WO2011047829A1

WO2011047829A1 - Process for reducing the viscosity of oil residues coming from distillation at atmospheric pressure or under vacuum

Info

Publication number: WO2011047829A1
Application number: PCT/EP2010/006371
Authority: WO
Inventors: Luigi D'elia; Giacomo Fernando Rispoli; Paolo Pollesel; Emilio Sentimenti
Original assignee: Eni S.P.A.
Priority date: 2009-10-22
Filing date: 2010-10-15
Publication date: 2011-04-28
Also published as: IT1396576B1; ITMI20091833A1

Abstract

A process for reducing the viscosity of oil residues coming from distillation at atmospheric pressure or under vacuum, substantially comprising a visbreaking area, having a coil visbreaker or soaker visbreaker, in which a thermal treatment is effected at temperatures ranging from 350 to 500°C characterized in that further treatment is effected, by irradiation with microwaves (in continuous or in a pulsed mode) operating at temperatures ranging from 100 to 500°C, for a period of time ranging from 1 second to 120 minutes and with frequencies ranging from 0.3 to 300 GHz.

Description

PROCESS FOR REDUCING THE VISCOSITY OF OIL RESIDUES COMING FROM DISTILLATION AT ATMOSPHERIC PRESSURE OR UNDER VACUUM

The present invention relates to a process for reducing the viscosity of oil residues coming from distillation at atmospheric pressure or under vacuum.

The process for reducing the viscosity, so-called visbreaking, is often used in refineries for reducing the viscosity of heavy oil residues, mainly coming from vacuum distillation and subsequently using them as fuel oil, bitumen and light products.

Under relatively mild thermal cracking conditions, it is possible to partially convert oil residues to distillates and produce tars having a lower viscosity, in order to reduce the quantity of flushing agent to be mixed in order to obtain a fuel oil within specifications .

The visbreaking process can be considered a mixed phase process, even if the residue is fed in liquid phase: vapours are in fact generated, as in the cracking reaction components within the range of gasoline and lighter products are also formed.

The visbreaking reactions are carried out with relatively short contact times (a few minutes) either in oven tubes (units of the coil visbreaker type) or, under milder conditions and higher contact times in the case of units equipped with reaction chamber (soaker visbreaker) , in a separate reaction chamber called soaker . The visbreaking product is subjected to fractionation to separate the products (naphtha, gas oil, and heavy vacuum gas oil) from the residue and recover them. The residue, in spite of the thermal treatment exerted, cannot normally be used as such but must be subjected to flushing with light hydrocarbons, such as, for example, gas oils, thermal tars, HCN, LCO, HCO to enhance the fluidification, facilitating the movement, for producing bitumens and/or fuel oils.

It has now been found that by inserting a suitable treatment by irradiation with microwaves in a traditional visbreaking process, coil visbreaker or soaker visbreaker, the drawbacks mentioned above can be overcome, allowing only a very mild flushing to be effected, to diminish the viscosity, or even to totally avoid flushing the visbreaking product obtained as it is already ready to be easily moved.

The flushing is in fact effected, as specified above, with valuable light hydrocarbon products: the possibility of eliminating or reducing the value of flushing offers economic and operative advantages . A method is thus obtained for fluidifying and facilitating the movability of heavy residues without having to add other products or additives.

This reduction is normally obtained by flushing with gas oil. The application of microwaves, using a suitable reactor and optimum reaction conditions, allows the viscosity of the visbreaking product to be permanently, and not temporarily, reduced, thus avoiding, or considerably diminishing the addition of the flushing agent.

In this way, the overall yield to medium distillates of the visbreaking process assisted by microwaves proves to be higher than that of traditional visbreaking .

The process, object of the present invention, for reducing the viscosity of oil residues coming from distillation at atmospheric pressure or under vacuum, substantially comprises a visbreaking area, having a coil visbreaker or soaker visbreaker, wherein a thermal treatment is effected at temperatures ranging from 350 to 500°C, preferably from 420 to 490°C, and is characterized in that it effects a further treatment by irradiation with microwaves (in a continuous or pulsed mode) operating at temperatures ranging from 100 to 500°C, preferably from 150 to 400°C, more preferably from 170 to 350°C, for a period of time ranging from 1 second to 120 minutes, preferably from 10 seconds to 60 minutes, more preferably from 20 seconds to 40 minutes, and ranging from 0.3 to 300 GHz, preferably from 0.5 to 30 GHz, more preferably from 0.8 to 7 GHz.

Said treatment with microwaves can be applied in the visbreaking area or downstream, but it could also be applied to the processing of the visbreaking charge, before the visbreaking area.

Said treatment with microwaves can allow the severity of the thermal treatment relating to the same visbreaking, to be diminished, reducing the dimensions of the visbreaking reactor and the severity of the reaction.

In the case of treatment with microwaves downstream of the visbreaking area, it is advisable:

if the reduction in viscosity is to be maximized, to eliminate gases and light products (gas, naphtha and gas oil) with a separator, possibly also the heavy vacuum distillates (for example with a vacuum column) and effect the irradiation on the residue in "hot cascade" , i.e. directly under the outlet conditions from the separations;

alternatively, when the fouling is to be minimized, to reduce the outlet temperature from the coil-visbreaker unit or soaker-visbreaker unit, with the same residence time. In this case, the desired reduction in viscosity is obtained, with a lower thermal severity and consequently with a lower surface temperature of the tubes, less fouling and an increase in the duration of the operative cycle.

In the case of treatment with microwaves in the visbreaking area, i.e. contemporaneously with the visbreaking, it is advisable to reduce the average bulk temperature to benefit from the microwave irradiation and at the same time reducing the occurrence of undesired reactions which cause the formation of deposits and unstable products.

Microwave treatment upstream of the visbreaking area is advisable for fluidifying heavy charges, above all in the case of traditional thermal conversion plants operating at the maximum limit of severity.

The process according to the invention could be further integrated by suitably exploiting the streams essentially consisting of heavy gas oil obtained in the separation sections normally present downstream of the visbreaking processes of the known art .

These streams, in fact, after being subjected to thermal cracking, can be mixed with the stream leaving the visbreaking area before treatment with microwaves or sent to treatment with microwaves.

The following examples, provided for a better illustration of the invention, should not be considered as a limitation of the invention.

EXAMPLES

A vacuum residue, obtained in an industrial thermal visbreaking plant (sample consisting of visbroken tar (VB TAR) ) , was used as sample for the experimentation.

The heavy refinery product called VB TAR is an industrial residue obtained from visbreaking treatment, characterized by a high content of heavy molecules and which, in order to be used in the production of bitumens or as fuel oil, needs the addition of suitable amounts of flushing agent.

The sample has a very high dynamic viscosity: 49160 mPa's at 70 °C. Other physico-chemical characteristics are indicated in the following table Table

Properties of the VB TAR sample

Property Value

Density 1.031

P-value 1.35

C7 Asphaltenes (% m/m) 16.5

THF insoluble ( m/m) 0.20

Example 1

110 g of VB TAR product are treated in a metal reactor (applicator) connected to an industrial microwave generator, according to the general scheme of fig. 1.

The microwave generation system consists of a magnetron, which emits radiations at 2.45 GHz with a maximum suppliable power of 2,000 W, connected to a circulator for the absorption, through a water charge, of possible reflected radiation, a directional coupler for measuring the direct and reflected power (through which the power absorbed by the sample can be estimated), a 3 -stub system for the impedance adjustment, a rectangular waveguide transition with a coaxial line suitable for high powers.

In particular, the sample is charged into an aluminium reactor having a useful capacity of 200 cc . The central conductor of the coaxial line protrudes from the pressure window and extends to the bottom of the reactor, fig. 2. The sample is charged into the reactor which is equipped with a resistance heating band in contact with the reactor walls. In this way, it is possible to irradiate the sample only when the latter has reached a sufficiently high temperature.

The pressure is measured by means of a pressure transducer connected to the pressure window, whereas the temperature is measured with a thermocouple through a cavity positioned at the bottom of the reactor.

The sample is charged into the reactor with an initial pressure of 3 bar of nitrogen; the temperature of the residue is brought to 180 °C by means of a resistance band fixed on the side walls of the reactor; the sample is subsequently irradiated with microwaves on average at 860 W, for 7' ; 785 W are generally absorbed. A maximum temperature of 210°C and a pressure of 8 bar are reached. At the end of the irradiation, the sample is maintained at a temperature of 175-180°C for 30', with a heating band and then left to cool.

After cooling, the viscosity of the treated product, at 70°C, is of 36340 mPa-s, with respect to the initial value of 49160 mPa-s at 70°C.

Figures 3 and 4 respectively show the graphic of the power supplied, reflected and absorbed, and the temperature and pressure profiles.

Example 2

120 g of VB TAR product are treated in a metal reactor connected to an industrial microwave generator.

The system upstream of the reactor (generator, directional coupler, tuner, waveguide/coaxial transition) is that of Example 1.

The sample is charged into the reactor according to the configuration of Example 1.

The sample is charged into the reactor with an initial pressure of 3 bar of nitrogen; the residue is brought to a temperature of 180°C by means of a resistance band fixed on the side walls of the reactor.

The sample is subjected to two irradiation cycles, both with an average supplied power of 1,000 W, of the duration of 6' and 7', respectively, interspersed by a cooling period of the sample to 180°C. The average power absorbed by the sample is about 900 W. A peak temperature of 210°C is reached, and a maximum pressure of 12 bar; before being cooled, the sample is maintained for 30' at a temperature of around 175°C.

The treatment reduced the viscosity to a value of 29,880 mPa-s (at 70°C) with a decrease of 39% with respect to the value of 49,160 mPa-s at 70°C of the residue as such.

Figures 5 and 6 respectively show the graph of the power supplied, reflected and absorbed, and the temperature and pressure profiles.

CHARACTERIZATION OF THE TREATED SAMPLES

Viscosity measurement The instrument used for the measurement of the dynamic viscosity is a viscosimeter AR 1500 of TA Instruments with a plate-cone coupling (40 mm, 2° steel) .

In order to effect the measurement, the coupling temperature is first regulated and the sample is then charged at room temperature or already hot onto the preheated fixed plate, using a spatula if the sample is very viscous or a dropper if it is fluid. The gap between the plates is brought to 52 microns, care being taken that the sample is well distributed and that there are no bubbles entrapped in its interior and the plate-cone is left to turn with a couple suitable for analysis for about 10 minutes before proceeding with the measurement.

CHARACTERIZATION OF THE PRODUCT FROM VB TAR OF EXAMPLE

2

The product obtained in example 2 by irradiation of the VB TAR (viscosity at 70°C of 49160 mPa-s) was analyzed at different times after the test (see Table) : as in the case of crude oil, the loss in viscosity with respect to the charge is permanent and equal to about 40%. VB TAR product of example 2. Monitoring of the stability with time

Time Viscosity [mPa-s] at 70°C

At the end of the test 29,880

After 1 hr 30,840

5

After 2 hrs 28,910

After 120 hrs 27,090

After 144 hrs 29,950

Claims

1. A process for reducing the viscosity of oil residues coming from distillation at atmospheric pressure or under vacuum, substantially comprising a visbreaking area, having a ■ visbreaker coil or visbreaker soaker, in which a thermal treatment is effected at temperatures ranging from 350 to 500°C characterized in that a further treatment is effected, by irradiation with microwaves (in continuous or in a pulsed manner) operating at temperatures ranging from 100 to 500 °C, for a period of time ranging from 1 second to 120 minutes and with frequencies ranging from 0.3 to 300 GHz.

2. The process according to claim 1, wherein the additional treatment by irradiation with microwaves is effected downstream of the visbreaking area.

3. The process according to claim 1, wherein the additional treatment by means of microwaves is effected in the visbreaking area.

4. The process according to claim 2, wherein the additional treatment by irradiation with microwaves is effected on the heavy residue of the product leaving the visbreaking, after separation of the lighter fractions .

5. The process according to claim 2, wherein the additional treatment by irradiation with microwaves is effected on the heavy residue of the product leaving the visbreaking, after separation of the lighter fractions and vacuum heavy distillate fractions.

6. The process according to claim 1, wherein the additional treatment by irradiation with microwaves is effected operating at temperatures ranging from 150 to 400°C, for a period of time ranging from 10 seconds to 60 minutes and with frequencies ranging from 0.5 to 30 GHz .

7. The process according to claim 4, wherein the additional treatment by irradiation with microwaves is effected operating at temperatures ranging from 170 to 350°C, for a period of time ranging from 20 seconds to 40 minutes and with frequencies ranging from 0.8 to 7 GHz .

8. The process according to claim 1, wherein the products leaving the treatment by irradiation with microwaves are sent to product separation areas in which streams essentially consisting of heavy gas oil are separated, which are subjected to thermal cracking before being mixed with the stream leaving the visbreaking area or directly sent to the treatment with microwaves.