One-column Process Research Articles

Innovative next-generation monoclonal antibody purification using activated carbon: A challenge for flow-through and column-free processes

Activated carbon (AC) is a porous solid with a larger surface area and lower cost than chromatography resins. AC has been used in the field of biopharmaceutical manufacturing for plasma-derived products and recombinant monoclonal antibodies (mAb). In our previous study, AC was employed in the purification process of therapeutic mAb as a replacement for Protein A affinity chromatography (PrA). In addition, we designed an all flow-through purification process using AC. In these investigations, greater effective clearance of high-molecular-weight species (HMW), low-molecular-weight species (LMW), host cell proteins (HCP), and DNA was observed compared to that of the conventional Protein A platform purification process. However, it was revealed that mAb recovery from the AC step was lower than that from the PrA step. In this work, to improve mAb recovery from the AC step while maintaining the effective removal of impurities, a pretreatment procedure conducted prior to the AC treatment was investigated. We found that both an ultrafiltration/dilution and reduction in the conductivity of the filtered cell culture supernatant after acid precipitation could improve both the impurity clearance and mAb recovery from the AC treatment. From the obtained results, we designed a two-step purification process in which AC treatment is followed by either cation exchange column chromatography or anion exchange column chromatography, and we compared this against the Protein A platform purification process. Excellent impurity clearance was achieved, even in the one-column process. Furthermore, we designed an innovative column-free flow-through purification process based on acid precipitation, clarification, ultrafiltration/dilution, and the implementation of an AC filter membrane and an anion exchange chromatography membrane. With this process in the pilot-scale, HCP level can be reduced to below 10 ng/mg, and HMW and LMW can be removed to below 1% while improving mAb recovery. From these results, it is strongly expected that AC is a promising candidate for the next generation of mAb purification processes to improve the economy and efficiency of the process.

Control of One- and Two-Column Distillation Systems with Maximum Temperature Limitations

Maximum temperature limitations are encountered in distillation columns in which thermally sensitive materials are being separated. The maximum base temperature often results in expensive refrigeration being required in the condenser because of the resulting low condenser temperature. The concept of using two columns instead of one column was discussed in a recent paper (Masel, R. H.; Smith, D. W.; Luyben, W. L. Ind. Eng. Chem. Res. 2013, 52, 5172−5176). Results demonstrated that a two-column process is economically better than the conventional one-column process when the feed contains a significant amount of the light component and when there is a large difference in the normal boiling points between the light and heavy components. The purpose of this paper is to explore the dynamic control issues in the one-column and two-column alternative flowsheets. The dynamic performances of several control structures are evaluated, and effective control schemes are developed that handle large disturbances in throughput and feed composition. The key concept is the need to have a structure in which both the base temperature and bottoms composition are controlled. The temperature must be tightly controlled because of the maximum temperature limitation. To maintain the bottoms composition at a constant temperature (in a binary system), the base pressure must be maintained, not the condenser pressure.

Comparing the performance of one-column process and four-zone simulated moving bed by computer simulation

A new one-column chromatography process, analogous to a four-zone simulated moving bed (SMB), was presented. The basic principle of the process was identical to that of a four-zone SMB. The process consisted of one chromatographic column and four tanks, instead of the four columns in the four-zone SMB (1-1-1-1), and has been used for the separation of two amino acids, phenylalanine and tryptophan, using an ion exchange resin. The operating parameters for the one-column process and four-zone SMB were obtained from equilibrium theory. Computer simulations were used to compare the performances of the new one column process to that of the general four-zone SMB, using Aspen Chromatography™ v 11.1. The differences between the one-column and SMB processes in terms of the purities and yields of phenylalanine and tryptophan were less than 4 and about 6%, respectively. The lower purities of the one-column process were due to the loss of the developed concentration profiles in the column when the liquid was stored in tanks. The one-column process gave great flexibility, and would be useful for reconstructing an existing conventional chromatography process to one of a SMB.

Economic and Dynamic Impact of the Use of Excess Reactant in Reactive Distillation Systems

Reactive distillation columns are sometimes operated with an excess of one of the reactants, but this mode of operation may have the disadvantage of requiring the recovery and recycle of the reactant that is in excess. The flowsheet typically consists of a two-column system: a reactive column and a recovery column. An alternative is to use a single reactive column that is operated “neat” (exact stoichiometric amounts of the reactants fed and consumed). The one-column process has lower capital investment and energy costs than the two-column system. However, Al-Arfaj and Luyben1 recently explored the control of a one-column “neat” system and demonstrated that a composition analyzer may be required to detect the inventory of one of the reactants so that the fresh feed can be adjusted. Because composition analyzers are expensive and sometimes unreliable, the economic advantages of the single-column system need to be assessed. The purpose of this paper is to quantitatively compare the single-column (neat operation) and the two-column system (excess of one of the reactants fed to the reactive column). The comparison includes both steady-state economics and dynamic controllability. The reversible reaction is A + B ⇌ C + D. The relative volatilities are favorable for reactive distillation; i.e., the reactants are intermediate boilers between the light product C and the heavy product D. In the two-column system, an excess of B is fed to the reactive column. The distillate from the reactive column is product C. The bottoms is a mixture of components D and B, which are separated in the second column. The distillate of the second column is mostly B and is recycled back to the first column. Steady-state economics show a very significant incentive for the single-column system. Total annual cost of the two-column system is 50% more than that of the single-column process if a 10% reactant excess is needed to compensate for flow-measurement uncertainties and fresh-feed composition changes. If a 20% excess is needed, the total annual cost is 100% more. Both systems are dynamically controllable, but the dynamic response of the two-column process is slower because of the presence of the recycle and is more complex. Only tray temperature control is required in the two-column process.

Modeling of separations by closed-loop steady-state recycling chromatography of a racemic pharmaceutical intermediate

Closed-loop steady-state recycling (SSR) is a cyclic, one-column process that is similar to simulated moving bed (SMB) chromatography in several respects. Both processes are cyclic. In both SMB and SSR, fractions are collected from the leading and trailing portions of the circulating chromatographic profile, and fresh sample is injected into the interior of the profile. However, SMB is a continuous process whereas SSR is a discontinuous, repetitive process. This paper presents a model for the closed-loop SSR process and its experimental validation in a case of practical importance. For this last purpose, we used the closed-loop SSR separation of the enantiomers of a racemic pharmaceutical intermediate. The experimental determination of the competitive adsorption equilibria was performed by frontal analysis in a system composed of a chiral HPLC column as the stationary phase and pure acetonitrile as the mobile phase. All the adsorption data were well correlated by the Langmuir model. The Langmuir model was used to calculate overloaded band profiles corresponding to the separation of racemic mixtures at both analytical and preparative scales. Theoretical band profiles were calculated using the equilibrium–dispersive model. With proper corrections for the contributions of the sources of extra-column band broadening, the model properly predicts the experimental band profiles obtained in the closed-loop SSR setup and demonstrates that a cyclic steady-state develops after the completion of a finite number of cycles. The results also show that the extra-column effects must be accounted for in order to model the closed-loop SSR process accurately.