Concentrating of Sugar Syrup in Bioethanol Production Using Sweeping Gas Membrane Distillation

Abstract

Membrane distillation (MD) is a relatively new and underdeveloped separation process which can be classified as a green technology. However, in order to investigate its dark points, sensitivity analysis and optimization studies are critical. In this work, a number of MD experiments were performed for concentrating glucose syrup using a sweeping gas membrane distillation (SGMD) process as a critical step in bioethanol production. The experimental design method was the Taguchi orthogonal array (an L9 orthogonal one) methodology. The experimental results showed the effects of various operating variables, including temperature (45, 55, and 65 °C), flow rate (200, 400, and 600 ml/min) and glucose concentration (10, 30, and 50 g/l) of the feed stream, as well as sweeping gas flow rate (4, 10, and 16 standard cubic feet per hour (SCFH)) on the permeate flux. The main effects of the operating variables were reported. An ANOVA analysis showed that the most and the least influenced variables were feed temperature and feed flow rate, each one with 62.1% and 6.1% contributions, respectively. The glucose rejection was measured at 99% for all experiments. Results indicated that the SGMD process could be considered as a versatile and clean process in the sugar concentration step of the bioethanol production.

The Application of Open Capillary Modules for Sweeping Gas Membrane Distillation

“…Forced convection of gas increases the rate of evaporation [4], which was confirmed by the results presented in Figure 8 (Tests 1 and 2-without feed pre-heating), showing that the permeate flux increased from 0.240 to 0.385 L/m 2 h (60%) when the fan was started and air was flowing between the capillaries at a velocity of 1.8-2.5 m/s. A similarly large effect of increasing the gas flow velocity was demonstrated in SGMD modules with a shell [20,32]. However, the process efficiencies obtained for such classical modules are presented in a wide range of 0.1-50 L/m 2 h [4, 16,22].…”

“…Conducting the SGMD process in small modules and at relatively high flows does not cause significant changes in the feed temperature [26]. Hence, in some studies a slight influence of the feed flow velocity was shown [26,32], which, however, changes when modules with a much larger membrane area are tested [10,17,20].…”

“…The MD process is most often proposed for water desalination, but other applications such as concentration of solutions are also contemplated. One of the examples is the use of SGMD to concentrate solutions of glycerol [29], sugar [32], or fruit juices [18]. In the case of solution concentration, there is no need to use a vapour condenser, which significantly simplifies the installation and allows the use of the open SGMD variant of the modules without the need to achieve a state of supersaturation of the vapour in the sweeping gas (inside condenser).…”

An Overview of Membrane Distillation Technology: One of the Perfect Fighters for Desalination

“…To develop high quality membrane for the membrane distillation process, the knowledge of membrane characteristics is very important. [8][9][10][11] Although, the basic characteristics of high quality membranes are hydrophobicity and microporosity. The hydrophobicity is required to restrict the passage of liquid; hydrophobicity must be as high as possible to make a well-controlled membrane.…”

Membrane Distillation Process

“…Bioethanol is generated, starting from renewable materials through saccharification and fermentation processes, and its production is linked to the sugar content in the prehydrolyzates. Sweep Gas Membrane Distillation (SGMD) was used to concentrate glucose syrup and the parameters that mostly affected the permeate flux were identified [ 7 ]. Feed temperature and sweep gas flow rate had the most significant impact; however, in all tests, 99% of glucose rejection was registered, confirming the efficiency of the process for obtaining concentrated glucose streams.…”