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Membrane Crystallization Via Membrane Distillation T ⁎ I

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Membrane Crystallization Via Membrane Distillation T ⁎ I Chemical Engineering & Processing: Process Intensification 123 (2018) 258–271 Contents lists available at ScienceDirect Chemical Engineering & Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep Membrane crystallization via membrane distillation T ⁎ I. Ruiz Salmón , P. Luis Materials & Process Engineering (iMMC-IMAP), Université catholique de Louvain, Place Sainte Barbe 2, 1348, Louvain-la-Neuve, Belgium ARTICLE INFO ABSTRACT Keywords: Crystallization is a solid-liquid separation technique in which solid crystals are formed from a liquid solution. It Membrane crystallization has been usually employed in separation and purification of industrial streams using traditional devices as Membrane distillation crystallizers or evaporators. Nowadays, membrane technology appears as the alternative technology that could Waste streams replace the conventional crystallizers because of its advantages related to its adaptability and the low energy Crystal recovery consumption in comparison with the conventional technology. In this review, membrane crystallization via membrane distillation is addressed. The membrane performance, operating conditions, technical obstacles and the novelties of the technology are presented, including the ap- plications and the future perspectives. 1. Introduction aqueous solutions [10] or the valorization of alkaline phosphate con- centrates [11]. However, the main drawback of conventional crystal- The continuous improvement of processes and products in the in- lization, from an economic and environmental perspective, is the large dustry is an essential requirement to ensure a sustainable future and amount of energy needed. This operation has been traditionally carried further contribution to human progress. Three main aspects play a key out using evaporators or crystallizers [12–15] where solute precipita- role in that improvement: the environment, the society and the tion is produced thanks to heating or cooling, respectively. Although economy. Thus, it is of utmost relevance to develop new technological the progress on this field makes crystallization less energy-consuming solutions that give response to current challenges that we are already than the past decades, it is still far to be a sustainable technology, facing. One of them is the climate change, caused by the increase of the knowing that a small increase in the temperature applied or in the re- global atmospheric concentration of carbon dioxide, from a pre-in- sidence time produces an important increment in the energy con- dustrial value of about 280 ppm to 379 ppm in 2005 [1] and 400 ppm sumption [16]. in 2016 [2]. Other challenges are the loss of biodiversity, the replace- During the seventies and more intensively during the eighties, re- ment of finite sources of energy, the search for cure of numerous and search on crystallization increased dramatically in order to improve the new diseases or the restoration and decontamination of ecosystems. design and operation of large scale systems, mainly to decrease the Thus, increasing process efficiency while minimizing waste production energy consumption. However, there is still a lack of knowledge about and keeping the quality of the final product are requirements that have the crystallization kinetics, the influence of additives and the modelling to be fulfilled by any new technological approach that is presented. and prediction of how polymorphs crystallize. Advances in fundamental Process updating in the industry may suppose the survival and the knowledge on the crystallization process would help in the develop- success of an enterprise. Crystallization is an example of the technolo- ment of sensors that allow getting a better control of crystallization gical evolution of a unit from the conventional operation to the high- processes (nucleation, crystal modification and sizes, supersaturation, efficiency process. Crystallization is a widely used unit operation for the liquid inclusion in the crystals, impurities) [17]. Therefore, improving separation and/or purification of crystalline solid products. This pro- the efficiency of crystallization techniques requires paying attention to cess has been industrially applied since the early nineteenth century, as these aspects while developing novel and more energy-efficient pro- in the case of the sugar industry [3–6], pharma and fine chemicals, bulk cesses. In this context, membrane crystallization appears as an in- and commodity production [7] or microelectronics [8]. Currently, re- novative idea to incorporate membrane technology in crystallization search is also focused on using this technology to recover valuable processes to take advantage of its intrinsic benefits (some of them still compounds from waste streams, such as the removal and recovery of under research because of potentiality of its innovation), such as a well- phosphorous from swine wastewater [9], phenol recovery from dilute controlled nucleation and growth kinetics, fast crystallization rates, ⁎ Corresponding author. E-mail address: [email protected] (I. Ruiz Salmón). https://doi.org/10.1016/j.cep.2017.11.017 Received 19 June 2017; Received in revised form 20 November 2017; Accepted 25 November 2017 Available online 27 November 2017 0255-2701/ © 2017 Elsevier B.V. All rights reserved. I. Ruiz Salmón, P. Luis Chemical Engineering & Processing: Process Intensification 123 (2018) 258–271 membrane surface promoting heterogeneous nucleation or good control the bulk feed to the membrane wall, ii) vaporization and diffusion of supersaturation [18]. In addition, membrane crystallization may be through the pores of the membrane, and iii) condensation in the performed via a membrane distillation process when a temperature membrane-liquid interface of the permeate side and diffusion into the and/or concentration gradient is used as driving force in high con- bulk of the permeate. Two main aspects have a large influence in the centrated solutions that are close to the supersaturation. importance of this extra resistance: the kind of membrane and the kind In this paper, membrane distillation is reviewed as crystallization of configuration. technology in addition to its consideration as concentration technology. Regarding the kind and morphology of membranes, the main The potential of membrane crystallization from an intensification and characteristics that affects the crystallization performance are: i) liquid integration point of view is addressed, with special attention to present entry pressure (LEP), which depends on the membrane hydrophobicity and future applications, i.e. green economy and added-value produc- and the maximum pore size, is the pressure applied that should not tion. This review also presents an overview of membrane distillation- exceed the limit pressure above which the liquid penetrates the hy- crystallization processes and its main technical limitations (polariza- drophobic membrane; if this happens, a decrease in the permeate flux tion, wetting, scaling, fouling) and economic and environmental im- occurs as well as an undesirable permeation of salts; ii) membrane plications (operating and investment costs, material and energy reuse) thickness, inversely proportional to the permeate flux; iii) membrane in order to show the current status of the technology and to address porosity (the void volume fraction of the membrane) and tortuosity (the further research on this field. deviation of the pore structure from the cylindrical shape), having a direct effect on the liquid entry pressure; if LEP increases, permeation 2. Technical approach decreases; iv) mean pore size and pore size distribution and v) thermal conductivity (hot losses are minimized using a high porosity and/or Membrane distillation is usually applied for concentrating but not thicker membrane) [25]. crystallizing. For this reason, knowing both the essential principles of On the other hand, the membrane configuration also determines the membrane performance and the current challenges of the technology crystallization since the water removal from the feed to the permeate is becomes essential. Therefore, membrane characteristics, system con- due to different sources of driving force and therefore, main para- figurations and operating conditions are addressed in this section from meters, such as the transmembrane flux, also vary. Fig. 2 shows the a technical point of view. most developed membrane distillation configurations: 2.1. Process description A.) Direct Contact Membrane Distillation (DCMD): A feed and colder aqueous solutions are maintained in direct contact thanks to the Membrane distillation is typically used for treating solutions that membrane, which should be hydrophobic in order to avoid that the need to be concentrated for further applications. In membrane dis- aqueous feed penetrates the membrane pores. Thus, the trans- tillation water crosses from the feed side to the permeate side through a membrane temperature difference induces the evaporation of the (hydrophobic) membrane due to the difference in temperature and/or feed volatile molecules that cross the membrane to the permeate partial pressures across the membrane. Heating is applied in the feed side and condense inside the module. solution to increase the vapor pressure of water at the feed side, leading B.) Osmotic membrane distillation (OMD): The approach is similar to to an increase of the driving force. The permeate is collected at the the DCMD. In this case, an osmotic agent (NaCl, MgCl2, etc.) is used other side of the membrane,
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