Thermal decomposition of methylene-4,4'-di(ethylphenyl-carbamate) to methylene-4,4'-di(phenylisocyanate)

During thermal decomposition of methylene-4,4'-di(ethylphenylcarbamate) (MDU), methylene-4,4'-di(phenylisocyanate) (MDI) appears to be the main product, provided that the ethanol formed in the reaction is carried away. Polycarbodiimides are the main by-products along with small amounts of 4,4'-di(aminophenyl)methane and its derivatives. Under the reaction conditions used in these studies, the latter compound together with its derivatives, reacts both with MDI and MDU. At 220-310 degrees C and a reaction time of 80-110 min, the selectivity of the MDU transformation to MDI in relation to consumed MDU is 60-87 mol.%. The selectivity of the transformation to polycarbodiimides is 7-20 mol.%, and that to amines and urea derivatives is about 1-2 mol.%.     

Dehydrochlorination of propylene chlorohydrin with sodium hydroxide and with catholyte

Dehydrochlorination of an aqueous solution of propylene chlorohydrin with sodium hydroxide (12·5 and 30% by weight), with catholyte (5 or 10% by weight NaOH + 14% by weight NaCl) and with milk of lime (15% by weight) were compared. The use of catholyte (10% by weight NaOH + 14% by weight NaCl) enables propylene oxide to be obtained in a yield of 94·3%, with 100% conversion of chlorohydrin. The concentration of 1,2-propylene glycol in the waste is 0·07% by weight.     

Detailed scheduling of batch production in a cell with parallel facilities and common renewable resources

The problem of scheduling production in a cell consisting of several parallel facilities, which arises in many process industries, is addressed. The cell produces a variety of items in required quantities. The production of an item requires an operation, which may be performed on one of a subset of the parallel facilities, and it consumes some base products at given rates. There are constrained resources and structural constraints. Resetting a facility to change from one operation to another may necessitate time-consuming changeover.

The problem is solved first by assuming that changeover times are negligible. This leads to forming complete schedules by combining in sequence a number of elementary production schedules (EPS), such that an objective function related to production cost is minimized. During each EPS, and therefore throughout the schedule, all constraints are respected. Subsequently, the EPSs are sequenced to minimize the number of changeovers among operations. Finally, all operations, including changeovers, are scheduled such that the makespan is minimized, while preserving precedence relationships among the operations such that the feasibility of the overall schedule is maintained.

The paper presents the overall approach, the models constructed for each sub-problem and the algorithms developed to solve these models. Illustrative examples and results of computational testing are given.     

Sphingolipid metabolism in colorectal adenomas varies depending on histological architecture of polyps and grade of nuclear dysplasia

Incidence of colorectal cancer (CRC) is growing worldwide. Pathogenetic mechanisms responsible for its onset and progression need further clarification. Colorectal adenomatous polyps are precancerous lesions with malignant potential dependent on histological architecture and grade of nuclear dysplasia. One of the factors conditioning CRC development are abnormalities in sphingolipid metabolism. The aim of this study was to assess the levels of sphingolipids in human colorectal adenomas. The control group (C, n = 12) consisted of patients with no colonic polyps. The examined group consisted of patients with prior diagnosed colonic polyps, qualified to endoscopic polypectomy. This group was further divided due to histological architecture into tubular adenomas group (TA, n = 10), tubulovillous adenomas with low‐grade dysplasia (LGD‐TVA, n = 10), and tubulovillous adenomas group with high‐grade dysplasia (HGD‐TVA, n = 11). In tissue samples, sphingolipd metabolite contents were measured using high performance liquid chromatography (HPLC). In cases of polypoid lesions with low malignancy potential (tubular adenomas), concentration of ceramide, which is characterized by proapoptotic and anti‐proliferative properties, increases compared with control group (p < 0.05), whereas content of sphingosine‐1‐phosphate with anti‐apoptotic and stimulating cellular proliferation properties is reduced in comparison with control group (p < 0.05). On the contrary, in cases of more advanced form of adenomatous polyps (tubulovillous adenomas with high‐grade dysplasia), the ceramide level decreases compared with control group (p < 0.05) while sphingosine‐1‐phosphate concentration is elevated (p < 0.05). We found that concentrations of pro‐apoptotic ceramide are decreased and pro‐proliferative S1P levels are increased in polypoid lesions with high malignancy potential, and it was the opposite in those with low malignancy potential.