Assessment of membrane distillation modules for seawater desalination and oilfield-produced water treatment applications

Alsairfi, Hussain

Thesis

Assessment of membrane distillation modules for seawater desalination and oilfield-produced water treatment applications

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Creator

Alsairfi, Hussain

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2025

Thesis identifier

T17223

Person Identifier (Local)

202087858

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Mechanical and Aerospace Engineering

Abstract

Membrane distillation (MD) is a technology that is emerging as a viable alternative to traditional desalination techniques such as Reverse Osmosis, Multistage flash distillation, Multiple-effect distillation, Vapour-compression evaporation, etc. The advantages of MD over conventional desalination technologies include higher ionic rejection capacity, greater feasibility for high saline brine treatments, ability to operate using low-grade heat energy, a single-stage process and remote operation using renewable energy, among others. In this dissertation, a parametric study was performed using experiments to assess the feasibility of using direct contact membrane distillation (DCMD) technology to desalinate saline water of different concentrations. The results showed that the permeate flux increased to 37.1 L/m².h from 11.6 L/m².h when the temperature was raised from 45 °C to 75 °C. Additionally, the permeate flux decreased to 13.6 L/m2 .h from 27.3 L/m2 .h, and the reduction in flux was around 50% when the concentration of sodium chloride in the feed solution was increased from 0% to 26%. The experimental results obtained using oilfield-produced water were highly encouraging. The permeate flux was 11.5 L/m².h and 12.5 L/m².h at 80 °C and 85 °C, respectively. The results indicate the enormous potential of DCMD to treat hypersaline oilfield-produced water, with an overall rejection of salts above 99%. The base-line technology is the DCMD technology. This study also evaluated the viability of air-gap membrane distillation (AGMD) and vacuum membrane distillation (VMD) for treating different types of saline water (3.5%, 7%, 15% and 26% NaCl solutions), including Arabian Gulf Seawater (AGS) and oilfield-produced water. AGMD experiments at different feed temperatures found that increasing the test temperature from 70 °C to 85 °C increased the permeate flux by 56.64%. In contrast, the VMD experiments showed that increasing the feed temperature from 65 °C to 85 °C resulted in a 26.87% increase in permeate flux. The results obtained from the experiments showed that VMD performed better at higher feed concentrations, while AGMD was superior at lower feed concentrations. The flow-rate experimental results showed that increasing the flow rate from 1.3 to 2.0 litres per minute resulted in a 1.2-fold increase in permeate flux for both configurations, with salt rejection close to 99.9% and unaffected by the feed flow rate. AGMD outperformed VMD at all flow rates, and the increase in permeate flux with flow rate was similar for both configurations. This study found lower gaps, i.e. air gap and vacuum space, were preferred in AGMD and VMD configurations, respectively, as they showed good flux, potentially due to the reduced effects of heat and mass-transfer mechanisms at smaller gaps. The experimental results showed that AGMD and VMD processes were highly efficient in treating oilfield-produced water and AGS, achieving high salt rejections as high as 99.97%. The results showed that the tested membranes achieved salt rejections as high as 99.97%, and the order of fluxes observed in the VMD configuration was Polyvinylidene fluoride (PVDF) > Polypropylene (PP) > Polytetrafluoroethylene (PTFE). In the AGMD configuration, the order of fluxes observed was Polypropylene (PP) > Polyvinylidene fluoride (PVDF) > Polytetrafluoroethylene (PTFE). This study’s results will provide valuable insights into the potential applications of AGMD and VMD processes in desalination, especially in regions where freshwater resources are scarce or contaminated. The information gained from this study can be used to optimise the performance of these processes, improve their costeffectiveness and energy efficiency, and enhance their viability as potential solutions for addressing water scarcity and pollution issues. The study discussed in this dissertation is the first to present laboratory-scale results of using AGMD and VMD technologies to treat AGS and oilfield-produced water in Kuwait while considering prevailing conditions. The findings of this study lay the groundwork for conducting pilot-scale studies on Arabian Gulf Seawater and oilfield-produced water utilising DCMD, AGMD and VMD technologies, not only in the Middle East region but globally.

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