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Microparticles Using Supercritical Anti-Solvent

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Microparticles Using Supercritical Anti-Solvent CLEAN TECHNOLOGY, Vol. 14, No. 4, December 2008, pp. 242-247 청 정 생 산 공 정 기 술 초 임 계 반 용 매 법 을 이 용 한 폴 리 비 닐 피 s리 돈 미 세 입 자 의 제 조 신 문 삼 , 김* 화 용 서 울 대 학 교 화 학 생 물 공 학 부 151-744 서 울 시 관 악 구 신 림 동 산 56-1 (2008 년 8월 25일 접 수 ; )*8 년 9월 12일 수 정 본 접 수 ; 2008년 9월 18 일 채 택 ) Prejmration of Poly(JV-vinyl-2-pyrrolidoiie) Microparticles Using Supercritical Anti-solvent Moon 幼 m Shin and Hwayong K* im School of Chemical and Biological Engineering, Seoul National University San 56-1, Shinlim-dong, Gwanak-gu, Seoul 151-744, Korea (Received for review August 25, 2008; Revision received September 12, 2008; Revision accepted September 18, 2008) 요 약 화 장 품 , 의 약 품 , 전 자 소 재 분 야 에 서 생 체 적 합 , 생 분 해 성 고 분 자 로 널 리 사 용 되 는 폴 리 비 닐 피 롤 리 돈 (PVP) 을 에 어 로 젤 용 매 추 출 방 법 에 의 해 미 세 입 자 를 제 조 하 였 다 . 용 매 로 는 이 염 화 메 탄 을 , 반 용 매 로 는 초 임 계 이 산 화 탄 소 가 사 용 되 었 다 . 온 도 , 압 력 , 이 산 화 탄 소 유 량 , 용 액 유 량 의 작 업 조 건 에 따 라 0.184 - 0.249 um입 자 크 기 를 얻 었 고 , 그 입 자 크 기 에 영 향 을 미 치 는 초 기 구 형 입 자 크 기 와 의 상 관 관 계 를 규 명 하 였 다 - 주 제 어 : 폴 리 비 닐 피 롤 리 돈 , 반 용 매 , 미 세 입 자 , 초 임 계 유 체 , 고 분 자 Abstract: Poly(iV-vinyl-2-pyrrolidone) (PVP) has been used as biocompatible and biodegradable polymer in cosmetics, pharmaceuticals and electronics. Micro-particles of PVP were produced using an aerosol solvent extraction system (ASES). Dichloromethane (DCM) and supercritical carbon dioxide were used as solvent and antisolvent, respectively. The mean diameter of the obtained polymer particles ranged from 0.184 to 0.249 pm. The relationship between particle size and initial drop size was also considered. Key words : Poly(7V-vinyl-2-pyrr이 idone), Anti-solvent, Microparticles, Supercritical fluids, Polymer Introduction distribution[l]. Supercritical fluids are a green solvent for extraction and purification of cosmetics, pharmaceuticals, food Micro- or nano-sized psuticles are used in various fields, such supplements and natural products. Using supacritical fluid may as cosmetics, pharmaceuticals, dyes, and electronics. Ccxiventicmal overcome the drawbacks of conventional processes. Several processes for preparing nano- and micro-particles are crushing, processes that use the supercritical fluid for micronization have grinding, ball milling, spray drying, and solvent evaporation. been studied intmsively. These conventional techniques have disadvantages such as Various pr(x〉esses using supercritical fluids are introduced in thermal and chemical degradation of products, broad particle size review articles[2-5]. Rapid expansion of supercritical solutions * To whom correspondence should be addressed. E-mail: [email protected] 242 dean Tech., Vol. 14, No. 4, December 2008 243 (RESS) process consists in dissolving the product in the 아 프 (3) supercritical fluid and rapidly depressurizing this solution through Re an adequate nozzle, causing an extremely rapid nucleation of the product into a highly dispersed material. This process is restricted Larger Oh and Re indicate the jet stream is better atomized[14]. to the products that present a reasonable solubility in supercritical There are many types of atomizers, and various empirical fluid. The concept of the gas anti-solvent (GAS) process consists equations for the initial droplet size are proposed for each type. in decreasing the solvent power of a liquid solvent in which the The most important properties of liquid atomization are surface substrate is dissolved, by saturating it with supercritical fluid, tension, viscosity and density. For a liquid injected into a gaseous causing the substrate precipitation or recrystallization. The medium, the only thermodynamic property generally considered of aerosol solvent extraction system (ASES) process consists in importance is the gas density. The significant variables for liquid atomizing a solution of the substrate in an organic solvent into flow are the velocity of the liquid jet or sheet and the turbulence a precipitator and causing precipitation of product by rapid mass in the liquid stream. The important gas flow variables are the transfer of supercritical fluid and organic solvent.. The ASES absolute velocity and the relative gas-to-liquid velocity[14]. In the process has been applied by various research groups to polymers, case of the atomizer used in our experiment (the air-blast type pharmaceuticals, and superconductor precursors [6-9]. Most research atomizer), the equations that estimate the initial droplet size groups have reported experimental results and the effects of consist of two terms of relative velocity and surface tension, and parameters, such as pressure, temperature, and concentration of have the same form even though parameters of each equation are solution. Mass transfer of supercritical fluids and solvents was not same. So the use of these equations is justified for the also researched[10, 11]. Bristow et al.[12] studied supersaturation description of the qualitative relationship between the initial in the ASES process. Rantakyla et al. [13] studied the effect of droplet size and the processed particle size. We chose the initial droplet size, but they did not consider the effect of other equation suggested by Lorenzetto and Lefevre[15] to calculate the parameters in their analysis. Poly(7V-vinyi-2-pyrrolidone) (PVP) initial drop size because of the similarity in atomizers. has been used as biocompatible and biodegradable polymer in cosmetics, pharmaceuticals and electronics. (oO033 In this study, micro-particles of PVP were produced using the SMD = 0.95 (1+%)L7O + ASES process to investigate the effect of pressure, temperature mG and solution flow rate. And the effect of initial droplet sizes on 0.13(•쓰 然 )05 (1+ 쓰 幻 1'70 the particle sizes was analyzed. (4) apL mG Mathematical Models where the subscript G and L represent air and liquid, and m is flow rate (kg/s). SMD is the acronym of ‘Sauter mean diameter’ When a liquid jet emerges from a nozzle, it can be broken. and is defined as follows: Two factors contribute to the jet break up. One is the Reynolds number (Re) which is the ratio of inertial force and friction force. SMD = 늠 -丄느 (5) YW Re = 저 지 1아 1 (1) Al where Ni is the number of drops in size range i, and A is the 、가 lere d0 is nozzle diameter (m), Ul is liquid velocity (m/s), p l middle diameter of size i. is liquid density (kg/m3), and /?l is liquid viscosity (kg/m s). According to equilibrium thermodynamics, the interface does The other is the Weber number (We), which is the ratio of not exist above the critical point. Hence, when considering the kinetic energy and surface energy. slow process of carbon dioxide (CO2) dissolution in a solvent portion above the critical point, the solvent portion might be We=d0UlpL (2) regarded as an effective droplet without the interface and interfacial tension[10, 11], However, the interface is often formed <7 very rapidly, and it may be erroneous to analyze this phenomenon where is interfacial tension (kg/s2) between gas and liquid. with equilibrium thermodynamics[ 16]. Lengsfeld et aL[17] The Ohnesorge number (Oh) is defined by Re and We: studied the surface tension of DCM and CCh at the critical point of the mixture, and they found that interfacial tension of DCM 244 청 정 기 술 , 제 14권 제 4호 , 2008년 12월 Table 1. The mean diameter of PVP particles at various conditions Mean Solution Experiment T P flow rate CO2 flow rate Cone, (wt particle number (MPa) (kg/hr) %) diameter (K) (cm3/min) Cum) 1 313.15 15.0 0.50 2.50 0.50 0.195 2 323.15 15.0 0.50 2.50 0.50 0.233 3 333.15 15.0 0.50 2.50 0.50 0.252 4 343.15 15.0 0.50 2.50 0.50 0.286 5 313.15 13.0 0.50 2.50 0.50 0.216 6 313.15 17.0 0.50 2.50 0.50 0.184 7 313.15 15.0 0.30 2.50 0.50 0.249 8 313.15 15.0 0.40 2.50 0.50 0.230 9 313.15 15.0 0.60 2.50 0.50 0.201 10 313.15 15.0 0.70 2.50 . 0.50 0.212 11 313.15 15.0 0.50 2.25 0.50 0.203 12 313.15 15.0 0.50 2.75 0.50 0.184 in CO2 at 8.5 MPa and 308 K approximated to 0.00001 kg/s2. in DCM was pumped with an HPLC pump (Hitachi, L-7110). The liquid CO2 was pumped with a non-pulsating high-pressure Materials and Methods pump (Nihon Seimitsu Kagaku, NP-AX-70). The nozzle was made by Valeo Instruments Co. and its inner diameter was 0.127 Materials mm. The precipitator was heated in an air convection oven and PVP (M.W. 55,000) and DCM (min. 99.6%) were supplied pressurized with CO2.
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