1

REVERSED LEATHER PROCESSING FOR CLEANER PRODUCTION S Saravanabhavan1, P Thanikaivelan2, J Raghava Rao1, Balachandran Unni Nair1

and T Ramasami1

1Chemical Laboratory, 2Centre for Leather Apparels and Accessories Development, Central Leather Research Institute, Adyar, Chennai 600 020, India.

email: clrichem@mailcity.com, Tel: +91 44 441 1630; Fax: +91 44 441 1630

Abstract Conventional leather processing generally involves a combination of single and multi-step processes that employs as well as expels various biological, inorganic and organic materials. It involves nearly 14 – 15 steps and discharge huge amount of pollutants. This accounts for nearly 98% of the total pollution from a tannery. This is primarily due to the fact that the conventional leather processing employs a ‘do – undo’ process logic. In addition, the conventional methods employed in leather processing subject the skin/hide to wide variation in pH. Such pH changes demand the usage of acids and alkalis, which leads to the generation of salts. This occurs to be a major dispute for many of the tanners around the globe due to the stringent environmental stipulations. In this study, the leather processing steps have been reversed to overcome the problems associated with the conventional method. The initial pH profiles have been judiciously used for reversing the process steps. We propose to use the neutral pH condition of the pelt after the deliming process for the addition of post-tanning chemicals followed by tanning the weakly acidic pelts that have been treated for the fixation of post-tanning chemicals. This modification eventually avoids several acidification and basification/neutralization steps in the conventional leather processing. Hence, the reversed leather processing technique involves principally six steps namely soaking, liming, reliming, deliming, addition of syntans, fatliquors and dyes followed by tanning. This has been substantiated through various analyses such as scanning electron microscopy, softness measurements and physical testing. Further, the performance of the leathers is shown to be on par with conventionally processed leathers through bulk property evaluation. The process enjoys significant reduction in COD and TS by 53 and 79%, respectively. And also, the process benefits from significant reduction in chemicals, time, water, power and cost compared to the conventional process.

2

Introduction Conventional leather processing involves four important sets of operations, viz.,

pre-tanning, tanning, post tanning and finishing. It includes a combination of single and multi-step processes that employs as well as expels various organic and inorganic materials.1 Conventional method of leather making involves 14–15 steps comprising soaking, liming, reliming, deliming, bating, pickling, chrome tanning, basification, rechroming, basification, neutralization, washing, retanning, dyeing, fatliquoring and fixing. This conventional technique discharges enormous amount of wastewater along with pollutants. This accounts for nearly 98% of the total pollution from a tannery.2 This includes biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), sulphides, chlorides, sulphates, chromium, etc. This is primarily due to the fact that the conventional leather processing employs ‘do-undo’ process schemes such as swell-deswell (liming-deliming); pickle-depickle (pickling-basification), rechroming–basification (acidification–basification) and neutralization–fixing (basification-acidification).3 In other words, conventional methods employed in leather processing subject the skin/hide to wide variations in pH.4 Such pH changes demand the use of acids and alkalis, which leads to the generation of salts. This results in a net increase in COD, TDS, chlorides, sulphates and other minerals in tannery wastewaters.5

Conventional chrome tanning generally involves pickling, tanning using basic

chromium sulphate (BCS) followed by basification processes. Spent pickle liquor has high dissolved solid content and a considerable amount of chemical oxygen demand, since pickling involves the use of 8-10% sodium chloride salt along with sulphuric acid.2 Spent chrome liquor contains significant amount of chromium, sulphates and TDS, due to the conventional chrome tanning practices. Conventional method of post-tanning process involves 7-8 major steps comprising rechroming, basification, neutralization, washing, retanning, dyeing, fatliquoring and fixing. Post tanning operation employs a pH range of 4.0-6.5 and a variety of chemicals. The post-tanning processes contribute to TDS, COD and heavy metal pollution significantly as reported by Simoncini and Sammarco.6 Several attempts have been made to render the leather processing steps cleaner.7,8 However, these improvements are specific to a unit operation. Implementation of all the advanced technologies and eco-friendly chemicals involves financial input and machinery requirements as well. This calls for the development of integrated leather processing technology and revamping the process sequence.

Very few attempts have been made to revamp the whole or part of leather

processing steps. Thanikaivelan et al have attempted to make leather in a narrow pH range from 4.0–8.0.5,9 Later a three-step tanning process has been developed which involves enzymatic dehairing, fibre opening using enzyme or alkali and pickle less chrome tanning at pH 8.0.10,11 Recently, an integrated one-step wet finishing processes have been evolved.12,13 Further, process integration has been attempted by combining tanning and post tanning steps in one bath.14

3

In this study, an attempt has been made to reverse the conventional leather processing steps. This is by treating the delimed pelts with post tanning chemicals such as syntans, dye and fatliquors followed by chrome tanning at pH 5.0-5.2.15 A comparative flow chart for conventional and reversed leather process is shown Fig. 1. The percentage offer of post tanning chemicals have been carefully designed and calculated taking into account of shaved weight parameters. The performance of the final leathers has been evaluated in terms of physical as well as organoleptic properties. Softness of the leathers has been quantified and compared with that of conventionally processed leathers. The pollution parameters such as COD and TS have been quantified and analyzed. Techno-economic viability of the developed process has also been examined.

Experimental Methods

Conventionally delimed/bated goatskins were chosen as the raw material. The chemicals employed for leather processing were of commercial grade. The chemicals used for analytical techniques were of laboratory grade.

Conventional Leather Process (C) (Ten delimed/bated skins were used; % based on fleshed pelt weight) Process/chemicals % Duration Remarks

Pickling

Water 100

Sodium chloride 10 10 min

Sulphuric acid Water for dilution

1.2 20

3 × 10 min + 1 h

The pH of the cross section of the pelt was found to be 2.8. 50% bath was drained.

Chrome tanning Basic chromium sulphate 5 1 h

Water 50 30 min

Sodium formate 1

Sodium bicarbonate Water for dilution

1 10

3 × 10 min + 2 h

The pH of the cross section of the tanned leather was found to be 3.8. Bath was drained.

Washing

Water 200 10 min Bath was drained.

4

The leathers were piled for 24 h. The leathers were then sammed and shaved to uniform thickness (1.0 – 1.1mm). The weight of the leathers was noted and termed as shaved weight. Rechroming was not done. Percentages of the following chemicals were based on shaved weight. Post-Tanning Process

Washing

Water 200 10 min Bath was drained.

Neutralization Water 100 Sodium formate 1

Sodium bicarbonate Water for dilution

1 10

3 × 10 min + 1 h

pH was found to be 5.0-5.2.

Relugan RE 2 30 min Bath was drained.

Washing I

Water 200 10 min Bath was drained.

Washing II

Water 200 10 min Bath was drained.

Retanning, dyeing and fatliquoring

Water 50 Basyntan DI 3

Vernaton OS 2 45 min

Veranol liquor PN 2 20 min Fatliquor was emulsified using 10% hot water at 60oC

Basyntan FB6 3 20 min

Luganil black FBO 3 30 min The complete penetration of dye was checked.

Vernol liquor SP 2

Vernol liquor ASN 2

Lipoderm liquor SLW 2 45 min Fatliquors were emulsified using 10% hot water at 60oC

Wattle GS 2 30 min

Fixing

5

Formic acid Water for dilution

2 10

3 × 10 min + 1 h

Bath was drained.

Washing Water 200 10 min Bath was drained.

The leathers were set and hooked for drying. The dried leathers were conditioned, staked, trimmed and toggled. Reversed Leather Process (E) (Ten delimed/bated skins were used; % based on fleshed pelt weight) Process/chemicals % Duration Remarks

Water 50

Relugan RE 0.65 30 min Basyntan DI 1 Vernaton OS 0.65 45 min Veranol liquor PN 0.65 20 min Fatliquor was emulsified using

10% hot water at 60oC. Basyntan FB6 1 20 min

Luganil black FBO 1 30 min The complete penetration of dye was checked.

Vernol liquor SP 0.65 Vernol liquor ASN 0.65

Lipoderm liquor SLW 0.65 45 min Fatliquors were emulsified using 10% hot water at 60oC.

Wattle GS 0.65 30 min

Formic acid Water for dilution

0.5 10

3 × 10 + 30 min

The pH of the cross section of the matrix was found to be 5.0-5.2.

Basic chromium sulphate 5 2.5 h The pH of the cross section of the leather was found to be 3.8-4.0.

Washing

Water 200 10 min Bath was drained.

The leathers were set and hooked for drying. The dried leathers were conditioned, staked, dry shaved to uniform thickness (1.0-1.1 mm), trimmed and toggled.

Objective assessment of softness through compressibility measurements

Softness of leathers can be numerically measured based on their compressibility.16 Circular leather pieces (2 cm2 area) from experimental and control crust leathers were obtained as per IUP method17 and conditioned at 26.6±2.2oC and 65±2% relative humidity over a period of 48 h. The samples were spread uniformly over the solid base of the C & R (compressibility and resilience) tester. The initial load acting on the grain surface was 100 g. The thickness at this load was measured 60 s after the load was

6

applied. Subsequent loads were added and the change in thickness was recorded one minute after the addition of each load. Logarithm of change in leather thickness (Y axis) was plotted against logarithm of load (X axis). Physical testing and hand evaluation of leathers

Samples for various physical tests from experimental and control crust leathers were obtained as per IUP method.17 Specimens were conditioned at 26.6±2.2oC and 65±2% relative humidity over a period of 48 h. Physical properties such as tensile strength, % elongation at break, tear strength and grain crack strength were examined as per the standard procedures.18-20 Experimental and control crust leathers were assessed for softness, fullness, grain tightness, grain smoothness and general appearance by hand and visual examination. The leathers were rated on a scale of 0–10 points for each functional property by experienced tanners, where higher points indicate better property. Chromium content and shrinkage temperature of leathers

Samples from the official butt portion17 of experimental (wet processed stage) and control wet blue leathers were taken for chromium estimation. A known weight (~1g) of the sample was taken and the amount of chromium was estimated as per standard procedures.21 Samples were initially analysed for moisture content22 and chrome content was expressed on dry weight basis of leather. The shrinkage temperature of the leathers was measured using a Theis shrinkage tester.23

Scanning electron microscopic analysis

Samples from experimental and control leathers after crust stage were cut from the official sampling position.17 Samples were cut into specimens with uniform thickness. All specimens were then coated with gold using Edwards E306 sputter coater. A Jeol JSM-840A scanning electron microscope was used for the analysis. The micrographs for the grain surface were obtained by operating the SEM at high vacuum with an accelerating voltage of 15 kV in different lower and higher magnification levels. Chromium exhaustion

Chrome liquor collected from the control chrome tanning process was analysed for chromium content as per the standard procedure and uptake of chromium was calculated.24 In the case of reversed leather process, the final liquor was collected and used for the analysis. Analysis of composite waste liquor

Composite liquors from control and experimental processes were collected from all the unit operations expect pre-tanning processes (soaking to deliming) and analysed for COD and TS (dried at 103–105oC for 1 h) as per the standard procedures.25 From this emission loads were calculated by multiplying concentration (mg/L) with volume of effluent (L) per tonne of raw skins processed.

7

Results and discussion Rationale of the reversed leather processing

It is known that the conventional post tanning auxiliaries such as syntans, dyes and fatliquors are anionic. The conventional process method involves neutralizing the cationic charge of the chrome tanned leather and elevating the pH of the leather to 4.5 to 6.5. This is followed by the application of post tanning auxiliaries after washing off the neutral salts and addition of acid to fix these auxiliaries with the leather matrix. Here, we propose to use the pH condition of the delimed/bated pelt, which is 7.0-8.0, for the application of post tanning auxiliaries, because the pelt is anionic in nature. After the penetration of post tanning auxiliaries, a slight decrement of pH to a level of 5.0-5.2 would not only facilitate the fixation of the post tanning auxiliaries but also provides proper conditions for the application of basic chromium sulphate salt. At this condition, the mechanism of chrome tanning would be similar to that of a pickle-less chrome tanning. In other words a simultaneous penetration cum fixation of chromium molecules would take place. The final pH of leather as well as the spent liquor would be around 4.0 due to the hydrolysis of chromium molecules. Hence, there is no need for separate basification step.

Chromium in leather and spent tan liquor

The amount of chromium present in the leather and spent tan liquor has been analyzed to assess the chromium uptake behaviour of the reversed process. The amount of chromium present in the leathers is given in Table I. The leathers from reversed process possess higher amount of chromium compared to the control leathers. This is due to the presence of carboxyl groups of collagen in ionised form during the entire course of chrome tanning of the reversed process. The mechanism of this process is similar to that of a pickle-basification free chrome tanning process.26 The chromium uptake values of conventional and reversed processes are presented in Table I. It is seen that the uptake of chromium is significantly increased in the reversed process compared to the conventional process. This is in accordance with the trend observed in the chrome content of leathers. The chromium concentration of the spent tan liquor from conventional and reversed process is 2286 and 528 ppm, respectively. The shrinkage temperature of leathers from both control and reversed processes is more than 120oC.

Softness measurement

Objective assessment of softness for both control and experimental leathers has been made through compressibility measurements. The logarithm of change in thickness was plotted against logarithm of change in load for the control and experimental leathers, which exhibited a linear fit.16 The plots are shown in Fig. 2a and 2b. The line equation was obtained from the fit. The negative slope angles were calculated from the line equation and the values are 8.40 and 8.46° for control and experimental leathers. Higher values imply more softness in the leather. It is seen that the experimental leathers exhibit comparable softness to that of control leathers.

8

Strength and organoleptic properties

The average strength values of the leathers from conventional and reversed process are given in Table II. Strength properties of the leathers made from the reversed process are comparable to that of conventionally processed leathers and all of them meet the Bureau of Indian Standards (BIS) specifications.27 Bulk properties of the control and the experimental leathers are given in Fig. 3. Softness, fullness, grain smoothness and grain tightness of the leathers from reversed process are comparable or even better than the conventionally processed leathers. This is because of the improved uptake of chemicals. Generally, the appearance and overall performance of the leathers from reversed process is comparable to the conventionally processed leathers.

Scanning electron microscopic analysis Scanning electron micrographs of crust leather samples from conventional and

reversed processes showing the grain surface at a magnification of ×50 are given in Fig. 4a and 4b. The grain surface and the hair pores of both control and experimental crust leather samples are clean without any solid foreign particles. This shows that there is no surface deposition of chromium or any other performance auxiliaries. There is no change in the surface morphology of leather upon reversing the conventional leather process steps. Scanning electron micrographs of crust leather samples from conventional and experimental processes showing the cross section at a magnification of ×100 are given in Fig. 5a and 5b. The fibre bundle weave pattern for both the samples are seems to be similar. Higher magnification (×500, Fig. 5c and 5d) micrographs show that the splitting of fibre bundles is similar for leathers from both conventional and reversed process method. Water consumption

In principle, the reversed process enables significant reduction in the consumption of water because it avoids several acidification, deacidification and washing steps. Hence, water audit has been made for conventional and reversed processes. The quantity of water employed and discharged for processing 1 kg of raw skin through conventional and reversed method is given in Table III. It is apparent that the reversed process enjoys a reduction in water consumption and effluent discharge by 65 and 64% for processing 1 kg raw goatskin. It has been reported that, by 2025 AD, 1.8 billion people will live in countries or regions with absolute water scarcity.28 In this context, the ability of the reversed process to reduce the water consumption is one of the significant achievements. Environmental benefits

The composite liquors have been collected from all the unit operations except soaking, liming and deliming. COD and TS have been chosen to analyse the environmental impact of the conventional and reversed process. A direct correlation of the observed COD and TS values may not give proper consequences on the environmental impact. Hence, these values have been converted into emission loads. The COD and TS values and the calculated emission loads are given in Table IV. It is interesting to note that the concentration of TS is significantly lower in the effluent from reversed process compared to the conventional process, in spite of the low hydraulic load. This is primarily due to the fact that the reversed process eliminates several acidification-

9

deacidification steps that are practiced in the conventional leather processing. It is known that acidification-deacidification steps would lead to the formation of neutral salts that contribute to dissolved or total solids. It is seen that the concentration of COD in the effluent from the reversed process is slightly higher than the conventional process. This is due to the presence of pollutants in significantly low amount of water. There is, however, a significant reduction in the COD and TS parameters when they are converted into emission loads. The reduction in COD and TS loads are 53 and 79%, respectively. These reductions are due to not only the elimination of several operations but also the better uptake of chemicals such as chromium, syntans, dyes and fatliquors. This is intriguing to note that these reductions are without altering the process chemicals.

Techno-economic viability Implementation of any developed process in the industry demands the technical

feasibility and cost effectiveness. In this study, reversed process has been developed to achieve reductions in water, time, power as well as better quality of leather and effluent. It is already shown (Table III) that the reversed leather process enjoys a reduction in water consumption by 65% compared to the control process, which provides savings in water cost. This reduction in water consumption lowers the hydraulic load by 64%, there by reduces the operating cost of ETP. The consumption of process time and power for the control and experimental processes is given in Table V. Time consumption of the reversed process (drumming time) is 48% lower than the control process. Further, there is also a significant reduction in the time lag between conventional chrome tanning and wet finishing, which is usually a minimum of 12 hours (overnight ageing). The reduction in the energy consumption for the reversed process is about 48% compared to the control process, which leads to a saving of about US$ 18 for processing 1 t of raw skins. The total chemicals consumption for conventional and reversed process is given in Table VI. It is seen that the reversed process reduces the total chemical consumption by 54%. The chemical costing was not carried out for BCS, syntans, dyes and fatliquors because there is no change in the type and percentage offer of chemicals between the two processes. However, the reversed process provides a considerable reduction in chemical cost of about US$ 20 by avoiding acidification and deacidification processes. Hence, it is evident that there is a significant reduction in the consumption of water, time, energy and chemicals. This would provide an overall reduction in the cost of leather processing. Conclusion

Global leather industry is looking for a viable cleaner leather processing methodology to overcome the environmental constraints. The sustainability of leather production would depend on the development of an alternative system for leather making. In this study, a reversed leather processing method has been attempted. Leathers obtained from reversed process possess comparable physical and bulk properties to that of leathers from conventional process. A significant increase in the chromium uptake and chrome content in the leather is observed for the reversed process. The reversed process technique results in remarkable reduction in pollution loads such as COD and TS by 53 and 79%, respectively. This reduction is possible by rationally changing the order of operations. More particularly, the water usage is reduced by nearly 65% for processing one tonne of raw skins from delimed to crust stage, which is one of the pioneering

10

achievements. Techno-economic viability study shows that there is a considerable reduction in the cost of leather production and the process is commercially viable. Acknowledgement The authors wish to thank Dr. R. Rajaram for physical testing measurements. One of the authors (SS) wish to thanks the CSIR, New Delhi for providing a senior research fellowship. Note Relugan RE: Acrylic co-polymer based syntan from BASF, Germany Basyntan DI: Phenol condensate based syntan from BASF, Germany Basyntan FB6: Melamine formaldehyde based syntan from BASF, Germany Luganil back FBO: Acid black dye from BASF, Germany Vernaton OS: Phenol condensate based syntan from Clariant Ltd, India Veranol liquor PN: Natural oil based fatliquor from Clariant Ltd, India Vernol liquor SP: Synthetic oil based fatliquor from Clariant Ltd, India Vernol liquor ASN: Synthetic oil based fatliquor from Clariant Ltd, India Lipoderm liquor SLW: Synthetic oil based fatliquor from BASF, Germany

11

References 1. Germann, H. P., Proceedings of the XXV IULTCS Congress, Tata McGraw-Hill

publishing company Ltd, New Delhi, (1999). 2. Aloy, M., Folachier, A. And Vulliermet, B., Tannery and pollution, Centre

Technique Du Cuir, Lyon, France (1976). 3. Bienkiewicz, K., Physical Chemistry of Leather Making; Krieger Publishing:

Malabar, FL (1983). 4. Heidemann, E., Fundamentals of leather manufacture, Eduard Roether KG,

Darmstadt (1993). 5. Thanikaivelan, P., Rao, J. R. and Nair, B. U., J. Soc. Leather Technol. Chem., 2000,

84, 276. 6. Simoncini, A. and Sammarco, U., Proceedings of the XXIII IULTCS Congress,

Germany, (1995). 7. Thanikaivelan, P., Rao, J. R., Nair, B. U. et al., Trends Biotechnol., 2004, 22, 181. 8. Thanikaivelan, P., Rao, J. R., Nair, B. U. et al., Crit. Rev. Environ. Sci. Technol.,

2005, 35, 1. 9. Thanikaivelan, P., Rao, J. R. and Nair, B. U., J. Soc. Leather Technol. Chem., 2001,

85, 106. 10. Thanikaivelan, P., Rao, J. R., Nair, B. U. et al., J. Amer. Leather Chem. Ass., 2003,

98, 173. 11. Thanikaivelan, P., Rao, J. R., Nair, B. U. et al., Environ. Sci. Technol. 2003, 37,

2609. 12. Ayyasamy, T., Thanikaivelan, P., Chandrasekaran, B. et al., J. Amer. Leather Chem.

Ass., 2004, 99, 367. 13. Ayyasamy, T., Thanikaivelan, P., Rao, J. R. et al., J. Soc. Leather Technol. Chem.,

(in press).

14. Saravanabhavan, S., Thanikaivelan, P., Rao, J. R. et al., J. Soc. Leather Technol. Chem., (submitted)

15. Saravanabhavan, S., Thanikaivelan, P., Rao, J. R. et al., Applied for Patent in India and PCT countries (2003).

16. Lokanadam, B., Subramaniam, V. and Nayar, R. C., J. Soc. Leather Technol. Chem., 1989, 73, 115.

17. IUP 2, J. Soc. Leather Technol. Chem., 2000, 84, 303.

18. IUP 6, J. Soc. Leather Technol. Chem., 2000, 84, 317.

19. IUP 8, J. Soc. Leather Technol. Chem., 2000, 84, 327.

20. SLP 9 (IUP 9), The Society of Leather Technologists and Chemists, Northampton (1996).

21. IUC 8, J. Soc. Leather Technol. Chem., 1998, 82, 200.

22. IUC 5, J. Soc. Leather Technol. Chem., 2002, 86, 277.

23. McLaughlin, G. D. and Theis, E. R., The Chemistry of Leather Manufacture, Reinhold Publishing Corpn., New York, 1945.

24. O’Flaherty, F., Roddy, W. T. and Lollar, R. M., The Chemistry and Technology of Leather, Vol IV, Krieger Publishing Company, Florida (1977).

12

25. Clesceri L. S., Greenberg, A. E., Trussell, R. R., Standard methods: for the estimation of water and waste water, 17th edition, American Public Health Association: Washington DC (1989).

26. Thanikaivelan, P., Rao, J. R., Nair, B. U. et al., J. Amer. Leather Chem. Ass., 2004, 99, 82.

27. Specification for glaze kid upper leather, Indian Standards Institution, IS 576, New Delhi, India (1989).

28. International Water Management Institute, Projected Water Scarcity in 2025. http://www.cgiar.org/iwmi/home/wsmap.htm (accessed October 2004)

13

TABLE I

Comparison of chromium content and shrinkage temperature of leathers and percentage exhaustion of chromium from conventional (C) and reversed (E)

processes*

Sample % Cr2O3

(dry weight basis)

% Exhaustion Ts (oC)

C 3.05±0.10 78 >120 E 3.84±0.08 92 >120

*Moisture free tanned leather weight

14

TABLE II Physical strength data of control (c) and experimental (E) leathers

Sample Tensile strength (kg/cm2)

% Elongation at break

Tear strength (kg/cm)

Grain crack strength (Average valueb)

Bursting strength (Average valueb)

Average valuea Average valuea Average valuea Load (kg) Distension (mm)

Load (kg)

Distension (mm)

C 223±8 65±2 57±2 45±0.5 11.2± 0.2 46±0.5 12.3±0.2 E 216±6 62±3 62±2 45±1.0 10.8± 0.4 47±0.5 12.0±0.3

BIS norms27

200 40-65 30 20 7 - -

aAverage of mean of along and across backbone values bAverage of load and distention values

15

TABLE III Comparison of water consumption and discharge for conventional (C) and reversed

(E) leather processing of 1 kg raw skinsa

C E Unit processes

Input (L)

Output (L)

Input (L)

Output (L)

Pickling 0.80 0.40 - - Chrome tanning/reversed process 0.40 0.78 0.40 0.38 Washing 1.60 1.60 1.60 1.58 Washing 0.60 0.48 - - Neutralization 0.30 0.28 - - Washing I 0.60 0.58 - - Washing II 0.60 0.60 - - Retanning, dyeing and fatliquoring 0.30 0.29 - - Washing 0.60 0.60 - - Dilution of acids/alkalis and emulsification of fatliquors

0.30 0.30 0.16 0.16

Total 6.10 5.91 2.16 2.12 aWeight of skins before soaking

16

TABLE IV Spent liquor analysisa

Emission load (kg/t of raw skinsb processed)

Process COD (ppm)

TS (ppm)

Volume of effluent (L/t of raw skinsb)

COD TS

C 6483±18 32432±32 5910 38 192

E 8150±22 18672±36 2120 18 40 aComposite liquors were collected from all the unit operations expect from soaking, liming and deliming; bWeight of skins before soaking; C – Conventional leather processing; E – Reversed leather processing

17

TABLE V Time and power consumption for the conventional (C) and reverse (E) processes

Time (h)

Unit operations C E

Pickling 1.67 - Chrome tanning/reversed process 4.0 6.66 Washing 0.16 0.16 Washing 0.16 - Neutralization 2.0 - Washing I 0.16 - Washing II 0.16 - Retanning, dyeing and fatliquoring 3.16 - Fixing 1.50 - Washing 0.16 - Total 13.13 6.82 Total power consumption (kWh) 393.9 204.6 Cost (US$) 36.77 19.09

@1 h running = 30 kWh; 1 kWh = Rs 4.20; 1 US$ = Rs. 45.00

18

TABLE VI Chemicals consumption for the conventional (C) and reversed (E) leather processing

C E Chemicals kg/t of raw skins processing

Sodium chloride 80 - Sulphuric acid 9.6 - BCS 40 40 Sodium formate 11 - Sodium bicarbonate 11 - Syntans 36 32 Dyes 9 8 Fatliquors 24 21.3 Formic acid 6 4 Total 226.6 105.3

19

Figure Caption Figure 1. Flow chart for conventional and reversed leather processes Figure 2. Plot of log of change in load Vs log of change in thickness for (a)

conventional and (b) reverse processed leathers Figure 3. Bulk properties of conventional and reverse processed leathers Figure 4. Scanning electron micrograph of crust leather samples showing the grain

surface at a magnification of ×50 from (a) conventional and (b) reversed leather processing

Figure 5. Scanning electron micrograph of crust leather samples showing the cross section at lower and higher magnifications; (a) control (x100), (b) experimental (x100), (c) control (x500) and (d) experimental (x500)

20

Fig. 1

21

Fig. 2 a)

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.62.60

2.65

2.70

2.75

2.80

2.85

Y =3.146431-0.147681 X

Log

of c

hang

e in

thic

knes

s (m

icro

ns)

Log of change in load (g)

Conventionally processed leather

b)

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

2.60

2.65

2.70

2.75

2.80

Log

of c

hang

e in

thic

knes

s (m

icro

ns)

Log of change in load (g)

Y =3.106494-0.148676 X

Reverse processed leather

22

Fig. 3

0

1

2

3

4

5

6

7

8

9R

atin

g

Softness Fullness Grainsmoothness

Graintightness

Generalappearance

Bulk properties

Control Experimental

23

Fig. 4 a) b)

24

Fig. 5

a) b)

c) d)