This invention relates to an improvement in a process and apparatus for delivering ultra high purity liquid carbon dioxide to a point of use at pressures above ambient without pumping. In the process a high purity carbon dioxide feed is charged to a vessel and at least partially solidified. Once filled, the slush or solid is isochorically heated, i.e., heated at constant vessel volume whereby the solid phase carbon dioxide is converted to a liquid. Liquid, then, is withdrawn from the vessel at a desired pressure at a rate at which the solid phase carbon dioxide is converted to a liquid. The improvement resides in effecting partial solidification and recycle of carbon dioxide.