Liquefaction Of DMF Distillation Dregs From Production Process Of Polyurethane Leather In Sub-and Supercritical Water

The phase behavior during liquefaction of polyurethane leather distillation (PULD) dregs in a fused-silica capillary reactor (FSCR) was carried out under a microscope. The PULD dregs obtained from N,N-dimethylformamide (DMF) distilation. The vapor phase products after liquefaction in FSCR were analyzed by Raman spectroscopy without sampling. The liquefaction of PULD dregs in sub-and supercritical water was carried out in a stainless steel autoclave reactor. The feedstock ratio (PULD dregs/water ratio of1:25-7.5:25), reaction temperature (280～400℃) and reaction time (5-60min) were used to investigate the effects on the conversion and oil yields. The vapor products were collected and analyzed qualitatively by FT-IR. The oil products were qualitatively identified by FT-IR and gas chromatography-mass spectrometry (GC-MS), respectively. The PULD dregs and liquefaction residues were analyzed by FT-IR and TG. The phase behavior of the PULD dregs in water during heating, reaction, and cooling was investigated in the FSCR. PULD dregs diffused gradually and started to dissolve in water during the heating process. When the reaction temperatures at195.2℃, it was observed that the solution color in FSCR started turning yellow, which indicated an oil phase formed initially. With increasing temperature, gas bubbles emerged. During the reaction stage at360℃, the PULD dregs dissolved and liquefied gradually. It was noted that the solution becoming much yellower in color. However, the carboniation phenomenon appeared with prolonged reaction time at360℃. During the cooling process, oil phase separation occurred at165.3℃and then formed a trail of opaque droplets at30℃or ambient temperature. Moreover, the vapor products were analyzed by Raman spectroscopy without sampling in FSCR, and H2n CO2and CH4were detected. Compared with the results of FT-IR, nonpolar H2were detected by Raman spectroscopy, but with no CO, C2H4and C2H6.The vapor phase consisted mainly of CO2, CO, CH4, C2H4, and C2H6, which was collected from the headspace and analyzed qualitatively by FT-IR. Complicated and various types of organic compounds were detected in the oil phase by FT-IR and GC-MS. The main organic compounds were emylcamate, phenol,2-ethyl-l-hexanol, o-toluidine,3,5-dimethyl-phenol and4,4’-methylenebis-benzenamine, suggesting the presence of mainly phenols, alcohols, ketones and phenylamines in the oil. The liquefied residues under different reaction temperatures were analyzed by FT-IR. The results indicated that the peak of the C-O bonds and the C=C bonds in the aromatic ring decreased with increasing reaction temperature. It demonstrated that organic substances in the PULD dregs gradually shifted to liquid phase. The PULD dregs and liquefied residues were analyzed by TG and the results indicated that the mass loss of the PULD dregs was higher than that of liquefied residues.The liquefaction of PULD dregs in sub-and supercritical water was carried out in a batch stainless steel autoclave reactor and the results are shown as follows:Both of the conversion and oil yields decreased with increasing feedstock ratio; when increasing reaction temperature and prolonging the reaction time, the conversion and oil yields increased initially and then decreased. The most suitable conditions for liquefaction was at360℃for30min with a PULD dregs/water ratio of1:5(w/w), and the conversion and oil yields reached accordingly82.75%and33.27%under the conditions, respectively.