Plastic pyrolysis heating/reaction recipe
Systems and processes for pyrolyzing waste plastics, including, in one or more heating stages, heating a waste plastic from an initial temperature to a peak pyrolysis temperature, and, in a final pyrolysis stage, providing heat input sufficient to maintain a temperature of the waste plastic at a pyrolysis reaction temperature less than the peak pyrolysis temperature and maintaining the waste plastic at the pyrolysis reaction temperature for a time period to convert a portion of the waste plastic to a pyrolyzed product and a pitch. The process further includes recovering the pyrolyzed product and recovering the pitch.
1 . A process for pyrolyzing waste plastics, the process comprising:
heating a waste plastic from an initial temperature to a first temperature in a reaction system and maintaining the waste plastic at the first temperature for a first time period, producing a first heated plastic;
heating the first heated plastic to a second temperature in the reaction system and maintaining the first heated plastic at the second temperature for a second time period, producing a second heated plastic;
pyrolyzing the second heated plastic by heating the second heated plastic to a third temperature in the reaction system and maintaining the second heated plastic at the third temperature for a third time period, producing a third heated plastic;
pyrolyzing the third heated plastic by heating the third heated plastic to a fourth, peak, temperature in the reaction system, producing a fourth heated plastic; and
pyrolyzing the fourth heated plastic by providing heat input sufficient to maintain a temperature of the fourth heated plastic at a fifth temperature in the reaction system and maintaining the fourth heated plastic at the fifth temperature for a fourth time period;
recovering a pyrolyzed product from each of the pyrolyzing steps as a vapor and recovering a pitch as a liquid from the reaction system;
wherein the first temperature is less than the second temperature, the second temperature is less than the third temperature, the third temperature is less than the fourth, peak, temperature, and the fifth temperature is less than the fourth, peak, temperature; and
wherein heating the third heated plastic to a fourth, peak, temperature comprises:
heating the third heated plastic at a rate of heating of greater than 50° C./min to an intermediate temperature; and
heating the third heated plastic from the intermediate temperature to the fourth, peak, temperature at a rate of heating in a range of 15° C./min to 30° C./min.
2 . The process of claim 1 , wherein an overall conversion of the waste plastic to pyrolyzed product is in a range from about 90 wt % to 97 wt %.
3 . The process of claim 1 , wherein a conversion of the waste plastic to pitch is in a range from about 3 wt % to 10 wt %.
4 . The process of claim 1 , wherein less than 1 wt % of the waste plastic is converted to coke or char.
5 . The process of claim 1 , wherein a rate of heating, in ° C./min, from the second temperature to the third temperature is less than a rate of heating from the third temperature to the fourth, peak, temperature.
6 . The process of claim 1 , wherein a rate of heating, in ° C./min, from the initial temperature to the first temperature is equal to a rate of heating from the first temperature to the second temperature.
7 . The process of claim 1 , wherein a rate of heating, in ° C./min, from the first temperature to the second temperature is equal to a rate of heating from the second temperature to the third temperature.
8 . The process of claim 1 , wherein the first time period, second time period, and fourth time period are each longer in duration than the third time period.
9 . The process of claim 8 , wherein a ratio of the third time period to the second time period is in a range from 1:10 to 1:30.
10 . The process of claim 8 , wherein a ratio of the fourth time period to the third time period is in a range from 3:1 to 12:1.
11 . The process of claim 1 , wherein:
the initial temperature is in a range from 0° C. to 35° C.;
the first temperature is in a range from 90° C. to 150° C.;
the second temperature is in a range from 250° C. to 350° C.;
the third temperature is in a range from about 300° C. to 450° C.;
the fourth, peak, temperature is in a range from 450° C. to 550° C.; and
the fifth temperature is in a range from 400° C. to 500° C.
12 . The process of claim 1 , wherein heating the third heated plastic at a rate of heating of greater than 50° C./min to an intermediate temperature comprises heating the third heated plastic at a rate in a range from 100° C./min to 200° C./min.
13 . A system for pyrolyzing waste plastics, the system comprising:
a reaction system having
a first heating zone configured for heating a waste plastic from an initial temperature to a first temperature and maintaining the waste plastic at the first temperature for a first time period, producing a first heated plastic;
a second heating zone configured for heating the first heated plastic to a second temperature and maintaining the first heated plastic at the second temperature for a second time period, producing a second heated plastic;
a third heating zone configured for heating the second heated plastic to a third temperature and maintaining the second heated plastic at the third temperature for a third time period, producing a third heated plastic;
a fourth heating zone configured for heating the third heated plastic to a fourth, peak, temperature, producing a fourth heated plastic; and
a fifth heating zone configured for providing heat input sufficient to maintain a temperature of the fourth heated plastic at a fifth temperature, less than the fourth, peak, temperature, and maintaining the fourth heated plastic at the fifth temperature for a fourth time period to recover a pyrolyzed product as a vapor and a pitch as a liquid from the reaction system,
wherein the third heating zone, the fourth heating zone and the fifth heating zone are configured to conduct the pyrolysis; and
wherein the fourth heating zone comprises two heating sections, including a first heating section configured to provide heat sufficient to heat the third heated plastic at a rate of 50° C./min to 200° C./min and a second heating section configured to provide heat sufficient to heat the third heated plastic at a rate of 15° C./min to 30° C./min.
14 . The system of claim 13 , further comprising a control system configured to control a heat input to each heating zone.
15 . The system of claim 13 , wherein the fifth temperature is in a range from 425° C. to 475° C.