Purification Of Ultra-High Saline And Contaminated Water By Multi-Stage Ion Concentration Polarization (Icp) Desalination (Massachusetts Institute of Technology)

Purification Of Ultra-High Saline And Contaminated Water By Multi-Stage Ion Concentration Polarization (Icp) Desalination (Massachusetts Institute of Technology)
United States Patent Application 20160115045
Kim; Bumjoo ;   et al.   April 28, 2016
Applicant: Massachusetts Institute of Technology
Abstract
A water stream is passed between two juxtaposed similar ion exchange membranes (AEMs or CEMs), forming an ion depletion and ion enrichment zones when an electric field is applied. As cations are selectively transferred through the CEMs, for example, anions are relocated in order to achieve electro-neutrality, resulting in the concentration drop (increase) in ion depletion (enrichment) zone. Trifurcation of the output channel allows collection of concentrated, dilute and intermediate streams, with the intermediate stream serving as input to the next stage of a serialized implementation.
BACKGROUND OF THE INVENTION
[0003] As water resources are rapidly being polluted, significant attention is now being paid to recovery of these waters through desalination and/or purification. In particular, with the adoption of horizontal drilling and hydraulic fracturing techniques to unlock the extensive natural energy resources from shale formations, issues regarding contaminated water from shale development are coming to the fore. Increasing development of shale gas sources has brought up an environmental issue concerning proper treatment of the often highly contaminated flowback or produced water. This produced water commonly contains various suspended solids as well as relatively large amounts of salts, often 1-5 times higher than seawater. Currently available technologies for desalination and treatment of produced water (e.g., thermal evaporation and reverse osmosis) are expensive because of multiple pretreatment steps necessary to remove suspended solids such as oil and organics, significant energy requirements for desalting, and the cost of equipment. In addition to produced water from shale development, a demand for economical purification of contaminated ground water is increasing globally.
[0004] In related applications [1], we presented the concept of ICP desalination such that each concentrate and dilute stream generated between two identical Ion Exchange Membranes (IEMs) can be separately acquired. Comparatively, conventional electrodialysis (ED) utilizes both Cation Exchange Membrane (CEM) and Anion Exchange Membrane (AEM) as shown in FIG. 1. Since different ionic diffusivity causes different thicknesses of ICP (ion depletion and enrichment) zone near the membrane, desalination performance could change depending on the kinds of major ion present in the source water and the installed membrane (CEM or AEM). Based on our analysis, CEMs in NaCl (Sodium Chloride) show better salt removal and current utilization/energy efficiency than electrodialysis (ED) [2] driving us to move towards developing ICP desalination for energy-efficient technology.
[0005] With the global market for water desalination/purification showing considerable growth and comprising variously segmented target sources, significant commercial opportunities exist for cost-effective water desalination and purification processes. The operational advantages of effectively and efficiently dealing with ultra-saline water coupled with the ability to simultaneously remove suspended solids could drive ICP to emerge as the preferred technology in the shale development industry. Although Reverse Osmosis (RO) is economical and dominant in the non-thermal desalination market, it is not economically viable for treating ultra-saline water (>40,000 ppm total dissolved solids, TDS). Thus, the shale development industry typically employs energy-intensive thermal desalination. [8]
Solutions for addressing these needs call for: [0006] a) Adaptable technologies for desalination of waters comprising a wide range of salinities, such as brackish water, seawater and produced water. [0007] b) Technologies and methods which permit en bloc desalination/purification of contaminated waters; i.e., technologies that demonstrate simultaneous elimination of a range of suspended solids such as red blood cells, crude oil-in-water emulsion, and salts. [0008] c) Cost-effective multi-stage strategies which leverage and improve technologies such as Ion Concentration Polarization (ICP).
SUMMARY OF THE INVENTION
[0009] The following are improvements of inventions described in U.S. application Ser. No. 14/857,133 filed on Sep. 17, 2015 which is incorporated herein by reference.
[0010] ICP technology can be economically developed for purification of produced water through trifurcated or bifurcated strategies comprising serial extraction of concentrate streams. These methods are advantageous to high salinity waters, offering significant cost reduction over existing technologies for pre and post treatment (e.g. elimination of suspended solids).
[0011] Based on the results described below, ICP desalination could be directly applicable to wide salinity range from Brackish water (<TDS 10,000 ppm) to produced water (>TDS 30,000 ppm) by single stage operation. However, in order to achieve output water with high purity by simple single stage ICP, it would require both extensive membrane area and exorbitant operating electricity. FIG. 5(A) shows a simulation result about current density distribution along the membrane when constant voltage applies between the membranes. According to this analysis, one can clearly find current flux through the membrane decreases along the membrane, thereby meaning most of ionic current flow in the earlier region of the membrane while later region of membrane does not contribute effective salt removal much. Consequently, we need enormous membrane area (but, with poor area efficiency) to remove most of salts in feed solution especially when we treat high saline water. In addition to membrane area efficiency, we have investigated trend of specific energy (EPIR: Energy Per Ion Removal) depending on salt removal ratio. As shown in FIG. 5(B), EPIR is increasing almost linear to the salt removal ratio in single-stage ICP, thereby meaning higher salt removal in single-stage should cause rapid increment of total power consumption. From the results, therefore, we can realize that smaller amount of salt removal with shorter membrane expenditure could save final water cost (summation of capital and operating cost) and it eventually drives us toward the multi-stage ICP operation for economical desalination.
[0012] While multi-stage approaches for cost-effective desalination have been used in Reverse Osmosis and Electrodialysis (ED) [5-7], it is important to establish appropriate strategies for multi-staging by fully considering the unique characteristics of ICP desalination. Since dilute and concentrate streams coexist between unit membrane pairs in ICP systems, constant in average concentration along the membrane, each stage in multi-staged ICP should involve extracting out certain streams from the ongoing process and delivering yet another stream to the next stage as feed water. Therefore, we considered two issues: 1) separation of the output channel to facilitate management of individual output flows; and 2) how the feed concentration changes in every stage corresponding to the separation strategy. Regarding the output channels, since there are three distinct concentration regimes between two identical membranes (CEMs) as shown in FIG. 6(a), bifurcation and trifurcation strategies were considered. Regarding the feed concentration, we investigated the Energy Per Ion Removed (EPIR) trend using feed solutions with a wide range of concentrations. Using Sodium Chloride (NaCl) 0.1M-1.7M, equivalent salinity TDS 6-100K ppm), FIG. 6(B), EPIR rapidly decreases as feed concentration increases up to 0.7M and then remains nearly constant. This result indicates that operating with higher feed salinity is generally a more energy-efficient strategy in ICP desalination.
Free Full Text Source:  http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=14&f=G&l=50&co1=OR&d=PG01&s1=desalination.TTL.&s2=desalination.AB.&OS=TTL/desalination+OR+ABST/desalination&RS=TTL/desalination+OR+ABST/desalination