Takanobu Sugo

The synthesis of a new type adsorbent for the removal of toxic gas by radiation-induced graft polymerization

Abstract A new type of adsorbent containing sulfulic acid group for the removal of ammonia gas was synthesized by radiation-induced graft polymerization of styrene onto fibrous and nonwoven type polypropylene followed by sulufonation with chlorosulfonic acid. The rate of the adsorption of ammonia gas by H-type adsorbent is independent of the ion-exchange capacity. The amount of ammonia gas adsorbed by the chemical adsorption was dependent on the ion-exchange capacity of H-type fibrous adsorbent and was kept constant value in spite of the equilibrium pressure of ammonia gas. Cu(II)- and Ni(II)-types fibrous adsorbent were prepared by the ion exchange reaction of Na-type fibrous adsorbent with metal nitrate solutions. Although, the rate of adsorption of ammonia gas by metal-type fibrous adsorbent is lower than that of H-type adsorbent, the amount of ammonia gas adsorbed increase compared to H-type adsorbent with the same ion exchange capacity. It was related to the highest coordination number of metal ion. The ratio of the number of ammonia molecules adsorbed chemically and the number of metal ion adsorbed in fibrous adsorbent was 4 for Cu-type and 6 for Ni-type fibrous adsorbent, respectivelly.

Bifunctional Cation Exchange Fibers Having Phosphonic and Sulfonic Acid Groups

Bifunctional cation exchange fibers were derived from polyethylene coated polypropylene fibers (PPPE). Two types of PPPEs were used. One is short cut fiber (PPPF-f, 0.9 denier) and the other non-woven cloth (PPPF-c, 1.5 denier). First, precursory fibers were prepared by graft copolymerization of chloromethylstylene and styrene onto PPPE-c and PPPE-f by electron beam pre-irradiation induced liquid phase graft polymerization technique. Second, the precursory fibers were functionalized by Arbusov reaction, sulfonation, and acid hydrolysis in successive, resulting in the bifunctional fibers FPS-c (from PPPE-c) and FPS-f (from PPPE-f) having both phosphonic and sulfonic acid groups. For comparison, monofanctional phosphonic acid fibers FP-c (from PPPE-c) and FP-f (from PPPE-f) were also prepared by Arbusov reaction and the subsequent acid hydrolysis. Batchwise study using FPS-c and FP-c clarified that the bifunctional fiber FPS-c exhibits the characteristic metal ion selectivity resulting from the cooperative recognition of metal ions by both functional groups, and the bifunctional fiber takes up Pb(II) more rapidly than the monofunctional phosphonic acid fiber (FP-c) and resin (Diaion CRP200). Column-mode study using both bifunctional and monofunctional fibers FPS-f and FP-f revealed that both exhibit flow rate independent breakthrough profiles of Pb(II) up to flow rate of 900 h-1 in space velocity, indicating their extremely rapid adsorption rates of Pb(II). The bifunctional fiber gave breakthrough capacities of 0.54 – 0.57 mmol/g, which are nearly twice those of monofunctional one (0.28 – 0.33 mmol/g).

Commercial Products by Radiation-Induced Graft Polymerization

Radiation-induced graft polymerization is a powerful tool for the following reasons: (1) From the macroscopic standpoint, the form of the adsorbent can be selected. For example, nonwoven fabrics and porous sheets may be adopted as trunk polymers instead of beads or granules. (2) From the microscopic standpoint, graft chains are relatively flexible, providing a novel space for ions and molecules. For example, proteins can be multilayered via multipoint binding, and inorganic precipitates can be immobilized through entanglement and penetration. (3) From an industrial standpoint, the pre-irradiation method is advantageous in that the processes, i.e., irradiation and grafting, are separable. An electron-beam-irradiated wound film and bobbins of gamma-ray-irradiated fibers can be used as trunk polymers in continuous and batch modes, respectively. Many polymeric adsorbents of various forms and components can be produced by radiation-induced graft polymerization.

Revolution in the Form of Polymeric Adsorbents 1: Porous Hollow-Fiber Membranes and Porous Sheets

Porous hollow-fiber membranes and porous sheets used for microfiltration can be modified into porous adsorbents by radiation-induced graft polymerization. The three-dimensional modification or modification over the entire volume of the porous trunk polymer provides a functional density comparable to that of conventional adsorbents. The ideal adsorption in a flow-through mode is achievable because the time required for a target to diffuse to the functional moiety is much shorter than the residence time of the target solution as it passes through the porous membrane or sheet. The multilayer binding of proteins via multipoints in the polymer brush is applied to the immobilization of an enzyme at a high density, leading to high activity in enzyme reactions such as the quantitative hydrolysis of 4 M urea solution.

Competition Between Graft Chains and Rivals

New polymeric adsorbents prepared by radiation-induced graft polymerization are superior to conventional adsorbents in terms of resolution in elution chromatography and dynamic binding capacity in the flow-through mode. However, currently used adsorbents cannot be easily replaced with our new graft-type adsorbents. Thus far, graft-type adsorbents have not been considered as alternatives. This chapter provides information indicating that graft-type adsorbents may be useful for separation. When a new need for separation that cannot be easily met using existing adsorbents arises, then graft-type adsorbents will be available as promising candidates to meet this need.

Revolution in the Form of Polymeric Adsorbents 2: Fibers, Films, and Particles

Commercially available adsorbents are in the form of beads, granules, and short-length fibers. A 15-cm-diameter bobbin consisting of a fiber can be modified by radiation-induced graft polymerization. The fiber of the resultant bobbin can be fabricated into a wound filter, a nonwoven fabric, or a braid depending on the conditions of practical separation. In this chapter, examples of the application of functional fibers are the recovery of uranium from seawater using a chelating-group-immobilized fiber and the resolution of neodymium and dysprosium using an extractant-impregnated fiber. In addition, a polyethylene film is modified into ion-exchange membranes installed in an electrodialyzer for the production of edible salt.

Innovative Polymeric Adsorbents

Among the various graft polymerization methods, radiation-induced graft polymerization is powerful in that various forms of existing polymers can be selected as trunk polymers and converted into polymeric adsorbents. In particular, preirradiation graft polymerization has an advantage that the graft polymerization step can be separated from the irradiation step, which will enhance the industrial production of graft-type materials. The grafting of an epoxy-group-containing vinyl monomer, glycidyl methacrylate, enables the introduction of different functional moieties such as ion-exchange and chelate-forming groups, and hydrophobic and affinity ligands. In this chapter, batch and flow-through modes are described as methods of evaluating the performance of adsorbents for metal ions and proteins.

Fundamentals of Radiation-Induced Graft Polymerization

Among the various graft polymerization methods, radiation-induced graft polymerization is powerful in that various forms of existing polymers can be selected as trunk polymers and converted into polymeric adsorbents. In particular, preirradiation graft polymerization has an advantage that the graft polymerization step can be separated from the irradiation step, which will enhance the industrial production of graft-type materials. The grafting of an epoxy-group-containing vinyl monomer, glycidyl methacrylate, enables the introduction of different functional moieties such as ion-exchange and chelate-forming groups, and hydrophobic and affinity ligands. In this chapter, batch and flow-through modes are described as methods of evaluating the performance of adsorbents for metal ions and proteins.

Scientific Findings on Graft Chains

A graft chain immobilized onto a trunk polymer by radiation-induced graft polymerization has a free end and an immobile end. Depending on the formation site, the graft chain is divided into a polymer brush extending from the surface of the trunk polymer and a polymer root entering the matrix of the trunk polymer. The graft chain will extend or shrink depending on the density of the charged group of the graft chain and the ionic strength of the liquid surrounding the graft chain. An extended polymer brush captures proteins in multilayers via multipoints. When a graft chain is immobilized over a porous membrane, the permeability of the liquid through the porous membrane reflects the static and dynamic behavior of the graft chain. Also, the graft-chain phase diffusion of metal ions and proteins occurs, driven by the gradient of the number of ions and proteins bound by the graft chain.