Preparation of Calcium Magnesium Acetate Deicer Using Raw Acetic

Research Article Cite This: ACS Sustainable Chem. Eng. 2018, 6, 4362−4369

pubs.acs.org/journal/ascecg

Preparation of Calcium Magnesium Acetate Deicer Using Raw Acetic Acid-Rich Bio-oil Obtained from Continuous Two-Stage Pyrolysis of Corncob Seung-Jin Oh, Gyung-Goo Choi, and Joo-Sik Kim* Department of Energy and Environmental System Engineering, University of Seoul, Republic of Korea 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 130-743, Republic of Korea ABSTRACT: Two-stage pyrolysis of corncob was performed to simultaneously produce acetic acid-rich and phenolic-rich bio-oils. The two-stage pyrolyzer consisted of an auger reactor and a fluidized bed reactor connected in series. The temperature of the auger reactor was varied between 320 and 400 °C, whereas that of the fluidized bed reactor was fixed at about 520 °C. The total bio-oil yield was over 50 wt %. The bio-oil produced from the auger reactor contained up to 48 wt % acetic acid based on the relative response factor method and low concentrations of lignin degradation products. In contrast, the bio-oil produced from the fluidized bed reactor was enriched with phenolic compounds with a maximum phenol concentration of about 19 wt %. Further, the acetic acid-rich bio-oil was used for the synthesis of calcium magnesium acetate (CMA), a nonchloride deicer, without any post-treatments for acetic acid separation or enrichment. CMA synthesized using bio-oil was chemically identical to the reference CMA. On the other hand, biochar, a byproduct, was activated using CO2 to produce microporous activated carbon with a BET surface area of about 580 m2/g. In summary, it was possible to produce value-added products (CMA and activated carbon) from the continuous two-stage pyrolysis of corncob. KEYWORDS: Two stage pyrolyzer, Calcium magnesium acetate, Pyrolysis, Bio-oil, Activated carbon

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INTRODUCTION Biomass is the only substitute resource for both fossil fuels and fossil fuel-derived chemicals. Biomass is usually converted via three ways: thermochemical, biological, and chemical conversion. Pyrolysis is one of the thermochemical processes conducted under an inert atmosphere. In particular, fast pyrolysis of biomass mainly involves the production of an oil product called bio-oil, and recently, great effort has been directed toward producing transportation fuels via upgrading of bio-oil such as by hydrotreating, hydrocracking, and solvent addition.1−5 Considering that bio-oil is a complex mixture of valuable chemicals, it would be worth using those chemicals as they are or after separation of desired chemicals. A representative chemical of bio-oil is acetic acid, which is mainly produced in industries by methanol carbonylation with carbon monoxide. Along with its representative use for the production of vinyl acetate monomer,6 acetic acid can be used for the preparation of calcium magnesium acetate (CMA), which is known as an effective control agent for SOx and NOx emissions in coal combustion. Nimmo et al. reported that SO2 and NOx reduction rates with CMA were greater than 80 and 70% and up to 80%, respectively.7 More broadly, CMA is known to be an environmentally benign nonchloride-based deicer. Presently, chloride-based deicers such as sodium chloride and calcium chloride are commonly used due to advantages such as ease of storage, transport, and handling, and inexpensiveness.8 However, chloride-based deicers have negative side effects: they can cause corrosion of roads, © 2018 American Chemical Society

vehicles, and concrete structures and are harmful to the growth of crops and freshwater resources.9 In contrast to chloride-based deicers, CMA is reported to be noncorrosive and benign to vegetation.10 However, replacement of chloride salts by CMA is limited due to its high cost. Considering the performance and price of deicers, there is no ideal deicing material in use at present.11 CMA is currently produced by the reaction of petroleumderived acetic acid with dolomitic lime (Ca/MgO) or limestone (Ca/MgCO3).12 The high price of CMA is largely attributed to the high price of petroleum-derived acetic acid, which comprises about 70% of the total CMA cost.13 Hence, CMA’s price can be reduced if fossil acetic acid is replaced by that derived from cheaper raw materials such as biomass. Several approaches to produce acetic acid-rich oils from biomass have been recently made through fermentation or hydrothermal processes only to demonstrate the possibility of producing such oils.14,15 As mentioned earlier, acetic acid is one main component of bio-oil, which is mainly produced from hemicellulose and cellulose16 and partly through the cracking of lignin.17,18 Generation of acetic acid from hemicellulose is the result of the ring scission of glucuronic acid and the elimination of acetyl group linked to xylose.19 Acetic acid from cellulose is the result of scission of levoglucosan, which is a product of cellulose degradation.20 Received: January 1, 2018 Revised: January 31, 2018 Published: February 14, 2018 4362

DOI: 10.1021/acssuschemeng.8b00013 ACS Sustainable Chem. Eng. 2018, 6, 4362−4369

Research Article

ACS Sustainable Chemistry & Engineering

The auger reactor conducts slow or intermediate pyrolysis, whereas the fluidized bed reactor conducts fast pyrolysis. In the present work, the preparation of CMA using a raw bio-oil was tested for the first time in the biomass pyrolysis research area. For this purpose, a raw acetic acid-rich bio-oil generated from the auger reactor was used without any distillation. A successful substitution of bio-oil for fossil acetic acid in the synthesis of CMA would pave the way for the economic production and wide use of CMA. Furthermore, the present work provides the characteristics of two-stage biomass pyrolysis, especially the effect of the first stage pyrolysis in the auger reactor on the production of phenol. Finally, activation of biochar, a byproduct of biomass pyrolysis, was performed using CO2 to produce activated carbon, which would enhance the economic feasibility of the two-stage biomass pyrolysis process.

Our group has recently started to synthesize CMA using bio-oil. A previous one-stage pyrolysis study conducted using a fluidized bed reactor at around 430 °C confirmed that only a distilled bio-oil could yield CMA.21 In addition, we found that bio-oil without acetic acid enrichment and removal of other hindering chemicals was inappropriate for CMA synthesis. In this study, a new type of two-stage biomass pyrolysis was conducted. There have been several attempts to use the staged pyrolysis principle. Most of them were conducted by using different reactors with a time interval.22,23 In contrast to the previous works, the two-stage pyrolysis process applied in the current study operates continuously and simultaneously produces two different bio-oils: acetic acid-rich and phenol-rich bio-oils. It has decoupled two pyrolyzers: auger and fluidized bed reactors.

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Table 1. Characteristics of Corncob wt %

Feed Material. In the present study, the feed material was the same corncob that was used in the previous work21 due to its high hemicellulose content24 (about 34 wt % in the present work). Table 1 shows the chemical characteristics of corncob.21 Pretreatment and specific characteristics of corncob are presented in detail in the literature. In an experiment of the current study, hot-water washing was conducted according to the literature25 to reduce the ash content of the corncob. Ash in biomass is known to play a catalytic role in the formation of gaseous and solid products during pyrolysis.26 A previous work reported that the contents of potassium, phosphorus, sulfur, and chlorine in ash were lowered after water washing.27 In the present work, the ash content of corncob reduced from 2.2 to 1.4 wt % after washing. On the basis of thermogravimetric analysis that showed the degradation range of holocellulose (hemicellulose and cellulose) of corncob as 200−400 °C,21 the temperature range of the auger reactor of the two-stage pyrolysis process, where acetic acid-rich bio-oils were expected to be generated, was selected to be between 320 and 400 °C. Pyrolysis Process and Reaction Conditions. The key part of the two-stage pyrolysis process is the auger and fluidized bed pyrolyzers,

Proximate Analysisa 91.7 ± 0.5 6.1 ± 0.5 2.2 ± 0.1

volatile matter fixed carbon ash Ultimate Analysisb

44.3 ± 0.1 5.5 ± 0.1 0.9 ± 0.1

C H N S Oc

50.3 Chemical Composition

cellulose hemicellulose lignin extractives a

27.5 33.6 19.6 14.3

± ± ± ±

MATERIALS AND METHODS

1.7 2.2 0.5 0.4

Dry basis. bAsh-free basis. cBy difference.

Figure 1. Diagram of the two-stage pyrolysis unit. 4363


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in an earlier paper.28 A diagram of the entire pyrolysis process is presented in Figure 1. The main reaction parameter in the present work was the reaction temperature of the auger reactor, which was varied from 318 to 404 °C. In contrast, the temperature of the fluidized bed reactor was fixed at about 520 °C. Table 2 shows the reaction conditions. In each experiment, 0.5 kg of corncob was used with a feed rate of about 5 g/min. Quartz sand (3.2 kg and 0.29 mm mean diameter) was used as the fluidized bed material, and product gas was used as the fluidizing medium with a flow rate of 28 NL/min for all the experiments. The residence time of corncob in the auger reactor was about 6−7 min. The calculated gas residence time in the fluidized bed was about 1 s. Activation of biochar was performed in a fixed bed reactor to produce activated carbon. For the activation, 100 g of biochar was heated from ambient temperature to the final activation temperature of 800 °C under a CO2 flow of 2 NL/min at a heating rate of 10 °C/min. The final temperature was then held without change for 1 h for final activation. CMA Synthesis. Raw bio-oil generated from the auger reactor was used for CMA synthesis. At first, 100 g of bio-oil was reacted with 10 g calcined dolomite at 40−50 °C for 1 h with the mixture stirred.

which are connected in series and heated by separate electric heaters. The auger reactor consists of a stationary vessel and screw. The inner diameter and length of the vessel are 28 and 700 mm, respectively, and the inner diameter and height of the fluidized bed reactor are 110 and 380 mm, respectively. They are all fabricated of 310 S tubes. The auger reactor in the two-stage pyrolyzer operates to degrade holocellulose, whereas the fluidized bed reactor mainly degrades lignin. In addition to the pyrolyzer, the two-stage pyrolysis process has a silo, two screw feeders, a char separation system composed of a cyclone and hot filter, condensers, an impact separator (IS), electrostatic precipitator (EP), and a compressor. Detailed explanations of the operation were presented

Table 2. Main Reaction Conditions parametersa reaction temp (°C)

AR FBR

total feed rate (g/min) pretreatment

run 1

run 2

run 3

run 4

318 517 5.4 N

373 523 5.1 N

399 521 5.1 N

404 519 4.8 W

AR, auger reactor; FBR, fluidized bed reactor; N, no pretreatment; W, water-washing. a

Table 3. Mass Balances of Two-Stage Pyrolysis of Corncob on As-Received Basis products

run 1

run 2

run 3

run 4

(wt %)

(318/517 °C)

(373/523 °C)

(399/521 °C)

(404/519 °C)

54.71 (13/87) 13.44 31.85 59.2 33.9

52.17 (18/82) 16.50 31.33 56.8 35.8

49.82 (21/79) 20.22 29.96 58.1 34.2

51.12 (25/75) 18.33 30.55 60.6 33.1

bio-oil (AR/FBR)a gas biochar water in bio-oil a

AR FBR

AR/FBR: weight ratio of oils obtained from auger reactor and fluidized bed reactor.

Table 4. Compositions of Bio-Oils from Corncob without Washinga run 1 (wt %) (318/517 °C)

a

run 2 (wt %) (373/523 °C)

compounds

group

RRF

AR

FBR

AR

ethyl alcohol methyl acetate acetic acid acetol 1-hydroxy-2-butanone furfural furfuryl alcohol acetol acetate dihydro-2(3H)-furanone 2-hydroxycyclopent-2-en-1-one phenol corylone o-cresol o-guaiacol p-creosol o-benzenediol 3-methoxy-pyrocatechol 2-methoxyphenethyl alcohol p-propylguaiacol vanillin lauric acid myristic acid palmitic acid oleic acid stearic acid unknown

alcohol ester acid alcohol ketone aldehyde alcohol ester ketone ketone phenol ketone phenol phenol phenol phenol phenol alcohol phenol phenol acid acid acid acid acid

0.96 2.16 1.75 2.16 1.03 1.00 0.87 1.69 1.25 0.91 0.46 0.70 0.45 0.60 0.58 0.53 0.68 0.69 0.65 0.74 0.53 0.51 0.50 0.49 0.49

1.7 1.85 32.4 6.44 1.38 1.11

0.17 2.77 6.99 9.84 1.89 5.61 2.44 1.98 0.88 0.72 17.98

1.2 3.28 37.21 7.54 1.47 2.14 1.03

0.41 0.14 0.21 0.17

54.19

1.48 0.82 2.04 0.98 4.13 0.35 2.61 1.79 2.44 1.61 1.55 28.74

0.89 0.53 0.44 0.37

43.9

FBR 2.54 7.16 8.83 1.94 5.94 2.64 2.14 0.69 0.64 18.05 2.84 0.64 2.81 1.64 0.59 1.94 0.84 3.72 0.4 2.84 1.88 2.67 1.83 1.67 22.98

run 3 (wt %) (399/521 °C) AR 1.1 3.29 36.41 7.14 1.62 1.84 1.24

1.32 0.88 0.51 0.49

44.16

FBR 2.09 6.91 9.67 1.84 5.04 2.81 2.09 0.66 0.59 17.44 2.28 0.58 2.11 1.57 0.76 2.15 1.09 4.04 0.31 2.95 1.98. 2.51 1.47 1.73 27.13

RRF, relative response factor; AR, auger reactor; FBR, fluidized bed reactor. 4364


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obtained from the auger reactor and fluidized bed reactor were about 57−61 and 33−36 wt %, respectively. Bio-oils. Table 4 shows the compositions of bio-oils generated from unwashed corncob and the concentrations of their main components. The concentration of each compound was obtained using RRFM. As can be seen in Table 4, the auger reactor yielded fewer numbers of bio-oil components than the fluidized bed reactor did, which indicates that the pyrolysis in the auger reactor was not as severe as in the fluidized bed reactor mainly due to the low temperatures of the auger reactor. The main components of bio-oils obtained from the auger reactor were typical degradation products of holocellulose (acetic acid, furfural, acetol, etc.). Phenolics found in the auger reactor bio-oils were simple phenols (phenol, cresol, etc.) with low concentrations. In contrast, the bio-oils obtained from the fluidized bed reactor comprised various chemicals, a great majority of which were phenolic compounds, the degradation products of lignin. Acetic acid was the main component of the bio-oils obtained from both the auger and fluidized bed reactors; its concentrations were 32−37 wt % in the auger reactor-produced bio-oils and about 7 wt % in the fluidized bed reactor-produced bio-oils. In comparison with a corncob pyrolysis performed using a pyrolysisgas chromatography/mass spectrometry at 500 °C (an acetic acid concentration of 25.6 area%),31 the acetic acid concentrations from the auger reactor were relatively high. The still high concentration of acetic acid in the bio-oil obtained from the fluidized bed reactor indicates both incomplete degradation of holocellulose in the auger reactor and the generation of acetic acid from

After reaching a constant temperature, the unreacted dolomite was filtered. Spray drying of the remaining solution (Spray dryer, B-290, BUCHI) produced CMA powder. The mass balance of the CMA synthesis could not be obtained because it was difficult to estimate the amount of CMA powder adhered to the dryer wall after spray drying. Product Analysis. Bio-oils were subjected to qualitative and quantitative analyses using a gas chromatograph−mass spectrometer (GC−MS, 5975 C, Agilent Instruments) and a gas chromatographflame ionization detector (GC−FID, 7890A, Agilent Instruments). The column used for GC analysis was an HP-5MS column (30 m × 250 μm × 0.25 mm), and helium was used as the carrier gas. For the quantitation of components in bio-oil, the relative response factor of each component was first obtained using the effective carbon number method according to the literature29 and then multiplied by the peak area of each component. This method is designated in the present paper as a relative response factor method (RRFM). For a more accurate acquisition of data on acetic acid concentration in bio-oil, the external standard calibration method (ESCM) was also applied. RRFM can provide contents of GC-detectable components in bio-oil. In contrast to RRFM, ESCM the content of an analyte concerned in the sample’s matrix which are all components of the sample other than the analyte. The R2 value of the calibration curve of ESCM was 0.9971. Karl Fischer titrator (Metrohm 870, KF Titrino) was applied to measure the water contents of the bio-oils with methanol as the titration solvent and HYDRANAL Composite 5K (Riedel-de Haen) as the titration reagent. CMA synthesized using bio-oil was analyzed using a Fourier transform infrared spectrometer (FTIR; Vertex 80 V, Bruker) and a field emission scanning electron microscope (FE-SEM; S-4700, Hitachi). The surface area of the activated carbon produced from biochar was determined using the Brunauer−Emmett−Teller (BET) equation. The pore size distribution of micropores was determined using the micropore analysis (MP) method, whereas for mesopores, the Barrett− Joyner−Halenda (BJH) model was employed. The total pore volume was obtained by summing the micropore and mesopore volumes.

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Table 5. Compositions of Bio-oil Obtained from Corncob after Washinga

RESULTS AND DISCUSSION Product Distribution. Bio-oil, biochar, and gas were obtained as product fractions. Mass balances were established in all the pyrolysis experiments on an as-received basis. In each mass balance, the bio-oil yield was determined from the sum of the liquid products collected in the condensers, IS, and EP. The biochar yield was calculated from the sum of the solids remaining in the auger and fluidized bed reactors after pyrolysis and the solids captured by the cyclone and hot filter. Finally, the gas yield was calculated from the difference between the amounts of feed material and bio-oil plus biochar. Bio-oils from the auger reactor formed a single phase and those from the fluidized bed reactor did not show a discrete phase separation. Table 3 presents the mass balance of each experiment. As shown in Table 3, the total bio-oil yields were about 50−55 wt %. A corncob pyrolysis study conducted using only a fluidized bed reactor at 500 °C reported a similar product distribution to the present work (bio-oil yield of 54.4 wt %).30 The weight ratio of bio-oils from the auger reactor at 318, 373, and 399 °C was 13:18:21. Hence, the bio-oil yield ratio from the auger reactor at 318, 373, and 399 °C was approximately 7:9:10, which shows an increasing trend of bio-oil yield from the auger reactor within the temperature range (320−400 °C). Along with the fact that gas production increased at higher auger reactor temperatures, a high temperature within the range must have favored for the production of light components. In contrast, the biochar yield slightly decreased from 32 to 30 wt % with increasing auger reactor temperature. A comparison between runs 3 and 4 showed that the effect of washing on bio-oil yield was not significant, with only a small increase in bio-oil yield obtained with washed corncob. The water contents of bio-oils

run 4 (wt %) (404/519 °C) compounds

group

RRF

AR

ethyl alcohol methyl acetate acetic acid acetol 1-hydroxy-2-butanone furfural furfuryl alcohol acetol acetate dihydro-2(3H)-furanone 2-hydroxycyclopent-2-en-1-one phenol corylone o-cresol o-guaiacol p-creosol o-benzenediol 3-methoxy-pyrocatechol 2-methoxyphenethyl alcohol p-propylguaiacol vanillin lauric acid myristic acid palmitic acid oleic acid stearic acid unknown

alcohol ester acid alcohol ketone aldehyde alcohol ester ketone ketone phenol ketone phenol phenol phenol phenol phenol alcohol phenol phenol acid acid acid acid acid

0.96 2.16 1.75 2.16 1.03 1.00 0.87 1.69 1.25 0.91 0.46 0.70 0.45 0.60 0.58 0.53 0.68 0.69 0.65 0.74 0.53 0.51 0.50 0.49 0.49

1.4 3.42 48.27 10.4 2.72 3.08 1.54

0.92 0.48 0.31 0.22

27.24

FBR 2.49 7.81 10.67 1.27 7.28 2.81 2.26 0.72 0.67 18.54 3.42 0.72 2.41 1.44 0.88 2.65 0.95 3.65 0.28 3.58 2.41 2.16 1.84 0.97 17.68

RRF, relative response factor; AR, auger reactor; FBR, fluidized bed reactor. a

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in ether bond length between the aromatic ring and methyl groups of coniferyl and sinapyl alcohols. As a result, the removal of the methoxy group will be facilitated even at not so high a reaction temperature, which, in the present study, is about 520 °C. The bio-oils produced from the fluidized bed reactor appeared to be appropriate for the phenol resin synthesis because they were abundant in phenol that has high reactivity toward aldehydes. Washing the corncob with hot water significantly changed the concentrations of several bio-oil components. Table 5 presents the compositions of the bio-oils generated from washed corncob and concentrations of their main components. An observable change in the concentration of acetic acid in bio-oil occurred after washing; that is, the acetic acid concentration significantly increased by about 10% (48 wt %). Ash appeared to severely prevent the formation of acetic acid during pyrolysis. Meanwhile, the production of phenol in the fluidized bed reactor was stimulated from 17.4 (run 3) to 18.5 wt % (run 4) when washed corncob was used. The acetic acid concentrations of bio-oils presented in Tables 4 and 5 were determined using RRFM of GC-FID, which is usually used for the quantification of hydrocarbons. Because the bio-oils in the present work contained high amounts of water and other components that cannot be detected solely by GC-FID, ESCM was additionally applied to more accurately quantify the acetic acid concentration of bio-oil. Table 6 shows the acetic acid concentration determined using ESCM. The acetic acid concentrations determined by ESCM were in the range from 7 to 12 wt %. The maximum concentration was obtained like the preceding RRFM with washed corncob.

the lignin of corncob. The highest acetic acid concentration was obtained at the auger reaction temperature of 373 °C. At the auger reaction temperature of 399 °C, the cellulose and lignin of corncob appeared to be highly cracked to significantly produce other chemicals and, as a result, lead to a low acetic acid concentration in bio-oil compared to that in the bio-oil at 373 °C. Another interesting chemical of bio-oil was phenol. The bio-oils produced from the fluidized bed reactor obtained with unwashed corncob contained a high concentration of phenol (up to 18 wt %). In biomass pyrolysis using one pyrolyzer, the phenol concentration in bio-oil is very low (up to 3 wt %).32 The low phenol production is mainly because the degradation of lignin at typical biomass pyrolysis temperatures (about 500 °C) cannot sufficiently remove the methoxy group of such lignin precursors as coniferyl alcohol and sinapyl alcohol yielding phenolic compounds containing methoxy groups. Considering that the feed material in this study contained only about 20 wt % lignin24 and that the reaction temperature of the fluidized bed reactor was about 520 °C, the high phenol concentration in bio-oil was a surprising result. Its main cause appeared to originate from the rise in the vibrational state of lignin molecules in the auger reactor. The vibrational state of lignin molecules increases at higher temperatures (in the present work, 320−400 °C), which would result in an increase Table 6. Acetic Acid Concentration Obtained Using External Standard Calibration Method external standard calibration method

run 1

run 2

run 3

run 4

acetic acid (wt %)

7.3

9.4

9.9

12.2

Figure 2. FTIR spectra of (A) reference CMA21 and (B) CMA synthesized using bio-oil (run 4). 4366


Research Article

ACS Sustainable Chemistry & Engineering Characterization of Synthetic CMA. CMA synthesis will be favored if a bio-oil contains a high concentration of acetic acid and, at the same time, minimal numbers of other compounds that could hinder CMA synthesis. From the above viewpoint, the bio-oil obtained from run 4 of the auger reactor appeared to be the best for CMA synthesis. To obtain a sufficient amount of bio-oil for CMA synthesis, pyrolysis experiments were conducted three times under the same conditions as those of run 4. Figure 2 shows the FTIR spectra of CMA synthesized using bio-oils obtained under similar reaction conditions as that of run 4, along with that of reference CMA synthesized using glacial acetic acid. The typical FTIR bands observed for CMA are as follows: a broad band at 3500−3300 cm−1 (stretching vibration of hydrogen bonded −OH groups of hydrated calcium or magnesium acetate), weak bands at 3000 and 2900 cm−1 (asymmetric and symmetric methyl stretching vibrations), strong bands at 1700−1400 cm−1 (−CO stretch or −COO− stretch), bands above 1000 cm−1 (bending or out-of-plane stretching of −CH3), and bands below 1000 cm−1 (C−C stretching of CH3COO−). As shown in Figure 2, the FTIR spectrum of CMA synthesized using the bio-oil produced from the auger reactor was similar in terms of band shape to that of the reference CMA; this indicates that the bio-oil obtained from the auger reactor could replace glacial acetic acid in the preparation of commercially available CMA. The microstructure of the CMA synthesized in this study was characterized using FE-SEM to confirm the result of CMA synthesis, which is shown in Figure 3C. The FE-SEM images of Figure 3A,B are those of calcined dolomite and a reference CMA synthesized using commercial glacial acetic acid and calcined dolomite, respectively. The FE-SEM image of the synthesized CMA shows that calcined dolomite is covered with spherical acetate particles. Along with FTIR analysis, the SEM results confirmed the successful synthesis of CMA using bio-oil. In particular, the fact that the bio-oil used for CMA synthesis did not need any pretreatment to enrich acetic acid concentration in the bio-oil and to remove any interrupting chemical from the bio-oil renders it attractive for CMA preparation. Activated Carbon. Biochar obtained after pyrolysis is a byproduct that can be used for soil improvement and remediation against environmental pollution, or as a fuel source. In addition, biochar can be used as a precursor for the production of activated carbon having a higher economic value compared to biochar. Activated carbon has micropore and mesopore structures in its macropores. According to the International Union of Pure and Applied Chemistry (IUPAC) classification, micro-, meso- and macropores have size ranges less than 2, 2−50, and over 50 nm, respectively.33 In the current study, CO2 instead of steam was selected as the activating agent because it is easy to handle. A previous work on the production of activated carbons with CO2 from agricultural and forest residues produced activated carbons having BET surface areas ranging from 400 to 1000 m2/g, dependent on the types of biomass and activation conditions.34 The biochar used for the preparation of activated carbon in the current study was obtained from run 4. The weight loss after activation was determined by burnoff, which was calculated from the following equation:

Figure 3. FE-SEM images of (A) calcined dolomite,21 (B) reference CMA,21 and (C) CMA synthesized using bio-oil (run 4).

Table 7 shows the textural properties of biochar and activated carbon. The burnoff after activation was 55.4%. The weight loss during activation with CO2 can be explained by the following Boudouard reaction:

C + CO2 ↔ 2CO

(2)

By the above reaction, the carbon in the biochar is removed to develop the pore structure of activated carbon. In addition, the table shows that the BET surface area and the micropore volume after activation were significantly increased from about 10 to 580 m2/g and from 0.0108 to 0.2490 m2/g, respectively. Figure 4 showing the pore size distributions of biochar and activated carbon confirms the development of micropores after activation.

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CONCLUSION Corncob was pyrolyzed to produce acetic acid-rich bio-oil using a continuous two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor. The bio-oils produced from the auger reactor were rich in acetic acid with the highest concentration of about 48 wt % based on the relative response factor method and 12 wt % based on the external standard calibration method. The bio-oil produced from the fluidized bed reactor

Burn‐off (%) (mass of initial pyrolytic char − mass after activation) = 100 mass of initial pyrolytic char (1) 4367


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ACS Sustainable Chemistry & Engineering Table 7. Textural Properties of Bio-char and Activated Carbon final activation temperature (°C)

final activation time (min)

burn-off (%)

SBET (m2/g)

Vmicro (cm3/g)

Vmeso (cm3/g)

Vtotal (cm3/g)

800

120

55.4

12 577

0.0108 0.2490

0.0058 0.0303

0.0166 0.2793

biochar activated carbon

Figure 4. Pore size distribution of (A) biochar and (B) activated carbon.

was enriched with acetic acid (about 7−8 wt %) and phenol (about 17−19 wt %). CMA was synthesized using the raw biooil generated from the auger reactor and calcined dolomite. The CMA synthesized in this study was chemically identical to commercial CMA. Finally, activated carbon having a BET surface area of about 580 m2/g could be produced from biochar through CO2 activation. In summary, it was possible to produce an eco-friendly deicer CMA using untreated bio-oil and activated carbon as well using the new two-stage pyrolysis process.

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AUTHOR INFORMATION

*Tel.: +822-6490-2868. Fax: +822-6490-5479. E-mail: joosik@ uos.ac.kr. ORCID

Joo-Sik Kim: 0000-0002-6077-4425 Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the 2017 Research Fund of the University of Seoul NOMENCLATURE

List of abbreviations

BET BJH CMA EP ESCM FTIR FE-SEM GC−MS GC−FID IS RRFM

REFERENCES

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Brunauer−Emmett−Teller Barrett, Joyner and Halenda calcium magnesium acetate electrostatic precipitator external standard calibration method Fourier transform infrared field emission scanning electron microscopy gas chromatography−mass spectrometry gas chromatography−flame ionization detector impact separator relative response factor method 4368


Research Article


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Preparation of Calcium Magnesium Acetate Deicer Using Raw Acetic

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