Study On The Process And Models For Extraction Of Medicinal Ingredients From Radix Bupleuri With Supercritical CO₂

Radix Bupleuri is widely used in traditional Chinese medicine, in which volatile oils and saikosaponins(SS) are considered as two major bioactive components. Volatile oils are described as anti-inflammatory and anti-pyretic agent. SS especially saikosaponin-a (SSa) and saikosaponin-d (SSd) have the functions of anti-inflammation, liver-protecting, reducing plasma-cholesterol, immunoregulatory and anti-cancer. Traditional extraction methods of volatile oils and SS may result in thermal degradation of them because of long extraction time or high extraction temperature. With the modernization and internationalization of Traditional Chinese medicine has become a very hot topic in China, it is of great importance to investigate the feasibility of supercritical fluid extraction (SFE) of volatile oils and SS with CO2, which is considered as high effective and clean separation technology.The process of extraction of volatile oils with SC-CO2 was firstly studied with lab-scale extraction apparatus. The absorbance and yield of the volatile oils were two main indexes for process control. The influences of particle size, flow rate and amount of CO2, extraction temperature and extraction pressure on the absorbance and yield were investigated. Experimental results show that under the conditions of extraction temperature of 50℃, extraction pressure ranging from 15-20MPa, CO2 flow rate of 1.5L/min with amount of 20L/g, the absorbance of volatile oils is 0.664-0.682, which is higher than the specified value of 0.625. The yield of valotile oils is 8 to 10 times of the specified value (>0.28%). The absorbance of valotile oils extracted with 5L extraction apparatus is 6% lower than that of the valotile oils extracted with lab-scale extraction apparatus, but still higher than the specified value, indicating that the experimental results can be successfully scaled up. Comparison between traditional steam distillation and SFE was made. The yield of valotile oils extracted with SC-CO2 is 5 times of that extracted with steam distillation. The chemical components of volatile oils obtained by these two methods also differed. Thirty-three components in the volatile oils were identified by GC–MS. The influences of different batch of herbs of radix bupleuri on the extraction yield, the absorbance and chemical components of the volatile oils were also compared and discussed.Extraction of SS from the residues of extraction of volatile oils with SC-CO2 was further investigated, in which ethanol-water solution was used as co-solvent. Three kinds of methods for adding co-solvent were studied, which include adding the co-solvent to the residues in static mode, adding the co-solvent to SC-CO2 in flowing mode and combination of these two modes. The effect of ethanol concentration and amount of the co-solvent used, extraction temperature and extraction pressure on the recovery ratios of the total extractives, SSa and SSd as well as the contents of SSa and SSd in the extractives were investigated, and the optimum conditions were obtained. Experimental results show that when 95% of ethanol liquor solution was added in flowing mode to CO2 with amount of 12ml/g residues, and the extraction temperature was 60℃, extraction pressure was 30MPa, the recovery ratios of the total extractives, SSa and SSd are 67.73%, 156.87% and 74.5%, respectively. The contents of SSa snd SSd in the extractives are 15.44mg/g and 14.68mg/g, respectively. Compared with the current used production method of water extraction followed by ethanol precipitation(WEEP), The time extracted with SC-CO2 and ethanol-water solution is shorter than half of the time extracted with WEEP, but the yield of the extract obtained with SC-CO2 in the presence of co-solvent is 50% higher than that extracted with WEEP. The content of SSa in the extractive is 3.2 time of that extracted with WEEP. Moreover, the special advantage of SFE is that it can effectively avoid thermal-degradation of SSd compared with no SSd could be detected in the extractive with WEEP.Lumped capacity method model (LCMM) was firstly found to simulate the process of extraction of volatile oils with SC-CO2 and the mass transfer coefficients were also calculated. The comparison between lumped capacity method model, empirical model (one and two parameters) and differential mass balance model(SM I and SM II) was also made. Simulating results show that empirical model with two parameters, differential mass balance model and LCMM with two parameters give satisfactory results. The average relative errors of empirical model with two parameters, differential mass balance model and lumped capacity method model are ranging from 1.67% to 9.90%, 1.06% to 7.44% and 1.98% to 7.89%, respectively. Mass transfer coefficients increase with the increasing pressure.