Green Biorefinery- Separation of Lactic Acid From Grass Silage Juice

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Bioresource Technology 99 (2008) 43684379

Green Biorenery: Separation of lactic acid from grass silage juice by chromatography using neutral polymeric resinVu Hong Thanga

a,b

, Senad Novalin

a,*

Department of Food Science and Technology, Vienna University of Natural Resources and Applied Life Sciences (BOKU), Muthgasse 18, A-1190 Vienna, Austria b Department of Fermentation Technology, Hanoi University of Technology, 1 Dai Co Viet Road, Hanoi, Vietnam Received 22 June 2006; received in revised form 14 June 2007; accepted 23 August 2007 Available online 1 November 2007

Abstract The aim of this work was to recover lactic acid in undissociated form from grass silage juice. For this aim, chromatographic separation using neutral polymeric resin Amberlite XAD1600 was investigated. Up to now, there is no hint in the literatures about using neutral polymeric resin for lactic acid separation from a mixture. Important factors (ow-rate, concentration of feed and loaded volume) that aect separation performance were rstly investigated with model solutions. The obtained results showed that lactic acid solutions with the purity varying from 93.2% to 99.9% could be obtained at the recovery yields over 99.4%. After that, trials with silage juice were carried out. Due to the complex composition of the feed, the purity of products decreased to 94% at a recovery yield of 97%. Although 99% of inorganic salts and sugars were separated from lactic acid organic acids in general and acetic acid in particular caused a purity problem. It seems that organic acids could not be separated from lactic acid by neutral resin Amberlite XAD1600. Besides the organic acid problem, some amino acids were remained in the products as impurities. 2007 Elsevier Ltd. All rights reserved.Keywords: Grass silage; Lactic acid; Amberlite XAD1600; Preparative chromatography

1. Introduction Agriculture in many European countries is currently undergoing structural changes, which are characterized by a decrease of livestock and dairy farming. One of the consequences is an increase of unused grassland biomass (grass) and uncultivated grassland (fallow land), respectively. It was estimated that, in the medium term, 750,000 tons of dry matter per year would be available from grassland in Austria (Forschungsforum BMVIT, 2004). Innovative technology concepts for the utilization of this unused grass can provide the raw material for the manufacture of future-oriented products, and thus strengthen regional economies. In the future, grass may be used for the sustainable production of chemicals, biomaterials and*

Corresponding author. Tel.: +43 1 36006 6288; fax: +43 1 36006 6251. E-mail address: Senad.Novalin@boku.ac.at (S. Novalin).

plant bers. The Austrian Green Biorenery is one approach towards the implementation of these objectives. The basic idea here is that, in analogy to concepts applied in petrochemistry, the raw material grassland biomass is used with the whole plant to produce several product groups without generating waste. As grassland biomass does not oer a specic major component, like sugar beet (sucrose) or corn (starch), it is compelling to establish a multi-product system (Biorenery system). A key element in the Austrian concept is the utilization of silage instead of fresh biomass. During the fermentation process sugars are converted into lactic acid and proteins are hydrolysed to free amino acids. Therefore, lactic acid and amino acids are seen as the key compounds in such a Green Biorenery system based on grass silage (Kromus et al., 2004). Besides amino acids, interest in producing lactic acid is growing because of its great potential in the manufacture of biodegradable polymers (Datta et al., 1995). However,

0960-8524/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.08.045

V.H. Thang, S. Novalin / Bioresource Technology 99 (2008) 43684379

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Nomenclature BV bed volumecolumn volume for a packed column C0 initial concentration of lactic acid in starting solution, g L1 * C amount of lactic acid adsorbed by the resin, g g1 CE lactic acid concentration at equilibrium, g L1 Dinner inner diameter of column, cm H length of column, cm HPLC high performance liquid chromatography k 0A ; k 0B capacity factors LA N R T V V0 VL Vfeed W a lactic acid theoretical plate number resolution temperature, C initial volume of starting solution, L dead volume, mL maximum loaded volume, mL loaded volume, mL weight of resin, g relative retention

one main diculty in lactic acid production lays on the recovery cost. To avoid the formation of gypsum generated in the conventional recovery process, several new techniques have been developed for lactic acid recovery. Some of these techniques are electrodialysis (Heriban et al., 1993; Bailly, 2002), distillation with the simultaneous esterication reaction (Choi and Hong, 1999), ion exchange resin (Evangelista et al., 1994; Evangelista and Nikolov, 1996; Ponnampalam, 2001; Cao et al., 2002; Tong et al., 2004) and extraction (Matsumoto et al., 2003; Yankov et al., 2004). In the case of grass silage juice, it seems somewhat dicult to apply the above-mentioned techniques. Due to the heterogeneous nature of the silage microora, the selective separation of lactic acid requires delicate unit operations to produce an end product of acceptable quality (Danner et al., 2000). Nevertheless, separation of lactic acid from silage juices was previously reported. It was shown that lactic acid with high content of impurities could be obtained and therefore only low-grade applications such as animal feed additive or road-de-icers were suggested (Danner et al., 2000; Madzingaidzo et al., 2002). Thang et al. (2004, 2005) reported that high-energy consumption was required for removing ions other than lactate in lactic acid recovery from grass silage juice by two-stage electrodialysis. Chromatography is a powerful separation method that was developed initially for the extraction and purication of complex mixtures of vegetal origin (Guiochon, 2002). It has been developed for many years as a very useful tool for industrial applications. The use of this technique is increasingly applied in the pharmaceutical industry, biotechnology as well as in the production of ne chemicals (Dechow, 1991). Several of the many advantages of chromatography can be mentioned such as reduction of the euent volume and of the pollution load, avoidance of chemical regenerants or a signicant decrease of energy consumption. The successful application of chromatography in sugar industry has inspired the researchers to develop new chromatography systems for other application in industrial scale.

On the other hand, it should be noted that the resins used for chromatographic separation in sugar industry separation are ion exchange resin, which will be soon exhausted if the feed contains dierent ions in high amounts. It can be seen that chromatographic separation using ion exchange resin as separation media will probably not be practicable for the feed as silage juice. Although ion exclusion chromatography has been successfully applied for separating components of molasses, namely very complex mixtures, it should be noted that the content of dierent inorganic salts in silage juice is much higher than that in molasses. Ion exchange chromatography was also tested for lactic acid separation but the resins required several regeneration steps and needed eluents other than water such as acids, methanol, ammonia or either their mixtures (Ponnampalam, 2001; Cao et al., 2002; Tong et al., 2004). From the fact mentioned above, it goes to a new idea that if a neutral resin is used, the regeneration step will be much reduced. On the other hand, a simple and cheap eluent such as water will also be preferred to mentioned eluents. However, very few applications of chromatography using neutral resin were found for lactic acid separation. Only one publication about using neutral polymeric adsorbent for separation of citric acid from fermentation broth was found (Kulprathipanja, 1988). Applications for Amberlite XAD1600 resin suggested in the data sheet from Rohm and Haas Company include recovery and purication of antibiotics, water-soluble steroids, amino acids and proteins; removal of non-polar compounds from polar solvents. There is, of course, no hint in the literature of using this resin for separation of lactic acid from a mixture. It is believed that this work is the rst report about separation of lactic acid using neutral polymeric resin. In this work, the recovery of undissociated lactic acid from grass silage juice by chromatography using neutral adsorbent Amberlite XAD1600 was preliminarily investigated. First of all, the eects of operating parameters such as ow-rate, feed concentration and loaded volume were tested with the model solutions. After that, the column separation with grass silage juices was carried out.

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V.H. Thang, S. Novalin / Bioresource Technology 99 (2008) 43684379

2. Methods 2.1. Grass silage juice The dierent silages, which were collected from dierent farms in the province of Styria, Austria, were mainly produced from red clover (Trifolium pratense) and ryegrass (Lolium perenne). Silage juice was prepared by pressing ensiled forages. Dierent silage juices were mixed and stored at 30 C for further uses. 2.2. Chemicals The resin used in experiments was polymeric adsorbent Amberlite XAD1600 (Rohm and Haas, Belgium). The original resin has water content of 63.8%. The resin was then rinsed several times with high quality water and then ltered by paper lter. The water-rinsed resin, which was used for experiments, has water content about 65%. The model solutions were prepared by mixing 50% sodium lactate solution with glucose. The pH of