Abstract
The molecular weights of lignosulfonates (LSs) are modified by a rather simple process involving an alkaline oxidative treatment at moderate temperatures (70–90 °C) and atmospheric pressure. Starting from LSs with an average molecular weight of 90,000 Da, and using such a treatment, one can prepare controlled molecular weight LSs in the range of 30,000 to 3500 Da based on the average mass molecular weight. The LS depolymerisation was monitored via reverse-phase and size-exclusion chromatography. It has been shown that the combination of O2, H2O2 and Cu as a catalyst in alkaline conditions at 80 °C induces a high LS depolymerisation. The depolymerisation was systemically accompanied by a vanillin production, the yields of which reached 1.4 wt % (weight percentage on LS raw basis) in such conditions. Also, the average molecular weight and vanillin concentration were correlated and depended linearly on the temperature and reaction duration.
Highlights
Depletion of natural and fossil resources, global warming, soil loss and degradation of agricultural lands are all symptoms of a world in degeneration and mankind “overconsuming the nature” [1]
The present work demonstrated the possibility of controlling LS molecular weight distribution (MWD) via an alkaline oxidative depolymerisation at low temperatures and atmospheric pressure
The depolymerisation reaction was discussed in light of size-exclusion chromatography (SEC) and RP–HPLC analyses, which were developed and validated in the present work
Summary
Depletion of natural and fossil resources, global warming, soil loss and degradation of agricultural lands are all symptoms of a world in degeneration and mankind “overconsuming the nature” [1]. LSs have many uses, such as animal feed, pesticides, surfactants, additives in oil drilling, vanillin precursors, stabilizers in colloidal suspensions, or as plasticizers in concrete admixtures They account for 90% of the total market of commercial lignin, and the total annual worldwide production of lignosulfonates is approximately 1.8 million tons [8]. The control of the molecular weight was demonstrated to be highly relevant for the production of lignin-based carbon fibers with good mechanical properties [10] or for use as a dye dispersant [9]. Wdeeppolryompeorsiesaitniotnh.e present work a rather soft method for a controlled LS depolymerisation in an alkaline mWeedpiurompousnedinerthaenparetsmenotswphoerkriac rparthesesrusoreft omfeothxoydgefonr (aacsosnisttreodlleodrLnSodtebpyolHym2Oer2is)aatniodn rinelaantively low teamlkapleinraetmureedsiu(7m0–u9n0d◦eCr )a.nFaotlmloowspinhgertihc ipsrmesestuhroedo,fwoxeycgaenn r(eadssuiscteedthoerLnSotmboyleHc2uOla2)rawndeirgehlattaivnedlymake it molroewsuteitmabpleera(tvuiraesth(e70p–r9o0d°uCc)t. iFoonlloofwpinhgenthoilsicmmetohnoodm, weerscaanndreodluigceomtheerLs)Sfmorofluecruthlaerrwaepipghlitcaatnidons in bioplmaapsatpikcleisc,aiattidomnhsoersieinvsebusiiootparblaclesatri(cbvsoi,ana-dtfihhbeeesrpivrpeorsdouodcruticcotanirobnoof.nT-pfhihbeeenrLoSplircdoedmpuoocnltyioommn.eerrTsihsaeatniLdoSnodwleigaposomlmyemorsne)riitfsooarrteiodfnubrtwyhaemsr eans of sizme-oenxictlourseidonbychmroeamnastoofgrsaizpeh-eyxc(lSuEsCio)nacnhdrormevaetorgsera-pphhyas(eSEchCr)oamndatoregvrearpseh-yph(RasPeCc)h.rComhraotmogaratopghryaphic meth(oRdPsCa)n. dCharhoommateomgraadpheipc rmogerthamodswaenred daevheolmopeemdadtoe mproongirtaomr thweerreeadcteivoenlo. ped to monitor the reaction
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