Perancangan proses pembuatan membran ultrafiltrasi selulosa asetat secara inversi fasa dari seluloa pulp kayu sengon (Paraserianthes Falcataria)

Abstract

Cellulose acetate ultrafiltration membrane has been utilized in a variety of separation and purification processes, including in agro-industry sector. In general, cellulose acetate is obtained from acetylation of cotton cellulose and wood pulp (abaca, straw, sawdust). In this study, cellulose from wood pulp of Sengon (Paraserianthes falcataria) was used. This plant is fast growing species and has potential as a raw material from its high cellulose content. The purpose of this study was to find a cellulose acetate manufacturing process conditions, to characterize cellulose diacetate and its performance on ultrafiltration process. There are three steps of cellulose diacetate manufacturing process. They are: (1) activation of cellulose using acetic acid, (2) acetylation, cellulose in acetic acid solvent is reacted with acetic anhydride reactant using sulfuric acid as catalyst, (3) hydrolysis to obtain cellulose diacetate. At each operating processes acetyl content was observed at temperature 50oC. In addition, effect of variation of anhydride acetate reactant and cellulose ratio, namely (3.35:1), (4:1) (5:1), and (6:1) were also investigated. Asymmetric cellulose diacetate membrane preparation by phase inversion method was carried out by the addition of cellulose diacetate (SDA) as a polymer, N, N-Dimethil formaida (DMF) as solvent, water as a non-solvent, and polyethylene glycol (PEG) as additive. At this stage, effect of PEG / SDA ratio (10%, 20%, 30%), PEG molecular weight variation (1450, 4000, and 6000 Da), and coagulation temperature (15oC, room temperature, and 50oC) were also investigated. Membrane pore size was determined by by measuring Molecular Weight Cut Off ( MWCO) using a standard solution of dextran (12 kDa) and Bovin Serum Albumin (67 kDa). Membrane morphology was observed by Scanning Electron Microscope (SEM). Cellulose acetate of acetyl content of 39.66% and number average molecular weight 130,221 Da was obtained at the activation time 30 minutes; one hour acetylation process for acetic anhydride to cellulose ratio 3.35:1; and 15 hours hydrolysis process. The addition of PEG produced a thicker layer and greater tensile strength membranes and suppress the formation of macrovoid. SEM analysis shows a denser structure of membrane morphology with better regularity of pore shape, so has a better pore density (porosity) distribution of large and visible pores. The addition of PEG with higher molecular weight produces a denser morphological structure with larger pore size, but smaller porosity with large pore distribution. The addition of PEG with the increasing of PEG / SDA ratio resulted in a denser pore structure and greater number of pores with a greater porosity and large pore distribution. Coagulation at higher temperatures produced a thinner layer and low tensile strength membrane. The structure of membrane morphology is more tenuous with a bigger pore size and greater number of pores so large porosity and pore distribution. Flux (water, dextran, and BSA) and rejection (dextran and BSA) are determined by the porosity and pore distribution of the membrane. High flux and rejection generated by large porosity and small pore distribution membrane. Membrane having small porosity and pore distribution produces low flux but high rejection. Conversely, high flux with low rejection obtained from the membrane with greater porosity and pore distribution. MWCO determination was based on the value of 80% rejection of dextran and BSA standard solution and the obtained pore size ranges obtained ≤ 67 kDa, and is still categorized as ultrafiltration membrane. For further research needs to use more standard solution so that the more precise determination of MWCO could be achieved. Cellulose diacetate membrane formulation produced by the addition of PEG 1450, PEG / SDA ratio 30% and coagulation at room temperature was applicated for patchouli alcohol (Pogostemon cablin Benth) to improve the content of patchouli alcohol and separation of the components of the sugarcane juice solution. Improvement of the essential oil of patchouli alcohol was carried out using the hydrophobicity difference principle. Results showed that there were elevated levels of 41,68% patchouli alcohol at a transmembrane pressure of 1.4 bar, patchouli oil flux of 134 L/m2. hour. Meanwhile, the permeate resulting from the separation of sugarcane juice solution components, with the increasing of transmembrane pressure from 0.6 to 1.8 bar obtained the increasing of flux solution from 36 to 165 L/m2.hour. Characteristics of permeate juice at 1.8 bar of transmembrane pressure increased the pH from 5.25 - 6 and decreased the turbidity about 34,95% from 90-54% (A) compared to raw sugarcane juice (nira).

Membran dapat diartikan sebagai penyaring atau penghalang berupa lapisan tipis dengan kemampuan selektifitas tinggi sehingga dapat memisahkan antara komponen satu dengan yang lainnya secara spesifik. Membran selulosa asetat merupakan salah satu membran yang banyak digunakan dalam berbagai proses pemisahan, seperti untuk pemisahan larutan senyawa-senyawa terlarut, pemisahan campuran gas atau uap pelarut, partikel/molekul dalam larutan, pemisahan ion-ion dan sebagainya. Pada bidang agroindustri, pemisahan menggunakan membran banyak dilakukan dengan jenis proses ultrafiltasi. Material membran berupa bahan organik yang banyak digunakan adalah polimer selulosa asetat yang dapat diperoleh dari kapas dan pulp kayu ( abaka, jerami, serbuk gergaji, tandan kosong sawit), namun selulosa asetat sendiri di Indonesia masih didatangkan dari luar (impor). Hal ini merupakan kendala dalam memproduksi membran di Indonesia sehingga membran yang digunakan pada dunia industri juga masih berupa membran impor. Sejauh ini selulosa pulp kayu sengon (Paraserianthes falcataria) belum dimanfaatkan sebagai bahan baku pembuatan polimer membran. Di Indonesia, tanaman ini mudah tumbuh dan memiliki potensi sebagai bahan baku pembuatan polimer membran karena kandungan selulosa yang tinggi sehingga dapat mengatasi kendala kelangkaan membran lokal. Tujuan penelitian ini adalah mendapatkan kondisi proses pembuatan selulosa diasetat (SDA) berbasis selulosa pulp kayu sengon serta mendapatkan kondisi rancangan proses pembuatan membran ultrafiltrasi selulosa asetat dengan penambahan polietilen glikol (PEG) sebagai porogen pada berbagai berat molekul PEG dan rasio PEG/SDA serta suhu koagulasi serta karakter membran. Membran selulosa diasetat bersifat hidrofilik dengan jenis ultrafiltrasi diharapkan dapat meningkatkan kadar patchouli alkohol dari minyak nilam serta pemurnian larutan nira.