Experiment and Kinetic Study of Elemental Mercury Adsorption over a

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Experiment and kinetic study of elemental mercury adsorption over a novel chlorinated sorbent derived from coal and waste polyvinyl chloride Yang Xu, Xiaobo Zeng, Bi Zhang, Xianqing Zhu, Mengli Zhou, Renjie Zou, Ping Sun, Guangqian Luo, and Hong Yao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01372 • Publication Date (Web): 31 Oct 2016 Downloaded from http://pubs.acs.org on November 8, 2016

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Energy & Fuels

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Experiment and kinetic study of elemental mercury adsorption over a novel

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chlorinated sorbent derived from coal and waste polyvinyl chloride

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Yang Xua, Xiaobo Zenga, Bi Zhanga, Xianqing Zhua, Mengli Zhoua, Renjie Zoua, Ping Suna,b, Guangqian Luoa *,

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Hong Yaoa *

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a

State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China

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b

Shenhua Guohua (Beijing) electric power research institute limited company, Beijing, 100025, China

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*: Corresponding Authors

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* E-mail: [email protected]; Tel: 86-27-87542417; Fax: 86-27-87545526

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ACS Paragon Plus Environment

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Graphical abstract

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Abstract

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This paper describes the synthesis of a novel chlorinated sorbent through one-step pyrolysis of

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waste polyvinyl chloride (PVC)/coal blends and its application for elemental mercury removal. The

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effects of pyrolysis temperature (600, 700, 800oC) and mixing ratio (9:1, 3:1) on Hg0 adsorption

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efficiency was tested in a laboratory-scale fixed bed reactor. For sorbents T8C9P1 and T83P1, a

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complete removal of mercury was maintained for 30 minutes at 140 oC. Ion chromatography (IC)

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analysis, Brunauer-Emmett-Teller (BET) surface area and X-ray photoelectron spectroscopy (XPS)

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analysis were used to characterize the sorbents. The results suggested that co-pyrolysis of PVC and

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coal could fix the pernicious element to a certain extent, leading to a few percent reduction of Cl

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emission (2.6-13.3%). The XPS and temperature programmed desorption (TPD) data showed that

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parts of C-Cl functional group were converted into ionic Cl during Hg0 adsorption process, which

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indicated that the C-Cl bond is the major active component for mercury removal via chemisorption.

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The adsorption kinetics analysis demonstrated that the elemental mercury adsorption on

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chlorine-modified sorbent was mainly controlled by chemisorption and the effect of intra-particle

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diffusion became apparent after an elapsed time of 25min. Most C-Cl bonds were assumed to be

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formed when high molecular weight carbon free radicals and HCl (or Cl free radical) appeared

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synchronously during co-pyrolysis. Based on the results, the co-pyrolysis of PVC and coal is a

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multi-functional process for Cl fixation and satisfies the requirements for the synthesis of candidate

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mercury sorbent.

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Key words: Mercury; Sorbent; Pyrolysis; Coal; PVC

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1. Introduction

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Coal is currently one of the most important energy sources in the world. According to the

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energy statistics announced by American government, the world’s coal consumption will increase

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from 122.5 quadrillion Btu in 2005 to 202.2 quadrillion Btu in 2030.1 However, coal emits various

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hazardous air pollutants during combustion including SOx, NOx, particulate matter and trace

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metals.2,3 Mercury is one of these trace heavy metals and receives particular concern due to its high

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toxicity, volatility, and negative impact on neurological health.4-6 Coal combustion is widely

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considered to be the largest anthropogenic source of mercury emission.7, 8 Mercury in coal-fired flue

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gas exists in three forms: elemental mercury (Hg0), oxidized mercury (Hg2+), and particulate-bound

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mercury (HgP).9-13 Coal initially liberates mercury as Hg0 when being burned in utility boiler

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chambers. The Hg0 is then partially oxidized into Hg2+ with the flue gas cooling.14 Hg2+ has high

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water-solubility, and it can be removed via the wet flue gas desulfurization (WFGD) units,15-18 which

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have been installed in almost all of the coal fired power plants in China. HgP is captured by particle

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control devices (PCDS)—electrostatic precipitators (ESP) and/or fabric filter (FF)—along with fly

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ash particulate. Nonetheless, Hg0 cannot be readily removed by current air pollution control devices

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because of its insolubility in water and high volatility.19-22

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Of all the Hg0 removal technologies, activated carbon injection (ACI) upstream of the PCDS is

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the most promising approach for mercury capture from coal-derived flue gas.23, 24 However, virgin

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AC shows poor Hg0 removal efficiency at typical flue gas temperature. Massive research efforts25, 26

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have demonstrated that modifying AC with S and halogens (Cl, Br and I) is successful for improving

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its capacity for mercury sorption, but the chemical impregnation procedure is complex27, 28 and a

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large number of chemical reagents such as hydrochloric acid are consumed.25 These results indicate

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an increased price of sorbents, which limits the extension of ACI technology. Thus, it is necessary to

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develop an alternative method to simplify the preparation technology of mercury sorbents.

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Waste polyvinyl chloride (PVC) is a kind of municipal solid waste (MSW) that increases largely

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with rapid economic growth and massive urbanization. PVC contains a large amount of chlorine

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(>50 wt. %), which brings about waste-disposal problem because hydrogen chloride released from

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thermal treatment of PVC is harmful and corrosive. Some studies29-31 have attempted research on the

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co-pyrolysis of carbon-based material/PVC blends. The results revealed that a chemical reaction

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between biomass and HCl occurred that could reduce HCl emissions significantly by fixing most of

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the Cl into co-pyrolyzed residue. Coal is a widely used carbon-based material besides biomass, and

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Saeed et al. reported that an interaction between coal and PVC degradation occurred. But it is not

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known whether coal could play the same important role as biomass in the fixation of Cl. Chlorine is

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an active element favorable for Hg0 removal.32-34 If the Cl emitted from PVC could be fixed into

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pyrolyzed residue, then the fixed Cl has the possibility to provide active sites for Hg0 removal. Hence,

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it is important to investigate whether the sorbents, derived from the co-pyrolysis of coal/PVC blends,

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can be used to remove Hg0 from coal-fired flue gas. If so, environmentally harmful Cl can be

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converted to useful Cl for Hg0 removal and the amount of Cl emission is partly reduced.

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The main purpose of this study is to investigate the feasibility of using simple single-step

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method (co-pyrolysis of coal/ PVC blends) to prepare sorbents for Hg0 removal. In this study, waste

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PVC was selected as the chlorine precursor and coal as the carbon-based material to synthesize

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chlorine-modified sorbents. The effects of pyrolysis temperature (600, 700, 800 oC) and mixing ratio

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(9:1, 3:1) on the Hg0 removal efficiency were explored. The sorbent properties were characterized

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with IC, BET, XPS and TPD analysis. Adsorption kinetics and adsorption mechanism were analyzed

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by employing the pseudo-first-order, pseudo-second-order and Web-Morris model.

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2. Experimental section

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2.1. Raw materials

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Experiment materials, commercially available waste PVC and Zhundong sub-bituminous coal

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from the west of China (Xinjiang), were selected in this study. The PVC and coal were ground and

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sieved to an appropriate particle size of 150-200 µm and dried in air for 3 days. The PVC/coal blends

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were mixed homogeneously at defined proportions and then used for pyrolysis. The main

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characteristics of materials are listed in Table 1. According to Table 1, coal was mostly composed of

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fixed carbon (FC) and volatile matter (V) with less ash (A) (2.84%). The low ash content had a

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positive impact on pore-creation during pyrolysis. The volatile content of the PVC was very high

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(94.55%)—this led to a low char yield after pyrolysis. PVC contained 52.33 wt. % Cl, and this was

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emitted as HCl during pyrolysis.

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2.2. Sample preparation

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The raw materials were pyrolyzed in a temperature-controlled reaction system, consisting of a

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tube furnace, a tube quartz reactor (diameter: 75 mm, length: 950 mm) and a water-cooling system.

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Before pyrolysis, a quartz boat (40 cm3) containing 1 gram (g) of coal/PVC blends, was placed into

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the cooling zone. A N2 flow (150 mL/min) was introduced into the reactor to remove air. When the

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reactor was heated to the scheduled temperature (600, 700, 800°C), the quartz boat was pushed to the

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center of the reactor and remained for 30 min. The quartz boat was then withdrawn from the reaction

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zone and put into cooling system under protection with N2. After being cooled to ambient

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temperature, the chars were collected as sorbents for Hg0 removal. The mixing ratios of coal /PVC

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blends were 3:1 (wt/wt), and 9:1 (wt/wt).

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The definition used throughout this text is to denote Cl-modified sorbents (in the presence of

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PVC during pyrolysis) as T0C0P0; the first number means the pyrolysis temperature; the second and

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third number mean the mass ratio of coal/PVC. For example, a sample defined as T7C3P1 is a

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sorbent prepared at 700°C and the ratio of coal to PVC is 3:1. Raw sorbents (in the absence of PVC

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during pyrolysis) are labeled as T0Char, in which “0” means the pyrolysis temperature.

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2.3. Sample characterization

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The proximate analyses of PVC and coal were determined using the method of GB/T212—2008.

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The moisture content was calculated from the weight loss of samples (1 g) dried in an oven at 110 0C

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until a constant weight was obtained. The ash content was measured by burning a sample (1 g) in a

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muffle furnace at 815±10°C for 4 hours. Samples were put in a crucible with a lid (under inert

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atmosphere) and then placed in a muffle furnace at 900±10

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volatile matter content. Fixed carbon content was calculated by the mass balance of samples. The

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ultimate analysis was performed by the Chinese National Standards (GB476-91). The C and H

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contents were determined by weighing the generated CO2 and H2O after sample burning, respectively.

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The N in the samples was converted into NH3 to determinate its content. The S in the samples was

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converted into SO2 and SO3 in order to measure the content of S. The O content was calculated by

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mass balance of samples. The Cl content of the samples was analyzed with ion chromatography

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(IC-2010) following digestion with nitric acid (HNO3, Guaranteed Reagent) and hydrogen peroxide

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(H2O2, Guaranteed Reagent). About 0.045 g of sample was mixed with 2 ml HNO3 and 2 ml H2O2

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and heated in an oven at 180°C for 10 h. The solution was then diluted to an appropriate

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concentration and analyzed by IC-2010. The specific surface area (SBET) and pore volume were

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measured by nitrogen (N2) adsorption at 77 K using a Micromeritics ASAP 2020. X-ray

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0

C for 7 min to determine

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photoelectron spectroscopy (XPS, AXIS ULTRA DLD-600W) was applied to verify the elemental

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states on the surface of sorbent. The binding energy was corrected by the C 1s peak at 285 eV.

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The powdered samples of PVC and coal were subjected to thermogravimetric analysis (TGA,

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PerkinElmer Instruments). About 8 mg (150-200 µm) of sample was heated under 100 mL/min N2

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flow at a heating rate of 20°C/min from 50°C to 1000°C.

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2.4. Hg0 adsorption tests

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A schematic representation of the experimental apparatus is shown in Fig. 1. This was used to

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evaluate the sorbent’s performance for Hg0 adsorption. A constant N2 flow (1 L/min) passed through

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the mercury vapor permeation tube (VICI Metronics Inc., USA) placed in a U-type glass tube. This

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was housed in a constant-temperature water bath to keep the Hg0 concentration at about 100 µg/m3.

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The N2 flow was introduced into the quartz reactor (length: 700 mm, internal diameter: 20 mm) with

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a sieve-disk inside; 0.35 g sorbent was loaded on the sieve-disk. The quartz reactor was maintained

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at 140°C by a temperature-controlled furnace. The Hg0 concentration at the outlet of the quartz

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reactor was recorded continuously by an online mercury analyzer (VM3000, Mercury Instruments,

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Germany) based on cold vapor absorption spectrometry. The Hg0 removal efficiency η of different

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sorbents was calculated by Eq. (1). η=

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× 100%

(1)

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C and C represent the Hg0 concentration (µg/m3) at the reactor’s inlet and outlet,

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respectively.

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The accumulative amount of Hg0 captured on sorbents at time t was expressed by the Hg0 removal efficiency η, as in Eq. (2)

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q =

× ×

8


(2)

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where Q represents the gas-flow rate (m3/min), W represents the mass of sorbent (g), and t (min)

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represents the adsorption time.

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2.5 Temperature programmed desorption experiment

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Temperature programmed desorption (TPD) is widely used to study the characteristics of

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mercury species on the sorbent surface. The TPD experiment was performed in the same apparatus

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as Hg0 adsorption tests. 0.35 g mercury-adsorbed sorbents was heated from ambient temperature to

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600°C at 10°C/min in N2 flow (1 L/min). The released Hg0 from sorbents was monitored

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continuously by VM3000. Then mercury desorption curve was obtained. For comparison, TPD

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experiment of fresh sorbents was carried out to ensure that no mercury was released. The mercury

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mass balance between adsorption and desorption was calculated by Eq. (3)

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Mass balance (%) =

(CTPD ×QTPD )

.η×Cinlet ×Qad 2

× 100%

(3)

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CTPD (µg/m3) denotes the concentration of mercury released in TPD experiment. Qad and QTPD

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(m3/min) denotes the N2 flow rate of mercury adsorption tests and TPD experiment, respectively. In

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this study, the mass balances of Hg0 in all cases were matched within 100±8% (the desorption

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amount was within ±10%).

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3. Results and discussion

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3.1. Pore structure analysis

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Table 2 is the summary of pore structure parameters of the stated sorbents. The analysis results

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indicated that the SBET of sorbents followed the ascending order: T6C3P1 < T7C3P1 T7C9P1), which confirmed that high

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PVC/coal mixing ratios and pyrolysis temperatures could enhance the mercury adsorption ability.

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A negative correlation between the value of qe and the reaction rate constant (k2) was found, which

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conformed to a previous study.41 For example, the qe values followed an increasing order: T7C9P1
T7C3P1 > T8C9P1 >

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T8C3P1. It was evident from Table 3 that the R2 of chlorine-modified sorbent increased significantly

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versus the raw sorbent (T7Char) for the pseudo-second-order model. This implied that the role of

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chemisorption process in adsorption process became strong with the addition of PVC, which was in

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consistent with the Hg0 adsorption experimental results discussed above.

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3.6. The assumption of C-Cl bonds formation mechanism

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In order to comprehend the thermal degradation behavior of materials and the mechanism of

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Cl-fixed in the co-pyrolysis process, TGA analysis was adopted. The TG and DTG curves of PVC

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are presented in Fig. 8a. It could be acquired that the PVC decomposition involved two distinct

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stages. The first stage started at 270°C，peaked at approximately 315°C, and ended at 380°C (step I).

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It has been demonstrated that the first stage could be attributed to the dehydrochlorination with

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subsequent generation of conjugated double bonds, in which 96-99% of HCl was released.48 Some

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small hydrocarbon molecules were formed simultaneously, such as benzene. During the process of

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dehydrochlorination, the Cl free radical (Cl3) formed as intermediate medium. The generated Cl3 had

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high chemical reactivity and needed to be stabilized by reacting with other mediums. Then the HCl

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and other Cl-containing compounds formed.49 The second stage began at 380°C and corresponded to

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the olefin chain cleavage (step II), accompanied by the generation of aromatic hydrocarbons.

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Fig. 8b shows the TG and DTG curves of coal. It was indicated that four steps comprised the

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process: dehydration (53-158°C), degassing (158-350°C), severe decomposition (350-700°C) and

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coke formation (700-1000°C). H. Juntgen50 has described the mechanism of coal pyrolysis

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persuasively. Herein, free radicals were generated by cracking the lamellae’s of coal cross-linked

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network at above 350°C (step III, IV). Smaller and larger radicals began recombining and reacted

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rapidly to produce low molecular weight gas compounds (particularly methane) and tar, which could

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easily spread to the surroundings from the interior of particles (step III).

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Some high molecular weight carbon free radicals (C3) on the polynuclear systems could not

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diffuse out of the solid matter. Thus, they reacted with other mediums to form coke (step IV). In the

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case of coal/PVC blends, the Cl3 or HCl originated from PVC pyrolysis participates in the recapping

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of high molecular weight C3 derived from coal. Thus the C-Cl functional group was generated. The

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increasing temperature caused more fragmentation of coal into Cl-fixing active sites and then more

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Cl was captured. The mechanism of C-Cl formation was described as follows:

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−(CH = CH) C3HCHClCH= − → −(CH = CH)IE C3H − +HCl

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(10)

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−(CH = CH) C3HCHClCH= − → −(CH = CH)IE C3H= − +Cl3

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(11)

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Coal − C − R → Coal − C3 + R3

(12)

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Coal − C3 + Cl3 → Coal − C − Cl

(13)

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Coal − C3 + HCl → Coal − C − Cl + H3

(14)

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To verify this mechanism of C-Cl formation, another sorbent was prepared under

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non-isothermal conditions (pyrolyzed from room temperature to 800°C at a ramping rate of

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10°C/min and remained for 30min) —this was denoted as TPC3P1. The Cl content of TPC3P1 was

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0.450%, which was lower than that of T8C3P1 (1.307%). The Hg0 removal efficiency of TPC3P1

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and T8C3P1 were 17.2% and 100%, respectively. This indicated that isothermal pyrolysis was more

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favorable for the formation of C-Cl than non-isothermal method. This might be because the

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temperature ranges of high molecular weight C3 formation were not in accordance with that of HCl

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release. In this case, high molecular weight C3 and HCl (or Cl3) were not produced synchronously.

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Thus, most C-Cl is formed when step I of PVC pyrolysis and step IV of coal pyrolysis overlap.

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5. Conclusions

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In summary, sorbents prepared by co-pyrolysis of waste PVC and Zhundong coal for Hg0

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removal was explored and the following conclusions were drawn:

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(1) A pyrolysis temperature of 800 oC with 3:1 (or 9:1) mass ratio of coal-PVC was feasible to

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prepare sorbents for Hg0 removal under N2 atmosphere. These two sorbents showed 100% Hg0

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removal efficiency within 30 min at 140 oC.

389 390 391

(2) The Cl content of chlorine-modified sorbents was higher than that of raw sorbents. Increasing pyrolysis temperature and PVC/coal mixing ratios could improve the Cl content of the sorbents. (3) The addition of PVC had a negative impact on the development of pore structure; increasing the

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PVC/coal mixing ratio could reduce the specific surface area of chlorine-modified sorbents more

393

obviously.

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(4) The adsorption kinetics analysis demonstrated that the elemental mercury adsorption on

395

chlorine-modified sorbent was mainly controlled by chemisorption and the effect of intra-particle

396

diffusion became apparent after an elapsed time of 25min.

397

(5) Cl existed in the form of Cl- and C-Cl on the surface of Cl-modified sorbents. The C-Cl bond was

398

shown to be the major active component for mercury removal via chemisorptions. Most C-Cl

399

formed when the high molecular weight carbon free radical and HCl (or Cl free radical) are

400

produced synchronously in the reaction process. This was a key factor in fixing Cl into sorbents.

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AUTHOR INFORMATION

402

Corresponding Authors

403


404


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Notes

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The authors declare no competing financial interest.

407

Acknowledgements

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The National Natural Science Foundation of China (51476066 and U1261204), the National

409

Program

of

International

Science

and

Technology

Cooperation

410

Science and Technology Planning Project of Guangdong Province, China

411

gratefully acknowledged. The authors also gratefully acknowledge the Analytical and Testing Center

412

of Huazhong University of Science and Technology for experimental measurement.

20


(2015DFA60410)

and

(2014A050503063)

are

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Supporting Information The yield of sorbents prepared by the coal/waste PVC blends, Hg0 breakthrough curves of

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various sorbents and ESEM micrographs of raw and Cl-modified sorbent are shown in Table S1

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References:

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(1) International energy outlook, available at< http://www.eia.doe.gov/oiaf/ieo/coal.html2009>.

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C.; Giménez, A. Fuel Process. Technol. 2011, 92 (9), 1764-75.

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(24) Scala, F. Environ. Sci. Technol. 2001, 35, 4373-4378.

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(27) Zhang, B.; Xu, P.; Qiu, Y.; Yu, Q.; Ma, J.; Wu, H. et al. Yao, H. Chem. Eng. J. 2015, 263, 1-8.

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Database 20, Version 4.1 (web version) (http://srdata.nist.gov/xps/Default.aspx), 2012

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Energy & Fuels

488

Table captions

489

Table 1 Analysis of the coal and waste PVC

490

Table 2 BET analysis of sorbents

491

Table 3 Kinetic parameters for adsorption of Hg0 on raw and chlorine-modified sorbent

492

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Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

493

Page 26 of 38

Table 1 Analysis of the coal and waste PVC Proximate analysis (wt%)

Ultimate analysis (wt%)

Cl (wt%)

Samples

494

Vd

Ad

FCda

Cd

Hd

Nd

Sd

Cld

coal

34.08

2.84

63.08

72.82

3.73

0.56

0.48

0.31

PVC

94.55

0.35

5.10

38.93

4.98

0.03

0.11

52.33

Note:

a

Calculated by difference

d

dry basis

495

26


Page 27 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

496

Energy & Fuels

Table 2 BET analysis of sorbents SBET

Pore volume

Average pore width

(m2/g)

(cm3/g)

(nm)

T6Char

167.48

0.059

2.04

T7Char

264.65

0.116

1.82

T8Char

343.76

0.144

1.97

T6C9P1

128.71

0.043

2.11

T7C9P1

211.38

0.084

1.99

T8C9P1

285.26

0.119

2.45

T6C3P1

39.87

0.014

2.18

T7C3P1

69.53

0.026

2.73

T8C3P1

135.10

0.045

2.06

Samples

497

27


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

498

Page 28 of 38

Table 3 Kinetic parameters for adsorption of Hg0 on raw and chlorine-modified sorbent Pseudo-first-order

Pseudo-second-order

Web-Morris model

Sorbents qe

k1

R2

qe

k2

R2

C

1.3

0.6152

-0.03

0.21 0.9442

5.8E-05 0.9913

-8.18

3.86 0.9952

T7Char

0.24

2.5250 0.9572

0.46

T7C9P1

62.23

0.0225 0.9083

89.61

kid

R2

T8C9P1 107.83 0.0162 0.8803 934.58 5.6E-07 0.9729 -30.09 8.08 0.9762 T8C3P1

94.11

0.0145 0.9127 990.10 4.5E-07 0.9707 -26.04 7.22 0.9811

T7C3P1

97.61

0.0170 0.8790 502.51 1.8E-06 0.9960 -22.50 6.68 0.9738

499 500

28


Page 29 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

501

Figure captions

502

Fig. 1. Schematic representation of the experimental apparatus of Hg0 adsorption test.

503

Fig. 2. The effects of PVC/coal mixing ratios and pyrolysis temperatures on the Cl content of

504

sorbents.

505

Fig. 3. The effects of PVC/coal mixing ratios and pyrolysis temperatures on Hg0 removal efficiency

506

of sorbents.

507

Fig. 4. The XPS spectra of Cl 2p for the fresh and used T8C3P1.

508

Fig. 5. The XPS spectra of Hg 4f for the fresh and used T8C3P1.

509

Fig. 6. Temperature programmed desorption of mercury for used and fresh T8C3P1.

510

Fig. 7. Kinetic models for adsorption of Hg0 on raw and chlorine-modified sorbent: (a) the

511

pseudo-first-order model; (b) the pseudo-second-order model; and (c) the Web-Morris model.

512

Fig.8. TG and DTG curves of PVC and coal.

29


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

513 514

Fig. 1. Schematic representation of the experimental apparatus of Hg0 adsorption test.

515

30


Page 30 of 38

Page 31 of 38

516

1.5 1.2 Cl content (%)

0.9 0.6 0.3

3 T 7 P1 C 3 T 8 P1 C 3P 1

C T6

C 9 T 7 P1 C 9 T 8 P1 C 9P 1

517

T6

C

h T7 ar C h T8 ar C ha r

0.0 T6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

518

Fig. 2. The effects of PVC/coal mixing ratios and pyrolysis temperatures on the Cl content of

519

sorbents.

520 521

31


Energy & Fuels

100 80 60 40

r

r

C ha

ha

T8

C T7

522

T6

C

ha

r

0

C 9 T7 P 1 C 9 T8 P1 C 9P 1 T6 C 3 T7 P1 C 3 T8 P1 C 3P 1

20

T6

0

Hg removal efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

523

Fig. 3. The effects of PVC/coal mixing ratios and pyrolysis temperatures on Hg0 removal efficiency

524

of sorbents.

32


Page 32 of 38

Page 33 of 38

Fresh T8C3P1

Cl 2p

199.8 201.1

198.6 Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Used T8C3P1

194 525 526

202.6

196

Cl 2p

198 200 202 Binding energy (eV)

204

Fig. 4. The XPS spectra of Cl 2p for the fresh and used T8C3P1.

527 528

33


Energy & Fuels

Fresh T8C3P1

530

105.5

Used T8C3P1

96 529

Hg 4f

102.5

101.7

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 38

98

Hg 4f

100 102 104 106 Binding energy (eV)

108

110

Fig. 5. The XPS spectra of Hg 4f for the fresh and used T8C3P1.

531 532

34


Page 35 of 38

600 500 400 300

Used T8C3P1

200

0

3

Hg concentration (µg/m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

100

Fresh T8C3P1

0

0 533 534

100

200 300 400 o Temperature ( C)

500

600

Fig. 6. Temperature programmed desorption of mercury for used and fresh T8C3P1.

535 536

35


Energy & Fuels

2.0

T7C9P1 T8C3P1 T8C9P1 T7C3P1

1.0

-0.5

T7Char

-1.0

lg(qe-qt)

lg(qe-qt)

1.5

0.5

-1.5 -2.0

0.0

0.0

0.4

0

0.8 t (min)

1.2

40

80

537

t (min)

538

(a)

4.0

120

160

8 T7Char

t/qt

7

3.5

6 5 4

t/qt

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 38

0.0

0.4

0.8

1.2

T7C9P1 T8C3P1 T8C9P1 T7C3P1

1.6

t (min)

3.0

2.5

2.0 0

40

539

80 t (min)

540

(b)

36


120

160

Page 37 of 38

80 0.20 T7Char 0.15 qt

60

0.10 0.05

40

0.00 0.3

qt

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.6

1/2

t

0.9

1.2

1/2

(min )

20 T7C9P1 T8C3P1 T7C3P1 T8C9P1

0 2

4

6

8

10

12

1/2

541

t

542

(c)

543

Fig. 7. Kinetic models for adsorption of Hg0 on raw and chlorine-modified sorbent: (a) the

544

pseudo-first-order model; (b) the pseudo-second-order model; and (c) the Web-Morris model.

545

37


(a) DTG

-0.4 -0.8

TG DTG

70

I

(b)

III

II 200

547

-36 PVC Coal 0.0

II

90 80

546

-27

100

60

-9 -18

TG

I

0

400

IV 600

800

Temperature （ ℃） Fig.8. TG and DTG curves of PVC and coal.

38


-1.2 -1.6

1000

-1

100 80 60 40 20 0

Page 38 of 38

DTG(%/min )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Weight loss(wt%)

Energy & Fuels

Experiment and Kinetic Study of Elemental Mercury Adsorption over a

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