Characterisation of bubble diameter and gas hold-up in simulated hydrocarbon-based bioprocesses in a bubble column reactor

The effect of Alcanivorax borkumensis SK2, a hydrocarbon-metabolising organism, on gas holdup in a 4-phase bubble column bioprocess

To design bioprocesses utilising hydrocarbon-metabolising organisms (HMO) as biocatalysts, the effect of the organism on the hydrodynamics of bubble column reactor (BCR), such as gas holdup, needs to be investigated. Therefore, this study investigates the first use of an HMO, Alcanivorax borkumensis SK2, as a solid phase in the operation and hydrodynamics of a BCR. The study investigated the gas holdup in 3-phase and 4-phase systems in a BCR under ranges of superficial gas velocities (U_G) from 1 to 3 cm/s, hydrocarbon (chain length C₁₃-₂₁) concentrations (H_C) of 0, 5, and 10% v/v and microbial concentrations (M_C) of 0, 0.35, 0.6 g/l. The results indicated that U_G was the most significant parameter, as gas holdup increases linearly with increasing U_G from 1 to 3 cm/s. Furthermore, the addition of hydrocarbons into the air-deionized water -SK2 system showed the highest increase in the gas holdup, particularly at high U_G (above 2 cm/s). The solids (yeast, cornflour, and SK2) phases had differing effects on gas holdup, potentially due to the difference in surface activity. In this work, SK2 addition caused a reduction in the fluid surface tension in the bioprocess which therefore resulted in an increase in the gas holdup in BCR. This work builds upon previous investigations in optimising the hydrodynamics for bubble column hydrocarbon bioprocesses for the application of alkane bioactivation.

Characteristics of carbide slag slurry flow in a bubble column carbonation reactor

The direct aqueous mineral carbonation of carbide slag was investigated. The flow characteristics of carbide slag-CO2-water reaction system in a bubble column were studied, which included the bubble Sauter mean diameter, gas holdup, bubble residence time, and the gas-liquid interfacial area. Bubble flow behaviors in the reactor were characterized by analyzing the bed pressure signals. The effects of the gas velocity (U g ) and liquid to solid ratio (L/S ratio) were discussed and analyzed. The results showed that the larger bubbles were easy to form at the larger L/S ratio, which indicated that the bubble coalescence was promoted. The gas holdup was larger when increasing U g or reducing the L/S ratio. The better gas-liquid interfacial areas were found in a wide range of L/S ratio at U g  = 0.082 m/s. The optimum conditions were found at U g  = 0.082 m/s and L/S ratio = 15–30 mL/g for the better gas-liquid interfacial area and the higher carbide slag conversion. The work provided the theoretical basis for the direct aqueous carbonation of the carbide slag and the operation condition optimization.

Amidation Reaction System: Kinetic Studies and Improvement by Product Removal

The amidation reaction to produce fatty acid diethanolamide is an important unit process to produce surfactants from renewable sources rather than from petroleum sources. Amidation is a liquid-phase reaction between diethanolamine with a fatty acid methyl ester. Since the reaction is reversible, the conversion is limited by equilibrium, the side product being methanol, which is volatile. Hence, mass transfer effects need to be considered in the interpretation of kinetic data. Further, the elimination of methanol can help to shift the reaction forward. Thus, the process has the potential for process intensification. This paper provides a batch reactor model to interpret the simulation data and includes mass transfer effects analyzed using a dimensionless mass transfer parameter (α_lg). Using values of this parameter greater than 4 leads to an equilibrium model where the methanol partial pressure in the bulk gas approaches that at the interface. Using this model, the kinetic and equilibrium parameters for the amidation reaction were determined using experimental data in the first part of this study. The experimental data for fitting the parameters are obtained from a closed batch reactor operated with an initial pressure of 1 bar and a temperature range of 70-80 °C. The second part of the paper examines two process-intensification concepts-viz., inert gas and vacuum stripping of methanol from the reactor-and simulates the process in the form of mass-transfer-based models. Improvement in the final conversion was demonstrated in both approaches, and predictions of the vacuum stripping model are in good agreement with the experimental results. Thus, the developed vacuum stripping model is useful for accurate analysis and design of a reactor with vacuum stripping. The novelty of the work is obtaining rate and reaction equilibrium constants, enthalpy of reaction, and liquid activity coefficient for amidation, which have no prior reporting, and providing the viability of options for side product removal. The applied modeling approaches and the experimental facilities and methods are established.

Quantification of oxygen transfer coefficients in simulated hydrocarbon-based bioprocesses in a bubble column bioreactor

This study investigates the overall volumetric oxygen transfer coefficient (K_La) in multiphase hydrocarbon-based bioprocess under a range of hydrocarbon concentrations (H_C), solid loadings (deactivated yeast) (S_L) and superficial gas velocities (U_G) in a bubble column reactor (BCR). K_La increased with increasing U_G in the air-water system; due to an increase in the number of small bubbles which enhanced gas holdup. In air-water-yeast systems, the initial addition of yeast increased K_La significantly. Further increases in S_L reduced K_La, due to increases in the bubble size with increasing S_L. K_La decreased when H_C was added in air-water-hydrocarbon systems. However, U_G, S_L and H_C affected K_La differently in air-water-yeast-hydrocarbon systems: an indication of the complex interactions between the yeast and hydrocarbon phases which changed the system's hydrodynamics and therefore affected K_L. This work illustrates the effect of the operating conditions (S_L, H_C and U_G) on oxygen transfer behaviour in multiphase systems.