U.S. patent application number 17/002445 was filed with the patent office on 2022-03-03 for process for production of useful hydrocarbon materials from plastic waste and reaction system therefor.
This patent application is currently assigned to Resonante LLC. The applicant listed for this patent is Resonante LLC. Invention is credited to John William Hemmings.
Application Number | 20220064539 17/002445 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-03 |
United States Patent
Application |
20220064539 |
Kind Code |
A1 |
Hemmings; John William |
March 3, 2022 |
PROCESS FOR PRODUCTION OF USEFUL HYDROCARBON MATERIALS FROM PLASTIC
WASTE AND REACTION SYSTEM THEREFOR
Abstract
A process for production of useful hydrocarbon materials from
plastic waste and reaction system therefor is provided. The process
includes frequentatively thermolyzing of high molecular weight
hydrocarbons such as plastic waste to produce useful medium
molecular weight hydrocarbons and low molecular weight
hydrocarbons. The process utilizes low molecular weight
hydrocarbons as solution reactants which helps in reducing the
viscosity of the material for more effective heat transfer. The
process also includes addition of one or more low molecular weight
olefins and solution reactants to high molecular weight
hydrocarbons to augment the free radical environment. The process
also includes hydrogenating and oxidizing the high molecular weight
hydrocarbons. The process enables production of the useful,
predominantly hydrocarbon materials such as waxes, lube oil
base-stocks, refinery feedstocks, intermediates or fuel additives.
The present invention also provides a reaction system comprising
thermolysis reactor including a primary zone and an optional
secondary zone for production of useful hydrocarbon materials from
plastic waste.
Inventors: |
Hemmings; John William;
(Fripp island, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Resonante LLC |
Houston |
TX |
US |
|
|
Assignee: |
Resonante LLC
|
Appl. No.: |
17/002445 |
Filed: |
August 25, 2020 |
International
Class: |
C10G 1/10 20060101
C10G001/10; C10G 1/00 20060101 C10G001/00; C10G 1/02 20060101
C10G001/02; C07C 29/48 20060101 C07C029/48; B01J 6/00 20060101
B01J006/00 |
Claims
1. A process for production of hydrocarbon materials from at least
one of plastic waste and high boiling hydrocarbons or combination
thereof comprising: a. mixing high molecular weight hydrocarbons,
and lower molecular weight hydrocarbons to obtain a uniform mixture
representative of low viscosity dissolved polymer phase, wherein
the high molecular weight hydrocarbons being selected from a group
consisting shredded waste plastic, un-shredded waste plastic, high
boiling hydrocarbons, other similar materials such as ethers and
substituted hydrocarbons, and combinations thereof, wherein the
uniform mixture comprises 70% wt-30% wt of the high molecular
weight hydrocarbons, and 30% wt-70% wt of the lower molecular
weight hydrocarbons; b. heating the uniform mixture to obtain a
molten state; c. separating heavy contaminants and light
contaminants from molten uniform mixture prior to thermolysis
reaction; d. frequentatively thermolyzing the molten uniform
mixture at a predefined temperature, pressure and duration to
initiate free radical chemical reactions and causing breakdown of
the uniform mixture, wherein the predefined temperature ranges from
350.degree. C. to 425.degree. C., the predefined pressure ranges
from 3-20 bar, and predefined duration ranges from 1 to 4 hours;
and separating thermolyzed uniform mixture into at least three
streams, wherein the at least three streams comprises dissolved
hydrocarbon gases including light naphtha range material, naphtha
through light wax material, and a crude thermolyzed product
material.
2. The process as claimed in claim 1, wherein the lower molecular
weight hydrocarbons are selected from a group consisting
naphtha/distillate range material, n-paraffin, decalin, coker gas
oils and diesel.
3. The process as claimed in claim 1, wherein the uniform mixture
comprises 40% wt of the high molecular weight hydrocarbons, and 60%
wt of the low molecular weight hydrocarbons.
4. The process as claimed in claim 1, wherein the uniform mixture
being heated at temperature ranging from 180.degree. C. to
250.degree. C.
5. The process as claimed in claim 1, wherein the frequentatively
thermolyzing of the molten uniform mixture is carried out at 15 bar
pressure.
6. The process as claimed in claim 1, wherein the crude thermolyzed
product material from the at least three streams comprises heavy
waxes with molecular weight ranging from 1,500 to 6,000 Dalton.
7. The process as claimed in claim 1, wherein the steps (a) to (e)
are operated intermittently in a batch mode.
8. The process as claimed in claim 7, wherein the batch mode is
configured to convert medium molecular weight hydrocarbons to low
molecular weight hydrocarbons.
9. The process as claimed in claim 1, wherein the steps (a) to (e)
are operated in a continuous mode.
10. The process as claimed in claim 1, further comprises recycling
the three streams by supplying back to at least one step of the
mixing of high molecular weight hydrocarbons and lower molecular
weight, the heating of the uniform mixture, and the frequentatively
thermolyzing molten uniform mixture.
11. The process as claimed in claim 10, wherein the recycling of
the three streams by supplying back comprises supplying the light
naphtha range material as fuel for one of the heating the uniform
mixture and the thermolyzing the molten uniform mixture.
12. The process as claimed in claim 10, wherein the recycling of
the three streams by supplying back comprises supplying back the
stream of naphtha through light wax as solution reactant to the
mixing step.
13. The process as claimed in claim 1, further comprises adding one
or more low molecular weight olefins selected from a group
comprising 1 octene and 1-hexene to the step (a) to undergo
supplementary reactions in the free radical environment.
14. The process as claimed in claim 1, further comprises adding a
solution reactants after the thermolysis and before hydrotreating
process to reduce viscosity of the product to accelerate a
hydrogenation process, wherein the adding of the solution reactants
after the thermolysis enables separation of waxy molecules from
non-waxy molecules by differential solidification, wherein the
solution reactants comprise the lower molecular weight
hydrocarbons.
15. The process as claimed in claim 1, further comprises carrying
out short path distillation (SPD) to separate the crude thermolyzed
product into fractions.
16. The process as claimed in claim 15, wherein the SPD is carried
out at temperature 360.degree. C.
17. The process as claimed in claim 1, further comprises
hydrogenating the high molecular weight hydrocarbons.
18. The process as claimed in claim 1, further comprises oxidizing
the high molecular weight hydrocarbons.
19. A reaction system, comprising: at least one surge hopper
adapted to receive high molecular weight hydrocarbons, wherein the
high molecular weight hydrocarbons being selected from a group
consisting shredded waste plastic and un-shredded waste plastic; a
melter fluidically connected to the at least one surge hopper via
first set of one or more valves, wherein the melter is adapted to
mix the high molecular weight hydrocarbons and the lower molecular
weight hydrocarbons, via mixing means, to obtain a uniform mixture
representative of low viscosity dissolved polymer phase, and heat
the uniform mixture to yield a molten state, and wherein the melter
comprises one or more openings to receive at least one of low
molecular weight hydrocarbons as solution reactant and heavy wax,
and one or more openings to release dissolved hydrocarbon gases
including light naphtha range material, and a molten uniform
mixture of the high molecular weight hydrocarbons and the low
molecular weight hydrocarbons; a thermolysis reactor fluidically
connected to the melter via second set of one or more valves and
adapted to produce hydrocarbon materials comprising medium
molecular weight hydrocarbons to low molecular weight hydrocarbons,
wherein the thermolysis reactor comprises a primary zone, an
optional secondary zone, one or more openings to receive
hydrocarbon liquids, and one or more openings to release at least
one of a vapour phase of the thermolysis reactor and a thermolyzed
material, wherein the primary zone being adapted to convert the
molten mixture into a condensed phase at a moderate temperature
with a relatively long residence time, and the optional secondary
zone being adapted to convert the molten mixture into a vapor phase
at high temperature with a short residence time, and wherein the
optional secondary zone is adapted to receive vapors circulated
from the primary zone.
20. The reaction system as claimed in claim 19, wherein the melter
is adapted to melt the uniform mixture at a temperature ranging
from 180.degree. C. to 250.degree. C.
21. The reaction system as claimed in claim 19, wherein the low
molecular weight hydrocarbons are selected from a group consisting
naphtha/distillate range, n-paraffin, decalin, diphenyl ether,
coker gas oils and diesel.
22. The reaction system as claimed in claim 19, wherein the mixing
means comprises at least one of an agitator and an impeller.
23. The reaction system as claimed in claim 19, wherein the mixing
means comprises an external pump circuit which circulates liquid
for effective mixing.
24. The reaction system as claimed in claim 19, wherein the
optional secondary zone is adapted to have a surface temperature
between 500.degree. C. and 1000.degree. C., preferably between
600.degree. C. and 750.degree. C.
25. The reaction system as claimed in claim 19, wherein the
optional secondary zone is adapted to produce low molecular weight
olefins from low molecular weight hydrocarbons, where the low
molecular weight olefins comprise ethylene and propylene.
26. The reaction system as claimed in claim 19, wherein the
thermolyzed material comprises dissolved hydrocarbon gases
including light naphtha range material, naphtha through light wax
material, and a crude thermolyzed product material.
27. The reaction system as claimed in claim 19, wherein the
thermolysis reactor being operated at isothermal condition by soft
heating by circulating hot oil.
28. The reaction system as claimed in claim 19, further comprises a
riser and a downcommer fluidically connected to the melter via
third set of one or more valves, wherein the riser and downcommer
combination operates as a trap, and adapted to receive the molten
uniform mixture and automatically separate heavy contaminant and
light contaminants from the molten mixture.
Description
FIELD OF INVENTION
[0001] Embodiments of a present invention relates to recycling of
plastic waste, and more particularly to a process for production of
useful hydrocarbon materials from plastic waste and a reaction
system characterized to implement the process.
BACKGROUND
[0002] Waste plastics, that is synthetic polymer-containing
compounds, pose an environmental threat because of the difficulties
associated with disposal and recycling of a large volume of
non-biodegradable material. Over the years, incineration has become
the most common method of dealing with combustible waste
efficiently as it decreases the volume and mass of municipal solid
waste. However, there is a lot of controversy about the
incineration of plastic wastes, due to the release of greenhouse
gases and toxic gases. An additional disadvantage of the
traditional incineration method for disposal of plastic wastes is
that it completely destroys all its organic matter which could be
otherwise useful for different applications.
[0003] Wherefore, there is a growing need to recycle waste
plastics. In past few decades, various technologies and methods
have been developed which can recover energy or material from waste
plastics and use the recovered energy or material as feedstock for
the production of liquid fuels such as diesel, gasoline and fuel
oil.
[0004] U.S. Pat. No. 2,372,001, discloses the production of
unsaturated hydrocarbons of any desired chain length by thermal
cracking of polyethylene resins (including copolymers of ethylene
and other polymerizable organic compounds) using moderately high
temperatures and low absolute pressures, such that the desired
products report to the vapor phase and are collected by condensing.
This patent recognizes that, under such conditions, side branch
substituents tend to be removed from the main chain leaving behind
a straighter chain molecule with a double bond. Thus, the total
unsaturation of the product is a function of the extent to which
the main chain is broken down plus an additional effect in cases
where side branches can be removed to form relatively simple
molecules, leaving a double bond on the main chain. The examples
cited in the patent include the removal of acetic acid in the case
of ethylene vinyl acetate copolymers and hydrochloric acid in the
case of ethylene vinyl chloride copolymers. In both cases,
resulting in an internal double bond on the main polymer chain with
the side chain removed to form a simple molecule. The objective of
the invention was to produce wax like substances (however
containing significant unsaturation), to which end temperatures
employed were between 325.degree. C. and 550.degree. C. The patent
teaches that the pressure employed should be consistent with the
products that it is desired to produce, which in the case of
products in the wax range means vacuum conditions. Five out of the
eight examples in the patent are at absolute pressures between 5
and 40 mmHg. Another example is at atmospheric pressure using CO2
as a sweep gas. A third example is at higher pressure (300-500
psi), enabling alternative pathways and producing a different
product slate. The final example was using a nickel catalyst.
[0005] The possibility to use the unsaturated hydrocarbons produced
by the process as a feedstock in a variety of chemical reactions is
discussed in the patent. The patent addresses in particular:
condensation reactions with aromatic hydrocarbons (to produce alkyl
benzenes), oxidation to carboxylic and hydrocarboxylic acids and
reaction with sulfur followed by oxidation to form sulfonic
acids.
[0006] W. G. Oakes et al., 1949, in their paper, The thermal
degradation of ethylene polymers, published in J. Chem. Soc.
Faraday Trans., disclosed how the different types of chemical bonds
in polyethylene might have different rates of reaction with respect
to thermally induced cracking. Prior work in the Chemical
literature had typically assumed all carbon-carbon bonds equally
likely to scission. Oakes and Richards work showed clearly that not
all carbon-carbon bonds are the same. The paper considers three
different types of unsaturation that are present in the pyrolysis
fragments, and the mechanisms by which they form. The unsaturated
fragments in question being vinyl R--CH:CH2, internal olefin
R--CH:CH--R' and side chain methylene RR''C:CH2. The paper
discloses, ethylene polymers breakdown by a complex mechanism in
which more highly branched material is more reactive and therefore
with commercial polymers (that initially contain significant side
branches), the initial reaction rate is higher than final reaction
rate, reasonable rate of reaction is possible at temperatures above
330.degree. C., final product from thermolysis reactions contains
the above mentioned three different types of unsaturation.
[0007] F. M. Rugg et al. of the Bakelite Company (part of Union
Carbide, 1953), in their paper, Branching in polyethylene,
published in Annals of the New York Academy of Science, disclosed
branching in polyethylene synthesis which does not relate directly
to thermal cracking of polymers but does explain some aspects of
the underlying free radical reactions that are of great
significance and which also apply in the context of cracking and
rebuilding of hydrocarbons. The paper describes a mechanism in
which the initial free radical reaction affecting a polymer chain
is that of oxygen removing a secondary or tertiary hydrogen to form
a secondary or tertiary free radical (unless specific measures are
taken to exclude oxygen, it will be present in tens to hundreds of
ppm levels when dealing with raw materials that have been in
contact with the atmosphere). The principle chemical reaction of
interest in the context of cracking of high molecular weight
hydrocarbons is carbon-carbon bond scissioning, this reaction is
one of the chain propagation reactions that can occur as the
initially formed free radical reacts further. With chain
scissioning, the free radical breaks down to a shorter chain free
radical and the original chain terminated with either vinyl,
internal olefin or side chain methylene groups as discussed above.
In addition to these scissioning reactions, chain transfer
reactions (where the free radical abstracts hydrogen from a
different molecule or from a different place on the same molecule)
are possible indeed are significantly favored over scission
reactions as well as over termination reactions. The termination
reactions happen when two free radicals react together to form a
stable molecule. Note that the addition of low molecular weight
olefins (if present) to a free radical forms a side branch
terminating in a free radical. Consequently, low molecular weight
olefins can be added step wise to form branches of significant
length. Consequently, in the event that there are light olefins
present they are extremely likely to attach to a free radical
center and grow a side branch.
[0008] Reading Oakes et al. (which is concerned with large
molecules and teaches that there is typically a single olefin group
per molecule on the average) in conjunction with Rugg et al., who
teaches that the rate of reaction for addition reactions with
ethylene is very large, it is reasonable to conclude that the
reactivity of olefins with respect to addition reactions is
strongly influenced by the molecular weight of the olefin. That is
to say that light olefins will tend to form side branches while
heavy olefins will react the same way as paraffins.
[0009] N. A. Slovokhotova et al., 1964, in their paper, Thermal
degradation of polyethylene, published in Vysokomol soyed 6,
disclosed the pyrolysis of polyethylene under vacuum at
temperatures in the range 325.degree. C. to 450.degree. C. The work
makes extensive reference to Oakes et al., cited above, and is
mainly concerned with gaining understanding of secondary reactions,
in particular accounting for different types of unsaturation. The
paper shows the thermal degradation of polyethylene has been
extensively researched for decades.
[0010] J. K. Y. Kiang et al., 1980, in their paper, Polymer
reactions part VII: thermal pyrolysis of polypropylene, published
in Polymer degradation and stability, disclosed how polypropylene
preforms in fires, but is relevant in understanding products which
are to be expected from polypropylene decomposition.
Table 1 shows the products obtained from pyrolysis.
TABLE-US-00001 TABLE 1 THERMAL DECOMPOSITION PRODUCTS OF
POLYPROPYLENE IN MOLE PER CENT 388.degree. C..sup.a 414.degree.
C..sup.b 438.degree. C..sup.c Product Isotactic Atactic Isotactic
Atactic Isotactic Atactic Methane 0.5 0.5 0.6 0.4 0.5 0.6 Ethane
3.3 2.7 4.5 2.9 3.7 3.2 Propylene 15.7 19.3 24.0 22.8 22.6 27.9
Isobutylene 3.0 4.4 3.1 4.4 4.0 3.4 2-Pentene 18.9 19.4 22.7 21.2
19.1 18.2 2-Methyl-1-pentene 12.3 12.9 12.0 10.4 10.6 11.9
3-Methyl-3,5-hexadiene 1.0 1.0 1.2 1.3 1.4 1.6
2,4-Dimethyl-1-heptene 33.6 30.8 23.0 28.3 29.7 25.4
2,4,6-Trimethyl-1-heptene 1.0 1.1 1.0 1.3 1.3 1.4
4,6-Dimethyl-2-nonene 1.9 1.4 1.1 0.8 0.9 0.8
2,4,6-Trimethyl-1-nonene 7.8 5.9 6.3 5.7 5.4 4.8 C.sub.12H.sub.22
0.8 0.7 0.6 0.6 0.9 0.8 .sup.aTime of pyrolysis, 60 min. .sup.bTime
of pyrolysis, 3 min. .sup.cTime of pyrolysis, 3 min.
[0011] The polypropylene tends to breakdown readily into naphtha
and distillate range materials at temperatures around 400.degree.
C. Consequently, it is to be expected that polypropylene will break
down more readily than polyethylene due to the large number of
tertiary hydrogens present. What is interesting is that certain
molecules are highly favoured, regardless of whether the material
is isotactic or atactic. The interpretation in the case of waste
plastic is that, it is possible to crack the polypropylene content
down to naphtha range material and fuel gas. The naphtha in
question is highly branched therefore a good gasoline material.
[0012] U.S. Pat. No. 3,441,628 discloses production of wax like low
molecular weight, substantially linear ethylene polymers and
copolymers by thermal degradation of high molecular weight ethylene
polymers and copolymers. Using temperatures between 360.degree. C.
to 420.degree. C. and residence times 30 seconds to 5 hours.
[0013] U.S. Pat. No. 3,441,628 discloses importance of feeding the
polymer into a melt of partially degraded material with intense
stirring so that the temperature within the reacting mass is
uniform.
[0014] U.S. Pat. No. 3,441,628 discloses various examples for both
batch and continuous processes. In the batch version, the equipment
is essentially an autoclave and plastic is added to a melt already
present. In the continuous case, there is a vigorously stirred
reactor and a plug flow section. This manipulates the residence
time distribution so that no material has a zero-residence time
which is advantageous when dealing with polymer range materials as
it ensures that no unreacted polymer is able to avoid the reaction
zone. The product is generally the material directly from the
reactor, with no further processing described.
[0015] U.S. Pat. Nos. 8,378,161 and 8,446,332 describe method and
apparatus for microwave depolymerization of hydrocarbon feedstocks
deal with the continuous depolymerization of high molecular weight
organic feedstocks using microwave energy.
[0016] These patents teach the importance of good mixing conditions
to obtain reasonably uniform temperature and discuss the
relationship between extent of material breakage and viscosity,
however, still marred with one or the other drawbacks.
[0017] Hence, there is need for an efficient process for production
of useful hydrocarbon materials from waste plastic.
SUMMARY
[0018] In accordance with an embodiment of the invention, a process
for production of useful hydrocarbon materials from plastic waste
is provided. The process includes mixing high molecular weight
hydrocarbons and lower molecular weight hydrocarbons to obtain a
uniform mixture representative of low viscosity dissolved polymer
phase. The high molecular weight hydrocarbons being selected from a
group consisting shredded waste plastic and un-shredded waste
plastic. The uniform mixture comprises 70% wt-30% wt of the high
molecular weight hydrocarbons, and 30% wt-70% wt of the low
molecular weight hydrocarbons. The process includes heating the
uniform mixture to obtain a molten state. The process includes
separating heavy contaminants and light contaminants from molten
uniform mixture prior to thermolysis reaction. The process includes
frequentatively thermolyzing the molten uniform mixture at a
predefined temperature, pressure and duration to initiate free
radical chemical reactions and causing breakdown of the uniform
mixture. The predefined temperature ranges from 350.degree. C. to
425.degree. C., the predefined pressure ranges from 3-20 bar, and
predefined duration ranges from 1 to 4 hours. The process also
includes separating thermolyzed uniform mixture into at least three
streams, wherein the at least three streams comprises dissolved
hydrocarbon gases, including light naphtha range material, naphtha
through light wax material, and a crude thermolyzed product
material.
[0019] In accordance with another embodiment of the invention, high
molecular mass, generally hydrocarbon materials (such as residual
material from crude oil, residual material recovered from the oil
produced by pyrolysis of tires), herein referred to as "residuum"
may take the place of mixed waste plastic, in all or in part in any
proportion up to 100%.
[0020] In accordance with yet another embodiment of the invention,
at least three streams are recycled by supplying back to at least
one step of the mixing of high molecular weight hydrocarbons and
lower molecular weight, the heating of the uniform mixture, and the
frequentatively thermolyzing molten uniform mixture.
[0021] In accordance with an embodiment of the invention, one or
more low molecular weight olefins selected from a group comprising
maleic anhydride, 1-octene and 1-hexene being added to augment the
free radical environment.
[0022] In accordance with another embodiment of the invention,
solution reactants are added after the thermolysis and before
hydrotreating process to reduce viscosity of the product to
accelerate a hydrogenation process.
[0023] In accordance with yet another embodiment of the invention,
short path distillation (SPD) is carried to separate the crude
thermolyzed product into convenient fractions.
[0024] In accordance with an embodiment of the invention, high
molecular weight hydrocarbons are hydrogenated.
[0025] In accordance with another embodiment of the invention, high
molecular weight hydrocarbons are oxidized.
[0026] In accordance with yet another embodiment of the invention,
a reaction system for production of hydrocarbon materials from
plastic waste is provided. The reaction system comprises at least
one surge hopper adapted to receive high molecular weight
hydrocarbons. The high molecular weight hydrocarbons being selected
from a group consisting shredded waste plastic and un-shredded
waste plastic. The reaction system comprises a melter fluidically
connected to the at least one surge hopper via first set one or
more valves. The melter comprises one or more openings to receive
at least one of the low molecular weight hydrocarbons as solution
reactant, the recycled heavy wax, and one or more openings to
release dissolved hydrocarbon gases including light naphtha range
material and a molten uniform mixture of the high molecular weight
hydrocarbons and the low molecular weight hydrocarbons. The melter
is adapted to mix the high molecular weight hydrocarbons and the
lower molecular weight hydrocarbons, via mixing means, to obtain a
uniform mixture representative of low viscosity dissolved polymer
phase, and heat the uniform mixture to yield a molten state. This
could be accomplished for example by adding the solid materials to
a heated pool of liquid materials with mixing so that the solid
materials melt and dissolve into the liquid pool. The reaction
system also comprises a thermolysis reactor fluidically connected
to the melter via second one or more valves. The thermolysis
reactor comprises a primary zone, an optional secondary zone, one
or more openings to receive hydrocarbon liquids, and one or more
openings to release at least one of a vapour phase of the
thermolysis reactor and a thermolyzed material. The primary zone
being adapted to react or convert the molten mixture in a condensed
phase (liquid) at a moderate temperature with a relatively long
residence time. The optional secondary zone being adapted to react
or convert the vapors arising from the primary zone in the vapor
phase at high temperature with a short residence time. The optional
secondary zone is adapted to receive vapors circulated from the
primary zone and to return reacted vapors to the primary zone. The
reactions that take place in the optional secondary zone form
relatively low molecular weight materials, particularly olefins,
which then participate further in reactions in the primary
zone.
[0027] In accordance with an embodiment of the invention, a
reaction system comprises a riser and a downcommer combination
fluidically connected to the melter via third set of one or more
valves. The riser and the downcommer combination operate as a trap
which separates light and heavy contaminants from the molten
uniform mixture and automatically directs the heavy contaminant and
light contaminants to separate zones for removal and disposal.
[0028] To further clarify the advantages and features of the
present disclosure, a more particular description of the disclosure
will follow by reference to specific embodiments thereof, which are
illustrated in the appended figures. It is to be appreciated that
these figures depict only typical embodiments of the disclosure and
are therefore not to be considered limiting in scope. The
disclosure will be described and explained with additional
specificity and detail with the appended figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The disclosure will be described and explained with
additional specificity and detail with the accompanying figures in
which:
[0030] FIG. 1 is a flow diagram 100 representing steps involved in
a process for production of useful hydrocarbon materials from
plastic waste, in accordance with an embodiment of the present
invention;
[0031] FIG. 2 is a schematic representation of a reaction system
200 used for batch mode thermolysis reaction, in accordance with an
embodiment of the present invention;
[0032] FIG. 3 is a schematic representation of a riser 401 for
automated separation of heavy contaminants and light contaminants
from the uniform mixture flowing from the melter 201, in accordance
with an embodiment of the present invention; and
[0033] FIG. 4 is a schematic representation of a device 400 for
automated collection of batch distillation, in accordance with an
embodiment of the present invention.
[0034] Further, those skilled in the art will appreciate that
elements in the figures are illustrated for simplicity and may not
have necessarily been drawn to scale. Furthermore, in terms of the
method steps, chemical compounds, and parameters used herein may
have been represented in the figures by conventional symbols, and
the figures may show only those specific details that are pertinent
to understanding the embodiments of the present disclosure so as
not to obscure the figures with details that will be readily
apparent to those skilled in the art having the benefit of the
description herein.
DETAILED DESCRIPTION
[0035] For the purpose of promoting an understanding of the
principles of the disclosure, reference will now be made to the
embodiment illustrated in the figures and specific language will be
used to describe them. It will nevertheless be understood that no
limitation of the scope of the disclosure is thereby intended. Such
alterations and further modifications in the illustrated system,
and such further applications of the principles of the disclosure
as would normally occur to those skilled in the art are to be
construed as being within the scope of the present disclosure.
[0036] The terms "comprises", "comprising", or any other variations
thereof, are intended to cover a non-exclusive inclusion, such that
a process or method that comprises a list of steps does not include
only those steps but may include other steps not expressly listed
or inherent to such a process or method. Similarly, one or more
components, compounds, and ingredients preceded by "comprises . . .
a" does not, without more constraints, preclude the existence of
other components or compounds or ingredients or additional
components. Appearances of the phrase "in an embodiment", "in
another embodiment" and similar language throughout this
specification may, but not necessarily do, all refer to the same
embodiment.
[0037] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by those
skilled in the art to which this disclosure belongs. The system,
methods, and examples provided herein are only illustrative and not
intended to be limiting.
[0038] In the following specification and the claims, reference
will be made to a number of terms, which shall be defined to have
the following meanings. The singular forms "a", "an", and "the"
include plural references unless the context clearly dictates
otherwise.
[0039] Embodiments of the present invention relates to a process
for production of useful hydrocarbon materials from plastic waste.
The process mainly focuses on frequentative thermolysis
process.
[0040] The present invention deals with the production of useful,
predominantly hydrocarbon materials such as waxes, lube oil
base-stocks, refinery feedstocks, intermediates or fuel additives
from high molecular weight hydrocarbon materials such as plastic
waste with possible supplementary use of low molecular weight
hydrocarbon materials. The present invention uses low molecular
weight hydrocarbon materials as "solution reactants", functioning
as solvents or swelling agents for the high molecular weight
materials. The solution reactant helps in reducing the viscosity of
the material for more effective heat transfer. The solution
reactant also function as selective solvents for the secondary
purpose of dissolving the more desirable materials for the process
(such as aliphatic resins) while leaving fewer desirable materials
(such as highly polar resins and inert fillers) as undissolved
solids or immiscible liquids. Further, in certain cases the
solution reactant acts as a reactant, combining with fragments from
the plastic to form new substances.
[0041] FIG. 1 is a flow diagram 100 representing steps involved in
the process for production of useful hydrocarbon materials from
plastic waste, in accordance with an embodiment of the present
invention.
[0042] The process for production of useful hydrocarbon materials
from plastic waste begins with mixing high molecular weight
hydrocarbons and lower molecular weight hydrocarbons to obtain a
uniform mixture representative of low viscosity dissolved polymer
phase at step 102. The high molecular weight hydrocarbons being
selected from a group consisting shredded waste plastic and
un-shredded waste plastic. The low molecular weight hydrocarbons
are selected from a group consisting naphtha/distillate range,
n-paraffin, decalin, diphenyl ether, coker gas oils and diesel. The
uniform mixture comprises 70% wt.-30% wt. of the high molecular
weight hydrocarbons, and 30% wt.-70% wt. of the low molecular
weight hydrocarbons. The uniform mixture preferably comprises 40%
wt of the high molecular weight hydrocarbons, and 60% wt of the low
molecular weight hydrocarbons.
[0043] The use of shredded plastic is convenient in the process.
However, it is possible to deal with the un-shredded plastic. The
un-shredded plastic is used by mechanically circulating a hot
liquid on the un-shredded plastic. The hot liquid includes solution
reactant, wax, or plastic mixture.
[0044] The process may also be applied to high boiling hydrocarbons
or other heavy materials which may substitute for waste plastic in
any proportion up to 100%. In an embodiment, the other heavy
material include high molecular mass or high boilinghydrocarbon
materials such as, but not limited to, residual material from crude
oil, residual material recovered from the oil produced by pyrolysis
of tires, herein referred to as "residuum".
[0045] In an embodiment, the process includes heating the uniform
mixture to obtain a molten state at step 104. In such an
embodiment, the uniform mixture may be heated at temperature
ranging from 180.degree. C. to 250.degree. C.
[0046] In alternative embodiment, the process may start with
heating the low molecular weight hydrocarbon material and then
adding the high molecular weight material over time while
continuing heating to finish with a uniform mixture at a
temperature between 180.degree. C. and 250.degree. C.
[0047] In an embodiment, the process includes separating heavy
contaminants and light contaminants from molten uniform mixture
prior to thermolysis reaction at step 106. The separating the heavy
contaminants and light contaminants from the molten uniform mixture
enables removal of impurities from the high molecular weight
hydrocarbons.
[0048] In an embodiment, the process includes frequentatively
thermolyzing the molten uniform mixture at a predefined
temperature, pressure and duration to initiate free radical
chemical reactions and causing breakdown of the uniform mixture at
step 108. In such an embodiment, the predefined temperature may
range from 350.degree. C. to 425.degree. C., the predefined
pressure may range from 3-20 bar, and predefined duration may range
from 1 to 4 hours. The frequentatively thermolyzing of the molten
uniform mixture is preferably carried out at 15 bar pressure. The
pressure, temperature and residence time are selected so that the
short to medium length hydrocarbons are able to participate in the
free radical reactions (in addition to the long chain
hydrocarbons). This is accomplished by using moderately high
pressure to ensure such materials are significantly present in the
liquid phase at process temperature. The process temperature may
range from 350.degree. C. to 425.degree. C. and it is selected so
that reaction rate remains moderate and consequently the process is
controllable and coke formation is suppressed. The residence time
is typically relatively long, from 1 to 4 hours consistent with the
deliberate, relatively slow rate of reaction.
[0049] The small to medium sized molecules present in a liquid
phase are liable to lose a hydrogen atom to become a free radical
(due to chain reaction with pre-existing free radicals, i.e. by
chain-transfer reaction). Such low molecular weight free radicals
readily disproportion into a smaller radical and an olefinic
fragment. The olefin fragment being of low carbon number is highly
active (compared to other materials present) and readily attaches
as a side chain to a free radical in the substrate molecule.
Alternatively, the free radicals initially formed (or the free
radical fragment remaining after an olefin has formed) participate
in the free radical chain reactions, including possibly chain
termination by attaching to a free radical in the substrate. As a
consequence, the process is able to convert at least a portion of
less desirable naphtha and/or distillate range molecules into
lightly branched higher molecular weight molecules.
[0050] The high molecular weight hydrocarbons crack to mainly wax
range materials with a less amount of liquid range materials and
lesser gas range materials. The low molecular weight hydrocarbons
initially crack to smaller olefins and paraffins. The olefins
attach to the wax range material making it more highly branched
while the paraffins are less reactive but eventually are able
themselves to react to form smaller olefin and paraffin fragments.
Consequently, if reaction is continued for a very long time, the
final material has a broad molecular weight distribution with less
amount of very high molecular weight hydrocarbons, a large amount
of medium molecular weight hydrocarbons (somewhat branched chain)
and low molecular weight predominantly paraffinic material.
[0051] In an embodiment, the process includes separating
thermolyzed uniform mixture into at least three streams at step
110. The at least three streams comprises dissolved hydrocarbon
gases (including light naphtha range material), naphtha through
light wax material, and a crude thermolyzed product material. The
crude thermolyzed product material from the at least three streams
comprises heavy waxes with molecular weight ranging from 1,500 to
6,000 Dalton.
[0052] In another embodiment, the steps 102 to 110 of the process
for production of useful hydrocarbon materials from plastic waste
being operated intermittently in a batch mode without adding high
molecular weight hydrocarbons. The batch mode is configured to
convert medium molecular weight hydrocarbons to low molecular
weight hydrocarbons.
[0053] In yet another embodiment, the process in the batch mode is
carried out using batch distillation as a product recovery step.
The batch distillation is carried out in at least one of
thermolysis reactor and separate equipment which is specifically
designed for the purpose. In either situation, the large mass of
material is maintained at a high temperature, but somewhat lower
than the thermolysis temperature to slow down the rate of reaction.
The steps 102 to 110 are performed in this embodiment under reduced
to atmospheric pressure. Thereafter, the temperature is maintained
while the pressure is further reduced using vacuum equipment.
Reducing the pressure at this stage is typically advantageous. This
is feasible using several boosters (such as roots blowers) with a
primary vacuum pump (such as a liquid ring pump). Initially the
boosters operate at low speed and the vacuum is essentially
provided by the primary pump. The distillate material gradually
becomes heavier as the distillation continues and can be collected
in fractions. It is possible to automate the collection by
fractions with fractions defined by melting point using a device
such as that depicted in FIG. 4 (described later).
[0054] In an embodiment, the steps 102 to 110 of the process for
production of useful hydrocarbon materials from plastic waste being
operated in a continuous mode.
[0055] The process in the continuous mode includes feeding shredded
plastic waste with recycled liquid and recycled heavy wax into a
heated, well stirred tank known as a melter or dissolver. The
shredded plastic waste comprises clean recycle polyethylene (PE) or
mixed waste plastic, which can have contaminants within reason. The
melter is maintained at a temperature ranging from 180.degree. C.
to 250.degree. C. using a steam, hot oil or electric coil. The
melter is maintained at atmospheric pressure, which is convenient
for addition of the shredded plastic waste. The electric coil used
with wall temperature limited to 400.degree. C. or less. The melter
therefore contains a solution of molten plastic and wax in
hydrocarbon liquid together with minor amounts of contaminants
(heavy contaminants and light contaminants) which came with the
plastic and recycled wax. For example, small amounts of polar
resins (such as PET), paper from labels, inorganic materials from
pigments and fillers, or possibly coke from downstream. The heavy
contaminants and the light contaminants from the solution of molten
plastic and wax in diesel is separated prior to thermolysis
reaction. The vapours from the melter are continuously withdrawn
and condensed. Condensate thus collected is added to the
thermolysis reactor. The frequentative thermolysis reaction is
carried causing breakdown of the solution of molten plastic and wax
in diesel. The solution of molten plastic and wax in diesel is
separated into at least three streams, wherein the at least three
streams comprise dissolved hydrocarbon gases, including light
naphtha range material, naphtha through light wax material, and a
crude thermolyzed product material. This is a very unique aspect of
the present invention.
[0056] In the continuous mode of the process for production of
useful hydrocarbon materials from plastic waste, the thermolysis
reactor consist of a continuous stirred tank reactor (CSTR)
followed by a plug flow reactor (PFR). Residence time of the CSTR
is maintained significantly higher than that of the PFR. The PFR is
adapted to avoid any possibility of unreacted plastic bypassing. A
system employing the CSTR followed by the PFR confers the ability
to engineer both the residence time distribution and the
temperature history of the material.
[0057] In a further embodiment of the process for production of
useful hydrocarbon materials from plastic waste, the process
comprises recycling the at least three streams by supplying back to
at least one step of the mixing of high molecular weight
hydrocarbons and lower molecular weight, the heating of the uniform
mixture, and the frequentatively thermolyzing molten uniform
mixture. The recycling of the at least three streams by supplying
back comprises supplying the light naphtha range material as fuel
to provide a hot utility required for the process (for example to
supply the fuel for a hot oil system or for direct heating). The
recycling of the at least three streams by supplying back comprises
supplying back the stream of naphtha through light wax as solution
reactant to the mixing step. All the aliphatic molecules that are
not in the desired size range for the products are recycled back to
a thermolysis reaction zone (frequentative thermolysis) being part
of the solution reactant material.
[0058] The recycled solution reactant material has beneficial
actions such as a high affinity for aliphatic resins (such as
polyethylene and polypropylene), a much lower affinity for polar
resins (such as polyethylene terephthalate and PVC) and inert
solids (such as coke and fillers) and consequently enables a degree
of separation of the materials (such as PE and PP) that are
precursors to desirable waxy molecules from materials (such as PET
and PVC). The solution reactant greatly reduces the viscosity of
the melt which facilitates efficient heat transfer and also makes
it possible to separate undesirable materials (solids and
incompatible melts or liquids) from the desirable materials, either
by settling or filtration.
[0059] In a further embodiment of the process for production of
useful hydrocarbon materials from plastic waste, the process
comprises adding one or more low molecular weight olefins to the
step 102. The low molecular weight olefins are selected from a
group comprising maleic anhydride, 1-octene and 1-hexene, such
materials being available to react with the substrate material in
the free radical environment. The addition of low molecular weight
olefins, such as 1-octene and 1-hexene increases the amount of
branched chain material in the product as these materials typically
graft to the substrate to form a short side chain of 8 or 6 carbon
atoms respectively. The addition of maleic anhydride introduces
alkenyl succinic anhydride functionality to the product of the
thermolysis reaction. Since maleic anhydride is an extremely polar
material, thus has limited solubility in aliphatic solvent and
consequently only a limited amount of maleic anhydride is
introduced. The amount of maleic anhydride can be increased by
selecting a solvent which has higher capacity for maleic anhydride
while retaining adequate solvency for the polyolefins. For example,
decalin or the commercially available eutectic mixture of biphenyl
and diphenyl ether (known as Dowtherm A). The maleic anhydride can
be gradually added during the course of the reaction using a
volatile solvent with high capacity for maleic anhydride, such as
tetrahydrofuran. In such case, the solvent or maleic anhydride
mixture can be added drop-wise over the course of the reaction.
[0060] In a further embodiment of the process for production of
useful hydrocarbon materials from plastic waste, the process
comprises adding the solution reactants after the thermolysis and
before hydrotreating process to reduce viscosity of the product to
accelerate a hydrogenation process. The adding of the solution
reactants after the thermolysis enables separation of waxy
molecules from non-waxy molecules by differential
solidification.
[0061] In a further embodiment of the process for production of
useful hydrocarbon materials from plastic waste, the process
comprises carrying out short path distillation (SPD) to separate
the crude thermolyzed product into convenient fractions. The SPD
being carried at temperature 360.degree. C. which enables the
process to operate with a less extreme vacuum system. Using higher
than typical SPD temperatures reduces cost by requiring less
extreme vacuum and the associated equipment.
[0062] In a further embodiment of the process for production of
useful hydrocarbon materials from plastic waste, the process
comprises hydrogenating the high molecular weight hydrocarbons.
[0063] A further embodiment of the process is a method to produce
essentially straight chain materials (n-paraffins) from feed rich
in polyethylene. This embodiment exploits the fact that the most
common polyethylene materials available are actually comonomers of
ethylene and 1-butene and as such have ethyl side branches. Since
ethyl side branches are very stable, compared to longer branches,
thermolysis is more likely to result in scission of the
carbon-carbon bond in what would normally be described as the main
chain. This leads directly to one of two distinct types of
molecules:
##STR00001##
The molecule (1) is more common and accounts for approximately 70%
of the total of the above two types of molecules. After
hydrogenation, the molecule (1) and molecule (2) convert into the
following:
##STR00002##
Note that after hydrogenation, .about.30% of the material is
straight chain and 70% is lightly branched having a methyl group on
the 3.sup.rd carbon from chain end. In many cases such material is
sufficiently straight chained. The presence of the methyl group in
a predictable place (3.sup.rd carbon from chain end) makes it
possible for such materials to crystalize more easily than
equivalent materials with the side branch randomly assigned.
However, in cases where minimizing the amount of branched chain
materials is important, it is possible to obtain fully normal
paraffin material by subjecting such hydrogenated materials to a
second thermolysis treatment. The methyl branch on the third carbon
is a quite stable group and additional thermolysis will involve
scission on the main chain, either removing 2-butene or removing
2-methyl 1-butene, in either case the mildly branched material is
replaced by an unbranched molecule containing 4 or 5 fewer carbon
atoms. The resulting molecules are typically hydrogenated and
separated a second time; however, the additional processing helps
in production of a high yield of n-paraffinic material.
[0064] In a further embodiment of the process for production of
useful hydrocarbon materials from plastic waste, the process
comprises oxidizing the high molecular weight hydrocarbons.
[0065] The present invention also provides for a reaction system
200 designed specifically for production of hydrocarbon materials
from plastic waste.
[0066] FIG. 2 is a schematic representation of the reaction system
200 used for batch mode thermolysis reaction, in accordance with an
embodiment of the present invention.
[0067] In an embodiment, the reaction system 200 comprises at least
one surge hopper 102 adapted to receive high molecular weight
hydrocarbons via a flowline 101. The surge hopper 102 also enables
delivery of the high molecular weight hydrocarbons at a
predetermined rate to the melter 201 via a flowline 103. The high
molecular weight hydrocarbons being selected from a group
consisting shredded waste plastic and un-shredded waste
plastic.
[0068] In an embodiment, the reaction system 200 comprises the
melter 201 fluidically connected to the at least one surge hopper
102 via first set of one or more valves 104. The melter 201
comprises one or more openings to receive at least one of the low
molecular weight hydrocarbons as solution reactant, the heavy wax,
and one or more openings to release dissolved hydrocarbon gases
including light naphtha range material from the melter 201, and a
molten uniform mixture of the high molecular weight hydrocarbons
and the low molecular weight hydrocarbons. The melter 201 receives
the solution reactant through a flowline 202. The melter 201
receives the heavy wax through a flowline 203 from holding tanks
using pumps or other conventional methods to induce flow such as
gravity or head-space pressure. The melter 201 first receives heavy
wax, secondly the solution reactant and finally the high molecular
weight hydrocarbons. The particular sequence of receiving the
components helps in maintaining the low viscosity in the melter
201.
[0069] The melter 201 is adapted to mix the high molecular weight
hydrocarbons and the lower molecular weight hydrocarbons, via
mixing means 209, to obtain a uniform mixture representative of low
viscosity dissolved polymer phase. The mixing means may comprise of
an agitator or impeller, alternatively mixing may be obtained by
circulating liquid externally using a pump. The melter 201 is also
adapted to heat the uniform mixture to yield a molten state,
alternatively to heat the liquid prior to addition of the solids
over time so that the material remains "pumpable" (low viscosity)
throughout the process. The heating of the uniform mixture may be
performed at temperature ranging from 180.degree. C. to 250.degree.
C. The low molecular weight hydrocarbons are selected from a group
consisting naphtha/distillate range, n-paraffin, decalin, diphenyl
ether, coker gas oils and diesel. The melter 201 also comprises
heating coil 208 to provide at least part of the heat needed to
melt the plastic. The part of the heat needed to melt the plastic
is received by hot recycled wax. The hydrocarbon vapours may be
formed in the melter 201 as a result of heating. A vapour flowline
204 connects the vapor phase of the melter 201 to a condenser 205
which recovers liquid from the vapours. The recovered liquid is
directed towards storage via flowline 206 and releases uncondensed
vapours via flowline 207. The recovered liquid is separately
directed towards the thermolysis reactor 301. The fraction of
recycled liquid which is able to evaporate ranges between 0% to 20%
of total recycled liquid.
[0070] Once the molten state of uniform mixture is obtained, the
heavy contaminants and the light contaminants are manually
separated from the molten uniform mixture. The manual separation of
the heavy contaminants and the light contaminants is carried using
a sight glass and manual valves. The separation can be automated
based on an online physical measurement such as infra-red
spectroscopy or can be passively automated using density
differences to open and close appropriate paths for the discharged
material. A flow-line 210 is directed towards a valve 211 which is
closed during the dissolution cycle and opened to allow the molten
uniform mixture to flow towards valves 212, 213 and 214. The valve
212 is adapted to purge the heavy contaminants. The valve 213 is
adapted to direct the molten uniform mixture to the thermolysis
reactor 301. The valve 214 is adapted to purge the light
contaminants. The sequence of operation is such that, the valve 212
is opened first, until the appearance of the draining liquid, or
continuously measured density or other convenient property
indicates that the heavy contaminants have been purged. The valve
212 is then closed and the valve 213 is opened until light
contaminants are detected. The valve 213 is then closed and the
valve 214 is opened to purge the light contaminants. The molten
uniform mixture may contain small amounts of solids and entrained
liquids. These may be removed between the melter 201 and
thermolysis reactor 301 using suitable filters such as a cartridge
filter not shown in the FIG. 2. Transferring the molten uniform
mixture to the thermolysis reactor 301 may be done using a pump,
head space pressure differential or gravity as convenient.
[0071] In an embodiment, the reaction system 200 comprises the
thermolysis reactor 301 fluidically connected to the melter 201 via
second set of one or more valves 213. The thermolysis reactor 301
being operated at isothermal condition by soft heating by
circulating hot oil. The thermolysis reactor 301 comprises a
primary zone, an optional secondary zone, one or more openings to
receive hydrocarbon liquids, and one or more openings to release at
least one of a vapour phase of the thermolysis reactor 301 and a
thermolyzed material. The thermolyzed material comprises at least
three streams comprising dissolved hydrocarbon gases, including
light naphtha range material, naphtha through light wax material,
and a crude thermolyzed product material.
[0072] The thermolysis reactor 301 also comprises a heating coil
302 and a gas induction agitator 303. The heating coil 302 provides
a heat required for thermolysis reaction. The gas induction
agitator 303 ensures proper mixing of components of the thermolysis
reactor 301. The thermolysis reactor 301 is operated at a
temperature ranging from 350.degree. C. to 425.degree. C. and at
pressure about 20 bar for a duration ranging from 30 minutes to 4
hours. The thermolysis reactor 301 headspace can be filled with
either nitrogen or hydrogen prior to commencing the thermolysis
reaction. Trace amounts of oxygen play a role as initiators of the
free radical reactions. The oxygen required for initiating free
radical reaction is entrained either with the molten uniform
mixture initially fed to the thermolysis reactor 301 or in the
nitrogen stream.
[0073] A flowline 305 is directed towards a condenser 306 adapted
to condense vapours coming out of the vapour phase of the
thermolysis reactor 301. The condensed liquid from the condenser
306 being removed via flowline 307 and directed towards the storage
or back to the thermolysis reactor 301 via flowline 308. The
condensed liquid may be sent to the storage and an equal amount of
liquid pumped from the storage via flowline 304. The uncondensed
vapours are directed to the fuel system via flowline 309. The
pressure in the thermolysis reactor 301 is controlled by modulating
the amount of vapour flow from the condenser using a conventional
pressure control loop. The purpose of the condenser 306 during the
thermolysis reaction is to recover material as liquid for recycle
to the thermolysis reaction, so initially the condenser 306
operates with effectively 100% reflux and retention of all
molecules within the thermolysis reactor 301.
[0074] The primary zone is adapted to react the molten mixture in
the condensed phase at a moderate temperature with a relatively
long residence time. The moderate temperature applied in the
primary zone for reacting the molten mixture ranges from
325.degree. C. to 450.degree. C. A vapor zone is always present
above the primary zone and in all cases vapor from the vapor zone
is recirculated through the liquid in the primary zone. The vapor
space may optionally function as a secondary zone, which employs
high temperature and short residence time to crack vapor phase
components. This requires suitable optional secondary zone heating
such as an electrical coil (not shown). The optional secondary zone
is adapted to produce low molecular weight olefins (predominantly
ethylene and propylene) from low molecular weight hydrocarbons. For
example, by inclusion of a heating coil within the optional
secondary zone which has a surface temperature between 500.degree.
C. and 1000.degree. C., preferably between 600.degree. C. and
750.degree. C.
[0075] The optional secondary zone is incorporated within the vapor
phase of the thermolysis reactor 301 that operates using a gas
induction agitator 303 to circulate gases through the reacting
liquid bulk.
[0076] The low molecular weight hydrocarbons crack to small olefins
during the short residence time of the optional secondary zone at
temperature above 650.degree. C. The resulting vapor from the
optional secondary zone contain a significant amount of low
molecular weight olefins in particular ethylene and propylene. The
hot gases or vapours leaving the optional secondary zone are
immediately quenched in the primary zone. The ethylene, propylene
and other low molecular weight olefins attach to the liquid phase
material in the primary zone to form side branches. The use of such
a secondary thermolysis zone effectively eliminates naphtha range
liquids and significantly increases the degree of branching of the
primary zone product which is useful when a branched chain material
is the target product such as the case of lube base stock.
[0077] After the reaction has been substantially completed, the
thermolysis reactor 301 is gradually depressurized. The
depressurization is accomplished by directing the liquid phase from
the condenser 306 to storage rather than reflux. (the pressure
control valve which directs vapour phase to fuel gas will tend to
close as the low molecular weight hydrocarbons are sent to storage
rather than refluxed). A significant amount of vapor flushes off
during this process and is condensed in the condenser 306 of the
thermolysis reactor 301. The rate of cooling of the thermolysis
reactor 301 is dependent on the sizing of the condenser 306. As the
thermolysis reaction time progresses the condensed material
gradually increase in carbon number, starting out as a naphtha
range material and finishing up as distillate making possible (but
not essential) to send the liquid to different tanks as the
molecular weight changes, which is done automatically, for example
based on density. As a result, sufficient light liquid is retained
as a supplementary fuel while the heavier liquid is all recycled to
extinction.
[0078] After the depressurization of the thermolysis reactor 301
above atmospheric pressure, the crude thermolyzed material is
transferred via flowline 310 to the crude thermolyzed material
storage tank.
[0079] In a further embodiment of the reaction system 200, the
reaction system 200 comprises a riser 401 and downcommer 402
combination fluidically connected to the melter 201 via third set
of one or more valves. The riser 401 and downcommer 402 combination
operates as a trap which separates light and heavy contaminants
from the molten uniform mixture and automatically directs the heavy
contaminant and light contaminants to separate zones for removal
and disposal.
[0080] FIG. 3 is a schematic representation of the riser 401 for
automated separation of heavy contaminants and light contaminants
from the uniform mixture flowing from the melter 201, in accordance
with an embodiment of the present invention.
[0081] The riser 401 receives the molten uniform mixture via the
flowline 210. The riser 401 is sized so that the up flow velocity
remains low, thereby enabling settling of the heavy contaminants
against the rising flow. The heavy contaminants are purged
periodically via the valve 212. The light contaminants are purged
from the riser 401 via the flowline 214. The molten uniform mixture
is then released from the riser 401 through the valve 213.
[0082] The FIG. 4 is a schematic representation of a device for
automated collection of liquid product from batch distillation, in
accordance with an embodiment of the present invention. The device
uses the fact that the congeal temperature of the overhead product
steadily increases as lighter materials are withdrawn as product.
Indeed, a key specification for wax products is the congeal point.
The concept of the device is to automatically redirect the
distillate once the congeal temperature passes certain threshold
values. For illustrative purposes in FIG. 4, the device is shown to
comprises three heat exchangers. It will be clear to one skilled in
the art that more or fewer exchangers could be employed in the same
concept. The liquid from the condenser passes through a horizontal,
heat traced or jacketed pipe with a number of full bore tees with
the branches oriented vertically downwards. From each tee, piping
runs vertically downwards into a jacketed section. The jacketed
section functions as a double pipe heat exchanger and cools any
liquid passing through to a temperature defined by the temperature
of the coolant and the diameter of the inner pipe. The coolant
circulating in the three exchangers shown is controlled at three
different temperatures, with the first exchanger coolest and the
third exchanger hottest of the three. Initially, the liquid flows
through the first exchanger to a collection tank below as this is
the "path of least resistance" for the overhead liquid. However, as
the distillation progresses, the material becomes higher in congeal
point until a time is reached when the material freezes in the
first heat exchanger. After that flow is no longer possible through
the first exchanger which blocks with frozen hydrocarbon,
consequently the new "path of least resistance" is through the
second heat exchanger. This exchanger uses a higher temperature
coolant and consequently will initially be open and will remain
open until the congeal temperature is exceeded and the second
exchanger plugs in its turn with liquid directed to the next new
"path of least resistance". In principle any number of such devices
could be used to collect fractions by melting point. In the
embodiment shown in FIG. 4, 3 such devices are used. Typically the
circulating coolant temperatures will be 20.degree. C., 55.degree.
C. and 75.degree. C. which enables the overhead condensate to be
collected in distinct cuts: liquids (congeal point <20.degree.
C.), light wax (congeal point 20-55.degree. C.), medium wax
(congeal point 55-75.degree. C.) and heavy wax (congeal point
>75.degree. C.). Once distillation of a batch is finished, the
outlets are cleared by increasing the coolant temperatures in each
device and then resetting the temperatures ready for the next
batch.
[0083] The present invention discloses an efficient process for
production of useful hydrocarbon materials from plastic waste. The
process enables reducing energy requirement as bulk liquid is also
considered as product along with vapour phase. The process provided
by the present invention is energy efficient and ensures purity of
the product. The process provides higher yield due to recycling of
all aliphatic molecules that are not in the desired size range for
the products. The process enables recycling heavy molecules to
extinction and alternative to consider them as heavy waxes creates
significant flexibility and potential for high value products. The
process provides the possibility to incorporate externally sourced
medium carbon number molecules including specialty materials such
as decalin which creates significant flexibility and potential for
high value products. The possibility to operate the process in
batch mode allows to operate the process intermittently without
heavy feed (i.e. without waste plastics) thus can be configured to
convert any outside low cost medium molecular weight materials
(heavy naphtha, distillate, light wax) to lightly branched
molecules. Addition of low molecular weight olefins from external
sources enables valuable lube base stocks to be produced from
ethylene and lube range materials. Arrangement of the second zone
into the thermolysis reactor 301 to produce low molecular weight
olefins enables lube base stocks to be produced from medium and low
molecular weight materials. Maintaining the thermolysis reactor 301
at isothermal conditions avoids the complications of coke
formation. Addition of solution reactant after thermolysis and
before hydrotreating facilitates finishing process. The separation
of the thermolyzed material into different streams facilitates
maximizing the product slate value while recycling less valuable
material and providing fuel for the process. The present invention
also provides a reaction system 200 for production of useful
hydrocarbon materials from plastic waste. The reaction system 200
comprises the thermolysis reactor 301 comprising primary zone and
optional secondary zone. The optional secondary zone enables
optional further cracking of low molecular hydrocarbons to smaller
olefins which contribute to obtaining the product in various ranges
of hydrocarbons.
[0084] While specific language has been used to describe the
disclosure, any limitations arising on account of the same are not
intended. As would be apparent to a person skilled in the art,
various working modifications may be made to the method in order to
implement the inventive concept as taught herein.
[0085] The figures and the foregoing description give examples of
embodiments. Those skilled in the art will appreciate that one or
more of the described elements may well be combined into a single
functional element. Alternatively, certain elements may be split
into multiple functional elements. Elements from one embodiment may
be added to another embodiment. Moreover, the actions of any flow
diagram need not be implemented in the order shown; nor do all of
the acts need to be necessarily performed. Also, those acts that
are not dependant on other acts may be performed in parallel with
the other acts. The scope of embodiments is by no means limited by
these specific examples.
* * * * *