铬屑碱解过程中铬与胶原分子量分布特征

Dechromation and molecular weight distribution of hydrolyzed collagen from chromium-containing leather during alkaline

酸碱法对含铬革脱铬时,由于胶原水解过程中胶原分子分布的不可控性,导致资源化利用生产的工业明胶和蛋白中残余铬达不到产品要求.通过实际生产过程模拟,探讨了不同碱解程度下铬屑水解液中胶原分子量分布与铬的分布规律.研究结果表明,随着碱浓度增加,铬屑脱铬率逐渐上升.碱水解24 h协同硫酸淋洗1 h的脱铬率为91.60%,加入柠檬酸可促进了铬屑上铬的溶解和分离,脱铬率达到97.96%.不同碱解液中溶解性胶原分子量分布表现出显著差异,而铬与水解胶原分子量则存在着明显的非均匀性分布,其中55.63%-72.66%的总铬分布在>1000 kDA区间;0-26.53%的总铬与1000-250 kDA区间的水解胶原结合;7.92%-18.53%的总铬与胶原分子和明胶混合物结合;0-4.60%的总铬与工业明胶结合;<50 kDA的多肽混合物上未结合铬.上述残存的铬除大量[Cr(H_(2)O)_(6)]^(3+)外,部分以络合态与水解胶原结合.结合的铬含量占比最高达到20%,水解过程中从铬屑中脱除的铬与小分子胶原片段发生了再络合.追踪水解液中>250 kDA区间总铬占比约55.63%-88.89%,可以认为制革鞣制过程中铬经渗透后主要结合在胶原微纤维或亚纤维层次结构上.加入的柠檬酸在促进了铬从固相中分离出铬的同时,柠檬酸及柠檬酸-铬络合物可与皮胶原形成复合物,铬脱除的过程中以上两种结合皮胶原的方式,是铬与皮胶原无法彻底分离的主要原因.

The uncontrollable distribution of collagen molecules during collagen hydrolysis in the acid-base method for chromium-containing leather results in the production of gelatin and protein with residual chromium that does not meet industrial product requirements.In this study,the distribution patterns of collagen molecular weight and chromium in chromium scrap hydrolysate under different alkali concentrations were investigated by simulating the actual production process.The results showed that the rate of chromium removal from chromium chips gradually increased with the increase of alkali concentration.The chrome removal rate of alkali hydrolysis for 24 h in cooperation with sulfuric acid drenching for 1 h was 91.60%,while the addition of citric acid promoted the dissolution and separation of chromium on the chips,and the chrome removal rate reached 97.96%.The chromium and hydrolyzed collagen molecular weight showed a significant nonuniform distribution,where 55.63%-72.66%of total chromium was distributed in the>1000 kDA interval;0-26.53%of total chromium was bound to 1000-250 kDA interval;7.92%-18.53%of the total chromium was bound to the collagen molecules and gelatin mixture;0-4.60%of the total chromium was bound to the industrial gelatin;and no chromium was bound to the peptide mixture of<50 kDA.The above residual chromium was partially bound to hydrolyzed collagen as complex,except for a significant amount of[Cr(H_(2)O)_(6)]^(3+).The bound chromium content accounted for up to 20%,and the chromium removed from the chromium chips during hydrolysis underwent recomplexation with small molecule collagen fragments.The experimental data confirmed that the percentage of total chromium in the>250 kDA interval in the hydrolysate was about 55.63%-88.89%,which can be assumed that chromium was mainly bound to the collagen microfibrils or sub-fibrillar hierarchy after penetration during the tanning process.While the added citric acid facilitated the separation of chromium from the solid phase,citric acid and citric acidchromium complexes can reform complexes with collagen,and the above two ways of binding collagen in the process of chromium removal are the main reasons why chromium and collagen cannot be completely separated by acid-base method.