Cellulose carbamate prodn. by reacting cellulose with urea

摘要

The prodn. of cellulose carbamate (I) as described in DE4242437.2 comprises (a) mixing cellulose (II) with excess aq. urea soln., (b) replacing the water with inert organic reaction medium (III), (c) reacting (II) with urea at 130 deg C or higher and (d) separating and washing the prod. (I). The novelty is that: - in stage (b) the aq. mixt. from (a) is added to (III), and some of the water plus some (III) is evapd. at temp. T1 in a first evaporator; the vapour from this is used to heat a second evaporator in which the rest of the water and more (III) is evapd. at a temp. T2 lower than T1, and - in stage (d): (d1) (III) is mechanically sepd. as far as possible and returned to stage (b); (d2) the filter cake from (d1) is washed with methanol or ethanol and then with water, and moist prod. (I) is worked up; (d3) residual (III) is sepd. from the combined filtrates and washings by extn. with water and returned to stage (b), and (d4) the extn. residue from (d3) is sepd. by rectification to give MeOH or EtOH which is returned to (d2) and aq. urea soln. which is returned to (a).