Design and control of an extractive distillation system for tetrahydrofuran (THF) dehydration with ethylene glycol as entrainer is investigated. The main module is a two-column system containing an extractive distillation column, whose top stream is the desired product THF, and an entrainer recovery column. Economic analysis with total annual cost as the objective function is developed. Two kinds of control strategies are explored for THF dehydration. The responses reveal that the control structure with fixed reflux ratio cannot maintain the bottom liquid level of the entrainer recovery column, while the control scheme with fixed reboiler heat duty/feed flow ratio exhibits good control performance in spite of large deviations in feed flow rate and feed composition.

Silicon (Si) not only plays an important role in plant growth but also contributes significantly to the long‐term terrestrial carbon sink in the form of phytoliths. This study investigated Si content of 184 plant species in meadow steppe and typical steppe of northern China to examine the influential factors of Si distribution and evaluate the potential phytolith carbon sequestration of these grasslands. Our results indicated that the average Si content generally decreased in the following order of Equisetopsida > Monocotyledoneae > Dicotyledoneae. Within angiosperms, although most Si accumulator plants were commelinid monocots, many eudicots also accumulated abundant Si in their above‐ground tissues. The Si content of plant above‐ground parts in typical steppe (6.53 ± 2.88 g/kg) was significantly higher than that in meadow steppe (2.15 ± 0.92 g/kg). The estimated phytolith‐occluded carbon (PhytOC) production flux in typical steppe (0.81 ± 0.36 kg CO2 ha−1 year−1) was higher than that in meadow steppe (0.54 ± 0.23 kg CO2 ha−1 year−1). This study demonstrates that plant phylogeny influences the Si content of individual species, whereas grassland type with different mean annual precipitation and mean annual temperature may significantly affect the abundance of high Si species. We conclude that increasing the abundance of grass species with high Si content in meadow steppe and appropriate grazing and fertilizer application in typical steppe will enhance the phytolith carbon sequestration in grasslands of northern China.

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