Separation and purification of lactic acid from fermentation broth by reverse osmosis

Abstract

Brackish water reverse osmosis (BWRO) and seawater reverse osmosis (SWRO) membranes were used in the 2-stage reverse osmosis (RO) unit to recover, pre-purify, and pre-concentrate lactic acid. Calcium lactate (CaLAC), sodium lactate (NaLAC), and ammonium lactate (NH4LAC) were used as model feed solutions. The operating pressure showed a pronounced effect on lactate passage through the first BWRO unit, and the Donnan exclusion effect and hydrogen bonding were responsible for cation rejection. Calcium ions were rejected at the BWRO unit because of low diffusion rate and charge interaction at the surface. However, monovalent ions formed hydrogen bonds with the carbonyl group of the membrane that allowed passage across the membrane. The second SWRO unit was for pre-concentrating lactic acid. A high lactate purity of 99.2% with a total recovery of 50.5% was acquired from calcium lactate feed solution. Lower purity with higher lactate recovery was obtained when the feed solution was sodium lactate and ammonium lactate. Process and cost models for lactic acid recovery from fermentation broths at an annual capacity of 100,000 kg were developed as a research tool in evaluating an alternated process technology. The models were developed using SuperPro® Designer software by gathering the optimized data from the laboratory scale experiments. Sizing of unit operations, chemicals and utility consumptions, and estimation of capital and operating costs with the cost breakdown analysis were acquired from the simulation. Membrane based process design was proposed in this study. The processes mainly consisted of microfiltration for cell removal, a series of ultrafiltration for eliminating proteins, and the integrated reverse osmosis systems to recover, preconcentrate, and prepurify lactic acid. Among the 3 proposed process designs, in-parallel membrane based process exhibited the highest lactic acid recovery yield while the purity remained sufficiently high in comparable to the commercial grade products. The number of unit operations was found to be responsible to high production cost both investment and operating costs. Omitting centrifugation and ultrafiltration at 30 kDa molecular weight cut-off with integrated brackish water reverse osmosis membrane in parallel units in the design could lower the operating cost by 23.33-31.29% for different fermentation broths entering the downstream processing units.