FR2883567A1 - Treatment of waste polyethylene/polyolefins for producing hydrocarbons, comprises immersing the wastage in compressed water to displace occluded air by a piston and thermal cracking the wastage - Google Patents

Abstract

In the immersion, a perforated tube is supplied, where the surplus water is expelled by the holes towards the outside of the tube to penetrate only minimum of water to the cracking room and the wastage is retained.

Description

2883567 1

  The present invention relates to a process for treating waste polyethylene or other polyolefins prior to their subsequent thermal cracking.

  This process is based on the French patent N 02 133 34 which claims the immersion of the waste in a hot solvent polyethylene to be able to crack later directly in the liquid phase and to expel the air before their subsequent cracking. It also claims the introduction of waste continuously in a melting chamber by a feed tube in which they advance under the effect of the push of a piston mu by any device known in the art.

  Since the discovery of polyethylene during the 1920s it is known that its thermal decomposition leads to hydrocarbons mainly oc-olefinic. The low-temperature thermal cracking of polyethylene or polyolefins in general, whatever the types, leads to the production of hydrocarbons, especially aliphatic, liquid or gaseous in the atmosphere.

  The present invention is for its part intended to treat "all-in" waste polyolefin articles, even very wet and sometimes heavily loaded with inert materials or whose decomposition is not very troublesome during cracking, and in particular waste " all from "greenhouses, mulches and tunnels made of polyolefins used in agriculture, soiled with moist soil and plant debris, used bags, empty packaging (empty) or household waste roughly sorted films, bottles (empty) and miscellaneous packaging, without the need for prior cleaning. Several types of polyolefins may be present together and mixed without inconvenience because the cracking for which they are intended will provide whatever their type of hydrocarbons of similar types such as oc-olefins techniques, products of great value for oxo synthesis, but which also constitute an excellent fuel analogous to domestic fuel for heavier or solvents of higher quality than the usual aliphatic solvents of the type of white spirit for light fractions. The total absence of sulfur is an additional asset.

  One of the difficulties in cracking polyolefins is the existence of a very large quantity of air occluded in the waste when it is introduced into the cracking chamber, which tends to oxidize the products of the pyrolysis by producing undesirable tars and increasing the rate of coke formed during cracking.

  The process by pre-immersion of the waste in a (hot) solvent of the polyethylene described in the patent N 02 133 34 (solvent which partially evaporates subsequently during cracking) prevents this disadvantage but leads to a certain consumption and an undesirable cracking of the solvents used.

  The preceding process by immersion consists of first immersing the waste in kerosene or fuel oil, then expressing the excess of these solvents by compression in a perforated tube before pushing them back into a heated chamber until they are melting.

  The present invention partially takes up this technique, but substituting water for the heavy solvents required by the preceding invention, which allows both the removal of occluded air and the immersion in a heavy solvent without having the because the water is easier to handle and especially less expensive. But on the other hand the water thus introduced has, during the subsequent cracking behavior and effects very different from those of heavy solvents which were recommended for their ability to dissolve polyethylene hot. The water does not dissolve the polyethylene but the in situ vaporization of the small amount of residual water remaining in the waste (after having eliminated the excess by compression and leaving only the minimum possible) during the necessary heating subsequent cracking, causes a steam cracking effect with all the benefits that entails without requiring heavy equipment for producing superheated steam.

  According to the dip method of the patent N 0213334, the waste is compressed by a known means to force them into the melting chamber, and this compression in the feed tube has the effect of expelling the excess solvents which impregnate the waste through holes drilled in the first part of the feed tube while retaining the waste. On the other hand, this same patent claims the formation of a plug of compressed waste in the portion of the feed tube opening into the waste melting chamber, which plug is permanently reconstituted by arrival of new compressed waste.

  This technique will also be fully adopted in the present invention, however the compressed waste will no longer lead into a melting chamber but directly into a chamber where they will be cracked by any means known in the art.

Claims (1)

3 claims   (1) The present invention relates to a process for treating waste polyethylene or other polyolefins prior to their subsequent thermal cracking for the production of hydrocarbons, characterized in that before undergoing a cracking, the waste is first kept immersed in water to expel occluded air and compressed by a piston during their immersion in a feed tube leading them into a thermal cracking chamber where they are cracked according to the techniques already known.   (2) Thermal cracking method according to claim (1), characterized in that the feed pipe mentioned in claim (1) is perforated for a sufficient length from its origin so that, during compression by the plunger waste immersed in this feed tube, the excess water they contain is expelled by these holes to the outside of the tube while the waste is held there so that they enter the cracking chamber only with the minimum of water possible.