Design and Control of a Process to Extract β‐Carotene with Supercritical Carbon Dioxide

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Abstract
A strategy for locating optimal designs is applied to the extraction of β‐carotene with supercritical C02. With the modified Peng‐Robinson equation of state to estimate the phase equilibria, models are developed to simulate the three‐phase (solid, liquid, and supercritical fluid) extraction and separation processes. The design optimization minimizes the annualized cost while producing β‐carotene of the desired quality. The results demonstrate that despite high operating pressures, supercritical extraction can be competitive for the recovery of high‐value products at low production rates. Furthermore, the increases in solubility with small amounts of cosolvent can have a substantial impact on the economics of the proposed design. An example is given in which the addition of 1 % ethanol to the C02 solvent transforms an unfavorable design into a competitive one. In addition, a dynamic model is proposed for the product separator, and its differential‐algebraic equations are integrated with DASSL. Proportional (P) and proportional‐integral (PI) control schemes are studied to maintain the pressure by manipulating the vapor flow rate. Although the set‐point response of the PI controller is acceptable, disturbance rejection is poor. A disturbance in the feed flow rate causes lower quality β‐carotene to be produced. The desired quality is maintained when the separator is overdesigned, but this raises the annualized cost.