| Cashew nut shell is a kind of solid residues during producing cashew nuts. At present, the yearly output of the cashew nut shell all over the world is up to 1400000 tons. Cashew nut shells are rich in cashew nut shell liquids. Extracting cashew nut shell liquid and then preparing cardanol to synthesis such products as polymer resins and surfactants, is the main current utilization approach of cashew nut shells. Cardanol, a kind of natural polymer biomass phenol, superior to phenols from petroleum in many properties, is predicted as one of the most promising raw materials to produce some high-end materials used in cars, boats, aerospace crafts, electronic chemicals, etc.Currently, the mechanical pressing is adopted to extract cashew nut shell liquids, and then preparing cardanol by pyrolysis and vacuum distillation sequencely in production. There are problems such as low yield of cashew nut shell liquid, low purity of cardanol, no effective utilization way of the residues after extracting, etc. Thus the raw material is wasted and the properties of downriver products will be influenced seriously.In view of this, the extraction & separation methods and their technology of cashew nut shell liquid, the preparation technology of activated carbon from the residues after extracting are studied in this dissertation. The technology system of utilizing cashew nut shells totally is established, proposed of such items as extraction of natural cashew nut shell liquid, pyrolysis of natural cashew nut shell liquid, separation of pyrolytic cashew nut shell liquid to prepare cardanol, and preparation of activated carbon from the residues after extracting.The main research results of the dissertation are as follows:1. The main chemical compositions of cashew nut shells are analyzed by the national standard methods or the industry standard methods.The content of the moisture, the ash, the organic extractive, the holocellulose, the acid insoluble lignin and the poly pentose in cashew nut shells is 11.76%,2.04%,34.81%, 30.61%,11.20% and 17.28%, respectively.2. The HPLC method for quantification of cardanol is established.The optimal HPLC detection conditions are as follows:LA-20AT HPLC Tnstrument, LC Solution Lite workstation, Ultimate XB-C18 column (4.6×250 mm,5μm), the composition of the mobile phase acetonitrile:water:acetic acid=80:20:1 (v/v/v), the flow rate of the mobile phase:1.8 mL/min, the column temperature:30 ℃, the detection wavelength:280 nm, the injection volume:15μL.3. The organic solvent extraction, the soxhlet extraction and the supercritical CO2 extraction are adopted to extract cashew nut shell liquilds, and their technology conditions are optimized and contrasted. The enhancement effects of microwave and ultrasonic on the extraction process are studied.(1) The optimal technology conditions for the extraction of cashew nut shell liquilds by the organic solvent extraction method with cyclohexane is obtained as follows: particle size of the raw material 10～40 mesh, extracting temperature 80℃, extracting time 1 h, solid-liquid ratio 1:4 g/mL. The average yield of cashew nut shell liquid is 28.63%.(2) The optimal technology conditions for the extraction of cashew nut shell liquild by the soxhlet extraction method with cyclohexane is obtained as follows:particle size of the raw material 10～40 mesh, reflux rate 4 h-1, extracting time 2 hs. The average yield of cashew nut shell liquid is 29.13%.(3) The optimal technology conditions for the extraction of cashew nut shell liquilds by the supercritical CO2 extraction method is obtained as follows:particle size of the raw material 10～40 mesh, extracting pressure 30 MPa, extracting temperature 60℃, extracting time 3 hs. The average yield of cashew nut shell liquid is 28.46%.(4) Both microwave and ultrasound can enhance the extraction of cashew nut shell liquild by the organic solvent extraction method with cyclohexane. When the similar extraction result is obtained, the microwave can shorten the extraction time for a half and the ultrasonic can decrease the extraction temperature for a half as other technology conditions are same.(5) The main components of the homemade cashew nut shell liquid are anacardic acid, cardanol and cardol. The content of anacardic acid in the cashew nut shell liquid by the supercritical CO2 extraction method is the highest.4. The pyrolysis technology at atmospheric pressure of cashew nut shell liquid and the catalysis effect of CaO-NaOH for the pyrolysis are studied.(1) The optimal technology conditions for the pyrolysis of cashew nut shell liquid at atmospheric pressure is obtained as follows:the pyrolysis temperature 180 ℃, the pyrolysis time 30 min. The average content of cardanol in the pyrolytic product is 67.21%.(2) Compared with non-catalytic pyrolysis, CaO-NaOH can decrease the decarboxylatio reaction temperature for 40℃.5. The separation technology of cardanol from the pyrolytic cashew nut shell liquid by the chemical method is studied.The optimal technology conditions for the separation of cardanol from the pyrolytic cashew nut shell liquid by the chemical method is obtained as follows:2 g of pyrolytic cashew nut shell liquid is dissolved in 20 mL of methanol, and thenadd 10 mL of ammonium hydroxide(25%, m/m) to the mixture. Stirring the mixture for 15 min at the room temperature. After removing the compound into a separatory funnel, extracting it with 10 mL of n-hexane, standing for some time. Washing the extract with enough 5% (m/m) HCl-H2O till the lower layer liquid is neutral. After recovering the solvent from the upper layer liquid, the residue is collected as the separation product.Under the optimal technology mentioned above, the average yield of the separation product is 57.67 and 64.66% from the cashew nut shell liquid in sale (content of cardanol: 77.51%) and the homemade cashew nut shell liquid (content of cardanol:67.21%), respectively. The content of cardanol in the two kinds of separation product mentioned above is up to 88.25% and 76.26%, respectively.6. The preparation technology of activated carbon from the solid residues after extracting the cashew nut shells by the chemical method assisted with microwave with ZnCl2-H2O is studied for the first time.The optimal preparation technology of activated carbon from the solid residues after extracting the cashew nut shells by the chemical method assisted with microwave with ZnCl2-H2O is obtained as follows:particle size of the raw material 10～40 mesh, the concentration of ZnCl2 50%(m/m), impregnation ratio 1:3.5 g/mL, activating temperature 225℃, activating time 65 min, impregnation time 12 h. Under the optimal technology mentioned above, the average yield of the activated carbon is up to 42%, and its iodine adsorption value, the methylthionine chlorideadsorption value and the caramel decolorization rate is 856.6 mg/g,150 mg/g and 75.35%, respectively. The activated carbon posses rich internal porosity with 950.02 m2/g of the specific surface area and abundant functional groups such as carboxyl, hydroxyl and ether, etc. |
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