The issue of refining the crude oil obtained from the distillation of used engine oil

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This year, a new set of equipment was installed; it uses a yellow powder to refine the crude oil obtained through high-vacuum distillation in a kettle-type apparatus (I won’t specify what it is to avoid controversy). After adding this agent, sedimentation and slag removal take place, followed by filtration using clay. At present, there is a technical issue that I hope someone experienced can help resolve. The clear oil layer obtained after sedimentation has a coffee-like color – brownish and turbid. However, under the same conditions in the laboratory, the clear oil that results from sedimentation is transparent, with a brownish color. During more than 20 operations of the equipment, there was one instance when the clear oil after sedimentation was transparent, and the oil filtered out was colorless and transparent. If the clear oil after sedimentation is not transparent, then the filtered oil is yellow and the yield of oil obtained is low. Achieving better sedimentation results is therefore a major problem. Initially, it was suspected that the high moisture content in the crude oil was the cause, as kettle-type distillation cannot remove water as effectively as thin-film evaporation or molecular distillation. I tried many methods to reduce the water content in the crude oil to an extremely low level, but it didn’t work; the oil that settled out remained cloudy. I seek guidance from experts, thank you!