may be required by the temperatures and pressures that each divided wall column 40 50 may experience without being directly affected by those of the other corresponding divided wall column the independent sections are free to move independently from each other in response to whatever mechanical stresses are resulting from temperature and pressure differences thus the effect of the mechanical forces due to the temperature and pressure differences is largely eliminated except for the single area where divided wall column 40 50 is attached to the shell column 60 and the vapor seal is created in yet another embodiment and as illustrated in fig5 the divided wall columns 40 50 may be positioned proximate to each other such that the substantially flat walls 42 52 of each divided wall column 40 50 are in direct contact with each other in another embodiment the substantially flat walls 42 52 of each divided wall column 40 50 may be coupled to each other for example the top of each divided wall column 40 50 may be seal welded for example as illustrated in fig6 the divided wall columns 40 50 inside the shell column 60 may have different lengths for example the length of first divided wall column 40 may be longer than the second divided wall column 50 because the specific separation requirements for the first divided wall column 40 may require more theoretical stages for example the lengths of the divided wall columns 40 50 may also be substantially identical as illustrated in fig7 as illustrated in fig6 10 b the divided wall columns 40 50 may incorporate distillation trays 100 packing 110 or various combinations thereof as illustrated in fig8 a 10 b each divided wall column 40 50 may include a liquid distributor 180.