Synthesis of Bamboo Derived Sulfonated Solid Acid Catalyst for the Hydrolysis of Cellulose and Epoxidation of Cottonseed Oil

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Addis Ababa University


Nowadays the use of biomass derived sulfonated catalyst in the place of mineral acid becomes a hot research spot. Biomass derived catalysts own multiple quality regards to environment, reuse of catalyst and in facilitating down-stream process. In this work, bamboo derived sulfonated catalysts were prepared with consecutive carbonization and sulfonation process. The synthesized catalysts were characterized and its activity was evaluated through cellulose hydrolysis and epoxidation of cottonseed oil. The catalyst was prepared through carbonization of bamboo saw-dust at three different temperatures; 400 °C, 450 °C, and 500 °C and then sulfonated using concentrated sulfuric acid (> 96 %), at 150 °C temperature for 15 h. The synthesized catalyst was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), elemental analysis, thermogravimetric analysis (TGA) coupled with mass spectrophotometer, ammonia temperature-programmed desorption (TPD), total acid content (titration method), and surface area analyzer (surface area, total pore volume, and pore size). The FTIR spectroscopy result of the catalyst indicated a sulfonate group (-SO3H) which was not found in the respective char of the catalyst. Moreover, elemental analysis of the catalyst showed significant amount of elemental sulfur in the catalyst. The acid content analysis revealed maximum amount of acid density (0.58 mmol/g) in the catalyst which its char was prepared at 500°C. The catalyst activity was primarily studied in the hydrolysis of crystalline cellulose. The hydrolysis was performed using autoclave reactor with varying hydrolysis temperature and time. The final product for total reducing sugars were analyzed using dinitro salicylic acid (DNS) method. From this study, the highest of total reducing sugar yield was found (4.0 %) at a temperature of 150 °C over a hydrolysis period of 8 h. The reuse capacity of the catalyst was tested in three successive hydrolysis reactions and the results showed that the catalyst maintain its activity in each hydrolysis reaction. The catalyst activity was further studied using microwave reactor in the hydrolysis of crystalline cellulose. The converted cellulose and glucose yield after the hydrolysis were analyzed by total organic carbon (TOC) analyzer and high performance liquid chromatography (HPLC). The combined effects of the synthesized catalyst and microwave reactor in crystalline cellulose hydrolysis resulted higher glucose yield. The effects of the synthesized catalyst on the hydrolysis of crystalline cellulose was studied with varying operating temperature and time. The maximum yield of glucose was found 43.5 % at a reaction temperature of 180°C and 60 minute of reaction time. Similar conversion and glucose yield were attained in second run showing the reusable potential of the synthesized catalyst. Cellulose hydrolysis operating condition optimization was performed using response surface methodology. Three-factor and three- level Box-Behnken design was employed to study the effects of hydrolysis temperature, hydrolysis time and catalyst to substrate ratio on total converted cellulose and glucose yield. Additionally, prior to the hydrolysis took place, the crystalline cellulose was milled using vibrational mill. The XRD result of the milled cellulose showed that vibrational milling could decrease the crystallinity index from 96.4 % to 59.55 % and the crystallite size from 3.61 nm to 2.09 nm within 60 min milling time. The result of optimization revealed both response best explained in quadratic model. The respective analysis of variance (ANOVA) showed that the proposed quadratic models could be used to navigate the design space. The optimum hydrolysis conditions were found out to be hydrolysis temperature of 175 °C, hydrolysis time of 74 minutes and catalyst to substrate ratio of 1.25 g/g. Under these conditions the total amount of converted cellulose and glucose yield were 79.4% and 61.1%, respectively. Model validation was performed at the given operating conditions. A cellulose conversion of 78.5 ± 0.75 and glucose yield of 60.6 ± 0.4 were found. These results indicated that the predicted values were in a good agreement with the experimental results. In addition to running cellulose hydrolysis tests, the synthesized catalyst activity was tested in the epoxidation of cottonseed oil. Bamboo derived sulfonated catalyst (BSC) was used for all epoxidation reactions. The effects operating conditions such as: catalyst loading, epoxidation temperature, and amount of peroxide on the oxirane content were studied. In general, the results of relative percentage conversion of oxirane indicated that the given operating conditions significantly affected it. On the other hand, the maximum amount of relative percentage conversion of oxirane content 36.8 % was obtained at temperature of 60 °C, reaction time of 8 h, catalyst loading of 15 %, and mole ratio of hydrogen peroxide to double bond (DB) of the oil was 2.



Cottonseed Oil, Bamboo Derived Sulfonated Solid Acid Catalyst, Hydrolysis of Cellulose