Pilot–Scale Production of Carbon Hollow Fiber Membranes from Regenerated Cellulose Precursor-Part II: Carbonization Procedure

The simultaneous carbonization of thousands of fibers in a horizontal furnace may result in fused fibers if carbonization residuals (tars) are not removed fast enough. The optimized purge gas flow rate and a small degree angle in the furnace position may enhance the yield of high quality carbon fibers up to 97% by removing by-products. The production process for several thousand carbon fibers in a single batch is reported. The aim was developing a pilot-scale system to produce carbon membranes. Cellulose-acetate fibers were transformed into regenerated cellulose through a de-acetylation process and the fibers were carbonized in a horizontally oriented three-zone furnace. Quartz tubes and perforated stainless steel grids were used to carbonize up to 4000 (160 cm long) fibers in a single batch. The number of fused fibers could be significantly reduced by replacing the quartz tubes with perforated grids. It was further found that improved purge gas flow distribution in the furnace positioned at a 4-degree to 6-degree angle permitted residuals to flow downward into the tar collection chamber. In total, 390 spun-batches of fibers were carbonized. Each grid contained 2000–4000 individual fibers and these fibers comprised four to six spun-batches of vertically dried fibers. Gas permeation properties were investigated for the carbon fibers.