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Methanol (CH$_3$OH) is at the root of organic ice chemistry in protoplanetarydisks. However, its weak emission has made detections difficult. To date,gas-phase CH$_3$OH has been detected in only one Class II disk, TW Hya. We usethe Atacama Large Millimeter/submillimeter Array (ALMA) to search for a totalof four CH$_3$OH emission lines in bands 6 and 7 toward the disk around theyoung Herbig Ae star HD 163296. The disk-averaged column density of methanoland its related species formaldehyde (H$_2$CO) are estimated assuming opticallythin emission in local thermodynamic equilibrium. We compare these results tothe gas-phase column densities of the TW Hya disk. No targeted methanol lineswere detected individually nor after line stacking. The 3$\sigma$disk-integrated intensity upper limits are $< 51$ mJy km s$^{-1}$ for the band6 lines and $< 26$ mJy km s$^{-1}$ for the band 7 lines. The band 7 linesprovide the strictest 3$\sigma$ upper limit on disk-averaged column densitywith $N_{\mathrm{avg}} < 5.0 \times 10^{11}$ cm$^{-2}$. Themethanol-to-formaldehyde ratio is CH$_3$OH/H$_2$CO $< 0.24$ in the HD 163296disk compared to a ratio of $1.27$ in the TW Hya disk. Differences in thestellar irradiation of Herbig disks compared to T Tauri disks likely influencethe gaseous methanol and formaldehyde content. Possible reasons for the lowerHD 163296 methanol-to-formaldehyde ratio include: a higher than expectedgas-phase formation of H$_2$CO in the HD 163296 disk, uncertainties in thegrain surface formation efficiency of CH$_3$OH and H$_2$CO, and differences inthe disk structure and/or CH$_3$OH and H$_2$CO desorption processes thatrelease the molecules from ice mantles back into the gas phase. These resultsprovide observational evidence that the gas-phase chemical complexity found indisks may be strongly influenced by the spectral type of the host star.

Upper limits on CH$_3$OH in the HD 163296 protoplanetary disk: evidence for a low gas-phase CH$_3$OH/H$_2$CO ratio