JP3862816B2

JP3862816B2 - Reverse osmosis membrane separation method

Info

Publication number: JP3862816B2
Application number: JP17888997A
Authority: JP
Inventors: 雅彦廣瀬
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 1997-06-18
Filing date: 1997-06-18
Publication date: 2006-12-27
Anticipated expiration: 2017-06-18
Also published as: JPH1110146A

Description

【０００１】
【発明の属する技術分野】
本発明は逆浸透膜分離方法に関し、特にホウ素を多量に含有する原液、例えば、海水から飲料水を生産する場合に有用な方法である。
【０００２】
【従来の技術】
海水から飲料水を生産する方法として、海水を第１段目逆浸透膜モジュ−ルで処理し、その透過液をホウ素の除去に適したｐＨ値に調整のうえ、更に第２段目逆浸透膜モジュ−ルで処理することが提案されている（特開平９−１０７６６号、特開平８−２０６４６０号）。
【０００３】
【発明が解決しようとする課題】
周知の通り、所謂、おいしい飲料水としては、カルシウム等の蒸発残留物を適量に含有し、ｐＨ値が中性近傍であることが条件とされる。
上記の逆浸透膜分離による飲料水の製造方法において、第１段目逆浸透膜モジュ−ルの蒸発残留物に対する阻止率をａ、同じくホウ素に対する阻止率をｂ、第２段目逆浸透膜モジュ−ルの蒸発残留物に対する阻止率をａ’、同じくホウ素に対する阻止率をｂ’とすれば、最終的に得る生産水の蒸発残留物含有率は（１−ａ）（１−ａ’）であり、同じくホウ素含有率は（１−ｂ）（１−ｂ’）であり、このホウ素含有率を０．２ｐｐｍ以下に抑えている。
【０００４】
しかしながら、蒸発残留物含有率が（１−ａ）（１−ａ’）で定まってしまい、ａ，ａ’がｂ，ｂ’に従属的に変動するので、蒸発残留物含有率をホウ素含有率に独立的に所望値に設定し難く、ホウ素含有率０．２ｐｐｍ以下にすると、蒸発残留物含有量がおいしい飲料水の条件から外れ、またｐＨもアルカリ側になってしまう。
従って、特開平８−２０６４６０号等に開示された２段逆浸透膜分離法では、おいしい飲料水を生産することが難しい。
【０００５】
本発明の目的は、ホウ素を多量に含有する原液、例えば、海水から、２段逆浸透膜分離によりホウ素含有量を所望値に減量し、かつカルシウム等の蒸発残留物の含有量を所望値に減量し、しかもｐＨを中性側にした、所謂、おいしい飲料水を容易に生産できる逆浸透膜分離方法を提供することにある。
【０００６】
【課題を解決するための手段】
請求項１に係る海水の逆浸透膜分離方法は、海水を第１段目逆浸透膜モジュールによって処理し、更にその透過液の一部（１−ｘ）を第２段目逆浸透膜モジュールによって処理し、この第２段目逆浸透膜モジュールの透過液と第１段目逆浸透膜モジュールの残部の透過液ｘとを混合して飲料水を得る方法であり、海水が流通される圧力ケース内の上流側に上流側逆浸透膜モジュールエレメントを、同圧力ケース内の下流側に下流側逆浸透膜モジュールエレメントをそれぞれ収容した逆浸透膜モジュールを第１段目逆浸透膜モジュールとして使用し、上流側逆浸透膜モジュールエレメントの透過液を前記残部の透過液ｘとし、下流側逆浸透膜モジュールエレメントの透過液を前記透過液の一部（１−ｘ）とすることを特徴とする。
【０００７】
請求項２に係る逆浸透膜分離方法は、原液を第１段目逆浸透膜モジュ−ルによって処理し、更にその透過液の一部を第２段目逆浸透膜モジュ−ルによつて処理し、この第２段目逆浸透膜モジュ−ルの透過液と第１段目逆浸透膜モジュ−ルの残部透過液とを混合して原液中の蒸発残留成分とホウ素成分とを減量調整した調整液を得る方法であり、第１段目逆浸透膜モジュ−ルの透過液の一部を当該逆浸透膜モジュ−ルの下流側透過液とし、同残部透過液を当該逆浸透膜モジュ−ルの上流側透過液とし、第１段目逆浸透膜モジュ−ルの供給側ｐＨ値を８以下とし、第２段目逆浸透膜モジュ−ルの供給側ｐＨ値を８以上とすることを特徴とし、特に、海水、ホウ素を多量に含有するかん水や排水から飲料水を生産する場合は、第１成分を蒸発残留物とし、第２成分をホウ素とし、第１段目逆浸透膜モジュ−ルの供給側ｐＨ値を８以下とし、第２段目逆浸透膜モジュ−ルの供給側ｐＨ値を８以上とし、また、第１段目逆浸透膜モジュ−ルにおける、供給液３．５％食塩水、操作圧力５６kgf/cm^２、温度２５℃、ｐＨ６．５の条件で評価した食塩阻止率を９９％以上、より好ましくは９９．４％以上とし．同条件のもとでの透過流束を０．４m３/m^２・日以上とし、第２段目逆浸透膜モジュ−ルにおける、供給液０．０５％食塩水、操作圧力７．５kgf/cm^２、温度２５℃、ｐＨ６．５の条件で評価した食塩阻止率を９８％以上、より好ましくは、９９％以上とし、同条件のもとでの透過流束を０．６m^３/m^２・日以上とすることが好ましい。
【０００８】
【発明の実施の形態】
以下、図面を参照しつつ本発明の実施の形態について説明する。
図１は、本発明に係る逆浸透膜分離方法の処理フロ−を示している。
図１において、４１は第１段目逆浸透膜モジュ−ルを、４２は第２段目逆浸透膜モジュ−ルをそれぞれ示している。４０は第１成分Ａと第２成分Ｂとを含有する原液を示し、この原液４０を第１段目逆浸透膜モジュ−ル４１で回収率ｙ₁で処理し、第１段目逆浸透膜モジュ−ル４１の透過液をｘ量と（１−ｘ）量とに分け、透過液量（１−ｘ）を第２段目逆浸透膜モジュ−ル４２に供給し、更に回収率ｙ₂で処理し、その透過液と第１段目逆浸透膜モジュ−ル４１の残部透過液量ｘとを合流させて生産液を得る。
【０００９】
上記、ａ、ａ’、ｂ、ｂ’はｐＨ値や逆浸透膜モジュ−ルの膜材質等によって調整できる要素である。
而るに、本発明に係る逆浸透膜分離方法においては、これらの調整にとどまらず、第１段目逆浸透膜モジュ−ルの透過液の分流比ｘ、回収率ｙ₁更には、第２段目逆浸透膜モジュ−ルでの回収率ｙ₂によっても、生産液の第１成分Ａの含有率、第２成分Ｂの含有率ＸBを調整できる結果、生産液の第１成分含有量及び第２成分含有量を所望値に容易に設定できる。
すなわち、従来法での生産液の第１成分含有量ＸA’、第２成分含有量ＸB’は、ＸA’＝(1-a)(1-a')
ＸB’＝(1-b)(1-b')
で与えられ、ａ、ａ’、ｂ、ｂ’で決まってしまうが、本発明に係る逆浸透膜分離方法においては、分流比ｘ、回収率ｙ₁、ｙ₂によっても第１成分含有量ＸA’、第２成分含有量ＸB’を調整できるので、生産液の第１成分含有量及び第２成分含有量を多技的に調整でき、所望値にそれだけ容易に設定できるのである。
【００１０】
上記の分流比ｘは、０．２〜０．８、好ましくは０．３〜０．７の範囲内で設定される。
上記第１段目逆浸透膜モジュ−ル内においては、原液濃度が下流側に至るほど高濃度となり、従って同逆浸透膜モジュ−ルの透過液側においても、第１成分及び第２成分の濃度が下流側に至るほど高濃度となる。
而るに、本発明においては第１段目逆浸透膜モジュ−ルの下流側の透過液を第２段目逆浸透膜モジュ−ルに供給しており、第２段目逆浸透膜モジュ−ルの塩除去性能を効率よく発揮させ得る。
【００１１】
次に、ホウ素を多量に含有する原液、例えば海水（ホウ素含有量４．２ｐｐｍ）から、所謂、おいしい飲料水を生産する場合の実施例について説明する。
この実施例において、第１成分はカルシウム等の蒸発残留物であり、第２成分はホウ素である。
【００１２】
図２はこの実施例において使用する逆浸透膜分離装置を示している。
図２において、１はホウ素を多量に含有する原液のタンク（海水タンク）を、２は前処理槽を、３１は第１段目送液ポンプを、４１は第１段目逆浸透膜分離モジュ−ルを、４１１は第１段目逆浸透膜モジュ−ルの濃縮液を、４１２は第１段目逆浸透膜モジュ−ルの上流側透過液を、４１３は同じく下流側透過液をそれぞれ示している。
５は中間タンクを、３２は第２段目送液ポンプを、４２は第２段目逆浸透膜分離モジュ−ルを、４２１は第２段目逆浸透膜モジュ−ルの濃縮液を、４２４は第２段目逆浸透膜モジュ−ルの透過液をそれぞれ示している。この第２段目逆浸透膜モジュ−ルの濃縮液は、原液供給側に全量または一部をリタ−ンさせることができ（リタ−ン量を多くするほど、システム全体の回収率を向上でき、また、第１段目逆浸透膜モジュ−ルへの供給水自体の純度をアップでき、全体の水質を向上できる）、４２２はそのリタ−ン液を、４２３はその放流液をそれぞれ示している。
４００は第１段目逆浸透膜モジュ−ルの上流側透過液４１２と第２段目逆浸透膜モジュ−ル４２の透過液４２４とを混合させてなる生産液を示している。
また、カルシウムスケ−ルを防止するために、第１段目逆浸透膜モジュ−ル４１の供給液に酸を添加してｐＨ調整を行うこともでき、６１は酸液タンクを、７１は酸液送りポンプをそれぞれ示している。
また、第２段目逆浸透膜モジュ−ル４２のホウ素の除去率を大きくするために、ｐＨがアリカリ側にされ、６２はアリカリ液タンクを、７２はアルカリ液送ポンプを示している。
【００１３】
上記装置を用いて本発明により飲料水を生産するには、海水タンク１内の海水を前処理槽２で前処理したうえで、第１段目送液ポンプ３１により所定の圧力で第１段目逆浸透膜分離モジュ−ル４１に供給し、濃縮された非透過液は第１段目逆浸透膜モジュ−ルの濃縮液４１１として系内から排出する。前処理槽２は、第１段目逆浸透膜分離モジュ−ル４１の膜面を懸濁物質や有機物の付着、汚染から保護するために使用され、それらの懸濁物質や有機物等を除去するための手段、例えば、砂ろ過、精密ろ過、塩素や凝集剤の添加が施される。また、カルシウムスケ−ルを除去するために、第１段目逆浸透膜モジュ−ル４１の供給液に酸を酸液タンク６１からポンプ７１により添加してｐＨ調整を行うことができる。
第１段目逆浸透膜モジュ−ル４１の透過液を上流側透過液４１２と下流側透過液４１３とに分流させるには、例えば、第１段目逆浸透膜モジュ−ルの構成を、ベッセル（圧力ケ−ス）の上流側と下流側にそれぞれ独立の逆浸透膜モジュ−ルエレメントを収容し、上流側モジュ−ルエレメントの集水管下流側端を上流側透過液４１２の出口とし、下流側モジュ−ルエレメントの集水管下流側端を下流側透過液４１３の出口とすることができる。
而して、第１段目逆浸透膜モジュ−ル４１の下流側透過液４１３を一旦、中間タンク５に貯え、アルカリ液タンク６２のアルカリ液をポンプ７２により中間タンク５の貯液に添加し、更に、この貯液を第２段目送液ポンプ３２により所定の圧力で第２段目逆浸透膜分離モジュ−ル４２に供給し、濃縮された非透過液（第２段目逆浸透膜モジュ−ルの濃縮液４２１）の全量または一部をリタ−ン液４２２として第１段目送液ポンプ３１の入口側に戻し、残りを放流液４２３として排出していく。また、第２段目逆浸透膜モジュ−ル４２の透過液４２４と第１段目逆浸透膜モジュ−ルの上流側透過液４１２とを合流させて所定の生産液４００を得る。
【００１４】
上記において、第１段目液送ポンプ３１の圧力を高くして、第１段目逆浸透膜分離モジュ−ル４１の透過側に圧力を作用させ、その圧力で第２段目逆浸透膜分離モジュ−ル４２を作動させることもでき、この場合、中間タンク５及び第２段目送液ポンプ３２は省略できる。
上記において、第２段目逆浸透膜モジュ−ル４２の供給側ｐＨ値は８以上、好ましくは８．５以上とされる。また、第１段目逆浸透膜モジュ−ル４１の阻止性能は、供給液３．５％食塩水、操作圧力５６kgf/cm²、温度２５℃、ｐＨ６．５の条件で評価した食塩阻止率のもとで９９％以上とされ、第２段目逆浸透膜モジュ−ルの阻止性能は、供給液０．０５％食塩水、操作圧力７．５kgf/cm²、温度２５℃、ｐＨ６．５の条件で評価した食塩阻止率のもとで９８％以上とされる。
上記第１段目及び第２段目逆浸透膜モジュ−ルには、化学的に安定な架橋ポリアミド、より好ましくは、芳香族架橋ポリアミドをスキン層とする複合膜を用いた逆浸透膜モジュ−ルを使用することが好ましい。
更に、上記逆浸透膜モジュ−ル、特に、第２段目逆浸透膜モジュ−ル４２においては、膜面積の割には透過流束を大きくするために、スキン層の比表面積を３以上とすることが好ましい。
上記第１段目及び第２段目の逆浸透膜分離モジュ−ルには、スパイラル型、中空糸型、チュ−ブラ−型等を使用できる。
上記第２段目逆浸透膜分離モジュ−ルの後段に逆浸透膜分離モジュ−ルを接続して２段以上の多段で実施したり、第１段目逆浸透膜モジュ−ルの濃縮液を更に逆浸透膜モジュ−ル処理してシステムの回収率を高めることもできる。
【００１５】
【実施例】
〔実施例〕
図２に示す逆浸透膜分離装置を使用した。
第１段目逆浸透分離膜モジュ−ルには、３．５％食塩水を供給液としてのｐＨ６．５、温度２５℃、操作圧力５６kgf/cm²での塩阻止率が９９．６％であるスパイラル型逆浸透分離膜モジュ−ル〔日東電工（株）製ＮＴＲ−７０ＳＷＣ〕を用い、第２段目逆浸透分離膜モジュ−ルには、０．０５％食塩水を供給液としてのｐＨ６．５、温度２５℃、操作圧力７．５kgf/cm²での塩阻止率が９９．５％のスパイラル型逆浸透分離膜モジュ−ル〔日東電工（株）製ＥＳ１０〕を用いた。両逆浸透膜モジュ−ルとも、複合膜のスキン層に芳香族架橋ポリアミドを使用してある。
第１段目逆浸透分離膜モジュ−ルとしては、上記のＮＴＲ−７０ＳＷＣを６本直列に接続したものを使用し、第２段目逆浸透分離膜モジュ−ルとしては、上記のＥＳ１０を一本使用した。
原液には海水（ホウ素含有量４．２ｐｐｍ）を使用した。
第１段目逆浸透分離膜モジュ−ルを操作圧力５６kgf/cm²、回収率４０％にて運転して脱塩を行った。第１段目逆浸透膜モジュ−ルの上流側透過液は、上流側二本から採り、その透過液量は第１段目逆浸透膜モジュ−ル透過液総量の４６％、蒸発残留物含有量は１２０ｐｐｍ、ホウ素含有量は０．６ｐｐｍであった。
一方、第１段目逆浸透膜モジュ−ルの下流側透過液の蒸発残留物含有量は２７０ｐｐｍ、ホウ素含有量は０．８ｐｐｍ、ｐＨ値は５であった。この第１段目逆浸透膜モジュ−ルの下流側透過液に水酸化ナトリウムを添加してｐＨ値を９．５に調整し、この調整液を第２段目逆浸透膜モジュ−ルで操作圧力７．５kgf/cm²、回収率９０％にて脱塩した。この第２段目逆浸透膜モジュ−ルの透過液の蒸発残留物含有量は１０ｐｐｍ、ホウ素含有量は０．２ｐｐｍ、ｐＨ値は９であった（このままでは、蒸発残留物含有量が低すぎ、おいしい飲料水としての硬水の要件を欠如しており、ｐＨ値もアリカリ側であり、飲料水として不適格）。
第１段目逆浸透膜モジュ−ルの上流側透過液と第２段目逆浸透膜モジュ−ルの透過液との混合液である生産水の蒸発残留物含有量は６０ｐｐｍ、ホウ素含有量は０．４ｐｐｍ、ｐＨ値は７であり、おいしい飲料水としての要件を充足していた。
【００１６】
〔比較例〕
実施例に対し、第２段目逆浸透膜モジュ−ルの本数を実施例の２倍にし（２本にし）、第１段目逆浸透膜モジュ−ルの透過液の全量を第２段目逆浸透膜モジュ−ルに供給した以外、実施例に同じとした。
この比較例における、第１段目逆浸透膜モジュ−ルの透過液の蒸発残留物含有量は２００ｐｐｍ、ホウ素含有量は０．７ｐｐｍ、ｐＨ値は５であり、第２段目逆浸透膜モジュ−ルの透過液（生産液）の蒸発残留物含有量は８ｐｐｍ、ホウ素含有量は０．２ｐｐｍ、ｐＨ値は９であった。
この生産水は、蒸発残留物含有量が低く、アルカリ性であり、飲料水としては不適格であった。
【００１７】
【発明の効果】
本発明に係る逆浸透膜分離方法によれば、海水のようにホウ素を多量に含有する原液から、ホウ素を充分に除去して蒸発残留物が適量で、且つｐＨ値がほぼ中性の水を効率よく生産でき、逆浸透膜モジュ−ルの特性やｐＨ値の調整以外に第１段目逆浸透膜モジュ−ルの透過液の分流比や回収率及び第２段目逆浸透膜モジュ−ルの回収率の調整をも調整要素として所謂、おいしい水を容易に効率よく製造することができる。
更に、１段目逆浸透膜モジュ−ルの透過水量の一部を２段目逆浸透膜モジュ−ルに供給して処理しているので、１段目逆浸透膜モジュ−ルの透過水全量を２段目逆浸透膜モジュ−ルに供給し処理している従来法に較べ、２段目逆浸透膜モジュ−ルには小さい規模のものを使用すれば足り、設置する空間の省スペ−ス化や設備・運転コスト面での低減、省エネルギ化を図ることができる。
【図面の簡単な説明】
【図１】本発明に係る逆浸透膜分離方法の処理フロ−を示す図面である。
【図２】本発明の実施例において使用した逆浸透膜分離装置を示す図面である。
【符号の説明】
４１第１段目逆浸透膜モジュ−ル
４１２第１段目逆浸透膜モジュ−ルの上流側透過液
４１３第１段目逆浸透膜モジュ−ルの下流側透過液
４２第２段目逆浸透膜モジュ−ル
４０原液
４００生産液
６２アルカリ液タンク[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reverse osmosis membrane separation method, and is particularly useful when producing drinking water from a stock solution containing a large amount of boron, for example, seawater.
[0002]
[Prior art]
As a method of producing drinking water from seawater, seawater is treated with a first-stage reverse osmosis membrane module, and the permeate is adjusted to a pH value suitable for removing boron, and further, the second-stage reverse osmosis is performed. It has been proposed to treat with a membrane module (Japanese Patent Laid-Open Nos. 9-10766 and 8-206460).
[0003]
[Problems to be solved by the invention]
As is well known, so-called delicious drinking water is required to contain an appropriate amount of evaporation residue such as calcium and have a pH value in the vicinity of neutrality.
In the above-described method for producing drinking water by reverse osmosis membrane separation, the first stage reverse osmosis membrane module has a blocking rate for evaporation residue of a, the boron blocking rate for b, and the second stage reverse osmosis membrane module. -If the rejection rate for evaporation residue of a is a 'and the rejection rate for boron is b', the evaporation residue content of the final product water is (1-a) (1-a ') Yes, the boron content is (1-b) (1-b ′), and the boron content is suppressed to 0.2 ppm or less.
[0004]
However, the evaporation residue content is determined by (1-a) (1-a ′), and a and a ′ vary depending on b and b ′. However, if the boron content is 0.2 ppm or less, the evaporation residue content deviates from the conditions of delicious drinking water, and the pH also becomes alkaline.
Therefore, it is difficult to produce delicious drinking water by the two-stage reverse osmosis membrane separation method disclosed in JP-A-8-206460.
[0005]
The object of the present invention is to reduce the boron content to a desired value from a stock solution containing a large amount of boron, such as seawater, by two-stage reverse osmosis membrane separation, and to reduce the content of evaporation residues such as calcium to the desired value. An object of the present invention is to provide a reverse osmosis membrane separation method capable of easily producing so-called delicious drinking water with a reduced weight and a neutral pH.
[0006]
[Means for Solving the Problems]
In the reverse osmosis membrane separation method of seawater according to claim 1, seawater is processed by the first-stage reverse osmosis membrane module, and a part (1-x) of the permeate is further processed by the second-stage reverse osmosis membrane module. A pressure case in which seawater is circulated by treating and mixing the permeate of the second-stage reverse osmosis membrane module with the remaining permeate x of the first-stage reverse osmosis membrane module to obtain drinking water. A reverse osmosis membrane module containing the upstream reverse osmosis membrane module element on the upstream side and the downstream reverse osmosis membrane module element on the downstream side of the pressure case, respectively, as the first-stage reverse osmosis membrane module, The permeate of the upstream reverse osmosis membrane module element is the remaining permeate x, and the permeate of the downstream reverse osmosis membrane module element is a part (1-x) of the permeate.
[0007]
In the reverse osmosis membrane separation method according to claim 2 , the stock solution is processed by the first-stage reverse osmosis membrane module, and a part of the permeate is processed by the second-stage reverse osmosis membrane module. The second stage reverse osmosis membrane module permeate and the first stage reverse osmosis membrane module permeate were mixed to reduce the evaporation residual component and boron component in the stock solution. In this method, a part of the permeate of the first-stage reverse osmosis membrane module is used as the downstream permeate of the reverse osmosis membrane module, and the remaining permeate is used as the reverse osmosis membrane module. The supply side pH value of the first stage reverse osmosis membrane module is 8 or less, and the supply side pH value of the second stage reverse osmosis membrane module is 8 or more. characterized, in particular, sea water, when producing drinking water from high content to irrigation and drainage boron, evaporation residue of the first component The second component is boron, the supply side pH value of the first stage reverse osmosis membrane module is 8 or less, the supply side pH value of the second stage reverse osmosis membrane module is 8 or more, and In the first stage reverse osmosis membrane module, the salt blocking rate evaluated under the conditions of 3.5% saline solution, operating pressure 56 kgf / cm ² , temperature 25 ° C., pH 6.5 is 99% or more. Preferably it should be 99.4% or more. Under the same conditions, the permeation flux was 0.4 m3 / m ² · day or more, and the feed solution 0.05% saline solution, operating pressure 7.5 kgf / cm in the second stage reverse osmosis membrane module ^{2. The} salt rejection evaluated under the conditions of a temperature of 25 ° C. and a pH of 6.5 is 98% or more, more preferably 99% or more, and the permeation flux under the same conditions is 0.6 m ³ / m ² · It is preferable to set it to more than a day.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a processing flow of a reverse osmosis membrane separation method according to the present invention.
In FIG. 1, reference numeral 41 denotes a first-stage reverse osmosis membrane module, and 42 denotes a second-stage reverse osmosis membrane module. Reference numeral 40 denotes a stock solution containing the first component A and the second component B, and this stock solution 40 is processed by the first-stage reverse osmosis membrane module 41 at a recovery rate y ₁ to obtain a first-stage reverse osmosis membrane. The permeate of the module 41 is divided into x amount and (1-x) amount, the permeate amount (1-x) is supplied to the second-stage reverse osmosis membrane module 42, and the recovery rate y _{2 is} further increased. Then, the permeate and the remaining permeate amount x of the first-stage reverse osmosis membrane module 41 are merged to obtain a product solution.
[0009]
The above a, a ′, b, and b ′ are elements that can be adjusted by the pH value, the membrane material of the reverse osmosis membrane module, and the like.
Thus, the reverse osmosis membrane separation method according to the present invention is not limited to these adjustments, and the permeate splitting ratio x, recovery rate y _{1 of} the first-stage reverse osmosis membrane module, The content rate of the first component A and the content rate XB of the second component B in the production liquid can also be adjusted by the recovery rate y ₂ in the stage reverse osmosis membrane module. The second component content can be easily set to a desired value.
That is, the first component content XA ′ and the second component content XB ′ of the production liquid in the conventional method are: XA ′ = (1-a) (1-a ′)
XB '= (1-b) (1-b')
In the reverse osmosis membrane separation method according to the present invention, the first component content XA is also determined by the diversion ratio x and the recovery rates y ₁ and y ₂ . Since the second component content XB can be adjusted, the first component content and the second component content of the production liquid can be adjusted in a multi-technical manner and can be easily set to a desired value.
[0010]
The diversion ratio x is set within a range of 0.2 to 0.8, preferably 0.3 to 0.7.
In the first-stage reverse osmosis membrane module, the concentration of the stock solution increases toward the downstream side. Therefore, the first component and the second component of the reverse osmosis membrane module also on the permeate side. The higher the concentration is, the higher the concentration is.
Thus, in the present invention, the permeate downstream of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module, and the second-stage reverse osmosis membrane module is supplied. The salt removal performance of the water can be efficiently exhibited.
[0011]
Next, an example in which so-called delicious drinking water is produced from a stock solution containing a large amount of boron, for example, seawater (boron content: 4.2 ppm) will be described.
In this embodiment, the first component is an evaporation residue such as calcium, and the second component is boron.
[0012]
FIG. 2 shows a reverse osmosis membrane separation apparatus used in this embodiment.
In FIG. 2, 1 is a stock solution tank (seawater tank) containing a large amount of boron, 2 is a pretreatment tank, 31 is a first-stage liquid feed pump, and 41 is a first-stage reverse osmosis membrane separation module. 411 is the concentrated solution of the first-stage reverse osmosis membrane module, 412 is the upstream permeate of the first-stage reverse osmosis membrane module, and 413 is the downstream permeate. Yes.
5 is an intermediate tank, 32 is a second stage liquid feed pump, 42 is a second stage reverse osmosis membrane separation module, 421 is a concentrate of the second stage reverse osmosis membrane module, 424 is The permeated liquid of the second-stage reverse osmosis membrane module is shown. The concentrated solution of the second-stage reverse osmosis membrane module can be completely or partially returned to the stock solution supply side (the larger the return amount, the more the recovery rate of the entire system can be improved). In addition, the purity of the feed water itself to the first-stage reverse osmosis membrane module can be improved, and the overall water quality can be improved.) 422 indicates the return liquid, and 423 indicates the discharge liquid. Yes.
Reference numeral 400 denotes a production liquid obtained by mixing the upstream permeate 412 of the first-stage reverse osmosis membrane module and the permeate 424 of the second-stage reverse osmosis membrane module 42.
In order to prevent calcium scale, pH can be adjusted by adding acid to the supply liquid of the first-stage reverse osmosis membrane module 41, wherein 61 is an acid tank, 71 is an acid. Each of the liquid feed pumps is shown.
Further, in order to increase the boron removal rate of the second-stage reverse osmosis membrane module 42, the pH is set to the antkari side, 62 denotes an antari liquid tank, and 72 denotes an alkaline liquid feed pump.
[0013]
In order to produce drinking water according to the present invention using the above-described apparatus, the seawater in the seawater tank 1 is pretreated in the pretreatment tank 2, and then the first stage liquid pump 31 is used to produce the first stage at a predetermined pressure. The non-permeated liquid supplied and concentrated to the reverse osmosis membrane separation module 41 is discharged from the system as the concentrated liquid 411 of the first-stage reverse osmosis membrane module. The pretreatment tank 2 is used to protect the membrane surface of the first-stage reverse osmosis membrane separation module 41 from adhesion and contamination of suspended substances and organic substances, and remove these suspended substances and organic substances. Means for this, for example sand filtration, microfiltration, addition of chlorine and flocculants. In order to remove the calcium scale, the pH can be adjusted by adding an acid from the acid solution tank 61 to the supply solution of the first-stage reverse osmosis membrane module 41 from the acid solution tank 61.
In order to divert the permeate of the first-stage reverse osmosis membrane module 41 into the upstream permeate 412 and the downstream permeate 413, for example, the configuration of the first-stage reverse osmosis membrane module is changed to a vessel. An independent reverse osmosis membrane module element is accommodated on the upstream side and downstream side of the (pressure case), and the downstream end of the water collecting pipe of the upstream module element is used as the outlet of the upstream permeate 412. The downstream end of the water collecting pipe of the side module element can be used as the outlet of the downstream permeate 413.
Thus, the downstream permeate 413 of the first-stage reverse osmosis membrane module 41 is temporarily stored in the intermediate tank 5, and the alkaline liquid in the alkaline liquid tank 62 is added to the stored liquid in the intermediate tank 5 by the pump 72. Further, the stored liquid is supplied to the second-stage reverse osmosis membrane separation module 42 at a predetermined pressure by the second-stage liquid feed pump 32, and the concentrated non-permeate (second-stage reverse osmosis membrane module) is supplied. The whole or part of the concentrated liquid 421) is returned to the inlet side of the first-stage liquid feed pump 31 as the return liquid 422, and the rest is discharged as the discharge liquid 423. Further, the permeate 424 of the second-stage reverse osmosis membrane module 42 and the upstream permeate 412 of the first-stage reverse osmosis membrane module are merged to obtain a predetermined production liquid 400.
[0014]
In the above, the pressure of the first-stage reverse osmosis membrane separation module 41 is increased by increasing the pressure of the first-stage liquid feed pump 31, and the second-stage reverse osmosis membrane separation is performed at that pressure. The module 42 can also be operated, and in this case, the intermediate tank 5 and the second stage liquid feed pump 32 can be omitted.
In the above, the supply side pH value of the second stage reverse osmosis membrane module 42 is 8 or more, preferably 8.5 or more. Further, the blocking performance of the first-stage reverse osmosis membrane module 41 is the salt blocking rate evaluated under the conditions of a supply solution of 3.5% saline, an operating pressure of 56 kgf / cm ² , a temperature of 25 ° C., and a pH of 6.5. The blocking performance of the second-stage reverse osmosis membrane module was originally 0.05% saline solution, operating pressure 7.5 kgf / cm ² , temperature 25 ° C., pH 6.5. 98% or more based on the salt blocking rate evaluated under the conditions.
The first-stage and second-stage reverse osmosis membrane modules include a reverse osmosis membrane module using a chemically stable crosslinked polyamide, more preferably a composite membrane having an aromatic crosslinked polyamide as a skin layer. It is preferable to use
Furthermore, in the reverse osmosis membrane module, particularly the second-stage reverse osmosis membrane module 42, the skin layer has a specific surface area of 3 or more in order to increase the permeation flux relative to the membrane area. It is preferable to do.
As the first and second stage reverse osmosis membrane separation modules, spiral type, hollow fiber type, tuber type and the like can be used.
The reverse osmosis membrane separation module is connected to the subsequent stage of the second stage reverse osmosis membrane separation module, and the process is carried out in two or more stages, or the concentrated solution of the first stage reverse osmosis membrane module is used. Further, the recovery rate of the system can be increased by treating with a reverse osmosis membrane module.
[0015]
【Example】
〔Example〕
The reverse osmosis membrane separation apparatus shown in FIG. 2 was used.
The first-stage reverse osmosis separation membrane module has a salt rejection of 99.6% at pH 6.5 using a 3.5% saline solution as a feed solution, a temperature of 25 ° C., and an operating pressure of 56 kgf / cm ^2. A spiral reverse osmosis separation membrane module [NTR-70SWC manufactured by Nitto Denko Corporation] was used, and the second-stage reverse osmosis separation membrane module had a pH of 6% as a feed solution with 0.05% saline. Spiral reverse osmosis separation membrane module [ES10 manufactured by Nitto Denko Corporation] having a salt rejection of 99.5% at a temperature of 25 ° C. and an operating pressure of 7.5 kgf / cm ² was used. Both reverse osmosis membrane modules use aromatic crosslinked polyamide for the skin layer of the composite membrane.
As the first-stage reverse osmosis separation membrane module, six NTR-70SWCs connected in series are used, and as the second-stage reverse osmosis separation membrane module, the above ES10 is integrated. Used this book.
Seawater (boron content 4.2 ppm) was used as the stock solution.
Desalination was performed by operating the first-stage reverse osmosis separation membrane module at an operating pressure of 56 kgf / cm ² and a recovery rate of 40%. The upstream permeate of the first-stage reverse osmosis membrane module is taken from two upstream sides, and the permeate amount is 46% of the total permeate of the first-stage reverse osmosis membrane module and contains evaporation residue. The amount was 120 ppm and the boron content was 0.6 ppm.
On the other hand, the evaporation residue content of the downstream permeate of the first-stage reverse osmosis membrane module was 270 ppm, the boron content was 0.8 ppm, and the pH value was 5. Sodium hydroxide was added to the downstream permeate of the first stage reverse osmosis membrane module to adjust the pH value to 9.5, and this adjustment liquid was operated with the second stage reverse osmosis membrane module. Desalination was performed at a pressure of 7.5 kgf / cm ² and a recovery rate of 90%. The second stage reverse osmosis membrane module permeate had an evaporation residue content of 10 ppm, a boron content of 0.2 ppm, and a pH value of 9 (in this state, the evaporation residue content was too low. Lack of hard water requirements as delicious drinking water, pH value is also on the ants side, ineligible as drinking water).
The evaporation residue content of production water, which is a mixed solution of the upstream permeate of the first stage reverse osmosis membrane module and the permeate of the second stage reverse osmosis membrane module, is 60 ppm, and the boron content is 0.4 ppm and pH value were 7, which satisfied the requirements for delicious drinking water.
[0016]
[Comparative example]
The number of second-stage reverse osmosis membrane modules is doubled to that of the embodiment (doubled), and the total amount of permeate in the first-stage reverse osmosis membrane module is set to the second-stage reverse osmosis membrane module. The same as in the examples except that it was supplied to the reverse osmosis membrane module.
In this comparative example, the evaporation residue content of the permeate of the first stage reverse osmosis membrane module is 200 ppm, the boron content is 0.7 ppm, and the pH value is 5. The second stage reverse osmosis membrane module is The evaporation residue content of the permeated liquid (production liquid) was 8 ppm, the boron content was 0.2 ppm, and the pH value was 9.
This product water had a low evaporation residue content, was alkaline, and was not suitable for drinking water.
[0017]
【The invention's effect】
According to the reverse osmosis membrane separation method according to the present invention, from a stock solution containing a large amount of boron such as seawater, boron is sufficiently removed to obtain an appropriate amount of evaporation residue and neutral pH water. It is possible to produce efficiently, in addition to adjusting the characteristics and pH value of the reverse osmosis membrane module, the flow split ratio and recovery rate of the first stage reverse osmosis membrane module and the second stage reverse osmosis membrane module. The so-called delicious water can be easily and efficiently produced using the adjustment of the recovery rate as an adjustment factor.
Furthermore, since a part of the permeated water amount of the first-stage reverse osmosis membrane module is supplied to the second-stage reverse osmosis membrane module and processed, the total permeated water amount of the first-stage reverse osmosis membrane module Compared with the conventional method that supplies and processes the second-stage reverse osmosis membrane module, it is sufficient to use a small-scale second-stage reverse osmosis membrane module, which saves space for installation. Reduction in equipment, operating costs, and energy savings.
[Brief description of the drawings]
FIG. 1 is a drawing showing a processing flow of a reverse osmosis membrane separation method according to the present invention.
FIG. 2 is a drawing showing a reverse osmosis membrane separation apparatus used in an example of the present invention.
[Explanation of symbols]
41 First-stage reverse osmosis membrane module 412 First-stage reverse osmosis membrane module upstream permeate 413 First-stage reverse osmosis membrane module downstream-permeate 42 Second-stage reverse osmosis liquid Membrane module 40 Stock solution 400 Production solution 62 Alkaline solution tank

Claims

Seawater is processed by the first-stage reverse osmosis membrane module, and a part (1-x) of the permeate is further processed by the second-stage reverse osmosis membrane module. And the remaining permeate x of the first-stage reverse osmosis membrane module to obtain drinking water , the upstream reverse osmosis membrane module element on the upstream side in the pressure case in which seawater is circulated, A reverse osmosis membrane module that accommodates downstream reverse osmosis membrane module elements on the downstream side in the same pressure case is used as the first-stage reverse osmosis membrane module, and the permeate of the upstream reverse osmosis membrane module element is used for the remaining portion. A reverse osmosis membrane separation method for seawater, characterized in that a permeate x is used, and a permeate of a downstream reverse osmosis membrane module element is a part (1-x) of the permeate.

The stock solution is processed by the first-stage reverse osmosis membrane module, and a part of the permeate is further processed by the second-stage reverse osmosis membrane module. And the remaining permeate of the first-stage reverse osmosis membrane module is mixed to obtain an adjustment liquid in which the evaporation residual component and the boron component in the stock solution are reduced and adjusted. A part of the permeate of the reverse osmosis membrane module is used as the downstream permeate of the reverse osmosis membrane module, and the remaining permeate is used as the upstream permeate of the reverse osmosis membrane module. A reverse osmosis membrane separation method, characterized in that the supply side pH value of the reverse osmosis membrane module is 8 or less and the supply side pH value of the second stage reverse osmosis membrane module is 8 or more.

The reverse osmosis membrane separation method according to claim 2, wherein the stock solution is seawater.

In the first stage reverse osmosis membrane module, the salt rejection evaluated under the conditions of 3.5% saline solution, operating pressure 56 kgf / cm ² , temperature 25 ° C., pH 6.5 is 99% or more, In the second stage reverse osmosis membrane module, the salt rejection rate evaluated under the conditions of 0.05% saline solution, operating pressure 7.5 kgf / cm ² , temperature 25 ° C., pH 6.5 is 98% or more. The reverse osmosis membrane separation method according to claim 3.