Pretreatment of Petroleum Coke to Enhance the Reactivity of Catalytic

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Pretreatment of Petroleum Coke to Enhance the Reactivity of Catalytic Gasification in Fluidized Beds Renjie Zou, Liang Cao, Guangqian Luo, Zehua Li, Ruize Sun, Xian Li, and Hong Yao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01329 • Publication Date (Web): 29 Jun 2018 Downloaded from http://pubs.acs.org on July 1, 2018

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Energy & Fuels

Title page

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Title

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Pretreatment of Petroleum Coke to Enhance the Reactivity of Catalytic Gasification in

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Fluidized Beds

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Author names and affiliations

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Renjie Zou, Liang Cao, Guangqian Luo*, Zehua Li, Ruize Sun, Xian Li, Hong Yao

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State Key Laboratory of Coal Combustion (SKLCC), School of Energy and Power

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Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074,

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China

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Corresponding author

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Guangqian Luo:

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State Key Laboratory of Coal Combustion, School of Energy and Power Engineering，

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Huazhong University of Science and Technology, Wuhan, 430074, China

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Tel: +86-27-87545526

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Email: [email protected]

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ACS Paragon Plus Environment

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Abstract

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Catalytic gasification is a widely accepted approach to utilize petroleum coke for

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its high-quality products and less pollution. However, catalytic gasification of

22

petroleum coke in fluidized beds is seldom investigated, which has advantages of

23

sufficient heat and mass transfer and high uniformity of temperature. In this study, a

24

microfluidized bed (MFB) was used to study the catalytic gasification behaviors of

25

petroleum coke. Unexpectedly, the potassium carbonate showed poor catalytic effect

26

in the MFB, compared with the results from a thermogravimetric analyzer (TGA).

27

The BET results indicated that the pore structure of petroleum coke was highly

28

undeveloped, leading to the easy separation of catalyst from the surface of coke in the

29

MFB. To improve this situation, we proposed a preheating treatment method to

30

enhance the loading of potassium on coke. The experiment results showed that, the

31

preheated petroleum coke had a significantly higher rate of gasification than the

32

impregnated coke, owing to the formation of stable active intermediates. Furthermore,

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the effects of pretreament conditions were investigated. The FTIR results showed that

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the ratio of aliphatic hydrocarbons to aromatic hydrocarbons decreased with the

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increase of preheating temperature and time, while the ratio of oxygen-containing

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functional groups to aromatic hydrocarbons showed an opposite trend.

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Keywords:

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Petroleum coke; Catalytic gasification; Reactivity; Fluidized bed; Pretreatment

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1.Introduction

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Petroleum coke is a high value byproduct of the petroleum industry, owing to its

42

high carbon content (about 90 wt%). However, burning petroleum coke for power

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remains challenging due to its low reactivity and high sulfur content, which cause

44

serious air pollution problems. It remains an urgent challenge to utilize petroleum

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coke efficiently and environment-friendly.

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Gasification technology is regarded as a promising approach to utilize petroleum

47

coke for its high-quality products and reduced pollution.1-3 The produced synthesis

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gas is an essential raw material for the chemical industry, and the sulfur in petroleum

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coke can be collected after gasification. Some researchers have investigated the

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gasification characteristics of petroleum coke.4-8 Wu et al.6 studied the effect of

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pyrolysis conditions on the gasification characteristics of petroleum coke and coal

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char. The pyrolysis of petroleum coke at high temperature tends to make it more

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graphitized. The rate of petroleum coke gasification is much lower than that of coal

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char, and even lower than that of natural graphite. Gu et al.7 obtained similar results

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with seven different carbonaceous fuels; the rate of petroleum coke gasification was

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several times lower than that of coal char. Huo et al.8 investigated the CO2 gasification

57

behaviors of six carbonaceous samples, and they found that the degree of crystal

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structure order was a key factor of gasification rate. Besides, the high degree of

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graphitization, an undeveloped pore structure and low mineral content of petroleum

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coke results in low gasification rate.9


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How to improve the gasification reactivity becomes the key issue of petroleum

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coke utilization. Many researchers have found that the gasification activity of

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carbonaceous materials could be greatly enhanced by various alkali metal

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compounds.10-17 Yeboah et al.10 investigated the catalytic action of alkali metals on the

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gasification characteristics of coal by thermogravimetric analysis, and he found that

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the catalytic reactivity of different carbonates are sorted as Li > Cs > K > Ca > Na.

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Sharma et al.11 investigated the catalytic steam gasification of HyberCoal with K2CO3

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for production of H2 rich gas. The catalytic gasification reactivity is nearly four times

69

higher than raw coal, and no obvious deactivation of catalyst was found after

70

recycling it for several times. In existing studies about the mechanism of catalytic

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gasification of carbonaceous materials, there are four main theories for alkali metal

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catalysts: the oxygen-transfer,18,19 electrochemical,20 free-radical reaction21 and

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reaction intermediate.22-24 Wigmans et al.25,26 studied the mechanism of catalytic

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gasification of activated carbon and coal char with sodium and potassium carbonate.

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The results showed that the intermediate M-C-O- on the surface of carbon plays a

76

vital role in the catalytic gasification process ("M" refers to the alkali metal). Using

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quantum chemical methods, Chen et al.27,28 investigated the catalytic mechanism

78

involving the C-O-K intermediate, which formed on the surface of the carbon matrix

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structure in catalytic gasification with potassium. The results showed that the -O-K

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structure can improve the ability of the adjacent carbon atom to adsorb oxygen.

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There are three types of gasifiers according to the flow regime, viz. fixed bed,


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fluidized bed and entrained flow bed.29 Among them, the fluidized bed gasification

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technology has the advantages of a lower gasification temperature, uniform

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temperature field, sufficient heat and mass transfer, and ability to adapt to wide

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particle size distributions of raw materials. Yu et al.30 conducted experiments

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involving biomass pyrolysis in a microfluidized bed reactor, and the results showed a

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higher gas yield and less remaining carbon in the fluidized bed than that in a

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thermogravimetric analyzer. In addition, a microfluidized bed provides good mass and

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heat transfer to achieve good measurement of the reaction rate and kinetic

90

parameters.31 Based on the advantages mentioned above, it is desired to study the

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catalytic gasification of petroleum coke in fluidized beds which may be further

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improved.

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This paper is focused on the catalytic gasification of petroleum coke in a

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microfluidized bed. The gasification performance in a thermogravimetric analyzer is

95

also studied to compare the effect of two different types of reactors. Further, a

96

preheating treatment method is proposed to enhance the loading of potassium on coke.

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The effects of pretreatment conditions on the coke characteristics are also discussed.

98 99 100

2. Material and Methods 2.1 Sample preparation

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Petroleum coke (PC) was obtained from the Sinopec Qingdao Refining &

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Chemical Co., ltd. Activated carbon (AC) was prepared from coconut shells. Both


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petroleum coke and activated carbon samples were sieved to sizes ranging from 75 to

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150 µm. The proximate and ultimate analysis of petroleum coke and activated carbon

105

are presented in Table 1.

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Potassium carbonate was added as a catalyst to the samples by impregnation

107

method. For this, samples (petroleum coke or activated carbon) and K2CO3 were

108

weighted and added to a conical flask with 200 ml of deionized water. After stirring

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for 12 hours, the mixtures were filtered and then dried at 105 °C for 24 hours. The

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mole ratio of K/C in the mixture was 0.01. The mole ratio of K/C is based on amounts

111

of K2CO3 and petroleum coke put in the mixture, and the actual ratio might be slightly

112

different.

113

2.2 Pretreatment procedure

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The pretreatment of petroleum coke was conducted in a horizontal tube furnace

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reactor, as shown in Fig. 1. The origin petroleum coke (not impregnated) was

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mechanically mixed with K2CO3 and then sent into the furnace. The carrier gas was

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argon with a flow rate of 500 ml/min. The detailed conditions, including treatment

118

time, temperature, and K/C mole ratio are listed in Table 2. It should be noted that the

119

mole ratio of K/C is also based on amounts of K2CO3 and petroleum coke put in the

120

mixture, and the actual ratio might be slightly different.

121

2.3 Gasification process

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Two types of gasification apparatuses (ie, a fixed bed reactor and a fluidized bed

123

reactor) were both used in this study, to investigate the gasification behaviors of


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petroleum coke. A thermogravimetric analyzer (TGA) was chosen as a fixed bed due

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to its high accuracy and reliability. The weight of the sample was 300±5 mg, and the

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gasification temperature was set as 980 °C. Once the temperature of the furnace was

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steady, the Al2O3 basket containing the samples was lowered to the reaction zone

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rapidly. CO2 was used as a gasification agent with a flow rate of 600 ml/min.

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The gasification experiments were also conducted in a microfluidized bed (MFB)

130

reaction analyzer, as is shown in Fig. 2. Details of the MFB have been introduced in

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our previous work.32 A powdered sample with a weight of 20±0.5 mg was injected

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into the reactor by a small amount of pulse gas. The bed material was Al2O3 with the

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size of 100-150 µm and the purity of 99.7%. The CO2 gas flow was maintained at 600

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ml/min. To ensure the fluidization state of the sample in the reactor, the total flow rate

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of the fluidizing gas was controlled at 2 L/min (argon was used as the balance gas).

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The temperature was kept at 980 °C. The generated gas product was detected by a

137

mass spectrometry (LC-D 100, Ametek Dycor, USA). Each experiment was replicated

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at least twice to ensure reliability.

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2.4 Characterization

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The proximate analyses of the petroleum coke and activated carbon were carried

141

out using a commercial analyzer (TGA 2000, Las Navas, Spain). The ultimate

142

analyses were performed using an elemental analyzer (EL-2, Vario, Germany). The

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contents of potassium in petroleum coke samples were measured by an inductively

144

coupled plasma optical emission spectrometer (ICP-OES, Spectro Arcos, Germany).


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The specific surface area and total pore volume was obtained using an automated

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surface area analyzer (Tristar II 3000, Micromeritics, USA). The chemical structure

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analyses of the samples were conducted using a Bruker Vertex 70 Fourier Transform

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Infrared Spectroscopy (FTIR).

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2.5 Data analysis

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Petroleum coke or activated carbon gasification conversion in the TGA experiments is defined as X: X=

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m0 -mt m0 -mfinal

(1)

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where mt is the mass of the sample at time t, m0 is the initial mass of the sample,

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and mfinal is the final mass of the sample. mfinal is closed to the ash mass fraction of the

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sample and it can be considered that the sample is fully converted.

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The carbon conversion of petroleum coke or activated carbon in the MFB experiment is calculated as follows, considering the main reaction of C+CO2=2CO.

158

CCO =

159

VCO =

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X=

VCO 1/2VCO +600 600CCO 1-1/2CCO

(2) (3)

t V

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r=

mt mf

=

CO ×12dt ‫׬‬t 22400 0 t V

CO ×12dt ‫׬‬t f 22400

(4)

0

dX dt

(5)

162

where CCO is the volumetric content of CO, measured by mass spectrometry. VCO

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is the volume flow of CO at the outlet of the reactor. 600 ml/min is the volume flow

164

of CO2 at the inlet of the reactor. mt is the mass of carbon in CO formed during the


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reaction time from 0 to t. mf is the mass of carbon in CO formed during the whole

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reaction time. r is the reaction rate. It should be noted that the conversion calculated

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by Eq. (1) is the fuel conversion, which includes all elements converted to the gas

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phase. In Eq. (4), the conversion refers to the carbon conversion specifically.

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Although these values are slightly different, they are both considered as indicators of

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the rate of gasification, and to simply descriptions, they are both expressed in the form

171

of X in this paper.

172 173 174 175

Generally, the reactivity index Rs (min-1) is adopted to evaluate the overall gasification reactivity,33 which is calculated as follows: Rs =

0.5 t0.5

(6)

where t0.5 is the time required to reach the carbon conversion of 50%.

176 177

3. Results and Discussion

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3.1 Gasification behaviors of impregnated petroleum coke

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Fig. 3 shows the carbon conversion in gasification processes of impregnated and

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original petroleum coke. It is observed that both the non-catalytic and catalytic CO2

181

gasification rates of petroleum coke were very slow in the MFB, suggesting that

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impregnated K2CO3 played a negligible role in the gasification process. Compared

183

with the catalytic gasification characteristics of petroleum coke in the MFB, the

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gasification reaction time was significantly shortened upon loading K2CO3 in the

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TGA, indicating that K2CO3 greatly enhanced gasification rate of petroleum coke.


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However, the gasification rate of petroleum coke even added with a catalyst was still

187

much lower in the MFB reactor. (The different CO2 partial pressures used for TGA

188

and MFB experiments may have caused some discrepancy in the gasification rates.)

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The index Rs is an important parameter for characterizing gasification rate. As is

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shown in Fig. 3, the addition of the catalyst had little influence on petroleum coke

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gasification in the MFB, but it greatly enhanced the gasification rate of petroleum

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coke in the TGA.

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The generation of active intermediates on the surface of carbon plays a key role

194

in the catalytic gasification process. Petroleum coke has a highly condensed carbon

195

structure and a limited number of pores.9 It is believed that most of the catalyst was

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distributed on the outer surface of the petroleum coke, and perhaps there were almost

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no active intermediates generated on the surface of petroleum coke in the MFB. When

198

undergoing gasification in the MFB, the potassium carbonate may be easily separated

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from the surface of the petroleum coke, resulting in insufficient potassium-catalyzed

200

gasification of the petroleum coke. Therefore, compared with petroleum coke,

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carbonaceous materials with an extensive pore structure may exhibit better catalytic

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gasification performance in the MFB. To prove this hypothesis, activated carbon was

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also selected for gasification experiments in this study.

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Table 3 shows the BET surface area and total pore volume of activated carbon and

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petroleum coke. It can be seen that the surface area and total pore volume of activated

206

carbon is much higher than those of petroleum coke, which suggests that more


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potassium may adhere to the surface of activated carbon. Fig. 4 shows the gasification

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behaviors of impregnated and original activated carbon. As is shown in Fig. 4. the

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addition of a catalyst significantly improved the gasification rate of activated carbon

210

in the MFB reactor. It can be found that the rate of carbon conversion for activated

211

carbon before a conversion of 70% is much higher than that of the non-catalytic

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gasification. In particular, at the beginning of the reaction, the gasification rate of

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activated carbon was tremendously enhanced by the potassium carbonate. It is

214

considered that the catalyst exhibited good performance. When the reaction proceeded,

215

the catalyst was gradually separated from the activated carbon, which led to a reduced

216

rate of potassium-catalyzed gasification after the conversion rate reached

217

approximately 70%.

218

Furthermore, the potassium content of samples was measured to confirm the

219

combination of samples and catalyst. The partially gasified samples at the conversion

220

of 30% were tested. As shown in Table 4, the mass of potassium is 22.64 mg in 1 g of

221

petroleum coke after gasification in TGA, while it is only 0.19 mg in the fluidized bed

222

reactor, which means nearly no catalyst remained on the petroleum coke surface in the

223

fluidized bed reactor.

224

3.2 Gasification behaviors of preheated petroleum coke

225

From the experiment results above, we found that the impregnated K2CO3 will

226

be easily separated from the petroleum coke in a fluidized bed, owing to its high

227

gas-solid disturbance and the less developed pore structure of petroleum coke. The


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preheating treatment was proposed to improve the combination of potassium and coke.

229

The preheating treatment procedure is described in Section 2.2, and the petroleum

230

coke is treated under condition 2 (see Table 2). The obtained petroleum coke is named

231

as PC+K preheated 800 °C. Two groups of sample were tested for comparison. One

232

of them is the petroleum coke preheated with no K2CO3 (named PC preheated

233

800 °C), to isolate the effect of high temperature treatment. Another group of sample

234

was prepared by impregnating the pure preheated petroleum coke with K2CO3, which

235

is named as PC preheated 800 °C+K. Fig. 5 shows the gasification behaviors of these

236

preheated petroleum coke samples. As shown in Fig. 5, the catalyst in the PC

237

preheated 800 °C+K exhibited poor enhancement by the catalyst. However, the

238

catalyst in the PC+K preheated 800 °C exhibited much better catalytic performance.

239

It can be seen that the carbon conversion rate of the PC+K preheated 800 °C is much

240

faster than the rates of the two other samples before a conversion rate of

241

approximately 50% is reached.

242

Fig. 6 shows the CO2 gasification reactivity index (Rs) of different coke samples

243

in the MFB. The preheating treatment can enhance the catalytic gasification rate of

244

petroleum coke by approximately four times. This result is in agreement with the

245

earlier hypothesis. During the preheating treatment, various types of active

246

intermediates formed. The intermediates enhanced the coupling effects between the

247

catalyst and carbon, so the catalyst can maintain contact with the petroleum coke and

248

cannot be easily separated from its surface.


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3.3 The effects of pretreatment condition

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The gasification behaviors largely depend on the surface functional groups of

251

petroleum coke, and they will alter when undergoing the high-temperature treatment.

252

The effects of heat treatment temperature, amounts of catalyst, and preheating time on

253

the petroleum coke characteristic were investigated by FTIR. The pretreatment

254

conditions were listed in Table 2. Fig. 7 shows infrared spectrogram results of

255

petroleum coke samples under different pretreatment conditions. The absorption peak

256

of the aliphatic hydrocarbon, oxygen functional group, and aromatic hydrocarbon

257

exhibited many differences under different individual pretreatment conditions. The

258

aliphatic hydrocarbon absorption peak in the wavenumber range 3000-2700 cm−1 was

259

slightly weaker than the other two peaks. In the wavenumber range 1800-1000 cm−1, a

260

notable absorption peak of the oxygen-containing functional group could be seen in

261

different samples. However, the peak heights of different samples exhibited a different

262

behavior in this area. Based on the FTIR absorption peak distribution law, we can

263

infer that the peak at 1650 cm−1 was mainly formed by C=O and C=C aromatic

264

structures. In addition, the peak at 1400 cm−1 was mainly formed by methyl (CH3) and

265

methylene (CH2). The height of these two peaks reflected the development of C=O,

266

CH3 and CH2 structures. From samples 2, 3, 4, and 8, we can see that the peak at 1400

267

cm−1 increases with an increasing amount of catalyst. This may be explained by the

268

fact that K2CO3 can induce breakage of C=C bonds to form branched structures. From

269

samples 3, 5, 6, and 8, the amounts of CH3 and CH2 decreased with increasing heat


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treatment time.

271

The infrared spectrogram is the synthesized results of various functional groups

272

in coke. To investigate the effects of specific functional groups, peak-fitting was

273

conducted. Fig. 8 shows the peak-fitting result for sample 3. It is considered that the

274

aliphatic hydrocarbon absorption peak is in the wave number range 3000-2700 cm−1,

275

the oxygen-containing functional group absorption peak is in the range 1800-1000

276

cm−1, and the aromatic hydrocarbon absorption peak is in the range 900-700 cm−1.

277

The relative contents of each surface functional group were calculated based on the

278

area of absorption peaks.

279

As shown in Table 5, for samples 1 and 8, the ratio of aliphatic hydrocarbons to

280

aromatic hydrocarbons (CH2+CH3/C=C) increased. This may be caused by the

281

internal volatiles of petroleum coke that have moved to the coke surface at a

282

temperature of 700 °C for 10 min. However, at higher temperature (see sample 3 and

283

7), the structure of the aliphatic chain on the surface of coke was reduced due to the

284

bond breaking of the organic matter and of the chain structure of the coke surface.

285

Besides, it can be found that the relative contents of the carboxyl group and other

286

oxygen-containing

287

temperature. This was mainly because the potassium carbonate helps petroleum coke

288

attract more oxygen atom.

functional

groups

increased

with

increasing

preheating

289

By comparing the results of samples 2–4 and 8, we found that the

290

CH2+CH3/C=C increased with an increasing amount of catalyst in the preheating


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291

treatment. The alicyclic structure of coke surface will be reduced because of the

292

broken chain, while the aromatic structure will be consumed under the action of the

293

catalyst. In general, much more decrease of the alicyclic chain structure occured than

294

the aromatic structure. In addition, with an increasing amount of catalyst in the

295

preheating treatment, the ratio of oxygen-containing functional groups to aromatic

296

hydrocarbons (C=O/Car) exhibited an increasing trend. The more catalyst that was

297

loaded, the more active intermediates for oxygen transfer formed, and the more

298

oxygen atoms were transferred to the coke surface.

299

From the results of samples 3, 5, 6, and 8, it can be seen that CH2+CH3/C=C in

300

original coke was larger than that for the samples that underwent preheating treatment.

301

In addition, with increasing preheating time, CH2+CH3/C=C decreased. However,

302

C=O/Car increased with increasing preheating time. This is because the reaction

303

between the catalyst and petroleum coke was more sufficient, which made the surface

304

functional group structure of C=O increased with increasing heat treatment time.

305 306

4. Conclusions

307

The catalytic gasification behaviors of petroleum coke were studied in a

308

microfluidized bed (MFB), with sufficient heat and mass transfer and the high

309

uniformity of temperature. However, the potassium carbonate showed poor catalytic

310

effect in the MFB, compared with the results in a thermogravimetric analyzer (TGA).

311

The BET results indicated that the pore structure of petroleum coke was highly


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312

undeveloped, leading to the easy separation of catalyst from the surface of coke in the

313

MFB. To improve the situation, we proposed a preheating treatment method to

314

enhance the loading of potassium on coke. The experiment results showed that, the

315

preheated petroleum coke performed significantly higher gasification reactivity than

316

the impregnated coke, owing to the formation of stable active intermediates. Further,

317

the effects of pretreatment condition on the coke characteristic were investigated. The

318

FTIR results showed that the ratio of aliphatic hydrocarbons to aromatic hydrocarbons

319

decreased with the increase of preheating temperature and time, while the ratio of

320

oxygen-containing functional groups to aromatic hydrocarbons showed an opposite

321

trend. Besides, both of them increased with the amount of catalyst.

322 323 324

Acknowledgments The

National

Key

Research

and

Development

Program

of

China

325

(2016YFB0600603) and the Chinese National Natural Science Foundation (51776084

326

and 51476066) are gratefully acknowledged. The authors also gratefully acknowledge

327

the Analytical and Testing Center of Huazhong University of Science and Technology

328

for experimental measurements.

329


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330

References

331

(1) Zou, J. H.; Zhou, Z. J.; Wang, F. C.; Zhang, W.; Dai, Z. H.; Liu, H. F.; Yu, Z. H.

332

Chem. Eng. Process. 2007, 46(7), 630-636.

333

(2) Fermoso, J.; Arias, B.; Gil, M. V.; Plaza, M. G.; Pevida, C.; Pis, J. J.; Rubiera, F.

334

Bioresour. Technol. 2010, 101(9), 3230-3235.

335

(3) Fermoso, J.; Arias, B.; Plaza, M. G.; Pevida, C.; Rubiera, F.; Pis, J. J.; García-Peña,

336

F.; Casero, P. Fuel Process. Technol. 2009, 90(7–8), 926-932.

337

(4) Malekshahian, M.; Hill, J. M. Energ. Fuel. 2011, 25(9), 4043-4048.

338

(5) Lewis, A. D.; Fletcher, E. G.; Fletcher, T. H. Energy Fuels 2014, 28(7),

339

4447-4457.

340

(6) Wu, Y.; Wu, S.; Gu, J.; Gao, J. Process. Saf. Environ. 2009, 87(5), 323-330.

341

(7) Gu, J.; Wu, S.; Zhang, X.; Wu, Y.; Gao, J. Energ. Source Part A 2009, 31(3),

342

232-243.

343

(8) Huo, W.; Zhou, Z.; Chen, X.; Dai, Z.; Yu, G. Bioresour. Technol. 2014, 159(2),

344

143.

345

(9) Tyler, R. J.; Smith, I. W. Fuel 1975, 54(2), 99-104.

346

(10) Yeboah, Y. D.; Xu, Y.; Sheth, A.; Godavarty, A.; Agrawal, P. K. Carbon 2003,

347

41(2), 203-214.

348

(11) Sharma, A.; Takanohashi, T.; Morishita, K.; Takarada, T.; Saito, I. Fuel 2008,

349

87(4), 491-497.

350

(12) Yu, J.; Tian, F. J.; Chow, M. C.; Mckenzie, L. J.; Li, C. Z. Fuel 2006, 85(2),


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

351

127-133.

352

(13) Sheth, A.; Yeboah, Y. D.; Godavarty, A.; Yong, X.; Agrawal, P. K. Fuel 2003,

353

82(3), 305-317.

354

(14) Valenzuelacalahorro, C.; Pan, Y. G.; Bernaltegarcia, A.; Gomezserrano, V. Energy

355

Fuels 2002, 8(2), 348-354.

356

(15) Ohtsuka, Y.; Yamauchi, A.; Zhuang, Q. Spring National Meeting of the American

357

Chemical Society 1996, 221-225.

358

(16) Li, Y.; Yang, H.; Hu, J.; Wang, X.; Chen, H. Fuel 2014, 117(6), 1174-1180.

359

(17) Parvez, A. M.; Hong, Y.; Lester, E.; Wu, T. Energy Fuels 2017, 31(2), 1555-1563.

360

(18) Mckee, D. W. Fuel 1983, 62(2), 170-175.

361

(19) Mimsa, C. A.; Pabst, J. K. Fuel 1983, 62(2), 176-179.

362

(20) Jalan, B. P.; Rao, Y. K. Carbon 1978, 16(3), 175-184.

363

(21) Sancier, K. M. Fuel 1984, 63(5), 679-685.

364

(22) Wen, W. Y. Catal. Rev. 1980, 22(1), 399-401.

365

(23) Kapteijn, F.; Moulijn, J. A. Fuel 1983, 62(2), 221-225.

366

(24) Mims, C. A.; Rose, K. D.; Melchior, M. T.; Pabst, J. K. J. Am. Chem. Soc. 1982,

367

104(24), 6886-6887.

368

(25) Wigmans, T.; Göebel, J. C.; Moulijn, J. A. Carbon 1983, 21(3), 295-301.

369

(26) Wigmans, T.; Haringa, H.; Moulijn, J. A. Fuel 1983, 62(2), 185-189.

370

(27) Chen, S. G.; Yang, R. T. J. Catal. 1993, 141(1), 102-113.

371

(28) Chen, S. G.; Yang, R. T. Energy Fuels 1997, 11(2), 421-427.


Page 18 of 23

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Energy & Fuels

372

(29) Duchesne, M. A.; Champagne, S.; Hughes, R. W. Energy Fuels 2017, 31(7),

373

6658-6669.

374

(30) Yu, J.; Yao, C. B.; Zeng, X.; Geng, S.; Li, D.; Wang, Y.; Gao, S. Q.; Xu, G. W.

375

Chem. Eng. J. 2011, 168(2), 839-847.

376

(31) Yu, J.; Zhu, J.; Guo, F.; Duan, Z.; Liu, Y.; Xu, G. W. J. Fuel Chem. Technol. 2010,

377

38(6), 666-672.

378

(32) Fang, Y.; Zou, R.; Luo, G.; Chen, J.; Li, Z.; Mao, Z.; Zhu, X.; Peng, F.; Guo, S.;

379

Li, X.; Yao, H. Energy Fuels 2017, 31(3), 3243-3252.

380

(33) Ye, D. P.; Agnew, J. B.; Zhang, D. K. Fuel 1998, 77(11), 1209-1219.


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

381

Page 20 of 23

Table 1 Proximate and ultimate analysis of petroleum coke and activated carbon. Proximate analysis (wt %, ad)

Ultimate analysis (wt %, daf)

Samples

382

M

V

A

FC

C

H

N

S

O*

PC

0.49

9.26

0.18

90.07

88.11

3.62

1.15

6.23

0.89

AC

0.23

2.02

3.73

94.02

84.63

1.02

0.19

0.30

13.86

* By difference

383 384

Table 2 Pretreatment conditions. Number

Temperature (°C)

Time（min）

K/C molar ratio

1

700

10

0.02

2

800

10

0.01

3

800

10

0.02

4

800

10

0.04

5

800

20

0.02

6

800

30

0.02

7

900

10

0.02

8

Original petroleum coke sample

385 386

Table 3 BET and total pore volume of petroleum coke and activated carbon. Sample

SBET(m2/g)

Vtotal(cm3/g)

PC

1.99

0.009

AC

599.29

0.300

387 388

Table 4 Potassium content in samples.

Samples

K content (mg/g)

PC (raw)

0.05

PC

PC+K

PC+K

(K2CO3

(partially gasified

(partially gasified

impregnated)

in MFB )

in TGA )

24.48

0.19

22.64


Page 21 of 23 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

389 390

Table 5 Surface functional groups of coke samples under different pretreatments

391

conditions. Number

Conditions

CH2+CH3/C=C

C=O/Car

1

700 °C+10 min+0.02 K/C molar ratio

5.76

0.51

2


2.78

0.44

3


3.32

0.60

4


3.91

1.01

5


2.92

2.12

6


2.57

3.34

7


1.51

3.89

8

Original

4.11

0.07

392 393

Fig. 1. Schematic diagram of the horizontal tube furnace reactor.

394 395 396

Fig. 2. Schematic diagram of the microfluidized bed (MFB) reactor.

397 398


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

399

Fig. 3. Gasification characteristics of petroleum coke in MFB and TGA.

400 401 402

Fig. 4. Gasification characteristics of active carbon in MFB.

403 404

Fig. 5. Gasification characteristics of petroleum coke under different treatments in

405

MFB.

406 407 408

Fig. 6. Gasification reactivity index of different coke samples in the MFB.


Page 22 of 23

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409 410 411

Fig. 7. Infrared spectrogram of petroleum coke samples under different pretreatment

412

conditions.

413 414 415

Fig. 8. Peak fitting curves of sample 3.

416


Pretreatment of Petroleum Coke to Enhance the Reactivity of Catalytic

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