Process Of Continuous Synthesis Of Biurea Without Acids

As upstream product of ADC, an extensively used foaming agent, biurea, its quality and yield greatly influenced the market scale of ADC. Nowadays, hydrazine hydrate and urea are mainly applied to synthesize biurea in acidic media industrially. This path benefits from its high reaction rate. However, due to severe corrosion of metal equipment, great deal of waste acidic water produced in the courses of condensation and washing which are rich in ammonium and other inorganic salts, and batch operation and production, the production efficiency is especially constrained. Regarding drawbacks mentioned above, we put forward to produce biurea in non-acidic environment, and try to model processes of continuous synthesis of biurea.No publications are witnessed to report kinetics of biurea synthesis, using hydrazine hydrate and urea without acids. This study measured kinetics data in the temperature range (110-140)℃ in a closed batch kettle. The reliability of ASPEN in simulating ammonia-water system, and experimental measurement of solubility of biurea in water between 100 ℃ and 140 ℃, were conducted to aid the procure of kinetics. The result shows that both semicarbazide and biurea synthesis are reversible reactions. All components obey rule of first order reaction. Neither Arrhenius equation nor modified-Arrhenius equation could establish the relationship between rate constant and temperature, and describe kinetics behavior of the reaction, apart from the rigorous fitting of them. The kinetics equation of reaction was then acquired.To establish process of continuous synthesis of biurea, it should model theoretically feasible reactors, by means of kinetics, to predict their performance in producing biurea. This treatise aims at investigating serial multi-tank reactor (N-CSTR) and oscillatory flow reactor (OFR), and comparing their predicted results with those of ideal plug flow reactor (PFR) and continuous stirred tank reactor (CSTR). It results that both N-CSTR and OFR rank between PFR and CSTR in reaction conversion, under the conditions of equal reactor volume and equal flow flux. For N-CSTR, the conversion gradually approaches to that of PFR if number of tanks increases, namely, the flow pattern evolves to near plug flow. SMTB, SMTSIB, SMTDCSIIB models, considering back mixing, were applied to model OFR. Decreasing predicted conversions of three models with increasing oscillatory intensity was appeared, mainly because that the axial back mixing was enhanced in the changing process. Under the conditions of certain operation, conversions predicted by these three models were slightly lower than that of PFR, manifesting excellent property of OFR. If gas holdup was below 0.055, existence of gas leaded to a neglectable effect on predicted results. Then it would simplify the work of modeling when considering none gas is present in the reactor.