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interesting "ECF" ClO2 data

  at:   http://www.clo2.com/index.html  you'll find an interesting
  description of a new membrane/electrode based method to produce chlorine
  dioxide (ClO2) w/ far less imporities and only one input chemical.  the
  text version follow, but the doc. has diagrams (tho not critical) and other
  interesting documents.  it's sterling pulp chemicals, inc.; and they are
  moving into the water disinfenction field w/ their new ClO2 generating
  method, because it not only produces less Cl2 as a byproduct, but also less
  chlorate (apparantly disinfection byproducts such as chlorform & other
  trihalomethanes largely result from chlorate formation).
  they claim a conventional dioxide generator produces 31 mg/L of chlorine
  gas for every 1,000 mg/L of dioxide created (3.1%), yet in the (omitted)
  graphics it also states 100-1,000 ppm (ie mg/L) of Cl2 gas formed.  in
  either case that's a lot *AND OF INTEREST TO PULP & PAPER CLUSTER RULE
  ACTIVISTS*.  hope this is new info for folks, i believe i saw the reference
  to the web site on a post to the usenet group sci.environment, so it should
  looking up us patent # 468039 (twardowsky & mcgillvray), _awwa j._ nov.
  '92, or the contact for sterling may elucidate matters further.
  [ECF Technolgy]
                          [Chlorite to ClO2 and NaOH]
                     The Chlorine Dioxide Generation System
                                 of the Future.
            Presently, nearly 4.5 million pounds per day of chlorine
            dioxide are produced worldwide using Sterling developed
            technologies. The rapid growth in chlorine dioxide use
            over the last twenty years is primarily due to its
            proven effectiveness as an environmentally friendly
            bleaching and disinfectant agent.
            ECF� technology research began in 1985(1) and has
            continued since that time in Sterlings' Research
            Laboratories in Toronto, Canada. The primary aim was to
            develop a process with the following attributes:
               * Single chemical feed (no chlorine, sodium
                 hypochlorite, or hydrochloric acid, and potential
                 reduction in process safety management and SARA
                 reporting requirements).
               * High Efficiency (low operating cost).
               * High Purity Chlorine Dioxide (minimal chlorine,
                 sodium chlorite, sodium chlorate, or sodium
                 chloride in the product).
               * Ease of modulation and control (simple remote
                 method of tracking and controlling production
               * No Elemental Chlorine (single chemical feed).
            ECF� Development History
            A typical chlorite based generator using hydrochloric
            acid/sodium hypochlorite operates essentially as
             Conventional Small Scale Sodium Chlorite Based Chlorine
                                Dioxide Generator
            [Conventional Small Scale Sodium ChloriteBased ClO2 Generator]
            A two chemical generator uses gaseous chlorine injected
            with sodium chlorite in a similar fashion.
            These conventional chlorine dioxide processes using
            sodium chlorite require chlorine, or sodium hypochlorite
            and hydrochloric acid to convert sodium chlorite to
            chlorine dioxide.
                 NaClO2 + 1/2 Cl2 -> ClO2 + NaCl.
                 5 NaClO2 + 4HCl -> 4 ClO2 + 5 NaCl + 2H2O
                 2 NaClO2 + HOCl + HCl -> 2 ClO2 + H2O + 2 NaCl
            These systems are reliable and can be efficient but for
            continuous high efficiency/low by-product/low residual
            chlorine operation they require attention. In operations
            that require frequent capacity changes they are
            difficult to monitor for yield, efficiency and product
            These conventional processes require an excess of
            chlorine or acid to maximize sodium chlorite conversion.
            The amount of excess is dependent upon the generator
            design and can be 10-15% of the stoichiometric amount.
            The control and proportioning of two or three chemical
            feeds in these "once-through" systems is difficult, and
            if not carefully monitored, can lead to untreated
            chlorite or excessive amounts of chlorine leaving the
            system, which, in turn can lead to the formation of
            sodium chlorate via other side reactions or to the
            formation of chlorine related disinfection by-products
            in the finished water.
            ECF� System Development
            In the 1980's, significant strides were made in the
            development of membranes for a variety of applications.
            One such development was the hydrophobic gas pore
            During this time period Sterling began working with
            membrane materials which could withstand a chlorine
            dioxide environment and developing technology to take
            advantage of the potential selectiveness which could be
            achieved using such materials to allow some components
            of a solution to pass through the membranes while
            keeping the remaining components on the other side.
                                  Gas Pore Membrane
                                 [Gas Pore Membrane]
            In the 1990's the need to develop disinfecting systems
            which could deliver pure agents to water, with minimal
            or strictly limited disinfection by-products, presented
            the opportunity for Sterling to combine its
            electrochemical chlorine dioxide generating experience
            with its potential gas pore membrane technology and
            develop its new ECF� systems for on-site generation of
            pure chlorine dioxide from sodium chlorite.
            The chemical reaction involved in Sterling's ECF�
            process is as follows:
                  NaClO2 + H2O     --> ClO2     +NaOH       + 1/2 H2
                  (Sodium Chlorite     Chlorine  Caustic      Hydrogen
                  Solution)            Dioxide   Soda         (Vented from
                                                              the Cathode)
            The system is represented as follows:
                 ECF� System for On-site Production of Pure Chlorine
                             Dioxide from Sodium Chlorite
                 [ECF System for On_site Production of PureClO2 from Sodium
            Sodium chlorite solution is recirculated by a seal-less
            pump through the anode compartment of a cell. Chlorite
            ion is converted to chlorine dioxide gas in solution,
            and sodium passes through the cathode compartment, where
            it is discharged to form caustic soda and hydrogen. The
            hydrogen is separated and vented.
            The anolyte solution, which contains dissolved chlorine
            dioxide gas, then flows to the perstraction module,
            where chlorine dioxide and water vapor are transferred
            to the acceptor solution waterstream. The depleted
            solution then returns via the pump to the cell and is
            further fortified with sodium chlorite feed. Not shown
            on the diagram, is a small controll cell which maintains
            a pH of approximately 5-5.5 in the anolyte circuit.
            High Efficiency
            The perstraction membrane isolates the reaction system
            from the water being disinfected. It will only pass
            chlorine dioxide and other gases (oxygen and water
            vapor) to the acceptor solution. An excess of sodium
            chlorite is maintained in the reaction mixture which is
            recycled and cannot leave the system in any form but
            chlorine dioxide. Any sodium chlorate formed via side
            reactions, is either reconverted to chlorine dioxide or
            purged periodically from the circuit.
            By using a closed reaction system, the electrochemical
            conversion efficiency of chlorite to chlorine dioxide is
            high. This is because the concentration of sodium
            chlorite can greatly exceed chlorine.
            The cell is shown schematically in the following
                                      Main Cell
                                     [Main Cell]
            High Purity
            The chlorine dioxide purity using ECF� technology
            compared to conventional systems is shown in the
            following table:
                  PRODUCT SOLUTION (normalized to 1,000 mg/l)
                             ECF� Generator Conventional Generator
                             mg/L           mg/L
             Chlorine dioxide1,000 (min'm)  1,000 (min'm)
             Chlorine        3              31
             Chlorate        3              86
             Chlorite        10             66
            M.H. Griese et al (3) studied the reaction by-products
            in finished water from conventional generators,
            producing chlorine dioxide in the liquid and phases, and
            then compared the chlorite and chlorate ion
            concentrations in the treated water (see graphs).
            Surprisingly it was found that the gas stripped chlorine
            dioxide led to less chlorite and considerably less
            chlorate in the finished water. Analysis to date
            suggests that gas treatment of the water to be
            disinfected results in a 10-15% improvement in
            disinfection efficiency. This result is thought to be
            due to the absence of chlorine.
            Ease of Modulation and Control
            The ECF� system has a single set point adjustment for
            modulating capacity. The actual online production rate
            is available for the control room operator to confirm
            that the expected rate equals the actual rate of
            [Control Room/Feild Diagram]
            Thus a field unit can be controlled from a few hundred
            yards to several miles without any post-adjustment of
            other feeds to compensate for changes in quality etc. in
            the feedstocks. There is only ONE feedstock.
            The ECF� system as planned and developed, will allow
            municipalities and other users to realize the benefits
            of chlorine dioxide, such as its effectiveness in
            deactivating cryptosporidium and giardia, without
            exceeding EPA guidelines in disinfection by-products
            (chlorite, ion, etc.) and also to produce and apply the
            chlorine dioxide dose in an effective and economic
            US Pat# 4683039 Twardowski & McGillvray
            Can Pat. # Appl. 2162471 Cowley, Lipsztajn & Ranger
            M.H. Greise et al AWWA Journ. Nov. 1992
            for further information on the ECF� System contact:
             G. CowleyTel: 416-234-7522
                      Fax: 416-239-8091
                      Internet: Feedback & Inquiries
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  tony tweedale