Forward osmosis, reverse osmosis, and distillation membranes evaluation for ethanol extraction in osmotic and thermic equilibrium

https://doi.org/10.1016/j.memsci.2022.121292Get rights and content

Highlights

  • FO, RO, and MD membranes have the potential to dealcoholize a 12% v.v. Synthetic ethanol solution.

  • Membrane Distillation is a viable strategy for use as a complement in a hybrid FO-MD approach for Ethanol extraction.

  • Forward osmosis shows a higher ethanol flux than reverse osmosis due to the concentration polarization effect.

Abstract

One of the significant challenges of the industry is the economic extraction of ethanol from aqueous solutions of interest to the food industry. Specifically, in the alcoholic beverages industry, the non-alcoholic beverage market has gained importance, demanding more non-alcoholic drinks with higher organoleptic quality. In this context, the technology related to the use of membranes has shown great potential. Our research aims to determine the performance of forward osmosis using FO, RO, and MD membranes as an option in the extraction of alcohol in an osmotic (Δπ = 0) and thermal (ΔT° = 0) equilibrium process. The results showed that all the membranes have the potential to dealcoholize a 12% v.v. synthetic ethanol solution. The results showed that Membrane Distillation is a viable strategy as a complement in a hybrid FO-MD approach, achieving ethanol flux values close to those offered by FO membranes and much higher than those shown by RO membranes. We also proposed other technical criteria for membrane performance evaluation, such as maintaining a low reverse salt flux and a low or no water flux to keep the organoleptic properties of a hypothetical alcoholic beverage subjected to the FO-MD hybrid process. For a high Ethanol/Salt flux ratio, the RO-82V and FO-CTA membranes presented the best performance. Furthermore, in an Ethanol/Water flux ratio, RO membranes perform best when working in an osmotic equilibrium process with a water flux equal to zero. Regarding the FO membranes, in an Ethanol/Water flux ratio, the FO-TFC membrane presented the best performance.

Introduction

One of the significant challenges in the industry is the economic extraction of ethanol from aqueous solutions of interest [1], like food industries [2,3], sewage treatment [4] or fuel production [5]. For example, in the energy industry, ethanol appears as an alternative to fossil fuels [6], and fermentation is a well-known strategy to obtain it; however, the extraction of high-quality ethanol from the fermentation process presents challenges, one of them is the fact that the ethanol concentration is low in many fermentation processes because ethanol inhibits ethanol fermentation [6]. Hence, ethanol extraction during the fermentation process is desirable to increase the performance of the reactors [6,7].

On the other hand, the food industry is the one that presents the most significant challenges, trying to offer products that are traditionally associated with the containment of a particular alcoholic degree, now towards a market that demands the same product without alcohol, such as non-alcoholic beverages. According to according to market intelligence company Fact.MR [9] that non-alcoholic beer is becoming a new-found rage worldwide with changing alcohol consumption habits of consumers. As a result, the global non-alcoholic beer industry will account for a 5% market share in the worldwide beer industry by 2027.

In this context, in the food industries, the use of membranes for the extraction of alcohol from beverages has gained significant attention compared to traditional thermal processes, among them the possibility of not mistreating the product with alteration of the temperature, therefore low consumption energy in the process [8]. In contrast, thermal processes strongly alter the aroma [9,10]. According to Labanda [11], membrane separation allows the ethanol content to be reduced under milder conditions, thus preserving the sensory characteristics of the original product, like alcoholic beverages.

The most studied membranes process in ethanol extraction are Membrane Distillation (MD), Pervaporation (PV), Nanofiltration (NF), Reverse Osmosis (RO), Osmotic Distillation (OD), and Forward Osmosis (FO) [8].

FO is a technology still in development; despite this, it has aroused particular interest from both the scientific community and the industrial sector [12,13]. It has already begun to be applied in several areas, such as water desalination, municipal wastewater recovery [12,14,15], brines concentration [16], mining applications like coal mining [17,18], synthetic heavy metal wastewater [19], water recovery from acid mine drainage [20], and a recent case in dealcoholization from a synthetic solution [8], showed that FO could be used to extract low molar mass compounds such as ethanol from aqueous solutions.

If FO is the selected process for ethanol extraction, a draw solution (DS) is required, which could be a salt solution such as NaCl. Therefore, the ethanol will accumulate in this DS, requiring another technique to extract the ethanol from this DS. A quick alternative is thermal distillation; however, in this research, we seek to use low-energy consumption techniques, so the use of membranes is an exciting alternative; for this, we propose to use a distillation membrane.

According to Alkhudhiri [21], mass transfer in MD is controlled by three primary mechanisms, which are Knudsen diffusion, Poiseuille flow (viscous flow) and molecular diffusion. This gives rise to several types of resistance to mass transfer resulting from the transfer of momentum to the supported membrane (viscous), the collision of molecules with other molecules (molecular resistance) or with the membrane itself-(Knudsen) resistance (Fig. 1). In this context, the dusty gas model is used to describe the mass transfer resistances in the MD system. The mass transfer boundary layer resistance is generally negligible [22]. Similarly, the surface resistance is insignificant because the surface area of the MD is small compared to the pore area. On the other hand, the thermal boundary layer is considered the factor is limiting mass transfer [22].

According to Bandini [23], heat transfer is the only liquid-phase process contributing to the overall MD process rate.

In this context, the proposed research uses an equal temperature between both MD membrane sides (feed and permeate). With this option, water flux is cancelled. In this new configuration (cancelled temperature differences), a volatile organic compound like ethanol shows high mobility associated with the “adsorption-desorption” mechanism; this was demonstrated by Yao [24]. This makes it possible to obtain a dealcoholized FO draw solution with a high salt rejection (greater than 99%) [24].

Fig. 2 shows the FO-MD's conceptual proposed configuration. In this configuration, the FO module osmotic pressure difference is equal to 0.0 (Δπ = 0), and for the MD module, the temperature difference is equal to 0.0 (ΔT° = 0). In this way, the linkage FO-MD generates a hybrid process.

The FO−MD configuration is a less explored membrane-based hybrid technology. This FO-MD configuration combines the strengths of both processes: high product water quality, low fouling and low energy consumption [25]. Some research shows the FO-MD capacity in synthetic heavy metal wastewater [[26], [27], [28]], artificial oily wastewater [29,30] and shale gas drilling flow back fluid [31], but never in the configuration proffer in the current research proposal.

Therefore, our research aims to evaluate the extraction of alcohol from an alcoholic solution through Forward Osmosis processes through the use of RO, FO and Distillation membranes.

Section snippets

Feed and draw solution

For the Forward Osmosis process, as Feed Solution (FS), we prepared a synthetic alcoholic solution, ethanol 12%v.v. in distilled water (πFS = ∼47.9 bar), and as Draw Solution (DS), we used NaCl 1.0 M (πDS = ∼47.9 bar). With this, we seek to establish an initial Δπ = 0. All the tests were carried out at an average temperature of 16 °C to establish an initial ΔT = 0. For the Membrane Distillation process, as FS, we prepared a synthetic alcoholic solution of ethanol 12%v.v. in NaCl 1.0 M and used

Forward osmosis process

We divided the results into two types, membrane orientation (FO mode and PRO mode) and time elapsed. The elapsed time considers the entire time test lasted (3 h) and a second calculation 1 h after starting the essay. In Fig. 4, we observed that during the first hour of operation in FO mode, the ethanol flux (JE) started to decline in several tests. After 1 h, it stabilizes. According to Fick's law, the solute's (Ethanol) diffusion rate will decrease (as in this case) until reaching a certain

Conclusions

Regarding the Forward Osmosis process, working in a state of osmotic equilibrium with JW values of null (RO membrane) or low (FO membrane), we evaluated the FO and RO membranes in FO and PRO modes. The results show that FO membranes perform 2.5 times better than RO membranes concerning JE. In this case, the internal polarization concentration effect played an essential role in the ethanol flux.

Regarding the Membrane Distillation process, the results showed that MD is a viable strategy to use as

Authorship contributions

Category 1

  • Conception and design of study: J.C. Ortega-Bravo.

  • acquisition of data: J.C Ortega-Bravo, C. Guzman, N. Iturra.

  • analysis and/or interpretation of data: J.C Ortega-Bravo.

Category 2

  • Drafting the manuscript: J.C Ortega-Bravo, M. Rubilar;

  • revising the manuscript critically for important intellectual content: M. Rubilar.

Category 3

  • Approval of the version of the manuscript to be published (the names of all authors must be listed):

  • J.C. Ortega-Bravo, C. Guzman, N. Iturra, M. Rubilar.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors wish to express their thanks for the financial support provided by CONICYT/FONDECYT project N° 11200851, and DIUFRO 2021 project N° DI21-5016.

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