A new technique for cellulose nanocrystal (CNC) production based on hydrolysis with hydrogen chloride vapor is introduced. We further developed the existing technique based on HCl vapor pressure with a reactor applied for the degradation of cellulose with pressurized HCl (99.8 %) gas. Levelling-off degree of polymerization (LOPD) for cellulose cotton linter filter papers is now reached with less than 2 h reaction time, which is significantly shorter than the overnight reaction required with HCl vapor. The hydrolyzed cellulose surface was examined with several techniques including XPS, SEM, and FTIR. Additionally, the reaction kinetics of the degradation for industrial dissolving pulp was studied with pressurized HCl gas. This technique is a promising candidate for large scale production of CNCs with high yields, minimal water consumption, and short reaction times. Furthermore, recycling of the gas is effortless because it is spontaneously desorbed from the fibers by removal from the HCl atmosphere. Dispersions of hydrolyzed filter papers to nanocrystalline cellulose suspensions were studied with several techniques (e.g. functionalizing the hydrolyzed cellulose surface). So far, the lack of an industrial environmentally friendly, high yield production method for CNCs, motivates us in developing the novel CNC production technique aiming in replacement of the so-far existing low yield techniques with high water consumption and waste load.