Modeling mass transfer and chemical reaction in industrial nitrocellulose manufacturing processes

A series of models are proposed to describe the production of military grade nitrocellulose from dense cellulose materials in mixtures of nitric acid, sulfuric acid, and water. This effort is conducted to provide a predictive capability for analyzing the rate and extent of reaction achieved under a range of reaction conditions used in the industrial nitrocellulose manufacturing process for sheeted cellulose materials. Because this capability does not presently exist, nitrocellulose producers have historically relied on a very narrow range of cellulose raw materials and resorted to trial and error methods to develop processing conditions for new materials. This tool enables nitrocellulose manufacturers to rapidly adapt to changing market conditions, supply disruptions, or normal variation in the quality of cellulose raw materials and provides process engineers with an improved capability for process control and analysis. This work includes measurement of the kinetics of nitration for cellulose fibers in mixed acids, an evaluation of simultaneous mass transfer and swelling in slivers cut from sheeted cellulose materials, and a structural analysis of slivers cut on industrial rotary cutting machines to consider features that may increase the reactivity of these materials. The kinetics of nitration of all high purity cellulose fibers are demonstrated to be equivalent, and the nitration of dense cellulose materials is shown to be a mass transfer limited process except in the case of small wood pulp slivers in mixed acids used in the production of Grade B nitrocellulose. In addition, it is shown that diffusion and unidirectional swelling occur on similar timescales during the nitration of slivers cut from sheeted wood pulp, resulting in variable diffusivity of mixed acids through the wood pulp sliver structure during the nitration reaction. Finally, delaminated regions or galleries that are formed as a result of the shearing action of the rotary cutting machine used in the industrial nitrocellulose manufacturing process are observed, and the influence of these structural features on the reactivity of the resulting slivers is considered. Based on these findings, generalized models are proposed that can be used to identify optimal processing conditions for new cellulose raw materials to ensure that the resulting nitrocellulose meets quality specifications while avoiding the costs and delays associated with trial and error experimentation