Pyrolysis system and method of recovering carbon fibres from carbon-fibre-containing plastics

Abstract

The invention relates to a pyrolysis plant and a process for recovering (recycling) carbon fibers from carbon fiber-containing plastics, in particular from carbon fiber-reinforced plastics (CFPs or CFP materials), preferably from carbon fiber-containing and/or carbon fiber-reinforced composites (composite materials).

1 - 15 . (canceled) 
     
     
         16 . A pyrolysis plant for recovering carbon fibers from carbon fiber-containing plastics (CFP material),
 wherein the pyrolysis plant comprises:
 an elongated pyrolysis furnace for the continuous pyrolysis of CFP material which operates continuously during operation, 
   an input station for introducing CFP material to be processed into the pyrolysis furnace at its one end,   an output station for discharging recovered carbon fiber material from the pyrolysis furnace at its other end,   a gas offtake device for pyrolysis gas produced in the pyrolysis furnace, and   a control device for regulating at least individual constituents of the gas in the pyrolysis furnace;   wherein the pyrolysis furnace is an indirectly heated rotary tube furnace which has at least the following constituents:   an elongated rotary tube which forms the accommodation space for the CFP material to be processed and is connected to the input station and the output station, with the rotary tube being provided on its cylindrical wall with exit openings for discharging pyrolysis gas formed during the pyrolysis over at least part of its length, and   a housing which is insulated from the outside and at least partly surrounds the rotary tube and has openings for the input station and optionally also for the output station and has discharge lines for the pyrolysis gas, where a plurality of sections having different or differently regulatable gas temperatures are provided in the housing along the length of the rotary tube;   wherein the exit openings in the rotary tube are provided at least in the section having the highest gas temperature;   wherein the pyrolysis furnace has various sections, namely at least one heating-up zone, a first pyrolysis zone, a second pyrolysis zone and a cooling zone, and the composition of the gas and the temperature in the pyrolysis furnace in the various sections of the rotary tube can be regulated differently, namely with a defined proportion of oxygen and with a defined temperature in the first pyrolysis zone and with a defined proportion of oxygen and with a defined temperature in the second pyrolysis zone; and   wherein the pyrolysis plant additionally comprises a comminution apparatus for comminuting CFP material to be processed, with the comminution apparatus being arranged before or upstream of the input station.   
     
     
         17 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the rotary tube comprises a first heating section extending from the input station and a second, adjoining cooling section leading to the output station.   
     
     
         18 . The pyrolysis plant as claimed in  claim 17 ,
 wherein the rotary tube is configured so as to be coolable by means of water in the cooling section.   
     
     
         19 . The pyrolysis plant as claimed in  claim 17 ,
 wherein the rotary tube does not comprise any exit openings in the cooling section.   
     
     
         20 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the exit openings are distributed essentially uniformly over the circumference of the rotary tube.   
     
     
         21 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the size of the exit openings is adjustable.   
     
     
         22 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the rotary tube is arranged so as to be inclined downward from the input station to the output station.   
     
     
         23 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the rotary tube is provided in its interior with mixing elements.   
     
     
         24 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the rotary tube is provided firstly with mixing elements and secondly with a transport element.   
     
     
         25 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the input station is configured as an input lock.   
     
     
         26 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the comminution device is configured in the form of at least one of a shredder, hacking, chopping, milling, tearing and cutting device.   
     
     
         27 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the pyrolysis plant additionally comprises, arranged after the output station, a work-up device for working up the recycled carbon fibers obtained from the CFP material.   
     
     
         28 . The pyrolysis plant as claimed in  claim 16 ,
 wherein the pyrolysis plant additionally comprises a work-up device arranged after or downstream of the output station in the process direction for working up the recycled carbon fibers obtained from the CFP material.   
     
     
         29 . The pyrolysis plant as claimed in  claim 16 ,
 wherein heating of the pyrolysis furnace is effected from at least one external gas burner via heating gas lines in the housing.   
     
     
         30 . A process for recovering carbon fibers from carbon fiber-containing plastics, carbon fiber-reinforced plastics, carbon fiber-containing composites and carbon fiber-reinforced composites,
 wherein the process comprises using the pyrolysis plant as claimed in  claim 16 .   
     
     
         31 . A process for recovering carbon fibers from carbon fiber-containing plastics,
 wherein the process comprises the following steps:   an object based on a carbon fiber-containing plastic which comprises carbon fibers in a polymer matrix is subjected to a multistage pyrolysis in the presence of oxygen, with the polymer of the polymer matrix being decomposed during the pyrolysis to give the carbon fibers, and   the pyrolysis is carried out in a pyrolysis plant as claimed in  claim 16  and comprising a pyrolysis furnace, where the pyrolysis furnace comprises at least the following treatment zones in the order specified below and the object goes through the following treatment zones in this order:   (A) a heating-up zone A in which the object to be treated and to be recycled is heated to a defined temperature,   (B 1 ) subsequently, a first pyrolysis zone B 1  in which a pyrolysis of the polymer of the polymer matrix of the object to be treated is carried out at a defined temperature T(B 1 ) and a defined oxygen content G(B 1 ),   (B 2 ) subsequently, a second pyrolysis zone B 2  in which a final pyrolysis of the polymer of the polymer matrix of the object to be treated still present after the pyrolysis zone B 1  is carried out at a defined temperature T(B 2 ) and a defined oxygen content G(B 2 ) to at least essentially complete removal,   (C) subsequently, a cooling zone C for cooling the recycled carbon fibers obtained from the second pyrolysis zone B 2 ;   wherein the oxygen content G(B 2 ) in the second pyrolysis zone B 2  is increased by from 3% by volume to 25% by volume compared to the oxygen content G(B 1 ) in the first pyrolysis zone B 1  and   wherein the temperature T(B 2 ) in the second pyrolysis zone B 2  is increased by from 25° C. to 300° C. compared to the temperature T(B 1 ) in the first pyrolysis zone B 1 .   
     
     
         32 . Carbon fibers recycled pyrolytically from carbon fiber-containing plastics, wherein the recycled carbon fibers are obtainable by a process as claimed in  claim 31  and wherein the recycled carbon fibers:
 have a wettability relative to water, determined as tensiometrically measured contact angle by the Wilhelmy method by means of single fiber measurement at (23±0.5°) C., of not more than 75°, 
 comprise a proportion of pyrolysis residues of less than 0.5% by weight, based on the recycled carbon fibers and determined gravimetrically, 
 comprise oxygen-containing functional groups, namely polar or hydrophilic groups selected from among phenol, carboxyl, carbonyl, aldehyde, keto, hydroxy and oxo groups on their surface, determined by means of electron spectroscopy for chemical analysis (ESCA), and 
 comprise grooves, flutes, depressions, furrows, scratches or craters on their surfaces. 
 
     
     
         33 . The recycled carbon fibers as claimed in  claim 32 ,
 wherein the recycled carbon fibers have a wettability relative to water, determined as tensiometrically measured contact angle by the Wilhelmy method by means of a single fiber measurement at (23±0.5°) C., of not more than 73°, and   wherein the recycled carbon fibers have a proportion of pyrolysis residues in the range from 0.001 to 0.5% by weight, based on the recycled carbon fibers and determined gravimetrically.   
     
     
         34 . The recycled carbon fibers as claimed in  claim 32 ,
 wherein the recycled carbon fibers have a tensile strength in the range from 1,000 to 6000 MPa, and   wherein the recycled carbon fibers have a modulus of elasticity in the range from 20 to 1000 GPa, and   wherein the recycled carbon fibers have an average fiber diameter in the range from 0.1 to 100 μm.   
     
     
         35 . A material selected from the group consisting of plastic materials, building materials or cement-containing systems, the material comprising recycled carbon fibers as claimed in  claim 32 . 
     
     
         36 . A shaped body, a mold or a sheet-like material in the form of a composite material, comprising recycled carbon fibers as claimed in  claim 32 .