Direct esterification

Claim 1

IN A PROCESS FOR THE PREPARATIN OF DRAWABLE FILM AND FIBER-FORMING POLYESTERS FROMA DIOL WHICH CONTAINS 2 TO 10 CARBON ATOMS IN THE MOLECULE AND WHICH CONTAINS, OTHER THAN THE TWO HYDROXY GROUPS, ONLY CARBON AND HYDROGEN ATOMS AND FROM A PHTHALIC ACID WHOSE CARBOXYL GROUPS ARE SEPARATED BY AT LEAST THREE RING CARBON ATOMS SAID PHTHALIC ACID CONTAINING AT LEAST 65% TEREPHTHALIC ACID, THE IMPROVED STEPS COMPRISING HEATING WITH AGITATION AT A TEMPERATURE OF FROM 200 TO 300*C. IN THE ABSENCE OF OXYGEN A MIXTURE CONSISTING ESSENTIALLY OF FROM 2 TO 6 MOLES OF SAID DIOL FOR EACH MOLE OF SAID PHTHALIC ACID WHICH HAS A CARBOXYBENZALDEHYDE CONTENT OF LESS THAN 0.1 PERCENT BY WEIGHT IN A CLOSED REACTION SYSTEM AT THE AUTOGENETIC PRESSURE OF THE MIXTURE UNTIL A CLEAR FLUID PRODUCT IS OBTAINED WHERE IN AT LEAST 50% OF THE TOTAL CARBOXYL GROUPS OF SAID PHTHALIC ACID IS CONVERTED TO HYDROXY ESTER GROUPS, COOLING THE CLEAR FLUID PRODUCT TO A TEMPERATURE IN THE RANGE OF FROM 180 TO 200*C., REMOVING WATER PRODUCED BY THE ESTERIFICATION REACTION AND EXCESS DIOL BY MAINTAINING SAID COOLED CLEAR FLUID PRODUCT AT 180 TO 200*C. AND AT A PRESSURE OF FROM ATMOSPHERIC TO ABOUT 2.0 MMM. HG WHILE AGITATING SAID CLEAR FLUID IN AN OXYGEN-FREE ATOMSPHERE, AND HEATING THE RESULTING DEHYDRATED CLEAR FLUID WITH AGITATION IN AN OXYGEN-FREE ATMOSPHERE AT A TEMPERATURE ABOVE THE MELTING POINT OF THE POLYESTER PRODUCT AT A PRESSURE OF BELOW ABOUT 0.5 MM. HG UNTIL THE POLYESER PRODUCT HAS AN INTRINSIC VISCOSITY IN THE RANGE OF 0.4 TO 0.7.