Innovative Options to Add Value to Solid Leather Wastes

Transcription

1 Innovative Options to Add Value to Solid Leather Wastes S Booth & A Hudson (BLC Leather Technology Centre, UK) Karel Kolomaznik, (Thomas Bata University, Faculty of Technology in Zlin, Czech Republic) Jan Matyasovsky, (VIPO a.s. Partizanske, Slovak Republic) Jaume Cot, (CSIC, Barcelona Spain) Abstract The solid waste generated during leather making is significant. Whilst the leather industry is making use of a by-product from the meat industry, only 20% of the raw material ends up in the finished leather. This creates a huge environmental challenge for the modern tannery, as the traditional options for the disposal of this waste may become cost prohibitive in the future. Solid waste should therefore be viewed as a valuable resource for the production of value added products or as a fuel. Research is ongoing to determine innovative routes for the conversion of protein containing solid waste from tannery and beamhouse production to create value-added products. The resulting products have several potential uses in the following industries: As a fertiliser in the agricultural industry As additives in the building industry An ecoadhesive in the wood industry As a retannage in the leather industry As a finish in the leather industry A binder to partially substitute casein in the paper industry Some of these applications are discussed in the paper below.

2 Methodology In order to convert chrome shavings and leather to a useful product it is necessary to extract the chromium tanning material and digest the protein. In order to do this, chrome shavings and leather waste were treated enzymatically in the presence of low molecular weight organic amines. The process employed was a two-stage hydrolysis and took place using organic amines such as isopropylamine, di-isopropylamine, cyclohexylamine and ammonia. Following the process described above, two products are prepared, a protein hydrolysate and a chrome cake. The main technical advantages in the production of these are as follows: Reduction of ash content from 25% to 3% during the two-stage hydrolysis. The reduced ash content gives a higher quality product and a longer life cycle in the ion exchange and membrane filters used. Increase in the chrome oxide in the resulting cake making chrome saving and recovery more efficient Up to 60% of the organic bases used can be regenerated during the process concentrating the diluted solutions of the protein hydrolysate An increase of the protein yield from 60% to 80% The resulting protein hydrolysate has many uses within industries. The chrome extracted as cake can be recovered and re-used in the tanning process. Industrial Trial In order to evaluate the process of producing the protein hydrolysate and chrome cake, a process vessel was loaded containing: Water Cyclohexylamine Magnesium Oxide Wet blue shavings were gradually added to this mixture with constant stirring, followed by heating. It was determined that for larger pieces of wet blue, it is necessary to leave the mixture overnight before heating in order to ensure adequate degradation. The process was run for 5 hours and regular checks were made to ensure the temperature and ph were maintained. Adjustments required to the ph were achieved through the use of organic bases. Following this the hot heterogeneous mixture was then filtered, the filtrate collected in a storage tank and pumped continuously through a 3 stage vacuum evaporator. This was then subjected to the second stage of the hydrolysis as follows: Dilute with water, Adjusted the ph Add proteolytic enzyme. The mixture was stirred continuously and the elevated temperature maintained for a further 3 hours. The hot mixture was again filtered and the clear filtrate (hydrolysate) processed through a vacuum evaporator.

3 The filter cake obtained was returned to a reaction vessel, diluted with water then dosed with sodium dichromate and sulphuric acid. This resulted in a chrome-tanning salt. Applications of the Hydrolysate As previously mentioned the protein hydrolysate has many potential applications. Some of these are described below. 1. Use as a fertiliser. One of the most simple applications of the hydrolysate is as an organo-nitrogeneous fertiliser in the agricultural industry. Trials have been carried out in conjunction with the Regional Department of Soil, Agrochemistry and Plant Nutrition at the Agricultural Control and Testing Institute of the Czech Republic. During these trials comparisons were carried out using prepared hydrolysate and a commercially available fertiliser. This product evaluated was a blend of ammonium nitrate and urea in a 1:1 ratio based on their retrospective nitrogen contents. The crop assessed was lettuce and both fertilisers were used at levels to ensure that the mass of nitrogen remained constant within the dosage. A comparative control was also included using unfertilised soil. To assess the suitability of each of the fertilisers, the yield of lettuce was evaluated along with the percentage of nitrates detected in the crop obtained during each trial. Substantial differences were found in yield and particularly in the nitrate content of the lettuce and the results can be seen in Table 1 Table 1 Showing lettuce yield and nitrate content. FERTILISER YIELD (g/test) NITRATES (ppm NO 3 ) Commercial fertiliser Hydrolysate Unfertilised To conclude it can be seen that the hydrolysate showed a very positive effect on the yield of the crop with a markedly increased value as a food stuff due to a much lower nitrate content. 2. Seed Growth Enhancement Another potential agricultural application of the hydrolysate is in the use of sowing tape ; these are used to avoid the necessity for laborious thinning of seedlings. Specially treated seeds were fixed, at optimal distances, on biodegradeable sowing tapes. Machine sowing requires that the tapes have good mechanical properties and meet soil conditions for optimum seed sprouting. For this reason the normal polyvinyl alcohol (PVA) tape was modified by blow moulding molten PVA with protein hydrolysate. The resulting tape showed considerable improvement in mechanical properties and has a lower cost. The hydrolysate is 50% of the price of PVA. In addition the extra organic nitrogen added is slowly liberated into the soil and acts as a fertiliser.

4 3. An ecoadhesive in the wood industry This work has evaluated the potential for modification to the recipes for preparation of adhesive compounds. The aim of this being to obtain the best possible quality of adhesive joints in wood processing applications. Preparation of adhesive compounds and the necessary mechanical and chemical testing was also undertaken. Under laboratory conditions, liquid samples were prepared from the collagen hydrolysates. The ph was adjusted with inorganic acid to the value of ph 4 and resulting adhesive mixtures were condensed at a temperature of 140 C for both 30 and 45 minutes. After polycondensation and conditioning, the samples were ground and formaldehyde emission determined colorimetrically. Results of emissions confirmed a decrease (approx. 30 %) in the level of formaldehyde detected. These hydrolysates were used as 40% water gels and replaced 5% of the total adhesive. The reduction in formaldehyde levels can be seen in table 2 Table 2: Formaldehyde content in hardened adhesive mixture: Sample ph of hydrolysate Formaldehyde content (mg/litre) Standard UF adhesive + hardener 0,131 + Hydrolysate VIPO 6 0,054 + Hydrolysate VIPO 4 0,047 Following these evaluations bench scale industrial trials were carried out. During these trials, sufficient adhesive was prepared for bench scale trials evaluating the production of wood products and the optimising the manufacturing technology. Three-layer plywood was prepared in semi-industrial conditions, and formaldehyde emission, physical and mechanical properties of the UF adhesives measured. Formaldehyde emission was lower in all prepared samples compared to the reference sample. Physical properties were evaluated including shear strength and the chisel test. All samples fulfilled the required standards, although the shear strength was slightly reduced. Testing has also shown that the shear strength of the plywood after wetting meets the required standard although it is generally reduced in comparison to the reference sample. 4. As a retannage in the leather industry Another application for the collagen hydrolysate is as a retannage an filler in the dyeing process. To evaluate the possibilities for this, trials were carried out using matched sides. The protein hydrolysate was added prior to a traditional rechroming step to allow fixation and cross-linking of the collagen. The level of fatliquoring was kept the same for both trials, but all typical retannage material were removed from the test process. Tables 3 and 4 below illustrate the processes evaluated.

5 Table 3. Commercial Retannage Offer (%) Temp ( o C) Run (min) Float 200 Water Formic Acid 15 Refloat 100 Water 40 5 Chrome powder 40 2 Resin retan ph Refloat 100 Water Sodium Formate 0.5 Neutralising syntan ph 4.2/ Refloat 100 Water 50 4 Dyestuff 20 6 Filling Syntan 3 Mimosa 1 Resin Retan 40 7 Fatliquor 45 ph < 3.5 Wash

6 Table 4. Collagen Hydolysate Retannage Offer (%) Temp ( o C) Run (min) Float 100 Water 40 2 Sodium Formate Sodium Bicarbonate 40 ph 4.5/5.0 / 100 Water Float Refloat 100 Water Collagen Hydrolysate Formic Acid 20 ph 4.5/4.7 5 Chrome powder Water Water 60 Refloat 200 Water 40 2 Sodium Formate 1 Neutralising syntan 40 2 Sodium Bicarbonate 45 ph 6.0/6.5 Refloat 100 Water 30 4 Dyestuff Water 60 7 Fatliquor 45 ph < 3.5 Wash Following processing the two sides were found to be almost identical in appearance, feel and handle. The side prepared using the collagen hydrolysate was found to be slightly darker in shade than the commercial retannage. Further trials are planned to evaluate the retanning ability of the hydrolysate and work carried to investigate the feasibility of producing the hydrolysate within the tannery thus utilising wet blue wastes on site.

7 5. Potential uses in the Building Industry The protein hydrolystate has a number of potential applications within the building industry. Some of the areas being considered at present are: As an admixture in concrete. The hydrolysate can be used as an intensifying agent to facilitate the grinding of cement. In protective coating for buildings. The hydrolysate may provide a suitable key ingredient used for surface treatment to protect buildings from pollution. In the production of thin walled surface finishes. A pilot plant has been developed to incorporate the hydrolysate into gypsum and plasterboard partitions. In the manufacture of prefabricated powdered materials especially for surface finishes. To enhance the anti-slip properties of floors and tyres. The application of powdered hydrolysate has been shown to increase the coefficient of PVC floorings by 10% Conclusions. It is clear from the research described above that there is large potential for the application of a material seen as a waste product in the leather industry. The impact of tanning and associated activities on air, on surface and ground water, soil and resources arises from the chemicals applied, the raw materials used and the effluents, waste and off-gas generated in the process. Therefore provisions for pollution control, waste minimisation and disposal, chemical safety, and raw material, water and energy consumption are essential. As a result of the research described in this paper, a key area of waste generation shows the potential to become a useful value added product for the industry. Acknowledgement The authors would like to acknowledge the European Commission for financial support. Thanks also to all of the partners involved in the RESTORM project.