Co-pyrolysis characteristics of typical components of waste plastics in a falling film pyrolysis reactor

Waste plastics mainly come from MSW and usually exist in the form of mixed plastics. During the co-pyrolysis process of mixed plastics, various plastic components have different physicochemical properties and reaction mechanisms. Considering the high viscosity and low thermal conductivity of molten plastics, a falling film pyrolysis reactor was selected to explore the rapid co-pyrolysis process of typical plastic components(PP, PE and PS).The oil and gas yields and the compositions of pyrolysis products of the three components under different ratios at pyrolysis temperatures were analyzed to explore the co-pyrolysis characteristics of PP, PE, and PS. The study is of great significance to the recycling of waste plastics.

Molten waste plastic pyrolysis in a vertical falling film reactor and the influence of temperature on the pyrolysis products

Molten plastics are characterised with high viscosity and low thermal conductivity. Applying falling film pyrolysis reactor to deal with waste plastics can not only improve heat transfer efficiency, but also solve the flow problem.In this work, the pyrolysis process of molten polypropylene(PP) in a vertical falling film reactor is experimentally studied, and the influence of heating temperature on pyrolysis products is discussed. It has been found that with the temperature increases from 550 ℃ to 625 ℃, the yield of pyrolysis oil decreases from 74.4 wt%(± 2.2 wt%) to53.5 wt%(±1.3 wt%). The major compositions of the pyrolysis oil are C_9, C_(12) and C_(18), and β-scission reactions are predominant. The content of the light fraction C_6-C_(12) of pyrolysis oil is 69.7 wt%. Compared with other pyrolysis reactors, the yield of oil from vertical falling film pyrolysis reactor is slightly higher than that from tubular reactor,equal to that from rotary kiln reactor, and slightly lower than that in medium fluidised-bed reactor.

Chlorine removal from MSWI fly ash by thermal treatment: Effects of iron/aluminum additives

The high content of alkali chlorides in municipal solid waste incineration(MSWI) fly ash limit its resource reuse due to the potential environmental risks.In this paper, with superheated steam as the gasifying agent and inducer, chlorides in fly ash were removed by thermal treatment within a moderate temperature range.Thermal treatment experiments were performed under different conditions: temperature(500–800℃), steam addition(mass ratio of steam to fly ash = 0.25–1) and residence time(0.5–3 hr).Iron and aluminum powders were added to fly ash to improve the chlorine removal efficiency.Water-soluble chlorides included Na Cl and KCl, and insoluble chlorides mainly included Ca(OH)Cl.The heating process with the addition of water steam was more efficient than that without steam in terms of the removal performance of water-soluble chlorides.The removal efficiency of soluble chlorides reached 75.25% for a mass ratio of 1:1 after 1-hr thermal treatment at 700℃.When the residence time was increased above 1 hr, the total dechlorination efficiency was not increased dramatically.Moreover, adding iron and aluminum powder into the fly ash improved the removal of water-insoluble chlorides, and the total dechlorination efficiency was increased by 11.41%–16.64%.

Hydrothermal treatment of MSWI fly ash for simultaneous dioxins decomposition and heavy metal stabilization

Researches on the hydrothermal treatment of municipal solid waste incineration(MSWI)fly ash were conducted to eliminate dioxins and stabilize heavy metals.In order to enhance decomposing polychlorinated dibenzodioxins(PCDDs)and polychlorinated dibenzo-furans(PCDFs)during hydrothermal process,a strong reductant carbohydrazide(CHZ)is introduced.A hydrothermal reactor was set up by mixing raw MSWI fly ash or the pre-treated fly ash with water and then heated to a pre-set temperature;CHZ was spiked into solution according to specially defined dosage.Experimental results showed that under the temperatures of 518 K and 533 K,the decomposition rates of PCDDs/PCDFs were over 80%and 90%,respectively,by total concentration.However,their toxic equivalent(TEQ)decreased only slightly or even increased due to the rising in concentration of congeners 2,3,7,8-TCDD/TCDF,which might be resulted from the highly chlorinated congeners losing their chlorine atoms and being degraded during the hydrothermal process.Better results of TEQ reduction were also obtained under the higher tested temperature of 533 K and reactor with addition of 0.1%wt CHZ was corresponded to the best results.Good stabilization of heavy metals was also obtained in the same hydrothermal process especially when ferrous sulphate was added as auxiliary agent.

间歇性外斜视的调节灵活度和调节反应

目的 比较间歇性外斜视和正常眼位人群之间,间歇性外斜视注视眼和非注视眼之间的调节灵活度和调节反应.方法： 病例对照研究.选取2016年10月至2017年1月在温州医科大学附属眼视光医院门诊就诊的35例间歇性外斜视患者作为间歇性外斜视组,另选取24例正位眼或外隐斜斜视度≤6△的门诊患者作为对照组.采用±2.00 D的反转拍和开放视野式自动验光仪分别测量受试者在单眼和双眼注视近距视标时的调节灵活度和调节反应.采用t检验对数据进行分析.结果： 间歇性外斜视组的双眼调节灵活度为（8.8±4.1）cpm,显著低于对照组[（10.9±3.1）cpm],两者差异有统计学意义（t=-2.165,P=0.035）.间歇性外斜视组的非注视眼调节灵活度显著低于注视眼（t=4.657,P〈0.001）.双眼注视40 cm处视标时,间歇性外斜视组的注视眼调节反应高于对照组的主导眼 （t=-2.163,P=0.035）.双眼注视状态下,间歇性外斜视组注视眼的调节反应为（1.89±0.30）D,高于其在单眼注视状态下的调节反应[ （1.64±0.34） D],两者差异有统计学意义（t=3.801, P=0.001）.结论：间歇性外斜视患者的双眼调节灵活度低于对照人群,其注视眼和非注视眼的调节灵活度和调节反应均不一致,且双眼注视时调节反应高于单眼注视状态.

Effect of cultivation time on soil heavy metal accumulation and bioavailability in Phyllostachys praecox stands

Phyllostachys praecox is a bamboo species cultivated for edible shoots under intensive management.However,the potential pollution risk of heavy metals in bamboo soils is not clear under the intensive management for a long term.The objective of this study was to evaluate the effect of cultivation time on soil heavy metal accumulation and bioavailability in bamboo stands subjected to intensive management.Soil samples were collected from a chronosequence of bamboo stands which had been cultivated for 0,1,2,4,8,and 10 years in Lin’an,Zhejiang Province of China.Eight heavy metals(Cu,Zn,Pb,Ni,Cr,Cd,As,and Hg)present in the soil were selected,and their potential pollution risk was evaluated by chemical speciation analysis.Possible heavy metal sources were explored using multivariate and cluster analysis.Our results showed that Zn,Cu,Hg,and Cd contents in the soil increased with the cultivation time,while Ni,Cr,Pb,and As levels were similar among all stands.Furthermore,the bioavailabilities of all analyzed heavy metals increased with the cultivation time.Multivariate and cluster analysis showed that sources of Ni,Cr,Pb,and As were likely lithogenic in origin,whereas input of Zn,Cu,Hg,and Cd was mainly due to cultivation practices.Current bamboo management strategies raised the potential risks of heavy metal pollution in bamboo shoots in the long term.Soil acidification in P.praecox stands induced by intensive cultivation should be controlled since it stimulated and improved the bioavailability of heavy metals.Appropriate management strategies should thus be adopted to ensure safe and sustainable production of bamboo shoots.

Preparation and gaseous photocatalytic activity of smooth potassium dititanate film

A new smooth potassium dititanate film was prepared by sol-gel method and characterized by thermogravimetry(TG)and differential scanning calorimetry(DSC),X-ray diffraction(XRD),atomic force microscopy(AFM),UV-Visible diffuse reflectance and Raman spectroscopy.The gaseous photocatalytic activity of smooth K_(2)Ti_(2)O_(5)films was studied using contact angle analysis from the photocatalytic decomposition of octadecyltrichlorosilane(OTS)based self-assembled monolayers(SAMs)formed on K_(2)Ti_(2)O_(5)films.The photocurrent response of the film was determined by an electrochemical method.It was shown that the films were smooth,compact,and transparent when formed on glass.Compared with TiO_(2)film,the K_(2)Ti_(2)O_(5)film showed wide absorption in the ultraviolet and visible region.It was found that the monolayers on K_(2)Ti_(2)O_(5)decomposed much faster than those on TiO_(2)under UV irradiation of 254 nm in air.The film also exhibited a stronger photoresponse and a more stable anodic photocurrent.The K_(2)Ti_(2)O_(5)film efficiently decomposes the alkylsiloxane monolayers under UV irradiation in air and it was found to be a good photocatalyst for gaseous organic pollutant treatment.