Scheduling is a famous optimization problem that seeks the best strategy of allocating resources over time to perform jobs/tasks satisfying specific criteria. It exists everywhere in everyday life, particularly in manufacturing or industrial applications. An essential class of scheduling problems is a job shop scheduling problem (JSSP), an NPhard optimization problem. Several researchers have reported the use of heuristic methods to solve JSSP. This paper aims to investigate the performance of various heuristic algorithms to solve JSSP. Firstly, we developed a Genetic Algorithm (GA and compared the performance of some heuristic algorithms, including Particle Swarm Optimization (PSO), Upper-level algorithm (UPLA), Differential-based Harmony Search (DHS), Grey Wolf Optimization (GWO), Ant Colony Optimization (ACO), Bacterial Foraging Optimization (BFO), Parallel Bat Optimization (PBA), and Tabu Search (TS). The experimental results of the 28 benchmark test problems validated that the algorithms, except ACO, can provide the optimal solution of JSSP. PBA delivers the most impressive performance that solves 26 cases optimally, with the average error equal to 0.05%. Among those 28 test problems, TS, DHS, and PBA can solve 26 instances optimally, followed by GA that solves 21 cases.

High water content is one of the most concerning issues when implementing biodiesel as a diesel fuel blend. Vacuum heating is one of several methods to reduce the water content of biodiesel, at certain conditions, it may damage the stability of biodiesel. This study aims to understand the stability of biodiesel including water content, total acid number, and oxidation stability under vacuum heating process. The three stability parameters were tested according to ASTM D6304, ASTM D664, and EN 15751, respectively. Biodiesel with high water content was heated under a vacuum pressure of -720 mmHg. The heating temperature and time were varied to determine the effect of both variables on the stability of biodiesel. The result shows that higher heating temperature produces lower water content and higher reduction of oxidation stability. Similar effects were also observed at a longer heating time. However, either temperature or time variations gave no noticeable effect on the acid number, while oxidation stability can be maintained above 22 hours. The results of this study can be used as a recommendation in determining the limits of acceptable operating conditions in the biodiesel vacuum heating process.

Peanut skin as an agriculture waste has poor economic value. Utilizing subcritical methanol extraction (SME) to recover catechin and epicatechin as interest compounds from peanut skin is one of the solutions to valorize the agriculture waste into more valuable products. Therefore, the objective of this research is to examine the parameter impacts on peanut skin extract recovery by subcritical methanol. Extraction was conducted under three independent variables—pressure (6 to 10 MPa), flow rate (2.5 to 7.5 mL/min) and temperature (70 to 100 °C)—with the responses of catechin and epicatechin recovery. The optimum conditions were 8 MPa, 4.39 mL/min and 79.6 °C, with catechin responses of 178.66 µg/g and epicatechin responses of 336.41 µg/g. Conditions of high pressure and temperature are optimal for epicatechin and catechin enhancement. The Chrastil model fits the solubility of catechin and epicatechin in SM effectively since it has the lowest average absolute relative deviation (AARD), which is 4.97% and 5.97%, respectively. Consequently, this method (SME) may substitute for the standard technique in extracting catechin and epicatechin.

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