydrocarbonaceous residue, which comprises mixing a residual fraction of a product obtained by catalytic cracking or hydrocracking a hydrocarbonaceous feedstock, with a second hydrocarbonaceous fraction having such a boiling range that at least 50%w boils at a temperature above 400°C, and subjecting the resulting mixture to a subatmospheric distillation, yielding at least one distillate fraction and one residue. Due to the fact that the residual fraction is mixed with a second fraction, the relative amount of the mixture which is distilled, is reduced thereby avoiding entrainment problems, whereas the relatively increased amount of the bottom fraction ensures that the fine catalyst particles are well dispersed at a lower concentration so that fouling of the conduit system no longer occurs. It appears that the residue obtained shows surprisingly good properties as bitumen component. The problems referred to above, are more prominent in the handling of the product obtained by catalytic cracking than by hydrocracking. The process according to the present invention therefore finds suitable application in the handling of a residual fraction originating from catalytic cracking of a hydrocarbonaceous feedstock. The residual fraction which is subjected to the process according to the invention is generally obtained as the bottom fraction in the (atmospheric) distillation of the cracked product. The conditions under which the (atmospheric) distillation is carried out may vary so that the bottom fraction may vary in boiling characteristics. Moreover, not the entire bottom fraction needs to be subjected to the present process. Suitably the residual fraction which is subjected to the present process has an initial boiling point of at least 200°C. The second hydrocarbonaceous fraction must fulfil some requirements regarding its boiling range. These requirements ensure that the part of it which is distilled in the subatmospheric distillation, is not too big. Therefore, it must have such a boiling range that at least 50%w boils above 400°C. Preferably its boiling range is such that over 60%w boils at a temperature above 460°C. The second fraction can be selected from a wide range of heavy hydrocarbons, such as a long residue, short residue, a thermally cracked residue, a solvent extract of a lubricating oil fraction, in particular the furfural, phenol or methyl pyrrolidone extract or the extract of sulphur dioxide or a sulphur dioxide/benzene mixture, a deasphalted oil or a bitumen obtained after deasphalting. The deasphalting may be carried out by lower alkanes, in particular C₃-C₈ alkanes, such as propane, butanes or pentanes. The ratio in which the two residual fractions are mixed, depends to a great extent on their boiling characteristics and the conditions under which the subatmospheric distillation is carried out. In the resulting mixture the weight ratio between the second fraction and the residual fraction of the product obtained by cracking a hydrocarbonaceous feedstock preferably varies between 1:9 and 9:1. The subatmospheric distillation is preferably carried out at a temperature corresponding with the boiling point at the subatmospheric pressure of a hydrocarbon having an atmospheric boiling point of at least 400°C (400°C/bar hydrocarbons). In particular, the temperature is preferably above the boiling point of 460°C/bar hydrocarbons. By using these conditions the residue has a sufficiently reduced volatility to meet standards regarding its suitability as bitumen component. The distillation temperature is suitably in a range corresponding with the boiling point of hydrocarbons having an atmospheric boiling point in the range from 460 to 550°C. This ensures a suitable volatility of the residue. The reference to the hydrocarbon boiling point at atmospheric pressure (1 bar) is made after conversion of a subatmospheric boiling point in accordance with the Maxwell-Bonnell relation which is described in Ind. Eng. Chem., 49 (1957) 1187-1196. In practice, a boiling point of such hydrocarbons is determined at subatmospheric pressure. Since at many subatmospheric pressures many different boiling points can be determined the person skilled in the art prefers to refer to an unambiguous atmospheric boiling point. The subatmospheric distillation may be a conventional vacuum distillation. Preferably, it is a subatmospheric flash distillation. This implies that the mixture of the two residual fractions is heated to a temperature in the boiling range of the liquid at a lower pressure, and introduced into a subatmospheric flash zone to yield distillate and residue. Many subatmospheric pressures may be used in the distillation according to the invention. Each pressure applied determines the temperature limits within which the distillation suitably is carried out. Preferably the actual temperature in the distillation does not exceed 400°C. Below this temperature reactions between or of the hydrocarbons in the mixture, e.g. cracking reactions, are substantially excluded. Since at relatively long residence times cracking reactions can take place at high temperatures up to 400°C it is even more preferred to have somewhat lower actual distillation temperatures, in particular between 310 and 370°C. The pressure in the subatmospheric distillation is preferably between 2 and 120 mm Hg (0.27 and 16.0 kPa). The process according to the invention is preferably carried out such that 20-80%w of the resulting mixture is recovered as distillate(s) and the remainder as residue. This can be achieved by selecting the mixing ratio of the both residual fractions properly and by chosing suitable conditions of the subatmospheric distillation. The mixing ratio is not only determined by the boiling characteristics of the fractions, but also by their viscosities. When the second fraction is low in volatility and it further does not substantially increase the viscosity of the bottom product (residue) of the subatmospheric distillation, a relatively low content thereof is required in the present process. Such situations can especially arise when as second hydrocarbonaceous residual fraction a solvent extract of a lubricating oil fraction is used. The present invention also relates to a bitumen composition comprising a hydrocarbonaceous residue prepared as described hereinbefore. This bitumen composition shows good overall properties and in particular good adhesion. The oxidation stability, though satisfactory, can be increased by subjecting the hydrocarbonaceous residue to a blowing step. This can be done either before or after mixing the residue with other bituminous components. The blowing process is suitably carried out continuously in a blowing column, into which a liquid bitumen component is fed and wherein the level of the liquid is kept approximately constant by withdrawing bitumen. Air is blown through the liquid from a distributor near the bottom. Suitably, the blowing step is carried out at a temperature of 170 to 320°C. The temperature is preferably from 220 to 275°C. The bitumen composition according to the invention may comprise solely the residue prepared according to the invention. However, it is known in the art to blend many types of bituminous components to acquire a mixture with the desired properties. The composition according to the invention may therefore also contain other bituminous constituents. Preferably it contains from 50 to 99%w of a hydrocarbonaceous residue prepared in the present process. In the process according to the present invention as second fraction preferably a solvent extract of a lubricating oil fraction is used, since the hydrocarbonaceous residue thus obtained is a very suitable bitumen component. Not only has it the properties depicted above, but it also appears to be very well pigmentable, showing a satisfactory colour at a relatively low concentraction of a pigment e.g. 0.1-2%w, based on the total asphaltic composition. Suitable pigment include red and yellow iron oxide, titanium oxide, chromex green, cobalt blue etc. The ultimate asphalt compositions when used as road tracks, usually contain mineral aggregates and fillers, each in proportions of e.g. 5-98%w, preferably 20-95%w, based on the asphalt composition. Suitable mineral aggregates are stone chips, gravel, slate and sand. As filler e.g. dusts, ground chalk, ground limestone or talc may be employed. To the bitumen composition according to the invention additives may be added such as natural or synthetic rubbers, e.g. optionally, hydrogenated, linear or branched (star-shaped) block, tapered or random copolymers of styrene and a conjugated diene (e.g. butadiene or isoprene); waxes, such as paraffin waxes; polymers such as polyethene, polypropene, poly(iso)butene; tackifiers such a lithium salts of C 10-40 fatty acids of hydroxy fatty acids, e.g. lithium hydroxy stearate, etc. This invention will be elucidated by means of the following examples. Example 1 In this Example an atmospheric residue obtained from a catalytically cracked product having 50%w boiling below 450°C and 76%w below 500°C and a catalyst fines content of 0.2%w, was subjected in a laboratory-scale vacuum flash distillation column at a rate of 0.6kg/hr and at a temperature of 365°C and a pressure 29 mmHg (3.87kPa), corresponding with the boiling point of 500°C/bar - hydrocarbons. During the flashing experiment a serious fouling and plugging tendency was observed already after a few hours operation.(Distillate yield was 73%w). The experiment was repeated with a feed consisting of 85%w and 75%w of a thermally cracked residue from a North Sea crude, of which about 18%w boiled at 500°C, and 15%w and 25%w of the above catalytically cracked product, respectively. The flashing experiments covered an effective operational period of 60 hours. No fouling or plugging tendency was observed. The respective distillate yields were 25.9 and 32.7%w. Example II Some characteristics of bituminous compositions containing a residue obtained after flashing a mixture of a catalytically cracked residue and a thermally cracked residue, were determined. The flashing conditions corresponded with the boiling point of 470°C/bar hydrocarbons. In a thin film oven test (TFOT) according to ASTM D1754 the compositions were subjected to heat and air, and their ageing behaviour was determined. After the test the penetration was measured and compared with the original penetration, yielding a retained-penetration value (in %). The higher the retained-penetration value, the better the composition is able to stand up against heat and air. The loss of weight during the test was determined as well; and also the change in the softening point, determined by the Ring and Ball method, was measured (ΔR & B). For comparison purposes the results of a test with a composition which does not contain any catalytically cracked residue is included in Table I. Example III In this Example a bright stock furfural extract (BFE) was used as second fraction. A mixture comprising 25%w BFE and 75%w catalytically cracked residue, was subjected to a flashing operation at 365°C, 1.2 kPa, corresponding with the boiling point of 540°C/bar-hydrocarbons. The residue (22%w) showed a penetration of 21 dmm and a softening point of 56°C. The residue was blended with a Middle East BFE and some characteristics were determined. The results are indicated in Table II. The blend was excellently pigmentable.

Claims: 1. Process for the preparation of a hydrocarbonaceous distillate and a hydrocarbonaceous residue, which comprises mixing a residual fraction of a product obtained by catalytic cracking or hydrocracking a hydrocarbonaceous feedstock, with a second hydrocarbonaceous fraction having such a boiling range that at least 50%w boils at a temperature above 400°C, and subjecting the resulting mixture to a subatmospheric distillation yielding at least one distillate fraction and one residue. 2. Process according to claim 1, in which the residual fraction originates from catalytic cracking of a hydrocarbonaceous feedstock. 3. Process according to claim 1 or 2, in which the second hydrocarbonaceous fraction has such a boiling range that over 60%w boils at a temperature above 460°C. 4. Process according to any one of claims 1-3, in which the the weight ratio between second hydrocarbonaceous fraction and the residual fraction of the product obtained by cracking a hydrocarbonaceous feedstock is between 1:9 and 9:1. 5. Process according to any one of claims 1-4, in which the subatmospheric distillation is carried out at a temperature corresponding with the boiling point of the subatmospheric pressure of hydrocarbons having an atmospheric boiling point of at least 460°C. 6. Process according to any one of claims 1-5, in which the subatmospheric distillation is a flash distillation. 7. Hydrocarbonaceous distillate or hydrocarbonaceous residue whenever prepared in a process according to any one of claims 1-6. 8. Bitumen composition comprising a hydrocarbonaceous residue according to claim 7. 9. Bitumen composition according to claim 8, which contains from 50 to 99%w of a residue according to claim 7. 10. Bitumen composition according to claim 8 or 9, in which the hydrocarbonaceous residue is obtained after using a solvent extract of lubricating oil or a deasphalted oil as second hydrocarbonaceous fraction.

Inventors: BREUKER, JACOBUS HENDRIKUS, SYRIER, JOHANNES LEOPOLD MARIE, VAN GOOSWILLIGEN, GERRIT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1987
Main classification: C10G1
IPC codes: C10G7, C10C3, C10G55, C10G67