Gas‐Liquid Mass Transfer in Fibrous Bed Reactor with Counter‐Current Liquid Recycle

Abstract

In this work, the gas-liquid mass transfer in a lab-scale fibrous bed reactor with liquid recycle was studied. The volumetric gas-liquid mass transfer coefficient, k L a, is determined over a range of the superficial liquid velocity (0.0042-0.0126 m.s ), surface tension (35-72 mN/m), and viscosity (1-6 mPa.s). Increasing fluid velocities and viscosity, and decreasing interfacial tension, the volumetric oxygen transfer coefficient increased. In contrast to the case of co-current flow, the effect of gas superficial velocity was found to be more significant than the liquid superficial velocity. This behavior is explained by variation of the coalescing gas fraction and the reduction in bubble size. A correlation for k L a is proposed. The predicted values deviate within ± 15 % from the experimental values, thus, implying that the equation can be used to predict gas-liquid mass transfer rates in fibrous bed recycle bioreactors.

Mass transfer and mixing characteristics in an airlift‐driven fibrous‐bed bioreactor

“…Therefore, the K L a observed in the present study is comparable to that reported in other fibrous packed systems (Okada et al, 1996; Nikakhtari and Hill, 2005a; Kim and Deshusses, 2008; Martinov et al, 2009) and in STBs at similar mixing and aeration rate conditions (Chisti and Jauregui‐Haza, 2002; Puthli et al, 2004), suggesting that a fibrous bed packed ILALB may be expected to reach same cell densities as in well‐mixed bioreactors but with much limited costs.…”

“…The increased K L a observed in Figure 11 must be due to increased interfacial area associated with variation of the coalescing gas fraction and the reduction in bubble size (Höller et al, 2001; Nikakhtari and Hill, 2005b; Martinov et al, 2009; Kilonzo et al, 2010). An additional increase in K L a is expected in the fibrous bed bioreactor system proposed in this study, due to enhanced K L value by increased number of localised turbulent eddies in the packing.…”

“…The K L a value observed by Nikakhtari and Hill (2005a) in an ELALB packed with stainless steel mesh ( L p = 1.2 m, ϕ p = 0.99) and operated at high gas velocity approached 0.021 s −1 and about 1.1 times lower than the maximum K L a observed using PUF packing ( L p = 0.825 m, ϕ p = 0.96), but and about five times higher than that observed using cotton packing ( L p = 0.953 m, ϕ p = 0.93) in the present study. Recently, Martinov et al (2009) also observed increased K L a value from 0.01 s −1 (unpacked) to 0.026 s −1 in a laboratory‐scale glass column with recycling packed with PEVA fibrous bed ( L p = 0.26 m), which was only 1.1 times higher than that observed using PUF packing ( L p = 0.825 m, ϕ p = 0.96) and about 6.2 times higher that using cotton packing ( L p =0.953 m, ϕ p = 0.93) also in the present study. Okada et al (1996) also observed enhanced K L a value from 0.015 s −1 (unpacked) to 0.035 s −1 in an ELALB packed with 15 mm steel pall ring ( L p = 0–0.4 m), which was only about 1.5 times higher than that observed also using PUF packing and 8.3 times higher than that using cotton packing examined in the present study.…”

“…For the best operation of packed airlift bioreactors, a good understanding of oxygen mass transfer and mixing characteristics is very important in order to optimise the bioreaction conversions. Recently, Martinov et al (2009) studied gas–liquid mass transfer in 0.1 m i.d. glass bubble column filled with a PEVA [a co‐polymer of polyethylene (PE) and vinyl‐acetate (VA)] fibrous bed packing (0.26 m high).…”