Asphaltenes, which are the most aromatic component of heavy oil, are responsible for the fouling and impairment in flow lines, wellbores, and other production facilities in the petroleum industry. Aromatic solvents such as xylenes are commonly used for the asphaltenes’ cleaning process. Understanding the mechanism of asphaltenes’ dissolution in aromatic solvents is significant for the development of a remediation strategy. The reduction of a reactor’s characteristic length scale leads to the decrease in experimental period while providing high-throughput information. Microfluidic systems with in situ spectroscopy is an excellent platform for time-effective studies of the molecular behavior of asphaltenes in simulated sandstone reservoirs. Here, we injected the HZSM-5 zeolite nanoparticles (707 nm aggregate–1 in isopropanol solution) with varying Al2O3/SiO2 ratios (from 0 to 1/26) into the quartz porous media to represent reservoirs with different characteristic acidity. In-line ultraviolet–visible light (UV-vis) spectroscopy enabled the direct measurement of the dissolution percentage, while in situ Raman spectroscopy revealed where the dissolution occurred within the porous media. In addition to bed occupancy, sheet sizes of asphaltenes molecules can also be determined by in situ Raman spectroscopy. Our results show that the average sheet size of deposited asphaltenes molecules decreased from 2.97 ± 0.25 nm to 2.74 ± 0.26 nm after cleaning the porous media with xylenes. This trend is confirmed with the fluorescence emission spectra of dissolved asphaltenes molecules, where a 10–30 nm red-shift is present, when referenced to asphaltenes source samples. These results provide an explanation to why the dissolution percentage of asphaltenes in aromatic solvents increases from 20.15 wt % to 51.00 wt % as the Al2O3 content increases. We can speculate that this increase in weight percentage is attributed to the differences in deposited asphaltenes molecules’ sheet size. These results reveal the importance of π–π interactions during asphaltenes dissolution process in the aromatic solvent. Our results provide the fundamental understanding of asphaltenes dissolution, which otherwise would be challenging to observe using any other analytical methods.