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Crab shell-derived lotus root-like porous carbon for high efficiency isomerization of glucose to fructose under mild condition Feng Shen, Junyan Fu, Xiao Zhang, and Xinhua Qi ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b06512 • Publication Date (Web): 23 Jan 2019 Downloaded from http://pubs.acs.org on January 28, 2019

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ACS Sustainable Chemistry & Engineering

Crab shell-derived lotus root-like porous carbon for high efficiency isomerization of glucose to fructose under mild condition Feng Shena, Junyan Fub, Xiao Zhangc, and Xinhua Qia* a Agro-Environmental

Protection Institute, Chinese Academy of Agricultural Sciences, No. 31, Fukang Road, Nankai District, Tianjin 300191, China, Email: [email protected] b College of Environmental Science and Engineering, Nankai University, No. 94, Weijin Road, Nankai District, Tianjin 300071, China cSchool of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, China Corresponding Author Xinhua Qi, Email: [email protected] (X. Qi); Tel (Fax): 86-22-2361-6651. Abstract: Crab shell waste-derived carbon/CaO composite was synthesized by a facile one-step pyrolysis strategy. The composite was used as a solid base catalyst for isomerization of biomassderived glucose to fructose, which is a key intermediate in transformation of cellulosic biomass into chemicals and biofuels. Physicochemical structure of the composite was characterized by XRD, Raman spectra, SEM, ICP, BET and CO2-TPD. The composite showed lotus root-like porous structure with surface area of 85 m2/g and contained as high as 22.4 wt % of CaO. The isomerization of glucose to produce fructose with the prepared solid base catalyst was investigated, and a maximum fructose yield of 29.2% was obtained from 5% glucose aqueous solution at mild condition (80 oC and 40 min ). 25.0% yield of fructose still could be produced even the initial glucose concentration was as high as 20 wt%. Finally, mechanism of glucose isomerization by the synthesized solid base catalyst was studied. This work provided not only an alternative approach for utilization of crab shell waste, but also a better understanding of cellulose-derived sugar transformations with solid base catalyst. Keywords: Crab shell, biomass, solid base, glucose, fructose, isomerization

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INTRODUCTION

Crab shell waste, the main by-product of crab, was produced with millions of tons every year 1. The crab shell was normally dumped in landfill as waste or disposed with very high cost (e.g $150/t in Australia)2. Actually, the crab shell waste contains valuable chemicals such as chitin, calcium carbonate (CaCO3) and protein 2. From this point of view, the crab shell waste is an abundant and renewable bio-resource. Traditionally, the crab shell was grinded into powder and was used directly as fertilizers or animal feeds due to its protein and carbon content 3. It was also the main raw material for the production of chitin which has been widely used in the fields of cosmetics, food and biomedicines, etc. For example, low molecular weight of chitin with 92% purity was obtained from crab shell with 3-5 wt% acid catalyst 4. Besides, the crab shell waste can be used directly as adsorbents for the removal of nutrients 5, metals (Pb2+, Zn2+) 6 or Cu2+ 7), and organochlorine pesticides 8. Also, it can be used as the carbon precursor as well as hard-template for the preparation of porous carbon materials attributing to its high chitin and calcium carbonate content, respectively

9, 10.

Since the

chitin is nitrogen-containing polymer, the chitin rich-crab shell was an ideal candidate to produce nitrogen self-doped carbon which can be applied in energy storage electrode 9. However, little attention has been paid on the application of crab shell waste as catalyst, especially applied for the biomass transformation. Biomass resource has been regarded as the most promising alternative for the gradual depletion of traditional fossil resources due to its advantages of renewable, abundance and environmental friendliness 11. Biomass and its derived carbohydrates can be converted into various chemicals and bio-fuels such as glucose, levulinic acid, 5-hydroxymethylfurfural (5-HMF), and so on 12. Among them, glucose isomerization to fructose is one of the key steps. For example, fructose is the 2


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intermediate compounds in the conversion of cellulose into 5-HMF, which is a versatile chemical for production of plastics, paints, and a variety of fine chemicals 13, 14. Besides, fructose can be used as sweeteners since it is the sweetest among the naturally available carbohydrates

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Fructose

mainly comes from glucose via isomerization reaction which can be progressed by enzymes or chemical base catalysts 16. Although enzymatic process (e.g glucose isomerase) is widely used in industrial production of fructose 17, biological catalyst suffers from various drawbacks such as highcost and low reaction efficiency. On the other hands, the isomerization of glucose via the chemical process with base catalysts or Lewis acid could avoid these problems. Both homogeneous catalysts such as organic amines 18, basic amino acids 19, phosphates 20, and heterogeneous catalysts such as MgO21, Sn-Beta22, magnesium impregnated zeolites hydrotalcite

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23, 24,

metal-organic frameworks

25,

Mg-Al

and CaO doped ZrO2 27 were used for the glucose isomerization. Heterogeneous

catalysts present the advantages over homogeneous catalysts of being environmentally friendly and more easily recycled. However, most of the heterogeneous solid base catalysts were synthesized via multi-step method and alkali metal (Mg or Ca) modification was necessary. Thus, the development of facile and low cost methods for preparation of solid base catalysts is still important for the biomass utilization. In this work, crab shell which is an abundant and renewable bioresource was used for the preparation of solid base catalysts via one-step pyrolysis method without any addition of metal compound. The crab shell waste-derived catalyst was applied in the isomerization of glucose to produce fructose for the first time. As mentioned above, the crab shell contains high content of chitin and calcium carbonate. After thermal pyrolysis, the chitin could translate into carbon matrix while the calcium carbonate could decompose into CaO which could act as basic catalytic site. The 3



synthesized solid base catalysts were characterized by SEM, BET, CO2-TPD and ICP. The influence of reaction temperature, reaction time, catalyst dosage and initial glucose concentration on the catalytic performance of the crab shell-derived solid base catalyst in the isomerization of glucose into fructose was investigated. Mechanism of glucose isomerization by the crab shell-derived catalyst was also proposed.

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EXPERIMENTAL SECTION

Materials. Fructose and glucose were purchased from J&K Co., Ltd. (Beijing, China). Crab shell was provided by a local market (Tianjin, China). Before usage, the crab shell was washed with hot water to remove protein and other impurities. After that, the crab shell was dried at 80 oC for 12 h. The obtained crab shells were then ball milled for 30 min in a planetary ball miller (Retsch PM100) before use to ensure its homogeneity. Catalyst preparation and characterization. Typically, the crab shell powder was heated in a furnace under nitrogen atmosphere from room temperature to 400 oC at 5 oC/min and kept for 2 h. Then, the crab shell was further heated from 400 oC to 800 oC at 5 oC/min and kept at this temperature for another 2 h. The obtained material was denoted as CS-CaO-800. Morphologies of the composite were observed by scanning electron microscopy (SEM, Hitachi S4800). Nitrogen adsorption/desorption isotherms were performed on Micromeritics 3FLEX sorptometer (USA). The surface area of the material was calculated using adsorption data by Brumauer-Emmett-Teller (BET) method. Ca content was determined by an ICP instrument (Thermo ICP-9000).CO2-TPD was conducted by a chemisorption analyzer (Autochem II 2920). The X-ray diffraction (XRD) patterns of carbon samples were collected in an X-ray powder diffractometer (Bruker D8 Advance). Raman spectrum was analyzed by NRS-3100 spectrometer with 535 nm 4


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excitation. Catalytic test. The catalytic performance of the as-synthesized catalysts for isomerization of glucose to fructose was performed in a 10 mL autoclave. Typically, 30 mg of the catalyst was added into 5 ml of various concentrations of glucose aqueous solutions. The mixture was transferred to the autoclave and reacted at the designed temperature for different time with magnetically stirring (1000 r/min). After the reaction, the autoclave was cooled down with cold water rapidly. The liquid phase was filtered and the filtrate was detected by HPLC on a Waters ACQUITY UPLC H-CLASS equipped with a refractive index (RI) detector and a SHODEX SH1011 column. The mobile phase was 5 mM H2SO4. The flow rate was 0.5 mL/min. The temperature of RI detector and SHODEX SH1011 column were 35 °C and 50 °C, respectively. The injection volume was 10 µL. Conversion of glucose, yield of fructose and fructose selectivity were calculated according to the following equations. Conversion of glucose(%) =

moles of glucose reacted moles of initial glucose

× 100% [1]

moles of fructose formed × 100% [2] moles of initial glucose moles of fructose formed Selectivity of fructose(%) = × 100% [3] moles of glucose reacted Yield of Fructose (%) =

13C-NMR

study was performed as follows: 250 mg of glucose deuterated on the C2 position

(glucose-2-d1) was isomerized in water (5 mL) at 80 oC for 1 h with 30 mg of CS-CaO-800. At the end of reaction, sugar mixtures were concentrated with a rotary evaporator and then freeze-dried. The obtained sugars were dissolved in D2O for

13C-NMR

analysis (Bruker AVANCE 500 MHz

NMR spectrometer).

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Results and discussion 5



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Preparation and characterization of the catalyst. The solid base catalysts were synthesized via a facile and low cost pyrolysis method in which chitin and CaCO3 components of the crab shell acted as carbon and CaO precursor, respectively. Carbon/CaO composites were prepared from crab shell at different temperatures (600 oC, 800 oC and 1000 oC). XRD pattern and Raman spectrum of the resulting carbon/CaO composites are shown in Figure S1. For the carbon/CaO composite obtained at 600 oC, no characteristic crystalline phase of CaO is observed, since CaCO3 was not decomposed below 650 oC

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The carbon/CaO prepared at 800 oC (CS-CaO-800) shows crystalline phase

dominated by calcium oxide, indicating the presence of CaO in the composite synthesized from crab shell. Higher temperature (1000 oC) caused no change of crystalline phase of the resulting composite (CS-CaO-1000). Raman spectra shown in Figure S1(b) exhibit two conspicuous peaks at 1354 and 1596 cm-1 assigned to the well-recorded D and G bands of carbons, respectively

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The D band

represents the amorphous and imperfect structures of disordered carbon materials, and the G band represents the graphite structure of the carbons. Generally, the intensity ratio of the two bands (IG/ID) was used to estimate the graphitization degree of carbon materials. As shown in Figure S1(b), All the IG/ID values of the three samples were greater than 1, suggesting high graphitization degree of the composites. IG/ID values decreased slightly with the increased of temperature. ICP analysis indicates that the CS-CaO-800 and CS-CaO-1000 contained 22.4% and 22.9% CaO, respectively. Since both CaO content and structure of CS-CaO-800 and CS-CaO-1000 are similar, CS-CaO-800 was used for the glucose isomerization in the whole experiment.

The obtained CS-CaO-800 has lotus root-like porous structure as shown in Figure 1. The diameter of the pores was 1 μm-3 μm. The large pores of CS-CaO-800 would allow the entrance of glucose, thus benefiting its reaction with CaO in the pores. The specific Brunauer-Emmett-Teller 6


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(BET) surface area was calculated to be 85.4 m2/g. CO2-TPD was used to investigate the basicity of CS-CaO-800 and the CO2 desorption curves are showed in Figure 2. There are two main CO2 desorption regions. The one at low temperature (100-150 oC) could attribute to CO2 desorption by weak basic sites of surface hydroxyl groups in the CS-CaO-800 23. Another peak region located at 600-650 oC was ascribed to CO2 desorption on the strong basic sites of CaO. ICP measurement showed that the CS-CaO-800 has 22.4wt% of CaO. The CaO which acted as catalytic sites herein was self-provided by the crab shell and without any addition of extra-metal compound. Therefore, the preparation method of CS-CaO-800 from crab shell was facile and low cost.

Figure 1. SEM images of CS-CaO-800 at different magnifications

Figure 2. CO2-TPD spectrum of the CS-CaO-800

Fructose production from glucose by the CS-CaO-800. Catalytic performance of the as-prepared CS-CaO-800 composite for the production of fructose from glucose in water was evaluated. First, sugar adsorption ability on the carbon/CaO composite was performed and detailed process was 7



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shown in Supporting Information. As shown in Figure S2, The carbon/CaO composite showed very poor adsorption ability to both glucose and fructose (

Crab shell-derived lotus root-like porous carbon for ... - ACS Publications

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