Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process for cracking
heavy liquid hydrocarbons containing carbon residue.
~escription of the Prior Act
The present inventors previously proposed a process
for cracking hydrocarbons in Japanese Patent Application No.
97679/1976. This process is suitable for cracking heavy liquid
hydrocarbons and the feature is that a mist of a member selected
from the group consisting of basic compounds of alkali metals,
alkaline earth metals and mixtures thereof is used and the amount
of the molten salt is 0.01 - 1 part by weight per 1 part by
weight of the hydrocarbon.
However, it has been found that a mixture of the
molten salt and the carbon residue becomes viscous and is
apt to attach to the wall of the cracking reactor and sometimes
the inlet of the hydrocarbon feed is clogged when the amount
of the molten salt is small and the molten salt and the
heavy liquid hydrocarbon are mixed at a low temperature and
steam is not fed in a large amount upon cracking the heavy
liquid hydrocarbon containing a large amount of carbon residue.
From a commercial point of view, it is desirable
to lessen the amount of steam as far as possible, and a very
high temperature of the molten salt is not desirable from a
view-point of apparatus materials. Further, heavy liquid
hydrocarbons should not be pre-heated over a certain temperature
so as to prevent the heat decomposition before feeding to a
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1 ~¦ cxacking reactor. In addition it is desirable that the molten
2 ¦ I salt can be recirculated without any regeneration procedure.
3 ¦~ It has been demanded to develop a process which can
4 1l satisfy the above mentioned conditions and does not suffer
1 from the above-mentioned drawbacks upon cracking heavy oils
6 containing much carbon residue.
8 SUMMARY OF THE INVENTION
g An object of the present invention is to provide a
process for cracking hydrocarbons which is free from clogging
11 near the feed inlet of heavy liauid hydrocarbons.
12 Another object of the present invention is to provide
13 a process for cracking hydrocarbons in which steam consumption
14 is very little.
A further object of the present invention is to provide
16 a process for cracking hydrocarbons which utilizes remarkably
17 reduced quantities of circulating molten salt.
18 Still another object of the present invention is to
provide a process for cracking hydrocarbons in which a molten
salt can be reused without treatment for decreasing carbon.
21 A still further object of the present invention is
22 to provide a process for cracking hydrocarbons in which carbon , -
23 is eliminated by the water gas reaction with steam.
24 Still another object of the present invention is
to provide a process for cracking hydrocarbons which utilizes
26 only a small quantity of heat and can be conducted in a compact
27 apparatus.
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A still further object of the present invention is
to provide a process for cracking hydrocarbons which uses
only a small amount of a heat transfer medium and is free from
danger of fire.
Still another object of the present invention is to
- provide a process for cracking hydrocarbons which is free from
deposition of carbon and tar-like material in the heat de-
' composition device and the quenching device.
According to the present invention, there is provided
a process which comprises cracking heavy liquid hydrocarbons
containing carbon residue,
(A) in the presence of a molten salt of a member selected
from the group consisting of basic compounds of alkali metals,
alkaline earth metals and mixtures thereof,
(B) at least a part of the molten salt being used in a
form of mist having an average particle size not greater than
300 microns,
(C) the amount of the molten salt being more than 1 part
by weight, but not more than 10 parts by weight per 1 part by
weight of the heavy liquid hydrocarbons,
(D) the amount of the carbon residue being not more than
: 0.03 parts by weight per 1 part by weight of the molten salt, and
(E) amount of steam, reaction time, reaction temperature
and amount of the molten salt being controlled so as to render
the weight ratio of carbon after cracking to the molten salt
not more than 0.002.
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1 ~! BRIEF DESCRIPTION OF THE DRAWING
2 ll The drawing shows diagrammatically apparatus which
3 ll may be used for carrying out the present invention.
4 11
5 1I DESCRIPTION OF THE PREFERRED EMBODIMENT
6 l~ The representative heavy liquid hydrocarbons used in
7 1I the present invention are crude oil, heavy oil, light oil
8 ¦I from low pressure distillation, bottom residue from low pressure
distillation and the like. These heavy liquid hydrocarbons
contain carbon residue such as asphaltene, resins, high polymer
11 compounds and the like which become carbon upon heating.
12 Clogging at the feed inlet of the heavy liauid
13 hydrocarbon occurs when viscosity of the mixture of the heavy
14 liquid hydrocarbon and the molten salt is remarkably high.
Therefore, it is necessary to lower the viscosity for the
16 purpose of preventing clogging at the feed inlet. Thus the
17 amount of the carbon residue (Conradson carbon) is not more
18 than 0.03 parts by weight per 1 part by weight of the molten
19 salt, preferably 0.005 - 0.020 parts by weight per 1 part
by weight of the molten salt.
- 21 When the amount of carbon residue in the heavv liquid22 hydrocarbon per the molten salt is larger than the upper limit,
23 a mixture of the molten salt and the carbon residue is apt to
24 attach to the cracking reactor wall. On the contrary, when
the amount is too small, the amount of the molten salt is
26 ¦ unnecessarily large so that such procedure is not economical.
27 When the temperature of the mixture is lowered, the
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viscosity increases rapidly. Therefore, the amount of the
2 I molten salt is more than 1 part by weight, but not more than
3 1l 10 parts by weight, preferably not more than 5 parts by weight
4 ll per one part by weight of the heavy liquid hydrocarbon. At a
5 1 ¦ region over the upper limit the viscosity of the mixture does
I not remarkably decrease and it is not desirable to use such
7 a large amount of molten salt from an economical point of view.
On the contrary, at a region below the lower limit, a mixture
9 I of the molten salt and the carbon residue hecomes viscous and
is apt to attach to a wall of a cracking reactor and sometimes
11 the feed inlet of the heavy liquid hydrocarbon is clogged where
12 steam is not present in a large amount.
13 A molten salt is preferable which serves to lessen
14 the carbon (produced in the cracking reactor) by water gas
reaction as far,as possible. Therefore, according to the present
16 invention, as the molten salt there is used a member from the
17 group consisting of basic compounds of alkali metals, alkaline
18 earth metals and mixtures thereof. In order to avoid that
a mixture of the molten salt and the carbon residue becomes
viscous to clog the inlet of the heavy liquid hydrocarbon, a
21 molten salt having melting point of not higher than 450C is
22 preferable, and in particular, that having melting point of
23 not higher than 400C is more preferable. For example, a
24 mixture of Li2CO3(mp. 618C), Na2CO3(mp. 851C) and K2CO3
(mp. 891C), preferably, an equimolar mixture thereof (the
26 eutectic point is 385C), is used. A part of these compounds
27 may be the sulfide or sulfite.
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1 ~ For the purpose of effecting water gas reaction in the
2 ~ cracking reaction, steam is present in the reaction system. The
3 I amount of steam is not critical. However, it is not economical
4 I to use in a large amount, but where the amount is too small, the
S I water gas reaction can not occur sufficiently. In general, the
6 weight ratio of steam to the heavy liquid hydrocarbon is 0.5 - 5.0~ - -
I preferably 0.5 - 2Ø
8 ~ At least a part of the~olten salt is used in a form of
¦ mist and thereby even a small amount of molten salt can intimately !
I contact with the heavy liauid hydrocarbon to proceed smoothly the
11 water gas reaction. The average particle size of the molten salt
12 is usually not larger than 300 microns, preferably not larger
13 than 100 microns.
14 The molten salt mist may be easily produced by using
a venturi nozzle and passing steam.
16 Other method for producing the mist may be the use of a
17 pressure nozzle such as single hole nozzle, collision spray
18 valve, spiral spray valve, and the like; the method of rotation
19 ¦ such as rotating disk, rotating pan, rotating spray and the
¦ like; the method of gas-atomizing spray such as air or gas-
21 atomising nozzle and the like, and a vibration method.
22 , Further, the mist may be obtained by dissolving or
23 ~ suspending the salt in a heavy liquid hydrocarbon or water used
24 1¦ as a diluting vapor and supplying the resulting solution or
' suspension to the cracking apparatus.
26 ' Among these methods for producing mist, a method where
27 ~ at least a part of the molten salt is made into mist before the
28 molten salt is mixed with the heavy liquid hydrocarbon is preferred.
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The process of the present invention is particularly
2 l, effective when used for cracking of an external heating type.
3 I Naturally the process of the present invention can be applied
4 `~ to cracking of an internal heating type, but in case of cracking
1l of an internal heating type, a large amount of high temperature
6 ¦ gas for heating is used so that the above-mentioned partial
7 ¦I cooling of the molten salt can be avoided to some extent and
therefore the process of Japanese Patent Application No. 97679/1976
may be used in cracking of an internal heating type.
The cracking is usually carried out at 600 - 900C,
11 preferably 700 - 850C and for 0.001 - 2 seconds, preferably,
12 0.005 - 1.0 second, and more preferably, 0.01 - 0.3 seconds.
13 The reaction conditions such as amount of steam,
14 reaction time, reaction temperature and amount of the molten
salt are controlled so as to render the weight ratio of carbon
16 discharged from the cracking reactor to the molten salt not
17 more than 0.002, preferably not more than 0.001. Thus the molten
18 salt can be reused without subjec.ted to a regeneration treatment.
19 Where carbon amount is large after completion of the
reaction, there occurs foaming of the molten salt so that the
21 separation from the decomposition gas can not be smoothly
22 effected.
23 Quenching the reaction mixtures discharged from the
24 cracking reactor is preferable to prevent side reactions. The
reaction mixture is quenched to a temperature at which the
26 I molten salt does not solidifies. It is usually, for example,
27 1l 400 - 600C though it depends on each molten salt. After
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quenched, the molten salt is separated and recirculated, and
2 ~I the cracked gas may be separated into each component and
¦ purified in accordance with methods as used in usual ethylene
4 1` ¦ production plants.
S I EXAMPLES 1 - 3 and CO~ARATIVE EXAMPLES l - 3
Referring to the drawing, steam 1 superheated to 750C
7 ~ by a heater 2 was introduced into a venturi throat 7. The
8 venturi throat portion was provided with a small lateral bore
9 having a diameter of 2 mm. Through the small lateral bore
was supplied an equimolar mixture of Na2CO3-K2CO3-Li2CO3 kept
11 at 750C as a molten salt to produce a mist of the molten salt.
12 A mixture of Minas crude oil 3 (Conradson carbon
13 residue : 2.5% by weight) and steam 5 (10% of total steam feed)
14 was fed at 300C to an upper portion 9 of a reactor pipe 10
(21.7 mm. of outer diameter and 14.3 mm. of inner diameter and
16 11 m. in length) of an external heating type disposed below
17 the ventur1 throat and heated by a heater 11 to effect cracking.
18 The Minas crude oil 3 and steam 5 were heated by
19 heaters 4 and 6, respectively. After cracking, the reaction
mixture was quenched at a quenching portion 12 to 500C and
21 then the molten salt and the cracked gas were separated at
22 separator 13. The cracked gas 17 thus separated was sent to a
23 purification step and the molten salt thus separated was
24 collected in a drum 14, transferred by a pump 15 driven by
a motor M and heated by a heater 16 for reuse.
26 The reaction conditions and reaction results are
27 shown in Table 1 below.
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