Study On Lactic Acid Purification From Rhizopus Oryzae Broth Using Esterification-Hydrolysis Method

Lactic acid is an important organic acid which is widely used in food, chemical and pharmaceutical fields. Fermentation is the major method for production of L-lactic aicd, it is rather difficult to recovery lactic acid from broth due to its affinity to water, low volatility, easily to decompose at high temperature and tendency to self-polymerize. The recovery rate of lactic acid is low and the purity is not high.This paper focus on recovery of lactic acid from fermentation broth of Rhizopus oryzae, membrane filtration was used for separation of lactic acid and esterificaiton-hydrolysis method was employed for purification of lactic acid. The effects of operation conditions on the membrane flux, the esterificaiton of lactic acid with methanol and the hydrolysis of methyl lactate were investigated systematically, and the reactive distillation column for methyl lactate hydrolysis was conceptual designed, simulated and controlled using ASPEN PLUS. The main conclusions are as follows:1. Pretreatment of the broth, removal of the protection, residual sugar and color materials.The flocculation-sedimentation, acidolysis, ultrafiltration and nanofiltration were used for the recovery of lactic acid form broth. The content of protein was down to 44.26 mg·L^-1, and the residual sugar decreased to 75.64 mg·L^-1 after flocculation-sedimentation and acidolysis. The effects of operation pressure, temperature, and concentration of the solution on the membrane filtration were researched. Membrane flux of ultrafiltration and nanofiltration increased with pressure and temperature and decreased with concentration, the optimal operation parameters for ultrafiltration were 30³5℃, 0.8¹.0 MPa, and 30³5℃, 1.0 MPa for nanofiltration. The impurities were further removed by ultrafiltration after whtich the contents of protein and redidual sugar became 4.30 mg·L^-1 and 70.13 mg·L^-1, and the bivalent cation was partially retained. The nanofiltration process got rid off most bivalent cation, residual sugar and pigments, the protein was undetected and the content of residual sugar was 10.31 mg·L^-1 in the permeate of nanofiltration.2. Simultaneous determination of lactic acid and methyl lactate using reversed-phase high performance liquid chromatographic (RP-HPLC).The HPLC was equipped with Purospher STAR C18 reversed-phase column and diode array detector. The mobile phase was composed of 0.005 mol·L^-1 H₂SO₄ solution and chromatographically pure methanol (9:1, V/V) with flow rate of 1.0 ml·min^-1 and detection wavelength at 210 nm. The standard curve for lactic acid was Y=X/(6.28×10⁵)+0.0018, R²=0.9999, and the standard curve for methyl lactate was Y=X/(1.08×106)+0.0092, R²=0.9999. The recovery for lactic acid was 98.81¹01.65%, and the relative standard deviation(RSD) for lactic acid was1.280%. The recovery for methyl lactate was 98.72¹01.80%, and the RSD was 1.288%.3. Esterification of concentrated lactic acid(≥85%, w/v) with methanol catalyzed by strong acid cation exchange resins D001, and described by the pseudo-homogeneous model.(1) Esterification of concentrated lactic acid with methanol catalyzed by cation exchange resin D001 has been investigated. The influences of the catalyst type, catalyst size, the reaction temperature, catalyst loading and initial reactant molar ratio were studied in a stirred batch reactor. It was found that external mass transfer resistance was absent and internal mass transfer was not significant while the stirred speed between 400-900 rpm. The reaction rate has been found to increase with temperature and catalyst loading. A kinetic equation based on pseudo-homogeneous model for describing the reaction catalyzed by cation exchange resin was developed:The activation energy was 48.9 kJ·mol^-1, k₀ = 2586.3 mol^-1·L·min^-1, k_w = 1352.8 mol^-1·g^-1·L²Â·min^-1, K_e=1.1151, the mean relative deviation was 2.12.(2) Esterification of lactic acid with methanol in fixed bed loaded with D001 resins was researched, The conversion ratio increased and reached equilibrium with the decreasing of feeding rate. The reaction rate raised and the equilibrium conversion ratio kept the same while the reaction temperature rising. The equilibrium conversion ratio increased in lessened degree with the initial methanol/lactic acid molar ratio increasing. The optimal condition for esterfication in fixed bed was 343 K with methanol/lactic acid molar ratio 4:1. The reaction rate data were correlated with a kinetic model based on pseudo-homogeneous catalysis, the activation energy of the reaction was found to be 33.8 kJ·mol^-1. The mean relative deviation was 2.74.4. Hydrolysis of methyl lactate catalyzed by strong acid cation exchange resins D001 and described by pseudo-homogeneous mode.(1) The kinetic of methyl lactate hydrolysis over cation exchange resin D001 was presented. The reaction rate has been found to increase with temperature and catalyst loading. The experimental data were correlated by pseudo-homogeneous model.The activation energy of the reaction was found to be 45.8 kJ·mol^-1 in the presence of D001, k₀ = 600.52 mol^-1·L·min^-1, k_w = 44.34 g^-1·mol^-1·L²Â·min^-1. The equilibriumconstant was found to be a weak function of the temperature because of the small value of the heat of the reaction, lnK_e=-(1291.4/T)+2.5543. The pseudohomogeneous model was found to represent the hydrolysis reaction over D001 fairly well, MRD was 2.03.(2) Hydrolysis of methyl lactate in fixed bed loaded with strong acid cation exchange resins was researched. The conversion ratio increased and reached equilibrium with the decreasing of feeding rate. The reaction rate raised while the reaction temperature rising. The equilibrium conversion ratio increased in lessened degree with the initial water/methyl lactate molar ratio increasing. The optimal condition for methyl lactate in fixed bed were 353 K with the water/methyl lactate molar ratio 10:1¹5:1. The reaction rate data were correlated with a kinetic model based on pseudo-homogeneous catalysis, the activation energy of the reaction was found to be 39.7 kJ·mol^-1, The mean relative deviation was 3.89.5. Hydrolysis of methyl lactate in the self assembled reactive distillation column, and purification of lactic acid form broth.(1) Methyl lactate was hydrolyzed in the self assembled reactive distillation column, and the experiment procedure was formulated. The effects of feed velocity, reboiler heat duty, feed temperature, reflux ratio, initial water/methyl lactate molar ratio on the distillation process were investigated. The conversion yield increased with catalyst loading and decreased with feeding velocity, the conversion yield first increased and then decreased with reboiler duty, initial water/methyl lacate molar ratio and reflux ratio. The conversion yield reached 98% in the reactive distillation column after a pre-hydrolysis using fixed bed. The optimal operation parameters for methyl lactate in RD were as follows: catalyst loading 30%, feed velocity mL·min^-1, reboiler heat duty 70 w, water/methyl lactate molar ratio 10:1, reflux ratio 3 and prehydrolysis.(2) Lactic acid was purificated from fermentation broth of Rhizopus oryzae. Theoretically, the recovery rate of lactic acid could reach 95% by the technology proposed in this paper, CaSO4 was the major discharge of the―three wastes‖. The final lactic acid product could satisfy the requirements of GB2023-2003.6. Conceptual design, dynamic simulating and control of the reactive distillation column for hydrolysis of methyl lactate.(1) Hydrolysis of methyl lactate using RD column was explored on Aspen Plus V7.0 RadFrac. The UNIFAC model was used for activity coefficients, and the vapor phase nonideality was calculated based on the dimerization of carboxylic acid as described by the Hayden-O'Conell second virial coefficient model. The reactive distillation column was designed based on the objective function total annual cost. The optimum reactive distillation column had 44 stages with 4 rectifying trays and 40 reaction trays that feed on the eighth tray, the total annual cost was 2.348 million RMB.(2) Sensitivity analyses were performed on this hydrolysis RD process, in order to find the steady-state gains of tray temperature in the linear region, very small changes (±0.1% of the design value) were made in the reboiler heat duty and the reflux ratio. The temperature of fourth tray was chosen to be controlled by the reflux flow rate and the temperature of the nineteenth tray was chosen to be controlled by the reboiler heat duty. a dual-temperature control structure for this hydrolysis RD column was studied, and it performed well.