Study On The Preparation Of L-menthol

L-menthol is one of the monomer raw materials with the largest sales volume in the fragrance industry.L-menthol has a wide range of applications in daily necessities,fine chemicals,flavors,medical and health care and food industries,with its unique properties.At present,L-menthol is mainly derived from the extraction of essential oils from natural mint-like plants,however,the cultivation of mint is affected by a variety of factors such as weather and soil,which affect the yield and quality of menthol.In order to ensure the supply of L-menthol,organic synthesis technology has been applied to the preparation of L-menthol.China is a big consumer of L-menthol,but the output of L-menthol is small and the source is single(planting).There is no L-menthol manufacturer in China,natural L-menthol is mainly derived from India and synthetic L-menthol.L-menthol is mainly sourced from Dezinco products.With the growing local market requirement for L-menthol,it is particularly necessary to independently develop a method for preparing L-menthol.In this thesis,thymol is used as raw material,which is cheap and easily available,and L-menthol is prepared by catalytic hydrogenation through a self-developed catalyst.Firstly,this paper begins with the development of a catalyst for the catalytic hydrogenation of thymol,that is,the support,metal salt and metal loading of the catalyst for the catalytic hydrogenation of thymol.The results of the study show that the best catalytic performance was obtained for a Co/Ti O₂ composite catalyst with cobalt acetate as the metal salt,titanium dioxide as the carrier and a metal loading of 10%wt.The home-made catalysts were also characterised and confirmed by XRD,TEM and other tests.Secondly,the reaction conditions for the thymol hydrogenation reaction were investigated.The results were:the substrate thymol was 0.5 g,the catalyst was a Co/Ti O₂ catalyst with a loading of 10%wt(amount 0.06 g),cyclohexane 20 m L was used as the solvent,and the reaction was carried out in an autoclave,and the optimum reaction conditions were:temperature 160°C,pressure 5 MPa and time 8 hours.The conversion of thymol reached 97.8%and the content of D,L-menthol in the product was74.2%and D,L-isomenthol was only 1.1%.Lastly,the recycling of the catalyst was investigated.The results of the study were that the catalyst still maintained a high catalytic activity after seven cycles,and by comparing the XRD plots before and after the reaction,it was found that only the intensity of the corresponding diffraction peaks decreased,and the physical phases of both titanium dioxide and metallic cobalt remained unchanged,indicating that the catalyst was stable during the reaction,although the catalytic activity of the catalyst decreased.