J. Cent. South Univ. (2017) 24: 1745-1753

DOI: https://doi.org/ 10.1007/s11771-017-3582-x

Sustainable synthesis of 5-hydroxymethylfurfural from waste cotton stalk catalyzed by solid superacid-SO₄^2-/ZrO₂

MO Hong-bing(莫红兵), CHEN Xiang-ping(陈湘萍), LIAO Xiao-yan(廖孝艳), ZHOU Tao(周涛)

Hunan Provincial Key Laboratory of Efficient and Clean Utilization of Manganese Resources,

School of Chemistry and Chemical Engineering, Central South University, Changsha 410012, China

Central South University Press and Springer-Verlag GmbH Germany 2017

Abstract: A sustainable process was explored for the preparation of 5-hydroxymethylfurfural (HMF) by catalytic degradation of the waste cotton stalk. Solid super-acid (SO₄^2-/ZrO₂) was used as an efficient catalyst for the degradation of cotton stalk. Both decomposition experiments and kinetic study were conducted for the exploration of degradation condition and kinetics mechanism. The optimized experimental conditions are reaction temperature 503 K, reaction time 75 min and dosage of catalyst 30% (mass fraction) based on the decomposition experiments, under which a maximum yield of 27.2% for HMF could be achieved. Kinetic study was then carried out in the presence of SO₄^2-/ZrO₂. The theoretical results indicate that the activation energies for reducing sugar and HMF with catalyst are 96.71 kJ/mol, 84.21 kJ/mol in the presence of SO₄^2-/ZrO₂, and they are 105.96 kJ/mol and 119.37 kJ/mol in the absence of SO₄^2-/ZrO₂.

Key words: waste cotton stalk; cellulose; hydroxymethy furfural (HMF); SO₄^2-/ZrO₂; kinetic study

1 Introduction

As an important furyl compound, 5-hydroxymethylfurfural (HMF) can be synthesized by the decomposition of glucose from different biomass [1-4]. Active groups contained in HMF (e.g. aldehyde, hydroxymethyl) may make then an active intermediate and numerous derivatives can be prepared from HMF through oxidation, hydrogenation and condensation reactions [3, 5, 6]. As an important intermediate, HMF can be employed as the source material during the preparation of new-type green of “platform compound” levulinic acid (LA) by the degradation of cellulose [7]. As reviewed by TONG et al [8], it is expected that HMF may promise a significant intermediate and new platform compound between biomass chemistry and organic chemistry for the petrochemical industry. Nevertheless, the petrochemical industry may suffer from the depletion of non-renewable fossil resources [9]. It is, therefore, necessary to develop a sustainable process for the preparation of HMF from renewable biomass resources to alleviate the currently severe dependence on fossil resources.

Current attentions were mainly focused on the seeking of suitable solvent systems and efficient catalysts during the degradation of biomass [8, 10-22]. And single-phase and two-phase methods are the most commonly used methods according to different solvent systems [5]. It is discovered that single-phase method can be a preferable method over two-phase method during the degradation reaction in terms of homogeneous mixing, high yield etc [8, 23]. Hydrothermal and solvothermal methods [24-26] are the most commonly used methods in the single-phase method and the hydrothermal method can be a preferred choice for the degradation of biomass due to its easy availability of economical and convenient resources (e.g. water) [24]. Therefore, hydrothermal method was adopted for the sustainable synthesis of HMF from the renewable biomass resource.

Recently, a number of synthetic methods have been explored regarding the preparation of HMF from different biomass by catalytic decomposition and the main concerns were concentrated on the following three aspects: mineral acid catalysis, ionic liquid catalysis and solid acid catalysis. Mineral acids [2, 8, 21, 22, 24, 25, 27-29] were usually employed as catalysts during the traditional preparation process. The conventional mineral acid-catalyzed process presents some advantages such as simplified process, high operability, relatively low investment. However, the traditional processes may be discouraged by a number of drawbacks such as serious equipment corrosion, negative impacts on the environment, low yield of the target product, complicated by-products [8, 9, 25]. As an emerging catalyst, ionic liquid had recently attracted an increasing attention due to its superior performance (e.g. eco-friendly process, high yield and selectivity, mild degradation conditions) [8, 9, 11, 16, 25, 30-33]. Although these eco-friendly catalysts present numerous advantages, the synthesis of HMF may be frustrated by some disadvantages during the preparation process such as the enhanced cost, difficulty in catalysts recovery [8, 25]. Therefore, super solid acid catalyst may be an alternative to address the above issues. And ion- exchange resins, H-form zeolites, vanadyl phosphate and ZrO₂ are the widely reported solid acid catalysts [3, 4, 10-13, 34, 35]. Compared with liquid catalysts (mineral acid and ionic liquid), solid acid catalysts present the following superiorities: facilitating the separation of products and catalyst; recycling and reusing the catalyst; shortening the reaction time and favoring the formation of 5-HMF as the high tolerance of solid acid catalysts; potential capability to improve the selectivity of HMF by the adjustment of the surface acidity, which is very useful for the conversion of biomass.

The kinetic study for the preparation of target products from biomass is also a concern to explore the degradation mechanism. For example, a first-order reaction was established by HELLE et al [36] to prepare glucose by hydrolysis of levoglucosan and cellobiosan from pyrolysis oil. It can be also concluded that the activation energies for levoglucosan hydrolysis and cellobiosan hydrolysis to glucose are 99 kJ/mol and 114 kJ/mol, respectively. MOREAU et al [37] revealed that the dehydration of fructose using water as solvent is not controlled by external diffusion according to experimental results, which is conformed to a classical Langmuir-Hinshelwood mechanism and the product and solvent are not involved with the rate equation.

As a renewable biomass, cotton stalk has recently attracted an increasing attention to prepare HMF due to its high cellulose content. And a yield of 44.1% HMF could be achieved by catalytic degradation of cotton stalk [38]. Though numerous studies were carried out for the preparation of HMF from biomass, it has never been reported for the preparation of HMF from the degradation of waste cotton stalk using SO₄^2-/ZrO₂ as catalyst by hydrothermal method. As an inexpensive and renewable biomass resource, the preparation of HMF from the waste cotton stalk may promise environmental and economic benefits. Current study is, therefore, dedicated to explore a novel route for the preparation of 5-HMF from waste cotton stalk by catalytic decomposition. Solid super acid catalyst of SO₄^2-/ZrO₂ was innovatively employed during the decomposition reaction. Effects of reaction time, reaction temperature and catalyst dosage were investigated to obtain the optimized experimental conditions and kinetic study was also carried out for the investigation of the mechanism of the catalytic decomposition reaction.

2 Materials and methods

2.1 Materials and reagents

Waste cotton stalks were collected from local farmland in Changde, China. These stalks were subjected for the following pretreatment: drying, milling and sieving. Then powders (with particle size<0.19 mm) of waste cotton stalk were obtained in the degradation reaction. The chemical components of the powders were in a proportion of 42.05% cellulose, 19.30% hemi- cellulose, 12.74% lignin, 7.46% water, 14.41% neutral detergent soluble molecules and 4.04% ash. Methanol used in this study is of HPLC grade, and all other chemical reagents in the experiment are of analytical grade. And all chemical reagents used were without any further treatment or purification and deionized water was used for the dilution and preparation of different solutions.

2.2 Preparation and characterization of catalyst

At first, a quantitative amount of ZrOCl₂·8H₂O solid was dissolved in ethanol solution (V_water:V_ethanol=3:1) to prepare 8% ZrOCl₂ solution. Then, concentrated ammonia liquor was drop-wise added to the solution until pH=9.0 with magnetic stirring speed controlled at 400 r/min and a white gel could be obtained after an aging operation in the above solution for 48 h. Then, the aged precipitate was repeatedly washed with deionized water until no Cl^- could be detected in the filtrate (tested by adding AgNO₃ solution to the filtrate). Finally, the obtained precipitate was immersed in 0.5 mol/L (NH₄)₂SO₄ for 12 h and solid super acid catalyst of SO₄^2-/ZrO₂ could be obtained after thermal treatments of drying (in an oven at 378 K for 10 h) and calcination (in a muffle furnace at 825 K for 6 h).

The prepared SO₄^2-/ZrO₂ catalyst was characterized by ASAP-2020-V3.04-G (Micromeritics Instrument Corp.) under the condition of single point surface area at nitrogen relative partial pressure of 0.300005706 and 752S UV-Vis spectrophotometry (Shanghai Lengguang Technology Co., Ltd.) at detection wavelength of 256 nm to detect the equivalent of SO₄^2- presented on the surface of the catalyst to determine the BET surface area and the amount of pyridine, respectively. And the ultimate analysis of SO₄^2-/ZrO₂ catalyst and the start materials were also measured by the same method. Analytical results show that surface areas of the catalyst measured were 35.1 and 34.3 m²/g, and the equivalents of SO₄^2- on the catalyst surface were 0.082 and 0.080 mmol/g before and after degradation reaction. And the metal contents of detailed composition of the catalyst and start material were analyzed and determined by ICP.

2.3 Experimental procedures

All the batch experiments were carried out in a 250-mL magnetic stirring batch reactor (WHF, Weihai Automatically-controlled Reaction Kettle Co., LTD.). And experimental parameters were investigated to determine the optimal experimental conditions. The reaction temperature was investigated in a range from 473 K to 503 K with an interval of 10 K and the reaction time was varied from 15 min to 90 min with an interval of 15 min under conditions of different dosage of catalyst from 0 to 30% (mass ratio upon the cotton stalk) and agitation speed of 400 r/min. A fixed amount of waste cotton stalk powder (~1 g) and SO₄^2-/ZrO₂ (varied according to different experimental conditions) was precisely measured and simultaneously added to the reactor. Then the product in the filtrate will be subjected for the subsequent analysis after filtration.

The degradation rate of cellulose (X), residual reducing sugar content (C_{reducing-surgar}), initial concentration of reducing sugar (C₀) and productivity of HMF (y_HMF) can be calculated according to the following equations Eq. (1)-Eq. (4):

                                 (1)

                        (2)

                               (3)

                         (4)

where m and m₁ are the initial mass of cellulose and the mass of the residual cellulose, respectively; V₀=250 mL, V₁=1 mL and V is the volume of solvent; Y₁ is the absorbance of reducing sugar obtained by ultraviolet spectrophotometry; 10/9 is the degradation coefficient of cellulose into reducing sugar [18]; C₀ is the initial concentration of reducing sugar after accumulation; y_HMF is the yield of HMF; Y₂ is the concentration of HMF obtained by HPLC; n is the multiple of the dilution of sample; 126.11 and 180 are the molecular weights of HMF and reducing sugar.

2.4 Analytical methods

The composition in aqueous phase after decomposition reaction was detected and determined by an HPLC system (ASAP-2020-V3.04-G, Micromeritics Instrument Corp.) and UV detector (752S UV-Vis spectrophotometry, Shanghai Lengguang Technology Co., Ltd.). A Kromasil C-18 column operated at 293.15 K and HPLC-methanol solution (V_water:V_methanol=80:20) at a flow rate of 0.7 mL/min were applied for the detection of chemical constituent in the obtained aqueous phase. DNS method was employed for the analysis of reducing sugar by adding 1.5 mL DNS solution and then the mixture was incubated at 373 K for 10 min. The concentration of each compound in the aqueous phase was determined by calibration curves obtained from the analysis of standard solutions with known concentrations using the above UV detector. And the absorption wavelength was controlled at 520 nm for the component analysis of the aqueous phase. The content of Zr in the catalyst was measured and determined by ICP after dissolving SO₄^2-/ZrO₂ in aqua regia.

To avoid random errors, three parallel experiments were conducted during the decomposition reactions and the mean values would be treated as the final experimental results.

3 Results and discussion

3.1 Optimization of experimental conditions

3.1.1 Effect of reaction temperature

As an important influencing factor, reaction temperature was investigated in a range from 463 K to 503 K with an interval of 15 K under the experimental conditions of reaction time 90 min and 20% SO₄^2-/ZrO₂. According to Fig. 1, the conversion rate of cellulose and the yield of HMF increase with the growth of reaction temperature. The conversion rate of the cellulose experiences a slight increase from 463 K to 473 K and then a significant increase from 473 K to 493 K. Most of cellulose (over 90%) can be converted into reducing sugar over 493 K and a maximum conversion rate (over 94%) could be achieved at 503 K. The yield of HMF also witnesses a steady enhance with the increase of reaction temperature. The yield of HMF is only 1.8% at a low temperature of 463 K, which can be attributed to the low conversion rate of cellulose and insufficient reducing sugar in the reaction. The increased yield of HMF may be guaranteed by the remarkable increase of the conversion rate of cellulose and sufficient reducing sugar from 473 K to 503 K. A maximum yield of HMF (about 25.3%) can be achieved at 503 K under the conditions of reaction time 90 min and 20% SO₄^2-/ZrO₂.

Fig. 1 Effect of reaction temperature on conversion rate of cellulose and yield of HMF (1.000 g waste cotton stalk in 30 mL water; t=90 min and 20% SO₄^2-/ZrO₂)

3.1.2 Effect of reaction time

The influence of reaction time on the reaction was also studied from 15 min to 120 min with an interval of 15 min at conditions of reaction temperature 503 K and 20% catalyst. As demonstrated in Fig. 2, the conversion rate of cellulose experiences a steady increase while the yield of HMF attains 25% at 90 min. The conversion rate of cellulose steadily increases from 76% to 97% as the increase of reaction time is from 15 min to 120 min. As the prolonging of reaction time is from 15 min to 90 min, the yield of HMF increases from 6.1% to 25.3%. Then, the yield of HMF declines from 90 min to 120 min. This phenomenon may be ascribed to the accumulation of HMF in a shorter reaction time and then further decomposition or polymerization to other substances with the excessive accumulation of HMF [38]. Therefore, reaction time of 90 min would be the optimized reaction time, under which a maximum yield of 25.3% could be obtained.

Fig. 2 Effect of reaction time on conversion rate of cellulose and yield of HMF (1.000 g waste cotton stalk in 30 mL water; T=503 K and 20% SO₄^2-/ZrO₂)

3.1.3 Effect of catalyst dosage

The amount of catalyst plays an important role in the degradation of cellulose and preparation of HMF (see Fig. 3). The dosage of catalyst was manipulated in a range from 0 to 30% under conditions of reaction temperature 503 K and reaction time 90 min. The degradation of cellulose and the yield of HMF can be effectively facilitated with the increase of catalyst dosage from 0 to 25%. Afterwards, the conversion rate of cellulose almost levels off and the yield of HMF witnesses a descending trend (from 27% to 20%), demonstrating that the decomposition reaction can be accelerated by the addition of positive catalyst-SO₄^2-/ ZrO₂ and a shorter reaction time is needed for the preparation of HMF. With the excessive addition of SO₄^2-/ZrO₂ (over 25%), the yield of HMF reachs the maximum value within 90 min and HMF may be decomposed or polymerized into other substances after 90 min, resulting in the decline of the yield of HMF [26, 39-41]. Therefore, the optimal dosage of SO₄^2-/ZrO₂ is 25%, under which a maximum yield of 26.5% could be obtained for the preparation of HMF.

Fig. 3 Effect of catalyst dosage on conversion rate of cellulose and yield of HMF (1.000 g wasted cotton stalk in 30 mL water; T=503 K and t= 90 min)

3.1.4 Orthogonal experiment

Then three-factor (i.e. reaction temperature, reaction time and amount of catalyst) and three-level orthogonal experiment was conducted to obtain the maximum yield of HMF. It can be concluded from Table 1 that a maximum yield of 27.2% can be obtained at experimental conditions of reaction temperature 503 K, reaction time 75 min and amount of catalyst 30%, which is also approximate to the results of single factorexperiments.

Table 1 Results of three factors-three levels orthogonal experiment designed

3.1.5 Regeneration of SO₄^2-/ZrO₂ catalyst

It is important for the reutilization of SO₄^2-/ZrO₂ catalyst to meet the rigorous requirement of green and sustainable chemistry for the practical production of HMF. Therefore, the regeneration experiments and recycling tests were carried out for the regenerated catalyst. At first, the catalyst was recovered by simple suction filtration using a Hirsch funnel with the mixture products as follows: diluting with deionized water after the first reaction, washing them several times with methanol and drying at 40 ^oC for 20 h in a vacuum oven. Then, the recovered SO₄^2-/ZrO₂ was reused as catalyst for the preparation of HMF from cycle 1 to cycle 4 under the optimized reaction conditions. As reflected in Fig. 4, the yields of HMF (from cycle 1 to cycle 4) are 27.2%, 26.2%, 25.9% and 25.4%, respectively. A slightly reduced trend can be discovered from cycle 1 to cycle 4, which may be attributed to the formation of by-products on catalytic centers and the insufficient washing of methanol (this may prevent the accessibility of new reactant molecules to the catalyst acid sites). However, SO₄^2-/ZrO₂ still presents good activity after 4 cycles, indicating that the catalyst possesses a rigid structure and stable acidic active sites.

Fig. 4 Reusability of SO₄^2-/ZrO₂ catalyst in degradation of waste cotton stalk into HMF under optimized conditions: 1.000 g wasted cotton stalk in 30 mL water, T=503 K, t=90 min and 25% SO₄^2-/ZrO₂

In conclusion, it can be concluded according to above experiments that SO₄^2-/ZrO₂ presents positive catalytic effect on the degradation of cellulose and HMF preparation. The degradation rate of cellulose would be beneficial by higher temperature, extending of reaction time and larger SO₄^2-/ZrO₂ dosage. The maximum yield of HMF can be achieved under reaction temperature 503 K, reaction time 90 min and catalyst dosage 25%. The degradation rate of cellulose and the yield of HMF are 95.5% and 26.5% under the optimized conditions. A similar yield of HMF could be achieved as investigated by KUO et al [39] by hydrothermal conversion of cellulose using mesoporous zirconia nanoparticles in different ionic liquid systems. And the yield of HMF in this study is superior to the results investigated by HSU et al [40] and PENG et al [41] in (EMIM)Cl-based systems. However, this work may promise a preferable alternative for the industrialized application due to the superiorities of SO₄^2-/ZrO₂ in terms of catalyst recovery and regeneration, high tolerance, relatively low price etc.

3.2 Reaction kinetics

As reflected in Fig. 5, HMF can be obtained from the degradation of cellulose and semi-cellulose contained in waste cotton stalk. Cellulose and semi-cellulose will be firstly degraded into reducing sugar and then the reducing sugar can be decomposed into HMF and other byproducts. The obtained HMF can be further hydrolyzed into other byproducts such as LA, formic acid. According to the relevant references [36, 37, 42], the following proposed hypotheses are settled for the kinetics study of the decomposition reactions:

1) Minor byproducts are ignored and only the major products and by-products (including reducing sugar, HMF, LA, humins) are considered during the decomposition reactions;

2) The reaction rate constant (k) is only a function of temperature, ignoring the effect of the H⁺ concentration in aqueous phase of high temperature [43];

3) All the degradation reactions are assumed as pseudo-homogeneous first order irreversible reactions;

4) The concentration of reducing sugar is calculated according to the concentration of glucose.

Fig. 5 Relative degradation reactions concerning degradation of waste cotton stalk

According to the above assumptions, the first step of cellulose degradation to reducing sugar is an irreversible reaction. Then, reducing sugar is simultaneously decomposed to HMF and other main byproducts. The parallel reaction model can be applied to the decomposition reaction of reducing sugar and the reaction rate equations are listed as follows (Eq. (5)-Eq. (7)):

(5)

(6)

       (7)

where k₁, k₂, k₃ and k₄ are the reaction rate constants of the corresponding step (see Fig. 5); t is the reaction time; r_cellulose, r_{reducing sugar} and r_HMF are the corresponding reaction rates; X_cellulose is the degradation rate of cellulose; C_{reducing sugar} and C_HMF are the concentrations of reducing sugar and HMF; m and V are the initial mass of cellulose and the volume of solvent, respectively.

Little LA was detected according to the analysis results of HPLC. Therefore, we assume k₄≈0. The following equations (Eq. (8)-Eq. (10)) could be derived after the integrating the above equations (Eq. (5)-Eq. (7)).

                    (8)

                       (9)

          (10)

where t is the reaction time; X is the degradation rate of cellulose; C₀, C_glucose and C_HMF are the initial concentration of reducing sugar, the concentration of glucose and the concentration of HMF after degradation, respectively; k₁, k₂ and k₃ are the corresponding reaction rate constants.

The initial concentration of reducing sugar (C₀) can be obtained by measuring the conversion rate of cellulose. One cellulose molecule can generate 10/9 reducing sugar molecules during the degradation reaction. Thus k₁, k₂ and k₃ can be calculated according to the initial concentration of reducing sugar and the concentration of reducing sugar. The activation energy and Arrhenius constant can be obtained through the linear fitting of the k values at various temperatures by Arrhenius equation (Eq. (11)–Eq. (12)).

                            (11)

                            (12)

where k is the reaction rate constant; A, E_a and R are pre-exponential factor, apparent activation energy and molar gas constant, respectively.

According to the experimental results, k₁, k₂+k₃, and k₂ could be calculated from Eq. (8), Eq. (9) and Eq. (10), respectively. Then, k₃ can be also derived by the substituting k₂ from (k₂+k₃). Figures 6, 7 and 8 illustrate the different plots for the calculation of k₁, k₂+k₃, and k₂ through linear fitting. And the relevant linear fitting results are presented in Table 2 with or without the presence of SO₄^2-/ZrO₂. It can be concluded from Table 2 that both k₁ and k₂ experience a steady increase with the increase of reaction temperature with and without SO₄^2-/ZrO₂. However, the fitting results of k₃ indicate an opposite tendency with the increase of temperature. Besides, the value of k₃ with the presence of catalyst is lower than that without catalyst when the reaction temperature is over 493 K. The above analysis results can further demonstrate that the hydrolysis of cellulose and reducing sugar to HMF will be promoted by the increasing reaction temperature and the yield of other byproducts may be also discouraged and prevented by the increase of temperature.

Fig. 6 Rate constant (k₁) of degradation of cellulose to reducing sugar at different temperatures with or without catalyst based on Eq. (8)

Fig. 7 Total reaction rate constant (k₂+k₃) of decomposition of reducing sugar to HMF and byproducts at different temperatures with or without catalyst according to Eq. (9)

Fig. 8 Rate constant (k₂) at different temperatures with or without catalyst based on Eq. (10)

Table 2 Values of reaction rate constants k₁, k₂ and k₃ and goodness of fit (R²) between experimental data and kinetic model

Equations (13)-(16) are kinetics equations of hydrothermal synthesis of HMF from waste cotton stalk. Without the presence of SO₄^2-/ZrO₂, the kinetics equations of the degradation of cellulose and reducing sugar can be expressed as Eq. (13) and Eq. (14). And the degree of linear fitness of Eq. (13) (~0.98) is superior to that of Eq. (14) (~0.92).

                  (13)

                  (14)

Equations (15) and (16) show the hydrolysis of cellulose and reducing sugar for the preparation of HMF in the presence of catalyst-SO₄^2-/ZrO₂. The degree of linear fitness of Eq. (15) is 0.99 and the degree of linear fitness of Eq. (16) is 0.95.

                  (15)

                   (16)

It can be obtained from Eqs. (13) and (14) that activation energies for the hydrolysis of cellulose and reducing sugar remain at the similar level (105.96 kJ/mol and 119.37 kJ/mol) without catalyst. According to Eqs. (15) and (16), the reaction activation energies for cellulose degradation and reducing sugar degradation will obviously decline with the addition of SO₄^2-/ZrO₂. The reason for the remarkable decline of activation energy may be that ZrO₂ is an alkaline compound which presents a positive catalytic effect on isomerization of reducing sugar [31, 38, 40]. The yield of HMF can be also benefited from the enhanced degradation rate of reducing sugar by the addition of SO₄^2-/ZrO₂. Furthermore, SO₄^2- loaded ZrO₂ is a solid super acid and the degradation of cellulose into reducing sugar can be accelerated even under high acidic condition.

3.3 Evaluation of synthesis process

A sustainable process was developed for the synthesis of HMF from waste cotton stalk. The solid super acid-SO₄^2-/ZrO₂ was employed as an efficient catalyst for the hydrolysis and dehydration reactions. HMF was successfully prepared by a hydrothermal method from the waste cotton stalk with a maximum yield of 27.2%. This sustainable degradation process may promise a candidate for industrialized application with the following advantages:

1) Compared to other processes investigated [7, 10, 21], this synthetic process presents a maximum HMF yield of 27.2% and a maximum cellulose degradation rate of 95.5%;

2) Renewable waste cotton stalk was employed for the preparation of HMF, indicating a significant reduce on cost and a prospective environmental benefit over other synthetic process using pure chemicals [2, 4, 10, 15-18, 26, 30, 39].

3) Solid super acid-SO₄^2-/ZrO₂ employed presents excellent catalytic performance and the repeated usage of this catalyst would not also discourage the catalytic performance for the preparation of HMF. Furthermore, the solid catalyst reveals superiorities in terms of catalyst recovery, the separation of catalyst and products etc. [9, 10, 12, 13, 38, 39].

4 Conclusions

A sustainable and effective process was proposed for the preparation of HMF by catalytic degradation of waste cotton stalk. According to experimental results, the degradation rate of cellulose can be effectively accelerated by the addition of SO₄^2-/ZrO₂. And the optimized experimental conditions for the preparation of HMF are reaction temperature 503 K, reaction time 75 min and the catalyst dosage 30%, under which a desired degradation rate of cellulose (95.5%) and a maximum yield of HMF (27.2%) can be achieved. Kinetic study indicates that the decomposition of cellulose and the yield of HMF are facilitated using SO₄^2-/ZrO₂. The activation energies for the degradation of cellulose and reducing sugar decrease from 105.96 kJ/mol and 119.37 kJ/mol to 96.71 kJ/mol and 84.21 kJ/mol with the addition of SO₄^2-/ZrO₂, which further demonstrated the positive catalytic effect of SO₄^2-/ZrO₂ on the preparation of HMF from waste cotton stalk.

References

[1] CHHEDA J N, HUBER G W, DUMESIC J A. Liquid-phase catalytic processing of biomass-derived oxygenated hydrocarbons to fuels and chemicals [J]. Angewandte Chemie International Edition, 2007, 46(38): 7164-7183.

[2] MATSUMIYA H, HARA T. Conversion of glucose into 5-hydroxymethylfurfural with boric acid in moltenmixtures of choline salts and carboxylic acids [J]. Biomass & Bioenergy, 2015, 72: 227-232.

[3] YANG F L, LIU Q S, BAI X F, DU Y G. Conversion of biomass into 5-hydroxymethylfurfural using solid acid catalyst [J]. Bioresource Technology, 2011, 102: 3424-3429.

[4] ZHANG Y L, PAN J M, YAN Y S, SHI W D, YU L B. Synthesis and evaluation of stable polymeric solid acid based on halloysite nanotubes for conversion of one-pot cellulose to 5-hydroxymethylfurfural [J]. RSC Advances, 2014, 4: 23797-23806.

[5] SAHA B, ABU-OMAR M M. Advances in 5-hydroxymethylfurfural production from biomass in biphasic solvents [J]. Green Chemistry, 2014, 16: 24-38.

[6] GAO L C, DENG K J, ZHENG J D, LIU B, ZHANG Z H. Efficient oxidation of biomass derived 5-hydroxymethylfurfuralinto 2,5-furandicarboxylic acid catalyzed by Merrifield resin supported cobalt porphyrin [J]. Chemical Engineering Journal, 2015, 270: 444-449.

[7] CHHEDA J N, DUMESIC J A. Production of 5-hydroxymethylfurfural and furfural by dehydration of biomass-derived mono- and poly-saccharides [J]. Green Chemistry, 2007, 9(4): 342-350.

[8] TONG X L, MA Y, LI Y D. Biomass into chemicals: Conversion of sugars to furan derivatives by catalytic processes [J]. Applied Catalysis A: General, 2010, 385: 1-13.

[9] GIRREZABAL-TELLERIA I, GANDARIAS I, ARIAS P. Heterogeneous acid-catalysts for the production of furan- derivedcompounds (furfural and hydroxymethylfurfural) from renewable carbohydrates: A review [J]. Catalysis Today, 2014, 234: 42-58.

[10] OHARA M, TAKAGAKI A, NISHIMURA S, EBITANI K. Syntheses of 5-hydroxymethyl furfural and levoglucosan by selective dehydration of glucose using solid acid and base catalysts [J]. Applied Catalysis A: General, 2010, 383: 149-155.

[11] REN H F, GIRISUTA B, ZHOU Y G, LIU L. Selective and recyclable depolymerization of cellulose to levulinicacid catalyzed by acidic ionic liquid [J]. Carbohydrate Polymers, 2015, 117: 569-576.

[12] ZU Y H, YANG P P, WANG J J, LIU X H, REN J W, LU G Z, WANG Y Q. Efficient production of the liquid fuel 2,5-dimethylfuran from5-hydroxymethylfurfural over Ru/Co₃O₄ catalyst [J]. Applied Catalysis B: Environmental, 2014, 146: 244-248.

[13] YADAV G D, SHARMA R V. Biomass derived chemicals: Environmentally benign process foroxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran by using nano-fibrous Ag-OMS-2-catalyst [J]. Applied Catalysis B: Environmental, 2014, 147: 293-301.

[14] I, MORENO-RECIO M, - A. Mesoporous tantalum oxide as catalyst for dehydration of glucose to 5-hydroxymethylfurfural [J]. Applied Catalysis B: Environmental, 2014, 154-155: 190-196.

[15] SHEN Y, SUN J K, YI Y X, WANG B, XU F, SUN R C. 5-Hydroxymethylfurfural and levulinic acid derived from monosaccharides dehydration promoted by InCl₃ in aqueous medium [J]. Journal of Molecular Catalysis A: Chemical, 2014, 394: 114-120.

[16] HU L, WU Z, XU J X, SUN Y, LIN L, LIU S J. Zeolite-promoted transformation of glucose into 5-hydroxymethylfurfural in ionic liquid [J]. Chemical Engineering Journal, 2014, 244: 137-144.

[17] JIA S Y, XU Z W, ZHANG Z C. Catalytic conversion of glucose in dimethylsulfoxide/water binary mix with chromium trichloride: Role of water on the product distribution [J]. Chemical Engineering Journal, 2014, 254: 333-339.

[18] HU L, TANG X, WU Z, LIN L, XU J X, XU N, DAI B L. Magnetic lignin-derived carbonaceous catalyst for the dehydration of fructose into 5-hydroxymethylfurfural in dimethylsulfoxide [J]. Chemical Engineering Journal, 2015, 263: 299-308.

[19] PEDERSEN A T, RINGBORG R, GROTKJAR T, PEDERSEN S, WOODLEY J M. Synthesis of 5-hydroxymethylfurfural (HMF) by acid catalyzed dehydration of glucose- fructose mixtures [J]. Chemical Engineering Journal, 2015, 273: 455-464.

[20] CARUSO T, VASCA E, Electrogenerated acid as an efficient catalyst for the preparation of 5-hydroxymethylfurfural [J]. Electrochemical Communications, 2010, 12: 1149-1153.

[21] TAKEUCHI Y, JIN F M. Acid catalytic hydrothermal conversion of carbohydrate biomass into useful substances [J]. Journal of Materials Science, 2008, 43(7): 2472-2475.

[22] MEDNICK M L. The Acid-Base-Catalyzed Conversion of Aldohexose into 5-(Hydroxymethyl) -2- furfural [J]. The Journal of Organic Chemistry, 1962, 27: 398-403.

[23] DUTTA S, PAL S. Promises in direct conversion of cellulose and lignocellulosic biomass to chemicals and fuels: Combined solventenanocatalysis approach for biorefinary [J]. Biomass & Bioenergy, 2014, 62: 182-197.

[24] SHEN Y, XU Y F, SUN J K, WANG B, XU F, SUN R C. Efficient conversion of monosaccharides into 5-hydroxymethylfurfural and levulinic acid in InCl₃-H₂Omedium [J]. Catalysis Communications, 2014, 50: 17-20.

[25] PUTTEN R J, WAAL J C, JONG E, RASRENDRA C B, HEERES H J, VRIES J G. Hydroxymethyl-furfural, a versatile platform chemical made from renewable resources [J]. Chemical Reviews, 2013, 113: 1499-1597.

[26] KIMURA H, NAKAHARA M, MATUBAYASI N. In situ kinetic study on hydrothermal transformation of D-glucose into 5-hydroxymethylfurfural through D-fructose with ¹³C NMR [J]. Journal of Physical Chemistry A, 2011, 115: 14013-14021.

[27] BICKER M, HIRTH J, VOGEL H. Dehydration of fructose to 5-hydroxymethylfurfural in suband supercritical acetone [J]. Green Chemistry, 2003, 5: 280-284.

[28] ROMA’N-LESHKOV Y, CHHEDA J N, DUMESIC J A. Phase modifiers promote efficient production of hydroxymethylfurfural from fructose [J]. Science, 2006, 312: 1933-1937.

[29] TUERCKE T, PANIC S, LOEBBECKE S. Microreactor process for the optimized synthesis of 5-Hydroxymethylfurfural: A promising building block obtained by catalytic dehydration of fructose [J]. Chemical Engineering & Technology, 2009, 32: 1815-1822.

[30] TONG X L, MA Y, LI Y D. An efficient catalytic dehydration of fructose and sucrose to 5-hydroxymethylfurfural with protic ionic liquids [J]. Carbohydrate Research, 2010, 345: 1698-1701.

[31] ZHOU L L, HE Y M, MA Z W, LIANG R J, WU T H, WU Y. One-step degradation of cellulose to 5-hydroxymethylfurfural in ionic liquid under mild conditions [J]. Carbohydrate Polymers, 2015, 117: 694-700.

[32] WEI Z J, LI Y, THUSHARA D, LIU Y X, REN Q L. Novel dehydration of carbohydrates to 5-hydroxymethylfurfural catalyzed by Ir and Au chlorides in ionic liquids [J]. Journal of the Taiwan Institute of Chemical Engineers, 2011, 42: 363-370.

[33] BINDER J B, RAINES R T. Simple chemical transformation of lignocellulosic biomass into furans for fuels and chemicals [J]. Journal of the American Chemical Society, 2009, 131(5): 1979-1985.

[34] QI X H, WATANABE M, AIDA T M, SMITH R L. Efficient catalytic conversion of fructose into 5-Hydroxymethylfurfural in ionic liquids at room temperature [J]. Chem Sus Chem, 2009, 2: 944-946.

[35] QI X H, WATANABE M, AIDA T M, SMITH R L. Catalytic dehydration of fructose into 5-hydroxymethylfurfural by ion- exchange resin in mixed-aqueous system by microwave heating [J]. Green Chemistry, 2008, 10: 799-805.

[36] HELLE S, BENNETT N M, LAU K, MATSUI J, DULL S. A kinetic model for production of glucose by hydrolysis of levoglucosan and cellobiosan from pyrolysis oil [J]. Carbohydrate Research, 2007, 342: 2365-2370.

[37] MOREAU C, DURAND R, RAZIGADE S, DUHAMET J, FAUGERAS P, RIVALIER P, ROS P, AVIGNON G. Dehydration of fructose to 5-hydroxymethylfurfural over H-mordenites [J]. Applied Catalysis A: General, 1996, 145(1, 2): 211-224.

[38] YAN L L, LIU N, WANG Y, MACHIDA H, QI X H. Production of 5-hydroxymethylfurfural from corn stalk catalyzed by corn stalk-derived carbonaceous solid acid catalyst [J]. Bioresource Technology, 2014, 173: 462-466.

[39] KUO I J, SUZUKI N, YAMAUCHI Y, WU K C W. Cellulose-to- HMF conversion using crystalline mesoporous titania and zirconia nanocatalysts in ionic liquid systems [J]. RSC Advances, 2013, 3: 2028-2034.

[40] HSU W H, LEE Y Y, PENG W H, WU K C W. Cellulosic conversion in ionic liquids (ILs): Effects of H₂O/cellulose molar ratios, temperatures, times, and different ILs on the production of monosaccharides and 5-hydroxymethylfurfural (HMF) [J]. Catalysis Today, 2011, 174: 65-69.

[41] PENG W H, LEE Y Y, WU C, WU K C W. Acid–base bi-functionalized, large-pored mesoporous silica nanoparticles for cooperative catalysis of one-pot cellulose-to-HMF conversion [J]. Journal of Materials Chemistry, 2012, 22: 23181-23185.

[42] OROZCO A, AHMAD M, ROONEY D. Dilute acid hydrolysis of cellulose and cellulosic bio-waste using a microwave reactor system [J]. Process Safety and Environmental Protection, 2007, 85(B5): 446-449.

[43] AKIYA N, SAVAGE P E. Roles of water for chemical reactions in high-temperature water [J]. Chemical Reviews, 2002, 102(8): 2725-2750.

(Edited by YANG Hua)

Cite this article as: MO Hong-bing, CHEN Xiang-ping, LIAO Xiao-yan, ZHOU Tao. Sustainable synthesis of 5-hydroxymethylfurfural from waste cotton stalk catalyzed by solid superacid-SO₄^2-/ZrO₂ [J]. Journal of Central South University, 2017, 24(8): 1745-1753. DOI: https://doi.org/ 10.1007/s11771-017-3582-x.

Foundation item: Project(2010DFA41440) supported by China-Japan International Cooperation; Project(2016TP1007) supported by the Hunan Provincial Science and Technology Plan, China; Project(21376269) supported by the National Natural Science Foundation of China

Received date: 2016-04-29; Accepted date: 2016-10-06

Corresponding author: ZHOU Tao, Professor; Tel: +86-731-88876605; Fax: +86-731-88879616; E-mail: zhoutao@csu.edu.cn