Method for removing organic chlorine in pyrolytic oil of plastic

Abstract

The invention provides a method for removing organic chlorine in pyrolytic oil of plastics, which comprises the following steps: heating the pyrolytic oil of plastics to 200 DEG C, collecting a first fraction, further heating to 350 DEG C, and collecting a second fraction; after the first fraction reacts with a chlorine transfer agent, the first fraction is mixed with the second fraction, and plastic pyrolytic oil with organic chlorine removed is obtained. According to the method provided by the invention, cyclic utilization of waste plastic resources can be achieved through fraction segmentation and chlorine removal, chlorinated olefin and chlorinated alkane are removed through a nucleophilic substitution dechlorination technology, further removal of chlorinated aromatic hydrocarbon through catalytic hydrodechlorination is facilitated, and good environmental benefits and economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of plastics processing technology, and more particularly to a method for removing organochlorine compounds from the pyrolysis oil of plastics. Background Technology

[0002] The proportion of waste plastics in solid waste is increasing year by year. Using pyrolysis technology to convert waste plastics into fuel oil is currently the best option for treating waste plastics. Inorganic chlorine in fuel oil can be effectively removed, but removing organic chlorine still faces technical challenges.

[0003] Currently, the main technologies for removing organochlorines from oil products include adsorption dechlorination, catalytic hydrodechlorination, and nucleophilic substitution dechlorination. Among these, adsorption dechlorination is less effective because the presence of sulfur, nitrogen, and other elements in oil products inevitably affects the adsorption of chlorine by the adsorbent. Catalytic hydrodechlorination can achieve deep dechlorination, but it generates a large amount of HCl, which can corrode equipment and easily cause catalyst deactivation. The high cost of the catalyst is also a factor that must be considered. Nucleophilic substitution dechlorination can effectively remove chlorinated alkenes and chlorinated alkanes from organochlorines, but it has a low dechlorination rate for chlorinated aromatics.

[0004] CN113862024A discloses a method for removing organochlorine from inferior crude oil. The method includes removing organochlorine from crude oil by using a combination of two demulsifiers and a chlorine-converting agent, followed by an electro-desalting unit.

[0005] CN109181759A discloses a method for removing chlorinated organic compounds from waste oil. The method includes preparing an organochlorine transfer agent using triethylbenzylammonium chloride, an alkaline agent, and anhydrous ethanol to convert oil-soluble organochlorine into water-soluble inorganic chlorine, thereby separating the oil phase to achieve the effect of removing chlorinated organic compounds.

[0006] The above-mentioned methods for removing organochlorine are mainly aimed at removing organochlorine from industrial crude oil and waste oil. However, due to the variety of waste plastics, a certain amount of polyvinyl chloride is inevitably contained in them, resulting in a much higher chlorine content in waste plastic pyrolysis oil compared to industrial crude oil and waste oil. The organochlorine content is relatively high and the composition is complex. Therefore, specific organochlorine removal technologies need to be developed for waste plastic pyrolysis oil. Summary of the Invention

[0007] The technical problem this invention aims to solve is that existing dechlorination technologies for plastic pyrolysis oil are difficult to remove chlorinated aromatic hydrocarbons from organochlorine compounds, have high catalyst costs, and are prone to catalyst deactivation.

[0008] To address the aforementioned technical problems, in a first aspect, the present invention provides a method for removing organochlorine compounds from the pyrolysis oil of plastics, the method comprising the following steps:

[0009] The pyrolysis oil of the plastic is heated to 200°C, and the first fraction is collected. Then, the temperature is further increased to 350°C, and the second fraction is collected. The first fraction reacts with the chlorine transfer agent and is then mixed with the second fraction to obtain the pyrolysis oil of the plastic with organochlorine removed.

[0010] In this invention, the organochlorine compounds in the 0–200°C fraction include chlorinated alkenes, chlorinated alkanes, and chlorinated aromatics, with chlorinated alkenes and chlorinated alkanes accounting for 70% by mass and chlorinated aromatics accounting for 30% by mass. In the fraction above 200°C, the organochlorine compounds are primarily chlorinated aromatics, accounting for over 90% by mass. Chlorinated aromatics account for approximately 35% of the total organochlorine content.

[0011] The method provided by this invention, through fractionation, yields a fraction below 200°C containing 70% chloroolefins and chloroalkanes and 30% chloroaromatics, and a fraction above 200°C containing over 90% chloroaromatics. The fraction below 200°C, after nucleophilic substitution dechlorination, achieves a removal rate of over 90% for chloroolefins and chloroalkanes. Mixing the dechlorinated fraction with the fraction above 200°C results in a total organochlorine removal rate of over 60%. The mixed fraction has a lower chlorine content and a single organochlorine composition (all chloroaromatics), facilitating the selection of catalysts for catalytic hydrodechlorination. The lower chlorine content also reduces catalyst deactivation, lowering catalyst costs.

[0012] Preferably, the chlorine transfer agent comprises a phase transfer agent and a nucleophile.

[0013] Preferably, the phase transfer agent comprises any one or a combination of at least two of benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, or tetrabutylammonium hydroxide.

[0014] Preferably, the phase transfer agent is benzyltriethylammonium hydroxide.

[0015] The ratio of nucleophile to phase transfer agent is (1-2):1. Among them, the phase transfer agent, such as benzyltriethylammonium hydroxide, is synthesized from benzyltriethylammonium chloride. Therefore, the phase transfer agent will inevitably contain a certain amount of chlorine. So the amount of phase transfer agent added should be controlled during the reaction.

[0016] Preferably, the nucleophile comprises any one or a combination of at least two of sodium hydroxide, sodium methoxide, ethylenediamine, or triethylamine.

[0017] Preferably, the nucleophile is ethylenediamine.

[0018] Ethylenediamine is preferred in this invention because both nitrogen atoms in the ethylenediamine molecule contain lone pairs of electrons, which increases the nucleophilicity of the molecule and makes it easier to react with chlorinated hydrocarbons.

[0019] Preferably, the reaction temperature is 85–95°C.

[0020] In this invention, when the first and second fractions are mixed, catalytic hydrogenation is used for further dechlorination. At this point, the organochlorine in the oil is mainly chloroalkanes, and the organochlorine content is reduced. The catalyst can be selected specifically for the removal of chloroalkanes. After the chlorine content is reduced, the catalyst is less prone to deactivation, which greatly reduces the cost of the catalyst.

[0021] Implementing this invention has the following beneficial effects:

[0022] The method provided by this invention, through fractionation, yields a fraction below 200°C containing 70% chloroolefins and chloroalkanes and 30% chloroaromatics, and a fraction above 200°C containing over 90% chloroaromatics. The fraction below 200°C, after nucleophilic substitution dechlorination, achieves a removal rate of over 90% for chloroolefins and chloroalkanes. Mixing the dechlorinated fraction with the fraction above 200°C results in a total organochlorine removal rate of over 60%. The mixed fraction has a lower chlorine content and a single organochlorine composition (all chloroaromatics), facilitating the selection of catalysts for catalytic hydrodechlorination. The lower chlorine content also reduces catalyst deactivation, lowering catalyst costs. This invention enables the recycling of waste plastic resources, removes chloroolefins and chloroalkanes through nucleophilic substitution dechlorination, and facilitates further removal of chloroaromatics through catalytic hydrodechlorination, resulting in significant environmental and economic benefits. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] This embodiment provides a method for removing organochlorine compounds from the pyrolysis oil of plastics.

[0026] The pyrolysis oil of plastic was placed in a reactor and heated to 200°C. The first fraction was collected, and then the temperature was further increased to 350°C to collect the second fraction. The first fraction was reacted with benzyltriethylammonium hydroxide and ethylenediamine at 90°C for 1 hour, and the organochlorine removal rate of the first fraction was tested. Then the first fraction and the second fraction were mixed to obtain the pyrolysis oil of plastic with organochlorine removed, and the final organochlorine removal rate was tested.

[0027] Example 2

[0028] This embodiment provides a method for removing organochlorine compounds from the pyrolysis oil of plastics.

[0029] The pyrolysis oil of the plastic was placed in a reactor and heated to 200°C. The first fraction was collected, and then the temperature was further increased to 350°C to collect the second fraction. The first fraction was reacted with benzyltriethylammonium hydroxide and sodium hydroxide at 90°C for 1 hour, and the organochlorine removal rate of the first fraction was tested. Then the first fraction and the second fraction were mixed to obtain the pyrolysis oil of the plastic with organochlorine removed, and the final organochlorine removal rate was tested.

[0030] Example 3

[0031] This embodiment provides a method for removing organochlorine compounds from the pyrolysis oil of plastics.

[0032] The pyrolysis oil of the plastic was placed in a reactor and heated to 200°C. The first fraction was collected, and then the temperature was further increased to 350°C to collect the second fraction. The first fraction was reacted with benzyltriethylammonium hydroxide and sodium methoxide at 90°C for 1 hour, and the organochlorine removal rate of the first fraction was tested. Then the first fraction and the second fraction were mixed to obtain the pyrolysis oil of the plastic with organochlorine removed, and the final organochlorine removal rate was tested.

[0033] Example 4

[0034] The difference between this example and Example 1 is that benzyltriethylammonium hydroxide is replaced with tetrabutylammonium hydroxide.

[0035] Example 5

[0036] The difference between this example and Example 1 is that it does not contain ethylenediamine.

[0037] Example 6

[0038] The difference between this example and Example 1 is that it does not contain benzyltriethylammonium hydroxide.

[0039] Comparative Example 1

[0040] The difference between this comparative example and Example 1 is that the oil in this comparative example is waste plastic pyrolysis oil that has not undergone fractionation.

[0041] Comparative Example 2

[0042] The difference between this comparative example and Example 1 is that this comparative example does not contain a chlorine transfer agent.

[0043] The results of the organic chlorine removal rates of the first fraction and the final organic chlorine removal rates of the samples from the above embodiments and comparative examples are shown in Table 1 below.

[0044] Chlorine content: determined by a microcoulometric titrator.

[0045] Catalyst activity: Samples were taken every 2 hours to determine the chlorine content, and the catalyst activity was judged based on the change pattern of chlorine content.

[0046] Table 1

[0047]

[0048] The data in Table 1 show that the method of this invention achieves the best removal effect of organochlorines. However, the removal effect decreases significantly when nucleophiles or phase transfer agents are lacking. The effect decreases even more when chlorine transfer agents are absent from the reaction.

[0049] The method provided by this invention can achieve a final organochlorine removal rate of up to 69.8%, and the catalyst activity is maintained for a relatively long time.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing organochlorine compounds from pyrolysis oil of plastics, characterized in that, The method includes the following steps: The pyrolysis oil of the plastic is heated to 200°C, and the first fraction is collected. Then, the temperature is further increased to 350°C, and the second fraction is collected. The first fraction reacts with the chlorine transfer agent and is then mixed with the second fraction to obtain the pyrolysis oil of the plastic with organochlorine removed.

2. The method according to claim 1, characterized in that, The chlorine transfer agent includes a phase transfer agent and a nucleophile.

3. The method according to claim 2, characterized in that, The phase transfer agent includes any one or a combination of at least two of benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, or tetrabutylammonium hydroxide.

4. The method according to claim 3, characterized in that, The phase transfer agent is benzyltriethylammonium hydroxide.

5. The method according to claim 2, characterized in that, The nucleophile includes any one or a combination of at least two of sodium hydroxide, sodium methoxide, ethylenediamine, or triethylamine.

6. The method according to claim 5, characterized in that, The nucleophile is ethylenediamine.

7. The method according to claim 1, characterized in that, The reaction temperature is 85–95°C.

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