Effect selective boron extraction by polymer supported 2-hydroxylethylamino propylene glycol functions

2-hidroksietilamino propilen glikol fonksiyonlu polimerik reçine ile borun seçimli ekstraksiyonu

Abstract

Boron is widely distributed on the earth, mainly in the form of boric acid or borate salts. Presence of boron in irrigation water, as low as 4 ppm, induces marked plant stunting effect. Although no any harmful effect of boron on living organism has been reported, World Health Organization (WHO) recommends a maximum boron concentration of 0.3 $mg.L^{-1}$ for drinking water. Among various methods studied, such as adsorption on magnesium oxide and ion exchange resins, polymeric boron chelating resins have proven to be more efficient sorbents when trace boron is to be removed. Polymer bound sugar derivatives such as N-methyl D-glucamine, sorbitol and mannitol have been employed successfully in removal of trace boron. However regenerabilities of those materials are limited. For instance boronspecific resin Amberlite IRA-743 with sorbityl functional forms complexes with boron and is highly specific. Using this resin, it is possible to reduce water's boron concentration below 1 ppm. Despite a boron removal efficiency of 90%, this process is unsatisfactory because of expensive resin regeneration and capacity loss in each regeneration step. Recently we have introduced polymer supported imino bis–propyleneglycol function as boron selective chelating group. It was demonstrated that, these materials are also very efficient in sorption of trace boron from water. In a detailed study, Smith et al described modification of branched polyethyleneimines with suitable epoxy compounds to give monool, diol and triol functions on each amino group. They proved that polymers possessing more hydroxyl groups around the amine nitrogen are better boron chelators. It was demonstrated that, more than 99.5 % of boron can be removed from dilute boric acid solution by the polymers with triol chelating units on each amine group. Since bis–propyleneglycols are formed by ring opening of the oxirane functions in those studies, the resulting vic-diols created on polymeric supports must be trans- to each other. Although some authors suggest cis-diol behavior in vic-diols formed by ring opening of the epoxy moiety, easy recovery of loaded boron in the present case implies boron chelating mostly via transpropanediol. Both isomers may form boron complex, but the cis-isomer is expected to form more stable complex. In this configuration a neutral boron ester formation seems to be favor. But tetra coordinated borate formation is still possible with the helps of additional hydroxy group formed during ring opening of the epoxy function on the GMA component of resin. In other words boron binding by this chelating group occurs either by neutral boron ester formation or by formation of negatively charged borate. In the following studies, we have also investigated boron binding properties of polymer supported imino-bis-(2,3-cis-propanediol) functions. This resin with cis-diol functionality was found to be rapid in boron uptake while the capacity per chelating group was retaining almost the same. However the recovery of sorbed boron by acid leaching, in that case, was very slow due to formation of highly stable tetra coordinated borate esters. This result revealed that, recovery of boric acid by acid treatment is easy when hydroxy groups of vic-diols are in trans- configuration and three of four newly introduced hydroxy groups take part in chelating with boron as mentioned above. We have concluded that, if three of the hydroxy groups are employed, the fourth hydroxyl group might not be necessary in boron binding. In order to prove this assumption, in this work we have studied boron binding efficiency of 2- hydroxylethylaminopropylene glycol functions having one hydroxyl group less than the formers. It was concluded that, three hydroxy groups of 2- hydroxylethylamino propylene glycol, together with additional hydroxy group formed by the ring opening of the epoxy group might be satisfactory for the boron binding. For this purpose 2- hydroxylethylamino propylene glycol was prepared by reacting glycidol with ethanolamine. Then it was reacted with GMA (0.4mol) based terpolymer beads with 3.4 mmol.g-1 of oxirane group density. The resulting terpolymer having hydroxyethylaminopropylene glycol functions (1.82 mmol.g-1) was found to be as efficient as previously reported iminodipropylene glycol functional resins in removal of trace boron from water. The resin showed a boron loading capacity of 1.6 mmol.$g^{-1}$. Nearly second- order kinetics, with respect to the boric acid (k =1.65 $mol.L^{-1}.s^{-1}$,with a correlation factor of 0.99129) was determined in non-buffered conditions.

Özet

Eser miktarda borik asit ve borat yapısında olan borun uzaklaştırılması, bu maddenin bitki bodurlaştırma etkisi nedeniyle özel bir öneme sahiptir. 1960’lı yıllarda ticari olarak üretilmeye başlanan Amberlite IRA-743 reçinesi sulu çözeltilerdeki bor konsantrasyonunu 1 ppm düzeylerine indirebilir. Ancak bu reçine rejenerasyon sırasında aktivitesini kaybettiğinden büyük çapta suyun arıtılmasında kullanılamaz. Batı Anadolumuzdaki bor kirliliği göz önüne alınırsa konu ülkemiz için özel bir öneme sahiptir. Bu bakımdan yeni ve çok daha etkin bor spesifik reçinelerin geliştirilmesi elzemdir. Bu çalışmada eser borun sudan arındırılması amacıyla 2-hidroksietilamino propilen glikol fonksiyonlu bor-spesifik reçine sentezlenerek bor adsorplama yeteneği incelendi. 2-hidroksietilamino propilen glikol (HEP) glisidolün molce fazla etanolaminle NMP çözücü ortamında reaksiyonuyla hazırlandı. Süspansiyon polimerizasyonu ile küresel formda (210-420 $mu m$) GMA (0.4 mol), MMA (0.5 mol), DVB (0.1 mol) terpolimeri ile HEP reaksiyona sokuldu. Ele geçen 2- hidroksietilamino propilen glikol fonksiyonlu (1.82 mmol.$g^{-1}$) terpolimer daha önce rapor ettiğimiz iminodipropilen glikol fonksiyonlu reçineler kadar sulu çözeltiden eser miktardaki borun gideriminde etkili olmuştur. Reçinenin bor yükleme kapasitesi 1.6 mmol.$g^{-1}$ bulunmuştur. Tamponsuz çözeltide reçinenin bor bağlanmasının hemen hemen 2. mertebeden bir kinetikle gerçekleştiği (hız sabiti: k=1.65 $mol.l^{-1}.s^{-1}$, düzeltme faktörü: 0.99129) görülmüştür. Reçinenin 1gramı 100 ppm bor içeren 105ml borik asit çözeltisindeki boru 35 dakika içinde tamamen gidermektedir. Bor yüklenmiş polimer örnekleri HCl (4M) ile yıkanarak bordan arındırılırken NaOH (0.1 M) çözeltisiyle de rejenere edilebilir.