Study On The Mechanism Of Antistatic Agent In Gas Phase Fluidized Bed Polymerization Process

In the gas-phase polyethylene fluidized bed reactor,the friction and collision between insulating particles and the anhydrous and anaerobic reaction environment lead to the continuous accumulation of static electricity.Under the action of static electricity,the particles are easy to stick to the wall to form flakes or agglomerates,which affects the heat transfer and mass transfer inside the reactor.In severe cases,it may even cause the detonation to stop.Static electricity has become a major technical problem that has long plagued the long-term stable operation of gas-phase polyethylene plant.Suppressing static electricity is the key to ensure the stable operation of gas-phase polyethylene reactor.In industrial production,electrostatic initiator or antistatic agent is still used as the main electrostatic control method,but antistatic agent will lead to catalyst deactivation,and the antistatic agent specified by the process provider mostly depends on imports and is expensive.The mainstream antistatic technology is to increase the surface charge dissipation rate of particles by adsorbing water molecules by surfactants.However,this mechanism is not suitable for the strictly anhydrous reaction environment in the gas-phase polyethylene fluidized bed reactor,and the mechanism of antistatic agent in anhydrous environment has not been clearly understood.Therefore,it is of great research significance and practical application value to find out the action law of antistatic agent on the surface electrostatic of insulating dielectric in anhydrous environment and develop domestic antistatic agent suitable for gas phase polyethylene process.This paper focuses on the electrostatic problem of polyethylene particles in a gas-solid fluidized bed reactor.Firstly,the feasibility of electrochemical reduction reaction and thermal/photoelectron emission to identify the charge carrier in the bipolar charging process of polyethylene is investigated,which provides a reliable detection method for the experimental study of the de-ionization mechanism.Secondly,the The effect of anionic,cationic and non-ionic antistatic agents on the static electricity of polyethylene particles under dry conditions were studied experimentally,and their antistatic mechanism was explained by X-ray photoelectron spectroscopy,electron emission effect and molecular simulation.Finally,the The effect of different functional groups and molecular chain structures on the negative charge elimination performance of amine antistatic agents were explored,which provided guidance for the molecular structure design and development of new antistatic agents suitable for gas-phase fluidized bed polyethylene process.The main research contents and conclusions of this paper are as follows:1.The charge carriers of charged polyethylene particles were investigated by electrochemical reduction reaction and thermal/photoelectron emission,and the feasibility of the two methods in homogeneous bipolar charged system was analyzed.The results of both methods show that there are electrons in the charge carrier of the charging process of homogeneous polyethylene particles,and electrons exist on the surface of both positive and negative particles.In the electrochemical reduction reaction experiment,there are more electrons on the surface of the negatively charged particles that can undergo electrochemical reduction reaction with Cu2+.However,since the particle charge-to-mass ratio cannot accurately reflect the charge of a single particle and the reaction between the charged particles and the copper sulfate solution may be more complicated,this method is not suitable for quantitative analysis.For thermal/photoelectron emission,polyethylene particles can produce obvious photoelectron emission phenomenon.Under ultraviolet light irradiation,the charge of negatively charged particles decreases and the charge of positively charged particles increases.The proportion of electrons in charge carriers can be expressed by the change of particle charge during irradiation,and the quantitative results are better.The experimental method of photoelectron emission is preferred for the identification of charge carriers in the charging process of homogeneous polyethylene particles under the experimental conditions in this paper.2.The effect of anionic,nonionic and cationic antistatic agents on the static electricity of polyethylene particles under dry conditions were investigated.The results show that the anionic antistatic agent dodecylbenzenesulfonic acid needs a high air humidity(RH>60%)to eliminate the static electricity of polyethylene particles,and when the air humidity is less than 0.1%,it will enhance the negative charge of particles.Under dry conditions,anionic antistatic agent dodecyl benzene sulfonic acid has the effect of initiating negative charge at low concentration and eliminating negative charge at high concentration.Non-ionic antistatic agent ethylene oxide-propylene oxide-ethylene oxide block copolymer only has the effect of eliminating static electricity.Cationic antistatic agent dodecyl dimethyl tertiary amine has the effect of initiating positive charge at low concentration.Through XPS,molecular simulation and charge carrier characterization,it is confirmed that the electrostatic initiation of anionic and cationic antistatic agents is related to the change of the electronic state of their internal characteristic functional groups(sulfonic acid and amine).3.The amine antistatic agents commonly used in the gas-phase fluidized bed process were selected as the research object.The effect of the length of primary amine,secondary amine,tertiary amine,hydroxyl,carbonyl and lipophilic groups on the negative charge elimination of amine antistatic agents were investigated.For primary amine,secondary amine and tertiary amine with the same length of lipophilic chain segment,the elimination effect of primary amine on negative charge is stronger than that of secondary amine and tertiary amine.The introduction of terminal hydroxyl groups in tertiary amines can enhance the negative charge elimination ability of amine antistatic agents.The carbonyl group will limit the elimination of negative charge by its adjacent amino group.The increase of the length of the lipophilic segment can enhance the negative charge elimination ability of the amine antistatic agent.In summary,the use of primary amines or alkyl diethanolamines with a carbon number greater than twelve can achieve a better negative charge elimination effect.