Furfural acid is prepared from furfural as raw material, and in the presence of strong alkali medium and catalyst, furfural can be oxidized by air and acidified with sulfuric acid. However, a large amount of furfuryl alcohol is produced in the reaction. Therefore, it is of great significance to accurately determine the content of furfuric acid, furfuryl alcohol and furfural in the reaction solution and products to optimize the reaction conditions, monitor the production process and ensure product quality. Reversed-phase high-performance liquid chromatography was used to simultaneously separate and determine furfural, furfuryl alcohol and furfural. The method is simple, fast, sensitive, and accurate.
1.Experimental part of the instruments and reagents: The high-performance liquid chromatograph system includes a vacuum degasser, a quaternion pump, a diode array detector, an automatic sampler, and a chemical workstation for the liquid chromatograph system. Ultraviolet-visible spectrophotometer, digital precision electronic meter. Methanol is a special reagent for high performance liquid chromatography, the other reagents are analytically pure, and the experimental water is ultrapure water.
2) Chromatographic conditions: Column C18 (250mm, 4.)6 mM, 5 μm), mobile phase methanol 2 water (adjust to pH 4 with dilute sulfuric acid).0) (volume ratio 20:80), flow rate 10 ml.min, detection wavelength 220 nm, column greenhouse temperature, injection volume 10 microl.
3) Preparation of standard solution: 50mg of citric acid, decanol and furfural standard solution were accurately weighed, dissolved and diluted to 50ml with mobile phase to obtain 1g l of standard stock solution, which was stored at 4.
4) Sample Handling: The furfuric acid product is accurately called furanoic acid, which is dissolved in mobile phase and diluted to the desired concentration. Accurately take a certain amount of reaction solution and acidify it to pH 4 with dilute sulfuric acid0, and then mix with mobile phase and dilute to the desired concentration. Samples were sampled with 0A 45um filter filters and injects.
2 Results and discussed under optimal experimental conditions, all three components in the mixed standard solution were fully separated within 10 minutes. The HPLC is shown in Figure 1.
Figure 1: Chromatographic separation of mixed standards. furanoic acid; 2.furfuryl alcohol; 3.Selection of furfural detection wavelengths. The maximum absorption wavelengths of furfuric acid, furfural and furfural were determined by UV-Vis spectrophotometer at 242218 nm and 274 nm, respectively. At 274 nm, the absorption of channel acids and furfuryl alcohol is small, and at 220 nm the absorption of furfural and groove acids is larger. In the reaction solution, furfural is almost completely reacted and does not contain furfural. Since the detection of furfuric acid and furfuryl alcohol was mainly performed in this experiment, 220 nm was chosen as the detection wavelength.
2.After the selection experiment of 2 mobile phases, the methanol 2 water system was selected as the mobile phase to achieve the separation purpose. When the mobile phase flow rate is set to 1At 0 ml min, a change in the ratio of methanol to the mobile phase was observed. As the proportion of methanol increases, the retention time of each component decreases. When the volume fraction of methanol is greater than 30, the peaks are not fully resolved. When it is less than 10%, the peak time is too long, the peak shape is not good, and when the methanol volume fraction is 20%, the peak time is ideally separated. Finish.
The pH of the mobile phase was adjusted by dilute sulfuric acid, and the effects of furfuric acid, furfuryl alcohol and furfural at 25-7.0 conditions of separation. When the pH value is less than 3At 0, the peaks of furfural and furfural overlapped. When the pH value is 5At 0, the peaks of furfuryl alcohol and furfural partially overlapped. When the pH is 60-7.At 0, the peak separation is good, but the column efficiency is low, the peak shape is not good, and the retention time is short. It's long. When the pH value is 35-4.At 5 o'clock, the three components were fully separated, and the peak shape was symmetrical. 4pH of 0.
2.3. Using the mobile phase as the solvent, an appropriate number of stock liquids of each group were taken from the standard curve and linear range respectively, and a series of standard solutions with different mass concentrations were prepared, and each standard solution was analyzed in turn according to the above chromatographic conditions. The linear regression with mass concentration c(mg l) as the abscissa and peak area a as the ordinate showed that there was a good relationship between the strands of each group. The linear range of sulfuric acid, furan, and furan is ., respectively06～200 mg/l。The correlation coefficients are all greater than 09998, and the detection limits (n=3) are ., respectively010 and 0310 mg/l。
The relative standard deviations of furfuric acid, furfuryl alcohol and furfural were ., respectively10 and 082％。The relative standard deviations of furfuric acid, furfuryl alcohol and furfural were ., respectively10 and 082％。The standard accession method** rate is 978％≤100.8％。
2.5. Sample analysis: This method is used for the analysis of tannic acid products prepared by catalytic oxidation using furfural as raw material. The content of tannic acid in the product is 993％。In order to grasp the progress of the reaction in production, optimize the reaction conditions, control the conversion rate, and improve the yield of tannins, the solution after furfural oxidation (not yet acidified) was also determined, and tannic acid and decanool were determined. The mass concentrations were 16396 and 5978 mg / l;Their mass concentrations in acidified solutions are 32., respectively22 and 2919 mg / l;The mass concentration in the destaining solution was 2252 and 166mg / l.This method can be used to analyze and monitor the preparation process of tannic acid industry.