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Modern unhairing technologies for effective control of H2S release from Beamhouse operations (#55)
J. Fennen1, C. Gabagnou1, D. Herta1
1 TFL Ledertechnik AG, Research & Development, Muttenz, Basel-Land, Switzerland
The toxicity and unpleasant smell of hydrogen sulphide (H2S) gas is an issue for the leather industry that has been contained rather than eliminated in tannery practice. Completely eliminating H2S from tanneries while maintaining practical and economically feasible processing is still a big challenge to be addressed. Significant progress has, though, been made by introducing robust and reliable low sulphide unhairing systems based on selective soaking and specific enzymatic liming auxiliaries. These systems allow the reduction of sodium sulphide offers from the typical 2.5% to 1% of pelt weight. These lower levels reduce the amount of hydrogen sulphide gas released into the environment from the liming float, as well as the amount of sulphide that is carried over in the hide to subsequent processing steps. Overall, the H2S problem is not eliminated, but significantly reduced with this technology.
Alternatively to, or in combination with organic thio compounds, H2S scavengers can be used to reduce or eliminate hydrogen sulphide released from liming floats. Different types of scavengers are available, but the selection is limited for technical and economic reasons.
The paper on hand shows how the release of hydrogen sulphide from beamhouse operations can be effectively controlled by a combination of technologies involving more effective unhairing with lower amounts of reductive agents, replacement of inorganic sulphide by organic thio compound and the use of H2S scavengers.
- The release of toxic H2S from Beamhouse operations can be effectively controlled using modern unhairing technologies allowing to use no or low sulphide.
- These modern unhairing systems are based on a combination of selective soaking, unhairing assisted by enzymes with specific activity and the use of organic thio compounds.
Keywords: Beamhouse, unhairing, low sulphide, low toxicity
A Novel Preservation-cum-Unhairing Process for Sustainable Leather Manufacturing: An Unconventional Approach in Leather Making (#245)
R. R. Jonnalagadda1, S. Murali1, A. Rathinam1, T. Palanisamy1
1 CSIR, Central Leather Research Institute, Chennai, India
Preservation (or) curing is an important unit process for transportation and storage of raw hides/skins without any deterioration. Popular preservation process is mostly achieved by reducing the moisture content of hides/skins using common salt (NaCl). Usage of salt in preservation process leads to generation of large amount of contaminated salt, total dissolved solids (TDS) and consume huge amount of water for subsequent rehydration step. On the other hand, lime-sodium sulphide based reductive process is commonly employed for the removal of hair from hides/skins. This process leads to generation of lime sludge and possible evolution of toxic hydrogen sulphide gas thereby making the working atmosphere more unpleasant. Several alternative techniques for preservation as well as unhairing process have been developed individually to replace salt and sulfide, respectively. However, a single compound performing dual functions such as preservation and unhairing action in neutral pH conditions has not explored so far. In the present work, a novel formulation has been developed, which possess the both preservation and unhairing potential, and applied on the hides/skins for storage up to 6 months at ambient conditions without dehydration. Low level of sulphide was used during alkaline fiber opening for complete removal of hair. The strength and organoleptic properties are on par with salted skins/hides. The developed process completely eliminates the use of salt and 75% sulphide and also reduces the time and water required for soaking process. The developed system reduces 85% of pollution load discharged from soaking and unhairing processes.
One pot system for salt free preservation and low sulfide dehairing for sustainable leather manufacture.
Keywords: Salt-free, Less-sulphide, Preservation, Unhairing
Unhairing and Fiber bundle-opening of Cowhides using KCl and LiBr/[AMIm]Cl Assisted Neutral Protease for Leather Making (#223)
H. Liu1, Q. Zhang1, Y. Zhang1, X. Li1, K. Tang1, J. Liu1, X. Zheng1, Y. Pei1
1 Zheng Zhou University, School of Materials and Engineering, Zheng Zhou , China
Nowadays, tannery pollution is of great concern worldwide. The unhairing and fiber bundle-opening processes contribute the majority of the pollution by the use of sodium sulfide and calcium hydroxide, which were proposed to be replaced by neutral protease combined with (potassium chloride) KCl, (lithium bromide)LiBr/1-allyl-3-methylimidazolium chloride([AMIm]Cl) in the present work. Proper amount of KCl can speed up the unhairing with the grain not destroyed by the neutral protease. Four methods for unhairing and fiber bundle-opening were used as follows: 1. Two steps in different floats as KCl/neutral protease unhairing, followed by LiBr/[AMIm]Cl for fiber bundle-opening; 2. Two steps in different floats as neutral protease unhairing, followed by LiBr/[AMIm]Cl for fiber bundle-opening; 3. One step in the same float as neutral protease for unhairing firstly and then LiBr/[AMIm]Cl for fiber bundle-opening. 4. One step in the same float as neutral protease/KCl for unhairing firstly and then LiBr/[AMIm]Cl for fiber bundle-opening. It was found that using neutral protease/KCl solution for unhairing and LiBr/[AMIm]Cl solution for fiber bundle-opening is the best in fiber bundle-opening at the liming process. Besides, all the methods used here are better than the traditional liming processes (C) from viewpoints of unhairing and fiber bundle-opening.
1. The addition of potassium chloride can improve the stability of neutral protease solution.
2. The catalytic efficiency of the enzyme was improved because of adding potassium chloride can enhance the contact rate of neutral protease with substrate.
3. Ionic liquids have less hydrolysis of collagen and larger dissolution of polysaccharides.
Keywords: Ionic liquid/LiBr, KCl, unhairing, fiber bundle opening, leather
Adsorptive removal of sulfate, phosphate and chloride by Mg-Al and Zn-Al Layered Double Hydroxides from aqueous solutions (#241)
M. Maia1, O. Perez-Lopez1, M. Gutterres1
1 Federal University of Rio Grande do Sul, Chemical Engineering Department, Laboratory for Leather and Environmental Studies – LACOURO, Porto Alegre, Brazil
The wastewater of leather industry contains pollution loads which includes anionic contaminants such as chloride, sulfate and phosphate. Different treatment technologies for tannery wastewater have been investigated. Adsorption is a promising technique due to its greater selectivity, simple operation, faster regeneration kinetics and high uptake capacity even at trace levels. In the present study, Mg-Al and Zn-Al Layered Double Hydroxides were synthesized by the co-precipitation method at variable pH through a semi-batch system. The prepared material was characterized by XRD, BET surface area determination, TG-DTA and FTIR. The chloride, sulfate and phosphate adsorption properties onto Mg-Al and Zn-Al Layered Double Hydroxides from aqueous solutions were evaluated. The adsorption experiments of chloride, sulfate and phosphate were investigated through batch studies at initial concentrations of 100 mg/L of these anions as NaCl, K2SO4 and KH2PO4, respectively. The experiments were carried out separately for each anionic specie by mixing 10 ml of solution with 1 g/L of adsorbent for 5 h. Mixing was performed on a thermostatic shaker at 200 rpm and at room temperature (25 °C). The effect of co-existing anions on the adsorption capacity were also analyzed. After ion adsorption, chloride, sulfate and phosphate concentrations were measured by ion chromatography. The results showed a removal ratio for Mg-Al Layered Double Hydroxide of 24% and 51% for sulfate and phosphate, respectively, while chloride was not removed from the solution. For the adsorbent Zn-Al Layered Double Hydroxide, the removal ratio of sulfate, phosphate and chloride reached 12.76 %, 69.07 % and 6.34%, respectively.
Both adsorbents exhibited a satisfactory removal ratio of phosphate. Therefore, Mg–Al and Zn–Al LDHs can be used as effective adsorbents for phosphate removal from industrial wastewaters.
Keywords: Adsorption, layered double hydroxides, tannery wastewater treatment.