NO-pickling Chromitan Technology

There exist some unassailable problems in traditional chrome tanning, such as low exhaustion of chrome, salt pollution from pickling, and time-consuming process, etc. In order to solve those problems, no-pickling chromitan C-2000, a new clean chemical, was synthesized, which can increase the absorption of chrome. Leather tanned by C-2000 characterizes by tight grain and fullness. But the research time is limited; there are some problems in application to result in the poor softness and deep color. In order to solve the problem and to broaden the application of C-2000, research was carried out as follows. Strengthening reliming was carried out to compensate for the side effect from free pickling. The result of experiments shows that the side effect can be compensated if reliming time is prolonged to 6h, the softness and color are improved, and tensile strength and tear strength of leather are higher than those of conventional tanned method. The effect from pretreatment with varied chemicals on the lightening the color of wet-blue and postponing combination of chrome at the beginning of tanning process was studied. The optimum conditions for pretreatment before tanning without pickling are, dosage 2%, float length 1, temperature 40℃, time 30min.In order to solve the problem of deep-color, SO2 was used as reducer to prepare chromitan instead of sugar. The analysis result shows that 95% complexes in the fresh chrome solution are nonionic and anionic, which will change to various cationic complexes with digestion time prolonged. The conversion can be increased when the chrome solution is diluted and heated. Leather tanned with this chromitan characterizes by light color and tight grain. The influencing factors on oxydo-reduction reaction and the possible effect on the structure of complex were studied. The experiment result shows that SO2 is highly active, which make it react at very low activation energy; and temperature, acidity, and concentration of SO2 have different effect on the reaction rate, among which acidity has strong effect on the structure of complex. C-2000 was built-up with other tanning agents, and the result shows that the best application result is that built-up with syntan. Leather with light color and good softness is obtained by tanning with 2% syntan and 6% C-2000 (limed pelt). The UV spectrum shows that there is no chemical reaction between the syntan and C-2000.The exhausted liquid of conventional tanning and no pickling tanning was analyzed. The result shows that chlorine content is reduced by 99%; TDS, COD and Cr2O3 are also greatly decreased.