Method for purifying a feedstock resulting from a method for depolymerizing styrene compounds
A process for the purification of a feedstock resulting from a process for the depolymerization of styrene compounds, referred to as feedstock of the purification process, comprises at least a separation step producing an extract rich in light compounds, a raffinate rich in heavy compounds and a stream rich in styrene, and a step of separation of the stream rich in styrene into at least a stream comprising predominantly ethylbenzene, a stream comprising predominantly styrene and a stream of heavy compounds.
1 . A process for purification of a feedstock resulting from a process for depolymerization of styrene compounds, the process comprising at least the following steps:
(a) a separation step employing a distillation column fed at a bottom of the column with the feedstock and producing, at a top of the column, an extract rich in light compounds, at the bottom of the column a raffinate rich in heavy compounds and, by a sidestream withdrawal, a stream rich in styrene, the column having as sole heat supply the feedstock; and
(b) a step of separation of the stream rich in styrene into at least a stream comprising predominantly ethylbenzene, a stream comprising predominantly styrene, and a stream of heavy compounds.
2 . The purification process according to claim 1 , wherein the feedstock comprises at most 10% by weight of ethylbenzene.
3 . The purification process according to claim 1 , wherein the feedstock comprises at least 10% by weight of compounds having a boiling point greater than styrene.
4 . The purification process according to claim 1 , wherein a temperature of the feedstock is greater than 300° C.
5 . The purification process according to claim 1 , wherein the process for the depolymerization of styrene compounds is a pyrolysis process and the feedstock resulting from a pyrolysis reactor directly feeds step (a) of the purification process, without intermediate cooling, heating or separation operations.
6 . The purification process according to claim 1 , wherein the distillation column of step (a) comprises from 5 to 20 theoretical stages.
7 . The purification process according to claim 1 , wherein a condenser of the distillation column of step (a) is operated at a temperature of between 30° C. and 50° C. and a vapor effluent from the condenser is subsequently cooled to a temperature of between −5° C. and 10° C.
8 . The purification process according to claim 1 , wherein a styrene polymerization inhibitor is fed at the top of the column in step (a) of the process.
9 . The purification process according to claim 1 , wherein the separation step (b) is performed in two successive separation sections:
(1) a first separation section which is fed with the stream rich in styrene resulting from step (a) and which separates the stream comprising predominantly ethylbenzene and a styrenic raffinate, carried out in a distillation column comprising from 60 to 100 theoretical stages, and operated at a pressure of less than or equal to 0.25 bara at the top of the column, and
(2) a second separation section fed with the styrenic raffinate resulting from the first separation section and producing the stream comprising predominantly styrene and the stream of heavy compounds, carried out in a distillation column comprising from 40 to 100 theoretical stages, and operated at a pressure of less than or equal to 0.25 bara at the top of the column.
10 . The purification process according to claim 1 , wherein the separation step (b) is carried out in a divided wall distillation column fed with the stream rich in styrene resulting from step (a) and producing, at the top of the column, the stream comprising predominantly ethylbenzene, at the bottom of the column the stream of heavy compounds and, as the sidestream withdrawal, in a section separated from the feed section of the column by an internal wall, the stream comprising predominantly styrene, the divided wall distillation column comprising from 70 to 130 theoretical stages and being operated at a pressure of less than or equal to 0.25 bara at the top of the column.
11 . The purification process according to claim 10 , wherein the divided wall distillation column further comprises a lower common part comprising from 8 to 12 theoretical stages, of an upper common part comprising from 8 to 12 theoretical stages, and of a divided part comprising a remainder of the theoretical stages.
12 . The purification process according to claim 10 , wherein the divided wall distillation column further comprises a lower common part comprising from 2 to 12 theoretical stages and of a divided part comprising a remainder of the theoretical stages.